Diamond chemical vapour deposition on seeded cemented tungsten carbide substrates

Diamond particles were deposited onto seeded cemented tungsten carbide (WC-Co) substrates using conventional hot-filament chemical vapour deposition (HFCVD) and time-modulated CVD (TMCVD) processes. The substrates were pre-seeded ultrasonically with diamond particles of different grit sizes. In this investigation, we employ timed methane (CH₄) gas modulations, which are an integral part of our TMCVD process in order to enhance diamond nucleation density. During diamond deposition using the conventional HFCVD process, methane gas flow was maintained constant. The total hydrogen flow into the reactor during TMCVD process was higher than in the HFCVD process. Hydrogen etching can be expectedly more prominent in the TMCVD process than in HFCVD of diamond particles. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results showed that a proper selection of the diamond grit size for seeding using ultrasounds can lead to enhancement in the nucleation density values of about two orders of magnitude (10⁷ to 10⁹ cm^− 2). The TMCVD process using the different seeded substrates can result in high nucleation density values of up to 10¹⁰ cm^− 2.     

Nanocrystalline diamond films deposited using a new growth regime

Abstract

Time modulated chemical vapour deposition (TMCVD), a new method for depositing nanocrystalline diamond (NCD) coatings, is reported. The key feature of the process is that it utilises modulated methane flow to promote secondary nucleation of nanoscale diamond crystallites. The growth modes of films deposited using both TMCVD and conventional hot filament CVD methods are described. Moreover, a pictorial model showing the key stages of film growth during NCD deposition using TMCVD is presented. The ability of this new process to promote secondary diamond crystallites has been demonstrated.     

Crystalline quality and phase purity of CVD diamond films studied by Raman spectroscopy

Two series of diamond films grown—at different temperatures—by two chemical vapor deposition (CVD) methods, i.e., hot filament (HFCVD) and microwave-plasma (MPCVD), were investigated. Raman spectroscopy and scanning electron microscopy were employed to perform a study of both crystalline quality and phase purity of the films grown by the two techniques. It was found that high phase purity can be attained by both methods. However, at high temperatures, the MPCVD technique produced films with higher crystalline quality as compared to those grown by HFCVD. Finally, in order to shed some light into the mechanisms responsible for the lower crystalline quality observed in the HFCVD films, a study based in the phonon confinement model and stress was accomplished.     

电镀铬-金刚石复合过渡层提高金刚石膜/基结合力

在铜基体上沉积铬-金刚石复合过渡层, 用热丝CVD系统在复合过渡层上沉积连续的金刚石涂层. 用扫描电镜(SEM)、X射线(XRD)、拉曼光谱及压痕试验对所沉积的镶嵌结构界面金刚石膜的相结构及膜/基结合性能进行了研究. 结果表明, 非晶态的电镀Cr在CVD过程中转变成Cr₃C₂, 由于金刚石颗粒与Cr₃C₂的相互咬合作用, 金刚石膜/基结合力高; 在294 N载荷压痕试验时, 压痕外围不产生大块涂层崩落和径向裂纹, 只形成环状裂纹.     

Two-step growth of HFCVD diamond films over large areas

This paper reports the results of a two-step hot filament chemical vapor deposition method to improve the quality of diamond films. Diamond films were deposited on a Si(100) substrate having an area of 45 cm² and a thickness of 60 μm, employing a HFCVD system. The first step is the growth of CVD diamond in the HFCVD reactor. In the second step, the samples were treated in a saturated solution of H₂SO₄:CrO₃ and rinsed in a (1:1) solution of H₂O₂:NH₄OH. After this procedure, a second diamond layer was deposited. The diamond films were analyzed by Raman scattering spectroscopy (RSS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The films showed a high degree of purity with a thickness of 60 μm, presenting uniform characteristics over a large area.     

