ELECTRONIC TRANSPORT PROPERTIES OF RUTHENIUM AND RUTHENIUM DIOXIDE THIN FILMS

Electrical conductivity in solids is a remarkable property that spans twenty three orders of magnitude from insulators to metals. Surprisingly, transition-metal oxides themselves nearly span this range and can be insulators, semiconductors, metals, and even superconductors. My dissertation is an examination of the transport properties of thin films of one of the transition metals, ruthenium, and its most stable oxide, ruthenium dioxide, which is also a metal. The resistivities and Hall coefficients of polycrystalline thin films of these materials were measured at and above room temperature in vacuum, oxygen, and carbon monoxide atmospheres.
Ruthenium is a metal of the platinum group and is used as a hardener in metal alloys. Ruthenium dioxide finds uses in electronics as thick and thin film resistors and diffusion barriers. Perhaps most importantly, these metals are used as chemical catalysts and have been widely studied as a model system for the catalysis of carbon monoxide into carbon dioxide. Noting that the production of nearly 80 % of industrial chemicals relies at some point on catalysis, understanding of the catalysis process is considered important. For example, my references include an investigator of the ruthenium system who is a Nobel Prize winner in chemistry.
The thesis presents the first measurements of the Hall coefficient in ruthenium thin films, which determines the sign of charge carriers. It presents measurements showing how conduction can change from electrons to holes as dominant charge carriers in ruthenium dioxide, which is significant to the energy-band theory of physics. It shows how the transport properties of these metal films are related to their fabrication and resulting physical structures. A surprising oxygen loss from some ruthenium dioxide films is considered and is believed to be a unique finding. Transport measurements related to the catalysis process are another unique feature of the study. It is shown that exposure to carbon monoxide can change the transport properties of these metals. In particular, switching between carbon monoxide and oxygen can switch both the resistivity and Hall coefficient of these metals, which is believed to be a novel finding.