Materials Science Forum Vols. 654-656

Abstract: The silicon nitride films have been deposited by Electron Cyclotron Resonance-plasma enhanced chemical vapor deposition (ECR-PECVD) method at low temperature, and the pure nitrogen is introduced into the ECR chamber as the plasma gas, the silane(Ar diluted, Ar:SiH4=19:1) is used as precursor gas. The optimum deposition parameters of SiN films for photovoltaic application as an efficient antireflection coating(ARC) have been investigated. The actual composition of the films will be varied with the deposition conditions, such as gas flow rate ratio(N2/SiH4), substrate temperature, and microwave power. The effect of deposition parameters on the optical performance of SiN films was determined by Ellipsometry. The Si-N and N-H stretching characteristic peaks of SiN films have been observed by FTIR spectroscopy. Results shown that uniform silicon nitride films with low hydrogen content can be deposited at high deposition rate(10.7nm/min), and the refractive index increased with the increasing of substrate temperature and microwave power. The film shows good optical properties (refractive index is 2.0 or so) and satisfied surface quality (average roughness is 1.45nm) when the deposition parameter is 350oC and microwave power is 650W.

Abstract: Nitridation of Corning 7101 glass substrate and the following GaN deposition were carried out in a self-developed electron cyclotron resonance plasma enhanced metalorganic chemical vapor deposition (ECR-PEMOCVD) system equipped with in-situ reflection high-energy electron diffraction (RHEED) monitoring. RHEED pattern and X-Ray diffraction (XRD) spectrum showed that the nitridation can effectively improve the C-axis orientation of as-prepared GaN film. Atomic force microscope (AFM) analysis indicated that the average grain size increased significantly with 5 min of nitriding, but degraded as nitriding time increased. The optimum nitriding time was achieved as 5 min. The effect of nitridation on the GaN film deposition and its formation mechanism were discussed.

Abstract: In the paper, ion-assisted e-beam evaporation (IAEE) method was used to deposit SiO2 film on CBA(CaO-Al2O3-BaO) glass substrate, and the influence of processing parameters on the performance of the thin films was studied. The result shows that the ion energy, substrate temperature and evaporating rate are key factors that affect the abrasion resistance and transmission of the SiO2 film. Heat treatment was used to eliminate the absorption of H2O in spectrum range of 2.7~3.5μm. SiO2 film with good abrasion resistance and high transmission in spectrum range 3.0~5.0μm was deposited successfully on the special glass substrate.

Abstract: To synthesize an array of numerous ferromagnetic nanowires, iron-group metals such as Ni, Co, Fe, Ni-Fe and Co-Fe alloys were electrodeposited from aqueous solution into a nanoporous template with numerical cylindrical nanochannels . The shape of nanowires was precisely transferred from the nanochannel template and the aspect ratio reached to around 150. Magnetic hysteresis loops revealed that Ni, Co and Fe nanowires were spontaneously magnetized to the long axis direction. Coercive force of the nanowires with 6000 nm in length was increased in decreasing the pore-diameter. The coercive force of Co nanowires with 40 nm in diameter has increased up to 1084 Oe.

Abstract: Co/Cu multilayered nanowires with 40 nm in diameter were fabricated using a pulsed current deposition technique into a nanoporous template with numerous nanochannels. To determine the optimum electrodeposition condition of Cu and Co into the template, cathodic polarization behavior was examined at a wide range of cathode potential. Time-dependence of deposition current was monitored to determine the growth rate of Co and Cu nanowires. Co layer and Cu layer thicknesses were adjusted to several tens nanometers, by controlling the deposition times. With decreasing the each layer thickness, the coercive force of Co/Cu multilayered nanowires was decreased and the soft magnetic property was improved.

Abstract: ZnTe compound semiconductors were synthesized in acidic aqueous solution using a pulsed current electrodeposition technique. The optimum condition to obtain ZnTe deposits was determined by the cathodic polarization curves measured at a wide potential range. During the co-deposition of Zn and Te, under potential deposition (UPD) of Zn was observed. Increasing the solution temperature up to 353 K, UPD of Zn was promoted by the formation of Zn(OH)2. Crystal phase, structure and chemical composition of electrodeposited ZnTe was controlled by the solution composition and electrolysis condition. The band gap energy of ZnTe films annealed at 573 K was close to 2.26 eV.

Abstract: Iron-Platinum (Fe-Pt) and Cobalt-Iron-Platinum (Co-Fe-Pt) nanocrystalline thin films were deposited on brass substrates using a single bath electrodeposition system. The effects of addition of various concentrations of cobalt towards the composition, crystallographic structure, microstructure and magnetic properties of the Fe-Pt alloy films were investigated. Ammonium tartrate and ammonia solution were used as complex forming additives to stabilize the Fe2+ and Co2+ ions and to enhance co-deposition with platinum complexes. The as-synthesized thin films were characterized by energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and alternating gradient magnetometry (AGM). EDS results showed that cobalt was preferentially deposited compared to iron during Co-Fe-Pt film electrodeposition. SEM results showed that the microstructure of the films consisted of spherical granules. XRD showed formation of disordered face-centered cubic (fcc) Fe-Pt phase and all peaks were shifted to slightly higher diffraction angles with increasing cobalt content. The average crystallite size calculated from XRD peak broadening varied from 2.33nm to 6.54nm. The saturation magnetization and coercivity increased with increasing cobalt content.

Abstract: High quality GaN films are deposited on freestanding thick diamond films by electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). The characteristics of GaN films were investigated by x-ray diffraction analysis (XRD), reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). The high quality GaN films with small surface roughness of 8.3 nm and high c-orientation are successfully achieved at the optimized nitriding time with the diamond substrate. These properties of GaN films with small surface smoothness and high c-orientation are well used as piezoelectric films for surface acoustic wave (SAW) devices.

Abstract: In this study, Cu films doped with different Sn concentrations from 0.6-1.4 at.% were prepared by magnetron co-sputtering. The electrical resistivities and microstructures of Cu (Sn) films after annealings were investigated. The results showed that a sharp increase of the resistivity of Cu (1.4 at.% Sn) and Cu (1.1 at.% Sn) films were found after annealing above at 500°C. The existence of 0.6 at.% Sn in the Cu film is in solid solution state. A minimum electrical resistivity value of ~3.2μΩ•cm was obtained after annealing at 600°C for 1h . Even after a annealing at 700°C, the Cu/Si interface of Cu (0.6 at.% Sn) film still remained sharp without any Cu-Si and Cu-Sn compounds. The results confirmed that the lower resistivity and higher stability of Cu films can be achieved by strictly control of the doping concentrations and the existing state (solid solution without compounds and precipitates) of Sn element.

Abstract: Germanium carbon films were prepared on ZnS substrates by reactive RF magnetron sput- tering of a Ge target in Ar and CH4 mixtures for IR antireflective and protective purposes. IR transmit- ttance spectra of the specimens were measured, with which H content in the films was investigated. The C and Ge contents and the atomic binding state were studied by X-ray photoelectron spectroscopy. The results show that H involved in the films combine mainly with C at low substrate temperatures. IR absorption peaks caused by the C-H bonds decrease with increasing temperature, indicating the drop of the C-H bonds content in the film. At relatively low temperature the film is high in C content and low in refractive index; at high temperature the film is low in C content and high in refractive index. Both C-Ge and C-C bonds exist in the film and O impurity combines mainly with Ge.