Kyoung Jin Choi

Biaxial compressive strain has been used to markedly enhance the ferroelectric properties of BaTiO3 thin films. This strain, imposed by coherent epitaxy, can result in a ferroelectric transition temperature nearly 500 degrees C higher and a remanent polarization at least 250% higher than bulk BaTiO3 single crystals. This work demonstrates a route to a lead-free ferroelectric for nonvolatile memories and electro-optic devices.

In this article, we review gas sensor application of one-dimensional (1D) metal-oxide nanostructures with major emphases on the types of device structure and issues for realizing practical sensors. One of the most important steps in fabricating 1D-nanostructure devices is manipulation and making electrical contacts of the nanostructures. Gas sensors based on individual 1D nanostructure, which were usually fabricated using electron-beam lithography, have been a platform technology for fundamental

The effects of inductively coupled plasma (ICP) etching on electrical properties of n-type GaN Schottky contacts were investigated by observing ion damage using deep-level transient spectroscopy. An electron trap, not previously seen, localized near the contact, as well as a pre-existing trap, was observed in the ICP-etched sample. The ICP-etched surface was found to be N-deficient, which means that N vacancies (VN) were produced by ICP etching. From these, the origin of the ICP-induced electron

The temperature dependence of in-plane and out-of-plane lattice parameters of a compressively strained SrRuO3 thin film grown on a SrTiO3 substrate is reported. The structural transition temperature of the SrRuO3 thin film shifts by more than 200 °C toward the lower-temperature region due to compressive strain (see graph).

The performance of plasmonic Au nanostructure/metal oxide heterointerface shows great promise in enhancing photoactivity, due to its ability to confine light to the small volume inside the semiconductor and modify the interfacial electronic band structure. While the shape control of Au nanoparticles (NPs) is crucial for moderate bandgap semiconductors, because plasmonic resonance by interband excitations overlaps above the absorption edge of semiconductors, its critical role in water splitting i

Abstract Room‐temperature (RT) gas sensitivity of morphology‐controlled free‐standing hollow aluminum‐doped zinc oxide (AZO) nanofibers for NO 2 gas sensors is presented. The free‐standing hollow nanofibers are fabricated using a polyvinylpyrrolidone fiber template electrospun on a copper electrode frame followed by radio‐frequency sputtering of an AZO thin overlayer and heat treatment at 400 °C to burn off the polymer template. The thickness of the AZO layer is controlled by the deposition time

One-dimensional crystal growth allows the epitaxial integration of compound semiconductors on silicon (Si), as the large lattice-mismatch strain arising from heterointerfaces can be laterally relieved. Here, we report the direct heteroepitaxial growth of a mixed anion ternary InAsyP1-y nanowire array across an entire 2 in. Si wafer with unprecedented spatial, structural, and special uniformity across the entire 2 in. wafer and dramatic improvements in aspect ratio (>100) and area density (>5 × 1

Abstract Transparent solar cells (TSCs) are emerging devices that combine the advantages of visible transparency and light-to-electricity conversion. Currently, existing TSCs are based predominantly on organics, dyes, and perovskites; however, the rigidity and color-tinted transparent nature of those devices strongly limit the utility of the resulting TSCs for real-world applications. Here, we demonstrate a flexible, color-neutral, and high-efficiency TSC based on a freestanding form of n -silic

Variable-wavelength photodetectors are fabricated by a selective growth of ZnxCd1−xSe alloy nanowires on patterned Au catalysts thus forming nanowire air-bridges between two Pt pillar electrodes. From the composition-dependent linear changes of bandgap energies and lattice parameters, ZnxCd1−xSe nanowires are found to be perfectly alloyed in the entire range of Zn composition without any phase separation and have a structural transition from zinc blende to wurtzite at 0.31 < x < 0.72. The spectr

PEG-treated poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) exhibited an enhanced power factor with increased strain.

Transparent optoelectronics can enable a new class of applications such as transparent displays, smart windows, and invisible sensors. Here, we demonstrate all-transparent NO2 gas sensors based on aluminum-doped zinc oxide (AZO) freestanding hollow nanofibers. Freestanding AZO nanofibers are fabricated by sputtering AZO on template polyvinylpyrrolidone (PVP) nanofibers, which are electrospun on a glass frame with indium zinc oxide (IZO) transparent electrodes, followed by a heat treatment to rem

A highly-efficient DSSC/Si monolithic tandem cell utilizing PEDOT:FTS as an interfacial catalytic layer.