John Prater
Area(s) of Expertise
To enable the bottom-up design and fabrication of highly complex multifunctional materials with new and unprecedented properties, e.g. negative index composites with optical cloaking properties or new classes of smart materials that can alter their behavior in response to environmental stimuli. Identification of robust pathways for directed self-assembly of materials, developing new analytical techniques capable of characterizing materials at the nanoscale, and seeking to understand complex behavior that emerges in highly coupled systems, e.g. studying frustration effects in magnetic systems, or better understanding field coupling effects in multiferroics. Surface and interface engineering in support of materials integration. Development of in-situ and ex-situ analytical methods to characterize the nanoscale structure and determine the physical characteristics that will lead to the specific material properties being sought. Investigation of novel methods that will lead to large-scale, large-quantity processing of nanomaterials.
Publications
- An optimized sample preparation approach for atomic resolution in situ studies of thin films , Microscopy Research and Technique (2018)
- Diamond film growth by HFCVD on Q-carbon seeded substrate , Carbon (2018)
- Magneto-optical properties of BaTiO3/La0.76Sr0.24MnO3/BaTiO3 heterostructures , AIP Advances (2018)
- Polarized neutron reflectivity studies on epitaxial BiFeO3/La0.7Sr0.3MnO3 heterostructure integrated with Si (100) , AIP Advances (2018)
- Polarized neutron reflectivity studies on epitaxial BiFeO3/La0.7Sr0.3MnO3 heterostructure integrated with Si (100) , AIP Advances (2018)
- Structure-property correlations in thermally processed epitaxial LSMO films , Acta Materialia (2018)
- Control of Structural and Electrical Transitions of VO2 Thin Films , ACS Applied Materials & Interfaces (2017)
- Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures , AIP Advances (2017)
- Control of Magnetic Coercivity in epitaxial Ni/VO2/YSZ/Si(001) heterostructures by manipulation of Ni thin film growth modes , MRS Advances (2016)
- Diamagnetism to ferromagnetism in Sr-substituted epitaxial BaTiO3 thin films , Applied Physics Letters (2016)
Grants
Abstract: This ARO staff research program will investigate the epitaxial growth and characterization of (La,Sr)MnO3, BiFeO3, BaTiO3, SrRuO3 and SrTiO3 films and heterostructures integrated epitaxially on Si (100) substrates. The goal is to conduct a detailed investigation of defect behavior and interface structure in these oxide systems, in order to determine how these factors influence the resultant electronic and magnetic properties of the films and the cross coupling of electrical and magnetic fields within these structures. The focus of the research will be on conducting a detailed nanoscale characterization (with sub-angstrom reso1ution) of the atomic structure and chemistry of the heterostructures using a probe corrected FEI Titan 60-300 S/TEM with a complement of spectroscopy attachments. The primary motivation for this research program is to identify experimental approaches for achieving robust electrical switching of magnetic moments in these complex oxide heterostructures.
The proposed research will seek to correlate the structural properties of complex magnetic oxide films and heterojunctions with their magnetic and electrical properties. The oxides of interest are: ZnO dilute magnetic semiconductors (transition metal-doped), La-based manganate (half-metal), and BiFeO3 (a multiferroic). The research will address two major issues related to the epitaxial growth of magnetic oxides films. First, the research will continue studies to determine the mechanism for the ferromagnetism observed in transition-metal-doped ZnO (TM:ZnO). The second thrust will then focus on the epitaxial growth of (La,Sr)MnO3, BiFeO3 and TM:ZnO films on commercially ubiquitious sapphire (0001), Si(111) and Si(100) substrates, and investigate the formation of heterojunctions based on combinations of these oxides. This latter task will concentrate on the reduction of lattice-mismatch stress at heterojunctions and the reduction/passivation of defects (especially threading dislocations). This research program will emphasize detailed nanoscale characterization (with a reso1ution 0.16nm) of the atomic structure and chemistry of the heterostructures using JEOL-2010(GIF) atomic resolution TEM with STEM-Z and EELS attachments and then correlate these findings with the resulting electrical and magnetic properties of the films. Ultimately, the findings will be applied to the fabrication and characterization of test structures with field tunable properties.