Hexagonal Silicon Formation and Its Phase Transformability
Dr Kiran Mangalampalli, Sasidharan Nisha M., Chandran Y., Sagade A.A., Balakrishnan V., Courac A., Mangalampalli K.
Source Title: Advanced Functional Materials,
View abstract ⏷
The pivotal role of silicon (Si) in semiconductor technology is well-established; however, its hexagonal diamond (hd) crystal structure remains underexplored. This study addresses the paucity of microscopic evidence concerning the formation and phase transformation behavior of hd-Si up to 1000 °C. Utilizing instrumented nanoindentation and subsequent annealing, the hd-Si phase is obtained from a rhombohedral (R8) and body-centered cubic (BC8) mixture within a diamond cubic silicon (dc-Si) wafer. In situ characterization reveals that hd-Si undergoes a reversible phase transition to a metallic β-tin (Sn) phase under indentation loading, reverting to an R8/BC8 mixture upon unloading, thereby providing experimental confirmation of prior theoretical predictions. Thermal stability assessments indicate that hd-Si remains stable beyond ≈700 °C and transitions to dominantly dc-Si at 1000 °C, with traces of hd-Si persisting. Notably, annealing at 500 and 700 °C yields large-area textured hd-Si nanocrystals with slight misorientations featuring 2H, 4H, and 6H polytypes. Interestingly, the dc-Si formed from hd-Si upon annealing at 1000 °C also transforms to a metallic β-Sn phase during Berkovich indentation and reverts to an R8/BC8 mixture upon unloading. This work provides critical insights into the high-pressure phases of Si, paving the way for future studies on phase engineering and stabilization for advanced semiconductor applications and material innovations.
ZnO/CuI Heterojunction UV-Photovoltaic Gas Sensor for Self-Powered IoT-Integrated n-Butylamine VOC Detection
Dr Kiran Mangalampalli, Rekha S.M., Ghuge R.S., Vikraman H.K., Kiran M.S.R.N., Sivalingam Y., Bhat S.V.
Source Title: Advanced Materials Technologies,
View abstract ⏷
The increasing demand for low-power, compact, and efficient gas sensors for next-generation technologies like Internet of things (IoT) platforms and portable devices drives the advancements in self-powered gas sensing systems. Photovoltaic self-powered sensors have emerged as a promising solution, harvesting light energy without external power. However, existing designs are limited by complex fabrication processes and a focus on oxidizing gases, which leaves behind reducing gases, particularly the volatile organic compounds (VOCs). This study presents a transparent, solution-processed ZnO/CuI heterojunction-based UV light-induced photovoltaic self-powered (UV-PSP) gas sensor for the selective detection of VOC n-butylamine. The sensor exhibits good sensitivity (0.0709), detection limit (6.6 ppm), and response (10% at 25 ppm). The ZnO/CuI heterojunction provides high electron mobility, chemical stability, and hydrophobicity, ensuring robust real-time monitoring. The sensor also demonstrates long-term stability (>80% response retention over 25 days) and reduced humidity interference. The sensing mechanism is investigated via Scanning Kelvin Probe to reveal the charge transfer dynamics. A functional IoT-enabled prototype further validates its practical applicability for environmental and industrial applications, offering continuous and remote gas monitoring. This study establishes the ZnO/CuI heterojunction as a versatile and energy-efficient platform for VOC detection for sustainable and portable sensor systems.
Self-Powered, Photovoltaic-Driven NH₃ Sensor: Ultra-High Selectivity, High Sensitivity, and IoT-Enabled Real-Time Monitoring with Novel Organic Molecule Functionalized TiZnN2/p-Si Heterostructure
Dr Kiran Mangalampalli, George J., Vikraman H.K., Ghuge R.S., Reji R.P., Jayaraman S.V., Magna G., Paolesse R., Sivalingam Y., Di Natale C., Mangalampalli K.S.R.N.
Source Title: Small,
View abstract ⏷
Ammonia (NH₃) detection is vital for environmental monitoring, industrial safety, and food quality assurance. Conventional sensors based on metal oxides, conducting polymers, and 2D materials often require external power, limiting their efficiency. Here, a novel self-powered NH₃ sensor utilizing silicon corrole-functionalized TiZnN₂ (SipC-TiZnN)/p-Si heterostructure is presented. By integrating the photovoltaic effect of the TiZnN₂/p-Si junction with gas sensing, the device enables efficient charge separation under visible light without external power. It demonstrates outstanding NH₃ sensitivity (2.62 × 10⁻⁴ ppm⁻¹) and an ultra-low detection limit of 0.9 ppm. The sensor exhibits a superior selectivity for NH₃ over other gases, maintains stability for over 90 days, and operates reliably in humid conditions (≈75% RH). Mechanistic insights from Density Functional Theory calculations and Scanning Kelvin Probe measurements confirm strong NH₃ adsorption. A portable, IoT-enabled prototype validates real-time NH₃ monitoring for fish freshness assessment, highlighting its potential for environmental, food safety, and industrial applications. This work represents a significant advancement in energy-efficient sensing, bridging the gap between high-performance materials and real-world deployment.
Unveiling the effect of curing parameters in the mechanical properties of dental polymer
Dr Kiran Mangalampalli, Varma S., Nisha M.S., Mangalampalli K., Bandyopadhyay P.
Source Title: Engineering Research Express,
View abstract ⏷
The microstructural evolution during the polymerization process critically influences the mechanical properties. The present study investigates the influence of curing parameters, i.e., temperature, time, and bench-pressing pressure, on the microstructural evolution and the degree of conversion, which significantly affect the mechanical properties of heat-cured PMMA denture base polymers. Nanoindentation results reveal that the mechanical properties improve considerably with higher curing temperature and longer curing time, as evidenced by an 88% increase in Young’s modulus and a four times increase in hardness. The optical photomicrographs, XRD, and Raman spectroscopy elucidate the effect of systematic variations in curing parameters in the microstructure. The 12-month aging study reveals an increment of 5-10% in the mechanical properties, which is not changing after immersing in artificial saliva (pH 6.8) for 14 days. This comprehensive analysis provides insight into the microstructure-mechanical property correlation, which is important in optimizing PMMA denture base fabrication to enhance clinical outcomes and patient satisfaction.
Impact of atomic size misfit on lattice distortion in AlFeCoNiX (X = Cr/Mn/Zr) multicomponent alloys
Dr Kiran Mangalampalli, Vanaraj P.W., Ravi L., Patole S.P., Anjum D.H., Megha S.N., Kiran M.S.R.N., Perumal S., Ravikirana
Source Title: Journal of Materials Science,
View abstract ⏷
This study investigates the complex interplay among composition, microstructure, and hardness within the high-entropy alloy (HEA), AlFeCoNiX (X-Cr/Mn/Zr). Utilizing the vacuum arc melting process, compositionally graded alloys were fabricated and characterized in their as-cast condition. Microstructural analysis unveiled a complex blend of phases, including BCC, B2, FCC, and C15 (Laves) with the addition of Cr, Mn, and Zr to the quaternary AlFeCoNi HEA. Particularly noteworthy was the dominant Al-Ni-rich phase. The B2 chemical ordering within the Al-Ni-rich phase decreased significantly from 63.5% in AlFeCoNi to 4.5%, 28.8%, and 51% with the addition of Cr, Mn, and Zr, respectively. Furthermore, lattice distortion variations, determined by the atomic size difference parameter δ[%], for AlFeCoNiX (X = Cr, Mn, Zr) HEAs ranged from 5.25 to 10.12. Nanoindentation tests showed hardness variations when Cr, Mn, and Zr were added to AlFeCoNi HEA, ranging from 4.63 ± 0.18 GPa to 4.36 ± 0.19 GPa, 4.39 ± 0.38 GPa, and 9.25 ± 0.57 GPa, respectively. This hardness increase could be correlated with the atomic size difference parameter δ[%] and to the increased inherent defects within the Al-Ni-rich phase of the as-cast HEAs. Overall, this research underscores the potential for customizing high-entropy alloy properties through chemical composition adjustments, catering to specific demands.
Highly Selective, Room-Temperature Triethylamine Sensor Using Humidity-Resistant Novel TiZn Alloy Nanoparticles-Decorated MoS₂ Nanosheets
Dr Kiran Mangalampalli, Vikraman H.K., George J., Ghuge R.S., Painappallil Reji R., Jayaraman S.V., Kawazoe Y., Sivalingam Y., Mangalampalli S.R.N.K.
Source Title: Small,
View abstract ⏷
The future of environmental monitoring, medical diagnostics, and industrial safety depends on developing room-temperature, long-term operable, stable, miniaturized, ultrahigh-performance sensors integrated into the Internet of Things (IoT). While noble metals and high-entropy alloys (HEAs) lead in addressing the limitations of conventional transition-metal dichalcogenides (TMDs) like MoS₂, they face challenges such as high-cost, limited availability, and fabrication complexity. To address this, multifunctional, cost-effective, humidity-insensitive novel phase Ti₀.₅Zn₀.₅ (TiZn) alloy nanoparticle-decorated MoS₂ nanosheets (MoS₂_NP) is developed for ultra-selective and highly sensitive triethylamine (TEA) vapor detection at room temperature (RT). This exhibited a 24-fold increase in response compared to MoS₂, with a high signal-to-noise ratio, negligible humidity interference, sensitivity of 9.92 × 10⁻⁵ ppm⁻¹ at RT, and a detection limit of 48 ppm. The enhanced catalytic activity and defect concentration, the reduction of the edge oxidation resulting in strong Fermi-level pinning, and the relatively high adsorption energy lead to a target gas-specific carrier-type response, demonstrating the potential of binary alloy nanoparticles (NPs) as decorative materials for enhanced sensing applications. The superior performance of the sensor led to the development of a TEA detection prototype interfaced with a mobile device via IoT for continuous monitoring, enhancing practicality and usability by offering immediate access to critical information.
Annealing-driven phase transformation and property modulation in AlCoCrFeNi High-Entropy alloy
Dr Kiran Mangalampalli, Vanaraj P.W., Ravi L., Madhavan J., S.N M., Matada M.S.S., Kiran M.S.R.N., Sivalingam Y., Ravikirana
Source Title: Emergent Materials,
View abstract ⏷
High-entropy alloys (HEAs) offer exceptional tunability in microstructure and properties through thermal processing. This study investigates the phase evolution, mechanical properties, and corrosion behaviour of equiatomic AlCoCrFeNi HEA under varying annealing conditions. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal a homogeneous body-centred cubic (BCC) structure with B2 ordering in the as-melted alloy. Annealing at 800 °C induces multiphase segregation (BCC1 + BCC2 + face-centred cubic (FCC) + sigma (σ)), while annealing at 1000 °C eliminates the σ phase, stabilizing a BCC1 + BCC2 + FCC microstructure. Subsequent aging of the 1000 °C-annealed sample at 800 °C increases the FCC fraction while suppressing σ-phase precipitation, indicating enhanced phase stability. Nanoindentation measurements demonstrate high strain rate sensitivity (m = 0.1 ± 0.03) in the as-melted and 1000 °C-annealed states, promoting damage tolerance. The 1000 °C-annealed alloy exhibits an optimal balance of hardness (8.14 ± 1.66 GPa) and elastic modulus (268.4 ± 48.5 GPa). Electrochemical testing in 3.5 wt% NaCl solution reveals enhanced passivation behaviour in heat-treated samples, with the lowest corrosion current (0.1 and 0.2 nA/cm²) and highest pitting potential (126 and 143 mV) in the 1000 °C annealed and aged conditions. However, scanning Kelvin probe (SKP) and atomic force microscopy (AFM) reveal increased electrochemical heterogeneity and surface roughness in annealed samples, indicating latent susceptibility to localized attack. Immersion testing in 6 wt% FeCl₃ confirms this, with corrosion rates increasing from 4.49 mm/year in the as-melted state to 17.62 mm/year in the 800 °C annealed sample due to microgalvanic effects driven by phase segregation and topographical disparities.
Orthogonal and Antenna effects on the chemosensing behaviour of Porphyrins towards 2,4,6-Trinitrophenol: Colour recognition and portable photodiode device
Dr Venkatramaiah Nutalapati, Dr Kiran Mangalampalli, Prasanth Palanisamy, Mageshwari Anandan, Hajeesh Kumar Vikraman, Gurusamy Raman, S. R. N. Kiran Mangalampalli, Venkatramaiah Nutalapati
Source Title: Journal of Luminiscence,
View abstract ⏷
In this work, we have developed two modular freebase porphyrins containing triphenylamine (H2TPAP) and pyrene (H2PyP) units at meso position to understand the role of antenna and orthogonal effects on photophysical and chemosensing behaviour with different nitroaromatic compounds (NACs). The fluorescence studies demonstrate that H2TPAP exhibit strong electronic coupling over H2PyP to induce energy transfer process from peripheral units to porphyrin π-system and behave like strong donor materials. The sequential energy and electron transfer process upon addition of different NACs reveals that H2TPAP show unprecedented selectivity towards the detection of 2,4,6-Trinitrophenol (TNP) with a limit of detection (LODs) of ∼2.3 and ∼6.8 ppm for H2PyP. The mechanistic investigations through NMR and other spectroscopic methods evident that the strong donor-acceptor interactions, protonation at the central core of H2TPAP show both colorimetric and fluorimetric changes with the order of quenching efficiency as TNP>4-NP>2,4-DNP > DUN>4-NBA. A handheld portable photodetector was developed to monitor the dynamic change in photocurrent response. Further, a smartphone interfaced portable fluorimetric method was developed by recognizing colour variations in terms of RGB and the luminance (L) values facilitate sensitive and real-time sensing at low concentrations levels will have a significant impact on the development of new handheld chemosensor devices for real time detection of explosive compounds.
High thermoelectric performance in p-type ZnSb upon increasing Zn vacancies: an experimental and theoretical study
Dr Kiran Mangalampalli, Palraj J., Sajjad M., Moorthy M., Saminathan M., Srinivasan B., Singh N., Parasuraman R., Patole S.P., Mangalampalli K., Perumal S.
