Effect of filament biasing on nanocrystalline-Si films deposited by hot wire chemical vapor deposition

Nanocrystalline silicon (nc-Si) films were deposited by hot wire chemical vapor deposition with applying positive or negative filament biases. These films were characterized by Raman spectroscopy, field emission scanning electron microscopy and X-ray photoelectron spectroscopy. Plasmon loss of the Si(2p) band region was shifted to higher energy due to dielectric changes with applied filament biases from negative to positive voltage. A semi-quantitative study of the valence band structure was employed to analyze the bias effect of the valance band in nc-Si networks. Nc-Si with a positive filament bias shows better microstructural properties than those with a negative bias and without biasing nc-Si films.     

Effect of freon flow rate on tin oxide thin films deposited by chemical vapor deposition

High quality fluorine-doped tin oxide (SnO₂:F) films on glass substrates were been prepared using chemical vapor deposition (CVD) method. The electrical properties, surface morphologies, structural properties and optical properties of the films were studied by varying the freon flow rates. The structure was analyzed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the morphology. Energy-dispersive spectroscopy (EDS) was conducted to understand the surface fluorine composition of the film. The results showed that crystalline structure of the film had a have cassiterite-like diffraction patterns with a preferred orientation of (1 1 0). Surface roughness was evaluated by atomic force microscopy, characterized by root mean square (RMS) and average value (Ra). The SnO₂:F resistivity decreased as the freon flow rate increased. The films had a uniform thickness and a transmittance of 80–90% within the visible region of the spectrum.     

Nanoindentation of carbon microfibers deposited by laser-assisted chemical vapor deposition

Carbon microfibers were deposited using laser-assisted chemical vapor deposition at atmospheric and sub-atmospheric pressures. Precursor pressures and incident laser powers were varied. Fibers were cast in acrylic resin and polished to allow nanoindentation of the cross sections. Cross-sectional roughness was examined by optical profilometry. A radial change in mechanical properties was observed. The local elastic modulus (Youngs modulus) and hardness for the edge and core regions are reported. These mechanical properties were investigated with respect to deposition parameters and corresponding fiber microstructure. PACS 81.15.Fg; 81.05.Uw; 46.55.+d     

Characterization of diamond films deposited on Re substrate by magnetic field-assisted hot filament chemical vapor deposition

A periodically magnetic field (PMF) was used in a hot-filament chemical vapor deposited (HFCVD) for diamond growth on the rhenium substrate. The morphology, band structures and crystalline structure of the film were analyzed by the scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffractometer (XRD), respectively. The results show that the thickness of the diamond film is about 2900 nm by 4 h deposition with magnetic field-assisted. There is no interlayer between diamond film and the rhenium substrate. The result shows that the turn on voltage of the sample is enhanced from 3.3 to 2.6 V/μm with the PMF. Also the total emission current density at 6.2 V/μm increased from 6.3 to 21.5 μA/cm².     

Thin strain-relaxed SiGe grown by ultrahigh vacuum chemical vapor deposition

Large-scale preparation of thin strain-relaxed SiGe is achieved by combining ion implantation and ultrahigh vacuum chemical vapor deposition. The resulting materials were analyzed by double crystal X-ray diffraction, micro-Raman spectroscopy, and tapping mode atomic force microscope. Results revealed that 100-nm-thick Si_0.7Ge_0.3 layers with the diameter of 125 mm and full strain relaxation are successfully prepared by pre-modifying the Si substrates using 50 keV Ar⁺ ions. The strain relaxation is also disclosed to change with both ion species and energy. However, post-modification of SiGe by ion implantation will cause serious damage to the crystal structures, and result in the formation of poly-crystal SiGe.     

Nanomechanical characteristics of SnO2:F thin films deposited by chemical vapor deposition

The nanoindentation characterizations and mechanical properties of fluorine-doped tin oxide (SnO₂:F) films deposited on glass substrates, using chemical vapor deposition (CVD) method, were studied, which included the effects of the indentation loads, the loading time and the hold time on the thin film. The surface roughness, fractal dimension and frictional coefficient were also studied by varying the freon flow rates. X-ray diffraction (XRD), atomic force microscopy (AFM) and frictional force microscopy (FFM) were used to analyze the morphology of the microstructure. The results showed that crystalline structure of the film had a high intensity (1 1 0) peak orientation, especially at a low freon flow rate. According to the nanoindentation records, the Young's modulus ranged from 62.4 to 75.1 GPa and the hardness ranged from 5.1 to 9.9 GPa at a freon flow rate of 8000 sccm. The changes in measured properties were due to changing loading rate.     

