International Journal of Modern Physics B

A theory for the averaged optical characteristics of an ensemble of metal nanoparticles with different shapes has been developed. The theory is applicable both for the nanoparticle size at which the optical conductivity of the particle is a scalar and for the nanoparticle size at which the optical conductivity should be considered as a tensor. The averaged characteristics were obtained taking into account the influence of nanoparticle shape on the depolarization coefficient and the components of the optical conductivity tensor. The dependences of magnetic absorption by a spheroidal metal nanoparticle on the ratio between its curvature radii and the angle between the spheroid symmetry axis and the magnetic field vector were derived and theoretically considered. An original variant of the distribution function for nanoparticle shapes, which is based on the combined application of the Gaussian and “hat” functions, was proposed and analyzed.

In this study, the structural and unexplored elastic, electronic, optical and thermal properties of Pt-based alloys MPt₃ (M = Ti, Hf) and only optical and thermal properties of ZrPt₃ are subjected to investigation using the method of the first principles. The results of pressure dependence of mechanical and thermal properties are discussed. The electronic band structures and density of state data show metallic conductivity for all the compounds. The main contribution at Fermi level comes from Ti 3d and Zr 4d (for TiPt₃ and ZrPt${}_3)$ and Pt 5d (for HfPt${}_3)$ orbitals.

The materials’ optical reflectivity values, relatively high in the IR-visible-UV regions, range from $\sim$62% to 72% in the visible region which show better performance values in comparison to those of some representative materials PtAl₂, AuAl₂ and GdX₃ (X = In, Sn, Tl, Pb). The unexplored thermal behaviors are also investigated via quasi-harmonic Debye model at T = 0 and P = 0 as well as at elevated temperatures and pressures. In addition, when used as bonding materials, studied intermetallics with moderately high thermal expansion coefficients can match other substrates.

This coupled with the estimated thermal conductivities (k${}_{min}$) compared to several other species indicate that the intermetallics can be used in applications, such as thermal barrier coatings (TBC). This study has thus indicated possible alternative candidates for high-temperature applications which would initiate further research and development on the intermetallics under study.

In this paper, we investigated the impact of thickness and mole fraction AlInGaN back barrier on the DC performance of AlGaN/GaN high electron mobility transistors (HEMTs) by numerical simulation. The simulations are performed using the hydrodynamic transport model (HD). The simulation results indicated that an inserted AlInGaN back barrier with increasing thickness and mole fraction could effectively confine the electron in the channel, resulting in a significant improvement of the channel current and transconductance. Additionally, the variation of conduction band offset and the increase of total number electron in the channel led to the threshold voltage moving toward a more negative value.

In this work, the influence of the temperature (T) and RbCl asymmetrical semi-exponential confinement potential on intermediate coupling polaron in a polar slab was studied by applying the Lee-Low-Pines (LLP) unitary transformation and linear combination operation methods, based on the quantum statistical theory. We have derived the ground state energy (E₀) and the mean phonon number (N). According to the obtained results, E₀ increases with increasing T and parameter $\sigma$, whereas it is a decaying function with raising parameter U₀.

In the present paper, guided four beam (G4B) piezoelectric transducers with enhanced sensitivities have been designed. Based on the suggested G4B structures, piezoelectric energy harvesters (PEHs) and acceleration transducers with higher voltages than their previously reported counterparts and with lower displacements than the single-cantilever PEHs (SC-PEHs) have been proposed. We have shown that it is possible to arrive at much more output voltages in comparison with the conventional PEHs by redesigning the structure of the cantilever beams. In 1 g acceleration, the maximum output voltage obtained from the proposed PEHs has been 13.49 V whereas the output voltage for the conventional G4B-PEH is 2.87 V. This paper for the first time proposes G4B-PEHs with smaller displacements and larger voltages compared to a SC-PEH. The same G4B framework has been studied as a piezoelectric acceleration transducer. The effect of piezoelectric length on the extracted voltage in both unimorph and bimorph cantilevers has been discussed and the optimized length has been calculated. An analytical method is developed to compute the resonance frequencies of different beam shapes whose results are in a good agreement with numerical simulations.

