Contribution Of Structural Relaxation Research Articles

Remote imprinting of moiré lattices.

Two-dimensional moiré materials are formed by overlaying two layered crystals with small differences in orientation or/and lattice constant, where their direct coupling generates moiré potentials. Moiré materials have emerged as a platform for the discovery of new physics and device concepts, but while moiré materials are highly tunable, once formed, moiré lattices cannot be easily altered. Here we demonstrate the electrostatic imprinting of moiré lattices onto a target monolayer semiconductor. The moiré potential-created by a lattice of electrons that is supported by a Mott insulator state in a remote MoSe2/WS2 moiré bilayer-imprints a moiré potential that generates flat bands and correlated insulating states in the target monolayer and can be turned on/off by gate tuning the doping density of the moiré bilayer. Additionally, we studied the interplay between the electrostatic and structural relaxation contributions to moiré imprinting. Our results demonstrate a pathway towards gate control of moiré lattices.

Gap bowing of in Pb1-xCaxS, Pb1-xCaxSe and Pb1-xCaxTe alloys

The ab initio full potential linearized augmented plane wave (FP-LAPW) method within density func­tional theory was applied to study the effect of composition on the structural and electronic properties of Pb1-xCaxS, Pbl-xCaxSe and Pb1-xCaxTe temary alloys. The effect of composition on lattice parameter, bulk modulus, band gap was investigated. Deviations of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence were observed for all three alloys. In addi­tion, the microscopic origins of compositional disorder were explained by using the approach of Zunger and co-workers. The disorder parameter (gap bowing) was found to be strong for the three alloys and was mainly caused by the chemical charge transfer effect. The volume deformation contributions for all alloys were also found to be significant, while the structural relaxation contributions to the gap bowing parameter were relatively smaller for all alloys.

First-principales calculations on the origins of the gap bowing in Pb1−xCaxS, Pb1−xCaxSe and Pb1−xCaxTe alloys

The ab initio full potential linearized augmented plane wave (FP-LAPW) method within density functional theory was applied to study the effect of composition on the structural and electronic properties of Pb1−xCaxS, Pb1−xCaxSe and Pb1−xCaxTe ternary alloys. The effect of composition on lattice parameter, bulk modulus, band gap was investigate. Deviations of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence were observed for all three alloys. In addition, the microscopic origins of compositional disorder were explained by using the approach of Zunger and co-workers. The disorder parameter (gap bowing) was found to be strong for the three alloys and was mainly caused by the chemical charge transfer effect. The volume deformation contributions for all alloys were also found to be significant, while the structural relaxation contributions to the gap bowing parameter were relatively smaller for all alloys.

The calculations of thermodynamic and opto-electronics properties of Pb1-xCaxSe semiconducting ternary Alloys

The ab initio full potential linearized augmented plane wave (FP-LAPW) method within density functional theory was applied to study the effect of composition on the structural and electronic properties Pbl-xCaxSe temary alloys. The effect of composition on lattice parameter, bulk modulus, band gap was investigate. Deviations of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence were observed. In addition, the microscopic origins of compositional disorder were explained by using the approach of Zunger and co-workers. The disorder parameter (gap bowing) was found to be strong and was mainly caused by the chemical charge transfer effect. The volume deformation contributions for all alloys were also found to be significant, while the structural relaxation contributions to the gap bowing parameter were relatively smaller. On the other hand, the thermodynamic stability and optical properties are attempted in the calculations. The calculated refractive indices and optical dielectric constants for the parent compounds show better agreement with the known data when the Moss relation is used. Compositional dependence of the optical and electronic properties studied is also investigated. Keywords. Materials for opto-electronics, optical properties, FP-LAPW, bowing gap, Banb structure, critical temperature

Frequency dependences of the velocity and absorption coefficient of sound waves in a magnetic fluid

On the basis of molecular-kinetic theory, frequency-dependent expressions are derived for the velocity and absorption coefficient of sound in a magnetic fluid with allowance for the contribution of structural relaxation in the presence of an external inhomogeneous magnetic field. The asymptotic behavior of the expressions is investigated for both low-and high-frequency limits. A numerical study is carried out by taking as an example a magnetic fluid consisting of kerosene with magnetic particles of Fe3O4 suspended in it. The results of the numerical study show that the calculated frequency dependences of the velocity and absorption coefficient of sound in a magnetic fluid are in good agreement with the static experimental data.

