单晶硅表面STM成像理论模型与实验分析

结合扫描隧道显微镜(STM)成像实验和第一性原理原子级模拟计算的方法已经成为材料界面表征的重要手段。超高真空条件下的STM可用于直接观察单原子等微观结构,但其成像原理还未被理解清楚。STM扫描测得的试件表面原子级图像并不直接反映材料原子的形态,实际上是表面形貌和表面电子态局域密度的综合结果。为了解释STM成像,采用第一性原理Siesta方法,研究了Si(001)面STM成像过程的电子结构,对表面粒子的原子轨道和相应的电荷密度进行计算。讨论了等高模式下扫描高度对局域电子云密度分布的影响,并分析了STM针尖几何形状对模拟结果的影响。研究表明,材料表面原子的电子云密度分布可以用来解释STM成像精度和扫描高度对比的变化。

Theoretical Model and Experimental Analysis of STM Images on the Surface of the Monocrystalline Si

The method of combining scanning tunneling microscope(STM) imaging experiments and first principles atomistic simulations is considered as one of the important measures for the characterization of interfaces.STM operated under ultra-high vacuum conditions can be used to observe the microstructure of individual atoms.However,the STM imaging mechanism has not been explicitly understood.The STM imaging of surfaces with the atomic resolution cannot directly translated to the surface atomic features,however,it should be understood as a combination result of the surface morphology with the surface local electron density.The electronic structure of Si(001) surface in STM imaging was analyzed using first principles with Siesta method.The surface orbitals and the corresponding electron density of the surface particles were calculated for the purpose of interpreting STM images.The effect of STM scanning heights on the density distribution for local electron cloud under the contour model was investigated,and the influence of the geometry for STM tips on the simulation result was analyzed.The research results show that the surface electron cloud density distribution can be applied to interpret the contrast changes of the resolution for the STM imaging with different scanning heights.