William Jo 교수

We report the synthesis of superconducting MgB2 thin films grown in situ by molecular-beam epitaxy. Mg-rich fluxes are deposited with B flux by electron-beam evaporation onto c-plane sapphire substrates. The films exhibit c-axis oriented peaks of MgB2, and a full width at half maximum of 3° in their rocking curves. In-plane alignment of MgB2 shows 12-fold symmetry, which is observed by the selected area diffraction pattern in transmission electron microscopy. The MgB2 films show a superconductin

Recently, metal halide perovskite materials have received significant attention as promising candidates for optoelectronic applications with tremendous achievements, owing to their outstanding optoelectronic properties and facile solution-processed fabrication. However, the existence of a large number of grain boundaries in perovskite polycrystalline thin films causes ion migration, surface defects, and instability, which are detrimental to device applications. Compared with their polycrystallin

Ferroelectric Bi4Ti3O12 thin films have been grown on MgO (100) and MgO(110) substrates by the pulsed laser deposition. X-ray diffraction studies show that the films on both substrates have preferential crystallographic orientation such that most of their c axes are close to the substrate normal direction. The film on MgO(110) shows quadratic and hysteretic electro-optic characteristics with the effective coefficient of about 3.8×10−15 m2/V2.

There has been growing interest in organic-inorganic hybrid perovskites as a promising candidate for optoelectronic applications due to their superior physical properties. Despite this, most of the reported perovskite devices based on polycrystalline thin films suffer immensely from poor stability and high trap density owing to grain boundaries limiting their performance. Perovskite single crystal structures have been recently explored to construct stable devices and reduce the trap density comp

Bi4Ti3O12 thin films have been grown by laser ablation on SrTiO3(100) and SrTiO3(110) substrates. Substrate surface orientation is found to be an important growth parameter which determines crystal axis orientation, grain growth behavior, and electro-optic properties of the Bi4Ti3O12 thin films. The films grown on SrTiO3(110) shows a ferroelectric phase transition near 720 °C and a large quadratic electro-optic effect with the effective coefficient 1.1×10−16 m2/V 2.

We report charge retention in preferentially c-axis oriented ferroelectric Pb(Zr,Ti)O3 (PZT) thin films on LaNiO3 by electrostatic force microscopy. The surface charge density of the PZT films was observed as a function of time in a selected area where a region is single poled and another region is reverse poled. Retention behaviors of the regions are very different: the single-poled region shows a declined response and the reverse-poled region reveals a retained characteristic. Decay and retent

Abstract Understanding photogenerated charge transport is critical to further improving the performance of perovskite‐based devices. In this study, the low‐defect perovskite CH 3 NH 3 PbX 3 (X = Br or Cl) single crystals, which are an ideal platform for high‐quality optoelectronic devices, are fabricated to examine characteristics of photodetectors with electrodes with Au or Ag, and interlayer of TiO 2 . The transport mechanism of the photogenerated carriers in each device is elucidated by analy

The electrical properties of CH₃NH₃Pb(I_1-x Br _x )₃ (x = 0.13) perovskite materials were investigated under ambient conditions. The local work function and the local current were measured using Kelvin probe force microscopy and conductive atomic force microscopy, respectively. The degradation of the perovskite layers depends on their grain size. As the material degrades, an additional peak in the surface potential appears simultaneously with