Thin film growth, adsorption site, and ion-surface charge exchange phenomena studied by low energy ion scattering

by Zhang, Rui, Ph.D., UNIVERSITY OF HOUSTON, 2008, 115 pages; 3313509

Abstract:

This dissertation focuses on the investigation of the thin film growth, adsorption structure, and the mechanism of ion-surface charge exchange. Time-of-flight scattering and recoiling spectrometry (TOF-SARS) and scattering and recoiling imaging spectrometry (SARIS) has been applied to these surface studies. The large repulsive interaction between the low energy primary ions and target atoms makes TOF-SARS and SARIS extremely surface sensitive techniques.

A brief introduction to TOF-SARS and SARIS, along with experimental methods are described in Chapters 1 and 2. In Chapter 3, the carbonization process of Si (100) in acetylene at 840°C has been studied by combining in situ TOF-SARS and ex situ X-ray photoemission spectroscopy (XPS). It is shown that the scattering and recoiling from the first three atomic layers of the surface provide in situ information about the entire growth process of SiC. Direct evidence for a porous growth mechanism is obtained. Additionally, with the sensitivity of TOF-SARS to the several outermost surface atomic layers, it is possible to control the growth process to obtain either Si or C terminated SiC surfaces. Such surfaces have progressive applications in bioelectronic interface science.

Ion blocking in the low keV energy range is demonstrated to be a sensitive method for probing surface adsorption sites by means of the technique of TOF-SARS. In Chapter 4, we present a quantitative analysis of the blocking effects produced by sub-monolayer Na adsorbed on a Cu(111) surface at room temperature. The results show that, at a coverage &thetas; = 0.25 monolayer, Na atoms preferentially populate the fee threefold surface sites with a height of 2.7± 0.1 Å above the 1st-laver Cu atoms. At a lower coverage of &thetas; = 0.10 monolayer, there is no adsorption site preference for the Na atoms on the Cu(111) surface.

An electron-scattered ion/atom coincidence technique has been developed and applied to the interaction of 3 keV He+ ions with a Si(100)-(2 × 1)-H surface in Chapter 5. The technique extends SARIS to include electron-scattered particle coincidence methods. The scattered particles that induce electrons produce a coincidence SARIS image which is substantially different from the normal SARIS images that are produced by all of the scattered particles together. This primary study confirms that SARIS, coupled with coincidence measurements, is a promising technique for studying ion-surface charge exchange phenomena and surface structure.

Advisor
SchoolUNIVERSITY OF HOUSTON
Source TypeDissertation
SubjectsPhysical chemistry
Publication Number3313509

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