Electronic and optical properties of thiogermanate AgGaGeS: theory and experiment.

The electronic and optical properties of an AgGaGeS crystal were studied by first-principles calculations, where the full-potential augmented plane-wave plus local orbital (APW+lo) method was used together with exchange-correlation pseudopotential described by PBE, PBE+, and TB-mBJ+ approaches. To verify the correctness of the present theoretical calculations, we have measured for the AgGaGeS crystal the XPS valence-band spectrum and the X-ray emission bands representing the energy distribution of the electronic states with the biggest contributions in the valence-band region and compared them on a general energy scale with the theoretical results. Such a comparison indicates that, the calculations within the TB-mBJ+ approach reproduce the electron-band structure peculiarities (density of states - DOS) of the AgGaGeS crystal which are in fairly good agreement with the experimental data based on measurements of XPS and appropriate X-ray emission spectra.

Mexican-hat dispersions and high carrier mobility of γ-SnX (X = O, S, Se, Te) single-layers: a first-principles investigation.

The shape of energy dispersions near the band-edges plays a decisive role in the transport properties, especially the carrier mobility, of semiconductors. In this work, we design and investigate the γ phase of tin monoxide and monochalcogenides γ-SnX (X = O, S, Se, and Te) through first-principles simulations. γ-SnX is found to be dynamically stable with phonon dispersions containing only positive phonon frequencies.

First-principles study on the structural properties of 2D MXene SnSiGeN and its electronic properties under the effects of strain and an external electric field.

The MXene SnSiGeN monolayer as a new member of the MoSiN family was proposed for the first time, and its structural and electronic properties were explored by applying first-principles calculations with both PBE and hybrid HSE06 approaches. The layered hexagonal honeycomb structure of SnSiGeN was determined to be stable under dynamical effects or at room temperature of 300 K, with a rather high cohesive energy of 7.0 eV.

Electronic structure and interface contact of two-dimensional van der Waals boron phosphide/GaSSe heterostructures.

In this work, we systematically examine the electronic features and contact types of van der Waals heterostructures (vdWHs) combining single-layer boron phosphide (BP) and Janus GaSSe using first-principles calculations. Owing to the out-of-plane symmetry being broken, the BP/GaSSe vdWHs are divided into two different stacking patterns, which are BP/SGaSe and BP/SeGaS. Our results demonstrate that these stacking patterns are structurally and mechanically stable.

Novel Janus GaInX (X = S, Se, Te) single-layers: first-principles prediction on structural, electronic, and transport properties.

In this paper, the structural, electronic, and transport properties of Janus GaInX (X = S, Se, Te) single-layers are investigated by a first-principles calculations. All three structures of GaInX are examined to be stable based on the analysis of their phonon dispersions, cohesive energy, and Born's criteria for mechanical stability. At the ground state, The Janus GaInX is a semiconductor in which its bandgap decreases as the chalcogen element X moves from S to Te.

Optical and electronic properties of lithium thiogallate (LiGaS): experiment and theory.

We report the relation between the optical properties and electronic structure of lithium thiogallate (LiGaS) by performing XPS and XES measurements and theoretical calculations. According to the XPS measurements, the LiGaS crystals grown by the Bridgman-Stockbarger method possess promising optical qualities, low hygroscopicity and high stability upon middle-energy Ar-ion irradiation. The difference in the LiGaS band gaps obtained by theoretical calculations and experimental measurements was, for the first time, reduced down to 0.

Theoretical and experimental study on the electronic and optical properties of KRbPbBr: a promising laser host material.

The data on the electronic structure and optical properties of bromide KRbPbBr achieved by first-principle calculations and verified by X-ray spectroscopy measurements are reported. The kinetic energy, the Coulomb potential induced by the exchange hole, spin-orbital effects, and Coulomb repulsion were taken into account by applying the Tran and Blaha modified Becke-Johnson function (TB-mBJ), Hubbard U parameter, and spin-orbital coupling effect (SOC) in the TB-mBJ + U + SOC technique. The band gap was for the first time defined to be 3.

Manifestation of Anomalous Weak Space-Charge-Density Acentricity for a TlHgBr Single Crystal.

Density functional theory (DFT) calculations within the concept of the MBJ+U+SO (modified Becke-Johnson potential + U + spin orbit) approach were performed for a TlHgBr single crystal for the first time assuming weak noncentrosymmetry (space group P4nc). Excellent agreement was achieved between the calculated and experimental band-gap-energy magnitudes as well as the density of electronic states measured by the X-ray photoelectron spectroscopy method. It is a very principal result because usually the DFT calculations underestimate the energy-gap values.

Beam and phase effects in angle-beam-through-transmission method of ultrasonic velocity measurement.

The accuracy of a plane wave approximation for phase velocity measurements in isotropic and anisotropic material using the angle-beam-through-transmission method has been investigated numerically and experimentally. In this method the velocity is measured in different propagation directions as a function of incidence angle. The effect of two factors on the measurement accuracy have been discussed: intrinsic phase shift of the transmitted signal through a fluid-solid interface and beam diffraction due to the finite beam size of receiver and transmitter.

The use of the FEFF8 code to calculate the XANES and electron density of states of some sulfides.

The FEFF8 was used to calculate x-ray absorption spectra (XANES) and the local partial electron density of states (LDOS) for several sulfides: InPS4 (twice defective chalcopyrite), CdIn2S4 (normal spinel) and Tl3AsS3 (space group R3m). The calculated XANES are compared with experimental spectra. The self-consistent MT-potentials found for clusters of about 35 atoms were used to calculate XANES and LDOS for clusters of 87 atoms in the approach of full multiple scattering.

An ultrasonic method for determination of elastic moduli, density, attenuation and thickness of a polymer coating on a stiff plate.

An ultrasonic method proposed by us for determination of the complete set of acoustical and geometrical properties of a thin isotropic layer between semispaces (J. Acoust. Soc.

Ultrasonic measurement of the diffusion bond strength.

This paper presents an ultrasonic method for measurement of diffusion bond strength between two identical materials. The method requires a single normal-incidence ultrasonic measurement. When a diffusion bond is not perfect some ultrasonic energy is reflected from the interface separating the two substrates.