Transverse bias-enhanced nucleation of diamond in hot filament chemical vapor deposition

 The nucleation density of diamond films was greatly enhanced by inserting a transverse bias into hot filament vapor deposition chamber, which differs from the conventional used longitudinal bias method. In-situ Optical Emission Spectroscopy (OES) technique was used to investigate the diamond deposition process. The relative optical emission intensities of the atomic hydrogen and CH radical to argon near the substrate were calculated. The results show that the improvement of the nucleation density is due to the product of much more atomic hydrogen and CH radicals. Received: 18 March 1998 / Accepted: 22 May 1998     

Effects of Ti- and Zr-based interlayer coatings on the hot filament chemical vapour deposition of diamond on high speed steel

The prospect of obtaining good adhesion of diamond films onto steel substrates is highly exciting because the achievement of this objective will open up applications in the cutting and drilling industry. However, a major problem with depositing diamond onto steel is high diffusion of carbon into steel at chemical vapour deposition (CVD) temperatures leading to very low nucleation density and cementite (Fe₃C) formation. Therefore, the study of the nucleation and growth processes is timely and will yield data that can be utilised to get a better understanding of how adhesion can be improved. This work focuses on investigating the adhesion of thin diamond films on high speed steel previously coated with various interlayers such as ZrN, ZrC, TiC and TiC/Ti(C,N)/TiN. The role of seeding on nucleation density and the effect of diamond film thickness on stress development and adhesion has been investigated using SEM, XRD and Raman spectroscopy.The main emphasis in this study is the TiC interlayer which for the first time proved to be a suitable layer for diamond CVD on high speed steel (HSS). In contrast from other interlayer materials investigated here, no delamination was observed even after 3 h of CVD at 650 °C only when TiC was employed. Nevertheless, the increase of diamond film thickness on TiC coated HSS substrates led to the delamination of small areas in various regions of the substrate. This occurrence suggests that there was a distribution of adhesive toughness values at the diamond/TiC interface with stress development being dependent on film thickness.     

SiC fibre by chemical vapour deposition on tungsten filament

A CVD system for the production of continuous SiC fibre was set up. The process of SiC coating on 19 μ m diameter tungsten substrate was studied. Methyl trichloro silane (CH₃SiCl₃) and hydrogen reactants were used. Effect of substrate temperature (1300–1500°C) and concentration of reactants on the formation of SiC coating were studied. SiC coatings of negligible thickness were formed at very low flow rates of hydrogen (5 × 10⁻⁵ m³/min) and CH₃SiCl₃ (1.0 × 10⁻⁴ m³/min of Ar). Uneven coatings and brittle fibres were formed atvery high concentrations of CH₃SiCl₃ (6 × 10⁻⁴ m³/min of Ar). The flow rates of CH₃SiCl₃ and hydrogen were adjusted to get SiC fibre with smooth surface. The structure and morphology of SiC fibres were evaluated.     

Growth of diamond thin films by chemical vapour deposition

Deposition of diamond thin films on non-diamond substrates at low pressures (<760 torr) and low temperatures (<2000°C) by chemical vapour deposition (CVD) has been the subject of intense research in the last few years. The structural and the electrical properties of CVD diamond films grown on p-type 〈111〉 and high-resistivity (>100 kΩ-cm) 〈100〉 oriented silicon substrates by hot filament chemical vapour deposition technique are described in this review paper.     

Filament seasoning and its effect on the chemistry prevailing in hot filament activated gas mixtures used in diamond chemical vapour deposition

Tantalum hot filaments (HFs) find frequent use as a means of activating hydrocarbon/hydrogen mixtures used for chemical vapour deposition of thin film diamond. This contribution reports systematic studies of the power consumed by a tantalum HF, and companion laser based measurements of the relative H atom number densities in the gas phase adjacent to the HF surface, in pure H₂ and in dilute CH₄/H₂ gas mixtures, as a function of process conditions (filament temperature, gas pressure, extent of HF carburisation). The measurements serve to highlight the way in which the adjacent gas phase chemistry and composition affects the HF surface chemistry, and vice versa.     

