Jobst Johannes, Kautz Jaap, Mytiliniou Maria, Tromp Rudolf M, van der Molen Sense Jan
Huygens-Kamerlingh Onnes Laboratorium, Leiden University, NL-2300 RA Leiden, P.O. Box 9504, Netherlands; Department of Physics, Columbia University, New York, New York 10027, USA.
Huygens-Kamerlingh Onnes Laboratorium, Leiden University, NL-2300 RA Leiden, P.O. Box 9504, Netherlands.
Ultramicroscopy. 2017 Dec;183:8-14. doi: 10.1016/j.ultramic.2017.10.009. Epub 2017 Oct 25.
In a lot of systems, charge transport is governed by local features rather than being a global property as suggested by extracting a single resistance value. Consequently, techniques that resolve local structure in the electronic potential are crucial for a detailed understanding of electronic transport in realistic devices. Recently, we have introduced a new potentiometry method based on low-energy electron microscopy (LEEM) that utilizes characteristic features in the reflectivity spectra of layered materials [1]. Performing potentiometry experiments in LEEM has the advantage of being fast, offering a large field of view and the option to zoom in and out easily, and of being non-invasive compared to scanning-probe methods. However, not all materials show clear features in their reflectivity spectra. Here we, therefore, focus on a different version of low-energy electron potentiometry (LEEP) that uses the mirror mode transition, i.e. the drop in electron reflectivity around zero electron landing energy when they start to interact with the sample rather than being reflected in front of it. This transition is universal and sensitive to the local electrostatic surface potential (either workfunction or applied potential). It can consequently be used to perform LEEP experiments on a broader range of material compared to the method described in Ref[1]. We provide a detailed description of the experimental setup and demonstrate LEEP on workfunction-related intrinsic potential variations on the Si(111) surface and for a metal-semiconductor-metal junction with external bias applied. In the latter, we visualize the Schottky effect at the metal-semiconductor interface. Finally, we compare how robust the two LEEP techniques discussed above are against image distortions due to sample inhomogeneities or contamination.
在许多系统中，电荷传输受局部特征支配，而非像提取单一电阻值所暗示的那样是一种全局属性。因此，解析电子势中的局部结构的技术对于详细理解实际器件中的电子传输至关重要。最近，我们引入了一种基于低能电子显微镜（LEEM）的新电位测定法，该方法利用了层状材料反射光谱中的特征[1]。在LEEM中进行电位测定实验具有快速、视野大、可轻松缩放以及与扫描探针方法相比非侵入性等优点。然而，并非所有材料在其反射光谱中都显示出清晰的特征。因此，在这里我们关注低能电子电位测定（LEEP）的一种不同版本，它利用镜面模式转变，即当电子开始与样品相互作用而非在样品前方被反射时，电子反射率在零电子着陆能量附近的下降。这种转变是普遍存在的，并且对局部静电表面势（功函数或外加势）敏感。因此，与参考文献[1]中描述的方法相比，它可用于在更广泛的材料上进行LEEP实验。我们提供了实验装置的详细描述，并展示了在Si(111)表面与功函数相关的本征电位变化以及施加外部偏压的金属 - 半导体 - 金属结上的LEEP。在后者中，我们可视化了金属 - 半导体界面处的肖特基效应。最后，我们比较了上述两种LEEP技术对于由于样品不均匀性或污染导致的图像失真的鲁棒性。