Source Title: Journal of Materials Chemistry A,
View abstract ⏷
The high thermoelectric performance of dopant-free, low-cost and eco-friendly p-type Zn1−xSb (x = 0, 0.01, 0.03, and 0.06) is demonstrated by synergistically optimizing its electrical and thermal properties via Zn-vacancy engineering. Upon increasing Zn-vacancies in ZnSb, the bandgap is observed to reduce due to the formation of the impurity states above the valence band, which is theoretically validated using density functional theory (DFT). Remarkably, Zn vacancy-driven point defects significantly influence the hole concentration within the Zn1−xSb samples. At 300 K, the hole concentration (nH) is boosted from 3.6 × 1018 cm−3 (in ZnSb) to 3.4 × 1019 cm−3 for the Zn0.94Sb sample, culminating in a marked enhancement in electrical conductivity (σ) from 1.80 × 104 S m−1 to 7.57 × 104 S m−1 for Zn0.94Sb. Equally noteworthy is the substantial decrease in thermal conductivity (κ) observed in the Zn0.94Sb sample at 673 K, plunging from 2.29 W m−1 K−1 (in ZnSb) to 1.41 W m−1 K−1. This decline in thermal conductivity is attributed to the effective phonon scattering arising from Zn-vacancy-assisted point defects, combined with the efficient coupling of optical and acoustic phonons and the characteristic low group velocity, evidenced by the theoretically calculated phonon dispersion curve. Overall, the high thermoelectric figure of merit, zT of ∼0.8 at 673 K, is achieved for the sample with a 6 mol% Zn deficiency. Furthermore, a maximum theoretical conversion efficiency of ∼7% is predicted at a temperature gradient of 625 K, showing high potential for use in practical devices for mid-temperature applications, and the present work features the effect of a reliable dopant-free approach in improving the overall zT of eco-friendly and low-cost ZnSb.
Unprecedented Multifunctionality in Novel Monophase Micro/Nanostructured Ti-Zn Alloy
Dr Kiran Mangalampalli, Vikraman H.K., George J., Reji R.P., Kuppuswamy G.P., Sutar S.D., Swami A., Ramamoorthy S., Sundaramurthy A., Pramanik S., Velappa Jayaraman S., Perumal S., Sivalingam Y., Mangalampalli S.R.N.K.
Source Title: Small,
View abstract ⏷
It is always challenging to integrate multiple functions into one material system. However, those materials/devices will address society's critical global challenges and technological demands if achieved with innovative design strategies and engineering. Here, one such material with a broader spectrum of desired properties appropriate for seven applications is identified and explored, and a glucose-sensing-triggered energy-storage mechanism is demonstrated. To date, the Titanium (Ti)-Zinc (Zn) binary alloys are investigated only as mixed phases and for a maximum of three applications. In contrast, the novel single phase of structurally stable 50 Ti-50 Zn (Ti0.5Zn0.5) is synthesized and proven suitable for seven emerging applications. Interestingly, it is thermally stable up to 750 °C and possesses excellent mechanical, tribological properties and corrosion resistance. While exceptional biocompatibility is evident even up to a concentration of 500 µg mL−1, the antibacterial activity against E. coli is also seen. Further, rapid detection and superior selectivity for glucose, along with supercabattery behavior, unambiguously demonstrate that this novel monophase is a remarkable multifunctional material than the existing mixed-phase Ti-Zn compounds. The coin-cell supercapacitor shows outstanding stability up to 30 000 cycles with >100% retention capacity. This allows us to prototype a glucose-sensing-triggered energy-storage-device system for wearable point-of-care diagnostic applications.
Polymorphism-driven Distinct Nanomechanical, Optical, Photophysical, and Conducting Properties in a Benzothiophene-quinoline
Dr Kiran Mangalampalli, Bejoymohandas K.S., Redhu A., Sharma C.H., SeethaLekshmi S., Divya I.S., Kiran M.S.R.N., Thalakulam M., Monti F., Nair R.V., Varughese S.
Source Title: Chemistry - A European Journal,
View abstract ⏷
Polymorphic forms of organic conjugated small molecules, with their unique molecular shapes, packing arrangements, and interaction patterns, provide an excellent opportunity to uncover how their microstructures influence their observable properties. Ethyl-2-(1-benzothiophene-2-yl)quinoline-4-carboxylate (BZQ) exists as dimorphs with distinct crystal habits – blocks (BZB) and needles (BZN). The crystal forms differ in their molecular arrangements – BZB has a slip-stacked column-like structure in contrast to a zig-zag crystal packing with limited π-overlap in BZN. The BZB crystals characterized by extended π-stacking along [100] demonstrated semiconductor behavior, whereas the BZN, with its zig-zag crystal packing and limited stacking characteristics, was reckoned as an insulator. Monotropically related crystal forms also differ in their nanomechanical properties, with BZB crystals being considerably softer than BZN crystals. This discrepancy in mechanical behavior can be attributed to the distinct molecular arrangements adopted by each crystal form, resulting in unique mechanisms to relieve the strain generated during nanoindentation experiments. Waveguiding experiments on the acicular crystals of BZN revealed the passive waveguiding properties. Excitation of these crystals using a 532 nm laser confirmed the propagation of elastically scattered photons (green) and the subsequent generation of inelastically scattered (orange) photons by the crystals. Further, the dimorphs display dissimilar photoluminescence properties; they are both blue-emissive, but BZN displays twice the quantum yield of BZB. The study underscores the integral role of polymorphism in modulating the mechanical, photophysical, and conducting properties of functional molecular materials. Importantly, our findings reveal the existence of light-emitting crystal polymorphs with varying electric conductivity, a relatively scarce phenomenon in the literature.
Self-Powered Photodetectors with Nickel-Doped ZnO Nanorods for Operation in Low-Light Environments
Dr Kiran Mangalampalli, Bora A., George J., Sivalingam Y., Velappa Jayaraman S., Magna G., Kiran M.S.R.N., Vesce L., Paolesse R., Di Natale C.
Source Title: ACS Applied Nano Materials,
View abstract ⏷
The development of next-generation optoelectronic devices relies on the necessity for self-powered, fast, and high-sensitivity photodetectors with a wide-spectral response. This Article investigates the impact of nickel doping on the growth of ZnO nanorods (79-123 nm diameter) on a p-type silicon substrate, exploring alterations in photovoltaic characteristics compared to the pure counterparts. The results reveal enhanced performances in devices with nickel doping ranging from 1% to 5%, exhibiting superior behavior across tested parameters. Despite consistent morphology and geometric aspects of the grown nanorods, the persistent presence of nickel was evident. Illumination from UV and visible light sources demonstrated increased current in I-V plots with rising doping levels, showcasing robust photovoltaic behavior at 0 V and enabling functionality as a self-powered photodetector. Under UV light, self-powered operation was observed at an intensity as low as 20 mW/cm2, extending beyond 50 mW/cm2 for visible light exposure. These devices exhibit applicability in detecting a broad spectrum of solar radiation, as evidenced by the influence of the wavelength and light intensity on the photocurrent response at zero bias. With pulsed frequencies of a 405 nm laser, changes in the photocurrent were observed with variations in operating frequency. Hence, a high-performance, wide spectral, self-powered photodetector capable of detecting minimal light intensity was fabricated.
A self-powered photoactive room temperature gas sensor based on a porphyrin-functionalized ZnO nanorod/p-Si heterostructure
Dr Kiran Mangalampalli, Bora A., George J., Sivalingam Y., Surya V.J., Magna G., Mangalampalli S.R.N.K., Paolesse R., Di Natale C.
Source Title: Journal of Materials Chemistry C,
View abstract ⏷
The integration of self-powered photodetectors and highly selective gas sensors into a unified system has revolutionized the development of next-generation optoelectronic gas sensors towards overcoming the limitations of high power consumption and poor selectivity in traditional systems. In this scenario, this work describes a superior optoelectronic gas sensor based on 5-(4-carboxyphenyl)-10,15,20-triphenyl porphyrin (H2TPPCOOH)-functionalized vertically aligned 1D ZnO nanorods grown on p-Si. The dual impact of porphyrin functionalization on the powering and chemical sensing properties of the ZnO NR/p-Si heterostructure was investigated. The resulting porphyrin-functionalized device demonstrated a maximum VOC of 0.1 V and Isc of 12.16 μA with good sensitivity and fast response towards triethylamine (TEA) vapors at room temperature. The level of defects in the device and the gas sensing mechanism were studied using the Scanning Kelvin Probe system, and the photoelectric mechanism is explained through energy band diagrams. The ambipolar charge transport in the device plays a significant role in chemical sensing at room temperature at zero power consumption. Hence, this work offers valuable insights for designing self-sustained, stable, cost-effective, miniaturized smart chemical sensors, which are highly selective to specific VOC biomarkers in complex gas mixtures, with a potential for on-chip integration and point-of-care health monitoring.
Ultrafast Self-Powered Ti–Zn–N Photodetector-Based Optocoupler for Power Electronics Applications
Dr Kiran Mangalampalli, George J., Vikraman H.K., Sivalingam Y., Varadharaj E.K., Mangalampalli S. R. N. K.
Source Title: Energy Technology,
View abstract ⏷
This study presents an early exploration into the application of a self-powered photodetector based on titanium zinc nitride (TiZnN) films in power electronics, aiming to overcome inherent limitations of conventional optocouplers such as low switching speed and specific operating voltage requirements. The fabricated device demonstrates excellent performance metrics, including photosensitivity of 136, the responsivity of 3.22 mA W−1 at −8 V bias, and a peak detectivity of 1.76 × 108 Jones at 0 V bias. Remarkably, ultrafast rise (τs) and decay times (τd) of 0.11 and 0.10 ms, respectively, are achieved, alongside broad-band spectral absorption characteristics. Experimental validation showcases the efficacy of the TiZnN-based optocoupler in practical applications, notably in power electronics triggerable relay systems and AC–AC converters. Leveraging the self-powering capability inherent to the TiZnN photodetector, this optocoupler eliminates external power source dependencies, thereby enhancing its versatility and applicability in diverse electronic systems. The rapid response time of the device and broad spectral absorption further underscore its suitability for high-speed signal transmission across varied operating conditions. This research paves a path for developing stable, cost-effective, and self-powered ultrafast optocouplers, eliminating concerns about compromising electrical signal transit. These advancements hold significant implications for enhancing electronic system performance, reliability, and functionality in critical applications.
Realizing low thermal conductivity in Cr-doped nanostructured higher manganese silicide
Dr Kiran Mangalampalli, Saminathan M., Muthiah S., Parasuraman R., Sarkar D., Mangalampalli K., Perumal S.
Source Title: Ceramics International,
View abstract ⏷
Higher manganese silicides have evolved as an efficient thermoelectric material because of their exceptional thermoelectric performance at intermediate temperatures. In this work, we report the ultralow-thermal conductivity with improved thermoelectric properties of Mn1-xCrxSi1.8 (x = 0, 0.025, 0.05 and 0.1) prepared by induction melting followed by ball milling and uni-axial induction hot-pressing. Bragg diffraction patterns confirmed that the as-synthesized compound belongs to the Mn15Si26 phase along with the solid solubility of Cr in the HMS lattice. In addition, the backscattered electron micrographs revealed the precipitation of excess Si in the HMS matrix, originating from Si-rich stoichiometry. Furthermore, an elevation in electrical conductivity with increasing Cr content has been observed because of its acceptor dopant behaviour at the Mn site. On the contrary, the Seebeck coefficient decreased upon an increase in Cr content, and bulk MnSi1.8 has shown the highest Seebeck coefficient of 220 μV/K at 773 K. Impressively, nanostructuring along with the generated point defects as a result of Cr dopant facilitates an intensified phonon scattering at the nanostructured grain boundaries that results in a very low κtotal of 0.99 W/mK at 773 K for ball-milled Mn0.9Cr0.1Si1.8, leading to an elevated zT of 0.46 at 773 K.
Transparent TiO2/MoO3 Heterojunction-Based Photovoltaic Self-Powered Triethylamine Gas Sensor with IoT-Enabled Smartphone Interface
Dr Kiran Mangalampalli, Ghuge R.S., Madhavanunni Rekha S., Vikraman H.K., Velappa Jayaraman S., Kiran M.S.R.N., Bhat S.V., Sivalingam Y.
Source Title: ACS Sensors,
View abstract ⏷
Conventional gas sensors encounter a significant obstacle in terms of power consumption, making them unsuitable for integration with the next generation of smartphones, wireless platforms, and the Internet of Things (IoT). Energy-efficient gas sensors, particularly self-powered gas sensors, can effectively tackle this problem. The researchers are making significant strides in advancing photovoltaic self-powered gas sensors by employing diverse materials and their compositions. Unfortunately, several of these sensors seem complex in fabrication and mainly target oxidizing species detection. To address these issues, we have successfully employed a transparent, cost-efficient solution processed bilayer TiO2/MoO3 heterojunction-based photovoltaic self-powered gas sensor with superior VOC sensing capabilities, marking a significant milestone in this field. The scanning Kelvin probe (SKP) measurement reveals the remarkable change in contact potential difference (−23 mV/kPa) of the TiO2/MoO3 bilayered film after UV light exposure in a triethylamine (TEA) atmosphere, indicating the highest reactivity between TEA molecules and TiO2/MoO3. Under photovoltaic mode, the sensor further demonstrates exceptional sensitivity (∼2.35 × 10-3 ppm-1) to TEA compared to other studied VOCs, with an admirable limit of detection (22 ppm) and signal-to-noise ratio (1540). Additionally, the sensor shows the ability to recognize TEA and estimate its composition in a binary mixture of VOCs from a similar class. The strongest affinity of TiO2/MoO3 toward the TEA molecule, the lowest covalent bond energy, and the highest electron-donating nature of TEA may be mainly attributed to the highest adsorption between TiO2/MoO3 and TEA. We further demonstrate the practical applicability of the TEA sensor with a prototype device connected to a smartphone via the IoT, enabling continuous surveillance of TEA.
Electrical transport properties and impedance analysis of Pt/TiO2 Nanorods/FTO heterojunction device
Dr Kiran Mangalampalli, Kuppuswamy G.P., Matada M.S.S., Marappan G., Manoharan R., N M.S., Mangalampalli K.S.R.N., Jayaraman S.V., Sivalingam Y.
