硅基底上生长金刚石层细晶粒的研究

金刚石/硅声表面波基片的金刚石层晶粒的细化有利于传播损耗的降低,本文采用热丝化学气相沉积法进行了硅基体上沉积细晶粒金刚石工艺的初步探索.探讨了基体温度、气压、氩气和甲烷浓度等因素对金刚石细晶粒生长的影响.对相应样品进行了扫描电镜和拉曼散射谱分析.结果表明:在低气压范围,相同氩气浓度,随着气压的降低,甲烷浓度也要相应降低,能保证金刚石结晶质量.同时,降低气压达到一定值后,金刚石晶粒尺寸变小,经测试可达到纳米级.     

氢气浓度对掺氮超纳米金刚石薄膜的影响

采用微波等离子体化学气相沉积法,以甲烷和氮气为气源,通过改变反应气体中氢气的浓度,在硅衬底上沉积出掺杂氮的超纳米金刚石膜.并利用扫描电子显微镜,拉曼光谱仪,X射线衍射仪,霍尔效应测试仪分别对掺杂氮的超纳米金刚石膜的表面形貌,组成结构及导电性能进行了进行表征,重点研究了氢气浓度对薄膜特性的影响.结果表明:随着氢气浓度的增加,薄膜的晶粒尺寸逐渐增大;薄膜的质量提高,且由G峰漂移引起的压应力逐渐减小;薄膜导电性变差.     

加氮对直流电弧等离子体喷射金刚石膜生长、形貌和质量的影响

利用直流等离子体喷射化学气相沉积法制备掺氮的金刚石厚膜.本文研究了在甲烷/氩气/氢气中加入氮气对金刚石膜生长、形貌和质量的影响.反应气体的比例由质量流量计控制,在固定氢气(5000sccm)、氩气(3000sccm)、甲烷(100sccm)流量的情况下改变氮气的流量,即反应气体中氮原子和碳原子的变化比例(N/ C比)范围是从0.06到0.68.同时金刚石膜在固定的腔体压力(4kPa)和衬底温度(800℃)下生长.金刚石膜用扫描电镜(SEM)、拉曼谱和X射线衍射表征.结果表明,氮气在反应气体中的大量加入对直流等离子体喷射制备金刚石膜的形貌、生长速率、晶体取向、成核密度等有非常显著的影响.     

直喷式直流电弧等离子化学气相沉积法金刚石单晶外延层制备研究

采用非循环直流喷射(直喷式)直流电弧等离子化学气相沉积法,在Ar/H2/CH4气氛下,成功制备了金刚石单晶外延层.试验采用的是3 mm×3 mm×1.2 mm的高温高压Ib型金刚石单晶衬底.研究了不同衬底温度和甲烷浓度对金刚石单晶外延层的形貌,速率和晶体质量的影响.采用光学显微镜,激光共聚焦表征了样品的形貌,利用千分尺测量其生长速率,利用Raman表征其晶体质量,采用OES诊断Ar/H2/CH4等离子气氛下C2、CH与Hβ的相对浓度.研究表明,温度和甲烷浓度对单晶刚石形貌和质量产生了明显的影响.在衬底为温度980℃,甲烷浓度在1.5;的条件下,生长速率达到了36 μm/h,并且晶体质量较好(半高宽仅为1.88 cm-1).同时发现生长参数对金刚石单晶外延层的生长模式有着显著地影响.     

微纳米复合金刚石自支撑膜的制备及微观结构的研究

在30 kW级直流电弧等离子喷射化学气相沉积装置下,采用Ar-H2-CH4混合气体,通过控制工艺参数,在多晶钼衬底上制备了微纳米复合多层金刚石自支撑膜.采用拉曼光谱对其进行成份分析、SEM观察膜体表面形貌,采用聚焦离子束(FIB)技术对其进行原位刻蚀,用高分辨电镜观察对其进行微观表征.结果显示,同普通微米膜相比,多层膜体是由微米晶金刚石层和纳米晶金刚石层组成,表面光滑,微米层与纳米层间具有相互嵌套式的界面,微/纳米复合多层金刚石自支撑膜中包含有纳米级金刚石晶粒、微米级金刚石晶粒和无定形碳.     

采用DC Arc Plasma Jet CVD方法沉积微/纳米复合自支撑金刚石膜

在30kW级直流电弧等离子体喷射化学气相沉积(DC Arc P lasm a Jet CVD)设备上,采用Ar-H2-CH4混合气体,通过调节甲烷浓度以及控制其他沉积参数,在Mo衬底上沉积出微/纳米复合自支撑金刚石膜。实验表明,当微米金刚石膜层沉积结束后,在随后的沉积中,随着甲烷浓度的增加,金刚石膜表面的晶粒大小是逐渐减小的。当甲烷浓度达到20%以上时,金刚石膜生长面晶粒呈现菜花状的小晶团,膜体侧面已经没有了粗大的柱状晶,而是呈现出光滑的断口,对该层进行拉曼谱分析显示,位于1145 cm-1附近有一定强度的散射峰出现。这说明所沉积的晶粒全部变为纳米级尺寸。     

