Formation of GaAs nanowhisker arrays by magnetron sputtering deposition

The possibility is demonstrated of fabricating arrays of cone-shaped GaAs nanowhiskers with a surface number density of up to 10⁹ cm^-2, a characteristic height ranging from 300 to 10000 nm, and a transverse size of approximately 200 nm at the base and from 200 to 10 nm or smaller at the top. The characteristic height of GaAs nanowhiskers varies in direct proportion to the effective thickness of the deposited material layer and in inverse proportion to the transverse nanowhisker size at the top. The growth of GaAs nanowhiskers is studied as a function of the deposition rate, the temperature, and the crystallographic orientation of the substrate. From an analysis of the obtained dependences of the nanowhisker size on these parameters, it is concluded that GaAs nanowhiskers are formed through the diffusion mechanism.     

动力学晶格蒙特卡洛方法模拟Cu薄膜生长

利用动力学晶格蒙特卡洛方法模拟了Cu薄膜在Cu(100)面上的三维生长过程。模型中考虑了四个动力学过程:原子沉积、增原子迁移、双原子迁移和台阶边缘原子迁移,各动力学过程发生的概率由多体势函数确定。讨论了基底温度、沉积速率及原子覆盖率对Cu原子迁移、成核和表面岛生长等微观生长机制的影响;获得了Cu薄膜的表面形貌图并计算了表面粗糙度。模拟结果表明,随基底温度升高或沉积速率下降,岛的平均尺寸增大,数目减少,形状更加规则。低温时,Cu薄膜表现为分形的离散生长,高温时,Cu原子迁移能力增强形成密集的岛。Cu薄膜表面粗糙度随着基底温度的升高而迅速减小;当基底温度低于某一临界温度时,表面粗糙度随原子覆盖率或沉积速率的增大而增大;当基底温度超过临界温度时,表面粗糙度随原子覆盖率或沉积速率的变化很小,基本趋于稳定。     

Optimization of process parameters of titanium dioxide films by response surfaces methodology

An efficient approach for determination of the optimum process parameters for titanium dioxide coatings by using second-order response surface model is presented and investigated experimentally. Thin films were prepared by electron-beam evaporation associated with ion-beam assisted deposition by using different control factors, including starting materials, working pressure, substrate temperature, deposition rate and annealing temperature. The factorial design of the experiment was established to meet the equipment conditions and to avoid affecting the results. The main effect between various factors and interactions are independent. The significant level of both the main effects and the interaction are observed by analysis of variance (ANOVA) approach. Based on the statistical analysis, the results have provided much valuable information on the relationship between various control factors and thin film properties. Besides the optimum optical constants and surface roughness of TiO₂ thin films were obtained in the range of each parameter level. The factorial prediction model for preparation parameters of thin film was also established.     

Transition of Growth Mode in Homoepitaxy on Metal Surface

The process of the multilayer growth of Pt on Pt (111) is studied by using a Monte Carlo model with realistic physical parameters. The effects of the substrate temperature, the ES barrier, and the deposition rate on the growth mode have been investigated. Gradual transitions of the surface roughness from oscillatory to non-oscillatory behavior and then back to oscillatory behavior are observed while increasing the substrate temperature from 270 K to 620 K. It is found that the growth mode depends strongly on ES barrier over the whole temperatures and the deposition rate of atoms effectively affects the growth mode. The simulation results are consistent with many experimental observations for homoexpitaxy on a Pt (111) substrate.     

Microstructure and surface morphology of YSZ thin films deposited by e-beam technique

In present study yttrium-stabilized zirconia (YSZ) thin films were deposited on optical quartz (amorphous SiO₂), porous Ni-YSZ and crystalline Alloy 600 (Fe-Ni-Cr) substrates using e-beam deposition technique and controlling technological parameters: substrate temperature and electron gun power which influence thin-film deposition mechanism. X-ray diffraction, scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to investigate how thin-film structure and surface morphology depend on these parameters. It was found that the crystallite size, roughness and growth mechanism of YSZ thin films are influenced by electron gun power. To clarify the experimental results, YSZ thin-film formation as well evolution of surface roughness at its initial growing stages were analyzed. The evolution of surface roughness could be explained by the processes of surface mobility of adatoms and coalescence of islands. The analysis of these experimental results explain that surface roughness dependence on substrate temperature and electron gun power non-monotonous which could result from diffusivity of adatoms and the amount of atomic clusters in the gas stream of evaporated material.     

