Phenomena of Atomic Proximity Field induced by Atomic Force Microscopy

在超高真空中，非接触式原子力显微镜（ncAFM）已经实现了原子分辨率，并且一些实验组正在观察非常清晰的表面原子尺度图像。因此，本论文旨在从第一性原理出发，阐明纳米原子力显微镜的作用机理，发展纳米原子力显微镜图像的定量分析方法。为了阐明这一机制，有必要了解振荡频率是如何受到针尖和表面之间的非线性相互作用，以及净力及其微观分布和耗散的影响。在这一年中，我们开发了基于尖端-表面相互作用力的第一性原理计算的理论模拟方法，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。将理论应用于Si（111）_7 ×_7和Si（111）_3 ×_3-Ag表面，并与实验进行了比较。进一步发展了非接触耗散力显微镜的理论。该方法适用于表面原子/分子和纳米结构的纳米力学性质的检测。甚至原子的识别也可以通过这种方法来预期，使用取决于原子质量的不同耗散。

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.