Department of Physics

The authors regret the oversight in one of the author's (Manjunatha Thondamal) affiliation details occurred during the final proof reading. The affiliation detail for the author-Manjunatha Thondamal is: d Department of Biotechnology, School of Technology, Gandhi Institute of Technology and Management (GITAM), Visakhapatnam, Andhra Pradesh, 530045, India. The authors would like to apologise for any inconvenience caused.

Gold nanoclusters (Au NCs) have found wide range of applications in environmental, chemical and health sectors as sensors, catalytic agents and theranostic molecules, respectively, due to their ultrasmall size and excellent optical properties. However, a comprehensive battery of bioassays of Au NCs were lacking on a well-established biological model system, which would enhance its potential to be used as an optical probe with application in theranostics. The current investigation aims to address the in vivo compatibility of Au NCs to improve their design, evaluate their biological impact, and validate their potential for bioimaging applications. We have used the Caenorhabditis elegans as a model organism in our present study due to their short life cycle facilitating evaluation of drug effects in reasonable time frame and transparent body framework suitable for in vivo imaging. These features facilitate accurate information regarding the uptake and biodistribution of Au NCs inside the tissues and body parts. Additionally, different nanotoxicological studies such as biodistribution of NCs and its subsequent impact on the health span, brood size, pharyngeal pumping and tail thrashing of C. elegans were observed as a measure of the Au NCs biocompatibility. Our results strongly demonstrate that the human serum albumin (HSA)-bound Au NCs are non-toxic, biocompatible and do not exhibit any adverse effect on the physiology and survival of the C. elegans. This study, employing a comprehensive battery of bioassays, is the first to systematically evaluate the long-term biocompatibility and non-toxicity of Au NCs across the entire lifespan of an organism, measured through multiple physiological parameters. These findings underscore the potential of Au NCs as safe and effective diagnostic and therapeutic agents for medical and clinical applications.

This article reports facile fabrication of a multifunctional smart surface having superhydrophobic self-cleaning property, superoleophilicity, and antimicrobial property. These smart surfaces have been synthesized using the stereolithography (SLA) method of the additive manufacturing technique. SLA is a fast additive manufacturing technique used to create complex parts with intricate geometries. A wide variety of materials and high-resolution techniques can be utilized to create functional parts such as superhydrophobic surfaces. Various materials have been studied to improve the functionality of 3D printing. However, the fabrication of such materials is not easy, as it is quite expensive. In this work, we used a commercially available SLA printer and its photopolymer resin to create various micropatterned surfaces. Additionally, we applied a low surface energy coating with ZnO nanoparticles and tetraethyl orthosilicate to create hierarchical roughness. The wettability studies of created superhydrophobic surfaces were evaluated by means of static contact angle using the sessile drop method and rolling angle measurements. The effects of various factors, including different concentrations of coating mixture, drying temperatures, patterns (pyramids, pillars, and eggbeater structures), and pillar spacing, were studied in relation to contact angles. Subsequently, all the functional properties (i.e., self-cleaning, oleophilicity, and antibacterial properties) of the as-obtained surfaces were demonstrated using data, images, and supporting videos. This inexpensive and scalable process can be easily replicated with an SLA 3D printer and photopolymer resin for many applications such as self-cleaning, oil-water separation, channel-less microfluidics, antibacterial coating, etc.

The development of direct methanol fuel cells (DMFCs) relies on designing replacements for benchmark platinum (Pt)-based electrocatalysts toward methanol oxidation reaction (MOR) that exhibit high resistance to CO poisoning, improve kinetic sluggishness, devoid of unwanted intermediates, low catalyst cost, and wide operating conditions. This study presents the development of defect engineering N-doped graphene oxide (NG) supported ZnWO4 nanocuboids as an efficient catalyst for photoelectrochemical MOR and electrochemical ORR. Under visible light (420 nm), the NG/ZnWO4 nanohybrid exhibits exceptional photoelectrochemical MOR with low potential of 0.5V with a high oxidation peak current density of ≈10 mA cm−2 is recorded while comparing with benchmark catalyst Pt/C. In two electrode systems for DMFC, the catalyst reaches an impressive maximum power production of 111 mW cm−2 with very stable charge-discharge cycles of 0.33 mV cycle−1, which is far superior to ZnWO4’s alone. Simultaneously, the nanocomposite exhibits excellent ORR activity in alkaline medium with improved onset half-wave potential of 0.85V, high current density of 5.8 mA cm−2 at 1600 rpm, and robust stability, attributed to the synergistic effect between NG and ZnWO4. This work has reinforced these findings with theoretical insights using the Vienna Ab initio Simulation Package (VASP) to assess both PMOR and ORR performance and reaction intermediates.

