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In this paper, we consider the nonequilibrium Casimir pressure in the system of two parallel graphene-coated plates one of which is either warmer or cooler than the environment. The electromagnetic response of graphene coating characterized by the nonzero energy gap and chemical potential is described in the framework of the Dirac model by means of the polarization tensor. It is shown that the magnitude of the nonequilibrium Casimir pressure on a warmer plate than the environment is larger and on a cooler plate it is smaller than the magnitude of the standard Casimir pressure in the state of thermal equilibrium. According to our results, the spatially local theory underestimates the role of the effects of nonequilibrium. This underestimation increases for a smaller chemical potential of the graphene coating and at lower temperatures of the cooled plate. Possible applications of the obtained results are indicated.

This paper gives a brief overview of the polarization tensor approach to the Casimir effect. The fundamental principles of this approach are discussed, along with its various applications to both three-dimensional and two-dimensional systems, with a focus on its implications for graphene.

The plausible resolution of the Casimir puzzle implying that the dissipative Drude model is not applicable in the area of transverse electric evanescent waves is discussed. Calculations show that for the propagating waves, as well for the evanescent waves with transverse magnetic polarization, the Drude model can be used in calculations of the Casimir force by the Lifshitz theory with no contradictions with the measurement data. The lateral component of magnetic field of the magnetic dipole oscillating near a metallic surface is computed for the parameters of experiment in preparation which is aimed to directly check the validity of the Drude model in the area of transverse electric evanescent waves. By comparing with the case of graphene, whose dielectric response is spatially nonlocal and possesses the double pole at zero frequency, it is hypothesized that the success of the dissipationless plasma model in this area is also caused by the presence of a double pole.

Because the electron transport mechanism in graphene is heavily impacted by the strain and the ferromagnetic metal stripe as well as several other avenues, in this paper we investigate the effects of the strained barrier induced by the strain and the magnetic field generated by the ferromagnetic metal stripe on the valley polarization through numerical calculation. When the strength and the width of the strained barrier as well as the magnitude of the magnetic field are changed, the rapid variation of the valley polarization is observed. This study will be helpful for devising and manufacturing new-style valleytronic devices.

Lithium-ion batteries employing graphite as the anode material are now widely used in powering electronic gadgets like, mobile phones, laptops, electronic watches and calculators and also to provide required power to run engine of electric vehicles. However, storage capacity, open circuit voltage, energy density and battery life are the major considerations on which researchers are trying different alternatives to achieve better performance of the battery. In this research, Beryllium-doped and defective graphenes have been investigated by employing the ab initio DFT method. It has been found that graphene with a defect and Be–doped graphene with defects can serve as an efficient materials for anode in Li-ion batteries.

Graphene, celebrated for its remarkable atomic structure, stands as a key material in diverse fields such as nanoelectronics and materials science. This paper presents a thorough investigation into the metric dimensions of graphene, emphasizing its unique spatial properties and their broad implications. We analyze how these metric dimensions affect graphene’s electrical, thermal, and mechanical behavior in various applications. Our study delves into the physical mechanisms behind these properties, including atomic interactions, lattice dynamics, and external factors like temperature and pressure.

The metric dimension of a graph G is the minimum cardinality of a subset $W\subseteq V(G)$ such that every pair of distinct vertices $u,v\in V(G)$ is uniquely identified by their distance vectors relative to W and the resolving set, ensures for any $u,v\in V(G)$ with $u\ne v$, there exists a vertex $w\in W$ such that $d(u,w)\ne d(v,w)$, where d denotes the distance function in G. In this work, we will determine the metric dimension and Resolving set. However, these findings pave the way for innovative applications in electronics, composites, and beyond.

In this study, WC10Co4Cr (particle size $45\pm 15$$\mu$m) and WC10Co4Cr+Graphen nano-platelets (GNPs) of particle size $15\pm 10$$\mu$m cermet coatings were deposited on an ASTM A479 steel substrate utilising the High-Velocity Oxygen Fuel (HVOF) technique. The wear and corrosion of coated and uncoated surfaces were studied using the pin-on-disc and salt spray testing methods, respectively, and the micro-hardness of the cross-sections was tested using a Vickers micro-hardness testing machine at an applied force of 10N. Further, surface morphology of coated and uncoated substrate was investigated using scanning electron microscopy (SEM) and microscopic images. The analysis revealed that WC-10Co-$4\mathrm{\text{Cr}}+\mathrm{\text{GNPs}}$-coated (C2) surfaces outperformed WC10Co4Cr coated (C1) surfaces in terms of wear resistance.

