生长于微结构内点状结构的成核热力学

研究了汽相沉积过程中的衬底表面凹结构的成核热力学,指出可以通过衬底表面微结构设计来控制成核过程以实现点状结构的生长．计算了凹结构内的临界核形成能,表明与平面相比成核优先在凹结构发生．考虑凹结构的“等效势阱”效应,发现凹结构内稳定原子团的生长速率远远大于平面处稳定原子团的生长速率． 关键词：     

氮气氛下(100)织构金刚石薄膜的成核与生长研究

利用热丝化学气相沉积法研究了氮气浓度对金刚石薄膜成核和生长的影响.实验发现氮气的 加入对金刚石成核密度影响不大,但促进了已形成的金刚石核的长大.适量的氮气不仅使金 刚石生长速率得到很大的提高,而且稳定了金刚石薄膜(100)面的生长,使金刚石薄膜具有 更好的(100)织构.利用原位光发射谱对衬底附近的化学基团进行了研究.研究表明,氮气的 引入使得金刚石生长的气相化学和表面化学性质发生了很大变化.含氮基团的萃取作用提高 了金刚石表面氢原子的脱附速率,从而提高了金刚石膜的生长速率.而含氮基团的选择吸附 使金刚石 关键词： 氮气 金刚石薄膜 织构 原位光发射谱     

异质外延生长钙钛矿结构氧化物薄膜

影响直接外延生长氧化物薄膜的因素有很多,最主要的是保证氧化物薄膜的正确成相和在单晶衬底上成核．直接外延生长时,衬底温度影响到薄膜的成相．衬底温度还影响薄膜的生长动力学,并因此影响薄膜的外延生长取向．由于薄膜是首先在衬底表面成核、成相并生长的,因此衬底材料晶格的影响是不容忽视的．衬底材料（或异质外延材料）与薄膜的相互作用是影响外延生长的最直接因素,而晶格常数失配会造成薄膜样品中存在应力并影响样品性质．利用脉冲激光淀积法,我们成功地外延生长了ＹＢａ２Ｃｕ３Ｏ７超导薄膜、Ｓｒ０．５Ｂａ０．５ＴｉＯ３铁电介电薄膜、Ｌａ０．７Ｃａ０．３ＭｎＯ３铁磁巨磁电阻薄膜、Ｌａ０．５Ｓｒ０．５ＣｏＯ３导电薄膜等多种具有钙钛矿结构的氧化物功能薄膜．以这些钙钛矿结构氧化物薄膜的外延生长为例,本文讨论影响氧化物薄膜异质外延生长的因素     

GaAs(001)衬底上分子束外延生长立方和六方GaN薄膜

采用分子束外延方法在GaAs(001)衬底上生长出了03微米厚的GaN薄膜,X射线双晶衍射和室温光荧光测试结果表明,采用GaAs氮化表面作为成核层可获得高纯度立方GaN薄膜而采用AlAs氮化表面作为成核层可获得高纯度六方GaN薄膜.这一研究结果表明在GaAs衬底上生长GaN薄膜的相结构可以通过选择不同的成核层来控制. 关键词：     

正轴6H-SiC 衬底上3C-SiC薄膜的低压化学气相沉积生长

活性的O-和OH-被认为在苯酚形成过程中起了重要作用．通过低压化学气相沉积，在正轴6H-SiC(0001)衬底上沉积了3C-SiC薄膜，X射线衍射表明薄膜结晶质量良好．研究了生长参数对生长速率的影响，发现硅烷及其分解产物的输运是薄膜生长的限定因素．用原子力显微镜观察薄膜的表面形貌．这些结果表明薄膜的生长符合S-K方式．     

液滴外延下生长参数对InAs纳米结构形貌的影响

利用液滴外延法在GaAs(001)衬底表面制备InAs量子点,通过控制变量分别研究沉积速率、沉积量对In液滴在GaAs表面生长过程中的影响.使用原子力显微镜(Atomic Force Microscope, AFM)表征InAs纳米结构形貌,得出结论：(1)沉积速率主要通过影响In液滴成核率来控制液滴的密度,即随着沉积速率的增大,In原子在衬底表面的成核率增加,InAs量子点密度增加,实验符合生长动力学经典成核理论.(2)沉积量的改变主要影响液滴的熟化过程,即随着沉积量的增大,可参与生长的活跃的In原子增加,促进了液滴熟化,使得扩散坍塌的原子数量增加,导致在InAs纳米结构中出现多量子点现象.     

