Heeseung Yang

Surfactant‐Free Scalable Synthesis of Bi2Te3 and Bi2Se3 Nanoflakes and Enhanced Thermoelectric Properties of Their Nanocomposites

Surfactant-free nanoflakes of n-type Bi2 Te3 and Bi2 Se3 are synthesized in high yields. Their suspensions are mixed to create nanocomposites with heterostructured nanograins. A maximum ZT (0.7 at 400 K) is achieved with a broad content of 10-15% Bi2 Se3 in the nanocomposites.

Synthesis of surfactant-free SnS nanoplates in an aqueous solution

We report a synthetic route to produce surfactant-free SnS nanoplates with the Pbnm crystal structure. The process is quick and environmentally-friendly, accomplished under mild aqueous conditions. The synthesis involves two steps, formation of an intermediate tin oxide hydroxide (Sn6O4(OH)4) gel and its chemical transformation into SnS nanoplates in the presence of a sulfide precursor (Na2S). We found that addition of a small amount of PVP during the chemical transformation results in the formation of cubic SnS with the Cmcm crystal structure. We discuss the development of the crystal structures on the basis of density functional theory (DFT) calculations on the structure–energy relationship of SnS nanostructures. The optical properties of the SnS nanoplates and nanocubes are compared.

One-Step Solution Phase Growth of Transition Metal Dichalcogenide Thin Films Directly on Solid Substrates

Ultrathin transition metal dichalcogenides (TMDs) have exotic electronic properties. With success in easy synthesis of high quality TMD thin films, the potential applications will become more viable in electronics, optics, energy storage, and catalysis. Synthesis of TMD thin films has been mostly performed in vacuum or by thermolysis. So far, there is no solution phase synthesis to produce large-area thin films directly on target substrates. Here, this paper reports a one-step quick synthesis (within 45-90 s) of TMD thin films (MoS2 , WS2 , MoSe2 , WSe2 , etc.) on solid substrates by using microwave irradiation on a precursor-containing electrolyte solution. The numbers of the quintuple layers of the TMD thin films are precisely controllable by varying the precursors concentration in the electrolyte solution. A photodetector made of MoS2 thin film comprising of small size grains shows near-IR absorption, supported by the first principle calculation, exhibits a high photoresponsivity (>300 mA W-1 ) and a fast response (124 µs). This study paves a robust way for the synthesis of various TMD thin films in solution phases.

Synthesis of LiCoO 2 Powders using Recycled Cobalt Precursors from Waste WC-Co Hard Metal

[ ] a cathode material for lithium rechargeable batteries, was prepared using recycled . First, the cobalt hydroxide powders were separated from waste WC-Co hard metal with acid-base chemical treatment, and then the impurities were eliminated by centrifuge method. Subsequently, powders were prepared by thermal treatment of resulting . By adding a certain amount of and , the was obtained by sintering for 10 h in air at . The synthesized particles were characterized by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) analysis.

Synthesis of 2D Metal Chalcogenide Thin Films through the Process Involving Solution‐Phase Deposition

2D metal chalcogenide thin films have recently attracted considerable attention owing to their unique physicochemical properties and great potential in a variety of applications. Synthesis of large-area 2D metal chalcogenide thin films in controllable ways remains a key challenge in this research field. Recently, the solution-based synthesis of 2D metal chalcogenide thin films has emerged as an alternative approach to vacuum-based synthesis because it is relatively simple and easy to scale up for high-throughput production. In addition, solution-based thin films open new opportunities that cannot be achieved from vacuum-based thin films. Here, a comprehensive summary regarding the basic structures and properties of different types of 2D metal chalcogenides, the mechanistic details of the chemical reactions in the synthesis of the metal chalcogenide thin films, recent successes in the synthesis by different reaction approaches, and the applications and potential uses is provided. In the last perspective section, the technical challenges to be overcome and the future research directions in the solution-based synthesis of 2D metal chalcogenides are discussed.

Synthesis and Characterization of CuInS 2 Semiconductor Nanoparticles and Evolution of Optical Properties via Surface Modification

Copper composite materials have attracted wide attention for energy applications. Especially has a desirable direct band gap of 1.5 eV, which is well matched with the solar spectrum. nanoparticles could make it possible to develop color-tunable nanoparticle emitter in the near-infrared region (NIR) for energy application and bio imaging sensors. In this paper, nanoparticles were successfully synthesized by thermo-decomposition methods. Surface modification of nanoparticles were carried out with various semiconductor materials (CdS, ZnS) for enhanced optical properties. Surface modification and silica coating of hydrophobic nanoparticles could be dispersed in polar solvent for potential applications. Their optical properties were characterized by UV-vis spectroscopy and photoluminescence spectroscopy (PL). The structures of silica coated were observed by transmission electron microscopy (TEM).

Fabrication and Characterization of Silica Coated Fe 3 O 4 Nanoparticles in Reverse Micro Emulsion

The silica coated Fe3O4 nanoparticles have been synthesized using a micro-emulsion method. The Fe3O4 nanoparticles with the sizes 6 nm in diameter were synthesized by thermal decomposition method. Hydrophobic Fe3O4 nanoparticles were coated silica using surfactant and tetraethyl orthosilicated (TEOS) as a SiO2 precursor. Shell thickness of silica coated Fe3O4 can be controlled (11~20 nm) through our synthetic conditions. The Fe3O4 and silica coated Fe3O4 nano powders were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD) and vortex magnetic separation (VMS).