CVD金刚石膜的场发射机制

利用热灯丝化学气相沉积方法在光滑的钼上沉积了金刚石膜,用扫描电子显微镜和Raman谱对金刚石膜进行了分析。结果表明金刚石膜是由许多金刚石晶粒组成,晶粒间界主要是石墨相,并且在膜内有许多缺陷。金刚石膜的场发射结果表明高浓度CH4形成的金刚石膜场发射阈位电场较低浓度CH4形成的金刚石为低。这意味着杂质（如石墨）和缺陷（悬挂键）极大地影响了膜的场发射性能。根据以上结果,提出了一种CVD金刚石膜的场发射机制即膜内的缺陷增强膜内的电场,石墨增大电子的隧穿系数以增强CVD金刚石膜的场发射。     

Cyclic voltammetry response of an undoped CVD diamond electrodes

The polycrystalline undoped diamond layers were deposited on tungsten wire substrates by using hot filament chemical vapor deposition (HFCVD) technique. As a working gas the mixture of methanol in excess of hydrogen was used. The morphologies and quality of as-deposited films were monitored by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy respectively. The electrochemical activity of the obtained diamond layers was monitored by using cyclic voltammetry measurements. Analysis of the ferrocyanide–ferricyanide couple at undoped diamond electrode suggests that electrochemical reaction at diamond electrode has a quasireversibile character. The ratio of the anodic and cathodic peak currents was always close to unity. In this work we showed that the amorphous carbon admixture in the CVD diamond layer has a crucial influence on its electrochemical performance.     

金刚石膜在多孔硅发光中的应用

采用微波等离子体化学气相沉积（MPCVD）法成功地在多孔硅上沉积出均匀、致密的金刚石膜。光致发光测量表明,金刚石膜可以有效稳定多孔硅的发光波长和发光强度,具有明显的钝化效应。金刚石膜的这个特点再加上高硬度特性使金刚石膜成为多孔硅的一种潜在的钝化膜。     

甲烷浓度对金刚石薄膜质量的影响

纳米金刚石薄膜具有优异的性能,已在多个领域获得广泛应用.但微波等离子体化学气相沉积制备的金刚石薄膜质量却严重受沉积工艺的影响,为了深入了解沉积工艺对制备的金刚石薄膜质量的影响,本文详细研究了甲烷浓度对微波等离子体化学气相沉积( MPCVD)金刚石薄膜质量的影响,利用扫描电镜、X射线衍射、拉曼光谱以及原子力显微镜对其进行...     

微波CVD金刚石热沉片的制备研究

采用化学气相沉积法（CVD）制备的金刚石薄膜具有接近于天然金刚石的导热性能,是目前最为理想的热沉材料。利用微波等离子体化学气相沉积法（MPCVD）制备了金刚石热沉片,并在此基础上研究了不同沉积工艺对金刚石热沉片散热性能的影响。采用扫描电子显微镜（SEM）和激光拉曼光谱（Raman）检测了薄膜的表面形貌及纯度,金刚石热沉片的导热性能则通过测量封装LED后薄膜的散热效果来进行表征。结果表明,在其他条件不变的情况下,提高生长过程中的微波输出功率、降低反应气压以及增加基片温度有利于制备出散热性能更佳的金刚石热沉片。     

Nitrogen and hydrogen related infrared absorption in CVD diamond films

In this paper, we investigate on the presence of hydrogen and nitrogen related infrared absorptions in chemical vapour deposited (CVD) diamond films. Investigations were carried out in cross sections of diamond windows, deposited using hot filament CVD (HFCVD). The results of Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) and Raman spectroscopy carried out in a cross section of self-standing diamond sheets are presented. The FTIR spectra showed several features that have not been reported before. In order to confirm the frequency of nitrogen related vibrations, ab-initio calculations were carried out using GAMESS program. The investigations showed the presence of several C-N related peaks in one-phonon (1000-1333 cm^− 1). The deconvolution of the spectra in the three-phonon region (2700-3150 cm^− 1) also showed a number of vibration modes corresponding to sp^mCH_n phase of carbon. Elastic recoil detection analysis (ERDA) was employed to compare the H content measured using FTIR technique. Using these measurements we point out that the oscillator strength of the different IR modes varies depending upon the structure and H content of CVD diamond sheets.     

