International Journal of Modern Physics B

Electron-piezoelectric phonon interaction provides a significant extrinsic channel for energy relaxation in a graphene sheet placed on a polar substrate. We report in this paper our analytical and numerical investigations on energy relaxation rate and power loss density in graphene sheet on a polar substrate considering the electron-piezoelectric phonon scattering channel in the Boltzmann transport approach. We overcome the earlier crude approximations made to achieve the reported analytical results and compare the obtained results for their compliance with the numerical findings for the graphene sheet on the GaAs substrate. The obtained analytical expression for energy relaxation rate is valid for all temperatures and electron energies. The analytical result for power loss density limits its validity for low electron densities $(<{10}^{12}{\mathrm{\text{cm}}}^{-2})$. It is observed that the relaxation rate due to surface piezoelectric phonons in graphene on GaAs substrate is directly proportional to temperatures above $\sim 10\mathrm{\text{K}}$, below which temperature independence is seen. Also, it is observed that the relaxation rate is linearly dependent on electron energy, $E_k$ at low temperatures, and $E_k$ independent at high temperatures. Moreover, the relaxation rate is electron density-independent for all (low to high) temperatures. The seemingly odd (from earlier reported behavior) temperature-independent, linearly dependent $E_k$ and n independent relaxation rate behavior for low temperatures is attributed to the approximation used so far in the phononic statistical occupation factor in deriving the relaxation rate in the low-temperature Bloch-Gruneisen (BG) regime. In undoped graphene, we have found that the power loss behavior follows a crossover from $T_e^5$ to $T_e^4$ behavior while moving from low $(\sim 20\mathrm{\text{K}})$ to high $(\sim 1000\mathrm{\text{K}})$ electron temperature. This behavior contradicts the study by Zhang et al. [Phys. Rev. B 87, 075443 (2013)] and M. Ansari [Physica E: Low Dimens. Syst. Nanostruct. 131, 114722 (2021)] which reported low-temperature BG behavior of $T_e^3$. This behavior is again attributed to using BG regime approximation for statistical occupation factors. Our findings are in agreement with the experimental work by Chen et al. [Nature Nanotechnol.  3, 206 (2008)] and You et al. [Appl. Phys. Lett. 115, 043104 (2019)].

In this paper, CaO-B₂O₃-2SiO₂: Eu${}^{2+}$ and CaO-B₂O₃-2SiO₂: Eu${}^{2+}$, Ce${}^{3+}$ fluorescent glasses have been synthesized by a conventional melt-quenching method. First, under 350nm excitation, the CaO-B₂O₃-2SiO₂: Ce${}^{3+}$ luminescent glass emits light at about 400nm, and the optimum dosage is 0.3mol%. Then, under 400nm UV excitation, the CaO-B₂O₃-2SiO₂: Eu${}^{2+}$ luminescent glasses showed a strong emission with a peak around 460nm and a half wavelength of 95nm. The results showed that the luminescence of this glass was greatest when the doping amount was 0.3mol% and gradually decreased with increase of the doping amount. After calculation and analysis, it was found that this was due to the nonradiative energy transfer between Eu${}^{2+}$ ions. The mechanism of energy transfer was dipole–dipole interaction. Finally, Ce${}^{3+}$/Eu${}^{2+}$ co-doped luminescent glasses were also successfully prepared with strong emission. The existence of energy transfer was demonstrated by theoretical and practical measurement data. CaO-B₂O₃-2SiO₂: Ce${}^{3+}$, Eu${}^{2+}$ can be used as blue fluorescent glass for white light illumination.

Perovskite solar cells (PSCs) without hole transport layer (HTL) based on organic and inorganic metal halide perovskite have received vast consideration in recent years. For predigestion of device structure and construction process, the exclusion of the HTL is a marvelous way. By detaching the HTL part of the devices, we could reduce the cost and complexity of the structures. Currently, a novel 2D material named Ti₃C₂ MXene with high electron mobility, excellent metallic conductivity and functionalized surface groups applied for tuning the energy offsets has been reported to be added in the perovskite absorber layer, leading to a remarkable power conversion efficiency (PCE) improvement. In this work, the role of MXenes in controlling the work function of the involved layers to modify the band alignment towards better performance of the cells is explained. Two HTL free structures of FTO/mTiO₂/cTiO₂/MAPbI₃/Spiro-OMeTAD/Au named as HFRC, and FTO/mTiO₂+MXene/cTiO₂+MXene/MXene/MAPbI₃+MXene/Spiro-OMeTAD/Au named as HFMC were simulated by SCAPS-1D software to study the response of the photovoltaic devices and obtain the highest possible efficiency considering the physics behind. To the best of our knowledge, this is the first time such structures and the results of the current simulation are studied that may be used as a guideline for other practical purposes. We present a modeling procedure that optimizes the thickness of the involved layers and specifies the optimum level of the doping concentration. We also show that by optimizing the work function of the back contact, the device performance witnesses a significant improvement, proving the considerable role of the back contact in these cells. The simulated HTL-free devices illustrate attainably PCEs of about 20.32% and 21.04% for the cells without and with MXene, under AM 1.5G illumination and absorption up to 760 (nm).

