再结晶石墨对金刚石成核的影响

 本文结合实验现象，分析了在合成初期，碳源在溶剂-触媒金属中的分散，溶解及形成再结晶石墨的过程。并根据再结晶石墨与金刚石成核量的实验结果，初步定性地研究了膜生长法中，再结晶石墨对金刚石成核的影响。     

高温高压条件下石墨的再结晶与金刚石单晶的生长

 用电子显微镜观察到了在高温高压条件下再结晶石墨的形状随温度变化而改变的规律。实验表明：从石墨向金刚石的转变，与石墨在催化剂——溶剂合金中的再结晶状态有关，类球形再结晶石墨是转变成金刚石小单元的基础。金刚石晶体的不同形态及其多样化的表面结构表明金刚石单晶的生长具有比较复杂的过程。研究了具有一定规则形状由类球形再结晶石墨晶粒组成的聚合体，这种聚合体将在适当温度压力下转变成金刚石颗粒。本研究给出了生长粗颗粒、晶形完整的金刚石单晶的原则办法。     

高压熔渗生长法制备金刚石聚晶中碳的转化机制研究

在6 GPa和1500 ℃的压力和温度范围内, 利用高压熔渗生长法制备了纯金刚石聚晶, 深入研究了高温高压下金刚石聚晶生长过程中碳的转化机制. 利用光学显微镜、X-射线衍射、场发射扫描电子显微镜检测, 发现在熔渗过程中金刚石层出现了石墨化现象, 在烧结过程中金刚石颗粒表面形貌发生了变化. 根据实验现象分析, 在制备过程中存在三种碳的转化机制: 1)金属熔渗阶段金刚石颗粒表面石墨化产生石墨; 2)产生的石墨在烧结阶段很快转变为填充空隙的金刚石碳; 3)金刚石直接溶解在金属溶液中, 以金刚石形式在颗粒间析出, 填充空隙. 本文研究碳的转化机制为在高温高压金属溶剂法合成金刚石的条件下(6 GPa和1500 ℃的压力和温度范围内)工业批量化制备无添加剂、无空隙的纯金刚石聚晶提供了重要的理论指导.     

微波化学气相沉积中气压对金刚石薄膜生长速率和质量的影响

研究了微波化学气相沉积中沉积气压对金刚石薄膜生长速率和质量的影响.研究表明，金刚石薄膜的生长速率随沉积气压的提高而增大，生长速率与沉积气压为线性关系.在高沉积气压下生长的金刚石薄膜晶形完整，拉曼谱测量可得到锐利的金刚石相的峰，但电压-电流测量表明，随着制备时沉积气压的提高，金刚石薄膜的暗电流增大，膜的电学质量下降. 关键词： 金刚石薄膜 生长速率 沉积气压     

Fe基合金与金刚石单晶生长

 本文通过Fe基催化剂在生长金刚石单晶中获得的不同现象与Fe基合金晶格常数、组分、磁距、Mossbauer谱相比较，揭示了Fe基催化剂常温常压下磁性质与金刚石单晶生长的关系。     

在有金属或合金参与下人造金刚石形成机理的探讨

根据实践知道,在有金属或合金存在的情况下,利用高温高压装置能成功地使石墨或其它碳素材料转变成金刚石．现国外关于金刚石形成机理的说法各有不同,归结起来有三种：（１）溶剂说,（２）催化说,（３）固相转化说．但无论那种理论都无法完满地解释金刚石形成中出现的各种现象,并且都没有揭露过程的本质． 对人造金刚石形成机理进行深入的探讨,弄清合成金刚石过程中非金刚石型碳转变成金刚石的历程,有利于解决优质单晶大颗粒金刚石生产实践中的问题,和为发展金刚石新品种提供理沦依据． 本文总结了数十种金属与合金对合成金刚石影响的规律,提出了金刚石形成机理──催溶说．这一理沦认为,非金刚石型碳转变成金刚石时,碳在具有未饱和ｄ电子层的Ⅳ,Ⅴ,Ⅵ,Ⅶ,Ⅷ过渡族熔融金属或合金的作用下溶解并活化为具有ＳＰ３态．被活化的碳原子或原子团,在金刚石热力学稳定区内,在不同构型的金属或合金胞体、高熔点金属碳化物等杂质上非自发成核（自发成核几率极小）,并不断沉积长大．相应的,由于能量的涨落,同样可以出现石墨化和石里生长．同时形成少量的金属碳化物．木文包括如下几部分：非金刚石型碳在熔融金属或合金催溶剂中的溶解与活化;金刚石的成核与生长;金刚石的石墨化与石墨生长;     

