FABRICATION OF DIAMOND TUBES IN BIAS-ENHANCED HOT-FILAMENT CHEMICAL VAPOR DEPOSITION SYSTEM

Deposition of diamond thin films on tungsten wire substrate with the gas mixture of acetone and hydrogen by using bias-enhanced hot filament chemical vapor deposition（CVD）with the tantalum wires being optimized arranged is investigated.The self-supported diamond tubes are obtained by etching away the tungsten substrates.The quality of the diamond film before and after the removal of substrates is observed by scanning electron microscope（SEM）and Raman spectrum.The results show that the cylindrical diamond tubes with good quality and uniform thickness are obtained on tungsten wires by using bias enhanced hot filament CVD.The compressive stress in diamond film formed during the deposition is released after the substrate etches away by mixture of H2O2 and NH4 OH.There is no residual stress in diamond tube after substrate removal.

Preliminary Investigation on a Sheet Plasma Produced by a Single Hot-Filament Cathode Discharge

A sheet plasma is generated by a mesh anode and a single hot-filament cathode with a DC power supply, and its characteristics are experimentally investigated. The sheet plasma is observed to locate around the anode. Both electron density and electron temperature derived from the average energy of the energetic electrons in nitrogen are estimated to be 10s cm^-3 and 20- 40 eV, respectively, using the optical emission spectroscopy （OES） method based on a kinetic model of low-pressure nitrogen discharge. The electron density, electron temperature and their spatial distributions are found to be affected by the supplying voltage on the anode（70 V to 300 V）, filament temperature （600℃ to 780℃） and gas pressure （2 Pa to 20 Pa）. By adjusting these parameters the discharge status can be easily controlled.

Formation and Transport of Atomic Hydrogen in Hot-Filament Chemical Vapor Deposition Reactors

In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant is hydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless numbers for heat and mass transfer reveals that thermal conduction and diffusion are the dominant mechanisms for gas-phase heat and mass transfer, respectively. A simplified model has been established to simulate gas-phase temperature and H concentration distributions between the filament and the substrate. Examination of the relative importance of homogeneous and heterogeneous production of H atoms indicates that filament-surface decomposition of molecular hydrogen is the dominant source of H and gas-phase reaction plays a negligible role. The filament-surface dissociation rates of H2 for various filament temperatures were calculated to match H-atom concentrations observed in the literature or derived from power consumption by filaments. Arrhenius plots of the filament-surface hydrogen dissociation rates suggest that dissociation of H2 at refractory filament surface is a catalytic process, which has a rather lower effective activation energy than homogeneous thermal dissociation. Atomic hydrogen, acting as an important heat transfer medium to heat the substrate, can freely diffuse from the filament to the substrate without recombination.

Response of the low-pressure hot-filament discharge plasma to a positively biased auxiliary disk electrode

In a steady-state plasma,the loss rate of plasma particles to the chamber wall and surfaces in contact with plasma is balanced by the ionization rate of background neutrals in the hot-filament discharges.The balance between the loss rate and ionization rate of plasma particles(electrons and ions)maintains quasi-neutrality of the bulk plasma.In the presence of an external perturbation,it tries to retain its quasi-neutrality condition.In this work,we studied how the properties of bulk plasma are affected by an external DC potential perturbation.An auxiliary biased metal disk electrode was used to introduce a potential perturbation to the plasma medium.A single Langmuir probe and an emissive probe,placed in the line of the discharge axis,were used for the characterization of the bulk plasma.It is observed that only positive bias to the auxiliary metal disk increases the plasma potential,electron temperature,and plasma density but these plasma parameters remain unaltered when the disk is biased with a negative potential with respect to plasma potential.The observed plasma parameters for two different-sized,positively as well as negatively biased,metal disks are compared and found inconsistent with the existing theoretical model at large positive bias voltages.The role of the primary energetic electrons population in determining the plasma parameters is discussed.The experimentally observed results are qualitatively explained on the basis of electrostatic confinement arising due to the loss of electrons to a biased metal disk electrode.

