Phenomena of Atomic Proximity Field induced by Atomic Force Microscopy

在超高真空中，非接触原子力显微镜(NcAFM)已经实现了原子分辨率，几个实验小组正在观察非常清晰的表面原子尺度图像。因此，本工作的目的是从第一性原理理论出发，阐明纳米原子力显微镜的机理，并发展图像的定量分析方法。为了解释这一机制，有必要了解针尖与表面之间的非线性相互作用对振荡频率的影响，以及净力及其微观分布和耗散效应。在这一年里，我们发展了基于第一原理计算尖端-表面相互作用力的理论模拟方法，并借助二维傅立叶展开方法将其数学转换为形成图像的频移。将该理论应用于Si(111)7x7和Si(111)√3x√3-Ag表面，并与实验结果进行了比较。进一步发展了非接触式耗散力显微镜的理论。这种方法适用于检测原子/分子的纳米力学性质和表面的纳米结构。这种方法甚至可以预料到原子的认识化，使用的是依赖于原子质量的不同色散。

Atomic resolution has been achieved by the non-contact atomic force microscopy (ncAFM) in ultra high vacuum, and several experimental groups are observing very clear atomic scale images of surfaces. Therefore we aimed in the present work, elucidation of the mechanism of ncAFM and development of the quantitative analyses method of the images from the first-principles theory. To elucidate the mechanism, it is necessary to understand how the oscillation frequency is influenced by the nonoliniear interaction between the tip and the surface, as well as the net force and its microscopic distribution and the effect of the dissipation. In this year we developed the theoretical simulation method based on the first-principles calculation of the tip-surface interaction force, which is mathematically transformed to the frequency shift forming the image with the help of the 2-dimensional Fourier expansion method. The theory is applied to Si(111)7x7, and Si(111)√3x√3-Ag surface and compared well with experiments. Furthermore theory of the noncontact dissipasive force microscopy is developed. This method is found to be suitable to detect nano-mechanical properties of the atoms/molecules and nano-structures on surfaces. Even the idetification of the atoms can be expected by this method, using the different disspation depending on the atomic mass.