The frequency dispersion of dynamic transfer coefficients and elastic moduli of magnetic liquids

The analytic equations for viscosity coefficients and the corresponding elastic moduli obtained in [3] were used to calculate these values over a wide range of reduced frequency values (ω* ≈ 10−7−10). The volume ηv(ω) and shear ηs(ω) viscosity coefficients decreased as the frequency increased. The dispersions ηv(ω) and Kr(ω) were only caused by the contribution of structural relaxation, and the dispersions ηs(ω) and μ(ω), by translational and structural relaxation. The shear elastic modulus μ(ω) and relaxation volume elastic modulus Kr(ω) increased as the frequency grew. The results obtained were in satisfactory agreement with the conclusions from general relaxation theory.

Ab initio investigations of zinc chalcogenides semiconductor alloys

The present work performs self-consistent ab initio full potential-linearized augmented plane wave method to study the structural, electronic and thermodynamic properties of ZnS x Se 1− x , ZnS x Te 1− x and ZnSe x Te 1− x semiconductor alloys. The ground-state properties were determined for the bulk materials (ZnS, ZnSe, and ZnTe) and for their alloys in cubic phase at various concentrations ( x = 0.25 , 0.5 and 0.75). A marginal deviation of the lattice parameter from Vegard's law was observed for ZnS x Se 1− x and ZnSe x Te 1− x alloys, while the lattice bowing of ZnS x Te 1− x alloy was found to be significant. This is mainly because of the large mismatch of the lattice parameters of the binary compounds ZnS and ZnTe. A large deviation of the bulk modulus from linear concentration dependence was observed for all the three alloys. We have also investigated the effect of composition on bonding properties and correlated it to the charge-exchange effect in the optical bowing. Using the approach of Zunger et al. [21], the microscopic origins of the gap bowing were explained. The disorder parameter (gap bowing) for the alloys of interest was found to be mainly caused by the structural relaxation contributions. The charge-exchange contributions for all the three alloys were also found to be significant. The calculated phase diagram showed a broad miscibility gap for all the alloys of interest with a high critical temperature.

First-principles investigation of BN xP 1− x, BN xAs 1− x and BP xAs 1− x ternary alloys

First-principles calculations have been used to investigate the structural and electronic properties of boron ternary alloys (BN x P 1− x , BN x As 1− x and BP x As 1− x ) using full potential-linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). We investigated the effect of composition on lattice constants, bulk modulus and band gap. A strong deviation of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for BN x P 1− x and BN x As 1− x alloys, while in the case of BP x As 1− x alloy only a marginal deviation were found for both properties. This is mainly due to the large mismatch of the lattice parameter and bulk modulus of BN with the corresponding values at the other two binary semiconductors. In addition, the microscopic origins of compositional disorder were explained by using the approach of Zunger and co-workers. The disorder parameter (gap bowing) was found to be strong for BN x P 1− x and BN x As 1− x alloys and was mainly caused by the chemical charge transfer effect. The volume deformation contributions for both alloys were also found to be significant, while the structural relaxation contributions to the gap bowing parameter were relatively ignorable. The gap bowing of BP x As 1− x alloy was found to be much smaller than those of the other two alloys. In order to investigate the thermodynamic stability of BN x P 1− x , BeN x As 1− x and BP x As 1− x alloys we first calculated the excess enthalpy of mixing Δ H m as a function of concentration ( x). Then by using a regular model solution the x-dependent interaction parameter, Ω, was obtained from the result of Δ H m versus x. Finally, by using this Ω value, the phase diagram of the alloys was calculated. It was shown that all of these alloys are stable at low temperature.