Renewable energy has gained widespread recognition for its potential to drive sustainable power generation and mitigate climate change. However, the rapid expansion of these resources highlights inherent challenges arising from their non-dispatchable, intermittent, and asynchronous nature, underscoring the critical need for grid-scale energy storage. Although numerous storage technologies exist, cohesive insights into commercially available or nearing commercialization remain limited. The review addresses that gap by presenting a comprehensive analysis of marketable grid-scale energy-storage solutions. The discussion begins with an examination of growth dynamics and regional trends in energy-storage capacities worldwide. By using California and Saudi Arabia as representative samples of the Mediterranean and hot desert regions under the Köppen classification, the review illustrates how climatic zones influence energy-storage requirements. After highlighting recyclability challenges associated with lithium-ion batteries, the study explores emerging electrochemical and gravitational-storage technologies. It then articulates critical parameters for evaluating energy-storage solutions and provides a comparative performance analysis. The review concludes by identifying a range of commercialized innovations and recommending a holistic approach to strengthen reliance on renewable energy.

The hybridization of biomolecules with gold nanoclusters (AuNCs) has emerged as a promising research direction in bioelectronics, extending multidimensional prospects for diverse applications, from wearable health monitoring to advanced medical devices and tissue engineering. Here, we report a hybrid of bovine serum albumin (BSA) protein and gold nanoclusters of various concentrations to harness the distinctive properties of gold nanoclusters and enhance the electronic functionalities of biomolecules. Self-assembled monolayers (SAMs) of hybrid materials demonstrate enhanced electrical conduction with a film thickness of 10–15 nm as obtained from atomic force microscopy topographical images, revealing minimal aggregation. Current–voltage (I–V) characteristics at ±0.5 V showed significantly higher current densities for optimized hybrid material (BSA-Au6) SAMs, reaching 150 A/cm2. Compared to prior studies on BSA and metal hybrid thin films, the observed 100-fold enhancement in electrical conductivity for AuNC-doped SAMs highlights the novelty of this work. Moreover, our study with different AuNC concentrations demonstrated that six equivalents of AuNCs significantly boosted conductivity due to efficient electron transport mechanisms, which was further investigated with electrical impedance measurements. Our findings provide valuable insights into the underlying electronic transport mechanisms across hybrid materials for applications in bioelectronics and molecular electronics, marking a breakthrough compared to conventional protein films.

Reduced graphene oxide (rGO) has captivated the scientific community due to its exceptional electrical conductivity, high specific surface area, and excellent mechanical strength. The physical properties of reduced graphene oxide (rGO) are strongly dependent on the presence of different functional groups in its structural framework, along with surface roughness. In this study, laser annealing was employed by a nanosecond Nd:YAG laser to investigate the impact of varying laser energies on the wettability and conductivity of reduced graphene oxide (rGO) samples grown by the pulsed laser deposition (PLD) technique. The rGO films were annealed with different laser fluences, such as 10, 20, 30, 38, 48, 55, and 250 mJ/cm2. Our results reveal a notable transition in wettability, transforming the initially hydrophobic rGO samples into a hydrophilic state. Hydrophilic graphene oxide (GO) or reduced graphene oxide (rGO) surfaces have significant potential for use in biomedical applications due to their unique combination of properties, including biocompatibility, high surface area, and abundant oxygen-containing functional groups. Along with wettability properties, conductivity changes were also observed. The presented findings not only contribute to the understanding of laser-induced modifications in rGO but also highlight the potential applications of controlled laser annealing in tailoring the surface properties of graphene-based materials for diverse technological advancements.

Self-cleaning surfaces revolutionizing the technology world due to their novel property of cleaning themselves, and its multi-functional self-cleaning surfaces exhibit at least one or more functional properties (transparent, conducting, anti-bacterial, anti-corrosion, etc.) This review article focuses on the fundamentals of wettability, material parameters controlling surface wettability and three different paths to realization of self-cleaning surfaces, i.e., (i) super-hydrophobic, (ii) super-hydrophilic and (iii) photocatalytic. The subsequent part of the article mostly focuses on the super-hydrophobic path towards realizing self-cleaning surfaces. In the super-hydrophobic path, the objective is to make the surface extremely repellent to water so that water droplets slide and ‘roll off’ from the surface. The next section of the review article focuses on the role of additive manufacturing in the fabrication of super-hydrophobic micro-structures. Amidst the different fabrication processes of self-cleaning surfaces, additive manufacturing stays ahead as it has the manufacturing capacity to create complex micro-structures in a scalable and cost-effective manner. A few prominent types of additive manufacturing processes were strategically chosen which are based on powder bed fusion, vat photopolymerization, material extrusion and material jetting techniques. All these additive manufacturing techniques have been extensively reviewed, and the relative advantages and challenges faced by each during the scalable and affordable fabrication of super-hydrophobic self-cleaning surfaces have been discussed. The article concludes with the latest developments in this field of research and future potential. These surfaces are key to answer sustainable development goals in manufacturing industries.