Plasma-enhanced chemical vapor deposition of nanocrystalline diamond

Nanocrystalline diamond films have attracted considerable attention because they have a low coefficient of friction and a low electron emission threshold voltage. In this paper, the author reviews the plasma-enhanced chemical vapor deposition (PE-CVD) of nanocrystalline diamond and mainly focuses on the growth of nanocrystalline diamond by low-pressure PE-CVD. Nanocrystalline diamond particles of 200–700 nm diameter have been prepared in a 13.56 MHz low-pressure inductively coupled CH₄/CO/H₂ plasma. The bonding state of carbon atoms was investigated by ultraviolet-excited Raman spectroscopy. Electron energy loss spectroscopy identified sp²-bonded carbons around the 20–50 nm subgrains of nanocrystalline diamond particles. Plasma diagnostics using a Langmuir probe and the comparison with plasma simulation are also reviewed. The electron energy distribution functions are discussed by considering different inelastic interaction channels between electrons and heavy particles in a molecular CH₄/H₂ plasma.     

Plasma-enhanced chemical vapor deposition of nanocrystalline diamond

Nanocrystalline diamond films have attracted considerable attention because they have a low coefficient of friction and a low electron emission threshold voltage. In this paper, the author reviews the plasma-enhanced chemical vapor deposition (PE-CVD) of nanocrystalline diamond and mainly focuses on the growth of nanocrystalline diamond by low-pressure PE-CVD. Nanocrystalline diamond particles of 200–700 nm diameter have been prepared in a 13.56 MHz low-pressure inductively coupled CH₄/CO/H₂ plasma. The bonding state of carbon atoms was investigated by ultraviolet-excited Raman spectroscopy. Electron energy loss spectroscopy identified sp²-bonded carbons around the 20–50 nm subgrains of nanocrystalline diamond particles. Plasma diagnostics using a Langmuir probe and the comparison with plasma simulation are also reviewed. The electron energy distribution functions are discussed by considering different inelastic interaction channels between electrons and heavy particles in a molecular CH₄/H₂ plasma.     

The effective chemical vapour deposition rate of diamond

The effective chemical vapour deposition (CVD) rate of diamond, defined as the total thickness of diamond or as the mass of diamond deposited per unit time, may be increased by orders of magnitude by increasing the substrate area per unit volume. To obtain these high deposition rates, novel substrate designs are proposed that exploit three-dimensional arrays of small diameter wires or fibres. The analysis suggests that the increased diamond output should be achieved with no increase in the net gas flow or power consumption, which could lead to the more economic production of solid diamond shapes and of composites containing continuous or short diamond fibres, or particulate diamond. Estimates for the cost of CVD diamond made by the fibre array technique are compared with reported current and predicted costs for CVD diamond and estimates for the cost of CVD SiC.     

Diamond deposition on cemented carbide by chemical vapour deposition using a tantalum filament

Diamond deposition on WC-Co cemented carbide was examined by chemical vapour deposition using a tantalum filament. The filament was much superior to conventional tungsten filament for high-temperature use. Diamond film was deposited at a filament temperature up to about 2600 °C for tantalum filament, which was much higher than the maximum filament temperature available for tungsten (2000 °C). The critical methane concentration in H₂-CH₄ gas for diamond deposition became higher with increasing filament temperature. A deposition rate about 20 times higher was obtained when using a tantalum filament compared with a tungsten filament. The origin of the improved deposition rate of diamond on WC-Co substrate using a tantalum filament is discussed.     

热灯丝CVD金刚石膜的微结构和形貌对其电子性质的影响

利用热灯丝CVD法在硅衬底上合成出了金刚石膜。金刚石膜的质量和电子性质由扫描电子显微镜、拉曼谱、阴极发光及霍尔系数测量来表征。实验结果表明,沉积条件对金刚石膜电子性质和质量有重要影响。载流子迁移率随甲烷浓度增加而减少,但场发射随其增加而增强。压阻效应随微缺陷增多而降低。异质外延金刚石膜压阻因子在室温下100微形变时为1200,但含有大量缺陷的多晶金刚石膜压阻因子低于200,这是由于薄膜中缺陷态密度增加,并依赖于膜结构的变化。     

热丝化学气相沉积制备BDD薄膜电极的电催化特性

研究了热丝化学气相沉积法(HFCVD)制备得到掺硼金刚石膜电极电催化氧化典型有机物苯酚的特性.Raman光谱测试显示制备BDD电极具有较好的金刚石相,循环伏安测试表明该电极具有较高的析氧过电位(+2.3V vsSCE).在电催化氧化苯酚过程中,化学需氧量(COD)能够有效去除,降解过程中有较高的电流效率,在COD较高的情况下,瞬时电流效率(ICE)可达100%,随着COD的降低ICE逐渐减少.催化实验结果表明,BDD电极是一种优良的电催化降解有机物新型电极.     

