Sung Hwan Hwang

Layer-Controlled, Wafer-Scale, and Conformal Synthesis of Tungsten Disulfide Nanosheets Using Atomic Layer Deposition

The synthesis of atomically thin transition-metal disulfides (MS2) with layer controllability and large-area uniformity is an essential requirement for their application in electronic and optical devices. In this work, we describe a process for the synthesis of WS2 nanosheets through the sulfurization of an atomic layer deposition (ALD) WO3 film with systematic layer controllability and wafer-level uniformity. The X-ray photoemission spectroscopy, Raman, and photoluminescence measurements exhibit that the ALD-based WS2 nanosheets have good stoichiometry, clear Raman shift, and bandgap dependence as a function of the number of layers. The electron mobility of the monolayer WS2 measured using a field-effect transistor (FET) with a high-k dielectric gate insulator is shown to be better than that of CVD-grown WS2, and the subthreshold swing is comparable to that of an exfoliated MoS2 FET device. Moreover, by utilizing the high conformality of the ALD process, we have developed a process for the fabrication of WS2 nanotubes.

Kinetically controlled way to create highly uniform mono-dispersed ZnO sub-microrods for electronics

Highly uniform mono-dispersed ZnO sub-microrods were synthesized under the condition of a limited injection of Zn divalent ions into an aqueous solution of hexamethylenetetramine at 85 °C. The mechanisms governing the initial seed formation and growth of the ZnO sub-microrods were revealed as an oriented aggregation and classical growth, respectively, from an analytic observation with a high-resolution transmission electron microscope. To demonstrate the capability and possibility of forming uniform microrods for electronic applications, a monolayer of thermally annealed rods was produced on a flexible substrate.

Direct electrical junction formation of highly vertical aligned zinc oxide nanorods

A two dimensionally assembled monolayer of hexagonal convexo-convex β-cobalt hydroxide nanoplates as a self-disposable sacrificial epi-template leads to a highly vertical alignment of zinc oxide nanorods array having a good electrical contact with metal or semiconductor layer on a substrate in a hydrothermal process.

Silver Thin Film as a Temporal Template and Dopant Source for Vertically Aligned p–n homojunction of ZnO Nanorods

A silver thin film is introduced as a temporal template and dopant source for vertically aligned p-n homojunction of ZnO nanorods. The growth of Ag-doped ZnO nanorods was observed over time and the doping effect was determined through various characterization methods. Furthermore, a p-n homojunction diode of ZnO nanorods was fabricated.

Annealing Effect of Phosphorus-Doped ZnO Nanorods Synthesized by Hydrothermal Method

An effect of thermal annealing on activating phosphorus (P) atoms in ZnO nanorods (NR) grown using a hydrothermal process was investigated. used as a dopant source reacted with ions and sediment was produced in the solution. The fact that most of the input P elements are concentrated in the sediment was confirmed using an energy dispersive spectrometer (EDS). After the hydrothermal process, ZnO NRs were synthesized and their PL peaks were exhibited at 405 and 500 nm because P atoms diffused to the ZnO crystal from the particles. The solubility of the initially formed sediment varied with the concentration of . Before annealing, both the structural and the optical properties of the P-doped ZnO NR were changed by the variation of P doping concentration, which affected the ZnO lattice parameters. At low doping concentration of phosphorus in ZnO crystal, it was determined that a phosphorus atom substituted for a Zn site and interacted with two , resulting in a complex, which is responsible for p-type conduction. After annealing, a shift of the PL peak was found to have occurred due to the unstable P doping state at high concentration of P, whereas at low concentration there was little shift of PL peak due to the stable P doping state.

Synthesis of Hexagonal β-Ni(OH) 2 Nanosheet as a Template for the Growth of ZnO Nanorod and Microstructural Analysis

As a growth-template of ZnO nanorods (NR), a hexagonal nanosheet (NS) was synthesized with the low temperature hydrothermal process and its microstructure was investigated using a high resolution scanning electron microscope and transmission electron microscope. Zinc nitrate hexahydrate was hydrolyzed by hexamethylenetetramine with the same mole ratio and various temperatures, growth times and total concentrations. The optimum hydrothermal processing condition for the best crystallinity of hexagonal NS was determined to be with 3.5 mM at for 2 h. The prepared NSs were two dimensionally arrayed on a substrate using an air-water interface tapping method, and the quality of the array was evaluated using an X-ray diffractometer. Because of the similarity of the lattice parameter of the (0001) plane between ZnO (wurzite a