$α$相FeSi $_{2}$纳米岛的晶格动力学和极化相关声子阻尼
Lattice dynamics and polarization-dependent phonon damping in $α$-phase FeSi$_{2}$ nanoislands
摘要：
我们测定了在Si（111）表面上外延生长的亚稳态、表面稳定的$α$相FeSi $_2$纳米岛的晶格动力学，其平均高度和宽度分别为1.5至20 nm和18至72 nm。通过反射高能电子衍射、原子力显微镜和X射线吸收光谱等手段对纳米岛的晶体取向、表面形貌和局部晶体结构进行了研究。Fe-部分声子态密度（PDOS），核非弹性散射得到的，表现出显着的阻尼和加宽的光谱特征，降低平均岛的高度。第一性原理计算的偏振投影的Si-和Fe-部分声子色散和PDOS使解纠缠的贡献的$xy$ -和$z$ -偏振声子的实验PDOS。与理论结果的实验数据建模揭示了一个增强的阻尼的$z$极化声子的平均尺寸小于10 nm的岛屿。这一现象归因于低能$z$极化声子与低能表面/界面振动模的耦合。从实验数据中获得的热力学和弹性性质显示出明显的尺寸依赖行为。
英文摘要：
We determined the lattice dynamics of metastable, surface-stabilized $α$-phase FeSi$_2$ nanoislands epitaxially grown on the Si(111) surface with average heights and widths ranging from 1.5 to 20 nm and 18 to 72 nm, respectively. The crystallographic orientation, surface morphology and local crystal structure of the nanoislands were investigated by reflection high-energy electron diffraction, atomic force microscopy and X-ray absorption spectroscopy. The Fe-partial phonon density of states (PDOS), obtained by nuclear inelastic scattering, exhibits a pronounced damping and broadening of the spectral features with decreasing average island height. First-principles calculations of the polarization-projected Si- and Fe-partial phonon dispersions and PDOS enable the disentanglement of the contribution of the $xy$- and $z$-polarized phonons to the experimental PDOS. Modeling of the experimental data with the theoretical results unveils an enhanced damping of the $z$-polarized phonons for islands with average sizes below 10 nm. This phenomenon is attributed to the fact that the low-energy $z$-polarized phonons couple to the low-energy surface/interface vibrational modes. The thermodynamic and elastic properties obtained from the experimental data show a pronounced size-dependent behavior.
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