A comparative study of p-type diamond films using Raman and transport measurements

The influence of deposition temperature in the properties of synthetic diamond films grown by two different chemical vapor deposition (CVD) techniques, hot-filament- and microwave-plasma-assisted, was investigated. These samples were obtained using the optimal growth conditions previously achieved in this work. Raman spectroscopy was employed in order to investigate the diamond film quality as a function of the deposition temperature. It was found that the nondiamond carbon bands decrease as the deposition temperature increases for both the deposition methods, leading to higher-quality diamond films. The micro- and macro-Raman spectra showed that the nondiamond band is already present in a single diamond grain. Both techniques provided well homogeneous diamond films and with equivalently good quality. Boron-doped diamond films with different carrier concentration levels were also studied. In order to get details about the electrical properties of the films, resistivity as a function of the boron concentration—in association with Raman spectra—and temperature-dependent transport measurements were employed. The results showed that the boron doping is the main responsible for the conductivity and that the variable range hopping (VRH) mechanism dominates the transport in these doped diamond films.     

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.     

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.     

生长温度对CVD金刚石薄膜的影响

系统研究了ＣＶＤ金刚石薄膜成膜过程中生长温度对薄膜质量、生长率和力学性能的影响。研究结果表明：在典型沉积条件下，生长温度愈高、薄膜的晶体质量愈好；但薄膜的应力状况和附着性能变坏；在８００℃时，金刚石薄膜的生长速率最大。讨论了ＣＶＤ金刚石薄膜作为机械工具涂层的最佳生长温度。     

P型和N型金刚石薄膜研究进展

金刚石薄膜有着高的热导率,高的介质击穿场强,高的载流子迁移率以及宽的禁带等优点,是非常理想的功能材料。掺杂使金刚石薄膜具有独特的电学和热学性能,使其在半导体领域具有广阔的应用前景,近年来成为国内外研究的热点之一。综述了金刚石薄膜P型掺杂和N型掺杂的研究现状,对金刚石薄膜N型掺杂研究中存在的问题进行了分析和探索,并对N型金刚石的前景进行了展望。     

Influence of texture on optical and electrical properties of diamond films

The optical and electrical properties of variously textured diamond films have been investigated in this paper. SEM and Raman spectrum indicated that the films produced were of high quality with either (0 0 1) or (1 1 1) orientation. A four-layer model was used to fit the measured spectroscopic ellipsometry data. The results indicated that the properties of (0 0 1)-oriented diamond films were superior to those of (1 1 1)-oriented one. The refractive index and extinction coefficient of (0 0 1)-oriented diamond film in the infrared region of 2500-12500 nm was measured as 2.391 and of the order of 10⁻⁵, respectively and that for (1 1 1)-oriented one was 2.375 and of the order of 10⁻⁴, respectively. The dark current of the (0 0 1)-oriented diamond film was measured as 33.7 nA for an applied electric field of 100 kV cm⁻¹, its resistivity being about 2.33×10¹⁰ Ω cm. Current passing through the (0 0 1)-oriented diamond film during testing did not change significantly.     

[001]织构和非织构CVD金刚石膜的电学特性

研究了「００１」织构和非织构金刚石膜的暗电流－电压特性、电流－温度特性以及在稳定Ｘ射线辐照下的响应。结果表明「００１」织构的金刚石膜相对非织构多晶金刚石膜具有大的暗电流和Ｘ射线响应。主要由于非织构金刚石膜含有大量的晶粒间界,导致对载流子的传输产生强烈散射。在高于５００Ｋ的温度区域内,随着温度的上升「００１」织构和非强构的金刚石膜的电流都将以指数式上升,这与Ｓｉ占据金刚石格点产生１．６８ｅＶ的激活能有关。     

Mechanical properties of diamond thin films

Abstract

The mechanical properties of diamond films deposited via hot filament chemical vapour deposition have been determined using a range of techniques, and related to the composition and morphology of the diamond films as determined by laser Raman spectroscopy. As the quality of the film increases, its hardness (as determined by the volume law of mixtures hardness model) also increases until it is larger than values often reported for polycrystalline bulk material, a consequence of the very small grain size in the films. Coating adhesion, as determined from indentation adhesion tests, also appears to improve with coating quality. Variations in the behaviour of the friction coefficient between diamond films and diamond and steel counterfaces are less well defined, but it appears that the surface morphology of the film is important in dictating the behaviour rather than the quality of the diamond. These results are discussed in the context of the potential use of diamond coatings in tribological applications.