薄膜外延生长的计算机模拟

以Cu膜为例，用Monte-Carlo算法模拟了薄膜生长的随机过程，并提出了更加完善的模型.在合理选择原子间相互作用计算方法的基础上，考虑了原子的吸附、在生长表面的迁移及迁移所引起的近邻原子连带效应、从生长表面的脱附等过程.模拟计算了薄膜的早期成核情况以及表面粗糙度和相对密度.结果表明，随着衬底温度的升高或入射率的降低，沉积在衬底上的原子逐步由离散型分布向聚集状态过渡形成一些岛核，并且逐步由二维岛核向三维岛核过渡.在一定的原子入射率下，存在三个优化温度，成核率最高时的最大成核温度Tn、薄膜的表面粗糙度最低 关键词： Monte-Carlo算法 计算机模拟 薄膜生长     

钙钛矿结构氧化物薄膜 的外延生长

在成功地外延生长超导、铁电、铁磁等多种性质的钙钛矿结构氧化物薄膜的基础上,讨论影响氧化物薄膜 外延生长的一些因素.考虑到相形成和薄膜长征动力学,在利用脉冲激光淀积法外延生长氧化物薄膜中衬底温度是十分重要的工艺参数.衬底温度对成相和生长薄膜的取向都有影响.考虑到薄膜是首先在衬底表面成核、成相并生长.因此衬底材料晶格的影响是不容忽视的.观察到衬底材料对薄膜外延生长温度的影响.在适当的工艺条件下,利用低温三步法工艺制备得到有很强织构的外延薄膜.这突出表明界面层的相互作用对钙钛矿结构薄膜的取向有着相当大的影响. 关键词：     

SiO2/Si衬底上石墨烯的制备与结构表征

在分子束外延(MBE)设备中,利用直接沉积C原子的方法在覆盖有SiO₂的Si衬底(SiO₂/Si)上生长石墨烯,并通过Raman光谱和近边X射线吸收精细结构谱等实验技术对不同衬底温度(500℃,600℃,700℃,900℃,1100℃,1200℃)生长的薄膜进行结构表征.实验结果表明,在衬底温度较低时生长的薄膜是无定形碳,在衬底温度高于700℃时薄膜具有石墨烯的特征,而且石墨烯的结晶质量随着衬底温度的升高而改善,但过高的衬底温度会使石墨烯质量降低.衬底温度为1100℃时结晶质量最好.衬底温度较低时C原子活性较低,难以形成有序的C-sp²六方环.而衬底温度过高时(1200℃),衬底表面部分SiO₂分解,C原子与表面的Si原子或者O原子结合而阻止石墨烯的形成,并产生表面缺陷导致石墨烯结晶变差.     

SiH4/H2等离子体气相生长硅薄膜的动力学模型

在化学气相沉积微晶硅薄膜过程中,为了降低成本,必须提高生长速率,但薄膜的微观结构和光电性能则随之降低,原因是成膜先驱物在薄膜表面上的扩散长度降低了. 本文利用量子化学的反应动力学理论建立有关成膜先驱物SiH₃和H的反应平衡方程,求解薄膜生长速率和成膜先驱物的扩散长度,并找出影响生长速率与扩散长度的微观参数,发现生长速率不仅与流向衬底的SiH₃的通量密度有关,而且与H的通量密度有关;SiH₃的扩散长度与衬底温度和薄膜表面的硅氢键的形态有关,当     

CLUSTER NUCLEATION LIMITED BY GROWTH PATTERN COVERAGE IN THIN FILM PREPARATION FROM VAPOR

In the early stage of thin film preparation from vapor, growth patterns consisting of stable clusters will gradually cover almost the entire substrate surface. During this process, the density of single atoms is zero on growth patterns and the nucleation of clusters will proceed in the substrate parts uncovered by these patterns. The influence of growth pattern coverage on the nucleation of thin films has not been considered wholly in the classical theory of thin films. We will systematically study the influence of growth pattern coverage and give some correction formulas for the widely used classical theory of thin films. It was found that the classical nucleation rate is proportional to the square of the uncovered area. The corrected formulas are of particular importance in the dominant coverage case.     

高温下金属薄膜生长初期的模拟研究

采用实际的生长模型和物理参量,用Monte Carlo方法对高温下金属薄膜的生长过程进行了模拟研究.综合考虑了原子沉积、扩散、成核、生长和扩散原子的再蒸发、原子沿岛周界扩散和岛的合并等众多过程后,模拟得到与实验结果相当一致的薄膜生长形貌及其相应的定量结果.通过动态统计薄膜生长过程中的岛数目及薄膜生长率,得到实验中不易直接获得的高温下薄膜生长的许多细节,如岛数目和薄膜生长率随表面温度、覆盖度变化的详细情况等 关键词： 薄膜 Monte Carlo模拟 成核 岛密度 薄膜生长率     

Surface morphology for ion-beam sputtered Al layer with varying sputtering conditions

We study the growth morphology of thin macrostructure films which is known to be largely affected by the deposition conditions as thin film nucleation and formation is dependent on the kinetic energy and chemical free energy of the atoms. The ion-beam sputtering technique used for depositing thin layers is due to the advantage over other techniques, e.g. the independent control of many process parameters, such as the pressure and/or the energy of the ion-beam and the substrate temperature. Therefore, the dependence of various sputtering parameters such as: (i) sputtering pressure and/or the rate of deposition and (ii) the effect of substrate temperature on the growth has been studied by depositing a single layer of Al. The variations show some interesting dependencies on the structural parameters for the Al layer deposited which has been understood in terms of thin film growth and nucleation theory.     

