arXiv subjects

Ching-Lien Hsiao

Publications and source records attributed to Ching-Lien Hsiao.

3 recordsLinked to original sources

arXiv2026

Local coordination, structural softening, and polarization-switching energetics in Sc-alloyed GaN

Sc-alloyed wurtzite nitrides exhibit strongly tunable electromechanical and ferroelectric properties, yet the relationship between their lattice evolution and local bonding environment remains insufficiently established, particularly in Sc$_x$Ga$_{1-x}$N. Here, we investigate the structural and local bonding evolution of Sc$_x$Ga$_{1-x}$N across the dilute-to-intermediate composition range by combining X-ray diffraction, Sc K-edge X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and first-principles calculations. Sc incorporation produces an anisotropic lattice expansion and a progressive reduction in the c/a ratio. XANES and EXAFS reveal a concurrent modification of the local environment around Sc, with the effective Sc-N coordination number increasing from 4.1(4) to 4.5(2) and the average Sc-N bond length increasing from 2.045(7) to 2.081(8)Å over x=0.06-0.26. The local response is accompanied by a reduction in the Sc K-edge pre-edge intensity, consistent with a gradual reduction of the local tetrahedral asymmetry. First-principles calculations show that these structural changes are associated with site-selective distortions around Sc and progressive flattening of the structural energy landscape. The calculated intrinsic polarization-switching barrier decreases from 24.2 to 19.0 meV/Å$^3$ with increasing Sc content, while the calculated piezoelectric stress coefficient (e$_{33}$) increases from 0.82 to 1.66~C/m$^2$ and elastic constant (C$_{33}$) decreases from 380 to 227~GPa, resulting in an increase of piezoelectric strain coefficient (d$_{33}$) from 2.99 to 12.46~pC/N. These results show that Sc incorporation progressively modifies the local coordination environment and structural energetics of ScGaN while the long-range wurtzite structure remains preserved over the investigated composition range.

cond-mat.mtrl-sci↗

arXiv2024

Spectral Tuning of Polarization Selective Reflections Bands in GLAD deposited HfAlN chiral sculptured thin films

We present the first report on fabrication of Hafnium aluminum nitride chiral sculptured thin films (CSTFs) using reactive magnetron sputtering in a glancing angle deposition configuration, and the analysis of its optical polarization properties. The resulting CSTFs were designed to give interference extrema or so-called circular Bragg (CB) resonances at desired wavelengths in the region from 370 to 690 nm. This was achieved by tailoring the growth of the chiral thin films to obtain a dielectric pitch between 87 and 260.9 nm. The spectral positions of the obtained CB resonances were compared to values from analytical expressions. Contrary to the common case where the dielectric pitch is half of the growth-related rotational pitch due to a 180° symmetry, this pitch was shown to be the same as the rotational pitch. It is concluded that this is due to the c-axis of the CSTF being tilted about 45° from the substrate normal. The morphology and crystallographic characterizations were done using scanning electron microscopy and X-ray diffraction, respectively, while the tilt of the crystal lattice was corroborated using X-ray diffraction pole figures. The optical response from the CSTFs was analyzed using Mueller matrix spectroscopic ellipsometry from which the degree of circular polarization at the CB resonances was obtained. In addition, a strong non-reciprocal reflection was observed which could be attributed to the helicoidal morphology and the intrinsic crystal tilt. An optical layered model of the chiral structure including azimuthal twist and using the Cauchy dispersion relations was used to simulate the Mueller matrix elements and compare with the ellipsometry measurements. The correlation between the simulated and experimental data gave information of the morphological parameters of the CSTF and its optical properties.

physics.optics↗

arXiv2023

Electronic and optical properties of core-shell InAlN nanorods: a comparative study via LDA, LDA-1/2, mBJ and $G_0W_0$ methods

Currently, self-induced InAlN core-shell nanorods enjoy an advanced stage of accumulation of experimental data from their growth and characterization as well as a comprehensive understanding of their formation mechanism by the ab initio modeling based on Synthetic Growth Concept. However, their electronic and optical properties, on which most of their foreseen applications are expected to depend, have not been investigated comprehensively. $G_0W_0$ is currently regarded as a gold-standard methodology with quasi-particle corrections to calculate electronic properties of materials in general. It is also the starting point for higher-order methods that study excitonic effects, such as those based on the Bethe-Salpeter equation. One major drawback of $G_0W_0$, however, is its computational cost, much higher than density-functional theory (DFT). Therefore, in many applications, it is highly desirable to answer the question of how well approaches based on DFT, such as e. g. LDA, LDA-1/2, and mBJ, can approximately reproduce $G_0W_0$ results with respect to the electronic and optical properties. Thus, the purpose of the present paper is to investigate how the DFT-based methodologies LDA, LDA-1/2, and mBJ can be used as tools to approximate $G_0W_0$ in studies of the electronic and optical properties of scaled down models of core-shell InAlN nanorods. For these systems, we observed that band gaps, density of states, dielectric functions, refractive indexes, absorption and reflectance coefficients are reasonably well described by LDA-1/2 and mBJ when compared to $G_0W_0$, however, at a much more favorable computational cost.

cond-mat.mtrl-sci↗