Youngjun Hong

Visible-color-tunable light-emitting diodes (LEDs) with electroluminescent color that changes continuously from red to blue by adjusting the external electric bias are fabricated using multifacetted GaN nanorods with anisotropically formed 3D InGaN multiple-quantum wells. Monolithically integrated red, green, and blue LEDs on a single substrate, operating at a fixed drive current, are also demonstrated for inorganic full-color LED display applications.

This study demonstrates the enhanced Cu 2+ adsorption capability of polyaniline nanofibers (PAni NFs) by doping of phytic acid. The PAni NFs were synthesized by radical polymerization process using acidic solutions of hydrochloric and phytic acid, yielding chlorinated (Cl-) and phytic acid-doped (Ph-) PAni NFs. The Ph-PAni NFs showed remarkably higher Cu 2+ -adsorption efficiency than Cl-PAni NFs, presumably owing to high capacity and/or high ionic affinity of the doped phytic acid in Ph-PAni NF

wafer across graphene. The use of graphene allows the transfer of MR LED arrays onto a copper plate, and spatially separate MR arrays offer ideal device geometry suitable for deformable LED in various shapes without serious device performance degradation. Moreover, remote heteroepitaxy also allows the wafer to be reused, allowing reproducible production of MR LEDs using a single substrate without noticeable device degradation. The remote heteroepitaxial relation is determined by high-resolution

Semiconductor nanowire arrays integrated vertically on graphene films offer significant advantages for many sophisticated device applications. We report on van der Waals (VDW) epitaxy of InAs nanowires vertically aligned on graphene substrates using metal-organic chemical vapor deposition. The strong correlation between the growth direction of InAs nanowires and surface roughness of graphene substrates was investigated using various graphene films with different numbers of stacked layers. Notabl

Van der Waals (vdW) epitaxial double heterostructures have been fabricated by vdW epitaxy of InAs nanostructures on both sides of graphene. InAs nanostructures diametrically form on/underneath graphene exclusively along As-polar direction, indicating polarity inversion of the double heterostructures. First-principles and density functional calculations demonstrate how and why InAs easily form to be double heterostructures with polarity inversion.

We report on unconventional, noncovalent heteroepitaxy of vertical indium arsenide (InAs) nanowires on thin graphitic films in terms of van der Waals (VDW) interactions. Nearly coherent in-plane lattice matching (misfit of 0.49%) between InAs and the graphitic surface plays a critical role in the epitaxial formation of vertical InAs nanowires on graphitic substrates. Otherwise, gallium arsenide (misfit of -6.22%) is grown to be island morphologies. Cross-sectional transmission electron microscop

A novel method for shaping and positioning ZnO nanoarchitectures using conventional lithography and catalyst-free metal organic vapor-phase epitaxy is demonstrated. Nanowalls and nanotubes of desired shapes and arrangements can be grown heteroepitaxially on Si substrates, and their electron-emission characteristics were optimized by changing their diameter and spacing. This method can be readily expanded to create many artificial 1D and 2D structures, as required for various device applications.

Electroluminescence efficiency is crucial for the application of quantum-dot light-emitting diodes (QD-LEDs) in practical devices. We demonstrate that nitrogen-doped carbon nanodot (N-CD) interlayer improves electrical and luminescent properties of QD-LEDs. The N-CDs were prepared by solution-based bottom up synthesis and were inserted as a hole transport layer (HTL) between other multilayer HTL heterojunction and the red-QD layer. The QD-LEDs with N-CD interlayer represented superior electrical

The concept of remote epitaxy involves a two-dimensional van der Waals layer covering the substrate surface, which still enable adatoms to follow the atomic motif of the underlying substrate. The mode of growth must be carefully defined as defects, e.g., pinholes, in two-dimensional materials can allow direct epitaxy from the substrate, which, in combination with lateral epitaxial overgrowth, could also form an epilayer. Here, we show several unique cases that can only be observed for remote epi

Atmospheric pressure bioplasmas are being used in a variety of bio-medical and material processing applications, surface modifications of polymers. This plasma can generate the various kinds of radicals when it contacs with the water. Especially, hydroxyl radical species have very important role in the biological and chemical decontamination of media in this situation. It is very important to investigate the hydroxyl radical density in needle-typed plasma jet since it plays a crucial role in int

A combined experimental and theoretical investigation has clarified the nanometre-scale vapour-phase epitaxial growth of ZnO nanostructures on different crystal planes of GaN substrates. Under typical growth conditions, ZnO nanorods grow perpendicular to the GaN(0001) plane, but thin flat films form on GaN(101), (100) and (110). High-resolution X-ray diffraction data and transmission electron microscopy confirm the heteroepitaxial relationship between the ZnO nanostructures and GaN substrates. T

ZnO nanorod arrays are selectively grown on Si substrates using facet-controlled GaN micropatterns with highly anisotropic surface energies. Although we used facet-controlled GaN micropatterns for selective MOPVE growth, other micropatterns can be employed if the difference in surface energies between a top surface and the sidewalls of a micropattern is large enough to affect heteroepitaxial selective growth of the nanorods. This growth may be expanded to create many other position-controlled se