Friction and Cutting Properties of Hot-Filament Chemical Vapor Deposition Micro-and Fine-grained Diamond Coated Silicon Nitride Inserts

The micro-crystalline diamond (MCD) and fine-grained diamond (FGD) films are deposited on commercial silicon nitride inserts by the hot-filament chemical vapor deposition (HFCVD) method. The friction andcutting properties of as-deposited MCD and FGD films coated silicon nitride (Si3N4) inserts are comparatively investigated in this study. The scanning electron microscopy (SEM) and Raman spectroscopy are adopted to studythe characterization of the deposited diamond films. The friction tests are conducted on a ball-on-plate typereciprocating friction tester in ambient air using Co-cemented tungsten carbide (WC-Co), Si3N4 and ball-bearing steel (BBS) balls as the mating materials of the diamond films. For sliding against WC-Co, Si3N4 and BBS,the FGD film presents lower friction coeffcients than the MCD film. However, after sliding against Si3N4, the FGD film is subject to more severe wear than the MCD film. The cutting performance of as-deposited MCD and FGD coated Si3N4 inserts is examined in dry turning glass fiber reinforced plastics (GFRP) composite materials,comparing with the uncoated Si3N4 insert. The results indicate that the lifetime of Si3N4 inserts can be prolonged by depositing the MCD or FGD film on them and the FGD coated insert shows longer cutting lifetime than the MCD coated one.

Si3N4工程陶瓷基底金刚石涂层生长规律及性能

为了避免氮化硅材料因产生裂纹或延伸破裂等造成的失效,利用热丝化学气相沉积法(Hot filament chemical vapor deposition,HFCVD)在氮化硅基底上沉积具有高硬度的金刚石涂层,采用单因素影响试验,分别探究碳源浓度、腔室压力、基底温度对金刚石成膜过程的影响机制,探究微米和纳米金刚石涂层的最优生长工艺参数。利用拉曼光谱仪(Raman)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)和原子力显微镜(AFM)对不同参数制备出的金刚石的形核、表面形貌、薄膜质量、表面粗糙度等进行表征,利用洛氏硬度计分析膜基结合力。结果表明,腔室压力越大,活性物质到达基底的动能越小,不利于金刚石的成核和生长。生长速率和表面粗糙度主要受甲烷浓度的影响:甲烷浓度从1%到7%,生长速率从0.84μm/h上升到1.32μm/h;表面粗糙度Ra从53.4 nm降低到23.5 nm;甲烷浓度过高导致涂层脱落严重,膜基结合力变差;晶面形貌和金刚石含量受到基底温度的影响较为明显,随着温度升高,金刚石质量提高。综合基底温度、腔室压力对金刚石涂层的影响,确定最佳生长温度为900℃,气压为1 kPa。调节甲烷浓度1%为微米金刚石;甲烷浓度5%为纳米金刚石。研究方法可以优化在陶瓷基底上制备具有优异性能的金刚石薄膜的制备参数。

热丝化学气相沉积法制备单晶金刚石的试验研究

热丝化学气相沉积法沉积区域可达12英寸(30.48 cm),其具备大批量生产单晶金刚石的潜力。采用尺寸为3 mm×3 mm×1 mm,(100)取向的单晶金刚石为基体,利用热丝化学气相沉积法以甲烷和氢气为前驱体,同时通入少量氮气进行同质外延生长。结果表明,在热丝温度为2200℃、碳源浓度为4%、腔体气压为4 kPa的条件下,单晶金刚石以3.41μm/h的速度生长,表面无多晶、破口、孔洞等缺陷;外延层X射线衍射光谱在(400)面处峰值的半高宽为0.11°,低于基体的半高宽0.16°,证明外延层具有较高的晶体质量;氮气的引入可以提升单晶金刚石的生长速度,同时降低外延层的晶体质量,较高的氮气浓度还会使得单晶金刚石的生长模式转为岛状生长。

热阴极离子规阴极灯丝断裂机理研究

介绍热阴极离子规的工作原理及组成结构,从热阴极灯丝变细、材料缺陷和工艺缺陷3方面分析离子规阴极灯丝断裂机理,根据断裂机理提出使用过程中的一些建议,以便延长使用寿命。

CVD金刚石膜研究进展

金刚石由于其优异的声、光、电、热和力学性能,是重要的功能材料之一。金刚石的制备方法主要有高温高压方法和低压化学气相沉积方法。化学气相沉积法因制备得到的样品质量高、面积大,设备简单、可规模化等特性,是合成金刚石膜的重要方法。为了实现低合成压力条件下的金刚石膜的均匀、快速、大尺寸、高质量生长,目前研究人员在金刚石低压生长的控制方面做出了深入的研究。文章综述了近年来化学气相沉积法(包括热丝CVD法、离子体增强CVD法、燃烧火焰CVD法)生长金刚石膜的研究进展,包括金刚石膜的生长机理、关键设备、关键工艺参数等。此外,还详细讨论了生长过程中的关键工艺参数与金刚石膜生长速率和质量的关系,这些对化学气相沉积制备金刚石膜的研究、生产至关重要。

面向散热应用的碳化硅表面热丝化学气相沉积金刚石膜生长速率

金刚石具有极高的导热系数,在热管理中具有广阔的应用前景.基于热丝化学气相沉积法,采用多次沉积工艺在碳化硅表面制备了金刚石厚膜.采用扫描电子显微镜和拉曼光谱仪对金刚石膜进行了表征,系统地研究了热丝功率、碳源浓度和反应压力等工艺参数对金刚石生长速率及质量的影响.研究结果表明,当热丝功率为1600 W、碳源浓度在形核阶段为18/300和生长阶段为14/300、反应压力为4 kPa时制备的金刚石膜质量最佳,此时金刚石膜生长速率约为1.4μm/h.

