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

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 (101̲2) 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 (101̲2) 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 (101̲2) using Auger electron spectroscopy (AES) and TDS. The exchange of chlorine and oxygen is completely reversible. Chlorine is removed from the Cr₂O₃ (101̲2) surface following exposure to oxygen. Exposure of CFCl₂CH₂Cl reduces the surface oxygen concentration to that of the clean, nearly stoichiometric Cr₂O₃ (101̲2) surface. The exchange of chlorine with oxygen appears to involve only chemisorbed surface oxygen, not bulk lattice oxygen.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Chemical Engineering

Department dc:contributor.department

Chemical Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

1997

Author dc:creator

• Conway, Timothy James

Chair dc:contributor.committeechair

• Cox, David F.

Committee members dc:contributor.committeemember

• Conger, William L.
• Davis, Richey M.

• metal oxide surfaces
• scanning tunneling microscopy

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

etd-8297-192718

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/37007