Thomas Zac Ward

Thomas Zac Ward

Research Staff

Bio

Education:

  • University of Tennessee, Knoxville Ph.D. Physics 2008 (Advisors: Ward Plummer and Jian Shen)
  • University of Missouri, Columbia B.S. Physics 2004
  • University of Missouri, Columbia B.A. English Literature 1999

Research Experience:

  • 2009-Present Research Staff, ORNL
    —Thin films and nanostructures to probe fundamental correlated behaviors
  • 2009-2011 Wigner Fellow, ORNL
    —Interfaces in epitaxial complex oxides
  • 2005-2008 Graduate Research Assistant, University of Tennessee
    —Emergent phenomena in spatially confined manganites
  • 2002-2004 Undergraduate Research Assistant, University of Missouri
    —Optical studies of quantum well states in Si for 3D holography applications
  • 2003 Summer Research Assistant, Columbia University
    —Monte Carlo modeling of high energy particle collisions

Community Involvement:

  • Editorial Advisory Board: Journal of Applied Physics
  • Elected Executive Committee: AVS Magnetic Interfaces and Nanostructures Division
  • MRS Symposium Organizer
  • MRS Tutorial Organizer: “Oxide Film Growth—MBE/PLD faceoff for supremacy”
  • AVS Organizer: Magnetic Interfaces and Nanostructures symposia
  • Active member of American Physical Society, Materials Research Society, American Vacuum Society

  • Education and Outreach: ORNL ARC summer program mentor to high school students; ORAU-Siemens Teachers as Researchers mentor to high school teachers; Staffing of ORNL Travelling Science Fair; Regular classroom science demonstrations at the University of Tennessee’s Early Learning Center

Projects

Strain Doping

Helium ions can be used to control the length of a single axis in an epitaxial crystal lattice. Our recent work has demostrated that insertion of non-binding He atoms into functionally important materials allows never before possible control over electronic orbital populations, perovskite octahedra tilts, magnetic anisotropy, and optical bandgaps.  Strain doping provides unprecedented access to strong correlations in quantum materials. This method offers a critical advancement in our ability to minutely design strutural properties which drive many intriquing behaviors, such as superconductivity, multiferroicity, and magnetic textures. Strain doping opens many new intriguing

 

Multi-Phase / Multi-Function Materials

Electronic phase separation in complex materials has been linked to diverse exotic behaviors, such as colossal magnetoresistance, the metal–insulator transition, and high-temperature superconductivity. In these materials, competing regions with drastically different electronic properties can form nanoscopic and mesoscopic phase domains within the macroscopic crystal matrix. We are working to understand how these coexisting self-organized phases form and drive functionality. We are also interested in utilizing these coexisiting phases to access novel electronic behaviors that may be critical to the development of new logic states accessible when lowering device dimensionality to the scale of the inherent competing phases. Recent work has shown that these domains can be moved to form rewritable circuits and that new types of multimodal properties can be controlled through multiple stimuli. The huge catalog of phase-separated quantum materials, each offering unique combinations of competing phases, may aid design of specialized architectures for targeted multifunctional applications not possible with current single-chip, single-function approaches--a critical step in moving beyond Moore.

 

Correlated Solid - Ionic Liquid Interfaces

This project blends ORNL expertise in materials physics, chemistry, microscopy, and neutron sciences to advance a new method of designing materials properties and function through manipulation of solid crystals using interfaced ionic liquids. Ionic liquids have been well studied for use in catalytic and electrochemical applications. However, a new use for these liquid salts has recently emerged as a novel method for investigating electrostatic and electrochemical effects on fundamental physics problems in strongly correlated materials. Here, ionic liquids are interfaced with films or bulk crystals to create field effect heterostructures that allow small applied biases (< 4V) to control charge densities at the interface which are orders of magnitude higher than traditional solid-solid field effect transistors. Our efforts have focused on understanding the solid switching mechanisms, solid-liquid interface structure, field geometries, and accessing new functional properties using these interfaces.

Publications

Journal Publications (2016):