扬子克拉通西部砂矿型金刚石多晶的同步辐射研究及意义

基于金刚石多晶形成过程的复杂性、制样的困难性等在较大程度上制约了人们对其成核、生长等结晶过程及意义等的深入理解，采用同步辐射技术对扬子克拉通的金刚石多晶进行同步辐射显微红外光谱、显微红外光谱成像等方面的研究。金刚石多晶的同步辐射研究表明，金刚石多晶研究样品总体属于Ⅰ型金刚石，其总氮含量(N_T)约为500~1 300 μg·g-1，对氮心的含量(N_A)约为300~700 μg·g-1，四氮心的含量(N_B)约为150~550 μg·g-1。金刚石多晶在地幔中的停留时间约介于0.06~0.12 Ga；样品的生长经历了多个生长中心先分别生长，后连聚成多晶再生长的过程，且整个多晶体的结晶中心区形成后，晶体优先往有利于稳固结晶中心的方向生长、再各向生长之过程。同时，金刚石多晶的生长在各时期内呈各向差异生长而非均匀生长，且存在间歇性停止生长的现象。     

MPCVD金刚石的Raman光谱分析

用微波等离子体化学气相淀积法（MPCVD）在Si基片上生长了金刚石薄膜，通过对其进行Raman光谱分析，一次表征了金刚石的结构，纯度及应力状况等材料性能，同时并研究了生长过程中微波功率与金刚石性质的关系。研究表明，微波等离子体化学气相溶积法生长的金刚石薄膜，除了金刚石成分的生长外，还会有部分非金刚石成分的生长，金刚石的纯度与微波功率的关系不明显，另外此种方法生长的金刚石薄膜主要表现为张应力。     

人造金刚石生长速率的探讨

《在有金属或合金参与下人造金刚石形成机理的探讨》[1]一文中,阐述了非金刚石型碳转变成金刚石的历程──在有金属或合金作用下金刚石成核和长大的本质.本文着重探讨人造金刚石晶体的生长速率问题.所用碳素材料为石墨. 人造金刚石成核后的长大过程是一个复杂的过程,可以视为在各向异性的基体上在最有利的条件下所发生的个别过程的总和. 我们在用Ni-MnB合金作催溶剂的试验研究中,测量了合成条件下金刚石晶体的尺寸,通过图解,计算出了在这一条件下石墨转变成金刚石的活化能和活化体积,并且确定了金刚石生长速率与压力、温度的关系. 试验分…     

一氧化碳合成金刚石薄膜的形貌和结构分析

利用微波等离子体化学气相沉积(MPCVD)技术，采用偏压增加成核(BEN)、两步生长的方法在一氧化碳(CO)和氢气(H₂)的环境下制备了金刚石薄膜. 利用扫描电子显微镜(SEM)、Raman光谱仪和透射电子显微镜(TEM)对金刚石薄膜的形貌和结构进行了分析. 研究发现金刚石晶粒在第一步成核及生长的过程中产生了层错和孪晶，而在第二步的生长过程中产生的层错和孪晶很少，最终形成的金刚石晶粒外表面比较光滑，包含有近五次对称或者平行的片状的孪晶，并可以观察到少量的位错. 而在样品的边缘由于等离子体的不均匀产生了比样品中心成核密度低的区域. 在这个区域中，发现了一个新的非金刚石的碳结构.     

Application of Supersonic Molecular Jets in Semiconductor Thin Film Growth

The flux and the incident kinetic energy are the most important deposition variables in thin film growth processes. By changing these variables, one can, in principle, alter the reaction pathways and the rate at which they occur and produce a different material than under thermody-namic equilibrium conditions. The significance of supersonic molecular jets stems from the fact that both, the flux and the incident kinetic energy of neutral growth species, can be varied independently. The number of studies that are exploring these advantages in a wide range of materials systems is growing rapidly. In this article the application of supersonic molecular jets in semiconductor thin film growth is reviewed. The effects of both the superthermal incident kinetic energy and the flux on the growth and properties of elemental and compound semiconductors are examined.     