A mechanism for crystal twinning in the growth of diamond by chemical vapour deposition

A model for the formation of crystal twins in chemical vapour deposited diamond materials is presented. The twinning mechanism originates from the formation of a hydrogen-terminated four carbon atom cluster on a local {111} surface morphology, which also serves as a nucleus to the next layer of growth. Subsequent growth proceeds by reaction at the step edges with one and two carbon atom-containing species. The model also provides an explanation for the high defect concentration observed in 111 growth sectors, the formation of penetration and contact twins, and the dramatic enhancement in polycrystalline diamond growth rates and morphology changes when small amounts of nitrogen are added to the plasma-assisted growth environments.     

Carbon helixes produced by hot filament assisted chemical vapor deposition

Carbon helix nanofibers were synthesized by a hot filament assisted chemical vapor deposition at a substrate temperature of 600 °C. It was observed that the formation of a carbon helix structure was attributed to the mixing of cobalt catalyst particles with copper. The diameter of carbon helixes varied from 20 to 500 nm. The growth mechanism and the structure of these carbon helix nanofibers are discussed based on scanning electron microscopy and Raman spectroscopy measurements.     

High thermal conductivity diamond coated graphite by microwave plasma chemical vapour deposition

Diamond film was grown on high thermal conductivity graphite substrate using microwave plasma chemical vapour deposition method. Nanodiamond particles were uniformly seeded on the substrate to generate high nucleation density by a spray gun. The continuous and high purity diamond film was obtained, and growth rate was up to 2.7 μm h^??1. The thickness, surface morphology, quality and composite phase of the film were analysed by SEM, Raman and X-ray diffraction. It was shown that graphite coated with diamond presented a higher thermal conductivity (520?W?m^??1 k^??1) than copper. Furthermore, this coated material with high thermal conductivity, good strength and non-conductive surface will make it possible to be widely used in thermal management field.     

Structure of diamond and diamond like carbon thin films grown by hot-filament chemical vapour deposition technique

Micro-crystalline diamond (MCD) and diamond like carbon (DLC) thin films were deposited on silicon (100) substrates by hot-filament CVD process using a mixture of CH₄ and H₂ gases at substrate temperature between 400–800°C. The microstructure of the films were studied by X-ray diffraction and scanning electron microscopy. The low temperature deposited films were found to have a mixture of amorphous and crystalline phases. At high temperatures (> 750°C) only crystalline diamond phase was obtained. Scanning electron micrographs showed faceted microcrystals of sizes up to 2μm with fairly uniform size distribution. The structure of DLC films was studied by spectroscopic ellipsometry technique. An estimate of the amount of carbon bonds existing insp ² andsp ³ form was obtained by a specially developed modelling technique. The typical values ofsp ³/sp ² ratio in our films are between 1·88–8·02. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Ion irradiation-induced modifications of diamond nanorods synthesised by microwave plasma chemical vapour deposition

Diamond nanorods (DNRs) synthesised by the high methane content in argon rich microwave plasma chemical vapour deposition (MPCVD) have been implanted with nitrogen ions. The nanorods were characterised by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The DNRs consist of single-crystalline diamond cores of 3–5?nm in diameter and several tens of nanometres in length. For purification from non-diamond contents, hydrogen plasma etching of DNRs was performed. Structural modifications of etched DNRs were studied after irradiating with 50?keV nitrogen ions under the fluence of 5?×?10¹⁴, 1?×?10¹⁵, 5?×?10¹⁵ and 1?×?10¹⁶?ions?cm^?2. Nitrogen-ion implantation changes the carbon–carbon bonding and structural state of the nanocrystalline diamond (NCD). Raman spectroscopy was used to study the structure before and after ion irradiation, indicating the coexistence of diamond and graphite in the samples. The results indicated the increase in graphitic and sp²-related content, at the expense of decrease in diamond crystallinity, for ion implantation dose of 5?×?10^15?cm^?2 and higher. The method proves valuable for the formation of hybrid nanostructures with controlled fractions of sp³–sp² bonding.