Scanning Tunneling Microscopy and Adsorption Studies on Single-Crystal Metal Oxide Surfaces

Type of Document Master's Thesis
Author Conway, Timothy James
Author's Email Address Tim.Conway@lmco.com
URN etd-8297-192718
Title Scanning Tunneling Microscopy and Adsorption Studies on Single-Crystal Metal Oxide Surfaces
Degree Master of Science
Department Chemical Engineering
Advisory Committee
Advisor Name Title
Dr. David F. Cox Committee Chair
Richey M. Davis none
William L. Conger none
Keywords

* scanning tunneling microscopy
* metal oxide surfaces

Date of Defense 1997-09-01
Availability unrestricted
Abstract

Natural and synthetic SnO2 samples were studied using

scanning tunneling microscopy (STM). The SnO2 surface

flattens considerably following high temperature treatments

up to 1500 K. The conductivity of the synthetic SnO2 surface

is significantly reduced following annealing at temperatures

of approximately 1200-1500 K, making tunneling impossible. A

decrease in conductivity was not observed for the natural SnO2

sample following similar high temperature treatments, most likely

due to impurities which act as dopants. No atomic scale images were

collected on the SnO2 surface which provided information regarding atomic

positions and point defects on the surface.

Water adsorption was studied on the stoichiometric Cr2O3 (1012) surface,

using thermal desorption spectroscopy (TDS). Water was the only desorption

product observed during TDS. Adsorption is primarily dissociative following

exposure to water at 163 K. Approximately, 0.12 monolayers of water dissociate

on the clean, nearly stoichiometric Cr2O3 (1012) surface. The first order kinetics

observed for the recombination of dissociated water are not well understood. One

possible explanation is that the rate limiting step for desorption involves the

breaking of a Cr-O bond resulting in a freely diffusing OH species.

The exchange of halogen and oxygen was studied on Cr2O3 (1012) using Auger electron

spectroscopy (AES) and TDS. The exchange of chlorine and oxygen is completely reversible.

Chlorine is removed from the Cr2O3 (1012) surface following exposure to oxygen. Exposure

of CFCl2CH2Cl reduces the surface oxygen concentration to that of the clean, nearly

stoichiometric Cr2O3 (1012) surface. The exchange of chlorine with oxygen appears to

involve only chemisorbed surface oxygen, not bulk lattice oxygen.

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