Source Title: Surfaces and Interfaces,
View abstract ⏷
Presented study focuses on the hydrothermal growth of Titanium Oxide (TiO2) vertical nanorods on a FTO substrate, leading to the realization of a Schottky junction through the evaporation of platinum onto the TiO2 nanorods. I-V (current-voltage), EIS (electrochemical impedance spectroscopy) measurements were carried out to characterize the fabricated heterojunction devices. The barrier height of 0.6 eV and ideality factor value of 16 indicate the presence of an interfacial layer in the heterojunction devices. Effective charge carrier mobility of ∼ 0.01842 cm2/Vs is determined through the application of Mott-Gurney's law. Conductivity and density of deep trap states (ntrap) were found to be ∼ 1.5595 × 10−8 (Ω cm)−1 and ∼ 1.4 × 1022 m−3 respectively. Additionally, the scanning Kelvin probe (SKP) technique is employed to investigate the contact potential difference (CPD) and work function of TiO2, while the mechanical behaviour of TiO2 nanorod arrays is studied using nanoindentation.
Dehydration-Driven Nanomechanical Responses of the Antiviral Drug EIDD-1931
Dr Kiran Mangalampalli, Divya I.S., Mondal A., Bhunia S., Mangalampalli K.S.R.N., John J., Reddy C.M., Varughese S.
Source Title: Crystal Growth and Design,
View abstract ⏷
The hydrate dimorphs of the antiviral drug EIDD-1931 (EIDD) exist as tautomers possessing different conformations, synthon preferences, thermal decomposition profiles, and mechanical properties. This coexistence of manifold contrasting structural features is unusual and makes the hydrate dimorphs of EIDD-1931 exceptional. As analogs of uridine and cytidine, the tautomers corresponding to the crystal forms (Form I and Form II) of EIDD help effectively block viral RNA replication. With regard to the analogous nucleosides, the computed MESP of EIDD exhibits extensive alterations and disproportionate distribution of maxima and minima sites, contributing to its hydration characteristics. The water of crystallization and its efflorescence have a direct impact on the thermal decomposition profiles as well as the nanomechanical response of the crystal forms because of their distinct roles in the stabilization of the structure─as a two-donor, two-acceptor interaction center occupying isolated sites in Form I as opposed to a one-donor, one-acceptor moiety confined to a void-filling role in Form II. From a broader perspective, the nanomechanical responses correlated to the interaction characteristics, and dehydration events are remarkable in deriving a molecular basis of the properties in pharmaceutics wherein a major share of the pharmaceuticals exists as hydrates.
Plastic Deformation in a Molecular Crystal Enables a Piezoresistive Response
Dr Kiran Mangalampalli, Hasija A., Thompson A.J., Singh L., Megha S.N., Mangalampalli K.S.R.N., McMurtrie J.C., Bhattacharjee M., Clegg J.K., Chopra D.
Source Title: Small,
View abstract ⏷
Organic materials are promising candidates for the development of efficient sensors for many medicinal and materials science applications. Single crystals of a small molecule, 4-trifluoromethyl phenyl isothiocyanate (4CFNCS), exhibit plastic deformation when bent, twisted, or coiled. Synchrotron micro-focus X-ray diffraction mapping of the bent region of the crystal confirms the mechanism of deformation. The crystals are incorporated into a flexible piezoresistive sensor using a composite constituting PEDOT: PSS/4CFNCS, which shows an impressive performance at high-pressure ranges (sensitivity 0.08 kPa−1 above 44 kPa).
Designing the Mechanical Plasticity of Benzylidene Indanones Based Molecular Crystals by Crystal Engineering
Dr Kiran Mangalampalli, Manoharan D., Megha S.N., Kiran M.S.R.N., Emmerling F., Bhattacharya B., Ghosh S.
Source Title: Crystal Growth and Design,
View abstract ⏷
We herein report the tuning of mechanical plasticity of a series of 2-benzylidene-1-indanone derivative crystals through controlling intermolecular interactions for the first time. The roles of intermolecular interactions on plastic properties are rationalized by nanoindentation and energy framework calculations.
Novel Ternary Nitride Thin Film-Based Self-Powered, Broad Spectral Responsive Photodetector with a High Detectivity for Weak Light
Dr Kiran Mangalampalli, George J., Vikraman H.K., Reji R.P., Mamidipudi Ghanashyam K., Velappa Jayaraman S., Sivalingam Y., Mangalampalli Sri Rama Narasimha K.
Source Title: Advanced Materials Technologies,
View abstract ⏷
Self-powered, wide-spectral response, fast, and high-sensitivity photodetectors are essential for developing next-generation optoelectronic devices. In this work, the predicted optoelectronic properties of the ternary metal-zinc (Zn)-nitride (N) thin films are experimentally demonstrated. A novel phase of the Titanium (Ti)-Zn-N system (dominantly TiZnN2 film of ≈235 nm thickness) is developed on the p-Si substrate, which shows excellent optoelectronic properties. The Indium Tin Oxide (ITO)/TiZnN2/p-type Si (p-Si) photodetector of area ≈4 mm2 exhibits an impressive responsivity of 1.22 × 10–4 A W−1 at 0 V and 40 mA W−1 at −4 V, a specific detectivity up to 1.16 × 109 Jones at 0 V, and a response speed of 1.9 ms at zero external bias (i.e., self-powered mode). Benefiting from the broad-band absorption of the film and p-Si combination, the detection range is observed from the ultraviolet to near-infrared (300–1150 nm). Simultaneous operation of self-powered photo-triggered drip irrigation ON and street light OFF in the early morning and vice-versa in the evening is demonstrated for autonomous farming. The device is insensitive to humidity and ambiance, and generates a photocurrent with light intensity as low as 5 mW cm−2. The active layer is hydrophobic and highly stable, and the fabrication is cost-effective.
Investigation on the structural and electrical behavior of bioactive Ca10(PO4)6(OH)2 – K0.5Na0.5NbO3 ceramic
Dr Kiran Mangalampalli, Pandey S., Das A., Mangalampalli K.S.R.N., Dobbidi P.
Source Title: Ceramics International,
View abstract ⏷
The present study explores the structural, electrical and preliminary bioactivity of Ca10(PO4)6(OH)2 (HAP) – K0.5Na0.5NbO3 (KNN) composites. The composites and monoliths of KNN and HAP are synthesized individually by the sol-gel and solid-state routes. The composites have been prepared by varying their At. % (20, 40, 60, and 80%). The purity of composite formation with the presence of both hexagonal and orthorhombic phases for HAP and KNN respectively without any reaction between monoliths was observed through the X-Ray diffraction (XRD) and Raman spectroscopy. The optical band-gap (Eg) is studied using the UV/VIS/NIR spectroscopy that shows the major contribution of oxygen and OH vacancies towards the decrease of the bandgap. The morphology depicts the presence of both the nano-sized HAP and coarse KNN grains. The KNN grains are larger than HAP grains and a systematic variation is observed in composites with increasing At.% of KNN. The dielectric and impedance studies are carried out in the frequency range of 100 Hz–1 MHz. The dielectric constant (εr) lies between 20 and 40 measured at 100 kHz. The ionic behavior of HAP contributed to the dielectric phenomenon, and an increase in εr leads to conductivity. The impedance analysis draws a picture of the conduction phenomenon and the relaxation mechanism prevalent within the composites. The frequency-dependent ac conductivity (σac) curve follows Jonscher's universal power law. The comprehensive study of KNN – HAP bioceramic composites and understanding the electrical properties can open up possibilities for their applications in biomedical engineering.
Tracing shape memory effect and elastic bending in a conformationally flexible organic salt†
Dr Kiran Mangalampalli, Hasija A., Ranjan S., Guerin S., Mangalampalli S.R.N.K., Takamizawa S., Chopra D.
Source Title: Journal of Materials Chemistry C,
View abstract ⏷
Molecular crystals which respond to multiple external stimuli are of great research interest as next-generation energy transducing smart materials. This article introduces a polymorphic organic salt, diphenyl phosphate anion and o-chloroaniline cation where a single crystalline form of this salt displays thermoresponsive (such as shape memory effect, bending, jumping, and splitting) and mechanoresponsive (elastic flexibility) behaviour. The single crystal of Form I shows a reversible phase transformation (below room temperature) that enables investigation of the significance of flexible torsions that result in conformational and rotational changes in the crystalline assembly. This cooperative transformation with almost negligible fatigue while undergoing a temperature-dependent shape memory effect also exhibits mechanical compliance at room temperature, which contrasts with the behavior exhibited by the other form. Intriguingly, the three-point bending test allows for determination of the elastic modulus at varying temperatures over which phase transformation occurs, rationalising the shape memory effect between the parent-daughter phase. Nanoindentation experiments are used to quantify and rationalize the mechanical response of these polymorphs, with the softer polymorph with lower resistance to elastic deformation showing mechanical compliance. These values corroborated well with the DFT-calculated elastic modulus values which predict the ranks of elasticity for the polymorphs. This study emphasizes the significance of multi-functional molecular crystals with improved understanding of hybrid properties.
Diverse Mechanical Properties of 1,3-Bis(4-nitrophenyl) thiourea-DMSO Dimorphic Solvates
Dr Kiran Mangalampalli, Hasija A., Bhandary S., Mangalampalli S.R.N.K., Chopra D.
Source Title: Crystal Growth and Design,
View abstract ⏷
The distinct mechanical properties of concomitant dimorphs (Form α and Form β) of 1,3-bis(4-nitrophenyl) thiourea-DMSO solvate (TU-DMSO) have been investigated via experimental and computational techniques. This includes analysis of the molecular arrangement for the individual crystalline forms, considering the interaction energies responsible for stabilization of the dimers, comparing their lattice energies, and corroborating the results obtained from nanoindentation experiments. The work gives a plausible explanation for elastic bending of Form α crystals that includes synergistic contributions from electrostatic and dispersion components of intermolecular interactions. In addition to this, it suggests the role of the flexible torsions in thiourea along with expansion-compression in the outer-inner arc as a means to accommodate the strain due to bending. The relatively soft and compliant behavior of the former polymorph is highlighted by almost a 3-fold difference in hardness and elastic modulus values [Form α (115 MPa, 2.7 GPa) and Form β (334 MPa, 7.41 GPa)]. The nanoindentation experiments also support the observance of splitting of Form α crystals on excessive mechanical agitation.
Dielectric spectroscopy and ferroelectric studies of multiferroic bismuth ferrite modified barium titanate ceramics for energy storage capacitor applications
Dr Kiran Mangalampalli, Priya Balmuchu S., Mangalampalli S.R.N.K., Dobbidi P.
Source Title: Materials Science and Engineering: B,
View abstract ⏷
This study reports a single-phase solid-solution of barium titanate- bismuth ferrite (1-x) BaTiO3-xBiFeO3 (x = 0.0, 0.1, 0.2 and 0.3, abbreviated as BTO, BTBF1, BTBF2 and BTBF3) composition fabricated via conventional solid-state reaction technique. The BFO modified BTO ceramics exhibit a single perovskite structure with pseudo-cubic (x ≥ 0.1) symmetry, and the c/a ratio decreases with an increase in BFO content. Dielectric studies suggest that the ferroelectric-paraelectric phase transition around 150 °C for BTBF1 ceramic increases to 180 °C for BTBF3 ceramic, attributed to the higher transition temperature of BFO ceramic. The temperature-dependent impedance studies suggest non-Debye type relaxation and NTCR (negative temperature coefficient of resistance) behavior of the composition. Among the prepared ceramics, BTBF1 ceramic showed an improved energy density of 39.91 mJ/cm3 and energy efficiency of 60.92%. Thus, prepared ceramics can be considered a potential candidate for energy storage applications.
Advances in functional and structural ceramics: Development, characterization, and applications
Dr Kiran Mangalampalli, Mangalampalli S.R.N.K., Dobbidi P., Ramasubramanian L.N., Korimilli E.P., Perumal S., Bakshi S.R.
Source Title: Ceramics International,
Co substituted Ni–Zn ferrites with tunable dielectric and magnetic response for high-frequency applications
Dr Kiran Mangalampalli, Mohapatra P.P., Singh H.K., Kiran M.S.R.N., Dobbidi P.
Source Title: Ceramics International,
View abstract ⏷
Microwave ferrites are the most promising materials for high frequency and high-power devices. In this work, Co substituted Ni–Zn ferrites (Ni0.5-xZn0.5CoxFe2O4; x = 0–0.4) are synthesized, and the structural, morphology, dielectric, magnetic response are systematically investigated. The X-ray diffraction pattern (XRD) pattern confirmed the formation of pristine cubic phase alone without any secondary phase in all the samples. Substitution of Co2+ resulted in increased crystallite size and lattice constant. Raman peak intensity is suppressed, and a shift towards a lower wavenumber is observed with Co substitution. The change in position and intensity is analyzed and attributed to the change in cationic distribution in tetrahedral and octahedral positions by deconvoluting the Raman peaks. The Energy-dispersive X-ray spectroscopy (EDAX) analysis confirms the stoichiometry of compounds. The real permittivity and tan δ are decreased with the dilution of Co (x = 0: ε' = 24, tan δ = 0.015; x = 0.4: ε' = 11, tan δ = 0.035 @ 1 MHz). Further, permeability initially increased in the X band frequency range and decreased with increasing Co concentration. An increase in the saturation magnetization was observed initially with increased Co content and a decrease after x = 0.2. A maximum saturation magnetization (Ms = 63.3 emu/g) observed for x = 0.2 composition. Interestingly, a giant coercivity and high effective magnetocrystalline anisotropy are observed with the incorporation of Co at low temperatures (5 K). The low dielectric loss, high saturation magnetization, and low coercivity at room temperature of Co substituted Ni–Zn ferrites suggest that these compounds are potential candidates for high-frequency devices (circulators).
Advances in multi-scale mechanical characterization
Dr Kiran Mangalampalli, Mangalampalli K., Ghosh P., Volpi F., Kiener D., Useinov A.
Source Title: Journal of Applied Physics,
Mechanical characterization of piezoelectric materials: A perspective on deformation behavior across different microstructural length scales
Dr Kiran Mangalampalli, Kathavate V.S., Prasad K.E., Kiran M.S.R.N., Zhu Y.