Transition of Growth Mode in Homoepitaxy on Metal Surface

The process of the multilayer growth of Pt on Pt (111) is studied by using a Monte Carlo model with realistic physical parameters. The effects of the substrate temperature, the ES barrier, and the deposition rate on the growth mode have been investigated. Gradual transitions of the surface roughness from oscillatory to non-oscillatory behavior and then back to oscillatory behavior are observed while increasing the substrate temperature from 270 K to 620 K. It is found that the growth mode depends strongly on ES barrier over the whole temperatures and the deposition rate of atoms effectively affects the growth mode. The simulation results are consistent with many experimental observations for homoexpitaxy on a Pt (111) substrate.     

Selecting the shape of supported metal nanocrystals: Pd huts, hexagons, or pyramids on SrTiO3(001)

Increasing interest in oxide supported nanoparticle science and technology is stimulating research into controlling nanocrystal shape. Pd forms nanocrystals on the surface of SrTiO3(001), and depending on the crystallographic interface of the Pd with the substrate three shapes can be created: truncated pyramids, huts, and hexagonal shaped disks. Scanning tunneling microscopy reveals that the nanocrystal shapes are determined by the substrate reconstruction and the substrate temperature during deposition. A thermodynamic model is used to show that the pyramids and huts are stable structures, and that the hexagons are trapped in a metastable state.     

红荧烯薄膜生长及稳定性的研究

利用原子力显微镜研究了二氧化硅衬底上红荧烯薄膜的生长及稳定性。在较低沉积速率下,较低衬底温度时,红荧烯分子有充足的扩散时间,利于薄膜的横向生长,形成连续性、均匀性较好的薄膜。快速蒸镀及较高衬底温度使红荧烯薄膜转变为纵向生长模式,形成团粒状岛。横向生长的红荧烯薄膜在退火和空气中表现为亚稳特性,随着退火温度的升高和空气中放置时间的延长,红荧烯分子会自发地进行质量传输,发生纵向转移,转变为团粒状岛。获得了二氧化硅界面上红荧烯薄膜的生长及亚稳定机制模型。研究结果证明红荧烯分子与二氧化硅界面之间的作用力小于红荧烯分子间的作用力。     

Effect of the substrate temperature and deposition rate on the initial growth of thin lithium niobate-tantalate films deposited from a thermal plasma

Thin lithium niobate-tantalate (LiNb_0.5Ta_0.5O₃) films are studied at the initial stage of deposition from a thermal plasma. The effect of two deposition parameters (the substrate temperature and the deposition rate) on the film morphology, the film crystallinity, and the density of nuclei growing on a (0001) sapphire substrate are investigated. It is shown that the crystalline structure and roughness of a film are determined, for the most part, in the initial growth stage and therefore depend directly on both parameters. At the optimum temperatures and growth rates for obtaining good characteristics of (0006) texture, crystallinity, and surface roughness of the films, the film nuclei on the substrate have a high density and good epitaxial orientation to it. If the growth conditions are not optimum, the islands are either amorphous or have a low density on the substrate surface. The nucleation activation energy is observed to decrease as the deposition rate increases, which supports the assumption that the species that are active in film deposition are “hot” clusters forming in an oxygen-argon plasma in the immediate vicinity of the substrate.     

