热丝法化学气相沉积金刚石系统温度分布与薄膜生长关系研究

对热丝化学气相沉积金刚石薄膜系统内的三种传热方式（传导、对流和辐射）进行了比较分析,数值计算了气相空间温度分布和衬底表面二维温度分布。采用热丝化学气相沉积工艺制备了金刚石薄膜,扫描电镜结果显示金刚石薄膜在不同生长区域呈现出与温度分布相关的微观结构与形貌。     

Laterally organized carbon nanotube arrays based on hot-filament chemical vapor deposition

Lateral porous anodic alumina (PAA) templates were used to organize carbon nanotubes (CNTs) grown by a hot-filament assisted chemical vapor deposition (HFCVD) process. For the CNT growth, we used a modified “home-made” HFCVD system with two independently powered filaments which are fitted respectively on the methane (CH₄) gas line, which serves as a carbon precursor and on the hydrogen (H₂) gas line, which acts as an etching agent for the parasitic amorphous carbon. Various activation powers of the hot filaments were used to directly or indirectly decompose the gas mixtures at relatively low substrate temperatures. A parametric study of the HFCVD process has been carried out for optimizing the confined CNTs growth inside the lateral PAA templates.     

Simulations of the Dependence of Gas Physical Parameters on Deposition Variables during HFCVD Diamond Films

During the growth of the hot filament chemical vapor deposition （HFCVD） diamond films, numerical simulations in a 2-D mathematical model were employed to investigate the influence of various deposition parameters on the gas physical parameters, including the temperature, velocity and volume density of gas. It was found that, even in the case of optimized deposition parameters, the space distributions of gas parameters were heterogeneous due primarily to the thermal blockage come from the hot filaments and cryogenic pump effect arisen from the cold reactor wall. The distribution of volume density agreed well with the thermal round-flow phenomenon, one of the key obstacles to obtaining high growth rate in HFCVD process. In virtue of isothermal boundary with high temperature or adiabatic boundary condition of reactor wall, however, the thermal roundflow was profoundly reduced and as a consequence, the uniformity of gas physical parameters was considerably improved, as identified by the experimental films growth.     

热丝化学气相沉积纳米金刚石修复损伤PCD刀具的研究

利用热丝化学气相沉积装置, 以聚晶金刚石片为衬底, 在氢气/丙酮/氩气反应体系中研究了衬底温度对纳米金刚石生长的影响。采用扫描电子显微镜对生长结果进行了表征, 结果表明在衬底温度950℃的情况下, 金刚石薄膜表面结构呈\     

HFCVD金刚石膜过程的气氛模拟与分析

对热丝法化学气相沉积金刚石膜过程的气氛进行了模拟与分析。使用GRI－Mech3.0甲烷燃烧过程C／H／O／N四元体系热化学反应机理和动力学数据，模拟并分析了HFCVD金刚石膜的C／H气相化学反应，通过对反应流的简单模拟得到了衬底位置气相组成，结果与前人实验数据吻合，探讨了灯丝温度、碳源浓度和碳源种类等因素变化对衬底位置气相组成的影响。结果表明甲基是金刚石膜生长最主要的前驱基团，其作用远高于乙炔，而超平衡态原子氢的存在对金刚石膜的质量至关重要。     

Synthesis and Growth Mechanism of Carbon Filaments by Chemical Vapor Deposition without Catalyst

Carbon filaments with diameter from several to hundreds micrometers were synthesized by chemical vapor deposition of methane without catalyst. The morphology, microstructure and mechanical properties of the carbon filament were investigated by scanning electronic microscopy, optical microscopy, X-ray diffraction and mechanical testing. The results show that the carbon filament is inverted cone shape and grows up along the gas flow direction. The stem of it is formed of annular carbon layers arranged in a tree ring structure while the head is made up of concentrical layers. The tensile strength of the carbon filament is increased after graphitization for the restructuring and growing large of graphene. The growth mechanism of carbon filament was proposed according to the results of two series of experiments with different deposition time and intermittent deposition cycles.     

