An Analysis of the Si(111)-5*2 (s)-Au Surface Structure -The Ordered Structure of the Intermediate State of One and Two Dimensional Structures-

Abstract

In order to exactly analyze a crystal structure it is necessary to consider from two viewpoints of long range order (LRO) and short range order (SRO). The information on the reciprocal lattice which is obtained by electron diffraction or X-ray diffraction concerns mainly on the long range order. On the other hand, the images observed by STM (tunnel scanning microscopy) concern mainly with the short range order. For the analysis of the STM images, we must construct the structure which does not contradict to the diffraction patterns. We observe sometimes the streak reflections in LEED (low energy electron diffraction) and RHEED (reflection high energy electron diffraction) patterns taken from the surface structures. When such streak patterns appear, we are apt to deal with it as the case that the crystallinity is not good. There are actually such cases, but some cases suggest a deep meaning on the structure. In this paper, from the standpoint of diffraction theory, we consider the streak reflection patterns which were observed often in 5×2 (s)-Au surface structure formed on the Si(111) surface when Au atoms are deposited on the Si(111) surface. Since by coexisting with the streak reflections and the sharp diffraction points of 5 times structure in the pattern of this surface structure, it is the case of that we cannot simply neglect it by saying that the crystallinity is not good. When this diffraction pattern is examined in detail, an important hint of the structure is obtained which shows an intermediate state of one dimensional and two dimensional lattices. A suggested structure is that for one dimensional lattice of Au atoms (Au chain), the position of the neighboring chain is decided with a connection probability α. The calculation method of diffracted intensity of the streaks in the 5×2 (s)-Au structure is a typical example of diffraction theory and worthwhile to consider in details and instructive also to understand many other diffraction phenomena.