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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.

在扫描隧道显微镜(STM)中，通过对样品施加高于样品功函数的电压，从STM针尖发射的电子在样品表面附近具有正动能。在这种场发射模式下，在隧道势垒和样品附近的电势的适当边界条件下，电子驻波在真空禁带中被激发。电子轰击的本征态由样品表面附近的电势决定。因此，可以从ESW激励来估算样品表面附近的电场。可以从微分电导(Di/dV)对施加电压的曲线中检测到ESW：Di/dV曲线中的峰值对应于ESW激励。我们得到了Au(111)，Si(001)2x1，Si(111)7x7，Ge(001)2x1和Si(001)2x1：H等几个样品的dI/dV曲线和ESW峰。对W针尖进行了热场(T-F)处理，形成了类似的形状：在高电场下加热，导致了{110}面的膨胀。得到的di/dv谱按三角势模型进行分析，该模型具有与ESW谱相对应的能级本征值。此外，通过提高照射样品表面的场发射电子的能量，结合电子能谱分析仪，得到了半导体和金属表面背散射电子的电子能量损失谱(EELS)和俄歇电子能谱。这一结果显示了利用场发射扫描隧道显微镜在纳米尺度上进行元素分析的潜力。