时域极紫外漫散射光谱学研究纳米尺度表面声子
Time-domain extreme ultraviolet diffuse scattering spectroscopy of nanoscale surface phonons
AI总结：
该研究通过极紫外漫散射光谱学实现了对纳米尺度表面声子的时域观测，揭示了光学激发产生相干表面声子的机制，并为扩展表面声子光谱学的波矢范围提供了新方法。
摘要：
我们报告了在极紫外光对表面的漫散射中观察到动态条纹图案，该现象发生在飞秒光学激发之后。在探测器的每个点上，漫散射强度表现出在特定频率上振荡，这些频率对应于由散射几何决定的波矢的表面声子，表明光学激发产生了在所有方向上传播的相干表面声子，并覆盖从60到300纳米波长范围。这种现象在多种样品上被观察到，包括单层和多层金属膜以及体半导体。测量的表面声子色散关系与理论计算有良好一致。通过比较不同表面形态样品的信号振幅，我们发现激发机制与样品的自然表面粗糙度有关。然而，即使在极光滑的表面（亚纳米粗糙度）上，信号仍然可检测。我们的发现展示了一种简单有效的光学激发相干表面声子的方法，适用于广泛固体样品，并为在远超传统表面布里渊散射极限的波矢范围内进行表面声子光谱学奠定了基础。
英文摘要：
We report the observation of dynamic fringe patterns in the diffuse scattering of extreme ultraviolet light from surfaces, following femtosecond optical excitation. At each point on the detector, the diffuse scattering intensity exhibits oscillations at well-defined frequencies that correspond to surface phonons with wave vectors determined by the scattering geometry, indicating that the optical excitation generates coherent surface phonons propagating in all directions and spanning a wavelength range from 60 to 300 nm. This phenomenon is observed on a variety of samples, including single-layer and multilayer metal films, as well as bulk semiconductors. The measured surface phonon dispersions show good agreement with theoretical calculations. By comparing signal amplitudes from samples with different surface morphologies, we find that the excitation mechanism is linked to the natural surface roughness of the samples. However, the signal is still detectable on extremely smooth surfaces with sub-nanometer roughness. Our findings demonstrate a simple and effective method for optically exciting coherent surface phonons with nanoscale wavelengths on a wide range of solid samples and establish a foundation for surface phonon spectroscopy in a wave vector range well beyond the limit of conventional surface Brillouin scattering.
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