Growth and characterization of diamond particles,diamond films,and CNT-diamond composite films deposited simultaneously by hot filament CVD

It is important to understand the growth of CNT-diamond composite films in order to improve the inter-link between two carbon allotropes, and, in turn, their physical properties for field emission and other applications. Isolated diamond particles, continuous diamond thin films, and thin films of carbon nanotubes (CNTs) having non-uniformly distributed diamond particles (CNT-diamond composite films) were simultaneously grown on unseeded, seeded, and catalyst pre-treated substrates, respectively, using a large-area multi-wafer-scale hot filament chemical vapor deposition. Films were deposited for four different growth durations at a given deposition condition. The changes in surface morphology and growth behavior of diamond particles with growth duration were investigated ex situ using field emission scanning electron microscopy and 2D confocal Raman depth spectral imaging, respectively. A surface morphological transition from faceted microcrystalline nature to nanocrystalline nature was observed as a function of growth duration in the case of isolated diamond particles grown on both unseeded and catalyst pre-treated substrates. However, such a morphological transition was not observed on the simultaneously grown continuous diamond thin films on seeded substrates. 2D confocal Raman depth spectral imaging of diamond particles showed that the local growth of CNTs did not affect the growth behavior of neighboring diamond particles on catalyst pre-treated substrates. These observations emphasize the importance of surface chemical reactions at the growth site in deciding sp² or sp³ carbon growth and the final grain size of the diamond films.     

Wear of diamond particles for grinding ceramics

The relative wear of a single point diamond, defined in terms of the grinding force, was determined for a group of A1₂O₃ and Si₃N₄. It was found that the wear rate is directly related to the mechanical properties of the workpiece and the grinding environment.     

金刚石表面镀钨对铜/金刚石复合材料热导率的影响

利用粉末覆盖烧结法成功在金刚石表面镀覆W,并采用气体压力熔渗法制备Cu/diamond(W)复合材料。研究了不同镀覆温度对镀层微观结构以及复合材料热导率的影响。结果表明,金刚石表面镀钨有效的改善了界面结合,提高了复合材料热导率。镀层厚度随镀覆温度的提高而明显增加,复合材料热导率先增高再降低。当镀覆工艺为1 050℃保温15 min时,镀层厚度为2 000nm,复合材料热导率最高可达到670 W/mK。     

Self-organization of ultradisperse diamond particles heated at high pressures

Diamond single crystals with decahedral and icosahedral faceting and dimensions of 50–80 nm have been obtained by high-temperature high-pressure treatment of an ultradisperse detonation-synthesized diamond (UDD) powder. It is concluded that the growth of diamonds is related to the oriented association of initial UDD nanoparticles, the driving force of which is the tendency of the system to the state of minimum surface energy. The crystal habit is determined by the crystal morphology of UDD nanoparticles, which possess regular polyhedral shapes and flat facet morphology.     

On the mechanism of forming nanosized particles of diamond detonation synthesized from explosive decomposition products

A brief generalization of the known data on the structural state of detonation_synthesized ultradispersed diamond (UDD) and the mechanism of its formation have been discussed. The data of our electron microscopy studies of UDD have been considered and on their basis the structural “marks” (like crystal geometry, sizes of independent particles, the nature of their organization and consolidation in flaky aggregates, etc.) have been revealed, which are diagnostic indications of the UDD formation from graphite by martensitic mechanism. A possible mechanism of the formation of graphite as a primary phase in the detonation synthesis of UDD has been suggested.     

Temperature enhanced gas sensing properties of diamond films

Nanocrystalline diamond (NCD) film was used as a functional part of gas sensor. The gas sensing properties of H-terminated nanocrystalline diamond films were examined to oxidizing gases (i.e., COCl₂ and humid air). Pronounced increase in the surface conductivity (3 orders of magnitude) was found after sensor exposure to phosgene gas and was explained by the surface transfer doping effect. We also present a possible way how to achieve sensor selectivity, i.e. how to distinguish between phosgene and humid air (the mostly present background gas in a common environment).     

New method for preparing composite containing nanometre diamond particles

Abstract

Different powder mixing methods were used to prepare Al-5Cu and Cu-10Sn wt- based composites containing nanometre diamond. A new method for obtaining ultrafine Cu, Sn particles and a good distribution of nanometre diamond aggregates was developed. The nanometre diamond aggregates were well dispersed in the Cu-10Sn matrix. However, the distribution of nanometre diamond in the Al-5Cu based composite was unacceptable. Owing to the dispersion of nanometre diamond, Cu-10Sn based composite possessed higher hardness and lower bend strength than Cu-10Sn alloy.     