Si_(3)N_(4)基底表面粗糙度对HFCVD法制备金刚石薄膜摩擦学性能的影响

采用热丝化学气相沉积法(hot filament chemical vapour deposition,HFCVD)在不同表面粗糙度的Si3N4基底表面制备金刚石薄膜,并对薄膜的特性进行检测与分析。利用场发射电子扫描显微镜、原子力显微镜检测植晶后的Si3N4基底表面以及制备的金刚石薄膜表面形貌;利用多功能摩擦磨损实验机、探针式轮廓仪,在干摩擦条件下,测试金刚石薄膜的摩擦系数及磨损率。综合基底粗糙度对植晶质量的影响、金刚石薄膜表面形貌与摩擦磨损检测实验结果,确定了Si3N4基底表面粗糙度对金刚石薄膜耐磨性的影响。结果表明:基底表面粗糙度会影响植晶的均匀性及致密性,进而影响金刚石颗粒在基底表面的生长,同时基底的表面形貌也会复映在金刚石薄膜表面。表面粗糙度为0.15μm和0.20μm的基底所制备的金刚石薄膜拥有较好的耐磨性,可得到最低的磨损率1.75×10^(−7)mm^(3)/(m·N)和最低的摩擦系数0.078。

多片式衬底HFCVD系统沉积金刚石颗粒物理场的仿真优化

探索热丝化学气相沉积(hot filament chemical vapor deposition,HFCVD)合成高效优质的金刚石已成为研究热点。采用可提高金刚石颗粒单次沉积产量的新型多片式栅状衬底,应用FLUENT流体仿真软件,在原有单个出气口数量及进气总流量保持不变的情况下,优化传统模型,将单个进气口拆分成5个大小相等的进气口,对影响金刚石单晶颗粒均匀性的进气口数量和排布方式工艺参数进行仿真,对比分析HFCVD系统内气体的物理场。结果显示:4组优化模型均提高了衬底温度及流速的均匀性,有利于金刚石单晶颗粒的均匀生长,但对其沉积速率影响不显著;进一步分析优化模型的温度场,发现5个进气口及单个出气口分别位于反应腔体顶部和底部的中间位置时系统的温度差最低,最满足金刚石单晶颗粒在多片式硅衬底上均匀生长的条件。HFCVD金刚石单晶颗粒沉积试验验证了仿真结果的正确性。

化学前处理对硬质合金基材及金刚石涂层性能的影响

为提高金刚石涂层与硬质合金基体的适配性,采用热丝化学气相沉积技术在YG6硬质合金表面制备金刚石涂层,利用扫描电镜、能谱仪、原子力显微镜和固体颗粒冲蚀试验仪分析检测了试样的表截面形貌、成分深度分布、表面粗糙度、抗砂粒冲蚀性能等,研究了不同化学前处理对基材和涂层性能的影响。结果表明:两步法前处理去除钴的深度约4—5μm,并且形成了厚约1—2μm的脱钴脆性层;三步法前处理去除钴的深度约14—15μm,没有出现脱钴脆性层;三步法化学前处理后沉积的金刚石涂层抗砂粒冲蚀时间为两步法化学前处理的4倍以上,并且涂层脱落区宽度仅为两步法化学前处理的1/8,说明三步法化学前处理后所沉积的金刚石涂层的性能比两步法的更优越。

化学处理对刀具表面金刚石涂层薄膜的影响研究

阐述了热丝化学气相沉积法(HFCVD)涂覆金刚石涂层时,采用Murakami溶液和HNO3溶液进行化学预处理对刀具表面金刚石涂层薄膜的影响。采用扫描电子显微镜、能谱仪和拉曼光谱仪进行检测,结果表明,硬质合金中的黏结相Co元素和表面粗糙程度对涂层金刚石薄膜有较大影响,采用Murakami溶液浸蚀3min以上、HNO3溶液浸蚀5min以上的刀具涂层表现出优越的性能,刀具寿命是未涂层刀具的2~4.5倍。

