A5031805969- Magnetic and transport properties of perovskites and related materials
- Electronic and Structural Properties of Oxides
- Multiferroics and related materials
- Advanced Condensed Matter Physics
- Ferroelectric and Piezoelectric Materials
- Physics of Superconductivity and Magnetism
- Transition Metal Oxide Nanomaterials
- Acoustic Wave Resonator Technologies
- Magneto-Optical Properties and Applications
- Gas Sensing Nanomaterials and Sensors
- Semiconductor materials and devices
- Advanced Thermoelectric Materials and Devices
- Rare-earth and actinide compounds
- Ga2O3 and related materials
- ZnO doping and properties
- 2D Materials and Applications
- Magnetic Properties of Alloys
- Magnetic Properties and Applications
- Electron and X-Ray Spectroscopy Techniques
- Advanced Photocatalysis Techniques
- Perovskite Materials and Applications
- Dielectric properties of ceramics
- Photorefractive and Nonlinear Optics
- Surface and Thin Film Phenomena
- Seismic Waves and Analysis
Cornell University
2015-2024
Northrop Grumman (United States)
2024
Stanford University
2013-2021
Palo Alto University
2016
Sandia National Laboratories
2013
University of Virginia
2013
University of Connecticut
2013
Pennsylvania State University
2007-2010
University of Salerno
2004-2008
University of Cagliari
1996
Piezoelectric materials, which convert mechanical to electrical energy and vice versa, are typically characterized by the intimate coexistence of two phases across a morphotropic phase boundary. Electrically switching one other yields large electromechanical coupling coefficients. Driven global environmental concerns, there is currently strong push discover practical lead-free piezoelectrics for device engineering. Using combination epitaxial growth techniques in conjunction with theoretical...
We report a photovoltaic effect in ferroelectric BiFeO3 thin films. The all-oxide heterostructures with SrRuO3 bottom and tin doped indium oxide top electrodes are characterized by open-circuit voltages ∼0.8–0.9 V external quantum efficiencies up to ∼10% when illuminated the appropriate light. Efficiencies at least an order of magnitude larger than maximum efficiency under sunlight (AM 1.5) thus far reported for ferroelectric-based devices. dependence measured voltage on film thickness...
The polarization of the ferroelectric BiFeO3 sub-jected to different electrical boundary conditions by heterointerfaces is imaged with atomic resolution using a spherical aberration-corrected transmission electron microscope. Unusual triangular-shaped nanodomains are seen, and their role in providing closure understood through phase-field simulations. Heterointerfaces key performance devices, this first observation spontaneous vortex nanodomain arrays at reveals properties unlike surrounding...
The utility of ferroelectric materials stems from the ability to nucleate and move polarized domains using an electric field. To understand mechanisms polarization switching, structural characterization at nanoscale is required. We used aberration-corrected transmission electron microscopy follow kinetics dynamics switching millisecond temporal subangstrom spatial resolution in epitaxial bilayer antiferromagnetic (BiFeO(3)) on a ferromagnetic electrode (La(0.7)Sr(0.3)MnO(3)). observed...
We have studied the effect of biaxial strain on thin films (001) La0.7Sr0.3MnO3. deposited by reactive molecular-beam epitaxy different single crystalline substrates, varying substrate-induced from −2.3% to +3.2%. Magnetization and electrical transport measurements reveal that dependence Curie temperature is in very good agreement with theoretical predictions Millis et al. [J. Appl. Phys. 83, 1588 (1998)].
Above-band-gap optical excitation produces interdependent structural and electronic responses in a multiferroic BiFeO(3) thin film. Time-resolved synchrotron x-ray diffraction shows that photoexcitation can induce large out-of-plane strain, with magnitudes on the order of half one percent following pulsed-laser excitation. The strain relaxes same nanosecond time dependence as interband relaxation excited charge carriers. magnitude its temporal correlation carriers indicate an mechanism,...
We report high-resolution angle-resolved photoemission studies of epitaxial thin films the correlated 4d transition metal oxide ferromagnet SrRuO(3). The Fermi surface in ferromagnetic state consists well-defined Landau quasiparticles exhibiting strong coupling to low-energy bosonic modes which contributes large effective masses observed by transport and thermodynamic measurements. Upon warming material through its Curie temperature, we observe a substantial decrease quasiparticle coherence...
Here we demonstrate how the Fermi surface topology and quantum many-body interactions can be manipulated via epitaxial strain in spin-triplet superconductor ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ its isoelectronic counterpart ${\mathrm{Ba}}_{2}{\mathrm{RuO}}_{4}$ using oxide molecular beam epitaxy, situ angle-resolved photoemission spectroscopy, transport measurements. Near topological transition of $\ensuremath{\gamma}$ sheet, observe clear signatures critical fluctuations, while...
Controlled switching of resistivity in ferroelectric thin films is demonstrated by writing and erasing stable, nanoscale, strongly charged domain walls using an situ transmission electron microscopy technique. The resistance can be read nondestructively presents the largest off/on ratio (≈10(5) ) ever reported room-temperature devices, opening new avenues for engineering thin-film devices.
Aberration-corrected transmission electron microscopy was used to study atomic-scale processes in Pd–LaFeO3 catalysts. Clear evidence for diffusion of Pd into LaFeO3 and out LaFe0.95Pd0.05O3−δ under high-temperature oxidizing reducing conditions, respectively, found, but the extent which these occurred quite limited. These observations cast doubt that such phenomena play a significant role postulated mechanism self-regeneration this system as an automotive exhaust-gas catalyst.