分体圆柱谐振腔法用于金刚石膜微波介电性能测试的研究

针对金刚石膜微波介电损耗低、厚度薄带来的微波介电性能测试难点, 研制了一台分体圆柱谐振腔式微波介电性能测试装置。利用不同直径的蓝宝石单晶样品, 用上述装置对低损耗薄膜类样品微波介电性能的测试能力及样品直径对测试结果的影响进行了实验研究。在此基础上, 使用分体圆柱谐振腔式微波介电性能测试装置对微波等离子体化学气相沉积法和直流电弧等离子体喷射法制备的高品质金刚石膜在Ka波段的微波介电性能进行了测试比较。测试结果表明, 由Raman光谱、紫外-可见光谱等分析证明品质较优的微波等离子体化学气相沉积法制备的金刚石膜具有更高的微波介电性能, 其相对介电常数和微波介电损耗值均低于直流电弧等离子体喷射法制备的金刚石膜。     

Low Resistance Polycrystalline Diamond Thin Films Deposited by Hot Filament Chemical Vapour Deposition

Polycrystalline diamond thin films with outgrowing diamond (OGD) grains were deposited onto silicon wafers using a hydrocarbon gas (CH4) highly diluted with H2 at low pressure in a hot filament chemical vapour deposition (HFCVD) reactor with a range of gas flow rates. X-ray diffraction (XRD) and SEM showed polycrystalline diamond structure with a random orientation. Polycrystalline diamond films with various textures were grown and (111) facets were dominant with sharp grain boundaries. Outgrowth was observed in flowerish character at high gas flow rates. Isolated single crystals with little openings appeared at various stages at low gas flow rates. Thus, changing gas flow rates had a beneficial influence on the grain size, growth rate and electrical resistivity. CVD diamond films gave an excellent performance for medium film thickness with relatively low electrical resistivity and making them potentially useful in many industrial applications.     

Raman spectroscopy characterization of diamond films on steel substrates with titanium carbide arc-plated interlayer

Diamond chemical vapour deposition (CVD) on steel represents a difficult task. The major problem is represented by large diffusion of carbon into steel at CVD temperatures. This leads to very low diamond nucleation and degradation of steel microstructure and properties. Recent work [R. Polini, F. Pighetti Mantini, M. Braic, M. Amar, W. Ahmed, H. Taylor, Thin Solid Films 494 (2006) 116] demonstrated that well-adherent diamond films can be grown on high-speed steels by using a TiC interlayer deposited by the PVD-arc technique. The resulting multilayer (TiC/diamond) coating had a rough surface morphology due to the presence of droplets formed at the substrate surface during the reactive evaporation of TiC. In this work, we first present an extensive Raman investigation of 2 μm, 4 μm and 6 μm thick diamond films deposited by hot filament CVD on TiC interlayers obtained by the PVD-arc technique. The stress state of the diamond was dependent on both the films thickness and the spatial position of the coating on the substrate. In fact, on the top of TiC droplets, the stress state of the diamond was much lower than that of diamond in flatter substrate areas. These results showed that diamond films deposited on rough TiC interlayers exhibited a wide distribution of stress values and that very large compressive stress exists in the diamond film grown on flat regions of steel substrates with a TiC interlayer. Diamond films could accommodate stresses as large as 10 GPa without delamination.     

Electrochemical studies of nano-structured diamond thin-film electrodes grown by microwave plasma CVD

In this paper, we report the investigation of the electrochemical properties of nano-structured diamond thin-film electrodes on porous silicon (PSi) synthesized by microwave plasma chemical vapor deposition (MPCVD). For the application, boron-doped and undoped diamond thin film has been performed and fabricated into an electrode device, and its microstructure, electrical and chemical properties have been studied. In order to enlarge the surface area of diamond electrodes, a negative bias was applied to the MPCVD process to deposit diamond thin film in a nano-structured form, so that its surface remained rough and nano-fine structured. Diamond thin films were analyzed by Raman spectroscopy and SEM. The morphology of boron-doped diamond thin films on PSi reveals nano-rods in the shape of diamond crystallites. Their electrochemical properties were evaluated by performing cyclic voltammetry (CV) measurement in inorganic K₄[Fe(CN)₆] in a K₂HPO₄ buffer solution. Boron-doped diamond thin film on PSi has demonstrated good electrochemical properties, with a larger redoxidation current of CV, due to its rough surface, which provides a more active electrochemical interface.     

