A5016005712- Ferroelectric and Piezoelectric Materials
- Multiferroics and related materials
- Electronic and Structural Properties of Oxides
- Luminescence Properties of Advanced Materials
- Magnetic and transport properties of perovskites and related materials
- Electrodeposition and Electroless Coatings
- ZnO doping and properties
- Advanced X-ray Imaging Techniques
- Transition Metal Oxide Nanomaterials
- Perovskite Materials and Applications
- Advanced Condensed Matter Physics
- Ga2O3 and related materials
- Semiconductor materials and devices
- Copper Interconnects and Reliability
- Magnetic properties of thin films
- Glass properties and applications
- Physics of Superconductivity and Magnetism
- Nuclear Physics and Applications
- X-ray Spectroscopy and Fluorescence Analysis
- Metal and Thin Film Mechanics
- Copper-based nanomaterials and applications
- Integrated Circuits and Semiconductor Failure Analysis
- Gas Sensing Nanomaterials and Sensors
- Anodic Oxide Films and Nanostructures
- Metallic Glasses and Amorphous Alloys
Soongsil University
2014-2023
Oak Ridge National Laboratory
1997-2010
Seoul National University
1990-2009
University of Wisconsin–Madison
2009
Changwon National University
2009
University of Suwon
2009
Samsung (South Korea)
2004
Chungbuk National University
2003
Purdue University West Lafayette
1995-1999
The Ohio State University
1989-1990
We report on nanoscale strain gradients in ferroelectric HoMnO(3) epitaxial thin films, resulting a giant flexoelectric effect. Using grazing-incidence in-plane x-ray diffraction, we measured the which were 6 or 7 orders of magnitude larger than typical values reported for bulk oxides. The combination transmission electron microscopy, electrical measurements, and electrostatic calculations showed that flexoelectricity provides means tuning physical properties such as domain configurations...
Methods are derived for measuring local strain, stress, and crystallographic texture (orientation) in polycrystalline samples when 1–10 grains simultaneously illuminated by an energy scanable or broad-bandpass x-ray beam. The orientation unit-cell shape each grain can be determined from the diffracted directions of four Bragg reflections. volume is (wavelength) one reflection. methods include algorithm indexing reflections overlapping crystal Laue patterns determining average strain stress...
To investigate the critical thickness of ferroelectric BaTiO3 (BTO) films, we fabricated fully strained SrRuO3∕BTO∕SrRuO3 heterostructures on SrTiO3 substrates by pulsed laser deposition with in situ reflection high-energy electron diffraction. We varied BTO layer from 3to30nm. By fabricating 10×10μm2 capacitors, could observe polarization versus electric-field hysteresis loops, which demonstrate existence ferroelectricity layers thicker than 5nm. This observation provides an experimental...
Anatase Ti0.96Co0.04O2 films were grown epitaxially on SrTiO3 (001) substrates by using plused laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, PO2, during the growth was systematically varied. As PO2 decreased, behavior changed from a 2-dimensional layer-by-layer-like to 3-dimensional island-like one, which resulted in an increase saturation magnetization. These structural and magnetic changes explained terms of formation cobalt...
Ferroelectric tunnel junctions (FTJs) have attracted increasing research interest as a promising candidate for nonvolatile memories. Recently, significant enhancements of tunneling electroresistance (TER) been realized through modifications electrode materials. However, direct control the FTJ performance modifying barrier has not adequately explored. Here, adding new direction to research, we fabricated FTJs with BaTiO3 single barriers (SB-FTJs) and BaTiO3/SrTiO3 composite (CB-FTJs) reported...
We calculate the current-voltage characteristics of arrays resistively shunted Josephson junctions (RSJ's), with and without a transverse magnetic field. In zero field, finite-temperature effects are included via an effective temperature-dependent current noise in each shunt resistance. ordered array at calculated correlation length order-parameter susceptibility consistent Kosterlitz-Thouless transition, zero-temperature time-dependent voltage V(t) above critical resembles that single RSJ....