甲烷浓度对碳化硅基底金刚石薄膜摩擦性能影响

利用热丝化学气相沉积法(HFCVD)在碳化硅基底上制备金刚石薄膜,采用场发射扫描电子显微镜、拉曼光谱仪、原子力显微镜研究了在不同甲烷浓度条件下制备的金刚石薄膜表面形貌及物相组成,在干摩擦条件下通过往复式摩擦磨损实验测试并计算了已制备金刚石薄膜的摩擦系数和磨损率,结合物相分析及摩擦磨损实验结果分析了甲烷浓度的改变对金刚石薄膜摩擦磨损性能的影响。结果表明,由于甲烷气体含量的升高,金刚石薄膜结晶质量下降,薄膜由微米晶向纳米晶转变。摩擦磨损实验结果显示:3%甲烷浓度条件下制备的金刚石薄膜耐磨性较好,磨损率为2.2×10^-7 mm³/mN;5%甲烷浓度条件下制备的金刚石薄膜摩擦系数最低(0.032),磨损率为5.7×10^-7 mm³/mN,制备的金刚石薄膜的耐磨损性能相比于碳化硅基底(磨损率为9.89×10^-5 mm³/mN)提升了两个数量级,显著提高了碳化硅基底的耐磨性。     

微波等离子体化学气相沉积金刚石薄膜研究

本文系统研究了石英钟罩式微波等离子体辅助化学气相沉积装置对沉积金刚石薄膜的影响。与石英管式微波等离子体沉积装置相比，该装置能使用较高的沉积气压、较大的气体流量和较微波功率。本文着重研究了沉积气压、气体流量和甲烷浓度对金刚石薄膜形貌和生长速度的影响。发生生长速度随着沉积气压和甲烷浓度的增大而增大，晶体形态随着甲烷浓度的增大而差。并使用该装置成功地在４００℃低温沉积了Φ６０ｍｍ的金刚石薄膜。     

沉积温度对硬质合金表面MPCVD法制备SiC过渡层的影响

采用MPCVD法,以氢气和四甲基硅烷为先驱气体,YG6硬质合金刀片为基体材料,在不同沉积温度下制备了SiC涂层;并选用致密连续且附着性能优良的SiC涂层作为过渡层制备金刚石涂层.使用场发射扫描电镜、能谱仪和掠X射线衍射仪对SiC涂层和金刚石涂层的形貌和组成进行了分析,并对SiC涂层和金刚石涂层的附着力进行测试.结果表明,随着沉积温度升高,SiC涂层先由团聚在一起的β-SiC微晶相先转变为颗粒状和片状β-SiC,进而转变为团聚在一起的非晶态的SiC晶须;SiC涂层的厚度呈递增、致密度呈现先增强后减弱、表面粗糙度整体呈现先减小后增大、附着力呈先升高后降低的趋势.沉积温度为800℃时制备的片状SiC涂层与硬质合金基体有着良好的结合强度,将其作为过渡层时,能够在硬质合金表面制备出均匀、连续、致密的且附着力良好的金刚石涂层.     

石英衬底上大晶粒多晶Si薄膜的制备与结构表征

利用高频感应加热化学气相沉积工艺,以H2稀释的SiH4作为反应气体源,在未抛光的粗糙石英衬底上直接沉积制备了具有均匀分布的大晶粒多晶Si膜.采用扫描电子显微镜、X射线衍射和可见-紫外分光光度计等检测手段,测量和分析了沉积膜层的表面形貌、晶粒尺寸、择优取向与光反射等特性.结果表明,多晶Si膜中Si晶粒的尺寸大小和密度分布不仅与工艺参数有关,而且强烈依赖于衬底的表面状况.1000℃下沉积薄膜的平均晶粒尺寸为～3μm,择优取向为<111>晶向.反射谱测量表明,920℃下制备薄膜的反射率比1000℃下制备的更低,最低值达18.4;,这应归功于前者具有更大的表面粗糙度.     

Growth feature of layered self-standing diamond films by DC arc plasma jet CVD

Layered self-standing diamond films, two-, three- and four-layered films, were fabricated by varying the ratio of methane to hydrogen in high-power DC arc plasma jet CVD. Results of scanning electronic microscopy (SEM) and Raman spectra showed that the layered films were constructed by the micro-crystalline grains layer/nano-crystalline grains layer. The residual stress within the films were balanced, and even diminished in the certain layer. The grain size was calculated by X-ray diffraction (XRD). The layer containing nanocrystalline grains due to a plenty of secondary nucleation can weakly inherit the columnar growth feature of the overlaid layer containing micro-crystalline grains. The grain size and growth orientation of the layer containing micro-crystalline grains can be adjusted by introduction of a mid-layer containing nano-crystalline grains. Growth rate was over 10 mm/h in layered film fabrication.     

