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Tate Lab research and facilities

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.

* Amorphous TiO2: A Thin Film Synthesis Route to Stabilization of Metastable TiO2 Brookite, James Haggerty, Ph.D. (2018).
* Crystallization of TiO2 polymorphs from RF-sputtered, amorphous thin-film precursors, O. Agirseven, D.T. Rivella, Jr., J.E.S. Haggerty, P.O. Berry, K. Diffendaffer, A. Patterson, J. Kreb, J.S. Mangum, B.P. Gorman, J.D. Perkins, B.R. Chen, L.T. Schelhas, J. Tate, AIP Advances 10 (2020).
doi: 10.1063/1.5140368
* Selective brookite polymorph formation related to the amorphous precursor state in TiO2 thin films , J. S. Mangum, O. Agirseven, J. E. S. Haggerty, J. D. Perkins, L. T. Schelhas, D. A. Kitchaev, L. M. Garten, D. S. Ginley, M. F. Toney, J. Tate, B. P. Gorman, J. Non-Crystalline Solids 505, 109-114 (2019).
doi: 10.1016/j.jnoncrysol.2018.10.049
* High-fraction brookite films from amorphous precursors, J. E. S. Haggerty, L. T. Schelhas, D. A. Kitchaev, J. S. Mangum, L. M. Garten, W. Sun, K. H. Stone, J. D. Perkins, M. F. Toney, G. Ceder, D. S. Ginley, B. P. Gorman, J. Tate, Scientific Reports 7, 15232 (2017).
doi: 10.1038/s41598-017-15364-y

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.

* Synthesis and Analysis of Heterostructural Semiconductor Alloy Sn1-xCaxCh (Ch=S, Se) and Nitrides Zn1-xWxN and Zn 1-x(W1-yMoy)x N, Bethany Matthews, Ph.D. (2018).
* Templated growth of metastable polymorphs on amorphous substrates with seed layers , Y. Han, R. Trottier, S. Siol, B. Matthews, M. Young, C. B. Musgrave S. Lany, J. Tate, Q. Zhang, A. M. Holder A. Zakutayev, Physical Review Applied 13, 014012 (2020).
doi: 10.1103/PhysRevApplied.13.014012
* A map of the inorganic ternary metal nitrides , W. Sun, C. J. Bartel, E. Arca, S. R. Bauers, B. Matthews, B. Orvañanos, B.-R. Chen, M. F. Toney, L. T. Schelhas, W. Tumas, J. Tate, A. Zakutayev, S. Lany, A. M. Holder, G. Ceder, Nature Materials 18, 732-739 (2019). doi: 10.1038/s41563-019-0396-2
* Novel phase diagram behavior and materials design in heterostructural semiconductor alloys , A. M. Holder, S. Siol, P. F. Ndione, H. Peng, A. M. Deml, B. E. Matthews, L. T. Schelhas, M. F. Toney, R. G. Gordon, W. Tumas, J. D. Perkins, D. S. Ginley, B. P. Gorman, J. Tate, A. Zakutayev, S. Lany, Science Advances 3(6) e1700270 (2017). doi: 10.1126/sciadv.1700270
* Using heterostructural alloying to tune the structure and properties of the thermoelectric Sn1-xCaxSe , B. E. Matthews, A. M. Holder, L. T. Schelhas, S. Siol, J. W. May, M. R. Forkner, D. Vigil-Fowler, M. F. Toney, J. D. Perkins, B. P. Gorman, A. Zakutayev, S. Lany, J Tate, J. Mater. Chem. A 5, 16873-16882 (2017). doi: 1039/C7TA03694A

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
Rorrer Lab Raman spectrometer
Physical Vapor Deposition Systems
PLD chambers
Pulsed laser deposition laboratory
Sputter System
Sputtering system
Thermal evaporator
Schrader thermal evaporator
Thermal evaporator
Veeco thermal evaporator
Analytical Equipment
Lakeshore Hall
Hall effect measurement
Seebeck measurement
Janis liquid helium cryostat
with 9-tesla superconducting magnet
Liquid nitrogen cryostat
Closed-cycle fridge
Closed cycle refrigerator
Optical Equipment
Integrating sphere
Integrating sphere
(McIntyre Lab)
grating spectrometer
Grating spectrometer
(McIntyre Lab)
Bits and pieces
leak detector
Varian leak detector
Thermolyne oven
UV illuminator