Structural and photo-luminescence properties of nanocrystalline silicon films deposited at low temperature by plasma-enhanced chemical vapor deposition

Nanocrystalline silicon (nc-Si) films were prepared by a plasma-enhanced chemical vapor deposition method at a deposition temperature below 220 °C with different dynamic pressures (P_g), hydrogen flow rates ([H₂]), and RF powers, using SiH₄/H₂/SiF₄ mixtures. We examined the photo-luminescence (PL) spectra and the structural properties. We observed two stronger and weaker PL spectra with a peak energies around E_PL = 1.8 and 2.2-2.3 eV, respectively, suggesting that the first band was related to nanostructure in the films, and another band was associated with SiO-related bonds. The nc-Si films with rather large PL intensity was obtained for high [H₂] and/or low pressure values, However, effects of [H₂] are likely to be different from those of P_g. The average grain size (δ) and the crystalline volume fraction (ρ) at first rapidly increase, and then slowly increase, with increasing P_g. Other parameters exhibited opposite behaviors from those of δ or ρ. These results were discussed in connection with the changes in the PL properties with varying the deposition conditions.     

激光轴向偏焦法平整化CVD金刚石膜

利用Nd:YAG型金刚石精密激光切割机,采用激光轴向偏焦法对化学气相沉积（CVD）法制备的金刚石膜表面进行扫描式平整化处理,利用扫描电子显微镜（SEM）、粗糙度仪和金相显微镜对平整化后的金刚石表面进行表征,研究了激光充电电压和焦点位置对扫描凹槽宽度和深度的影响,以及扫描间距对平整化效果的影响。研究结果表明:扫描凹槽宽度随激光充电电压的升高而增大;凹槽深度随激光充电电压的升高而增大,随偏焦量的增大而增大。激光轴向偏焦法对CVD金刚石膜进行平整化处理后,其粗糙度显著减小,利用氢等离子体对其表面进行刻蚀处理,能够有效去除表层石墨,从而达到理想的平整化效果。     

激光轴向偏焦法平整化CVD金刚石膜

利用Nd：YAG型金刚石精密激光切割机,采用激光轴向偏焦法对化学气相沉积（CVD）法制备的金刚石膜表面进行扫描式平整化处理,利用扫描电子显微镜（SEM）、粗糙度仪和金相显微镜对平整化后的金刚石表面进行表征,研究了激光充电电压和焦点位置对扫描凹槽宽度和深度的影响,以及扫描间距对平整化效果的影响。研究结果表明：扫描凹槽宽度随激光充电电压的升高而增大;凹槽深度随激光充电电压的升高而增大,随偏焦量的增大而增大。激光轴向偏焦法对CVD金刚石膜进行平整化处理后,其粗糙度显著减小,利用氢等离子体对其表面进行刻蚀处理,能够有效去除表层石墨,从而达到理想的平整化效果。     

Deposition of thin rhodium films by plasma-enhanced chemical vapor deposition

Thin films of rhodium have been prepared starting from dicarbonyl-2.4-pentadionato-rhodium(I), Rh(CO)₂C₅H₇O₂, by plasma enhanced CVD. The dependence of the deposition rate and film properties on substrate temperature, partial pressure of the organometallic and on hydrogen has been studied. Metal contents of 100% and thin-film resistivities as low as 5 times the bulk resistivity of rhodium have been achieved.     

Effect of H2 dilution on a-CN:H films deposited by hot-wire chemical vapor deposition

Hydrogenated amorphous carbon nitride (a-CN:H) thin films were deposited by hot-wire chemical vapor deposition (HWCVD) using the gas mixture of CH₄, NH₃ and H₂ precursor gases. The structural and electronic environments studies of H₂ diluted a-CN:H films were carried out by Raman spectroscopy and X-ray photoelectron spectroscopy. The nitrogen content increases while the total carbon contents decreases with increase in H₂ flow rate from 0 sccm to 20 sccm in the a-CN:H films. Moreover, the detail analysis of the carbon core orbital, valence band and hole states of a-CN:H were discussed with different H₂ flow rate.     

金属有机化学气相淀积技术制备GaMnN薄膜材料光学性质研究

研究由MOCVD 技术制备的 GaMnN 外延薄膜光吸收谱.实验发现Mn掺杂后较未掺杂GaN吸收系数在近紫外区增加,在吸收谱低能区144 eV附近观察到吸收峰,吸收系数随Mn浓度的增加而增大.实验结果与基于密度泛函理论的第一性原理计算结果一致,结合理论计算分析认为144 eV附近的吸收峰源于Mn³⁺离子e态与t₂态间的带内跃迁⁵T₂→⁵E. 关键词： GaMnN MOCVD 密度泛函理论 光学性质     

Effects of pulsed plasma on low temperature growth of Pb-based ferroelectric films in direct liquid injection metalorganic chemical vapor deposition

We have investigated the effects of pulsed plasma on the low temperature (380 °C) growth of Pb-based ferroelectric films using direct liquid injection metalorganic chemical vapor deposition (DLI-MOCVD). With an appropriately tuned pulsed plasma, stoichiometric lead titanate (PT) films having pure perovskite phases could be obtained over a wider range of metalorganic precursor input flow rate ratio. The processing window for the fabrication of stoichiometric lead zirconate titanate (PZT) films was also expanded with the assistance of the pulsed plasma. The step coverage characteristic was not degraded by the application of the pulsed plasma.     

