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Elucidation and Control of Surface Electronic and Atomic Processes by the Tip

通过尖端阐明和控制表面电子和原子过程

基本信息

批准号：
06452044
负责人：
TSUKADA Masaru
金额：
$ 4.67万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

Various phenomena are induced by the nano-scale gap between the tip and the sample surface in the scanning probe microscopy. Among them the elementaly processes of electrons and atoms are most important both for the fundamental science and for the basis of thechnological applications. The purpose of this projet is to develop a theoretical method to describe and predics these processes and clarify their fundamental aspects. For that purpose the first・principles recursiontransfer matrix method is developped which is an extension of the Density Functional Theory for non-equilibrium open systems. In this method wavefunctions are solved in a scattering wave forms and the tunneling tails are very precisely determined. With the method quntitative analyzes of STM,tip induced chemical processes, atom transfer between the tip and over the surface can be studied from the first・principles.With this method the following problems are studied. The first is the microscopic contact between the two surfaces. A sharp onset of the electronic inceraction of sufaces is found and the details of the potential distribution are studied as well as the concept of the local workiunction.The mechanism of atom extraction by the tip of STM is clarified as follows. When the tip is negatively biased, the electron cloud is pushed cut in front of the tip apex. Then it is accumlated in the interstitial region between the tip apex atom and the surface atom confronted to it. With the further increase of the negative tip bias, the electron cloud forms a bridge structure with the surface, then a very strong force is acted on the suriace atom. The situationis quite dependent on the tip height and the tip surface materials.

在扫描探针显微镜中，针尖与样品表面之间的纳米尺度间隙会引起各种现象。其中电子和原子的基本过程无论是对基础科学还是对技术应用的基础都是最重要的。本项目的目的是发展一种理论方法来描述和预测这些过程，并阐明其基本方面。为此，我们发展了第一性原理递归传递矩阵方法，它是非平衡开放体系密度泛函理论的推广。在这种方法中，波函数在散射波的形式解决和隧道尾是非常精确地确定。利用STM的定量分析方法，从第一性原理出发，研究了针尖诱导的化学过程，针尖与表面之间的原子转移等问题。第一个是两个表面之间的微观接触。发现了表面电子相互作用的一个急剧的起始点，研究了电势分布的细节以及局域功函数的概念，阐明了STM针尖引出原子的机理。当尖端负偏置时，电子云在尖端顶点的前面被推动切割。随着负偏压的进一步增大，电子云与表面原子形成桥连结构，表面原子受到很强的作用力。这种情况很大程度上取决于尖端高度和尖端表面材料。