Source Title: Journal of Applied Physics,
View abstract ⏷
Piezoelectric materials (PEMs) find a wide spectrum of applications that include, but are not limited to, sensors, actuators, semiconductors, memory devices, and energy harvesting systems due to their outstanding electromechanical and polarization characteristics. Notably, these PEMs can be employed across several length scales (both intrinsic and extrinsic) ranging from mesoscale (bulk ceramics) to nanoscale (thin films) during their applications. Over the years, progress in probing individual electrical and mechanical properties of PEM has been notable. However, proportional review articles providing the mechanical characterization of PEM are relatively few. The present article aims to give a tutorial on the mechanical testing of PEMs, ranging from the conventional bulk deformation experiments to the most recent small-scale testing techniques from a materials science perspective. The advent of nanotechnology has led materials scientists to develop in situ testing techniques to probe the real-time electromechanical behavior of PEMs. Therefore, this article presents a systematic outlook on ex situ and in situ deformation experiments in mechanical and electromechanical environments, related mechanical behavior, and ferroelectric/elastic distortion during deformation. The first part provides significant insights into the multifunctionality of PEM and various contributing microstructural length scales, followed by a motivation to characterize the mechanical properties from the application's point of view. In the midst, the mechanical behavior of PEM and related mechanical characterization techniques (from mesoscale to nanoscale) are highlighted. The last part summarizes current challenges, future perspectives, and important observations.
Epimers with distinct mechanical behaviours
Dr Kiran Mangalampalli, Khandavilli U.B.R., Buckley A.M., Maguire A.R., Kiran M.S.R.N., Ramamurty U., Lawrence S.E.
Source Title: CrystEngComm,
View abstract ⏷
This study highlights the impact of relative stereochemistry in epimer compounds on their mechanical properties; the crystals of one series of esters are ductile and deform plastically upon bending, whereas the other series are all brittle. Nanoindentation studies show that the hardness,H, and elastic moduli,E, of the brittle crystals are substantially larger than those of the ductile ones. For the brittle crystals, theHvalues range from 153(10) to 293(37) MPa andEfrom 2.85(0.33) to 9.10(0.51) GPa, whereas for the ductile crystals, theHvalues range from 76(2) to 125(11) MPa andEfrom 1.40(0.36) and 2.75(0.06) GPa. These are rationalized by recourse to the distinct crystal structural features, especially in terms of interdigitation in the molecular planes in the brittle crystals and slip planes in the ductile crystals. The indentation fracture toughness,Kc, values of the (2′S) crystals are higher than those typically reported for molecular crystals, due to the corrugated nature of their crystal packing which enhances the crack tortuosity. TheKcvalues are in the range 0.215 (0.08) to 0.278 (0.06) MPa m½and the brittleness index values are in the range 711(19) to 1053(50) m−½
Activation Volume of the Elastic-Plastic Transition in Molecular Crystals
Source Title: Crystal Growth and Design,
View abstract ⏷
Nanoindentation experiments with a spherical indenter tip were performed on the major faces of l-alanine, p-nitroaniline, dl-tartaric acid, and sulfathiazole single crystals to measure the load at which an elastic-to-plastic deformation transition occurs, which is marked by a discrete displacement burst or pop-in. Large data sets (containing more than 100 points each) of the experimentally measured first pop-in loads, P1, were generated. By assuming that the statistical distribution in P1 is a consequence of the thermal fluctuations affecting the nucleation rate of incipient plastic events underneath the indenter, the activation volumes, λ, for the elastic-plastic transition are determined. For the four molecular crystals examined, λ values vary between 106 and 173 Å3, which are more than an order of magnitude than those in crystalline metals. However, they are similar to the molecular volume, ψ. A linear relationship between λ and ψ suggests that the plastic deformation in molecular crystals is intimately linked to the size of the molecules. These results are discussed in the context of slip planes and their orientations to the indentation direction, interplanar spacings, intermolecular interactions, etc.
Understanding Nanoscale Plasticity by Quantitative In Situ Conductive Nanoindentation
Dr Kiran Mangalampalli, George J., Mannepalli S., Mangalampalli K.S.R.N.
Source Title: Advanced Engineering Materials,
View abstract ⏷
Electronic materials such as semiconductors, piezo- and ferroelectrics, and metal oxides are primary constituents in sensing, actuation, nanoelectronics, memory, and energy systems. Although significant progress is evident in understanding the mechanical and electrical properties independently using conventional techniques, simultaneous and quantitative electromechanical characterization at the nanoscale using in situ techniques is scarce. It is essential because coupling/linking electrical signal to the nanoscale plasticity provides vital information regarding the real-time electromechanical behavior of materials, which is crucial for developing miniaturized smarter technologies. With the advent of conductive nanoindentation, researchers have been able to get valuable insights into the nanoscale plasticity (otherwise not possible by conventional means) in a wide variety of bulk and small-volume materials, quantify the electromechanical properties, understand the dielectric breakdown phenomenon and the nature of electrical contacts in thin films, etc., by continuously monitoring the real-time electrical signal changes during any point on the indentation load–hold–unload cycle. This comprehensive Review covers probing the electromechanical behavior of materials using in situ conductive nanoindentation, data analysis methods, the validity of the models and limitations, and electronic conduction mechanisms at the nanocontacts, quantification of resistive components, applications, progress, and existing issues, and provides a futuristic outlook.
Phase Transitions and Anisotropic Mechanical Response in a Water-rich Trisaccharide Crystal
Dr Kiran Mangalampalli, Seethalekshmi S., Kiran M.S.R.N., Ramamurty U., Varughese S.
Source Title: Crystal Growth and Design,
View abstract ⏷
Appreciating the mechanical response of molecular crystals in different hydration states is remarkable, and that under variable temperature conditions is hitherto unknown. We herein report the dehydration-driven anisotropic mechanical properties of raffinose pentahydrate (RF5W) single crystals as a function of temperature (T) using nanoindentation. The major face (011), with the initial loss of lattice water and the subsequent formation of defects, experienced a monotonous decrease in the hardness (H) and elastic modulus (E). Nonetheless, in the intermediate range of T, the minor face (002) exhibited a transient increase in the H and E due to dehydration-induced local structural rearrangements and the formation of slightly denser molecular packing and interactions. Beyond 65 °C, with the further loss of lattice water, the formation of defects predominates and interrupts the long-range ordering. The crystal-amorphous transformation leads to a drastic drop in the mechanical parameters. The optical and electron microscopy makes apparent observations on the expulsion of water from the crystal interior and the ensuing crystal surface transformations. The crystal hydrates are pervasive in drug formulations and could undergo dehydration to diminish the shelf life of a drug formulation. The mechanical response consequent to dehydration-driven crystal-amorphous transformation in an archetypal crystal hydrate highlights the probable ramifications on the pharmaceutical formulations.
Probing the distinct nanomechanical behaviour of a new co-crystal and a known solvate of 5-fluoroisatin and identification of a new polymorph
Dr Kiran Mangalampalli, Mondal P.K., Bhandary S., Javoor M.G., Cleetus A., Mangalampalli S.R.N.K., Ramamurty U., Chopra D.
Source Title: CrystEngComm,
View abstract ⏷
New crystalline forms (a polymorph and a co-crystal) and a previously reported solvate of the parent compound 5-fluoroisatin have been characterized by thermal, structural, and computational methods. The mechanical responses (hardness, H, and elastic modulus, E) of the co-crystal and the solvate have been characterized using nanoindentation experiments on the major faces. Results show that H and E of the solvated form of the molecule are 11 and 13 fold higher than those of the co-crystal, respectively. Energy decomposition analyses have been performed on these crystal structures to understand the primary building blocks and the role of different intermolecular interaction energies in the observed nanomechanical properties. These suggest that a nearly similar layered interaction topology of molecules is present in both the co-crystal and the solvated form. Interestingly, the presence of relatively strong interlayer interactions of molecules in the solvate prevents long-range molecular layer migration, which minimizes the scope for plastic deformation in comparison to the co-crystal.
On the indentation-assisted phase engineered Si for solar applications
Dr Kiran Mangalampalli, Mannepalli S., Sagade A.A., Mangalampalli K.S.R.N.
Source Title: Scripta Materialia,
View abstract ⏷
The rhombohedral phase of silicon is fabricated over a large-area within the diamond cubic Si wafer using spherical nanoindentation. The ultraviolet and visible spectrum showed a ~50% lower reflectance for the rhombohedral Si compared to the pristine Si. The estimated refractive index of ~6.7 at 630 nm for the rhombohedral Si is ~35% higher than the diamond cubic Si, which agrees well with the theoretical calculations. The rhombohedral Si with enhanced light absorption ability is utilized as a solar absorber layer for the bare p-n junction Si solar cell and observed to show ~10 times improvement in the photocurrent density.
The mechanism of bending in a plastically flexible crystal
Dr Kiran Mangalampalli, Bhandary S., Thompson A.J., McMurtrie J.C., Clegg J.K., Ghosh P., Mangalampalli S.R.N.K., Takamizawa S., Chopra D.
Source Title: Chemical Communications,
View abstract ⏷
Mechanically adaptable molecular crystals have potential applications in flexible smart materials and devices. Here, we report the mechanism of plastic deformation in single crystals of a small organic molecule (N-(4-ethynylphenyl)-3-fluoro-4-(trifluoromethyl)benzamide) that can be repeatedly irreversibly bent and returned to its original shape without concomitant delamination or loss of integrity. Along with the quantification of the crystals' local and bulk mechanical properties (hardness, indentation modulus and Young's modulus), micro-focus synchrotron X-ray diffraction mapping show that upon deformation, molecular layers lined with trifluoromethyl groups cooperatively slip past one another resulting in their impressive plastic malleability. This journal is
Structure Property Correlation of a Series of Halogenated Schiff Base Crystals and Understanding of the Molecular Basis through Nanoindentation
Dr Kiran Mangalampalli, Chinnasamy R., Arul A., Almousa A., Kiran M.S.R.N., Das P., Jalilov A.S., Peedikakkal A.M.P., Ghosh S.
Source Title: Crystal Growth and Design,
View abstract ⏷
Organic molecular crystals were perceived as brittle and inelastic entities; however, very recently there has been a sudden spurt of reports of soft molecular crystals. We describe a family of halogenated Schiff base molecular crystals with a design protocol aimed at achieving incorporation of structural features for a desired mechanical property. We were able to produce five crystals, of which two were elastically bendable and the remaining three were brittle. One of them is dimorphic, which means one form is brittle while the other form is elastically bendable. Delicate rebalancing between weak and dispersive noncovalent interactions along with packing features ultimately gives rise to two different polymorphs having different mechanical properties. Further, the nanoindentation technique was employed to understand the role of weak interactions so that the design of crystals with desired properties can be done more precisely in the future. This combination of elastic bending flexibility and fluorescence optical properties of molecular crystals can be used in various applications in flexible optoelectronics.
In-situ high temperature micro-Raman investigation of annealing behavior of high-pressure phases of Si
Source Title: Journal of Applied Physics,
View abstract ⏷
Among the 13 polymorphic phases of Si, the ambient temperature stable body-centered cubic (bc8) and rhombohedral (r8) polymorphs have gained significant interest due to their attractive optical and electronic properties suitable for photovoltaic applications. Though ex situ methods were extensively employed previously to understand the pressure-induced phase transformation kinetics of Si, the limited number of available in situ studies has significantly improved the knowledge in this field and clarified uncertainties. Similarly, in this article, we attempt to understand the thermal annealing behavior of nanoindentation-induced r8 and bc8 phases of Si and their volume dependence using in situ high temperature micro-Raman spectroscopy and cross-sectional transmission electron microscopy (XTEM). A spherical diamond indenter of ∼20-μm radius was chosen to indent diamond cubic (dc) Si (100) at different peak loads (Pmax) to create different volumes of high-pressure phases. The Raman spectra, Raman imaging, and XTEM of the pre- and postannealed indents confirm complete annealing of r8/bc8 phases at 200 ± 10 °C, irrespective of the volume of indents. In contrast to the previous ex situ studies, no signature of the presence of the hexagonal diamond (hd)-Si phase was found at elevated temperatures and the overall transformation observed is directly from r8 → polycrystalline dc-Si and bc8 → polycrystalline dc-Si rather than through other metastable phases such as Si-XIII/hd-Si. The present systematic in situ study provides evidence for a few earlier predictions and clarifies ambiguities involved in understanding the annealing behavior and transformation pathways of two high-pressure phases of Si at elevated temperatures.
Structural Landscape of an Antimicrobial Sulfa Drug Sulfachloropyridazine: Polymorphs, Solvates, and Cocrystals
Dr Kiran Mangalampalli, Seethalekshmi S., Amrutha S., Kiran M.S.R.N., Varughese S.
Source Title: Crystal Growth and Design,
View abstract ⏷
Experimentally identified unique crystal forms (polymorphs, solvates, and molecular complexes) of a particular compound logically reside in a certain low-energy point in the crystal landscape. The observed crystal forms offer an effective route to access different landmarks in the crystal landscape of a compound, which in turn is a profile of the structural and energetic changes occurring at the late stage of crystallization. We experimentally determined nine novel crystal forms - a polymorph, two solvates, and six cocrystals - of the sulfa drug sulfachloropyridazine. The spectral, thermal, and diffraction studies unequivocally establish the structural characteristics and the stability relationship of the polymorphs. The added coformers, with no specific chemical similarity but related by geometric and interaction types, lead to the convergence of torsional preferences and supramolecular synthons and hence a modular design of crystal structures.
Understanding Structural Variations in Elastic Organic Crystals by in Situ High-Pressure Fourier Transform Infrared Spectroscopy and Nanoindentation Study
Dr Kiran Mangalampalli, Ganguly S., Chinnasamy R., Parikh S., Kiran M.S.R.N., Ramamurty U., Bhatt H., Deo M.N., Ghosh S., Ghalsasi P.
