The Tate Lab group studies the optical, electrical and structural properties of materials, especially in thin-film form, with the goal of understanding how to make them useful in our everyday lives. We have studied high-temperature superconductors, luminescent semiconductors, transparent conductors, optical absorbers, heterostructural alloys, amorphous metals, and polymorphs of TiO2. Funding for this work has come from the Department of Energy, the National Science Foundation, the Research Corporation, the Office of Naval Research, among others, and of course, support from Oregon State University comes in many forms, especially student support!
Polymorphs of TiO2:
Titania, or TiO2, has many different structures or "polymorphs" of the same chemical composition. They differ markedly in their properties. For example, a mixture of the rutile and anatase polymoprhs is a more effective catalyst than either of the components. Another polymorph, brookite, has exhibited even better catalytic behavior under some conditions. It's therefore interesting to understand how and why each polymoprh forms.
Our group has developed a methods of selecting a particular polymorph of TiO2 by depositing amorphous precursor films of a particular thickness at particular pressures of oxygen. When the films are annealed, a specific polymorph crysatallizes. We've used amorphous precursors deposited by pulsed laser deposition and by sputtering, and both methods work, with subtle variations that we're investigating. We identify the crystal structures by Raman spectroscopy and examine the effect of annealing temperatures. This work was pioneered by grad student James Haggerty (now at Intel), and current grad student Okan Agirseven has made great strides forward, producing the largest-area brookite films known. Current grad student Pritha Biswas is extending the study to isotructural and possibly heterostructural alloys of TiO2 and SnO2. Collaborations with the Cann and Santala groups in Materials Science are beginning.
Heterostructural Alloys:
Many new properties result when two or more materials are "blended". Tuning of the semiconductor band gap is the most common example. Our group investigates what happens when different materials of the same structure (isostructural) and different structure (heterostructural) are alloyed to form a compound of the type A1-yByX from constituents AX and BX. For example, we showed that Sn1-yCaySe, a heterostructural alloy of orthorhombic SnS and cubic CaSe had superior thermoelectric properties near the critical composition. Former grad student Bethany Matthews (now a postdoc at PNNL) pioneered this work in chalcogenides and developed nitride counterparts during a fellowship at NREL.
Graduate and undergraduate theses from the Tate lab since 1989.
| Common Access facilities we often use | |
|---|---|
| OSU MaSC: Materials Synthesis and Characterization Facility | |
| OSU Electron Microscopy Facility | |
| ATAMI | |
| Rorrer Lab Raman spectrometer | |
| UO CAMCOR | |
| Physical Vapor Deposition Systems | |
 Pulsed laser deposition laboratory |
|
 Sputtering system |
 Schrader thermal evaporator |
 Veeco thermal evaporator |
|
| Analytical Equipment | |
 Hall effect measurement |
 Seebeck measurement |
 Janis liquid helium cryostat with 9-tesla superconducting magnet |
 Liquid nitrogen cryostat |
 Closed cycle refrigerator |
|
| Optical Equipment | |
 Integrating sphere (McIntyre Lab) |
 Grating spectrometer (McIntyre Lab) |
| Bits and pieces | |
 Varian leak detector |
 Thermolyne oven  UV illuminator |