Morphological stability analysis of the epitaxial growth of a circular island: Application to nanoscale shape control

In this paper, we present a comprehensive morphological stability analysis of a single, epitaxially growing, perturbed circular island by using a Burton-Cabrera-Frank (BCF) island dynamics model. We show that there exists a critical deposition flux for which a single mode perturbation remains unchanged. In the absence of an additional far-field mass flux, there exists a naturally stabilizing radius, so that beyond this radius, growth is always stable. Up to this radius, taking fluxes larger than the critical flux results in instability. The presence of kinetics makes sufficiently small islands grow stably, even without line tension or surface diffusion. The presence of desorption further introduces a range of parameters and island radii for which both stable and unstable shrinkage may occur. The presence of a far-field mass flux in the BCF model can eliminate the naturally stabilizing radius and unstable growth may be achieved for a wide range of island radii. We then demonstrate how these results may be exploited to control the shape of the island using the deposition flux and far-field mass flux as control parameters.     

Growth behavior of GaN film along non-polar [1 1 -2 0] directions

We studied the atomic assembly mechanisms of non-polar GaN films by the molecular dynamics method as a function of the N:Ga flux ratio at a fixed adatom energy on non-polar planes. Our study revealed that high quality crystal growth occurred only when off-lattice atoms (which are usually associated with amorphous embryos or defect complexes) formed during deposition were able to move to unoccupied lattice sites by thermally activated diffusion processes, which attests to the experimental difficulties in obtaining smooth surfaces due to dense stacking faults lying in non-polar GaN. Furthermore, surface structures on different planes played an important role. We further suggested favorable conditions for growing high quality GaN films and nano-structures along non-polar directions.     

Determination of the supercooling dependence of the (211) facet of BGO crystal on growth rate from the temporal dependence of supercooling at a prescribed melt-cooling rate

The results of determination of the supercooling dependence at the interphase boundary on the rate of growth from melt of the monocrystal Bi₄Ge₃O₁₂ in the [211] direction are presented. Determination of supercooling was based on optical pyrometer measurements of the intensity of heat emission from the interphase boundary through the growing crystal. The crystal was grown by the AHF method (axial heat flux near the front of crystallization) by cooling the AHF heater at a specified rate. The growth rate corresponding to the measured supercooling value was determined by calculations. The study has shown that the supercooling is high and varies nonlinearly with the growth rate.     

Morphology evolution of hierarchical ZnO nanostructures modulated by supersaturation and growth temperature

Three kinds of ZnO hierarchical structures, nanocombs with tube- and needle-shaped teeth and hierarchical nanorod arrays, were successfully synthesized through the chemical vapor deposition method. Combining the experimental parameters, the microcosmic growing conditions (growth temperature and supersaturation) along the flux was discussed at length, and, based on the conclusions, three reasonable growth processes were proposed. The results and discussions were beneficial to further realize the relation between the growing behavior of the nanomaterial and microcosmic conditions, and the hierarchical nanostructures obtained were also expected to have potential applications as functional blocks in future nanodevices. Furthermore, the study of photoluminescence further indicated that the physical properties were strongly dependent on the crystal structure.      

Coalescence of spreading droplets on a wettable substrate

We investigate experimentally and theoretically the coalescence dynamics of two spreading droplets on a highly wettable substrate. Upon contact, surface tension drives a rapid motion perpendicular to the line of centers that joins the drops and lowers the total surface area. We find that the width of the growing meniscus bridge between the two droplets exhibits power-law behavior, growing at early times as t1/2. Moreover, the growth rate is highly sensitive to both the radii and heights of the droplets at contact, scaling as ho3/2/Ro. This size dependence differs significantly from the behavior of freely suspended droplets, in which the coalescence growth rate depends only weakly on the droplet size. We demonstrate that the scaling behavior is consistent with a model in which the growth of the meniscus bridge is governed by the viscously hindered flux from the droplets.     