Graphene has amazing applications for sensors due to its excellent performances like high strength and good conductivity, but the transfer issue is in the way of its application perspective. Direct growth of spherical graphene films (SGFs) on cemented carbide may offer a good avenue for various applications in sensor technology, especially for electrochemical sensors. Four common methods for graphene preparation are chemical stripping, chemical vapor deposition (CVD), metal catalysis, and laser fabrication; and subject to transfer issues during usage. In order to overcome this limitation, the fabrication of in-situ growth of SGFs on carbide is proposed as a solution for constructing sensor matrices. This review explores various in-situ SGFs and their potential applications in sensors. The findings presented here shed light on transfer-free graphene with controllable structures that can serve as excellent candidates for sensor matrices.

High strength and low weight materials are highly demanded in today’s automotive, aerospace, marine, medical, military, and agricultural equipment applications. Using composite materials is the best approach to increase high-strength and low-weight materials. This study focuses on evaluating the density, micro hardness, tensile, and wear behaviors of C355 aluminum alloy hybrid nanocomposites added in nanosized Graphene Oxide (GO) and Bio Silica (BS). These reinforcements are sourced from waste materials such as Thunder Coconut Shell (TCS) and Napier Grass (NG). The three different C355 aluminum alloy composites that have been improved by graphene oxide and bio-silica nanoparticles have been made utilizing the very traditional stir casting process. The percentage of GO and BS nanosized reinforcements is varied from 3wt.%, and 6wt.%. The cast composites density, hardness, and tensile strength are assessed. Unidirectional friction and wear tests are performed for each composition under six different loading conditions, ranging up to 60N, while maintaining a sliding speed of 5m/s. The worn surfaces and composite components underwent additional scrutiny through SEM analysis. By adding 6wt.% more GO/BS nanoreinforcement to the C355 Al alloy nanocomposite, the study’s findings show that the nanocomposite has almost 52.42% more tensile strength and 27.26% higher hardness than the basic alloy.

Lower back pain is one of the most prevalent health issues, affecting more than 80% of adults worldwide. Thermotherapy including heat wrap and dry sauna has long been utilized for pain relief and relaxation. Far-infrared graphene-based thermography is a heat therapy method where the graphene emits far-infrared rays that can penetrate human skin. However, its effects remain largely unstudied compared to conventional thermotherapy. This study investigates the impact of far-infrared graphene-based thermotherapy on healthy individuals and individuals associated with nonspecific low back pain. Over four sessions, 24 subjects undergo 30 min treatments, with measurements including body heat profiles, blood oxygen levels, joint angles, pain scales, and Oswestry scores. Results indicate increased body heat and blood oxygen levels post-treatment, alongside significant reductions in pain scores. However, changes in joint angles were not statistically significant, suggesting no immediate impact on locomotion. In conclusion, far-infrared graphene-based thermotherapy shows promise for pain relief and improved blood oxygenation, however, it has not been proven to improve locomotion.

Lattice vibrations or phonons play an important role in determining material properties, including thermal conductivity. To model the phenomenon accurately and efficiently, the most important factors governing phonon physics need to be identified, for example, polarization branches. Research continues into many aspects of the fundamental physical processes involved in phonons and into possible applications of these processes in modern physics. One of the most interesting controversies in the thermal properties of graphene involves the importance of out-of-plane acoustic phonons. The need for clarity in understanding this importance dictates that the thermal conductivity of graphene should be evaluated in various circumstances. The nanoscale heat conduction properties of graphene are studied by iteratively solving the Boltzmann transport equation and rigorously treating the normal and Umklapp collisions in the frame of three-phonon interactions. This captures the mechanistic aspects of thermal conductivity by revealing what phonon branches are present. The thermal conductivity is evaluated in different crystallite sizes and at different frequencies and temperatures. The results indicated that out-of-plane acoustic phonons become increasingly important in the frame of three-phonon interactions. The out-of-plane acoustic branch dominates thermal transport whereas the other acoustic branches make small contributions. The importance of this branch is generally attributed to the high density of states and restrictions governing anharmonic effects. The three-phonon normal and Umklapp processes must be clearly accounted for and the contribution from optical branches is not negligible at higher temperatures. The results have implications in the quest for predictive and quantitative calculations of thermal conductivity.