Source Title: Crystal Growth and Design,
View abstract ⏷
Organic crystals possessing elasticity are gaining wide attention due to their potential applications in technology. From a design perspective, it is of utmost importance to understand the mechanical behavior of these crystals and their ability to handle stress. In this paper, we present an in situ high-pressure Fourier transform infrared spectroscopy study on 2,5-dichloro-N-benzylidene-4-chloroaniline (DPA) and 2,6 dichloro-N-benzylidene-4-fluoro-3-nitro aniline (DFA) crystals at pressures ranging from ambient pressure to 21.5 and 14.5 GPa respectively along with nanoindentation studies, at room temperature. The infrared stretching wavenumber of the aromatic and aliphatic C-H, H-C=N, and C-Cl bands on compression showed blueshifts and increased widths, which reflect structure perturbation caused by changes in intermolecular interactions in the crystals. It was noted that both crystals DPA and DFA behave in a different fashion under high-pressure prompting the derivation of different models based on structural changes in the lattice. Further, nanoindentation studies corroborated pressure-induced molecular movement in both crystals.
Guest Solvent-dependence of the Nanomechanical Response in Substituted Dihydropyrimidinone Crystals
Dr Kiran Mangalampalli, Bhandary S., Rani G., Mangalampalli S.R.N.K., Rao G.B.D., Ramamurty U., Chopra D.
Source Title: Chemistry - An Asian Journal,
View abstract ⏷
The nanomechanical responses of two crystalline phases of a dihydropyrimidine analogue (1) were similar irrespective of the presence (or absence) of the guest solvent. In contrast, the mechanical responses of two differently solvated forms of the second related (2) crystals were significantly different. These contrasting behaviors are rationalized in terms of intermolecular interactions and energy distributions.
Molecular Basis for the Mechanical Response of Sulfa Drug Crystals
Dr Kiran Mangalampalli, SeethaLekshmi S., Kiran M.S.R.N., Ramamurty U., Varughese S.
Source Title: Chemistry - A European Journal,
View abstract ⏷
Comprehension of the nanomechanical response of crystalline materials requires the understanding of the elastic and plastic deformation mechanisms in terms of the underlying crystal structures. Nanoindentation data were combined with structural and computational inputs to derive a molecular-level understanding of the nanomechanical response in eight prototypical sulfa drug molecular crystals. The magnitude of the modulus, E, was strongly connected to the non-covalent bond features, that is, the bond strength, the relative orientation with the measured crystal facet and their disposition in the crystal lattice. Additional features derived from the current study are the following. Firstly, robust synthons well isolated by weak and dispersive interactions reduce the material stiffness; in contrast, the interweaving of interactions with diverse energetics fortifies the crystal packing. Secondly, mere observation of layered structures with orthogonal distribution of strong and weak interactions is a prerequisite, but inadequate, to attain higher plasticity. Thirdly, interlocked molecular arrangements prevent long-range sliding of molecular planes and, hence, lead to enhanced E values. In a broader perspective, the observations are remarkable in deriving a molecular basis of the mechanical properties of crystalline solids, which can be exploited through crystal engineering for the purposeful design of materials with specific properties.
Crystal Structure-Mechanical Property Correlations in N-(3-Ethynylphenyl)-3-fluorobenzamide Polymorphs
Dr Kiran Mangalampalli, Bhandary S., Mangalampalli K.S.R.N., Ramamurty U., Chopra D.
Source Title: Crystal Growth and Design,
View abstract ⏷
During the solution-mediated crystallization of N-(3-ethynylphenyl)-3-fluorobenzamide, small variation in the process conditions can lead to two new polymorphic forms in addition to the three previously reported forms. Structural features of the two new forms and mechanical properties of the three stable polymorphs, among the five forms, have been investigated using instrumented nanoindentation. The results show that among the three stable forms (Form I, Form II, and Form III) of the compound, the Form II crystal exhibits the lowest hardness (H) and elastic modulus (E), while these values are nearly similar for Form I and Form III crystals. Interestingly, the direct correlation of mechanical properties with the density of crystals was found for three polymorphs, but their melting points do not follow similar trends. The quantitative analysis of structural features with the inputs from energy frameworks suggests that the anisotropy in mechanical properties of the three polymorphs originate from the different orientations of strong to moderate N-H⋯O hydrogen bonds and weak to strong π⋯π stacking interactions, which mainly stabilize the crystal packing of the three polymorphs.
Indentation plasticity and fracture studies of organic crystals
Source Title: Crystals,
View abstract ⏷
This review article summarizes the recent advances in measuring and understanding the indentation-induced plastic deformation and fracture behavior of single crystals of a wide variety of organic molecules and pharmaceutical compounds. The importance of hardness measurement for molecular crystals at the nanoscale, methods and models used so far to analyze and estimate the hardness of the crystals, factors affecting the indentation hardness of organic crystals, correlation of the mechanical properties to their underlying crystal packing, and fracture toughness studies of molecular crystals are reviewed.
Quantitative Investigation of the Structural, Thermal, and Mechanical Properties of Polymorphs of a Fluorinated Amide
Dr Kiran Mangalampalli, Mondal P.K., Kiran M.S.R.N., Ramamurty U., Chopra D.
Source Title: Chemistry - A European Journal,
View abstract ⏷
The discovery of three polymorphs of N-(3,5-difluorophenyl)-2,4-difluorobenzamide, of which two exist as concomitant polymorphs, highlights the significance of short, linear C−H⋅⋅⋅F intermolecular interactions in the solid state. The formation of these polymorphs can be regulated by monitoring the scan rate in differential scanning calorimetry. The phases have been characterized structurally and the investigation of the mechanical properties depicts that Form 1 is stiffer and harder than Form 2 by 50 % and 33 %, respectively.
Mechanical anisotropy in austenitic NiMnGa alloy: Nanoindentation studies
Source Title: Crystals,
View abstract ⏷
Mechanical anisotropy in an austenitic ferromagnetic shape memory alloy (SMA), Ni50Mn26.25Ga23.75, is investigated along (010), (120), (121), (231) and (232) using nanoindentation. While (010) exhibits the highest reduced modulus, Er, and hardness, H, (232) shows the lowest amongst the grain orientations examined in this study. The significant elastic anisotropy measured is attributed to differences in planar packing density and number of in-plane Ni-Mn and Ni-Ga bonds, whereas the plastic anisotropy is due to the differences in the onset of slip, which is rationalized by recourse to Schmid factor calculations. This would help determine the grain orientations in austenitic NiMnGa which exhibit better mechanical properties for SMA applications such as improving vibration damping characteristics of the alloy.
Cold nanoindentation of germanium
Dr Kiran Mangalampalli, Huston L.Q., Kiran M.S.R.N., Smillie L.A., Williams J.S., Bradby J.E.
Source Title: Applied Physics Letters,
View abstract ⏷
Diamond cubic Ge is subjected to high pressures via nanoindentation at temperatures between -45 °C and 20 °C. The residual impressions are studied using ex-situ Raman microspectroscopy and cross-sectional transmission electron microscopy. The deformation mechanism at 20 °C is predominately via the generation of crystalline defects. However, when the temperature is lowered, the analysis of residual indentation impressions provides evidence for deformation by phase transformation and formation of additional phases such as r8-Ge, hd-Ge, and amorphous Ge. Furthermore, these results show that at 0 °C and below, dc-Ge will reliably phase transform via nanoindentation.
Structural Snapshots of Metastable Intermediates Reveals Sequential Addition of Growth Units in the Formation of an Archetypal Coordination Complex: Anisotropic Layer Migration and Solid-State Thermochromic Transitions
Dr Kiran Mangalampalli, Seethalekshmi S., Mangalampalli K.S.R.N., Hareesh U.N.S., Ramamurty U., Varughese S.
Source Title: Crystal Growth and Design,
View abstract ⏷
Kinetically trapped partially preassembled metastable structures afford vital inputs on the reaction progression and the formation mechanism of technologically promising coordination assemblies. We report the structural and transformational relations in a series of coordination complexes, [Co(ad)2(H2O)4](btc-)2(H2O)2 (1), [Co(ad)2(H2O)4][Co(H2O)6](btc-)2(H2O)10 (2), [Co3(ad)2(H2O)14](btc-)2(H2O)4 (3), and [Co3(ad)2(btc-)2(H2O)8] (4), in which ad = adenine and btc = 1,3,5-benzenetricarboxylic acid, to provide insights on sequential structure evolution in an archetypal coordination assembly. Crystals of 3 undergo solid-state thermochromic transformation to a glassy phase 5 consequent to dehydration and anation reaction. With carefully optimized thermal treatment, we obtained a transient crystalline phase 4, which unambiguously proves a restructuring in the Co(II) coordination geometry from octahedral to trigonal bipyramidal. With the 3 → 4 transformation, the crystal surface undergoes drastic modification. Surface reconstruction events associated with photoreactions in the molecular crystals are noted, but analogous observations for thermally induced events are exceptional and unprecedented for coordination complexes. Correlative atomic force microscopy, nanoindentation, and structural inputs provide insights on the surface reconstruction events brought about by anisotropic long-range layer migration subsequent to 3 → 4 transition. The slip plane (011) that crosses the crystal face (010) at an optimal angle offers an energetically viable route for layer reorientation and migration.
On the loading rate sensitivity of plastic deformation in molecular crystals
Dr Kiran Mangalampalli, Raut D., Kiran M.S.R.N., Mishra M.K., Asiri A.M., Ramamurty U.
Source Title: CrystEngComm,
View abstract ⏷
The nanoindentation technique is being widely utilized to measure the mechanical properties of small single crystals of molecular materials. However, all the experiments reported hitherto were performed under quasi-static conditions and at relatively low loading rates. "Will the plastic response change if the tests are performed at high strain rates?" is a question we address in this communication. For this, we have examined the strain rate sensitivity of nanoindentation responses on the major faces of four different molecular crystals: l-alanine, saccharin, p-nitroaniline, and sulfathiazole. Experimental results indicate that the measured hardness values are loading rate insensitive. The possible reasons for this insensitivity and implications for applications in pharmaceutical manufacturing are discussed.
Temperature-dependent mechanical deformation of silicon at the nanoscale: Phase transformation versus defect propagation
Dr Kiran Mangalampalli, Kiran M.S.R.N., Tran T.T., Smillie L.A., Haberl B., Subianto D., Williams J.S., Bradby J.E.
Source Title: Journal of Applied Physics,
View abstract ⏷
This study uses high-temperature nanoindentation coupled with in situ electrical measurements to investigate the temperature dependence (25-200°C) of the phase transformation behavior of diamond cubic (dc) silicon at the nanoscale. Along with in situ indentation and electrical data, ex situ characterizations, such as Raman and cross-sectional transmission electron microscopy, have been used to reveal the indentation-induced deformation mechanisms. We find that phase transformation and defect propagation within the crystal lattice are not mutually exclusive deformation processes at elevated temperature. Both can occur at temperatures up to 150°C but to different extents, depending on the temperature and loading conditions. For nanoindentation, we observe that phase transformation is dominant below 100°C but that deformation by twinning along {111} planes dominates at 150°C and 200°C. This work, therefore, provides clear insight into the temperature dependent deformation mechanisms in dc-Si at the nanoscale and helps to clarify previous inconsistencies in the literature.
Nanoindentation of Silicon and Germanium
Dr Kiran Mangalampalli, Kiran M.S.R.N., Haberl B., Bradby J.E., Williams J.S.
Source Title: Semiconductors and Semimetals,
View abstract ⏷
Nanoindentation of silicon and germanium is of interest not only for the measurement of their mechanical properties but more importantly for the fact that they undergo a series of phase transformations under applied pressure. Indeed, after complete pressure release, the material does not return to the starting diamond cubic phase, but several metastable phases are possible, depending on the indentation conditions. In silicon, both crystalline (diamond cubic) and amorphous phases undergo a phase transformation to a dense metallic phase at around 11. GPa, a deformation process that defines the hardness of these materials. On pressure release, either a mixture of a rhombohedral (r8) phase and a body-centered cubic (bc8) phase or a pressure-induced amorphous silicon structure results. The mixed r8/bc8 phase is stable to 200. °C and has been shown to have properties of a narrow bandgap semiconductor and can be doped both n- and p-type. In germanium, the deformation processes under indentation are more complex with both plastic deformation by slip and twinning as well as phase transformation observed for diamond cubic germanium, depending on the indentation conditions. Amorphous germanium is easier to phase transform since slip-induced processes are avoided. Both crystalline and amorphous forms of germanium can be transformed to a high-density metallic phase under pressure, but several different transformation pathways are possible on pressure release, with the r8, hexagonal diamond and simple tetragonal end phases obtained under specific conditions. These deformation and phase transformation processes under indentation are reviewed in this chapter and compared with the behavior of these materials under diamond anvil cell pressure.
Pressure-induced bond rearrangement and reversible phase transformation in a metal-organic framework
Dr Kiran Mangalampalli, Spencer E.C., Kiran M.S.R.N., Li W., Ramamurty U., Ross N.L., Cheetham A.K.
Source Title: Angewandte Chemie - International Edition,
View abstract ⏷
Pressure-induced phase transformations (PIPTs) occur in a wide range of materials. In general, the bonding characteristics, before and after the PIPT, remain invariant in most materials, and the bond rearrangement is usually irreversible due to the strain induced under pressure. A reversible PIPT associated with a substantial bond rearrangement has been found in a metal-organic framework material, namely [tmenH2][Er(HCOO) 4]2 (tmenH22+=N,N,N',N'- tetramethylethylenediammonium). The transition is first-order and is accompanied by a unit cell volume change of about 10%. High-pressure single-crystal X-ray diffraction studies reveal the complex bond rearrangement through the transition. The reversible nature of the transition is confirmed by means of independent nanoindentation measurements on single crystals. A reversible pressure-induced phase transformation associated with a substantial bond rearrangement is discovered in the metal-organic framework [tmenH 2][Er(HCOO)4]2 (tmenH2 2+=N,N,N',N'-tetramethylethylenediammonium). The transition is first-order and is accompanied by a unit cell volume change of about 10%. X-ray diffraction studies reveal the complex bond rearrangement process. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Temperature dependent deformation mechanisms in pure amorphous silicon
Dr Kiran Mangalampalli, Kiran M.S.R.N., Haberl B., Williams J.S., Bradby J.E.