This paper systematically investigates the electronic structure and optical properties of zinc-blende ZnTe, ZnS systems, ZnTe/ZnS heterojunctions, and Y-doped ZnTe/ZnS heterostructions using the generalized gradient approximation (GGA) method under the density functional theory (DFT) framework. The results show that compared to the single-component ZnTe or ZnS systems, the ZnTe/ZnS heterojunction has a smaller bandgap width and undergoes a redshift in the absorption spectrum, which is favorable for more valence band electrons to be excited by light and transition to the conduction band, thereby enhancing the optoelectronic properties of the material. After Y-doping in the ZnTe/ZnS heterojunction system, when the doping concentration is between 1.56at% and 4.69at%, doping Y in the ZnS layer would result in the lowest energy formation of the system. Therefore, it can be inferred that in experiments, if the doping concentration is increased beyond this range, Y atoms are more likely to be arranged in the ZnS layer. Compared with the pure ZnTe/ZnS heterojunction system, increasing the Y doping concentration results in a wider bandgap and a more prominent blue shift in the absorption spectrum. Therefore, it is possible to adjust the bandgap of the heterojunction by changing the doping concentration to fabricate heterojunction device with different photoelectric effects and luminescence properties.

In this paper, we have established a design of dual-layer magnetoelastic metasurfaces and achieved the tunable asymmetric transmission of flexural waves by modulating magnetic field. Relying on the adjustable phase shift of flexural waves with a full 2$\pi$ range by applied different magnetic fields, the asymmetric transmission of flexural waves (i.e., asymmetric refraction and asymmetric focusing) can be realized without altering the structure based on the generalized Snell’s law. The results show that the proposed magnetoelastic metasurfaces exhibit the asymmetric refraction of flexural waves with the tunable working frequencies and incident angles. In addition, the asymmetric focusing of flexural waves can also be modulated by adjusting magnetic loading. The proposed magnetoelastic metasurfaces can provide a new way for actively controlling the asymmetric transmission of elastic waves, further broadening the potential applications in the field of vibration control as a dynamic tunable diode.

A first theoretical attempt is made to understand the characteristics of dust acoustic shock waves (DASWs) in a polarized electron-depleted plasma with a mixed nonextensive high energy–tail ion distribution and to examine the impact of the generalized nonthermal polarization force on DASWs in an electron-depleted dusty plasma. First, a short numerical investigation illustrating the behavior of the mixed nonextensive high energy–tail (or Cairns–Tsallis) ion distribution and the domain of validity of its two parameters (q and $\alpha$) is carried out. Next, the generalized nonthermal polarization acting on dust grain in electron-depleted dusty plasma is determined within the context of Tsallis’ statistical mechanics. The behavior of this generalized polarization force is significantly affected by the nonextensive character of the nonthermal ions. Specifically, we have shown that, for both space and experimental dusty plasmas, the magnitude of the polarization force (in the case where $-1<q<1$) decreases as the nonextensivity of the nonthermal ions becomes significant. As an application, we have analyzed the changes caused by the nonthermal nonextensive polarization force on the main characteristics of DASW (viz. phase velocity, polarity, amplitude, width, etc.). Numerical results showed that our plasma model supports rarefactive and compressive DASWs that are significantly affected by the effects of nonthermal ion nonextensivity and polarization force. In particular, we have shown that for large values of the nonthermal parameter $\alpha$, the increase in q allows the transition from rarefactive to compressive DASW structures. The present theoretical investigation is helpful to fully understand electrostatic disturbances in space and experimental dusty plasmas.

The optical properties of TiO₂ are changed while doped with impurity atoms. This paper made a systematical calculation of the bandgap, the density-of-states (DOS), the optical properties for pure TiO₂, and Bi-doped anatase TiO₂ according to the first-principles plane wave ultrasoft pseudopotential method which is primarily based on the density functional theory (DFT). The calculation results exhibit that the bandgap decreased after doping, and the impurity energy level is produced into the bandgap of Bi-doped TiO₂, which makes red-shift for the absorption band edge of Bi-doped TiO₂ and the absorption is enhanced more in the visible light range.