White light-absorbing materials are in high demand for catalysis and energy harvesting. Due to the UV (ultraviolet) light absorption capacity of graphene and zinc oxide (ZnO) nanoparticles, the light harvesting of the whole range of visible and near-IR (infra-red) light by utilizing these materials is a significant barrier. In this study, a graphene-ZnO nanoparticle composite was prepared from graphene and ZnO powder through a simple and novel hot solvent process at low temperatures without a catalyst or expensive instrumentation. The fabricated composite was found to absorb light efficiently at an extended range of wavelengths (400–1665nm) with strong absorption intensity. Notably, the in situ graphene-ZnO showed a considerably low intensity of absorption in the visible to the near-IR range; however, when the graphene and ZnO powder were combined as a graphene-ZnO composite by ex situ hot solvent synthesis process, the light absorption intensity significantly increased within the whole range. The observation in this study is the first one that indicates that the ex situ hot solvent process tunes the light absorption properties at the extreme level of the visible- to the near-IR range. The prepared composite also showed excellent electrical conductivity. The graphene powder was also prepared through a straightforward self-developed solvothermal process with the help of the exfoliating agent.

The friction and wear problem of the electrical contact system (ECS) is common in various electrical equipment. Once the electrical contact fails due to wear, the electrical system may not work normally, which brings serious safety risks. Surface texture has been shown to have a good potential to improve interface wear under no-current conditions, while few studies have been performed to study the relationship between surface texture and current-carrying tribological performance. In addition, graphene is also receiving attention in the field of electrical contact due to its high electrical conductivity. However, the wear consumption of graphene during the friction process limits its long-term role. Therefore, combining the ability of surface texture to reduce wear and the ability of graphene in conducting and lubrication, a texture-graphene composite surface (TS-G surface) is constructed. The effects of TS-G surfaces on the tribological properties of electrical contact surfaces are studied by comparing them with smooth surfaces (SS surfaces), textured surfaces (TS surfaces) and smooth-graphene surfaces (SS-G surfaces). The results show that TS-G can effectively reduce the friction coefficient (COF), and the COF stays at about 0.15 during the whole current-carrying friction process, and no visible fluctuation can be observed from the COF curve. In addition, the TS-G surface can effectively suppress the interface friction-induced vibration. More importantly, the TS-G surface has a good effect on the electrical contact stability. The surface topography analysis shows that the wear degree of the TS-G surface is quite slight, and the width of the wear track is only 30$\mu$m. The texture is found to be able to store graphene and continue to play the role of surface conduction and lubrication. The results of this study provide potential means for surface design to improve the stability of electrical contact.

We present a rigorous and rather self-contained analysis of the Verdet constant in graphene-like materials. We apply the gauge-invariant magnetic perturbation theory to a nearest-neighbor tight-binding model and obtain a relatively simple and exactly computable formula for the Verdet constant, at all temperatures and all frequencies of sufficiently large absolute value. Moreover, for the standard nearest-neighbor tight-binding model of graphene we show that the transverse component of the conductivity tensor has an asymptotic Taylor expansion in the external magnetic field where all the coefficients of even powers are zero.

We study the spectral properties of the two-dimensional Dirac operator on bounded domains together with the appropriate boundary conditions which provide a (continuous) model for graphene nanoribbons. These are of two types, namely, the so-called armchair and zigzag boundary conditions, depending on the line along which the material was cut. In the former case, we show that the spectrum behaves in what might be called a classical way; while in the latter, we prove the existence of a sequence of finite multiplicity eigenvalues converging to zero and which correspond to edge states.