A new orthorhombic phase of the multiferroic BiFeO3 has been created via strain engineering by growing it on a NdScO(3)(110)(o) substrate. The tensile-strained is ferroelectric and antiferromagnetic at room temperature. combination nonlinear optical second harmonic generation piezoresponse force microscopy revealed that polarization in along in-plane {110}(pc) directions. In addition, corresponding rotation axis this was observed using x-ray linear dichroism.
Single-phase epitaxial films of the monoclinic polymorph BiVO4 were synthesized by reactive molecular-beam epitaxy under adsorption-controlled conditions. The grown on (001) yttria-stabilized cubic zirconia (YSZ) substrates. Four-circle x-ray diffraction, scanning transmission electron microscopy (STEM), and Raman spectroscopy confirm growth with an atomically abrupt interface orientation relationship (001)BiVO4 ∥ (001)YSZ [100]BiVO4 [100]YSZ. Spectroscopic ellipsometry, STEM energy loss...
Continuous developments in nanotechnology require new approaches to materials synthesis that can produce novel functional structures. Here, we show nanoscale defects, such as nonstoichiometric nanoregions (NSNRs), act nano-building blocks for creating complex electrical polarization structures the prototypical multiferroic ${\mathrm{BiFeO}}_{3}$. An array of charged NSNRs are produced ${\mathrm{BiFeO}}_{3}$ thin films by tuning substrate temperature during film growth. Atomic-scale scanning...
We report the magnetic and transport properties of [(SrMnO3)n∕(LaMnO3)2n]m superlattices grown by molecular-beam epitaxy on (100) SrTiO3 with periodicities n=1, 2, 3, 4, 5, 6, 8, 16. Although superlattice constituents, LaMnO3 SrMnO3, are both antiferromagnetic insulators, for small n (n⩽2) behave like ferromagnetic conductor La0.67Sr0.33MnO3. As increases, become dominated layers, but electronic continue to be controlled interfaces.
Ferroelectric and ferroelastic domain structure has a profound effect on the piezoelectric, ferroelectric, dielectric responses of ferroelectric materials. However, walls strain field effects thermal properties are unknown. We measured conductance from 100–400 K epitaxially grown BiFeO3 thin films with different variants, each separated primarily by 71° walls. determined Kapitza across walls, which is driven induced variants. This wall lower than associated grain boundaries in all previously
Charged domain walls (CDWs) are of significant scientific and technological importance as they have been shown to play a critical role in controlling the switching mechanism electric, photoelectric, piezoelectric properties ferroelectric materials. The atomic scale structure CDWs, which for understanding emergent properties, have, however, rarely explored. In this work, using spherical-aberration-corrected transmission electron microscope with subangstrom resolution, we found that...
Abstract The transition temperature T c of unconventional superconductivity is often tunable. For a monolayer FeSe, for example, the sweet spot uniquely bound to titanium-oxide substrates. By contrast La 2−x Sr x CuO 4 thin films, such substrates are sub-optimal and highest instead obtained using LaSrAlO . An outstanding challenge thus understand optimal conditions in films: which microscopic parameters drive change how can we tune them? Here demonstrate, by combination x-ray absorption...
Abstract Controlling the structure of catalysts at atomic level provides an opportunity to establish detailed understanding catalytic form-to-function and realize new, non-equilibrium structures. Here, advanced thin-film deposition is used control La 2/3 Sr 1/3 MnO 3 , a well-known catalyst for oxygen reduction reaction. The surface sub-surface customized, whereas overall composition d -electron configuration oxide kept constant. Although addition SrMnO benefits reaction via electronic...
A new synthetic approach has recently been developed for the fabrication of freestanding crystalline perovskite oxide nanomembranes, which involves epitaxial growth a water-soluble sacrificial layer. By utilizing an ultrathin capping layer SrTiO3, here we show that this layer, as grown by pulsed laser deposition, can be stabilized in air and therefore used transferrable templates ex situ using other techniques. We find stability these depends on thickness On templates, superconducting SrTiO3...
The magnetic and electronic modifications induced at the interfaces in ${({\text{SrMnO}}_{3})}_{n}/{({\text{LaMnO}}_{3})}_{2n}$ superlattices have been investigated by linear circular dichroism $\text{Mn}\text{ }{L}_{2,3}$ x-ray absorption spectra. Together with theoretical calculations, our data demonstrate that charge redistribution across favors in-plane ferromagnetic (FM) order ${e}_{g}({x}^{2}\ensuremath{-}{y}^{2})$ orbital occupation, agreement average strain. Far from interfaces,...
The low-temperature $(<60\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ transport properties of as-grown ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ ultrathin films, deposited by the molecular beam epitaxy, have been investigated as a function sample thickness (from $40\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}3.5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$) and in presence an external magnetic field. With decreasing thickness, clear resistivity minimum...
Abstract Through mapping of the spatiotemporal strain profile in ferroelectric BiFeO 3 epitaxial thin films, we report an optically initiated dynamic enhancement gradient 10 5 –10 6 m −1 that lasts up to a few ns depending on film thickness. Correlating with transient optical absorption measurements, is attributed piezoelectric effect driven by screening field mediated excitons. These findings not only demonstrate new possible way controlling flexoelectric effect, but also reveal important...