基于STEM-EELS方法在纳米尺度上测量表面声子强度

Nanoscale measurement of surface phonon via STEM-EELS

单色仪和球差校正器的装备使得透射电子显微镜同时具备高空间和高能量分辨率。基于扫描透射电子显微镜-电子能量损失谱(STEM-EELS)方法可以实现在纳米尺度上测量材料的声子结构,这为研究表界面和缺陷的声子行为及其与微观结构之间的关系提供了强有力的手段。本文测量了六方氮化硼(h-BN)纳米片体内、表面、表面附近真空中声子信号的强度,利用多种拟合方法探究了其衰减行为并做出理论解释。对比了各种拟合方法的优缺点,讨论了它们的适用范围,提出了一套简单的经验公式来拟合真空中信号强度的衰减行为,并与其他拟合方法对比。

The recent advancement of monochromator and spherical aberration corrector in scanning transmission electron microscope（STEM） enables sub-10 meV inenergy resolution and sub-0.1 nm in spatial resolution. The electron energy loss spectroscopy（EELS） method therefore allows us to measure phonon structure at nanoscale or even atomic scale, providing an unprecedented opportunity to study the localized vibration properties. In this paper, the phonon of the hexagonal-boron nitride（h-BN） nanosheet is measured and various fitting methods are used to quantitatively study the intensity distribution behavior of the aloof mode. Based on the comparison, a simple empirical formula is proposed to fit the decaying of phonon intensity in vacuum and the underlying mechanism is discussed.