原子力显微镜中化学成键对力的贡献

迄今非接触原子力显微镜已经成为一个非常强大的工具. 它不仅能够得到表面的原子周期结构,还能给出分子内部的化学键信息. 针尖和样品之间的相互作用是原子力显微镜的有效信号,主要包括三种,即范德瓦尔斯相互作用、静电相互作用和化学键相互作用. 本文在生长于Si(111)-7×7 的铅薄膜上测量了针尖和样品之间的化学键相互作用. 通过获取该相互作用随偏压的变化,并且利用抛物线拟合有效局域接触势的位置,我们发现它是随着针尖和样品之间距离的增大而减小的. 这种趋势来自于针尖和样品之间波函数的交叠. 从而可以得到电子的衰减长度. 我们还测量到了该衰减长度随着铅薄膜厚度的变化会发生振荡,这种振荡归因于平顶楔形铅岛内电子的量子尺寸效应.

Contribution of Chemical Bonding to the Force in Atomic Force Microscopy

Non-contact atomic force microscope (NC-AFM) has become a powerful tool. It can provide the atomic structure and chemical bonding information at the atomic scale. Three kinds of tip- sample interactions are often concerned: including van der Waals interaction, electrostatic interaction, and chemical bonding interaction. In this work, the chemical bonding interaction between the tip and a Pb film is clearly demonstrated by NC-AFM based on a Q-plus force sensor. The tip-sample interaction energy versus the bias voltage was obtained and fitted by a parabolic function to find the effective local contact potential difference, which decreased with increasing tip- sample distance. Such a trend is caused by the wave function overlap. Thus, the decay length of the electron wave function was estimated. Oscillation of the decay length with film thickness was also observed, which can be attributed to the thickness-dependent quantum well states in the Pb islands.