  1. X. Gao, S. Lee, J. Nichols, T.L. Meyer, T.Z. Ward, M.F. Chisholm, H.N. Lee, Nanoscale self-templating for oxide epitaxy with large symmetry mismatch, Scientific Reports 6, 38168 (2016).
  1. T. Meyer, A. Herklotz, V. Lauter, J. Freeland, J. Nichols, E. Guo, S. Lee, T.Z. Ward, N. Balke, S.V. Kalinin, M. Fitzsimmons, H.N. Lee, Enhancing interfacial magnetization with a ferroelectric, Physical Review B 94, 174432 (2016). (Editor’s Suggestion)
  1. J. Nichols, X. Gao, S. Lee, T. Meyer, J. Freeland, V. Lauter, D. Yi, J. Liu, D. Haskel, J. Petrie, E. Gao, A. Herklotz, D. Lee, T.Z. Ward, G. Eres, M. Fitzsimmons, H.N. Lee, Emerging magnetism and anomalous Hall effect in iridate-manganite heterostructures, Nature Communications 7, 12721 (2016).
  1. S.F. Rus, T.Z. Ward, A. Herklotz, Strain-induced optical band gap variation of SnO2 films, Thin Solid Films 615, 103 (2016).
  1. A. Herklotz, H.W. Guo, A.T. Wong, H.N. Lee, P.D. Rack,  T.Z. Ward, Multimodal Responses of Self-Organized Circuitry in Electronically Phase Separated Materials, Advanced Electronic Materials 2, 1600189 (2016). (Cover Article)
  1. P.C. Snijders, C. Sen, M. McConnell, Y.Z. Ma, A. May, A. Herklotz, A.T. Wong, T.Z. Ward, Dynamic defect correlations dominate activated electronic transport in SrTiO3, Scientific Reports 6, 30141 (2016).
  1. M.G. Stanford, P.R. Pudasaini, A. Belianinov, N. Cross, J.H. Noh, M. Koehler, D.G. Mandrus, G. Duscher, A.J. Rondinone, I.N. Ivanov, T.Z. Ward, P.D. Rack, Focused helium-ion beam irradiation effects on electrical transport properties of few-layer WSe2: enabling nanoscale direct write homo-junctions, Scientific Reports 6, 27276 (2016).
  1. A. Herklotz, A.T. Wong, T. Meyer, M.D. Biegalski, H.N. Lee, T.Z. Ward, Controlling octahedral rotations in a perovskite via strain doping, Scientific Reports 6, 26491 (2016).
  1. D.S. Parker, A. Herklotz, T.Z Ward, M. McGuire, D. Singh, Enhanced ferroelectric polarization and possible morphotropic phase boundary in PZT-based alloys, Physical Review B 93, 174307 (2016).
  1. C. Beekman, W. Siemons, M. Chi, N. Balke, J.Y. Howe, T.Z. Ward, P. Maksymovych, J.D. Budai, J.Z. Tischler, R. Xu, W. Liu, H.M. Christen, Ferroelectric self-poling, switching, and monoclinic domain configuration in BiFeO3 thin films, Advanced Functional Materials 26, 5166 (2016).
  1. P.R. Pudasaini, J.H. Noh, A.T. Wong, O.S. Ovchinnikova, A.V. Haglund, S. Dai, T.Z. Ward, D. Mandrus, P.D. Rack,  Ionic Liquid Activation of Amorphous Metal-oxide Semiconductors for Flexible Transparent Electronic Devices, Advanced Functional Materials 26, 2820 (2016). (Cover Article)
  1. A. Herklotz, S.R. Rus, T.Z. Ward, Continuously Controlled Optical Band Gap in Oxide Semiconductor Thin Films, Nano Letters 16, 1782 (2016).
  1. Z.Q. Liu, L. Li, J.D. Clarkson, S.L. Hsu, A.T. Wong, S.S. Fan, M.-W. Lin, C.M. Rouleau, T.Z. Ward, H.N. Lee, A.S. Sefat, H.M. Christen, R. Ramesh, Full Electroresistance Modulation in a Mixed-Phase Metallic Alloy, Physical Review Letters 116, 097203 (2016).
  1. S.P. Bennett, A.T. Wong, A. Glavic, A. Herklotz, C. Urban, I. Valmianski, M.D. Biegalski, H.M.Christen, T.Z. Ward, V. Lauter, Giant Controllable Magnetization Changes Induced by Structural Phase Transitions in a Metamagnetic Artificial Multiferroic, Scientific Reports 6, 22708 (2016).
  1. M. Lin, H. Zhuang, J. Yan, T.Z. Ward,  A. Puretzky, C.M. Rouleau, Z. Gai, L. Liang, V. Meunier, B.G. Sumpter, P. Ganesh, P. Kent, D. Geohegan, D. Mandrus, K. Xiao, Ultrathin Nanosheets of CrSiTe3: A Semiconducting Two-Dimensional Ferromagnetic Material, Journal of Materials Chemistry C 4, 315 (2016).
  1. Z.Q. Liu, M.D. Biegalski, S. Hsu, S. Shang, C. Marker, J. Liu, L. Li, L. Fan, T.L. Meyer, A.T. Wong, J.A. Nichols, D. Chen, L. You, Z. Chen, K. Wang, T.Z. Ward, Z. Gai, H.N. Lee, A.S. Sefat, V. Lauter, Z. Liu, H.M. Christen, Epitaxial growth of intermetallic MnPt films on oxides and large exchange bias, Advanced Materials 28, 118 (2016).