In a semi-classical regime, we study a periodic magnetic Schrödinger operator in ℝ². This is inspired by recent experiments on artificial magnetism with ultra cold atoms in optical lattices, and by the new interest for the operator on the hexagonal lattice describing the behavior of an electron in a graphene sheet. We first review some results for the square (Harper), triangular and hexagonal lattices. Then, we study the case when the periodicity is given by the kagome lattice considered by Hou. Following the techniques introduced by Helffer–Sjöstrand and Carlsson, we reduce this problem to the study of a discrete operator on ℓ²(ℤ²;ℂ³) and a pseudo-differential operator on L²(ℝ;ℂ³), which keep the symmetries of the kagome lattice. We estimate the coefficients of these operators in the case of a weak constant magnetic field. Plotting the spectrum for rational values of the magnetic flux divided by 2πh where h is the semi-classical parameter, we obtain a picture similar to Hofstadter's butterfly. We study the properties of this picture and prove the symmetries of the spectrum and the existence of flat bands, which do not occur in the case of the three previous models.

Experimental measurements of photoresistivity under terahertz (THz) radiation in low magnetic fields at conditions of cyclotron resonance (CR) in two-dimensional electron system (2DES) of GaAs/AlGaAs nanostructures are presented and discussed. We report the experimental discovery of "CR-vanishing effect" (CRV) in GaAs/AlGaAs heterostructures with high mobility as a well-defined gap on CR-line that is independent on incident THz power. Our analysis shows that the CRV may appear in systems with well correlated state of 2D electrons such as plasma waves and others. Fundamental nature of these correlated states of electrons in 2DES is discussed. Future THz detectors utilizing the new correlated states in 2DES may expand horizons for supersensitive detection in sub-THz and THz frequencies ranges.

We report results of the experimental investigation of the low-frequency noise in graphene transistors. The graphene devices were measured in three-terminal configuration. The measurements revealed low flicker noise levels with the normalized noise spectral density close to 1/f (f is the frequency) and the Hooge parameter α_H ~10^-3. Both top-gate and back-gate devices were studied. The analysis of the noise spectral-density dependence on the gate biases helped us to elucidate the noise sources in these devices. We compared the noise performance of graphene devices with that of carbon nanotube devices. It was determined that graphene devices works better than carbon nanotube devices in terms of the low-frequency noise. The obtained results are important for graphene electronic, communication and sensor applications.

Graphene transistors using large area chemical-vapor-deposited (CVD) monolayer graphene and advanced dielectric stacks are constructed and examined. Top-gated devices with a SiO₂/Al₂O₃ gate-dielectric have a Dirac Point (DP) located at less than 5 V and asymmetric electron/hole mobility. In contrast, devices based on an advanced AlN interfacial layer have a DP located near 0V and a near symmetric carrier mobility- characteristics that could be more suitable for applications that require ambipolar behavior and low-power operation. For the first time, a measured RF cut-off frequency range of 1GHz is measured for top-gated transistors using CVD graphene. The results are of importance for the realization of graphene based, wafer-scale, high frequency electronics.

The grating-gate plasmonic crystal system represents a compelling arena for investigating strong light-matter interactions and diverse plasmon resonances. This study reviews the recent discovery of two distinctive terahertz phases of AlGaN/GaN plasmonic crystals that arise from varying the modulation of a two-dimensional electron density beneath the metallic gratings: the delocalized phase at weak modulation and the localized phase at strong modulation. Notably, we delve into an impact of the grating filling factor on the electrically driven transition between these phases. Our findings underscore the critical role of specific metal grating geometry parameters in facilitating this transition. Moreover, we explore the potential of utilizing graphene-based gratings as alternatives to metallic gratings. Through the integration of graphene, grown by Chemical Vapor Deposition method on copper foil and then transferred to the high electron mobility AlGaN/GaN heterostructures, we achieve an effective modulation of broadband absorption by free charge carriers within the 0.5–6 THz range via electrical biasing of the graphene electrode. However, while this approach successfully modulates absorption in a wide THz range, it does not elicit plasmon resonances within the graphene-based grating-gate plasmonic crystals. This intriguing observation poses a significant unresolved question warranting further theoretical and experimental exploration in subsequent studies.