Peculiarity of constant photocurrent method for silicon films with mixed amorphous–nanocrystalline structure

The results of conductivity, photoconductivity and constant photocurrent method absorption measurements by DC and AC methods in hydrogenated silicon films with mixed amorphous–nanocrystalline structure are presented. A series of diphasic silicon films was deposited by very high frequency plasma enhanced chemical vapor deposition technique, using different hydrogen dilution ratios of silane. The increase of hydrogen dilution ratio results in five orders of magnitude increase of conductivity and a sharp increase of grain volume fraction. The comparison of the absorption spectra obtained by DC and AC methods showed that they are similar for silicon films with the predominantly amorphous structure and films with high grain volume fraction. However we found a dramatic discrepancy between the absorption spectra obtained by DC and AC constant photocurrent methods in silicon films deposited in the regime of the structure transition from amorphous to nanocrystalline state. AC constant photocurrent method gives higher absorption coefficient than DC constant photocurrent method in the photon energy range of 1.2–1.7 eV. This result indicates the possibility of crystalline grains contribution to absorption spectra measured by AC constant photocurrent method in silicon films with intermediate crystalline grain volume fraction.     

Growth and real structure of diamond films synthesized on polycrystalline tungsten substrates

X-ray diffraction studies of diamond films obtained by chemical transport reactions at the concentrations of 2% methane and 98% hydrogen under pressures of 10.7 and 21.3 kPa showed that they are textured. The character of the texture depends on the substrate temperature. The films have {110}, {311}, or double {110} + {311} textures. It is established that the dependence of the growth rate of diamond films on the substrate temperature has maxima. The diamond films are finely dispersed and are characterized by pronounced micro-deformations and high dislocation densities. The temperature dependence of the growth rate correlates with the parameters of the real structure of the films.     

电铸自支撑金刚石-镍复合膜的制备

用电铸方法,采用低应力电镀液,制备出了自支撑金刚石-镍复合膜.电镀液PH值3.8-4.2,温度40～60℃,阳极与阴极间距100～150mm.用扫描电镜(SEM)和X射线衍射(XRD)方法检测了复合膜的表面形貌、晶体显微结构和复合膜中金刚石颗粒的分布情况.结果表明:阴极电流密度对自支撑金刚石-镍复合膜的品质影响很大,当阴极电流密度从1.3 A/dm2增加到3.3 A/dm2时,复合膜的显微应变从0.36;减小到0.28;;随着阴极电流密度的增加,复合膜中金刚石颗粒的含量增加.     

CVD法沉积金刚石薄膜中成核与生长的势垒研究

探明成核与生长的机理对于沉积高质量金刚石薄膜是十分重要的.本文采用PM3方法,计算了化学汽相沉积金刚石薄膜成核与生长阶段反应势垒.研究了对于不同反应气体(甲烷和乙炔)脱氢和增加沉积基团势垒的差异.结果说明,无论是成核阶段,还是生长阶段,脱氢势垒都小于加生长基团的势垒.然而,增加乙炔基的势垒大于增加甲基的势垒,这可能是因为乙炔分子必须打开C≡C键才能沉积到衬底表面.     

CVD金刚石薄膜亚表面层氢杂质对表面活化反应的影响

采用密度泛函理论平面波赝势法研究了氢杂质位于氢终止金刚石薄膜亚表面层中三种不同位点处时金刚石的结构变化,以及氢原子在三种金刚石薄膜表面上的吸附难易程度,并对表面活化反应进行了过渡态搜索以探究化学气相沉积(CVD)过程中金刚石薄膜亚表面层氢杂质对表面活化的影响。对比计算结果发现:生长过程中,亚表面层的氢杂质使其附近的金刚石结构产生了畸变,同时金刚石表面结构会对畸变程度产生影响。氢原子在含有氢杂质的三种金刚石薄膜上的吸附能与理想金刚石薄膜差异很小,但发生萃取反应产生活性位点的能垒比理想金刚石薄膜更低,这与亚表面层中的氢杂质使金刚石薄膜具有P型半导体特征这一现象有关。这一结果说明富氢反应气氛有利于活性位点的产生并以更高速率进行生长。     

Study of bound hydrogen in powders of diamond nanoparticles

Crystallography Reports - In order to access feasibility of increasing albedo of very cold neutrons from powder of diamond nanoparticles, we studied hydrogen bound to surface of diamond...     

Temperature gradient induced phase transitions and morphological changes in diamond thin film

The diamond films were deposited onto a wurtzite gallium nitride (GaN) thin film substrate using hot-filament chemical vapor deposition (HFCVD). During the film deposition a lateral temperature gradient was imposed across the substrate by inclining the substrate. As grown films predominantly showed the hexagonal phase, when no inclination was applied to the substrate. Tilting the substrate with respect to the heating filament by 6° imposed a lateral temperature gradient across the substrate, which induced the formation of a cubic diamond phase. Diamond grains were predominantly oriented in the (100) direction. However, a further increase in the substrate tilt angle to 12°, resulted in grains oriented in the (111) direction. The growth rate and hence the morphology of diamond grains varied along the inclined substrate. The present study focuses on the measurements of dominant phase formation and crystal orientation with varying substrate inclination using orientation-imaging microscopy (OIM). This technique enables direct examination of individual diamond grains and their crystallographic orientation.