Formation Of Crystalline Films Research Articles

High Performance Vanadium Oxide Thin Film Electrodes for Rechargeable Lithium Batteries

ABSTRACTPlasma Enhanced Chemical Vapor Deposition (PECVD) was used to prepare vanadium oxide thin films as cathodes for rechargeable lithium batteries. The reactants consisted of a high vapor pressure liquid source of vanadium (VOCl3) and hydrogen and oxygen gas. Deposition parameters such as the flow rates of H2, O2 and VOCl3, the substrate temperature and the Rf power were optimized, and high deposition rate of 11 Å/s was obtained. Vanadium oxide films with high discharge capacities of up to 408 mAh/g were prepared. The films also showed a superior cycling stability between 4 and 1.5 V at a C/0.2 rate for more than 4400 cycles. The films were amorphous up to a deposition temperature of 300°C, however, deposition on to substrates with textured surfaces facilitated the formation of crystalline films. We demonstrate that both the vanadium oxide material and the PECVD deposition method are very attractive for constructing thin-film rechargeable lithium batteries with high capacity and long-term cyclic stability.

Scanning Tunneling Microscopic Studies of Epitaxial Films of Polyurethane, Polyester, and Polysiloxane Formed during Step Polymerization

Crystalline films of poly(hexamethylene-hexamethylenediurethane) were found to grow on the basal plane of graphite during polyaddition of diol and diisocyanate in a homogeneous solution containing a graphite substrate. Direct observations by scanning tunneling microscopy indicate that the film has been grown epitaxially. Also, an epitaxial film of poly(hexamethylene sebacate), an aliphatic polyester having the same number of bonds per monomeric unit as the polyurethane, was grown on the graphite surface during polycondensation of diol and dichloride. These results demonstrate that step polymerization induces epitaxy of polymers during polymerization. Then, the same polycondensation procedures were applied to study the films of an aromatic polyester, poly(hexamethylene terephthalate), and a polyester containing a triple bond, poly(butynyl sebacate) on graphite. The aromatic ring and the triple bond can be considered as the structural «kinks» on the aliphatic backbones that cause a misfit with a polyethylene-like repeat of the graphite hexagonal lattice. Formation of epitaxial films of these polyesters indicates the importance of having molecular structures capable of forming a close packed state in two dimensions for this epitaxial growth. Lastly, ring-opening polymerizations of cyclic dimethylsiloxanes were performed with the presence of a graphite substrate either in a good solvent at room temperature or in melt at 160 o C. Formation of crystalline films even at the temperatures much higher than the melting point of bulk polymer (-42 o C) and entropically driven polymerization of siloxanes suggest the two-dimensional nature of the crystallization process. On the basis of the present results and the previous studies, a mechanism of the late stage of epitaxial growth induced by polymerization is proposed

Preparation and Application of Magnetic Films by Ferrite Plating in Aqueous Solution

ABSTRACTFerrite plating invented by the authors facilitates formation of crystalline films of spinel, (Fe, M)3O4 (M=Fe, Ni, Co, Mn, Zn, etc.), in an aqueous solution below 100 °C. This opened the door to new ferrite-film devices which use, as substrate, such non-heat-resistant materials as plastics and GaAs ICs. In this paper we describe the principle and the experimental methods of ferrite plating and report magnetic and structural properties of the films. We also describe various applications of the ferrite plating films to microwave, electrochemical and bio-medical devices.

Low-temperature 3C-SiC heteroepitaxial film growth on Si by reactive-ion-beam deposition

Heteroepitaxial growth of 3C-SiC on Si(111) and Si (100) at temperatures lower than 800 °C was investigated by using a low-temperature crystalline film formation method, reactive-ion-beam deposition. This method uses low-energy ionized species extracted from reactive electron-cyclotron-resonance plasma of SiH4 and C2H4. In the case of direct film growth on clean Si substrates, 3C-SiC film growth can be achieved at the low temperature of 770 °C±12° by adjusting the ion energy to 200 eV. To improve crystalline quality, Si homoepitaxial and Si-C transition layers, about 2–3 and 3–4 nm in thickness, respectively, were formed in the initial heteroepitaxial growth stage. Using these thin layers, 200-nm-thick 3C-SiC/Si(111) heteroepitaxial films with about 63 cm2 /V s (300 K) and about 21 cm2 /V s (700 K) in Hall mobility can be obtained at the same low temperature, although they included twins.

Formation of Crystalline Films by Laser Evaporation

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