2017, 6(4):2-9. DOI: 10.12146/j.issn.2095-3135.201704001
Abstract:In this paper, the microwave plasma chemical vapor deposition method was investigated to produce homoepitaxial single-crystal diamond by the growth of a diamond seed. The effects of substrate temperature on diamond growth were studied via characterizations of Raman spectroscopy, scanning electron microscope and optical microscope. The results show that substrate temperature is an important factor that affects the growth rate, mode and defects. Within a certain temperature range, the growth rate of diamond increases with the substrate temperature rising. Meanwhile, the growth mode also turns into step flow mode instead of hillock mode. The edge of CVD diamond layer is prone to producing crystalline defects such as twin crystals when the growth thickness of single crystal diamond exceeds 1 mm. Results by Raman spectroscopy demonstrat that single-crystal diamondobtained by the microwave plasma chemical vapor deposition method exhibits better quality than conventional high temperature and high pressure methods.
2017, 6(4):10-19. DOI: 10.12146/j.issn.2095-3135.201704002
Abstract:In order to improve the working life of micro end-mill, the diamond coatings were prepared by hot filament chemical vapor deposition (HFCVD) method with various methane concentrations. Scanning electron microscopy and Raman scattering analyses were carried out to characterize the surface morphology and coating property. With the increasing of methane concentration, the secondary nucleation rate was enhanced and the diamond grain size was decreased, which helped the diamond grain to embed into cemented carbide substrate, and improved film-substrate adhesion. Excess methane concentration weakened the etching ability of atomhydrogen on graphite phase, leading to higher fraction of non-diamond phase among diamond boundaries. While the methane concentration was 3%, the diamond coating deposited on micro end-mill possessed high crystallinity, good adhesion, more compact grains and low non-diamond phase. There was also no delamination occurred at the edge of end-mill. This work not only benefit us from understanding the effect of methane concentration on deposition of diamond film on cemented carbide micro end-mill and the mechanism of diamond film failure, but also provides basis for optimizing the parameters for diamond deposition on end-mills.
2017, 6(4):20-28. DOI: 10.12146/j.issn.2095-3135.201704003
Abstract:The optical lever method is one of the substrate curvature-based instrumentations, which has been widely used to measure the residual stress of thin films. In this work, the Ti and TiN films were prepared based on SUS304 substrate by arc with different thicknesses, and the morphology, density and phase of two films were studied. Curvature radius of the substrate before and after coating was measured by the optical lever method from the front side (positive test method) and the opposite side (negative test method). The residual stresses of films were calculated via Stoney method. The test error and the applicable scope of the negative test method were studied by comparing the results of the positive and negative test methods and the morphology, density, and crystal structure of the films. The results show that the measurement value of residual stress by the negative testmethod is lower than the positive test method. The higher of the residual stress, the closer of the measurement result to the positive test method. When the residual stress is high (＞1 GPa), the results measured by negative test method can reflect true level of the residual stress. However, when the residual stress is low (＜1 GPa), measurement accuracy of the negative test method is usually decreased.
2017, 6(4):29-37. DOI: 10.12146/j.issn.2095-3135.201704004
Abstract:Adhesion between the film and substrate is a key factor to determine the film performance. How to improve the film-substrate adhesive strength and ensure service life of tools has become an urgent technical problem for industrializing diamond coated tools. This article reviews major factors that affect the performances of diamond film adhesion. Based on the survey of recent research, works to improve diamond film-substrate adhesion, potential trends for diamond coating are also discussed.
2017, 6(4):38-48. DOI: 10.12146/j.issn.2095-3135.201704005
Abstract:In this paper, a new structure was designed and tested for the substrate holder of crystal diamondEffect of the proposed substrate holder was verified by several experiments. The experiments related to single diamonds were carried out on the traditional and the proposed substrate holders respectively. The experimental results show that the single diamond with the thickness of 1.66 mm is obtained by continually growing of 48 h, and achieved the high quality single diamond of 3 mm by repeating the growth on the proposed substrate holder. The proposed substrate holder can restrain the occurrence of temperature drifting of large grains during the deposited process and provide a suitable environment for diamond homoepitaxial growth. The polycrystalline diamonds around diamond seeds can be suppressed and high purity chemical vapor deposition single diamonds with thickness of larger than 3 mm can be successfully fabricated by the proposed substrate holder and high power density microwave plasma chemical vapor deposition method. seeds to solve the problems of inhomogeneously distributed temperature. A through-hole was drilled on the substrate holder, and the AlN sheets were added to the contacted areas where the diamond epitaxial growth process was carrying out. With such a substrate holder structure, direct contact between diamond seeds and substrate can be avoided, so as to ensure the essentially homogeneous temperature distributions simutaneouslyEffect of the proposed substrate holder was verified by several experiments. The experiments related to single diamonds were carried out on the traditional and the proposed substrate holders respectively. The experimental results show that the single diamond with the thickness of 1.66 mm is obtained by continually growing of 48 h, and achieved the high quality single diamond of 3 mm by repeating the growth on the proposed substrate holder. The proposed substrate holder can restrain the occurrence of temperature drifting of large grains during the deposited process and provide a suitable environment for diamond homoepitaxial growth. The polycrystalline diamonds around diamond seeds can be suppressed and high purity chemical vapor deposition single diamonds with thickness of larger than 3 mm can be successfully fabricated by the proposed substrate holder and high power density microwave plasma chemical vapor deposition method.