Simulations of Temperature Field in HFCVD Diamond Films over Large Area

A three-dimensional model was developed to investigate the influence of various hot filaments parameters on substrate temperature fields that significantly affect the nucleation and growth of diamond films over large area by hot-filament chemical vapordeposition (HFCVD). Numerical simulated results indicated that substrate temperature varies as a function of hot filamentsnumber, radius, temperature, emissivity, the distance between filaments, and the distance between substrate and filamentsarrangement plane. When these filaments parameters were maintained at the optimal values, the homogeneous substrate temperature region of 76 mm×76 mm with the temperature fluctuation no more than 5% could be obtained by a 80 mm×80 mmhot filaments arrangement plane. Furthermore, the homogeneous region could be enlarged to 100 mm×100 mm under thecondition of supplementary hot filaments with appropriate parameters. All of these calculations provided the basis for speciallyoptimizing the hot filaments parameters to dep     

Filament poisoning at typical carbon nanotube deposition conditions by hot-filament CVD

We report on the poisoning of tungsten filaments during the hot-filament chemical vapour deposition process at typical carbon nanotube (CNT) deposition conditions and filament temperatures ranging from 1400 to 2000 °C. The morphological and structural changes of the filaments were investigated using scanning electron microscopy and X-ray diffraction, respectively. Our results conclusively show that the W-filament is not stable during the carburization process and that both mono- and ditungsten-carbides form within the first 5 min. Cracks and graphitic microspheres form on the carbide layer during the first 15 min at the temperatures ≥1600 °C. The microspheres subsequently coalesce to form a graphite layer, encapsulating a fully carburized filament at the temperature of 2000 °C after 60 min, which inhibits the catalytic activity of the filament to produce atomic hydrogen. The structural changes of the filament also induce variations in its temperature, illustrating the instability of the filament during the deposition of CNTs.     

Effect of single-walled carbon nanotubes on Bacillus anthracis cell growth, sporulation, and spore germination

In this study, the effect of single-walled carbon nanotubes (SWCNTs) on B. anthracis cell growth, spore formation, and spore germination was studied. We found that SWCNTs at a concentration of 100 microg/ml exhibited obvious antimicrobial activity on 10(6) cfu/ml B. anthracis cells. At 300 microg/ml, 1 h of SWCNTs treatment could inactivate B. anthracis cells by approximately 2 log viable cell reduction. The SWCNT treatment did not induce spore formation. We also found that SWCNTs were not effective in the inactivation of B. anthracis spores at concentrations from 50 microg/ml up to 300 microg/ml. Fluorescence microscopy and scanning electron microscopy were used to examine the interactions between SWCNTs and B. anthracis cells/spores. Analysis of these microscopic images suggested that the direct contact between SWCNTs and B. anthracis cells lead to cell membrane damage and the inactivation of cells, whereas the lack of tight direct contact between SWCNTs and spores was the reason accounting for its ineffectiveness in inactivating spores.     

Sublimation and deposition of carbon during internal resistance heating of carbon fibers

A carbon fiber tow subjected to internal resistance heating often breaks when its surface temperature is raised higher than about 2200°C. In this study, the cause of the tow breakage was investigated. Internal resistance heating gives rise to a large temperature distribution in the tow cross section, the temperature being at a maximum in the central region of the tow cross section. Because of this temperature distribution, carbon filaments in the tow are sublimated from the central region of the tow cross section, leaving a growing cavity; as a result the tow breaks. Some of the sublimated carbon deposits on the filaments in the low temperature region surrounding the sublimating region, forming a laminar texture around the filament surface. The structure of the deposited carbon was investigated by reflected light microscopy, by scanning electron and transmission electron microscopy, and by electron and wide-angle X-ray diffraction. The deposited carbon was found to be composed of carbon layer stacks with low in-plane stacking regularity.     