The elastic constants and phonon dispersion of metallic C${}_{14}$ are calculated by first-principles calculations. The results show that the metallic C${}_{14}$ is mechanically and dynamically stable under high pressure. The variations of G/B ratio, Poisson’s ratio, elastic anisotropy, acoustic velocity and Debye temperature at the pressure range from 0 GPa to 100 GPa are analyzed. The results reveal that by adjusting the pressures the elastic anisotropy and thermodynamic properties could be improved for better applicability.

This paper reports the tunable transmission properties of asymmetric one-dimensional periodic structure (1DPS) composed of SiO₂ and anisotropic metamaterial (AMM) layers with defect of liquid crystal (LC) sandwiched by two SiO₂ layers, i.e., (SiO${}_2|$AMM)${}^3|$SiO${}_2|$LC$|$SiO${}_2|$(SiO${}_2|$AMM)³ using the transfer matrix method (TMM). We have studied the optical properties of the periodic structure (SiO${}_2|$AMM)³ $|$SiO${}_2|$LC$|$SiO${}_2|$(SiO${}_2|$AMM)³ with a different incident angle of the electromagnetic wave for particular director angle of LC molecules. The tunability of the transmission property of the considered 1DPS shows that the transmittance depends upon the orientation of LC molecules. Such an asymmetric periodic structure (1DPS) composed of SiO₂ and AMM with a defect of LC sandwiched by two SiO₂ layers, (SiO₂ $|$AMM)${}^3|$SiO${}_2|$LC$|$SiO${}_2|$(SiO${}_2|$AMM)³, may be used as a tunable optical filter and bi-stable device.

The mobility of holes in the spin polaron theory is discussed in this paper using a representation where holes are described as spinless fermions and spins as normal bosons. The hard-core bosonic operator is introduced through the Holstein–Primakoff transformation. Mathematically, the theory is implemented in the finite temperature (Matsubara) Green’s function method. The expressions for the zeroth-order term of the hole mobility is determined explicitly for hole occupation factor taking the form of Fermi–Dirac distribution and the classical Maxwell–Boltzmann distribution function. These are proportional to the relaxation time and the square of the renormalization factor. In the Ising limit, we showed that the mobility is zero and the holes are localized. The calculation of the hole mobility is generalized by considering the vertex corrections, which included the ladder diagrams. One of the vertex functions in the hole mobility can be evaluated using the Ward identity for hole-spin wave weak interaction. We also derived an expression for the hole mobility with vertex corrections in the low-temperature limit and vanishing self-energy effects. Our calculation is made up to second-order correction in the case where the hole occupation factor follows the Fermi–Dirac distribution.

Adding porous nanoparticles into fluid can modify the energy storage properties of working fluid in the thermodynamic cycles. The adsorption capacity and thermal energy storage of CO₂ in MOF-74 and UIO-66 at different temperatures and pressures are investigated in this paper via molecular simulations. The results denote that the adsorption of CO₂ in the two studied metal organic frameworks (MOFs) differ from each other due to the different structures. The adsorption capacity of CO₂ in MOF-74 is larger than that in UIO-66. However, the desorption heat of CO₂ in MOF-74 is lower than that in UIO-66. Also, UIO-66 impacts more than MOF-74 on the thermal energy storage property of CO₂.

We present a novel method to judge the entanglement of two-qubit system, the density matrix of a two-qubit system can be constituted by the principle density matrix ${\rho }_p$ and the separable density matrices ${\rho }_1$–${\rho }_4$. The necessary and sufficient conditions for the two-qubit system, the three involved coefficients p ${}_p\ge$ 0, p ${}_1\ge$ 0, p ${}_2\ge$ 0, and the principal density matrix ${\rho }_p$ being separable, then the two-qubit system is separable, otherwise the two-qubit system is entangled. Finally, the criterion for several known density matrices have been verified in this way.