Source Title: Journal of Applied Physics,
View abstract ⏷
High temperature nanoindentation has been performed on pure ion-implanted amorphous silicon (unrelaxed a-Si) and structurally relaxed a-Si to investigate the temperature dependence of mechanical deformation, including pressure-induced phase transformations. Along with the indentation load-depth curves, ex situ measurements such as Raman micro-spectroscopy and cross-sectional transmission electron microscopy analysis on the residual indents reveal the mode of deformation under the indenter. While unrelaxed a-Si deforms entirely via plastic flow up to 200°C, a clear transition in the mode of deformation is observed in relaxed a-Si with increasing temperature. Up to 100°C, pressure-induced phase transformation and the observation of either crystalline (r8/bc8) end phases or pressure-induced a-Si occurs in relaxed a-Si. However, with further increase of temperature, plastic flow rather than phase transformation is the dominant mode of deformation. It is believed that the elevated temperature and pressure together induce bond softening and "defect"formation in structurally relaxed a-Si, leading to the inhibition of phase transformation due to pressure-releasing plastic flow under the indenter. © 2014 AIP Publishing LLC.
Heterogeneity of carbon fibre
Dr Kiran Mangalampalli, Huson M.G., Church J.S., Kafi A.A., Woodhead A.L., Khoo J., Kiran M.S.R.N., Bradby J.E., Fox B.L.
Source Title: Carbon,
View abstract ⏷
A range of polyacrylonitrile (PAN) and pitch based carbon fibre types (high, standard and intermediate modulus fibres) have been characterised using both physical and chemical techniques, the results highlighting the heterogeneity of the fibre. Nano-indentation showed variation in stiffness between different fibres of the same type as well as variation along a 20 μm length of a single fibre. Tensile tests showed variance of approximately 25% in tenacity for three different carbon fibre types but less variability in modulus with values from 8% to 19%. Raman spectroscopy showed variation in the graphitic content both between fibres of different origin as well as variation, with 0.5 μm spatial resolution, along the length of a single fibre. Inverse gas chromatography surface energy measurements of larger samples of fibres were carried out using the novel approach of incremental surface coverage by varying the probe molecule concentration and revealed different levels of energetic heterogeneity for PAN based fibres collected at different stages of carbon fibre production. The heterogeneity of the unoxidised fibres (collected after carbonisation) was restricted to about 15% of the fibre surface whereas the surface oxidised fibre sample (collected after the electrolytic oxidation bath) was heterogeneous over more than 30% and the sized fibres were shown to be quite homogeneous. © 2013 Elsevier Ltd. All rights reserved.
Real time monitoring of petroleum leakage detection using etched fiber Bragg grating
Dr Kiran Mangalampalli, Shivananju B.N., Kiran M., Nithin S.P., Vidya M.J., Hegde G.M., Asokan S.
Source Title: Proceedings of SPIE - The International Society for Optical Engineering,
View abstract ⏷
Detection of petroleum leakages in pipelines and storage tanks is a very important as it may lead to significant pollution of the environment, accidental hazards, and also it is a very important fuel resource. Petroleum leakage detection sensor based on fiber optics was fabricated by etching the fiber Bragg grating (FBG) to a region where the total internal reflection is affected. The experiment shows that the reflected Bragg's wavelength and intensity goes to zero when etched FBG is in air and recovers Bragg's wavelength and intensity when it is comes in contact with petroleum or any external fluid. This acts as high sensitive, fast response fluid optical switch in liquid level sensing, petroleum leakage detection etc. In this paper we present our results on using this technique in petroleum leakage detection. © 2013 SPIE.
Physical and chemical heterogeneity of carbon fibre
Dr Kiran Mangalampalli, Huson M., Church J., Kafi A., Khoo J., Mangalampalli K., Bradby J., Fox B.
Source Title: 8th Pacific Rim International Congress on Advanced Materials and Processing 2013, PRICM 8,
View abstract ⏷
Carbon fibre composites have been employed commercially for more than 50 years and their use is growing rapidly in the aerospace and automotive industries. In spite of its commercial success the relationship between the fibre structure and its physical properties are still poorly understood. This paper utilises a range of physical and chemical techniques to characterise both polyacrylonitrile and pitch based carbon fibre and highlights the heterogeneity of the fibre. Physical methods include nano-mechanical indentation whilst the use of focussed ion beam (FIB) milling for the preparation of flat surfaces for nano-indentation experiments has also been investigated. Chemical analysis involves inverse gas chromatography under finite concentration conditions and confocal Raman spectroscopy. The later includes both depth profiling showing the variation in structure from the surface to the core of the fibre and high spatial resolution (0.5 μm) mapping of the surface of the fibres.
Mechanical and electrical contact resistance characteristics of a cellular assembly of carbon nanotubes
Source Title: Nanotechnology,
View abstract ⏷
We employ nanoindentation coupled with electrical contact resistance measurements for simultaneous characterization of the electrical and mechanical behaviors of a cellular assembly of carbon nanotubes (CNTs). Experimental results reveal two different responses that correspond to relatively dense and porous regions of the cellular structure. Distinct nonlinear electron transport characteristics are observed, which mainly originate from diffusive conductance in the CNT structure. In the denser region, differential conductance shows asymmetric minima at lower bias, implying that conductivity mainly results from bulk tunneling. However, the porous regions show insignificant differential conduction as opposed to the denser region. © 2013 IOP Publishing Ltd.
Nanoindentation in crystal engineering: Quantifying mechanical properties of molecular crystals
Dr Kiran Mangalampalli, Varughese S., Kiran M.S.R.N., Ramamurty U., Desiraju G.R.
Source Title: Angewandte Chemie - International Edition,
View abstract ⏷
Nanoindentation is a technique for measuring the elastic modulus and hardness of small amounts of materials. This method, which has been used extensively for characterizing metallic and inorganic solids, is now being applied to organic and metal-organic crystals, and has also become relevant to the subject of crystal engineering, which is concerned with the design of molecular solids with desired properties and functions. Through nanoindentation it is possible to correlate molecular-level properties such as crystal packing, interaction characteristics, and the inherent anisotropy with micro/macroscopic events such as desolvation, domain coexistence, layer migration, polymorphism, and solid-state reactivity. Recent developments and exciting opportunities in this area are highlighted in this Minireview. Poking crystals: The application of nanoindentation in crystal engineering provides an important breakthrough in establishing links between microscopic structures and macroscopic properties. This Minireview highlights some of the advantages of this technique for studying the mechanical behavior of organic crystals. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
The relationship of solid-state plasticity to mechanochromic luminescence in difluoroboron avobenzone polymorphs
Dr Kiran Mangalampalli, Krishna G.R., Kiran M.S.R.N., Fraser C.L., Ramamurty U., Reddy C.M.
Source Title: Advanced Functional Materials,
View abstract ⏷
In solid-state mechanochromic luminescence (ML) materials, it remains a challenge to establish the origin of fluorescence color changes upon mechanical action and to determine why only some fluorophores exhibit ML behavior. The study of mechanical properties by nanoindentation, followed by ML experiments on green- and cyan-emitting polymorphs of difluoroboron avobenzone reveals that upon smearing, the plastically deformable cyan form shows a prominent color change to yellow, while in the harder green form the redshifted emission is barely detectable. Crystal structure analysis reveals the presence of slip planes in the softer cyan form that can facilitate the formation of recoverable and low energy defects in the structure. Hence, the cyan form exhibits prominent and reversible ML behavior. This suggests a potential design strategy for efficient ML materials. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Mechanical properties of a metal-organic framework containing hydrogen-bonded bifluoride linkers
Dr Kiran Mangalampalli, Li W., Kiran M.S.R.N., Manson J.L., Schlueter J.A., Thirumurugan A., Ramamurty U., Cheetham A.K.
Source Title: Chemical Communications,
View abstract ⏷
We report the mechanical properties of a framework structure, [Cu2F(HF)(HF2)(pyz)4][(SbF6)2]n (pyz = pyrazine), in which [Cu(pyz)2]2+ layers are pillared by HF2− anions containing the exceptionally strong F-H⋯F hydrogen bonds. Nanoindentation studies on single-crystals clearly demonstrate that such bonds are extremely robust and mechanically comparable with coordination bonds in this system. © 2013 The Royal Society of Chemistry.
Nanoindentation studies on waveguides inscribed in chalcogenide glasses using ultrafast laser
Dr Kiran Mangalampalli, Sabapathy T., Kiran M.S.R.N., Ayiriveetil A., Kar A.K., Ramamurty U., Asokan S.
Source Title: Optical Materials Express,
View abstract ⏷
Optical straight waveguides are inscribed in GeGaS and GeGaSSb glasses using a high repetition-rate sub-picosecond laser. The mechanical properties of the glasses in the inscribed regions, which have undergone photo induced changes, have been evaluated by using the nanoindentation technique. Results show that the hardness and elastic modulus of the photo-modified glasses are significantly lower as compared to the other locations in the waveguide, which tend to be similar to those of the unexposed areas. The observed mechanical effects are found to correlate well with the optical properties of the waveguides. Further, based on the results, the minimum threshold values of hardness and elastic modulus for the particular propagation mode of the waveguide (single or multi), has been established. © 2013 Optical Society of America.
Kinematic and mechanical profile of the self-actuation of thermosalient crystal twins of 1,2,4,5-tetrabromobenzene: A molecular crystalline analogue of a bimetallic strip
Dr Kiran Mangalampalli, Sahoo S.C., Sinha S.B., Kiran M.S.R.N., Ramamurty U., Dericioglu A.F., Reddy C.M., Naumov P.
Source Title: Journal of the American Chemical Society,
View abstract ⏷
A paradigm shift from hard to flexible, organic-based optoelectronics requires fast and reversible mechanical response from actuating materials that are used for conversion of heat or light into mechanical motion. As the limits in the response times of polymer-based actuating materials are reached, which are inherent to the less-than-optimal coupling between the light/heat and mechanical energy in them, a conceptually new approach to mechanical actuation is required to leapfrog the performance of organic actuators. Herein, we explore single crystals of 1,2,4,5-tetrabromobenzene (TBB) as actuating elements and establish relations between their kinematic profile and mechanical properties. Centimeter-size acicular crystals of TBB are the only naturally twinned crystals out of about a dozen known materials that exhibit the thermosalient effect - an extremely rare and visually impressive crystal locomotion. When taken over a phase transition, crystals of this material store mechanical strain and are rapidly self-actuated to sudden jumps to release the internal strain, leaping up to several centimeters. To establish the structural basis for this colossal crystal motility, we investigated the mechanical profile of the crystals from macroscale, in response to externally induced deformation under microscope, to nanoscale, by using nanoindentation. Kinematic analysis based on high-speed recordings of over 200 twinned TBB crystals exposed to directional or nondirectional heating unraveled that the crystal locomotion is a kinematically complex phenomenon that includes at least six kinematic effects. The nanoscale tests confirm the highly elastic nature, with an elastic deformation recovery (60%) that is far superior to those of molecular crystals reported earlier. This property appears to be critical for accumulation of stress required for crystal jumping. Twinned crystals of TBB exposed to moderate directional heating behave as all-organic analogue of a bimetallic strip, where the lattice misfit between the two crystal components drives reversible deformation of the crystal. © 2013 American Chemical Society.
The role of weak interactions in the phase transition and distinct mechanical behavior of two structurally similar caffeine co-crystal polymorphs studied by nanoindentation
Dr Kiran Mangalampalli, Ghosh S., Mondal A., Kiran M.S.R.N., Ramamurty U., Reddy C.M.
Source Title: Crystal Growth and Design,
View abstract ⏷
Although weak interactions, such as C-H⋯O and π-stacking, are generally considered to be insignificant, it is their reorganization that holds the key for many a solid-state phenomenon, such as phase transitions, plastic deformation, elastic flexibility, and mechanochromic luminescence in solid-state fluorophores. Despite this, the role of weak interactions in these dynamic phenomena is poorly understood. In this study, we investigate two co-crystal polymorphs of caffeine:4-chloro-3-nitrobenzoic acid, which have close structural similarity (2D layered structures), but surprisingly show distinct mechanical behavior. Form I is brittle, but shows shear-induced phase instability and, upon grinding, converts to Form II, which is soft and plastically shearable. This observation is in contrast to those reported in earlier studies on aspirin, wherein the metastable drug forms are softer and convert to stable and harder forms upon stressing. To establish a molecular-level understanding, we have investigated the two co-crystal polymorphs I and II by single-crystal X-ray diffraction, nanoindentation to quantify mechanical properties, and theoretical calculations. The lower hardness (from nanoindentation) and smooth potential surfaces (from theoretical studies) for shearing of layers in Form II allowed us to rationalize the role of stronger intralayer (sp2)C-H⋯O and nonspecific interlayer π-stacking interactions in the structure of II. Although the Form I also possesses the same type of interactions, its strength is clearly opposite, that is, weaker intralayer (sp3)C-H⋯O and specific interlayer π-stacking interactions. Hence, Form I is harder than Form II. Theoretical calculations and indentation on (111) of Form I suggested the low resistance of this face to mechanical stress; thus, Form I converts to II upon mechanical action. Hence, our approach demonstrates the usefulness of multiple techniques for establishing the role of weak noncovalent interactions in solid-state dynamic phenomena, such as stress-induced phase transformation, and hence is important in the context of solid-state pharmaceutical chemistry and crystal engineering. © 2013 American Chemical Society.
Structural and mechanical properties of room temperature sputter deposited CrN coatings
Dr Kiran Mangalampalli, Thulasi Raman K.H., Kiran M.S.R.N., Ramamurty U., Mohan Rao G.
Source Title: Materials Research Bulletin,
View abstract ⏷
Chromium nitride (CrN) thin films were deposited at room temperature on silicon and glass substrates using DC reactive magnetron sputtering in Ar + N 2 plasma. Structure and mechanical properties of these films were examined by using XRD, FESEM and nanoindentation techniques. XRD studies revealed that films are of mixed phase at lower nitrogen partial pressure (P N2) and single phase at higher (P N2). Microscopy results show that the films were composed of non-equiaxed columns with nanocrystallite morphology. The hardness and elastic modulus of the films increase with increasing nitrogen partial pressure (P N2). A maximum hardness of ∼29 GPa and elastic modulus of 341 GPa were obtained, which make these films useful for several potential applications. © 2012 Elsevier Ltd. All rights reserved.
