Jim-Yang Lee

Graphene-like MoS2/amorphous carbon composites with high capacity and excellent stability as anode materials for lithium ion batteries

A facile process to synthesize graphene-like MoS2/amorphous carbon (a-C) composites was developed. MoS2/C composites were firstly prepared by hydrothermal method employing sodium molybdate, sulfocarbamide and glucose as starting materials. The graphene-like MoS2/a-C composites were obtained after annealing at 800 °C in H2/N2. The samples were characterized by XRD, SEM, EDS and HRTEM. It was confirmed that in the composites MoS2 has a structure of single-layer, which is named graphene-like nanostructure. The graphene-like MoS2 nanosheets were uniformly dispersed in amorphous carbon. The interlaminar distance of the adjacent graphene-like MoS2 nanosheets in the composites measured was ∼1.0 nm. The mechanism of the formation of the graphene-like MoS2/a-C composites was investigated. The graphene-like MoS2/a-C composites exhibited high capacity and excellent cyclic stability used as anode materials for Li-ion batteries. The composite prepared by adding 1.0 g of glucose in hydrothermal solution exhibited the highest reversible capacity (962 mAh g−1) and excellent cyclic stability. After 100 cycles, it still retained 912 mAh g−1. The significant improvements in the electrochemical properties of the graphene-like MoS2/a-C composites could be attributed to the graphene-like structure of the MoS2 nanosheets and the synergistic effects of graphene-like MoS2 and amorphous carbon.

Observation of saturable and reverse-saturable absorption at longitudinal surface plasmon resonance in gold nanorods

0.1 M cetyltrimethylammonium bromide CTAB was prepared in a conical flask. Next, 0.12 ml of ice cold 0.01 M NaBH4 solution was added to the solution all at once while stirring. The solution turned pink immediately after adding NaBH4, indicating particle formation. The particles in this solution were used as seeds within 2‐5 h after preparation. Second, 5 ml 110 x7f3 M HAuCl4 and 5 ml 0.2 M CTAB were mixed together in a clean beaker. Then, 0.25 ml 0.004 M AgNO3 solution and 0.065 ml of 0.0788 M fresh ascorbic acid solution were added into the solution in turn. It was found that the solution turned from orange to colorless after the addition of ascorbic acid. Finally, 0.020 ml of the seed solution was added. Within 30 min, the color of the

Modified Ligand-Exchange for Efficient Solubilization of CdSe/ZnS Quantum Dots in Water: A Procedure Guided by Computational Studies

One of the methods to render CdSe/ZnS core-shell quantum dots(QDots) water-soluble is to functionalize the surface with carboxylate groups by the use of heterobifunctional ligands such as 3-mercaptopropionic acid, where the thiolic end binds onto the outer ZnS shell. However, currently available ligand-exchange procedures starting with TOPO-capped quantum dots often lead to significant loss of quantum yields and poor stability of the colloids in water. As part of our efforts to overcome these problems, we used computational methods to understand the nature of binding between alkyl thiols and ZnS wurtzite surfaces. Guided by the computational results, we modified the ligand-exchange method and increased the reactivity of 3-mercaptopropionic acid toward the ZnS surface in chloroform. The functionlization reaction required only mild reaction conditions and led to QDot nanoparticles that were individually dispersed in water with good colloidal stability. Importantly, the photoluminescence performance of the QDots was highly preserved.

Mesoporous zinc-blende ZnS nanoparticles: synthesis, characterization and superior photocatalytic properties.

This paper describes the development of a novel and simple chemical route to mass production of mesoporous ZnS nanoparticles in high yield. XRD, FESEM, TEM, SAED, EDS and XPS analyses show that spherical nanoparticles are crystalline ZnS in a zinc-blende structure. The resulting nanoparticles have an average diameter of about 30 nm and pore sizes in the range of 3-6xa0nm. The formation of mesoporous nanostructures could be attributed to higher nucleation rate in the course of preparation that resulted in the quick aggregation of initial crystallites and the formation of pores between them. The as-prepared mesoporous ZnS exhibited excellent photocatalytic activities. This preparation method provides one possible route to the synthesis of other mesoporous structures for exploratory studies on the applications of mesoporous nanocrystals.

Towards three-dimensional and multilayer rod-split-ring metamaterial structures by means of deep x-ray lithography

Presently existing THz electromagnetic metamaterials were mostly produced as planar single layer structures, either deposited on a substrate or embedded in a polymer matrix, and patterned by a primary pattern generator such as an electron beam writer or a laser writer. Some attempts to produce more voluminous structures were made using ultraviolet photolithography and a stacking process. We explore deep x-ray lithography and subsequent stacking of chips to fabricate, with good yield, substantial quantities of rod-split-ring structures that come closer to three dimensions than before. Samples were characterized layer-by-layer using Fourier transform interferometry in the far infrared.