Physical systems with nonreciprocal or dissipative forces evolve according to a generalization of Liouville's equation that accounts for the expansion and contraction of phase space volume. Here we connect geometric descriptions of these non-Hamiltonian dynamics to a recently established classical density matrix theory. In this theory, the evolution of a "maximally mixed"classical density matrix is related to the well-known phase space contraction rate that, when ensemble averaged, is the rate of entropy exchange with the surroundings. We extend the definition of mixed states to include statistical and mechanical components, describing both the deformations of local phase space regions and the evolution of ensembles within them. As a result, the equation of motion for this mixed state represents the rate of contraction for an ensemble of dissipative trajectories. Recognizing this density matrix as a covariance matrix, its contraction rate is another measure of entropy flow characterizing nonequilibrium steady states.

Perovskite solar cells (PSCs) are improving in efficiency, but their stability remains a challenge compared to other solar technologies due to the use of hybrid organic–inorganic materials. To overcome this, researchers have shifted focus from methylammonium-based PSCs to more stable cesium (Cs)-based PSCs. By optimizing multi-layer structures to enhance solar spectrum absorption, substantial performance improvements are possible. In this study, we explored single (CsPbIBr2), dual (CsPbIBr2/KSnI3), and triple (CsPbIBr2/KSnI3/MASnBr3) absorber layer designs. The optimization of bilayer and triple-layer PSCs takes into account various factors, such as absorber layer thickness, defect density, and interface defect density for each PSC type. Finally, using the optimal triple-absorber layer combination, we optimized the electron transport layer, hole transport layer, series resistance, and shunt resistance. In this research, we attained impressive efficiencies of 34.22% for the triple-layer solar cell, 20.41% for the bilayer solar cell, and 7.32% for the single-junction PSC. This design approach led to an optimal configuration that showed substantial improvements over the experimental benchmark, including a 7.08% increase in open circuit voltage, a 256.9% increase in short circuit current, a 22.32% increase in fill factor, and a 367.5% increase in efficiency. By meticulously aligning multiple absorber layers in perovskite solar cells, we can unlock new pathways to developing highly efficient solar cells for the future.

We show that the inequality in the divergent acoustic energy release rate in quasistatically compressed nanoporous materials can be used as a precursor to failure. A quantification of the inequality in the evolution of the energy release rate using social inequality (such as Gini and Kolkata) indices can predict large bursts of energy release. We also verify similar behavior for simulations of viscoelastic fiber bundle models that mimic the strain-hardening dynamics of the samples. The results demonstrate experimental applicability of the precursory signal for fracture with a diverging energy release rate using social inequality indices.

We have recently put forth several schemes of unconventional, nonlinearly-enabled thermodynamic (TD) devices that can operate in either the classical or the quantum domain by transforming thermal-state input in multiple uncorrelated modes into non-gaussian state output in selected modes: a four-mode Kerr-nonlinear interferometer that acts as a heat engine; two coupled Kerr-nonlinear Mach-Zehnder interferometers that act as a phase microscope with unprecedented phase resolution; and a noise sensor that can distinguish between unknown nonlinear quantum processes. These schemes reveal the unique merits of nonlinear TD devices: their ability to act in an autonomous, fully coherent, dissipationless fashion, unlike their conventional counterparts. Here we present the opportunities and challenges facing this new paradigm of nonlinear (NL) quantum and classical TD devices along the following lines: (A) Linear versus nonlinear multimode transformations in TD devices: what are the principal distinctions between the two types of transformations? (B) Classical versus quantum effects in NL TD devices: what are their main differences? Is quantumness an advantage or a disadvantage? (C) Deterministic methods of achieving giant nonlinearity at the few-photon level via coherent processes, including multiatom-bath interactions which can paradoxically yield NL Hamiltonian effects: their comparison with probabilistic, measurement-based methods that can achieve similar NL effects in the quantum domain.

Within the general Uð1Þ scenario, we demonstrate that the ultrahigh-energy neutrinos recently detected by KM3NeT could originate from a decaying right-handed neutrino dark matter, with a mass of 440 PeV. Considering dark matter production via freeze-in, we delineate the parameter space that satisfies the observed relic abundance and also lies within the reach of multiple gravitational wave detectors. Our study provides a testable new physics scenario, enabled by multimessenger astronomy.

