Pittsburgh, PA 15260
Solid State Chemistry and Thermodynamics
Professor Butera's current research is concerned with two areas: (1) the investigation of the physical and thermodynamic properties associated with the superconducting transition that occurs in the "High Temperature Superconductors" such as YBa2Cu3O7-d; and (2) the determination and modelling of the chemistry that occurs within reactive interfaces such as are formed by ultra high vacuum deposition of metal (or other reactant) atoms onto clean surfaces of semiconductors,insulators or a second metal.
High Temperature Superconductors
The exact nature of the superconducting transition that occurs in these oxide based materials and the effect of variations of the oxygen content is central to the understanding of these materials. Our investigations involve the use of high resolution adiabatic heat capacity measurements to study both the nature of the transition and the effect of variations in the oxygen content and thermal history on the transition temperature. We have determined that for the YBa2Cu3O7-dcompounds the heat capacity exhibits a very sharp transition indicating that the superconductivity in these materials has a significant 3-dimensional character. The effect of oxygen content variations and thermal history is presently under investigation. This work involves the preparation of materials with well defined oxygen content and very precise determination of the heat capacity as a function of temperature.
Reactive Interface Chemistry
The ultimate goal of this research is to obtain a understanding of the factors which control the mechanism which control the chemical products formed, and their spatial distribution, within the interfacial region which is formed by the vapor deposition of a metal, or other gaseous reactant, onto the atomically clean surface of a semiconductor, second metal or insulator. In many cases these interfaces are formed reactively with a room temperature substrate. Thus far we have been successful in developing a thermodynamic-kinetic model that quantitatively account for the chemistry of the V/Ge and VInSb interfaces using photoelectron emission spectroscopic data obtained as these interfaces are formed. These efforts have yielded, for the case of V/Ge, the chemical composition and spatial extent of the compounds formed within the interfacial region for interfaces formed both at room temperature and elevated temperatures. We have recently successfully extended the application of this model to the more complicated V/InSb system. This has proven to be a more severe test of the model as the chemistry involving both components of the binary semiconductor with the metal must be accounted for by the same mechanism. The results thus far indicate that the extent of the reaction, as well as the compounds formed, is determined by an interplay of the thermodynamic driving force and the dynamic effect of both thermal and atomic diffusion. The successful extension of this model to other chemical systems will provide the generally applicable basis for both the determination and control of the factors governing reactive interface formation.