2017, 6(4):49-60. DOI: 10.12146/j.issn.2095-3135.201704006
Abstract:The coefficient of thermal expansion (CTE) is an important thermal parameter for thin films, which is a critical issue in the calculation and analysis of the thermal stress and residual stress of thin films. In this paper, the CTEs of titanium nitride (TiN) and aluminum (Al) films were measured by single-substrate and dualsubstrate method based on the thermally induced bending principle, respectively. Feasibility and tolerance of the dual-substrate method were mainly investigated. The results show that difference in the elastic modulus of films is an important factor affects the calculation accuracy of CTEs tested by the dual-substrate method. When the difference of elastic modulus is small, the CTEs measured by the dual-substrate method agree well with the results by the single-substrate method. The dual-substrate method became inapplicable when there is big elasticmodulus difference of the films on different materials. In addition, the difference of CTE values between the thin film and bulk TiN and Al were also discussed according to the characterizations of the morphology, structure and residual stress of the films. The results also show that the compressive residual stress will increase the film CTE, while the tensile residual stress can decrease the film CTE.
2017, 6(4):61-69. DOI: 10.12146/j.issn.2095-3135.201704007
Abstract:Boron doped diamond thin films have been widely used in the electrochemical sensing applications for its outstanding electrochemical properties. In this work, the preferred (100) growth orientation of boron doped diamond films was successfully synthesized by applying different boron/carbon (B/C) concentration ratio in a homemade microwave plasma enhanced chemical vapor deposition system and its formation mechanisms was further studied. Moreover, the influences from substrate temperature and carbon source concentration were also debated to achieve better (100)-oriented diamond. The experimental results showed that B/C concentration ratio played a more important role on diamond morphology compared with substrate temperature and carbon sourceconcentration. While the B/C concentration ratio was constant with 4 000 ppm, crystal edges and face of the tetrahedral diamond particles became smoother and flatter, which indicated quality improvement of the obtained diamond particles. Keeping the B/C concentration constant, the secondary diamond nucleation density was enhanced when the temperature and carbon source concentration were increased. The results show that the highly oriented diamond thin film electrodes could be obtained by applying appropriate B/C concentration ratios.
2017, 6(4):70-79. DOI: 10.12146/j.issn.2095-3135.201704008
Abstract:Benefited from the excellent physical and chemical properties of diamond, chemical vapour deposition (CVD) diamond thin films have attracted continuous attentions among researchers regarding to both basic research and industry application like cutting tools, biomedicine, thin film sensors and micro-electromechanical systems etc. In this paper, recent progress in the field of diamond film research is reviewed. It is mainly focused on various synthesis methods of diamond thin films and comparison of their pros and cons. By introducing the growing mechanism of CVD diamond thin films, strategies to improve the deposition rates and quality of diamond thin films are also discussed.
2017, 6(4):80-88. DOI: 10.12146/j.issn.2095-3135.201704009
Abstract:In this paper, to improve the adhesive strength of diamond films for the cemented substrates before depositing process, a new approach combined with heat-treatments and acid treatments was investigated. Relations between heat-treatments and surface morphologies, quality of diamond films and the adhesive strength were analyzed within the temperature range of 800~1 000℃. Heat treatment on the cemented substrate was an effective method to improve the adhesive strength for diamond films. With the heating process, large tungsten particles can be refined to small size which can enhance the “interlock functions” between diamond films and the substrate, and improve the density of secondary nucleation. The redundant metal cobalt was removed effectivelyto prevent the catalytic actions, which may cause the transformation from diamond to graphite. However, the adhesive strength was decreased with high temperature heating process subject to the holes left on the substrate surface. Results show that the samples heated at 900℃ owned the strongest adhesive strength and least compressive stress for diamond films.