The aim of this study is to present forced convective nanofluid flow over a moving plate embedded in an absorbent medium. Following Darcy law’s for porous medium, the flow analysis is explored in attendance of warmth basis/drop. The main objective of this study is to explore the effects of Brownian motion and thermophoresis. The plate is considered to move in both directions: in the way of movement of fluid and in the opposite route of fluid movement. Similarity alterations have been applied to alter the leading partial differential equations (PDEs) to ordinary differential equations (ODEs). Numerical solutions have been obtained with the help of MATHEMATICA software. Dual solutions have been obtained when the plate and liquid go in reverse ways. Wall shear stress, Nusselt and Sherwood numbers all are found to rise with the rising permeability parameter of absorbent medium. For Nusselt and Sherwood numbers, ranges of dual solutions diminish by the mounting values of permeability parameter K. The critical values for porosity parameter $K=0.01$, 0.02, 0.03 are $R_{c_1}=1.872909$, $R_{c_2}=1.927211$, $R_{c_3}=1.9824284$, respectively. For decreasing values of s, range of dual solutions decreases. For $s=-0.45$, dual solutions exist in the range $(1.19,1.20)$.

Squeezing or squeeze flows have tremendous applications in applied fields, like engineering, biomedical sciences and rheological studies. This paper demonstrates the squeezing flow of kerosene-based nanoliquids between parallelly aligned plates, with a Riga-type fixed lower boundary. The effects of dispersing two types of copper-functionalized carbon nanotubes (CNTs), single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) are examined. Using appropriate transformations, a self-similar ordinary differential system is derived from the governing model of partial differential equations and substantial boundary conditions. Using the homotopy analysis method (HAM) and the $bvp4c$ package, analytical and numerical estimates are obtained, respectively. For higher values of the squeezing parameter, dimensionless temperature increases, while velocity patterns are upside-down. Moreover, increments in dimensionless parameters representing Riga constituent width, modified Hartmann number, nanoparticle concentration and radiation parameter improve heat transfer rates and thermal boundary layer thickness, however, adversely affect velocity. Despite enhanced friction effects, numerical results show that the Nusselt number increases as nanoparticle loads and radiation parameters increase. This suggests that convection rates are improved over conduction rates. Excellent agreement is found between analytical and numerical evaluations. Apparently, it is noticed that MWCNTs perform better than SWCNTs.

The combined effects of diffusion-thermo and radiative absorption on free convective hydromagnetic heat-generating chemically reactive flow of Cu-water nanofluid past an instantaneously accelerated unlimited vertical plate nested in a porous medium are investigated. A comparative analysis is executed for both isothermal and ramped conditions. The set of transformed domain equations has been obtained using a closed form of the Laplace transform method with the help of the Heaviside step function. Graphical and tabular explanations are provided for the physical characteristics of several flow parameters affecting the problem. Graphs are generated using MATLAB computing software. Findings of the problem manifest that the diffusion-thermo parameter and the radiation absorption parameter intensify the velocity and fluid temperature in the entire fluid area. This augmentation is most prominent for copper nanoparticles. Concentration, temperature, and velocity profiles in the case of ramped conditions are less than in isothermal conditions. Furthermore, the ramped parameter amplifies the heat transfer rate while reversing the mass transfer rate. It is also established that the volume concentration of nanoparticles enhances the heat transfer rate. The present study is of great interest in numerous fields of industry and machine-building applications.

This paper reports the flow features and distributions of concentration and temperature of a micropolar type nanofluid (water-based) past a stretchable and shrinkable wedge, influenced by variable magnetic force, nonlinear sort thermal radiation and chemical reaction. Along with the consideration of multiple convection, the model of Buongiorno is stated. The Brownian motion and thermophoresis have been kept in the analysis. Suitable similarity alteration is approached to renovate the foremost equations to dimensionless ordinary differential equations (ODEs). Associated conditions became nondimensional forms according to this conversion. Then the numerical solutions of the reduced governing equations with boundary conditions are obtained by adopting the RK-4 technique with shooting criteria. The language MAPLE 17 assisted in developing this solution. Significant upshots of prime parameters on the fluid transmission, mass and heat transport properties are represented with suitable tables and graphs. In tabular form, we have reckoned the physical quantities of heat, mass transfer rates and drag friction coefficients to fulfill the engineering interest. This study acquaints that the material parameter negatively influenced nanofluid’s angular velocity. The fluid’s temperature improves with thermal and mass Biot numbers, but this response goes opposite for the parameter of wedge angle. Chemical reaction and wedge angle parameters amplify mass transport. This study can be beneficial in the blowing of chilled air by AC panels, the abstraction of crude oils, the nuclear power hub, the working of warships, making flaps on the wings of aeroplanes for advanced lift, submarines, the extraction of polymers and several other sectors in advanced science and industrial developments.