We grew epitaxial SrRuO${}_{3}$ (SRO) films on SrTiO${}_{3}$ (STO) (001) substrates with SRO layer thicknesses ($t$) between 10 and 200 pseudocubic unit cells (uc). Using the square net of cubic STO surface, we were able to epi-stabilize tetragonal phase at room temperature for ultrathin $t$ \ensuremath{\leqslant} 17 uc. On other hand thicker \ensuremath{\geqslant} 19 uc have an orthorhombic crystal structure similar that bulk temperature. With increasing temperature, undergo a structural...
We report the growth of high-quality GaN films on large-size graphene for visible light-emitting diodes (LEDs). The were synthesized by chemical vapor deposition and then transferred onto amorphous silica (SiO2) substrates that do not have an epitaxial relationship with GaN. Before growing thin films, ZnO nanowalls grown as intermediate layer. structural optical characteristics investigated, exhibited stimulated emission even at room temperature, a highly c-axis-oriented crystal structure,...
A differential coating method is described for fabricating high-performance x-ray microfocusing mirrors. With this method, the figure of ultrasmooth spherical mirrors can be modified to produce elliptical surfaces with low roughness and errors. Submicron focusing demonstrated prototype The deposition creates stiff monolithic which are compact, robust, easy cool align. Prototype have gains more than 104 in beam intensity while maintaining submilliradian divergence on sample. This producing...
Several defect configurations including oxygen vacancies have been investigated as possible origins of the reported room-temperature ferroelectricity strontium titanate (STO) thin films [Y. S. Kim et al., Appl. Phys. Lett. 91, 042908 (2007)]. First-principles calculations revealed that Sr–O–O vacancy complexes create deep localized states in band gap SrTiO3 without affecting its insulating property. These results are consistent with electronic structural changes determined from optical...
The possibility of controlling transport properties colossal magnetoresistance manganite films using substrate-induced strain has attracted great interest. We have investigated La0.9Ca0.1MnO3, La0.92Ba0.08MnO3, La0.8Ba0.2MnO3, and LaMnO3 films. When the were post-annealed at proper conditions, all them showed metal–insulator transitions. Their transition temperatures TMI much higher than corresponding bulk values, irrespective type biaxial strain. This surprising fact demonstrated that could...
Structural studies on ultrathin SrRuO3∕BaTiO3∕SrRuO3 capacitors, with BaTiO3 thicknesses of between 5nm and 30nm, show well-defined interfaces ferroelectric electrode SrRuO3 layers. In these we cannot observe any extrinsic electrical effects due to either the formation an insulating interfacial passive layer or passive-layer-induced charge injection. Such high-quality result in very good fatigue endurance, even for thick capacitor.
We investigated the inhomogeneous electronic properties at surface and interior of $\mathrm{V}{\mathrm{O}}_{2}$ thin films that exhibit a strong first-order metal-insulator transition (MIT). Using crystal structural change accompanies MIT, we used bulk-sensitive x-ray diffraction (XRD) measurements to estimate fraction metallic volume ${p}^{\mathrm{XRD}}$ in our film. The temperature dependence was very closely correlated with dc conductivity near MIT fitted percolation theory predictions...
High-quality epitaxial thin films of Co-doped anatase TiO2 (Co:TiO2) were grown epitaxially on SrTiO3 (001) substrates by using pulsed laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, PO2, during the growth was systematically varied. As PO2 decreased, behavior altered from a two-dimensional layer-by-layer-like to three-dimensional island-like pattern. Electrical conductivity and saturation magnetization increased, seemingly consistent...
The authors investigated the role of oxygen partial pressure on epitaxial growth an artificial hexagonal GdMnO3 phase, which should exist in orthorhombic structure bulk. film showed diverse, but obvious, magnetic phase transitions with highly enhanced ferromagnetic properties. Its remnant magnetization at 4.2K is higher than those other RMnO3 (R=Ho, Er, and Yb) compounds, Curie temperature increases by around 25K. results demonstrate that stabilization technique a promising method for...
The initial growth behavior and resulting microstructural properties of heteroepitaxial ZnO thin films prepared by pulsed laser deposition on sapphire (0001) substrates were investigated. High-resolution x-ray diffraction transmission electron microscopy studies revealed that the microstructure significantly dependent parameters employed. grown at 700°C with an O2 partial pressure 20mTorr initiated in a columnar mode contained two types domains. These domains plane orientated either...