Reactive biased target ion beam deposited W-DLC nanocomposite thin films – Microstructure and its mechanical properties
Dr Kiran Mangalampalli, Vijai Bharathy P., Yang Q., Kiran M.S.R.N., Rha J., Nataraj D., Mangalaraj D.
Source Title: Diamond and Related Materials,
View abstract ⏷
Tungsten incorporated diamond like carbon (W-DLC) nanocomposite thin films with variable fractions of tungsten were deposited by using reactive biased target ion beam deposition technique. The influence of tungsten incorporation on the microstructure, surface topography, mechanical and tribological properties of the DLC were studied using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Atomic force microscope (AFM), transmission electron microscopy (TEM), nano-indentation and nano-scratch tests. The amount of W in films gets increases with increasing target bias voltage and most of the incorporated W reacts with carbon to form WC nanoclusters. Using TEM and FFT pattern, it was found that spherical shaped WC nanoclusters were uniformly dispersed in the DLC matrix and attains hexagonal (W 2C) crystalline structure at higher W concentration. On the other hand, the incorporation of tungsten led to increase the formation of C-sp 2 hybridized bonding in DLC network and which is reflected in the hardness and elastic modulus of W-DLC films. Moreover, W-DLC films show very low friction coefficient and increased adhesion to the substrate than the DLC film, which could be closely related to its unique nanostructure of the W incorporated thin films. © 2011 Elsevier B.V. All rights reserved.
Bioactivity and mechanical properties of nickel-incorporated hydrogenated carbon nanocomposite thin films
Dr Kiran Mangalampalli, Bharathy P.V., Nataraj D., Yang Q., Kiran M.S.R.N.
Source Title: Surface and Interface Analysis,
View abstract ⏷
In this paper, the influence of nickel incorporation on the mechanical properties and the in vitro bioactivity of hydrogenated carbon thin films were investigated in detail. Amorphous hydrogenated carbon (a-C:H) and nickel-incorporated hydrogenated carbon (Ni/a-C:H) thin films were deposited onto the Si substrates by using reactive biased target ion beam deposition technique. The films' chemical composition, surface roughness, microstructure and mechanical properties were investigated by using XPS, AFM, TEM, nanoindentation and nanoscratch test, respectively. XPS results have shown that the film surface is mainly composed of nickel, nickel oxide and nickel hydroxide, whereas at the core is nickel carbide (Ni 3C) only. The presence of Ni 3C has increased the sp 2 carbon content and as a result, the mechanical hardness of the film was decreased. However, Ni/a-C:H films shows very low friction coefficient with higher scratch-resistance behavior than that of pure a-C:H film. In addition, in vitro bioactivity study has confirmed that it is possible to grow dense bone-like apatite layer on Ni/a-C:H films. Thus, the results have indicated the suitability of the films for bone-related implant coating applications. © 2011 John Wiley & Sons, Ltd.
Effect of dehydration on the mechanical properties of sodium saccharin dihydrate probed with nanoindentation
Dr Kiran Mangalampalli, Kiran M.S.R.N., Varughese S., Ramamurty U., Desiraju G.R.
Source Title: CrystEngComm,
View abstract ⏷
Nanoindentation is used to explore the variation of mechanical properties associated with the dehydration process in sodium saccharin dihydrate. Upon indenting using a Berkovich tip, (011) and (101) faces exhibit explicit mechanical anisotropy that is consistent with the underlying crystal structure and intermolecular interactions. For freshly grown crystals, (011) is stiffer than (101) by 14%, while (101) is harder than (011) by 8%. Being a heavily hydrated system, the measured mechanical responses contain information pertinent to the fluidity associated with lattice water. Indentation on (011) with a sharp cube-corner tip induces a fluid flow; this observation is uncommon in molecular crystals. The crystals effloresce over a period of time with the generation of a more compact crystal structure and consequently increasing H and E. © The Royal Society of Chemistry 2012.
Nanoindentation as a probe for mechanically-induced molecular migration in layered organic donor-acceptor complexes
Dr Kiran Mangalampalli, Varughese S., Kiran M.S.R.N., Ramamurty U., Desiraju G.R.
Source Title: Chemistry - An Asian Journal,
View abstract ⏷
Nanoindentation and scratch experiments on 1:1 donor-acceptor complexes, 1 and 2, of 1,2,4,5-tetracyanobenzene with pyrene and phenanthrene, respectively, reveal long-range molecular layer gliding and large interaction anisotropy. Due to the layered arrangements in these crystals, these experiments that apply stress in particular directions result in the breaking of interlayer interactions, thus allowing molecular sheets to glide over one another with ease. Complex 1 has a layered crystal packing wherein the layers are 68° skew under the (002) face and the interlayer space is stabilized by van der Waals interactions. Upon indenting this surface with a Berkovich tip, pile-up of material was observed on just one side of the indenter due to the close angular alignment of the layers with the half angle of the indenter tip (65.35°). The interfacial differences in the elastic modulus (21 %) and hardness (16 %) demonstrate the anisotropic nature of crystal packing. In 2, the molecular stacks are arranged in a staggered manner; there is no layer arrangement, and the interlayer stabilization involves C-H⋯N hydrogen bonds and π⋯π interactions. This results in a higher modulus (20 %) for (020) as compared to (001), although the anisotropy in hardness is minimal (4 %). The anisotropy within a face was analyzed using AFM image scans and the coefficient of friction of four orthogonal nanoscratches on the cleavage planes of 1 and 2. A higher friction coefficient was obtained for 2 as compared to 1 even in the cleavage direction due to the presence of hydrogen bonds in the interlayer region making the tip movement more hindered. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
A broad pore size distribution mesoporous SnO 2 as anode for lithium-ion batteries
Dr Kiran Mangalampalli, Shiva K., Kiran M.S.R.N., Ramamurty U., Asokan S., Bhattacharyya A.J.
Source Title: Journal of Solid State Electrochemistry,
View abstract ⏷
We demonstrate here that mesoporous tin dioxide (abbreviated M-SnO 2) with a broad pore size distribution can be a prospective anode in lithium-ion batteries. M-SnO 2 with pore size ranging between 2 and 7.5 nm was synthesized using a hydrothermal procedure involving two different surfactants of slightly different sizes, and characterized. The irreversible capacity loss that occurs during the first discharge and charge cycle is 890 mAh g -1, which is smaller than the 1,010-mAh g -1 loss recorded for mesoporous SnO 2 (abbreviated S-SnO 2) synthesized using a single surfactant. After 50 cycles, the discharge capacity of M-SnO 2 (504 mAh g -1) is higher than that of S-SnO 2 (401 mAh g -1) and solid nanoparticles of SnO 2 (abbreviated nano-SnO 2<4 mAh g -1) and nano-SnO 2. Transmission electron microscopy revealed higher disorder in the pore arrangement in M-SnO 2. This, in turn imparts lower stiffness to M-SnO 2 (elastic modulus, E R≈14.5 GPa) vis-a-vis S-SnO 2 (E R≈20.5 GPa), as obtained using the nanoindenta-tion technique. Thus, the superior battery performance of M-SnO 2 is attributed to its intrinsic material mechanical property. The fluidity of the internal microstructure of M-SnO 2 resulted in a lower degree of aggregation of Sn particles compared to S-SnO 2 and nano-SnO 2 structural stabilization and long-term cyclability. © 2012 Springer-Verlag Berlin Heidelberg.
Thermally reversing window in Ge 15Te 85 – XIn x glasses: Nanoindentation and micro-Raman studies
Dr Kiran Mangalampalli, Varma G.S., Kiran M.S.R.N., Muthu D.V.S., Ramamurty U., Sood A.K., Asokan S.
Source Title: Journal of Non-Crystalline Solids,
View abstract ⏷
Nanoindentation studies on Ge 15Te 85 - xIn x glasses indicate that the hardness and elastic modulus of these glasses increase with indium concentration. While a pronounced plateau is seen in the elastic modulus in the composition range 3 ≤ x ≤ 7, the hardness exhibits a change in slope at compositions x = 3 and x = 7. Also, the density exhibits a broad maximum in this composition range. The observed changes in the mechanical properties and density are clearly associated with the thermally reversing window in Ge 15Te 85 - xIn x glasses in the composition range 3 ≤ x ≤ 7. In addition, a local minimum is seen in density and hardness around x = 9, the chemical threshold of the system. Further, micro-Raman studies reveal that as-quenched Ge 15Te 85 - xIn x samples exhibit two prominent peaks, at 123 cm - 1 and 155 cm - 1. In thermally annealed samples, the peaks at 120 cm - 1 and 140 cm - 1, which are due to crystalline Te, emerge as the strongest peaks. The Raman spectra of polished samples are similar to those of annealed samples, with strong peaks at 123 cm - 1 and 141 cm - 1. The spectra of lightly polished samples outside the thermally reversing window resemble those of thermally annealed samples; however, the spectra of glasses with compositions in the thermally reversing window resemble those of as-quenched samples. This observation confirms the earlier idea that compositions in the thermally reversing window are non-aging and are more stable. © 2012 Elsevier B.V.
Manifestation of intermediate phase in mechanical properties: Nano-indentation studies on Ge-Te-Si bulk chalcogenide glasses
Dr Kiran Mangalampalli, Das C., Kiran M.S.R.N., Ramamurty U., Asokan S.
Source Title: Solid State Communications,
View abstract ⏷
Nano-indentation studies have been undertaken on bulk Ge 15Te85-xSix glasses (0≤x≤9), to estimate hardness, H and elastic modulus, E. It is found that E and H increase initially with the increase in the atomic percent of Si. Further, a plateau is seen in the composition dependence of E and H in the composition range 2≤x≤6. It is also seen that the addition of up to 2 at% Si increases the density ρ of the glass considerably; however, further additions of Si lead to a near linear reduction in ρ, in the range 2≤x≤6. Beyond x=6, ρ increases again with Si content. The variation of molar volume Vm brings out a more fascinating picture. A plateau is seen in the intermediate phase suggesting that the molecular structure of the glasses is adapting to keep the count of constraints fixed in this particular phase. The observed variations in mechanical properties are associated with the Boolchand's intermediate phase in the present glassy system, in the composition range 2≤x≤6, suggested earlier from calorimetric and electrical switching studies. The present results reveal rather directly the existence of the intermediate phase in elastic and plastic properties of chalcogenide glasses. © 2012 Elsevier Ltd.
Nanomechanical and optical properties of highly a-axis oriented AlN films
Dr Kiran Mangalampalli, Jose F., Ramaseshan R., Tripura Sundari S., Dash S., Tyagi A.K., Kiran M.S.R.N., Ramamurty U.
Source Title: Applied Physics Letters,
View abstract ⏷
This paper reports optical and nanomechanical properties of predominantly a-axis oriented AlN thin films. These films were deposited by reactive DC magnetron sputtering technique at an optimal target to substrate distance of 180 mm. X-ray rocking curve (FWHM = 52 arcsec) studies confirmed the preferred orientation. Spectroscopic ellipsometry revealed a refractive index of 1.93 at a wavelength of 546 nm. The hardness and elastic modulus of these films were 17 and 190 GPa, respectively, which are much higher than those reported earlier can be useful for piezoelectric films in bulk acoustic wave resonators. © 2012 American Institute of Physics.
Structure and mechanical properties of TiC films deposited using combination of pulsed DC and normal DC magnetron co-sputtering
Dr Kiran Mangalampalli, Raman K.H.T., Kiran M.S.R.N., Ramamurty U., Rao G.M.
Source Title: Applied Surface Science,
View abstract ⏷
Titanium-carbon (TiC) thin films of different compositions were prepared by a combination of pulsed DC (for Ti target) and normal DC (for graphite target) magnetron co-sputtering on oxidized silicon and fused quartz substrates. At 33.7 at.% of C content, pure hcp Ti transforms into fcc-TiC with a preferential orientation of (2 2 0) along with (1 1 1) and (2 0 0). A clear transformation in the preferential orientation from (2 2 0) to (1 1 1) has been observed when the C content was increased to 56 at.%. At 62.5 at.% of C, TiC precipitates in an amorphous carbon matrix whereas further increase in C leads to X-ray amorphous films. The cross-sectional scanning electron microscope images reveal that the films with low carbon content consists of columnar grains, whereas, randomly oriented grains are in an amorphous carbon matrix at higher carbon content. A dramatic variation was observed in the mechanical properties such as hardness, H, from 30 to 1 GPa and in modulus, E, from 255 to 25 GPa with varying carbon content in the films. Resistance to plastic deformation parameter was observed as 0.417 for films containing 62.5 at.% of C. Nanoscratch test reveals that the films are highly scratch resistant with a coefficient of friction ranging from 0.15 to 0.04. © 2012 Elsevier B.V. All rights reserved.
Improved mechanical properties of polymer nanocomposites incorporating graphene-like BN: Dependence on the number of BN layers
Dr Kiran Mangalampalli, Kiran M.S.R.N., Raidongia K., Ramamurty U., Rao C.N.R.
Source Title: Scripta Materialia,
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The mechanical properties of composites of polymethylmethacrylate (PMMA) with two-dimensional graphene-like boron nitride (BN) have been investigated to explore the dependence of the properties on the number of BN layers. This study demonstrates that significantly improved mechanical properties are exhibited by the composite with the fewest number of BN layers. Thus, with incorporation of three BN layers, the hardness and elastic modulus of the composite showed an increase of 125% and 130%, respectively, relative to pure PMMA. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Substrate-dependent structure, microstructure, composition and properties of nanostructured TiN films
Dr Kiran Mangalampalli, Kiran M.S.R.N., Ghanashyam Krishna M., Padmanabhan K.A.