Nucleation and Oriented Textured Growth of Diamond Films on Si(100) via Electron Emission in Ho.t Filament Chemical Vapor Deposition

1. IntroductionIn recent years, there has been increasing illterest in the heteroepitaxial growth of diamond films'by chemicisl vapor deposition(CVD) owing to theirpromising applications for the electronic devices. Epitaxial diamond films have been successfully grown onc-BN and monocrystal diamond substrated~4]. However, it is a more imperative task to deposit heteroepitarial diamond films on St which was anticipated tobe as a low cost substrate to achieve synthesis of singlecrystalline diam…     

The dispersion of SWCNTs treated by dispersing agents in glass fiber reinforced polymer composites

It is an obstacle issue for carbon nanotubes (CNTs) particularly for single-wall carbon nanotubes (SWCNTs) with nano-level dispersion in fiber reinforced polymer matrix composites. In this paper, the dispersing agents such as Volan and BYK-9076 were employed to treat SWCNTs to improve their dispersion in the glass fiber/epoxy (GF/EP) composites. The dispersing results of SWCNTs in composites were observed by scanning electron microscopy (SEM). Then the glass transition temperature (T_g) of these kinds of composites with treated and untreated SWCNTs were obtained by dynamic mechanical thermal analysis (DMTA). Moreover, the flexural tests were performed on these composites. Based on the experiment results, the dispersion of SWCNTs was improved and the flexural property of SWCNTs/GF/EP composite was enhanced too.     

Covalent functionalization of single-walled carbon nanotubes with anthracene by green chemical approach and their temperature dependent magnetic and electrical conductivity studies

Single-walled carbon nanotubes (SWCNTs) were covalently functionalized with anthracene in molten urea by a green chemical approach. The anthracene functionalized single-walled carbon nanotubes (Ant-f-SWCNTs) were examined along with SWCNTs, using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, powder X-Ray diffraction (XRD), and scanning, and transmission electron microscopy. The observations revealed the functionalization of SWCNTs by anthracene. The temperature dependent magnetization (300–5 K) and electrical resistivity were also measured for both SWCNTs and Ant-f-SWCNTs. The electrical resistivity of Ant-f-SWCNTs at 300 K was found to be 1.27 KΩm, which is much lower than 388.55 KΩm for pristine. This indicated a 300 fold increase in conductivity at room temperature for Ant-f-SWCNTs when compared to SWCNTs. The temperature dependence of the conductivity provided an indication of the semiconducting behaviour.     

洁净单壁碳纳米管在Fe2O3／Al2O3二元气凝胶催化剂上的水辅助合成

分别以甲烷-氧气和甲烷-氢气-水的混合气作为反应气源,利用Fe2O3/Al2O3二元气凝胶作为催化剂于900℃反应30min合成了单壁碳纳米管.并采用SEM、XRD、TEM,高分辨透射电子显微镜(HRTEM)以及Raman光谱等分析技术对所制得的碳产物的结构和形貌进行了表征,以研究反应气氛中水蒸气的引入对单壁碳纳米管生长的影响.结果表明:反应气氛的组成对最终所形成的碳产物的产率和结构有着密切的关联.通过控制氢气载入甲烷-氢气-水的混合气氛中水蒸气的量可以合成低无定形碳的沽净单壁碳纳米管.     

利用场发射显微镜研究单壁碳纳米管的场发射特性

利用场发射显微镜研究了单壁碳纳米管(SWCNTs)的场发射特性.由于实验中所用的SWCNTs的长度基本一致,因此能同时观察到多根SWCNTs的场发射像.SWCNTs的场发射像随着热处理温度的升高而变化,直至热处理温度过高而塌缩.在一定的实验条件下,观察到了具有精细结构的单根碳纳米管顶端"帽子"的场发射像.电流-电压(I-U)曲线分析表明,SWCNTs的电流来源于场发射.     

