Papers by Keyword: Chemical Vapor Deposition (CVD)

Abstract: An overview of various cleaning procedures for silicon surfaces is presented. Because in-situ cleaning becomes more and more important for nanotechnology the paper concentrates on physical and dry chemical techniques. As standard ex-situ wet chemical cleaning has a significant impact on surface quality und thus device properties, its influence on further processes is also considered. Oxygen and carbon are unavoidable contaminations after wet chemical treatment and therefore we discuss their in-situ removal as one of the main goals of modern silicon substrate cleaning. As surface roughness strongly influences the electrical quality of interfaces for epitaxy and dielectric growth, we concentrate on techniques, which meet this requirement. It will be shown that multi-step thermal sequences in combination with simultaneous passivation of the clean surface are necessary in order to avoid recontamination. This can be achieved not only for ultra hich vacuum but also for inert gas atmosphere. In this case the process gases have to be extremely purified and the residual partial pressure of contaminats such as oxygen and carbon has to be negligible. It will be demonstrated that 800°C is an upper limit for thermal treatment of silicon surfaces in the presence of carbon because at this temperature SiC formation in combination with a high mobility of silicon monomers leads to surface roughness. In addition mechanical stress causes dislocations and crystal defects.

Abstract: Diamond film was deposited on spherical molybdenum substrate by DC arc plasma CVD method. Diamond film morphology, purities and orientation evolution, obtained from atomic force microscopy, scanning electron microscopy, Raman spectroscopy, X ray diffraction respectively, has showed that grains on the growth surface are compact, continuous and uniform. Characteristic diamond (111), (220), (311) peaks were found and (111) facets were predominant. It revealed that diamond film was polycrystalline texture characteristic. There is a typical diamond Raman spectrum peaks at 1332.0 cm-1, and not graphite and amorphous carbon characteristic peak. High purity diamond film was deposited. When methane concentration was increased, diamond film has more local clusters and vacancy defects such as voids, graphite inclusion, and hydrogen cluster. Therefore, some important parameters such as methane concentration and substrate temperature should be optimized in depositing diamond film.

Abstract: In this paper, a new polishing technique was proposed to polish concave spherical surface by diamond spherical shell deposited by DC-Plasma Jet CVD(chemical vapor deposition), and preparation was studied from both experiment and theory. The deposited films were investigated by some techniques including: scanning electron microscopy (SEM), atom force microscopy (AFM), Raman spectroscopy, and roughness-profile-meter, which were used to analyze surface phase, microstructure, internal quality and surface roughness. The results show that the deposited diamond spherical shell film has some remarkable properties, such as high surface density, high hardness. Compared to traditional polishing techniques, it will have some potential advantages as convenient, flexible, efficient and precious. To adjust some important parameters as methane concentration, depositing time, and it can deposit the different size grain diamond spherical shell films, which are used to polish different precision degree concave spherical surfaces. Meantime, to change curvature of diamond spherical shell, it can adapt to polish various curvature radius concave spherical surfaces.

Abstract: Diamond spherical shell thick film was prepared by high power DC-plasma jet CVD. Atom force microscopy, scanning electron microscopy, Raman spectroscopy and roughness-profile-meter were used to characterize microstructure, morphology, impurities and orientation evolution of diamond spherical shell thick film. The results show that, when nucleation begins, grains grow random orientation. The grain size of spherical diamond film prepared is compact, clear, uniform, continuous and no remarkable bigger grain over the whole surface of film. On the growth surface, (100) facets were dominant, and the cross-section SEM indicated that film columnar spreading grew from the substrate surface to the diamond film surface. The roughness of the growth surface was much more than that of the nucleation surface. To adjust some important parameters as methane concentrate, depositing time, and matrix temperature, and high quality diamond spherical shell thick film was deposited.

Abstract: Ceramic matrix composites reinforced by carbon or SiC-based fibers achieve high toughness and damage tolerance through the disposal of weak fiber coating which can deflect cracks and promote debonding at the fiber/matrix region. The methods for fabrication, as well as different techniques including SEM/EDS, XPS, XRD, AFM, micro Raman for evaluation of properties of the interphase zone are considered. The morphology, composition, topography, roughness, tensile properties of coated carbon and SiC fibers are discussed in details. The behavior of coated fibers is governed by the chemistry, procedure for coating fabrication, nanostructural factors.