Kinetic Monte Carlo simulation of thin film growth

A three-dimensional kinetic Monte Carlo technique has been developed for simulating growth of thin Cu films. The model involves incident atom attachment, diffusion of the atoms on the growing surface, and detachment of the atoms from the growing surface. The related effect by surface atom diffusion was taken into account. A great improvement was made on calculation of the activation energy for atom diffusion based on a reasonable assumtion of interaction potential between atoms. The surface roughness and the relative density of the films were simulated as the functions of growth substrate temperature and film thickness. The results showed that there exists an optimum growth temperatureT _opt at a given deposition rate. When the substrate temperature approaches toT _opt, the growing surface becomes smoothing and the relative density of the films increases. The surface roughness minimizes and the relative density saturates atT _opt. The surface roughness increases with an increment of substrate, temperature when the temperature is higher thanT _opt.T _opt is a function of the deposition rate and the influence of the deposition rate on the surface roughness depends on the substrate temperatures. The simulation results also showed that the relative density decreases with the increasing of the deposition rate and the average thickness of the film.     

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.     

Optimization of a thermal-CVD system for carbon nanotube growth

We illustrate the optimization of the operation of a thermal chemical vapor deposition (CVD) system for the growth of carbon nanotubes (CNT). We have studied the deposition parameters using the Taguchi matrix robust design approach. The CVD system, which employs solid precursors (camphor and ferrocene) carried by nitrogen gas flow through a hot deposition zone, where the deposition of carbon nanostructures takes place, involves a large number of tunable parameters that have to be optimized.With the aim of getting the best configuration for the development of massive and well-oriented CNT carpets, the Taguchi method allowed us to improve our system leading to the growth of extremely long CNTs (few millimeters) at a high deposition rate (500 nm/s) and yield (30% in weight of the carbon precursors feedstock), which were characterized by electron microscopy.We found that the growth temperature had the most important influence on the CNT diameter, whereas the substrate tilt wit respect to gas flow did not influence their growth (i.e. CNTs grow on every side of the silicon wafer substrates, always normal to the substrate surface). The carrier gas flow and catalyst concentration both showed a secondary impact on CNT growth, though they showed a consistent correlation to the growth temperature.     

In液滴在GaAs(001)表面扩散行为的研究

量子点的物理与光电性质主要依赖于其尺寸及密度参数,而量子点的密度、高度等参数又控制着原子在衬底上的成核行为。本文采用液滴外延法在GaAs(001)表面生长金属In液滴,研究了In液滴的扩散运动与衬底温度和沉积速率之间的关系,研究发现,随着衬底温度的升高和沉积速率的降低,In液滴尺寸增大密度却降低。通过得到的实验数据,拟合关于In液滴密度与衬底温度和沉积速率的曲线,分析了量子环的生长机制,并根据原子的表面迁移行为,进一步分析其表面原子扩散机理。     

Study of the influence of the substrate temperature and the deposition rate and time on surface morphology

An original model of the growth of thin-film surfaces is proposed. It is a stochastic cellular automaton taking particle diffusion into account. It makes it possible to study the influence of the substrate temperature and the deposition rate and time on the parameters characterizing the surface morphology. The results of the comparison of experimental data obtained using atomic-force microscopy and our theoretical data obtained by means of simulation using the proposed diffusion model are presented.     

Heating of condensation surface during magnetron sputtering

Chromium films deposited by magnetron sputtering on non-heated substrates from non-thermalized atoms crystallize in regular bcc Cr phase, with non-uniform microstructure and lattice constant along the thickness. These non-uniformities decrease with elevation of the substrate temperature and vanish at a certain value. However films deposited on non-heated substrates from thermalized atoms crystallize in a low-temperature Cr phase and have almost uniform microstructure. We have developed a model explaining this effect, which is based on the supposition of the formation of a “hot” layer on the growth surface during deposition, whose temperature depends on the flux of energy delivered to the condensation surface and can be noticeably higher than the substrate temperature. Detailed investigation of the structure of Cr films deposited at various temperatures and energy fluxes delivered to the growth surface, correlate well with the above model.     