We propose a methodology to infer the reheat temperature (TRH) of the Universe from the collider signal of freezing in dark matter (DM). We demonstrate it for the mono-γ signal at the electron-positron colliders, which indicates to a low-scale TRH, after addressing observed DM abundance, BBN, and other relevant constraints. The method can be used to correlate different reheating dynamics, DM models, and collider signals.

The transition from the end of inflation to a hot, thermal Universe, commonly referred to as (re)heating, is a critical yet often misunderstood phase in early Universe cosmology. This short review aims to provide a comprehensive, conceptually clear, and accessible introduction to the physics of (re)heating, tailored to the particle physics community. We critically examine the standard Boltzmann approach, emphasizing its limitations in capturing the intrinsically non-perturbative and non-linear dynamics that dominate the early stages of energy transfer. These include explosive particle production, inflaton fragmentation, turbulence, and thermalization; phenomena often overlooked in perturbative treatments. We survey a wide range of theoretical tools, from Boltzmann equations to lattice simulations, clarifying when each is applicable and highlighting scenarios where analytic control is still feasible. Special attention is given to model-dependent features such as (pre)heating, the role of fermions, gravitational couplings, and the impact of multifield dynamics. We also discuss exceptional cases, including Starobinsky-like models and instant (pre)heating, where (re)heating proceeds through analytically tractable channels without requiring full non-linear simulations. Ultimately, this review serves both as a practical guide and a cautionary tale, advocating for a more nuanced and physically accurate understanding of this pivotal epoch within the particle physics community.

In the minimal gauged B − L extension of the Standard Model, we demonstrate that PeV-scale dark matter (DM) and the baryon asymmetry of the Universe (BAU) can be simultaneously explained through the three right-handed neutrinos (RHNs) present in the theory. The DM candidate undergoes rare decay into light neutrinos, providing an explanation for the observed IceCube events, while the other two RHNs generate the BAU via leptogenesis. The breaking of gauge symmetry gives rise to detectable gravitational waves (GWs) from decaying cosmic strings (CS), making this framework testable at several future GW detectors—despite being beyond the reach of conventional collider experiments due to the extremely weak gauge coupling. The symmetry-breaking scale establishes a connection between particle masses, couplings, and the GW spectrum, offering a unified and predictive scenario.

Dark matter (DM) genesis via Ultraviolet (UV) freeze-in embeds the seed of reheating temperature and dynamics in its relic density. Thus, discovery of such a DM candidate can possibly open the window for post-inflationary dynamics. However, there are several challenges in this exercise, as freezing-in DM possesses feeble interaction with the visible sector and therefore very low production cross-section at the collider. We show that mono-photon (and dilepton) signal at the ILC, arising from DM effective operators connected to the SM field strength tensors, can still warrant a signal discovery. We study both the scalar and fermionic DM production during reheating via UV freeze-in, when the inflaton oscillates at the bottom of a general monomial potential. Interestingly, we see, right DM abundance can be achieved only in the case of bosonic reheating scenario, satisfying bounds from big bang nucleosynthesis (BBN). This provides a unique correlation between collider signal and the post-inflationary dynamics of the Universe within single-field inflationary models.

We examine the impact of charged lepton Yukawa equilibration on leptogenesis during gravitational reheating. During the post-inflationary era, the inflaton field is assumed to oscillate around the minimum of a monomial potential, leading to the gravitational production of Standard Model (SM) particles, constituting the radiation bath. The heavy right-handed neutrinos (RHN), responsible for generating baryon asymmetry via leptogenesis, are also produced through graviton-mediated scattering of the homogeneous inflaton field and thermal bath, as well as from the inverse decay of the bath particles. By considering both minimal and non-minimal gravitational contributions to SM, we demonstrate that flavour effects can be safely neglected in the minimal reheating scenario. However, with large non-minimal coupling, these effects may become important, depending on the choice of the RHN mass. We identify the corresponding viable parameter space that satisfies the observed baryon asymmetry in each case.

We study the generation of baryon asymmetry as well as dark matter (DM) in an extended reheating period after the end of slow-roll inflation. Within the regime of perturbative reheating, we consider different monomial potential of the inflaton field during reheating era. The inflaton condensate reheats the Universe by decaying into the Standard Model (SM) bath either via fermionic or bosonic decay modes. Assuming the leptogenesis route to baryogenesis in a canonical seesaw framework with three right handed neutrinos (RHN), we consider both the radiation bath and perturbative inflaton decay to produce such RHNs during the period of reheating when the maximum temperature of the SM bath is well above the reheating temperature. The DM, assumed to be a SM gauge singlet field, also gets produced from the bath during the reheating period via UV freeze-in. In addition to obtaining different parameter space for such nonthermal leptogenesis and DM for both bosonic and fermionic reheating modes and the type of monomial potential, we discuss the possibility of probing such scenarios via spectral shape of primordial gravitational waves.