MST/1695     

硫化锌窗口上CVD法制备金刚石膜的研究进展

金刚石具有优异的红外透过性能,可作为硫化锌红外窗口的保护膜。但由于CVD金刚石的沉积过程会刻蚀硫化锌衬底,导致在窗口表面直接生长金刚石膜比较困难。本文主要综述了近年来通过添加过渡层沉积金刚石薄膜的方法和光学焊接金刚石厚膜的方法来增强硫化锌窗口的性能,并介绍了CVD金刚石膜的光学应用及其目前所存在的问题,最后对未来CVD金刚石膜发展的方向作出了展望。     

Electrical properties of diamond films grown at low temperature

The unique electronic properties of diamond, associated with the emergence of chemical vapour deposition (CVD) methods for the growth of thin films on non-diamond substrates, have led to considerable interest in electronic devices fabricated from this material. In our previous work, we found that polycrystalline diamond films can be deposited at 250 °C using CH₄---CO₂ gas mixtures. Studying the electrical properties and the upcoming problems of applications of low-temperature diamond films are relevant concerns.

In this work, the electrical properties of diamond films grown at low temperatures were studied and compared with those of conventional diamond films. Platinum was used as the upper electrode. The resistivity of low-temperature diamond was around three orders of magnititude lower than that of conventional diamond. However, both the low temperature and conventional growth diamond exihibited rectifying behavior when platinum was used as the upper electrode.     

金刚石膜技术研究开发进展——专利文献分析

金刚石膜具有特别优异的性能,在高技术领域有着极为广泛的应用。本文采集1985年到2008年6月世界金刚石膜技术专利文献,并对其发展脉络和竞争格局进行定量和定性分析,揭示出国际上金刚石膜技术已处于较成熟阶段,工具级、热沉级金刚石膜产品已进入实用阶段,光学级和器件级金刚石膜技术尚未成熟;美国、日本技术实力占优势;德国、美国、日本市场被看好;不同应用领域竞争态势差异很大;通过引证分析得出了相关领域的核心的基础专利。     

Enhanced field emission from ZnO nanoneedles on chemical vapour deposited diamond films

ZnO nanoneedles were coated on hot filament chemical vapour deposited diamond thin films to enhance the field emission properties of ZnO nanoneedles. The virgin diamond films and ZnO nanoneedles on diamond films were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The field emission studies reveal that the ZnO nanoneedles coated on diamond film exhibit better emission characteristics, with minimum threshold field (required to draw a current density ~ 1 μA/cm²) as compared to ZnO needles on silicon and virgin diamond films. The better emission characteristic of ZnO nanoneedles on diamond film is attributed to the high field-enhancement factor resulting due to the combined effect of the ZnO nanoneedles and diamond film.     

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 and impedance studies of undoped diamond films

The undoped, polycrystalline diamond films were deposited on tungsten wire substrates by hot filament chemical vapor deposition (HF CVD), using a precursor gas mixture of methanol with excess of hydrogen. The morphology and quality of the as-deposited films were monitored by scanning electron microscopy (SEM) and Raman spectroscopy. The surface morphology analyzed by SEM resembles a continuous and well faceted diamond film. Raman results showed essential differences in qualities of diamond films grown at different hydrocarbon concentrations. The electrochemical properties of diamond electrodes were examined with cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS). The CV experiments revealed a large chemical window (>～4.3 V) of undoped diamond. Analysis of the ferrocyanide-ferricyanide couple at a diamond electrode suggests some extent of electrochemical quasi-reversibility, but the rates of charge transfer across the diamond substrate interface vary with diamond quality.     

表面镀钛对金刚石薄膜场发射特性的影响

利用等离子体化学气相（MWPCVD）沉积法在Si（100）面上沉积了金刚石薄膜,采用SEM、AFM、XRD、Raman、XPS等方法对薄膜的结构及表面形貌进行了分析。为提高薄膜的场发射性能,在金刚石表面溅射了金属Ti,对比金刚石薄膜、金刚石／金属Ti复合薄膜的场发射性能,结果表明,金刚石／金属Ti薄膜的发射电流密度更大,且随着电场的增加电流密度急剧增加,开启电场低,约为3V／μm,当电场为25V／μm时发射电流密度可达到1400mA／cm2,并在机理上进行了一些探索,对金刚石／金属复合结构薄膜的场发射性能研究有重要意义。     

Optical and electrochemical properties of optically transparent,boron-doped diamond thin films deposited on quartz

