独立纳米晶硅膜中受限声子模式滤波
Dynamics of confined acoustic phonon modes in nanocrystalline silicon membranes
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中文总结 AI 辅助
研究通过飞秒时间分辨测量独立纳米晶硅膜中受限声子，对比晶体硅，发现纳米晶中高阶模式受抑制且依赖频率，确定晶界相关衰减通道，测量声速，表明相干声子可探微观结构散射，晶界能过滤高频声子。
中文摘要 AI 辅助
我们报告了对独立纳米晶硅膜中受限声子的飞秒时间分辨测量，并将其与晶体硅对应物直接比较。后者展现出分辨良好的高阶模式，而在通过热退火控制晶粒尺寸分布的纳米晶样品中，这些模式受到强烈抑制。这种抑制强烈依赖于频率，且随着声子波长接近特征晶粒尺寸而变得更加显著。通过分离声子寿命的本征和非本征贡献，我们确定了一个与晶界相关的额外频率依赖衰减通道，散射率遵循接近$f^{2}$的幂律依赖，其中$f$是频率。测量的声速与先前关于纳米晶硅的报告一致，表明由多个晶体学取向产生有效弹性响应。这些结果确立了相干声子作为纳米晶材料中微观结构依赖散射的灵敏探针，并表明晶界对高频声子起到有效光谱滤波器的作用。
英文摘要
We report femtosecond time-resolved measurements of confined acoustic phonons in free-standing nanocrystalline silicon membranes and compare them with the crystalline silicon counterpart. While the latter exhibit well-resolved higher-order modes, a strong suppression of these modes is observed in nanocrystalline samples. The suppression is strongly frequency dependent and becomes more pronounced as the phonon wavelength approaches the characteristic grain size. Analysis of the phonon lifetimes reveals an additional frequency-dependent scattering mechanism in nanocrystalline silicon, with a scattering rate that scales approximately as $f^2$, where $f$ is the phonon frequency. The measured sound velocity is consistent with previous reports for nanocrystalline silicon and indicates an effective elastic response arising from multiple crystallographic orientations. These results establish coherent phonons as a sensitive probe of microstructure-dependent scattering in nanocrystalline materials and indicate that grain boundaries act as an effective spectral filter for high-frequency acoustic phonons.
