Study of electric field close to a sample surface utilizing the electron standing wave excited in a vacuum gap of scanning tunneling microscopy

利用扫描隧道显微镜真空间隙中激发的电子驻波研究样品表面附近的电场

基本信息

批准号：
12450022
负责人：
TOMITORI Masahiko
金额：
$ 9.09万
依托单位：
Japan Advanced Institute, of Science and Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

By applying a voltage higher than a sample work function to a sample in scannging tunneling microscopy (STM), electrons field-emitted from an STM tip have positive kinetic energy near a sample surface. In this field emission regime, an electron standing wave (ESW) is excited in the vacuum gap under proper boundary conditions of a tunneling barrier and a potential near the sample. The eigenstates of ESW are determined by a potential near the sample surface. Thus the electric field near sample surface can be evaluated from the ESW excitation. The ESW can be detected from the differential conductance (dI/dV) versus the applied voltage curve : the peaks in the dI/dV curve correspond to the ESW excitation. We have obtained the dI/dV curves with ESW peaks for several samples : Au(111), Si(001)2x1, Si(111)7x7, Ge(001)2x1 and Si(001)2x1:H. To evaluate the field, there is a difficult problem that the tip shape regulates the electric field in the vacuum gap as a boundary condition. The thermal-field (T-F) treatment was applied for W tips to form a similar shape : the tip is heated under a high electric field resulting in expansion of {110} facets. The obtained dI/dV spectra were analyzed according to a model with a triangle potential, which has eigenvalues of the energy levels corresponding to the ESW spectra. It is concluded that the peak interval can be an index of the field evaluation.Furthermore, by raising the energy of the field emitted electron that irradiates sample surfaces, we have obtained electron energy loss spectra (EELS) and Auger electron spectra of backscattered electrons from semiconductors and metal surfaces with the same setup of field emission STM combined with an electron energy analyzer. This result exhibits the potential of elemental analysis on a nano scale with a combined instrument with the field emission STM.

通过在扫描隧道显微镜 (STM) 中向样品施加高于样品功函数的电压，从 STM 尖端场发射的电子在样品表面附近具有正动能。在此场发射体系中，在隧道势垒和样品附近电势的适当边界条件下，真空间隙中会激发电子驻波 (ESW)。 ESW 的本征态由样品表面附近的电势决定。因此，可以通过 ESW 激励来评估样品表面附近的电场。 ESW 可以通过微分电导 (dI/dV) 与施加电压的关系曲线来检测：dI/dV 曲线中的峰值对应于 ESW 激励。我们获得了几个样品的 dI/dV 曲线和 ESW 峰：Au(111)、Si(001)2x1、Si(111)7x7、Ge(001)2x1 和 Si(001)2x1:H。为了评估电场，存在一个难题，即尖端形状将真空间隙中的电场作为边界条件进行调节。对 W 尖端进行热场 (T-F) 处理，形成类似的形状：尖端在高电场下加热，导致 {110} 面膨胀。根据三角势模型对获得的 dI/dV 谱进行分析，该模型具有与 ESW 谱相对应的能级特征值。得出峰值间隔可以作为场评价的一个指标。此外,通过提高照射样品表面的场发射电子的能量,我们获得了背散射电子的电子能量损失谱(EELS)和俄歇电子谱。半导体和金属表面，采用相同的场发射 STM 装置与电子能量分析仪相结合。这一结果展示了使用场发射 STM 组合仪器进行纳米级元素分析的潜力。