Degradation and silicidation of Ta- and W-filaments for different filament temperatures

Using typical conditions for hot wire chemical vapour deposition (HWCVD) of high quality thin silicon films in a UHV deposition chamber, we studied the silicidation of different filaments mainly varying the filament temperatures between 1700 °C and 2130 °C. The experiments were done with constant current, running the filament for 5 to 8 h and even longer. The changes of filament resistance and filament temperature with time will be shown and discussed. We investigated the material changes over the whole filament by Scanning Electron microscopy (SEM), especially the thickness of the formed silicide layers. The change of filament resistance depending on the filament temperature was also monitored, pointing out the different behaviour of tungsten and tantalum filaments. As a result, optimum temperature regimes for tantalum and tungsten filaments could be derived with respect to the filament degradation reducing the filament lifetime. Using a specially developed protection for the cold ends, a tungsten filament could be run for more than 139 h under silane with a filament temperature of T_fil ≈ 2000 °C.     

Surface transformations of carbon (graphene, graphite, diamond, carbide), deposited on polycrystalline nickel by hot filaments chemical vapour deposition

The deposition of carbon has been studied at high temperature on polycrystalline nickel by hot filaments activated chemical vapor deposition (HFCVD). The sequences of carbon deposition are studied by surface analyses: Auger electron spectroscopy (AES), electron loss spectroscopy (ELS), X-ray photoelectron spectroscopy (XPS) in a chamber directly connected to the growth chamber. A general scale law of the (C/Ni) intensity lines is obtained with a reduced time. Both, shape analysis of the AES C KVV line and the C1s relative intensity suggest a three-step process: first formation of graphene and a highly graphitic layer, then multiphase formation with graphitic, carbidic and diamond-like carbon and finally at a critical temperature that strongly depends on the pretreatment of the polycrystalline nickel surface, a rapid transition to diamond island formation. Whatever the substrate diamond is always the final product and some graphene layers the initial product. Moreover it is possible to stabilize a few graphene layers at the initial sequences of carbon deposition. The duration of this stabilization step is strongly depending however on the pre-treatment of the Ni surface.     

On the role of activation mode in the plasma- and hot filaments-enhanced catalytic chemical vapour deposition of vertically aligned carbon nanotubes

Catalytic chemical vapor deposition (CCVD) with different activation modes (thermal; hot filaments-enhanced; direct current plasma-enhanced and both hot filament and direct current plasma-enhanced) are achieved in order to grow vertically aligned carbon nanotubes (VA CNTs). By widely varying the power of the different activation sources of the gas (plasma, hot filaments, substrate heating) while keeping identical the substrate temperature (973 K) and the catalyst preparation, the results point out the important role of ions in the nucleation of carbon nanotubes (CNTs), as well as the etching behaviour of highly activated radicals such as H˙ in the selective growth of vertically aligned films of CNTs. Moreover, it is demonstrated that, within the deposition conditions (temperature, pressure, flow rate) used in this study, oriented carbon nanotubes can be grown only when both ions, mainly generated by the gas discharge plasma, and highly reactive radicals, mainly formed by the hot filaments, are produced in the gas phase. We propose that highly energetic ions are needed to nucleate the carbon nanotubes by increasing the carbon concentration gradient whereas the highly reactive radicals allow the selective growth of vertically aligned CNTs by preventing carbon deposition on the whole surface through chemical etching of edge carbons in graphene sheets.     

热丝法化学气相沉积大面积金刚石膜中辐射场和温度场的尺寸效应

对热丝法化学气相沉积金刚石膜中的辐射场和温度场进行了计算，结果表明，在样品平面沿Ｘ，Ｙ方向均辐照度（温度）区的线性尺寸比高温梯度区的尺寸快速增大，沿Ｚ方向均匀辐照度（温度）区的深度随样品到加热丝距离的增加而增大，辐照度（温度）的大小可通过改变加热丝间距得到控制。     

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.