The optical and electrochemical properties of transparent, boron-doped diamond thin film, deposited on quartz, are discussed. The films were deposited by microwave-assisted chemical vapor deposition, for 1-2 h, using a 0.5% CH4/H2 source gas mixture at 45 Torr and 600 W of power. A high rate of diamond nucleation was achieved by mechanically scratching the quartz. This pretreatment leads to the formation of a continuous film, in a short period of time, which consists of nanometer-sized grains of diamond. The thin-film electrode was characterized by cyclic voltammetry, atomic force microscopy, and UV-visible absorption spectrophotometry. The film's electrochemical response was evaluated using Ru(NH3)6(3+/2+) in 1 M KCl, Fe(CN)6(3-/4-) in 1 M KCl, and chlorpromazine (CPZ) in 10 mM HClO4. The film exhibited a low voltammetric background current and a stable and active voltammetric response for all three redox systems. The optical transparency of the polycrystalline film in the visible region was near 50% and fairly constant between 300 and 800 nm. The optical and electrical properties were extremely stable during 48-h exposure tests in various aqueous (HNO3, NaOH) solutions and nonaqueous (e.g., chlorinated) solvents. The properties were also extremely stable during anodic and cathodic potential cycling in harsh aqueous environments. This stability is in stark contrast to what was observed for an indium-doped tin oxide thin film coated on quartz. The spectroelectrochemical response (transmission mode) for CPZ was studied in detail, using a thin-layer spectroelectrochemical cell. Thin-layer voltammetry, potential step/ absorption measurements, and detection analytical figures of merit are presented. The results demonstrate that durable, stable, and optically transparent diamond thin films, with low electrical resistivity (approximately 0.026 omega x cm) laterally through the film, can be deposited on quartz.     

Filament-assisted growth of diamond films

Filament-assisted pyrolytic growth of diamond films on (100) Si wafers was investigated in an attempt to grow quality layers for semiconductor applications. The work was carried out in hydrogen ambient under a reduced pressure condition of about 100 torr (133, 322×10² Pa). Using isopropanol and methanol as carbon source chemicals, the growth process and film properties were characterized as functions of reactant concentration, filament and substrate temperature, reaction pressure and the total gas flow rate. Diamond films of good quality were grown under condition of low source concentration and small flow rate. However, the growth rates were generally slow. The films were polycrystalline. The filament and substrate temperatures were fairly critical to the nucleation and growth processes. The substrate surface finishing from diamond paste polishing predominated the nucleation site and grain size of the deposits.     

高速钢基体表面金刚石涂层研究的进展

高速钢衬底上生长金刚石非常困难.分析了高速钢衬底上生长高质量金刚石涂层的不利因素,综述了国内外消除不利因素所采取的措施和研究趋势,比较了预处理方法和沉积温度对金刚石涂层质量的影响,并在此基础上提出了低温条件下在高速钢刀具表面制备高质量金刚石涂层的新方法.     

Neuron Adhesion on Diamond: Competition between Polymer Treatment and Surface Morphology

The ability to form an efficient interface between material and neural cells is a crucial aspect for construction of neuroelectrodes. Diamond offers material characteristics that could, to a large extent, improve the performance of neuroelectrodes. The greatest advantage of diamond is a large variety of material and surface properties such as electrical conductivity, surface morphology, and surface chemistry. Such a variety of material characteristics can lead to various cellular responses. Here, the authors compare survival, adhesion, and neurite formation of primary neurons on diamond thin films of various morphologies and treatments with several types of polymers commonly used to enhance cell adhesion. The authors find that the variation of surface roughness of nanocrystalline diamond film when coated with polymer does not have a major influence on neuron survival or adhesion. The adhesion of neurons can be influenced by the selected type of polymer coating. High molecular weight of polyethylenimine results in lower viability, adhesion, and neurite formation. The addition of laminin to treated films do not lead to significant improvements in neuron adhesion and neurite development. Their findings emphasize the importance of the correct polymer treatment over morphological properties of diamond thin films as a material for forming interfaces with primary neurons.

     

氢等离子作用下Fe、Co对金刚石膜刻蚀的研究

金刚石具有很高的硬度,加工困难,为寻找一种刻蚀效率较高的材料,利用微波等离子体化学气相沉积（MPCVD）技术,在氢等离子体作用下,研究了Fe、Co对CVD金刚石膜表面的刻蚀效率。用SEM观察刻蚀效果,用Raman光谱对其表面结构进行表征。结果表明：在氢等离子体的作用下,Fe、Co对金刚石表面都有明显的腐蚀作用,其中Fe的刻蚀速率较高,并且可以通过对溶碳材料的厚度控制,来实现对刻蚀速率与刻蚀量的有效控制。对刻蚀后的样品用混合酸及丙酮处理后,得到了可与原始金刚石相媲美的质量。