Effects of the grain size of CVD diamond films on the detector performance

Although the unique properties of CVD diamond films have made it a candidate material for radiation detectors, the detector performance is strongly dependent on the film quality. In this paper, three CVD diamond films with different grain size were grown by using a hot-filament chemical vapor deposition (HFCVD) technique and the ratio of the grain size to the film thickness is high to 50%. 5.9 keV ⁵⁵Fe X-rays measured the photocurrents and the pulse height distributions (PHDs) of these CVD diamond detectors. The detector performance is improved with the grain size increasing. The dark-current of 16.0 nA and the photocurrent of 15.9 nA are obtained at an electrical field of 50 kV⋅cm⁻¹ and the PHD peak is well separated from the noise pedestal.     

Simultaneous fabrication of nanocrystalline and {100} textured large-grained diamond films

In this work, we report the simultaneous synthesis of both nanocrystalline and {100} textured large-grained diamond films in one deposition run performed in a 5-kW microwave plasma chemical vapor deposition (MPCVD) reactor. This was achieved by employing the coupled effect of nitrogen addition in the gas phase and substrate temperature on the growth of diamond films. In one deposition run, different substrate surface temperatures were obtained by a novel substrate arrangement, nanocrystalline diamond of high growth rate around 3 μm/h was formed at low temperature, while {100} textured large-grained diamond of much higher growth rate about 11 μm/h was grown at high temperature. This new method opens way for mechanical and tribological applications of both nano-diamond and {100} textured diamond in industrial level. This result indicates that distinct growth modes or growth mechanisms were involved at different substrate temperatures with a certain amount of nitrogen addition. The coupled effect of nitrogen addition and temperature on the growth of CVD diamond films and the involved growth mechanism is briefly discussed from the point of view of gas phase chemistry and surface reactions.     

微波等离子体刻蚀处理对金刚石薄膜涂层刀具附着力和切削性能的影响

用HFCVD法在硬质合金（YG6）刀具衬底上沉积金刚石薄膜,用氢微波等离子体刻蚀的方法对衬底进行表面预处理,研究了该预处理技术对WC硬质合金衬底表面成分的影响,进一步探讨了所沉积金刚石薄膜的表面形貌和附着力,并通过难加工材料实际切削试验。研究了所制备的金刚石薄膜涂层刀具的切削性能。试验结果表明,Ar-H2微波等离子体刻蚀脱碳处理是提高金刚石薄膜附着力和改善涂层刀具切削性能的有效预处理方法。     

Surface activation pre-treatments for NCD films grown by HFCVD

The control of the nucleation density is essential for the production of ultra-thin, continuous and well adhered nanocrystalline diamond coatings. Surface pre-treatments such as abrasive scratching with diamond powder or bias enhanced nucleation are commonly used methods. In this work, surface activation by a pre-growth step is done using the hot-filament chemical vapour deposition (HFCVD) technique prior to seeding with diamond. The Si surface is modified during exposure to typical CVD diamond growth conditions. After ultrasonication with suspension of diamond in ethanol or n-hexane, an amorphous carbon layer is revealed at the surface of the Si substrates. The densest NCD films were obtained for the surface activation step done using a lower temperature and poorer methane mixture due to the improved seeding allowed by the amorphous carbon layer. Intermediate growth temperature of 750 °C resulted in high nucleation density while lower temperatures decrease it and higher ones produce a DLC nanostructured layer along with moderate NCD nucleation density.     

The nature of stresses in hot-filament chemical vapour deposited diamond thin films on WC substrates

The nature of film stresses in hot-filament chemical vapour deposited (HFCVD) diamond thin films on tungsten carbide substrates, is reported. Commercial WC substrates were subjected to various surface treatments. Subsequently, they were coated with a diamond film and examined for stresses using X-ray diffraction. All but one of the stress measurements indicated various levels of compressive stresses in the film and at the film–substrate interface. These stresses are compared with those obtained by other researchers. Intrinsic film stresses were also computed for diamond films and found to be tensile. WC drills, of 0.125 in. diameter, were also diamond coated and the stress levels measured along drill flanks and flutes. Significant variations were found in these stresses, and the results were analysed from a film–substrate adhesion perspective.