Rapid nucleation of diamond films by pulsed laser chemical vapor deposition

The nucleation of diamond films could be greatly enhanced on mirror-polished Si substrate by a pulsed Nd:YAG laser beam without any thermal- and plasma-assisted processes during a very short time. The nucleation density increased with decreasing laser power density from 1.38×10¹⁰ to 1.17×10⁹ W/cm² and deposition pressure from 1013 to 4 mbar. The pulsed laser beam made no contribution to enhance nucleation at substrate temperature as low as 650°C. X-ray diffraction measurements showed the (1 1 1) diffraction peak of diamond for the samples obtained using only pulsed laser during 40 min. The enhanced nucleation and growth of diamond crystallites were attributed to effective excitation of reactive gases and etching of non-diamond carbon phases by the pulsed laser beam.     

Thin films of magnesium oxide prepared by plasma-enhanced chemical vapour deposition

Thin films of magnesium oxide have been deposited on glass, quartz, stainless steel, and nickel by plasma enhanced chemical vapour deposition using 2,2,6,6-tetramethyl-heptanedionato-3,5-magnesium(II) (Mg(thd)₂) as precursor. The films show (100)-orientation when deposited at temperatures 673 K. The influence of experimental parameters on deposition rate and film properties has been studied.On leave from the Beijing Solar Energy Research Institute, Beijing, China     

The influence of Mn content on luminescence properties in Mn-doped ZnO films deposited by ultrasonic spray assisted chemical vapor deposition

Mn-doped ZnO (Zn_1−xMn_xO, 0 ≤ x ≤ 0.1) films are prepared by an ultrasonic spray assisted chemical vapor deposition method. X-ray diffraction and Raman scattering show that all the Zn_1−xMn_xO films are good wurtzite structures without any impurity phases. Cathodoluminescence spectra show that ultraviolet emission and green luminescence can be observed. The intensity of ultraviolet emission decreases with the increment of x, while the intensity of green luminescence increases with the increment of x when x ≤ 0.02. However, when x (x > 0.02) is further increased, the intensity of green luminescence decreases gradually, and the green luminescence disappears when x is above 0.075. We consider that the change of the luminescence is related to the competition between the radiative recombination and the non-radiative recombination.     

Plasma-enhanced chemical vapor deposition of organic particle thin films

Five organic precursors, 2,5-dimethyl-2,4-hexadiene, 2,5-norbornadiene, α-terpinine, limonene, and styrene have been studied as precursors for plasma deposition of low-k films. The films have been produced under particle-forming conditions in the plasma. Accordingly, films have a granular structure with grain sizes in the range 40–400 nm, as determined by AFM. Annealing at 400 °C preserves the granular structure of the films while the grain size decreases. Of the five precursors examined, 2,5-dimethyl-2,4-hexadiene and 2,5-norbornadiene produce films with the lowest dielectric constant, with a value of 3.3. While the dielectric constant varies with deposition conditions (pressure, flow rate, concentration of precursor), we find that the grain size of the films correlates most closely with the dielectric constant and conclude that the lowest value of the dielectric constant are obtained under conditions that promote the formation of particles larger than about 200 nm.     

Silicon rich silicon oxide films deposited by radio frequency plasma enhanced chemical vapor deposition method: Optical and structural properties

Silicon rich silicon oxide films have been deposited by plasma enhanced chemical vapour deposition using a gas mixture of silane, carbon-di-oxide and hydrogen. Silicon nanocrystals formations in the as deposited silicon rich silicon oxide films have been detected by high resolution transmission electron microscopy, scanning electron microscopy, Raman scattering and X-ray diffraction studies. Structural changes under different deposition condition have been studied by Fourier transform infrared spectroscopy. The oxygen and hydrogen bonding configurations have been obtained from Fourier transform infrared spectroscopy. Room temperature photoluminescence spectra have been observed for the as deposited films. The structural properties together with photoluminescence spectra allowed us to gain insight about the Si nanocrystal formation.     

Low-temperature growth of high-Tc superconducting films by plasma-enhanced metal-organic chemical vapor deposition

Plasma-enhanced MOCVD in which metal-organic compounds are sublimated directly into the growth chamber is studied for the first time as a new low-temperature process for growing superconducting YBa₂Cu₃O-_-x thin films. Y(THD)₃, Ba(THD)₂, Cu(THD)₂ and oxygen are used as metal sources and oxydizing agent. Emission spectroscopy reveals that activated metal-organic compounds and activated oxygen species are present during film growth. Superconducting YBa₂Cu₃O_7-x films whose zero-resistivity temperature are 50 K and 82 K are grown at 550°C and 600°C.