硼掺杂金刚石涂层拉丝模具的制备与应用

采用热丝化学气相沉积法制备出硼掺杂金刚石薄膜,激发出了金刚石薄膜的电学性能,结合金刚石薄膜在工具方向的应用,成功制备出硼掺杂金刚石涂层拉丝模具,在硼掺杂金刚石薄膜制备过程中使用扫描电子显微镜、X射线衍射仪和显微拉曼光谱仪进行物相分析。利用硼掺杂金刚石薄膜的电学性能,探讨硼掺杂金刚石拉丝模芯与慢走丝切割之间的应用,结果表明:慢走丝切割硼掺杂金刚石拉丝模芯后,模芯抛光余量大幅减小,模芯制备效率和成品率大幅提高,在实际拉拔测试时硼掺杂金刚石拉丝模具表现出优异的性能,模具寿命和拉拔质量远高于未掺杂的金刚石涂层拉丝模具。

基于多元线性回归的烘丝出口水分影响因素的研究

在制丝生产线中滚筒式烘丝机是关键设备之一,通过干燥方法来去除叶丝或梗丝中的水分,使其含水率从18%左右下降至13%左右,同时含水率允差控制在±0.5%以内,满足卷烟工艺技术要求。采用多元线性回归分析方法,通过对烘丝入口水分稳定变化下适时调整烘丝风速,以达到稳定出口水分数据的分析,计算出出口叶丝含水率与HT入口烟丝含水率、HT蒸汽压力、筒壁温度的回归方程。通过试验验证得出,在实际制丝线生产过程中,当HT入口水分发生变化时,按照该方程可以有效指导热风风速的调整。

HFCVD衬底三维温度场有限元法模拟

热丝化学气相沉积(Hot filament chemical vapor deposition,HFCVD)方法制备金刚石薄膜设备简单,成本低廉,适合大面积金刚石膜的产业化生产,其中衬底温度是沉积高质量CVD金刚石膜的重要参数之一。基于此,首先分析大面积HFCVD系统的热交换过程,建立大面积HFCVD系统衬底温度场的三维有限元模型。与传统纯热辐射模型相比,本模型更加接近实际系统,并较好符合试验测定的结果。根据三维有限元模型开展对大面积HFCVD系统衬底温度场的有限元仿真研究,得到HFCVD系统衬底温度场的三维分布规律,并讨论热丝直径、热丝温度、热丝根数、热丝-衬底距离和水冷散热系数等对衬底温度大小及均匀性的影响。仿真结果表明,在适宜金刚石膜生长的参数范围内,热丝参数和衬底接触热阻对衬底温度大小有显著影响,由于衬底内部的三维热传导使得衬底温度场更加均匀,各参数对衬底温度场的均匀性影响不大。研究结果为高质量制备金刚石膜提供理论基础。

热丝CVD大面积金刚石薄膜的生长动力学研究

在传统工业型热丝化学气相沉积(HFCVD)反应腔内,相关工艺参数取模拟计算优化值的条件下,采用XRD,SEM及Ram an光谱等分析手段研究了单晶S i(100)上较大面积金刚石薄膜的动力学生长行为,讨论了晶格取向的变化规律。结果表明:优化工艺参数条件下,在模拟计算的衬底温度和气体温度分布均匀的区域内,沉积的金刚石薄膜虽存在一定的内应力,但整体薄膜连续、均匀,几何晶形良好,质量较高,生长速率达1.8μm/h。薄膜生长过程中晶形显露面受衬底温度和活性生长基团浓度的影响较大。

高性能复杂形状金刚石薄膜涂层刀具的制备和切削性能研究

通过偏压辅助增强热丝化学气相沉积法,采用螺旋形热丝排布方式以及优化的预处理方法和沉积工艺,在硬质合金印刷电路板铣刀的表面沉积了均匀的金刚石薄膜,采用扫描电镜和拉曼光谱研究了金刚石薄膜的表面特征。随后,通过铣削试验研究了金刚石涂层刀具的附着强度和切削性能。试验结果表明,复杂形状金刚石薄膜涂层铣刀既具有附着力强、耐磨性好的特点,同时又具备优异的切削性能,并且其制备无需后续抛光处理就能得到平整光滑的表面,这对于推动金刚石薄膜在复杂形状刀具上的产业化应用具有重要意义。

连续多试样纳米金刚石膜沉积设备及工艺

首先对热丝化学气相沉积(Chem ica l vapor depos ition,CVD)系统进行改造,设计了在真空室外对室内试样进行操纵的机械手系统和储料台,实现了一次热丝碳化后完成多个不同工艺条件下试样的连续沉积。有限元仿真研究结果表明,多衬底温度场比较均匀,适合于金刚石膜的生长。最后,采用改进沉积系统,在A r-CH4-H2气氛中,在多晶钼衬底上成功制备了纳米金刚石薄膜。R am an,XRD和AFM等结果表明,制备的金刚石纯度较高,晶粒大小在30 nm左右,表面光滑。