The effects of 3d alloying elements on grain boundary cohesion inγ-iron: a first principles study on interface embrittlement due to the segregation

By the use of a first principles density functional theory, two kinds of models, namely theRice–Wang thermodynamics model and the Seah quasi-chemical model, are employed toevaluate the embrittling tendency of a grain boundary (GB) due to the 3d elementsegregation. The first principles method based on those two models is appropriate forcalculating the chemical and structural relaxation contributions to the changes of GBcohesion with the 3d segregants. The effects of the 3d transition elements, suchas Ti, V, Cr and Mn, on a stable fcc Fe GB are studied and the difference between these two models is interpreted. When thechemical and the structural relaxation effects are taken into account, the calculated resultsfor these two models are coincident for most of the elements studied, except for chromium.After analysing their chemical bonding in detail, we find that this discrepancy may beattributable to a lower susceptibility of the Seah model to the bonding anisotropy causedby Cr in the GB. It is proposed that the Seah model should be prudently usedfor some elements, especially those lying in the middle of a transition period.

Fictive temperature dependence of density fluctuation in SiO2 glass

Fictive temperature dependence of density fluctuation in SiO2 glass was investigated by the small-angle x-ray scattering measurement. The density fluctuation in SiO2 glass varies linearly to the fictive temperature. Contribution of structural relaxation to the density fluctuation is larger than that of phonons. Isothermal compressibility, relaxational isothermal compressibility and high-frequency adiabatic compressibility are estimated. If N, ̄, and Δ represent the number of SiO4/2 unit, average and difference from average, respectively, the density fluctuation in SiO2 glass is less than 3.6% as (ΔN)2¯/N̄.

On the Contribution of Structural Relaxation to the Magnetic Softening During the Amorphous-Nanocrystalline Transformation

In the present paper the contribution of structural relaxation to the net magnetic softening will be treated taking place during the amorphous-nanocrystalline transformation. Isothermal heat treatments were carried out well below the crystallization, in the temperature range of (350-440)°C. Significant decrease of Hc and increase of permeability (50 Hz) can be found already due to these heat treatments. The beneficial role of stress relaxation (resulting from low heating rates) can be also detected in the resulting permeability at 50 Hz.

First-principles study of the segregation effects on the cohesion of F.C.C. grainboundary

A scheme to evaluate the Griffith work of interfacial separation, 2γint, isproposed based on first principles to investigate the segregation effectson a Σ11[11̄0]/(113̄) γ-iron grain boundary. The chemical interaction of substitutionalsegregants Cr and Mn is able to enhance the cohesion of the grain boundary byanisotropic bonding, which weakens the bondings in the grain boundary plane andstrengthens those in the vertical plane. However, their structural relaxationcontributions are both detrimental to the cohesion of the grain boundary.After combining these two contributions, Cr acts as a cohesion enhancer but Mnas an embrittler. The interstitial segregants carbon and nitrogen canstrengthen the cohesion of the grain boundary by forming strong bonding withtheir neighbour Fe atoms and restraining their surrounding Fe atom relaxation.The ability of carbon and nitrogen to improve the property of the grainboundary is relative to the environment of their segregation sites. Theconsistency between the present work and the previous reports gives evidencefor the correctness of the scheme.

Vibrational energy migration in a hydrogen-bonded dimer probed with ultrafast time-resolved spectroscopy

We demonstrate transient spectroscopy within the OH-stretching region of 2,2-dimethyl-3-ethyl-3-pentanol diluted in CCl4, which associates to hydrogen-bonded dimers only. Strong evidence for migration of vibrational excitation from the proton acceptor to the donor and vice versa is deduced from the data with a time constant <1 ps. Reorientation of the OH-group of the proton donors and acceptors proceeds notably slower with time constants of 8 and 4 ps, respectively, indicating the minor contribution of structural relaxation to the measured fast dynamics.