Laser-produced plasma in Ne and O₂ gases and Ne–O₂ gas mixture with different O₂ fractions have been investigated. The plasma were produced by focusing a laser beam of 5 ns pulse duration from a Nd:YAG laser ($\lambda$ = 1064 nm) through a lens of 5 cm focal length into the chamber filled with different gas species at different pressures. Possible enhancement in O-atom densities through collisions with metastable Ne atoms by the laser-created plasma in Ne–O₂ gas mixtures and possible energy transfer mechanism was studied. Study of energy transfer through collisions was carried out by comparisons of the line intensities of the emitted spectra from laser-created plasma in gas mixtures and pure gases with the technique of optical emission spectroscopy (OES). Strong evidence of energy transfer from Ne to O was recorded. From the result, it was suggested that the high-lying metastable levels of Ne were responsible for enhancement of O-atoms density in gas mixture and Ne also play important role in energy transfer mechanism through collision. Also, behaviors of the line intensities under different laser energies were studied. Behaviors of line intensities and line widths were the main parameters measured. Stark broadening of lines in Ne with different laser energies was recorded. The electron temperature T${}_{\mathrm{\text{e}}}$ and number density N${}_{\mathrm{\text{e}}}$ were found to be 1.01 eV and 9.44 × 10${}^{16}$ cm${}^{-3}$ in Ne at different laser energy/pulse with total pressure of 1000 mbar.

We have examined the magnetic stability; antiferromagnetic (AFM) ordering; electronic and magnetic properties of composition XMn₂Y₂ (X = Ca, Sr; Y = Sb, Bi) using framework of full-potential linearized augmented plane wave (FP-LAPW) method within generalized gradient (PBE-GGA) approximations in AFM phase. We have specified that AFM state is most suitable for these compounds as compared to other configurations at their relaxed lattice parameters. An AFM spin configuration of Mn atoms is shown to be impressive state for these compounds. Based on its electronic properties, these compounds have a metallic nature in Paramagnetic (PM) but in AFM phase it shows different nature from PM phase. From a suitable phase, it has been cleared that both Mn atoms well-adjusted antiferromagnetically.

In recent decades, microfluidics in biological applications have experienced significant growth due to their advantages of small volume, low cost, short reaction time and high throughput. Almost all cross-section shapes of micro-channels in microfluidic chips are rectangular or triangular by the existing chip fabricating technologies, including hot embossing, lithography, etching and injection molding, etc. However, compared with the above micro-channel shapes, the circular one has the advantages in aspects of fluid flow, droplet generating, heat transfer and its replication for blood vessels. This paper presents a T-junction droplet microfluidic chip with circular cross-section micro-channels. The effect of micro-channel wettability, interfacial tension, velocity and flow rate of continuous phase on droplet size are simulated and mechanism of droplets generating process is explored. Comparing with continuous phase viscosity and interfacial tension, flow rate plays a decisive role in determining the droplet size which is in the range of 100–350 $\mu$m according to the simulation result. The Capillary number is affected by the above three parameters and an estimating numerical method for generated droplet size was proposed according to the above simulation results and calculated by Capillary number. The droplets, the sizes of which were in the range of 20–400 $\mu$m, were produced by varying the parameters of water and oil flow rates in the designed T-junction droplet microfluidic chip with circular cross-section micro-channels.

Rare earth-doped Sr₃Gd(PO₄)₃ and emission color tunable phosphors Ce${}^{3+}$/Sm${}^{3+}$ co-doped Sr₃Gd(PO₄)₃ have been synthesized by a traditional solid-state method. These phosphors were characterized by X-ray diffraction (XRD), FE-SEM, diffuse reflectance spectra (DRS), photoluminescence spectra and lifetime measurements. The quenching concentration of Ce${}^{3+}$ ions in Sr₃Gd(PO₄)₃ was about 9 mol.%. An effective energy transfer (ET) from Ce${}^{3+}$ ions to Sm${}^{3+}$ ions in Sr₃Gd(PO₄)₃ was speculated by the overlapped spectrum for the emission peak of Ce${}^{3+}$ and the excitation peak of Sm${}^{3+}$ ions. It is demonstrated that the ET mechanism is resonant through the dipole–dipole interaction and the critical distance between Ce${}^{3+}$ and Sm${}^{3+}$ in Sr₃Gd(PO${}_4{)}_3$ is calculated to 15.22 Å. Moreover, Sr₃Gd${}_{1-x}$(PO₄)₃:0.09Ce${}^{3+}$, xSm${}^{3+}$ can be adjusted systematically by generating blue light to white light in the CIE diagram which coincide with the ET process of Ce${}^{3+}$ ions to Sm${}^{3+}$ ions. The Sr₃Gd${}_{0.90}$(PO₄)₃:0.09Ce${}^{3+}$, 0.01Sm${}^{3+}$ phosphor also perform at a good thermal stability. All of these experimental results in this work can be served as a potential multicolor tunable phosphor for ultraviolet pumped white light appliance.