Generation of short wavelengths is obtained using the gas cells having different lengths. A Ti:sapphire laser system at 1kHz or 10Hz repetition rate is used to produce high harmonic generation (HHG). The gas cell producing optimum harmonic spectrum is determined using the 1kHz laser system. The optimum harmonic signal is obtained under the phase-matched condition. The total harmonic yield is increased by adjusting argon gas pressure in the different gas cell lengths (length of the interaction mediums). Harmonics up to the 27th order are obtained. The 1D model is used for the calculation of harmonic yield at different interaction lengths. The high-power laser system at the 10Hz repetition rate is used to generate high-order harmonics. The harmonic orders are extended to the 35th harmonic in argon gas. A harmonic spectrum in H₂ gas is generated using different pump laser power. The power dependence of the harmonic signal from H₂ gas is obtained. The variation of the harmonic spectrum for the different cell parameters is explained as a constructive or destructive buildup of generated harmonics while they propagate through the gas cell.

This research examines the analytical investigations for radiating Casson nanofluid models with unsteady convecting flow, which are valued by the order of Caputo fractional derivative (CFD). Ethylene glycol (EG) is used as a base fluid, and graphene oxide (GO) and carbon nanotubes (CNTs) are used as nanoparticles. The problem’s leading PDEs are nondimensionalized by applying the proper nondimensional variables. The solutions to the dimensionless governing equations are found by using the Fourier sine and Laplace transformation techniques together. For an enormous study of the problem, graphical illustrations and tables are developed by using MATLAB software programming with the help of Euler inversion. We examine the impact on the fractional heat and momentum equation of the $\alpha$, Gr, Pr, $\varphi$, R, $\beta$, oscillations. Using the properties of the fluid, important discoveries were made that indicated a number of elements for a number of flow parameters as well as fractional parameters. The thermal profiles are increased for $R,\varphi$ decreased for $\alpha$ at $\tau =0.4$ and $\tau =1.4$. The velocity profiles are increased for R and Gr decreased for $\beta$ and $\varphi$ at $\tau =0.4$ and 1.4. Different shapes of nanoparticles are performed for ordinary fractional parameters, which are increased for temperature as well as velocity.

In this study, we are analyzing the effect of the Hilbert Transform (HT) on diffraction of a plane wave by an oscillating half-plane. Both the incident wave and oscillating half-plane have different oscillating frequencies. After the necessary mathematical computations for several types of time-dependent oscillating functions, it is verified graphically that the HT induces a shift of ${90}^{\circ }$, which can be observed from the flipping effect in the magnitude of the sinusoidal components occurring in their respective diffracted fields. Graphical illustrations presenting the effects of the HT are presented and discussed.

The heat transfer occurring on boundary layer flows during dilute suspension of Cu–Al₂O₃ nanoparticles-based non-Newtonian Casson hybrid nanofluid over diverging channel is to be characterized in this model. The governing equations comprise continuity, momentum, energy and concentration equations which incorporated variable viscosity and magnetic effects in the momentum equation, variable thermal conductivity, chemical reaction, thermal radiative heat flux, uniform magnetic field, Joule heating and viscous dissipative effects in the energy equation and Brownian motion and thermophoretic effects in the concentration equation. The modeled equations are nondimensionalized using nonsimilar variables and linearized using quasilinearization technique. The system of linearized partial differential equations is solved numerically using implicit finite difference and successively iterated with the help of Varga’s algorithm. The physical impacts of viscous dissipation parameter (Ec), Brownian motion ($N_b$) on velocity, temperature, concentration and Schmidt number (Sc) influences on skin friction, Nusselt number, Sherwood number profiles, Bejan lines and total entropy production profiles are simulated graphically. The velocity profiles are enhanced and the temperature profile declines for augmented values of Eckert number. Moreover, for augmented values of Schmidt number the heat and mass transfer rates are enhanced and the Bejan lines dropped a decreasing trend whereas total entropy production is augmented near the wall region. The improved values of the Schmidt number physically increased Sc in the heat transfer rate. The ascending profile of the mass transfer rate with increased values of the viscous dissipation parameter Ec demonstrated that the graph is raised for larger values of the viscous dissipating parameter (Ec). The physical behavior of incremental mass transfer rate led to the conclusion that the relative diffusivity of nanoparticles is characterized by both nondimensional numbers Ec and Sc which are directly proportional to the viscous forces.