Probing Surface Photovoltage Effect Using Photoassisted Secondary Electron Emission
Probing Surface Photovoltage Effect Using Photoassisted Secondary Electron Emission
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利用光辅助二次电子发射探测表面光电压效应
DOI：
10.1021/acs.jpca.0c02543
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Liao, Bolin
中科院分区：
文献类型：
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作者：
Li, Yu;Choudhry, Usama;Ranasinghe, Jeewan;Ackerman, Alex;Liao, Bolin
虽然表面和界面的性质对现代器件至关重要，但它们通常难以探索，因为来自体的信号经常掩盖表面的贡献。在这里，我们介绍了一种基于扫描电子显微镜（SEM）与脉冲激光源相结合的方法，该方法能够检测材料的最顶层，以研究表面光电压（SPV）相关的效应。这种方法依赖于脉冲光激光瞬时诱导SPV和连续的初级电子束产生二次电子（SE）发射，并监测激光照射下的SE产率的变化。我们观察到的对比行为的SPV引起的SE产量变化的n型和p型半导体。我们进一步研究了SPV诱导的SE产率对初级电子束能量、光通量和光激发的调制频率的依赖关系，揭示了在表面内建势存在下光生载流子动力学的细节。这种快速、无接触和无偏压的技术为探测表面电子现象提供了一个方便而强大的平台，在探测具有高空间分辨率的纳米级效应方面具有很大的潜力。我们的结果进一步提供了一个基础，以了解新兴的时间分辨电子显微镜技术，如扫描超快电子显微镜的对比机制。
While the properties of surfaces and interfaces are crucial to modern devices, they are commonly difficult to explore since the signal from the bulk often masks the surface contribution. Here we introduce a methodology based on scanning electron microscopy (SEM) coupled with a pulsed laser source, which offers the capability to sense the topmost layer of materials, to study the surface photovoltage (SPV) related effects. This method relies on a pulsed optical laser to transiently induce an SPV and a continuous primary electron beam to produce secondary electron (SE) emission and monitor the change of the SE yield under laser illumination. We observe contrasting behaviors of the SPV-induced SE yield change on n-type and p-type semiconductors. We further study the dependence of the SPV-induced SE yield on the primary electron beam energy, the optical fluence, and the modulation frequency of the optical excitation, which reveal the details of the dynamics of the photocarriers in the presence of the surface built-in potential. This fast, contactless, and bias-free technique offers a convenient and robust platform to probe surface electronic phenomena, with great promise to probe nanoscale effects with a high spatial resolution. Our result further provides a basis to understand the contrast mechanisms of emerging time-resolved electron microscopic techniques, such as the scanning ultrafast electron microscopy.