MgO(111)上NbN和AlN薄膜的生长研究

在制备NbN/AlN/NbN隧道结的工艺过程中,为了获得具有优质单晶结构的NbN薄膜,我们在MgO(111)基片上探索了直流溅射法制备NbN薄膜的生长工艺条件,XRD研究分析表明,我们获得了单晶结构良好的NbN薄膜;为了支持作为上电极的NbN薄膜的生长,也需要良好的AlN薄膜用作势垒层,我们采用射频磁控溅射设备和纯净的Al靶对AlN薄膜进行了制备研究.实验结果表明,所获得的AlN薄膜具有六方c-轴取向,并讨论了衬底和薄膜界面处可能的结构情况.     

The kinetic process of non-smooth substrate thin film growth via parallel Monte Carlo method

A Monte Carlo simulation model of thin film growth based on parallel algorithm is presented. Non-smooth substrate with special defect mode is introduced in such a model. The method of regionalizing is used to divide the substrate into sub-regions. This method is supposed to be modulated according to the defect mode. The effects of surface defect mode and substrate temperature, such as the nucleation ratio and the average island size, are studied through parallel Monte Carlo method. The kinetic process of thin film growth in the defect mode is also discussed. Results show that surface defect mode contributes to crystal nucleation. Analyzing parallel simulation results we find that density defect points, substrate temperature and the number of processors contribute decisively to the parallel efficiency and speedup. According to defect mode we can obtain large grain size more feasibly and the parallel algorithm of this model can guide the non-smooth substrate simulation work.     

Direct visualisation of homogeneous and heterogeneous crystallisation in an ensemble of confined domains of poly(ethylene oxide)

We present a study of homogeneous and heterogeneous nucleation in polymer crystallisation. In bulk samples the crystallization is typically dominated by nucleation from defects (heterogeneous nucleation), and consequently studies must rely on sample preparation to minimize this effect. We present a study of nucleation within discrete droplets of poly(ethylene oxide) that are formed by the dewetting of a thin film on an unfavourable substrate. The samples provide an ensemble of impurity-free droplets, with length scales that can easily be measured. We show that the data for heterogeneous and homogeneous nucleation is qualitatively different, and that the data mirrors the fundamental differences in the underlying mechanisms for the two nucleation processes. The experiments presented here provide a simple method that can be used to study heterogeneous and homogeneous nucleation in great detail.Received: 1 January 2003, Published online: 30 October 2003PACS: 61.41. + e Polymers, elastomers, and plastics - 68.55.-a Thin film structure and morphology - 81.10.-h Methods of crystal growth; physics of crystal growth     

Desorption and crystallization kinetics in nanoscale thin films of amorphous water ice

The amorphous to crystalline ice phase transition is studied by measuring the water desorption rate from nanoscale thin films of water vapor deposited on Au(111) and Ru(001) single crystal metallic substrates. The desorption kinetics are substrate dependent and suggest strongly that the film morphology is governed by the hydrophilicity of the substrate. The crystallization kinetics are independent of substrate but depend strongly on both temperature and film thickness and are consistent with a spatially random nucleation and isotropic growth model.     

脉冲激光晶化超薄非晶硅膜的分子动力学研究

利用准分子脉冲激光晶化非晶硅薄膜是制备高密度尺寸可控的硅基纳米结构的有效方法之一.本文将脉冲激光对非晶硅超薄膜的影响处理为热传导问题,采用了基于Tersoff势函数的分子动力学方法模拟了在非晶氮化硅衬底上2.7 nm超薄非晶硅膜的脉冲激光晶化过程.研究了不同激光能量对非晶硅薄膜晶化形成纳米硅的影响,发现在合适的激光能量窗口下,可以获得高密度尺寸可控的纳米硅薄膜,进而模拟了在此能量作用下非晶硅膜中成核与生长的机理与微观过程,并对晶化所获得的纳米硅薄膜的微结构进行了分析. 关键词： 非晶硅 分子动力学 脉冲激光晶化     

离子束溅射法薄膜生长中结瘤微缺陷的生长机理

用离子束溅射法制备了锆单层薄膜.用设计新型夹具和预置种子方法，对薄膜中结瘤微缺陷的生长过程进行了研究.在高分辨率光学显微镜和扫描电子显微镜下观察发现，结瘤在其生长初期呈现出分形的特征.用分子动力学和薄膜生长的扩散限制聚集模型，薄膜中结瘤微缺陷成核时的分形现象得到了很好的解释. 关键词： 结瘤微缺陷 锆薄膜 扩散限制聚集模型     

Effect of substrate impurities on layering transitions

We investigate the influence on thin film growth of substrate impurities distributed throughout the substrate bulk. In particular, using a method discussed in a previous paper, we show that the case of correlated disorder will enhance film growth via two mechanisms. Both the chemical potential, and the adatom-adatom interactions are effectively shifted in the intermediate temperature range, thus having the effect of encouraging film growth.