Min-Han Yang

On the growth of CuInS2 thin films by three-source evaporation

CuInS2 thin films were prepared by three-source evaporation. Special features of the system design are described. The material characterization by compositional, photoluminescence and electrical analyses are reported. Both p and n films were produced: the resistivities were between 0.01 and 10 ω cm, the grain size was between 2 and 8 Ωm, the best electron mobility was 21.84 cm2 V−1 s−1 and the best hole mobility was 1.42 cm2 V−1 s−1. Both of the latter values are higher than those reported with other methods.

Large-scale synthesis of uniform Cu2O nanocubes with tunable sizes by in-situ nucleation

Uniform Cu2O nanocubes with various sizes were synthesized by reducing Cu(OH)2 using ascorbic acid in the presence of various amounts of sodium citrate. The monodispersed nanocubes with an edge length of approximately 80 nm used as an anode exhibit excellent lithium storage behavior.

Porous titanium oxynitride sheets as electrochemical electrodes for energy storage.

A flexible, porous TiOxNy sheet consisting of numerous conductive fibers was synthesized by nitridation of titanate and further used as an electrochemical electrode. The high surface area and mixed-oxidation state of titanium make TiOxNy sheets to be promising candidates for a good supercapacitor.

Anatase and brookite TiO2 with various morphologies and their proposed building block

In this work, brookite TiO2 has been synthesized by a simple hydrothermal approach using sodium titanate as a precursor in the presence of a sodium fluoride aqueous solution. The ratio of brookite and anatase TiO2 can be tailored by the NaF concentration. In a concentrated NaF solution, high quality brookite TiO2 was acquired. Pure anatase nanoparticles were obtained in only deionized water. Moreover, the morphology and size of brookite TiO2 can be tailored by using various acid treated titanates which influence the stability of the building blocks and nucleation points of TiO2. Micro-sized flower-like brookite, submicro-sized urchin-like brookite and brookite nanorods with anatase nanoparticles were obtained. The micro-sized flower-like brookite remains the same shape and phase even at 800 °C, whereas obvious grains were formed on the matrix with brookite, rutile and anatase mixture phases at 900 °C. On the other hand, as the submicro-sized urchin-like brookite was heated, a rutile phase appeared at 750 °C and 100% grain-like rutile was obtained at 900 °C.

RuO2/MnO2 core–shell nanorods for supercapacitors

RuO2/MnO2 NRs as an electrode for supercapacitors show a high electrochemical performance with a specific capacitance of 793 F g−1 (based on MnO2) by cyclic voltammetry (CV) at a scan rate of 2 mV s−1 in 1 M Na2SO4 aqueous solution. A good rate capability with a specific capacitance of 556 F g−1 at a current density of 1 A g−1 and a good cycling stability (20% degradation after 1000 cycles) were also achieved. The enhancement of capacitive behavior can be attributed to the conductive RuO2 template with a series resistance of 0.75 Ω and a charge transfer resistance of 0.75 Ω. The results show that an active material such as a MnO2 hybrid with highly conductive 1D nanowires may greatly improve the electrochemical performance for supercapacitors.

Alkali metal ion assisted synthesis of faceted anatase TiO2

This work reports on a simple hydrothermal method for tuning the shape and exposed face of TiO2 nanocrystal by using sodium titanate as a precursor in the presence of different alkali metal ion salts. The {101}-exposed anatase TiO2 was synthesized in lithium salt solution. The formation of anatase TiO2 with exposed high-index {301} facet, obtained in the presence of sodium ions, has never before been reported upon. When the reaction proceeded in potassium salt solution, the obtained anatase TiO2 with a high aspect ratio was elongated in the direction. Anatase TiO2 with a high aspect ratio was obtained in hydrothermal process in the presence of low charge density high atomic number alkali metal ions, which were not easily absorbed by the {001} planes of anatase, so the growth along this direction was not restrained. The photodegradation of methylene blue, assisted by anatase TiO2 with various exposed faces reveals that the photoactivity of anatase {101} planes is larger than that of {301} planes.

Self-powered electrochemical deposition of Cu@Ni(OH)2 nanobelts for high performance pseudocapacitors

Two aluminum-driven spontaneous electrochemical reactions are developed for depositing Cu@Ni(OH)2 nanobelts on carbon/aluminum electrodes. The Cu@Ni(OH)2 NBs function as pseudocapacitor electrodes, which exhibit a high specific capacitance of 2426 F g−1 and a remarkable rate performance.

Some observations on stoichiometry and p-type doping in CdTe

Abstract This paper describes a chemical scheme for CdTe compositional analysis based on titration, and an error between 0.06-0.2% has been attained. This technique was applied to analyze the stoichiometry of CdTe single crystals grown by THM. This paper also comments on p-type doping in CdTe, in which electron beam pulse annealing of phosphorus implanted CdTe will be particularly discussed. This has been demonstrated as an efficient way of p-type doping, and a carrier concentration of 5 × 10 19 cm -3 has been obtained.

Size-controlled wurtzite zinc oxide spheres with the characteristics of visible absorption and Mie scattering

The enhancement of the light harvesting efficiency over a metal oxide is crucial to optic-related applications which can convert solar energy into chemical energy. Here, we demonstrated a method to develop the characteristics of visible light absorption and visible Mie scattering over wurtzite ZnO microspheres. Size-controlled ZnO microspheres were successfully prepared in the thermal decomposition of amorphous/layered basic zinc salt (LBZ) spheres. Firstly, trisodium citrate was employed as the chelating agent to synthesize amorphous/LBZ microspheres in a nucleation-controlled method. The sphere size was controlled by the nuclei number, which depends on the competition between hydroxyl ions and citrate to the ligand with Zn2+. Secondly, visible-active wurtzite ZnO spheres were obtained by thermal decomposition. The uniform sized microspheres exhibited Mie scattering in the visible range due to the interaction with specific incident electromagnetic radiation, and the full absorption spectrum was easily obtained by tuning the size of the spheres. Such uniform spheres exhibited superior visible absorption and scattering effects and thus are expected to be good candidates for the optic-related applications.

Photo-induced nucleation of rutile nanorods—an ignored parameter in crystallization

This work presents a surfactant-free and economical sol–gel method to synthesize multi-branched rutile TiO2 nano-trees. Simple illumination by incandescent light during synthesis causes numerous branches to grow from the sides of nanorods, this process is accompanied by hydroxylation of the crystal surface. A {101} twin is demonstrated to connect the trunk to the branches. The extents of branching and surface hydroxylation are controlled by either photo-illumination or the addition of an exciton scavenger (H2O2). The relationship between the quantity of the branches and the excitons can be elucidated by considering photo-induced defects.