具有凸台结构的高照明均匀度倒置型植物光源设计

针对现有植物工厂采用的植物培养架照度、混色均匀度差导致农产品作物品质参差不齐的现状,提出一种高混光、高混色均匀度的植物培养架设计方案。不同于光源在上种植面在下的培养架设计模式,将红、蓝LED灯珠间隔排列阵列光源安装在植物种植平面上的凸台上,并把培养架顶部设计成漫反射面。漫反射面的引入起到增加混光距离的作用,提高光线耦合程度,从而达到了提高混光、混色均匀度的效果。进一步引入光量子通量密度均匀度以及混色均匀度共同作为考察指标,利用Taguchi方法设计并进行实验,研究不同因子对植物种植区光源均匀性的影响,再利用ANOVA理论分析了各因子对品质的影响程度多次优化后,最终获得照度均匀度为94.58%、混色均匀度为90%、能量利用率为41.42%的最优系统设计方案。然后研究了不同配光曲线的灯珠对培养架均匀度的影响,最后通过测量植物在不同高度时种植面和植物表面的照度及光谱的分布情况检测植物的生长是否会遮挡光线。结果表明该植物照明系统可以在植物生长过程中提供均匀的照明,遮挡问题几乎可以忽略不计。     

Monte Carlo investigation of the influence of V/III flux ratio on GaAs/GaAs(001) submonolayer epitaxy

The influence of the V/III flux ratio on the submonolayer growth of GaAs on the GaAs (001) surface is simulated by the Monte Carlo method. Growth is carried out using the method of molecular beam epitaxy at different values of process parameters. The surface density of islands against the V/III flux ratio is calculated. The saturation value of the surface density at 580°C is found to be 2 × 10¹² cm^–2, which is in agreement with the experimental data. The V/III flux ratio influences the island density most strongly at a reduced temperature (550°C) and an elevated growth rate (a monolayer per second), when the arsenic desorption is weak. The fraction of arsenic atoms in the growing film is estimated under different process conditions. It has been shown that, as the surface coverage rises, the influence of the V/III flux ratio on the fraction of arsenic atoms becomes weaker.     

Kinetic step bunching instability during surface growth

We study the step bunching kinetic instability in a growing crystal surface characterized by anisotropic diffusion. The instability is due to the interplay between the elastic interactions and the alternation of step parameters. This instability is predicted to occur on a vicinal semiconductor surface Si(001) or Ge(001) during epitaxial growth. The maximal growth rate of the step bunching increases like F4, where F is the deposition flux. Our results are complemented with numerical simulations which reveal a coarsening behavior in the long time evolution for the nonlinear step dynamics.     

Different-dimensional structures of antimony formed selectively on graphite

When antimony (mostly Sb₄) is deposited on highly oriented pyrolytic graphite (HOPG), in situ scanning tunneling microscopy images reveal that three-dimensional (3D) spherical islands, quasi-2D films and 1D nanowires (NWs) are formed. The spherical islands develop into faceted crystallites in the later growth stage. The lattice parameters of the 2D and 3D structures are close to those of α-Sb bulk, whereas the NWs appear in a compressed state. The Laplace pressure, which can reach the GPa range in a nanostructure, is considered the driving force for the compressive lattice structures of Sb NWs. We found conditions of controlling the dimensionality of Sb nanostructures in their self-assembly on HOPG to a certain extent. At room temperature and with a low Sb flux, 3D islands grow exclusively. At a substrate temperature of 100 °C, 2D and 1D structures are dominant when a high deposition flux is used, whereas only NWs are formed initially when a low flux is used. These results are explained in terms of different activation energies for Sb₄ diffusion and conversion to a chemisorption or dissociation state on HOPG. As the temperature increases, the rate of conversion to the chemisorption or dissociation state increases more rapidly than that of diffusion since the chemisorption activation energy is much higher than the diffusion barrier of physisorbed Sb₄, resulting in enhanced 2D and 1D structural nucleation and growth, which are further favored with the increase in deposition flux. The bonding nature of various Sb structures with a graphite surface and the conditions for growing aligned Sb NWs exclusively are discussed. PACS 61.46.+w; 64.70.Nd; 68.37.Ef; 68.65.-k; 81.07.-b