金刚石颗粒增强铝基复合材料的力学性能

采用压力熔渗法制备Al/金刚石复合材料,探讨金刚石粒度对复合材料微观形貌、力学性能和断口形貌的影响。结果表明复合材料的力学性能随金刚石粒径的减小逐渐升高,金刚石粒度为400/500目时,Al/金刚石复合材料的抗拉强度为145MPa,抗压强度为1020MPa,抗弯强度达到310MPa。     

Size distributions of nanoscaled particles and gas temperatures from time-resolved laser-induced-incandescence measurements

Laser-induced-incandescence (LII) signal decays are measured in sooting premixed atmospheric and low-pressure flames. Soot particle temperatures are obtained from LII signals measured at two wavelengths. Soot particle size distributions P(r) and flame temperatures T are measured spatially resolved by independent techniques. Heat and mass transfer kinetics of the LII process are determined from measured soot particle temperatures, flame temperatures, and particle sizes. Uncertainties of current LII models are attributed to processes during the absorption of the laser pulse. Implications for LII experiments are made in order to obtain primary soot particle sizes. Soot particle size distributions and flame temperatures are assessed from measured particle temperature decays by use of multi-D nonlinear regression.     

Discharge of a gas with solid particles from nozzles at critical velocities

Problems of the gas dynamics of two-phase flow with critical discharge conditions are considered. The flow parameters (pressure, density, and velocity of the gas) are calculated in one-dimensional approximation in convergent and cylindrical nozzles. The calculated data are compared with the experimental results obtained by investigating the discharge of a mixture of air and solid particles.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 4, pp. 648–652, April, 1970.     

Synthesis of carbon films containing diamond particles by electrolysis of methanol

Carbon films containing diamond particles were deposited onto a Si (100) substrate by electrolysis of methanol under a direct current potential of 1200 V, with a current density of about 52 mA/cm², at atmospheric pressure and in the temperature range of 50-55 °C. The surface morphology, microstructure and crystalline structure of the deposited films were characterized by scanning electron microscopy (SEM), Fourier transformation infrared (FTIR) spectroscopy, Raman spectroscopy and transmission electron microscopy (TEM) respectively. The SEM images show that the films are formed by particle clusters and a surrounding glassy phase. The Raman spectra of the films indicate that the particle clusters are composed of diamond and that the glassy phase is composed of amorphous carbon. The FTIR measurements suggest the existence of hydrogen which is mainly bonded to the sp³ carbon in the films. The transmission electron diffraction patterns further indicate that the particles in the films consist of single-crystalline diamond. Both TEM and Raman measurements have confirmed unambiguously the formation of diamond crystals in the deposit, although the particles are not uniformly distributed on the entire surface.     

The influence of working gas on CVD diamond quality

The effect of the working gas pressure and its composition on diamond quality and particles size was investigated. The diamond layers were grown in Hot Filament Chemical Vapor Deposition (HF CVD) reactor. A methanol–hydrogen gas mixture was used as the precursor gas. The structure of these films was characterized by scanning electron microscopy (SEM) and micro-Raman spectroscopy. Typically, the diamond's crystallite size decreased with increasing pressure and increasing with methanol concentration. Additionally the admixture of non-diamond (sp²-hybridized carbon) phase also increased with increasing both of deposition pressure and of methanol concentration. It was observed that the deposition pressure has a weaker influence on diamond quality than the methanol concentration.     

Effective thermal conductivity of Cu/diamond composites containing connected particles

An analytical model for the thermal conductivity of Cu/diamond composites with connected particles is presented by replacement of a cluster of connected particles with an equivalent polycrystal subsequently using a multiple effective medium approach. By applying this model to the measured thermal conductivity of Cu/diamond composites prepared by high pressure high temperature sintering technique reported in the literature, we show that it quite well describes the observed thermal conductivity enhancement induced by the connected particles. We estimate the value of connected particle loading in real composites and show that large particles are easier to form the bonding contact than small particles. The present work also demonstrates that the sensitivity of thermal conductivity contribution from the connected particles strongly depends on the particle size, and their pronounced thermal conductivity enhancement should lie within the certain particle size range.     

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.     

金刚石微米聚晶结构的生长及其场发射特性研究

在覆盖金属钛层的陶瓷上,利用微波等离子体化学气相沉积(MPCVD)法制备出类球状微米金刚石聚晶薄膜.利用扫描电子显微镜、拉曼光谱、X射线衍射,分析了薄膜的结构和表面形貌.测试了类球状微米金刚石聚晶膜的场致电子发射特性.开启电场仅为0.55V/μm,在2.18V/μm的电场下,其场发射电、流密度高达11mA/cm2.对类球状微米金刚石聚晶阵列形成机理和场发射机理进行了研究.     

Dissolution behaviour of fine particles of diamond under high pressure sintering conditions

On leave from: Chengdu University of Science and Technology, Chengdu, People's Republic of China.