基底显微结构对薄膜生长影响的Monte Carlo模拟研究

利用Monte Carlo方法研究了基底显微结构对薄膜生长的影响. 对不同显微结构基底上薄膜生长的初始阶段岛的形貌和尺寸与薄膜覆盖度和入射粒子沉积速率之间的关系进行了模拟和分析. 模型中考虑了粒子沉积、吸附粒子扩散和蒸发等过程. 结果表明,基底显微结构对薄膜生长具有明显影响. 当沉积温度为300K、沉积速率为0.005ML/s（Monolayer/second,简称ML/s）、覆盖度为0.05ML时,四方基底上薄膜生长呈现凝聚生长. 随着覆盖度增加,岛的尺寸变大,岛的数目减少. 而对于六方基底,当覆盖度从0.05ML变化到0.25ML时,薄膜生长经历了一个从分散生长过渡到分形生长的过程. 无论是四方还是六方基底,随着沉积速率的增加,岛的形貌由少数聚集型岛核分布状态向众多各自独立的离散型岛核分布状态过渡.     

Deposition of transparent indium tin oxide electrodes by magnetron sputtering of a metallic target on a cold substrate

Indium tin oxide layers with a surface resistance of 50 Ω/□ and a transmission in the visible range of up to 100% are obtained by magnetron sputtering of a metallic target on a cold substrate without ion enhancement of deposition and subsequent annealing. It is shown that the above parameters of the layers can be achieved in a wide range of oxygen partial pressures by controlling the deposition rate and in a wide range of deposition rates by controlling the oxygen partial pressure. An unambiguous dependence of the deposition rate on the oxygen partial pressure in the chamber is constructed.     

Strong Surface Diffusion Mediated Glancing-Angle Deposition： Growth, Recrystallization and Reorientation of Tin Nanorods

Different from usual glancing-angle deposition where low surface diffusion is necessary to form nanorods, strong surface diffusion mediated glancing-angle deposition is exemplified by growing tin nanorod films on both silicon and glass substrates simultaneously via thermal evaporation. During growth, the nanorods were simultaneously baked by the high-temperature evaporator, and therefore re-crystallized into single crystals in consequence of strong surface diffusion. The monocrystalline tin nanorods have a preferred orientation perpendicular to the substrate surface, which is quite different from the usual uniformly oblique nanorods without recrystallization.     

沉积温度对钛硅共掺杂类金刚石薄膜生长、结构和力学性能的影响

采用中频磁控溅射Ti80Si20复合靶在单晶硅表面制备了共掺杂的类金刚石薄膜.研究了沉积温度对薄膜生长速率、化学成分、结构、表面性质和力学性能的影响.结果表明:随沉积温度升高,薄膜生长速率降低,薄膜Ti和Si原子浓度增加,C原子浓度降低;在高温下沉积的薄膜具有低sp3C含量、低表面接触角、低内应力和高的硬度与弹性模量.基于亚表层注入生长模型分析了沉积温度对薄膜生长和键合结构的影响,从薄膜生长机制和微观结构解释了表面性质和力学性能的变化.     

二氧化钛薄膜表面粗糙度研究

为了探究二氧化钛(TiO₂)薄膜表面粗糙度的影响因素, 利用离子束辅助沉积电子束热蒸发技术对不同基底粗糙度以及相同基底粗糙度的K9玻璃完成二氧化钛(TiO₂)光学薄膜的沉积。采用TalySurf CCI非接触式表面轮廓仪分别对镀制前基底表面粗糙度和镀制后薄膜表面粗糙度进行测量。实验表明, TiO₂薄膜表面粗糙度随着基底表面的增大而增大, 但始终小于基底表面粗糙度, 说明TiO₂薄膜具有平滑基地表面粗糙的作用; 随着沉积速率的增大, 薄膜表面粗糙度先降低后趋于平缓; 对于粗糙度为2 nm的基底, 离子束能量大小的改变影响不大, 薄膜表面粗糙度均在1.5 nm左右; 随着膜层厚度的增大, 薄膜表面粗糙度先下降后升高。