Abstract: In this paper, mass production of quasi-aligned CNTs was achieved with a new tri-metallic catalyst (Fe-Ni-Mo/MgO) by thermal CVD method, using methane as carbon precursor. The growth process was in-situ monitored by thermal gravimetry/differential scanning calorimetry (TG-DSC) technique, and the yield of CNTs over 2200% was attained under the mixture atmosphere of CH4 and H2 with flow rate about 25 ml/min and 5 ml/min respectively at 900°C for 30 min. The as-prepared products were characterized. Raman spectrums showed that the CNTs are multi-wall structure. The diameter of the CNTs was estimated to be 20-30 nm. We think the synergism of FeNi3 alloy and Mo is the main reason for the high catalytic activity of tri-metallic catalyst.

Abstract: The effects of deposition temperature on the growth characteristics of CVD SiC coatings were investigated. CVD SiC coatings were made by pyrolysis of methyltrichlorosilane (MTS) in hydrogen at a low pressure of 5kPa. The ratio of MTS to hydrogen was 1/12. The deposition temperatures were varied from 1373K to 1503K. Optical microscope and SEM were used to observe the surface morphology and microstructure of the coatings. XRD was used for characterization of the phase composition. Results indicated that the deposition rate and the surface roughness varied with deposition temperature. At 1373K, the deposited grains were mainly equiaxed with the crystallite size of 22 nm. However, when the deposition temperature was 1503K, the SiC grains were mainly showed faceted columnar structure with the crystallite size of 32 nm. Grain size increased with the increase of deposition temperature.

Abstract: After removal of the resin from PAN-carbon fibers, the fibers were coated with C or SiC by chemical vapor deposition (CVD) and the effects of these CVD coatings on the mechanical and chemical properties of carbon fibers were investigated. DTG analysis was conducted at different temperatures (993K, 1053K and 1113K) to establish the oxidation reaction models of the C/C or C/SiC coated fibers. The results showed that the CVD coatings enhance the oxidation resistance of the carbon fibers. The surface morphology of the CVD C or SiC fibers was investigated by SEM. The tensile strength of the fibers was found to decrease rapidly after CVD, while the Young’s modulus remained almost constant. These changes can be explained by the interface performance of the carbon fibers and the mechanism of CVD C or SiC deposition. The difference in dilatability between the CVD C or SiC layers and the carbon fibers was the main reason for the tensile failure.

Abstract: Carbon nanotube (CNT) can be thought of as a hexagonal network of carbon atoms that has been rolled up to make a seamless cylinder. If they are consisting of one layer, they are termed singled-walled CNTs (SWNTs) while if there are multiple walls, they are called multi-walled CNTs (MWNTs). For most functional devices application, an aligned arrangement of CNTs is desired. Aligned multiwalled carbon nanotubes (MWNTs) have been successfully grown by the inclusion of a buffer layer of oxidized Al. An Al2O3 layer has been proven to be an important contributing factor towards obtaining good quality aligned CNTs. In this work, Al is deposited onto the Si wafer using electron beam evaporation and later oxidized by heating in air. A thin layer of iron catalyst is then deposited on top of the oxidized Al layer and annealed at 400oC. The result shows an improvement in the intensity of the graphitization peak (G-band) in the Raman spectra and aligned MWNTs is observed in these samples compared to the ones that have undergone the same process parameter except the Al2O3 layer.

Abstract: In the present work, high power DC arc plasma jet chemical vapor deposition (CVD) is used to prepare diamond films with full width half magnitude (FWHM) less than 10 wave numbers at 1332 cm−1 Raman peak. During the polishing process, diamond film is hold against the stainless steel holder, which rotates and swings when the sample comes into contact with the cast-iron plate. Average surface roughness of the forming nucleus polished surface and growing polished surface is 560nm, 90nm respectively. And the materials removal rate is quite different. Fine crystal grain of the forming nucleus surface and the thick column crystal of growing surface are dominant in structure. In the meantime, effects of the size of the abrasive power, the applied force and polishing direction are also discussed. A profilometer, an Raman spectroscopy, X-ray diffraction and a scanning electron microscope have been used to evaluate the surface states of diamond films before and after polishing. This result reveals an. improvement of polishing efficiency and a great potential for commercial application.