Source Title: Solid State Communications,
View abstract ⏷
Titanium nitride films of a thickness of ∼1.5 μm were deposited on amorphous and crystalline substrates by DC reactive magnetron sputtering at ambient temperature with 100% nitrogen in the sputter gas. The growth of nanostructured, i.e. crystalline nano-grain sized, films at ambient temperature is demonstrated. The microstructure of the films grown on crystalline substrates reveals a larger grain size/crystallite size than that of the films deposited on amorphous substrates. Specular reflectance measurements on films deposited on different substrates indicate that the position of the TiN 2s band at 2.33 eV is substrate-dependent, indicating substrate-mediated stoichiometry. This clearly demonstrates that not only structure and microstructure, but also chemical composition of the films is substrate-influenced. The films deposited on amorphous substrates display lower hardness and modulus values than the films deposited on crystalline substrates, with the highest value of hardness being 19 GPa on a lanthanum aluminate substrate. © 2010 Elsevier Ltd. All rights reserved.
Influence of tungsten content in W-DLC nanocomposite thin films prepared by hybrid target biased ion beam assisted deposition technique
Dr Kiran Mangalampalli, Bharathy P.V., Nataraj D., Mangalaraj D., Kiran M.S.R.N., Silvestre-Albero J., Yang Q.
Source Title: International Journal of Nanoscience,
View abstract ⏷
Tungsten incorporated diamond like carbon nanocomposite films were deposited onto Si substrate by using target biased ion beam assisted deposition. The effect of W target bias voltage on the chemical bonding, structure, surface morphology and mechanical properties of DLC films were investigated by means of XPS, Raman spectroscopy, AFM and Nanoindentation. It was found that the content of W in the films increased from 6 at.% to 13.7 at.% due to the increase in target bias voltage from -300 V to -700 V. XPS analysis revealed that most of the tungsten starts to react with carbon to form WC nanoparticles. Raman analysis shows that with the increase of W fraction in the DLC matrix, the intensity ratio ID/IG increases and the G band shifts to higher wavenumber. Thus it proves that the incorporation of tungsten leads to increase in sp2 hybridized carbon content, and hence decrease in the hardness of W-DLC films compared to that of the pure DLC films. The result of AFM indicates that the surface roughness of the DLC gets modified with the incorporation of tungsten. © 2011 World Scientific Publishing Company.
Magnetic and mechanical anisotropy in a manganese 2-methylsuccinate framework structure
Dr Kiran Mangalampalli, Li W., Barton P.T., Kiran M.S.R.N., Burwood R.P., Ramamurty U., Cheetham A.K.
Source Title: Chemistry - A European Journal,
View abstract ⏷
Hybrid inorganic-organic framework materials exhibit unique properties that can be advantageously tuned through choice of the inorganic and organic components and by control of the crystal structure. We present a new hydrothermally prepared 3D hybrid framework, [Mn(2-methylsuccinate)]n (1), comprising alternating 2D manganese oxide sheets and isolated MnO 6 octahedra, pillared via syn, anti-syn carboxylates. Powder magnetic characterization shows that the compound is a homospin MnII ferrimagnet below 2.4 K. The easy-axis is revealed by single-crystal magnetic susceptibility studies and a magnetic structure is proposed. Anisotropic elastic moduli and hardness, observed through nanoindentation on differing crystal facets, were correlated with specific structural features. Such measurements of anisotropy are not commonly undertaken, yet allow for a more comprehensive understanding of structure-property relationships. Magnetic and mechanical anisotropy: A 3D manganese 2-methylsuccinate framework was constructed by alternating manganese oxide layers and isolated MnO6 octahedra, pillared via syn, anti-syn carboxylates (see figure). Single-crystal studies reveal that it exhibits highly anisotropic homospin ferrimagnetism, elastic moduli, and hardness along different single-crystal directions. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Interaction anisotropy and shear instability of aspirin polymorphs established by nanoindentation
Dr Kiran Mangalampalli, Varughese S., Kiran M.S.R.N., Solanko K.A., Bond A.D., Ramamurty U., Desiraju G.R.
Source Title: Chemical Science,
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Nanoindentation is applied to the two polymorphs of aspirin to examine and differentiate their interaction anisotropy and shear instability. Aspirin provides an excellent test system for the technique because: (i) polymorphs I and II exhibit structural similarity in two dimensions, thereby facilitating clear examination of the differences in mechanical response in relation to well-defined differences between the two crystal structures; (ii) single crystals of the metastable polymorph II have only recently become accessible; (iii) shear instability has been proposed for II. Different elastic moduli and hardness values determined for the two polymorphs are correlated with their crystal structures, and the interpretation is supported by measured thermal expansion coefficients. The stress-induced transformation of the metastable polymorph II to the stable polymorph I can be brought about rapidly by mechanical milling, and proceeds via a slip mechanism. This work establishes that nanoindentation provides "signature" responses for the two aspirin polymorphs, despite their very similar crystal structures. It also demonstrates the value of the technique to quantify stability relationships and phase transformations in molecular crystals, enabling a deeper understanding of polymorphism in the context of crystal engineering. © The Royal Society of Chemistry 2011.
Preparation and nanomechanical characterisation of metal containing amorphous hydrogenated carbon nanocomposite films
Dr Kiran Mangalampalli, Bharathy P.V., Nataraj D., Yang Q., Mangalaraj D., Kiran M.S.R.N.
Source Title: Advanced Materials Research,
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The relationship between metal-induced chemical bonding and the mechanical properties of Me/a:C-H (Me-Ti and Ni) films are discussed. Nanocomposite films were deposited onto the Si substrates via biased target ion beam sputtering of metal combined with reactive ion beam deposition of a:C-H using CH 4/Ar gas mixture. The chemical composition, microstructure and mechanical properties were characterized using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and nanoindentation. XPS analysis revealed that both Ti and Ni atoms were preferentially bonded to carbon to form its metal carbide phase. Irrespective of its kind, both the metal carbide clusters induces more graphite like bondings in a:C-H matrix. From the nanoindentation analysis it was found that there is no crack propagation and damage around the indent region even at very high indentation loads. Additionally, it was found that a:C-H film shows higher hardness compared to that of Ti/a:C-H and Ni/a:C-H films. © (2010) Trans Tech Publications.
Effect of titanium incorporation on the structural, mechanical and biocompatible properties of DLC thin films prepared by reactive-biased target ion beam deposition method
Dr Kiran Mangalampalli, Bharathy P.V., Nataraj D., Chu P.K., Wang H., Yang Q., Kiran M.S.R.N., Silvestre-Albero J., Mangalaraj D.
Source Title: Applied Surface Science,
View abstract ⏷
Amorphous diamond like carbon (DLC) and titanium incorporated diamond like carbon (Ti-DLC) thin films were deposited by using reactive-biased target ion beam deposition method. The effects of Ti incorporation and target bias voltage on the microstructure and mechanical properties of the as-deposited films were investigated by means of X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy and nano-indentation. It was found that the Ti content in Ti-DLC films gets increased with increasing target bias voltage. At about 4.2 at.% of Ti, uniform sized well dispersed nanocrystals were seen in the DLC matrix. Using FFT analysis, a facility available in the TEM, it was found that the nanocrystals are in cubic TiC phase. Though at the core, the incorporated Ti atoms react with carbon to form cubic TiC; most of the surface exposed Ti atoms were found to react with the atmospheric oxygen to form weakly bonded Ti-O. The presence of TiC nanocrystals greatly modified the sp 3 /sp 2 hybridized bonding ratio and is reflected in mechanical hardness of Ti-DLC films. These films were then tested for their biocompatibility by an in vitro cell culturing test. Morphological observation and the cell proliferation test have demonstrated that the human osteoblast cells well attach and proliferate on the surface of Ti incorporated DLC films, suggesting possible applications in bone related implant coatings. © 2010 Elsevier B.V. All rights reserved.
Mechanical anisotropy in crystalline saccharin: Nanoindentation studies
Dr Kiran Mangalampalli, Kiran M.S.R.N., Varughese S., Reddy C.M., Ramamurty U., Desiraju G.R.
Source Title: Crystal Growth and Design,
View abstract ⏷
The nanoindentation technique has been employed to relate the mechanical properties of saccharin single crystals with their internal structure. Indentations were performed on (100) and (011) faces to assess the mechanical anisotropy. The load-displacement (P-h) curves indicate significant differences in the nature of the plastic deformation on the two faces. The P-h curves obtained on the (011) plane are smooth, reflecting homogeneous plasticity. However, displacement bursts (pop-ins) are observed in the P-h curves obtained on the (100) plane suggesting a discrete deformation mechanism. Marginal differences exist in the hardness and modulus on the two faces that may, in part, be rationalized, although one notes that saccharin has a largely three-dimensional close-packed structure. The structural origins of the fundamentally different deformation mechanisms on (100) and (011) are discussed in terms of the dimensionality of the hydrogen bonding networks. Down the (100) planes, the saccharin dimers are stacked and are stabilized by nonspecific van der Waals interactions mostly between aromatic rings. However, down the (011) planes, the molecules are stabilized by more directional and cross-linked C-H⋯O hydrogen bonds. This anisotropy in crystal packing and interactions is reflected in the mechanical behavior on these faces. The displacements associated with the pop-ins were found to be integral multiples of the molecule separation distances. Nanoindentatixon offers an opportunity to compare experimentally, and in a quantitative way, the various intermolecular interactions that are present in a molecular crystal. © 2010 American Chemical Society.
Nanomechanical properties of silicon surfaces nanostructured by excimer laser
Source Title: Science and Technology of Advanced Materials,
View abstract ⏷
Excimer laser irradiation at ambient temperature has been employed to produce nanostructured silicon surfaces. Nanoindentation was used to investigate the nanomechanical properties of the deformed surfaces as a function of laser parameters, such as the angle of incidence and number of laser pulses at a fixed laser fluence of 5 J cm-2. A single-crystal silicon [311] surface was severely damaged by laser irradiation and became nanocrystalline with an enhanced porosity. The resulting laser-treated surface consisted of nanometer-sized particles. The pore size was controlled by adjusting the angle of incidence and the number of laser pulses, and varied from nanometers to microns. The extent of nanocrystallinity was large for the surfaces irradiated at a small angle of incidence and by a high number of pulses, as confirmed by x-ray diffraction and Raman spectroscopy. The angle of incidence had a stronger effect on the structure and nanomechanical properties than the number of laser pulses. © 2010 National Institute for Materials Science.
Structural, optical and nanomechanical properties of (111) oriented nanocrystalline ZnTe thin films
Dr Kiran Mangalampalli, Kiran M.S.R.N., Kshirsagar S., Krishna M.G., Tewari S.P.
Source Title: EPJ Applied Physics,
View abstract ⏷
Structural, optical and nanomechanical properties of nanocrystalline Zinc Telluride (ZnTe) films of thickness upto 10 microns deposited at room temperature on borosilicate glass substrates are reported. X-ray diffraction patterns reveal that the films were preferentially oriented along the (111) direction. The maximum refractive index of the films was 2.74 at a wavelength of 2000 nm. The optical band gap showed strong thickness dependence. The average film hardness and Young's modulus obtained from loaddisplacement curves and analyzed by Oliver-Pharr method were 4 and 70 GPa respectively. Hardness of (111) oriented ZnTe thin films exhibited almost 5 times higher value than bulk. The studies show clearly that the hardness increases with decreasing indentation size, for indents between 30 and 300 nm in depth indicating the existence of indentation size effect. The coefficient of friction for these films as obtained from the nanoscratch test was ~0.4. EDP Sciences. © EDP Sciences.
Nanomechanical characterization of indium nano/microwires
Source Title: Nanoscale Research Letters,
View abstract ⏷
Nanomechanical properties of indium nanowires like structures fabricated on quartz substrate by trench template technique, measured using nanoindentation. The hardness and elastic modulus of wires were measured and compared with the values of indium thin film. Displacement burst observed while indenting the nanowire. 'Wire-only hardness' obtained using Korsunsky model from composite hardness. Nanowires have exhibited almost same modulus as indium thin film but considerable changes were observed in hardness value. © The Author(s) 2010.
Growth, surface morphology, optical properties and electrical resistivity of ε-TiN x (0.4 < x ≤ 0.5) films
Dr Kiran Mangalampalli, Kiran M.S.R.N., Krishna M.G., Padmanabhan K.A.
Source Title: Applied Surface Science,
View abstract ⏷
The growth, structure, surface morphology, optical properties and electrical resistivity studies on TiN x (0.4 < x ≤ 0.5) films is presented. The films of thickness 116-230 nm were grown on fused silica substrates by RF magnetron sputtering in 100% pure nitrogen atmosphere at ambient temperature and pressures from 12 to 25 mTorr. For the as-deposited films, the refractive index decreased from 1.86 to 1.6 with increasing N 2 pressure from 12 to 25 mTorr. The absorption edge for the film deposited at 12 mTorr was 4.7 eV and it decreased to 3.5 eV on increasing the N 2 pressure to 25 mTorr. Post-deposition annealing of the films at 873 K for 1 min did not cause any variation in the optical properties. The film deposited at 25 mTorr and annealed at 873 K showed a nanocrystalline peak corresponding to ε-Ti 2 N (3 1 1) with a crystallite size of 60 nm. Surface morphologies varied dramatically with N 2 pressure. The electrical resistivity of the film deposited at 12 mTorr was 37 MΩ cm whereas it is 270 kΩ cm for the films deposited at 25 mTorr. Therefore, the current work provides signatures for the ε-Ti 2 N phase in terms of refractive index, optical absorption edge and electrical resistivity, that can be used to identify the presence of the sub-stoichiometric forms in a TiN film. © 2008 Elsevier B.V. All rights reserved.
Chromium and nickel substituted iron oxide thin films by DC sputtering
Dr Kiran Mangalampalli, Kiran M.S.R.N., Sudheendran K., Ghanashyam Krishna M., James Raju K.C., Bhatnagar A.K.
Source Title: Vacuum,
View abstract ⏷
Chromium and nickel substituted iron oxide thin films have been deposited by DC sputtering. Films were coated in the thickness range of 130-400 nm, on boro silicate glass and quartz substrates. The films showed transmission as high as 90% in the visible region. The refractive index of the films was 1.6-2.1. The microwave dielectric constant varied as a function of composition from 24 to 12 at frequencies of 8.98 and 11.88 GHz. All the films were X-ray amorphous independent of deposition and post deposition annealing conditions. Surface morphology indicates that roughness is a function of both sputtering pressure as well as inter-electrode distance. © 2006 Elsevier Ltd. All rights reserved.
