金刚石薄膜红外椭圆偏振参量的计算与拟合

用红外椭圆偏振仪对热丝化学气相沉积法制备的金刚石薄膜的光学参量进行了测量。由于表面状态和界面特性的差异，分别对镜面抛光硅片和粗糙氧化铝基片上的金刚石薄膜建立了不同的模型，并在此基础上进行了测试结果的计算拟合。为了综合反应诸如表面粗糙度等表面界面因素对测试结果的影响，根据衬底特性将表面层和界面层分离出来，并采用Bruggeman有效介质方法对它们的影响进行了近似处理。结果表明，硅衬底上金刚石薄膜的椭偏数据在模型引入了厚度为879nm的表面粗糙层之后能得到很好的拟合。而对于氧化铝衬底上的金刚石薄膜而言，除了在薄膜表面引入了粗糙层之外，还必须在衬底和金刚石界面处加入一层由体积分数为0．641的氧化铝、体积分数为0．2334的金刚石和体积分数为0．1253的空隙组成的复合过渡层(厚度995nm)，才能使计算值与实验参量很好地吻合。     

Is There an Optimal Substrate Geometry for Wetting?

Within a 1+1-dimensional SOS type model with a periodic rough substrate, we show that the differential wall tension, which governs wetting, has a maximum as a function of a certain aspect ratio of the substrate. This result is based on a low-temperature expansion leading, in a first approximation, to Wenzel's law for the wall tension and allowing us to study the corrections to this law. It implies that the contact angle is minimum for a substrate with the corresponding aspect ratio. Our results are in agreement and explain recent numerical simulations.     

Effect of surface roughness on multilayer film growth

NbC/Si multilayers grown on silicon substrates of different roughness have been used to study the influence of surface quality on growth characteristics. Surface morphology of substrate and multilayer film are characterized by topographic measurements using atomic force microscopy (AFM) technique and power spectral density analysis (PSD). Grazing incidence x-ray reflectivity (GIXR) technique in combination with PSD analysis reveals a growth characteristic of multilayer film on substrates of different roughness. It is revealed that the stochastic growth of NbC on rough substrate leads to formation of clusters of varying size depending on initial substrate roughness. Details of growth characteristic are discussed.     

衬底表面覆盖对薄膜成核和生长的影响

在薄膜生长的成核阶段,稳定聚集体将逐渐覆盖衬底表面．同时,薄膜的生长将发生在被覆盖的衬底部分,而成核则发生在未被覆盖的部分．本文研究了衬底表面被覆盖的程度对薄膜成核和生长的影响,对广泛应用的薄膜理论,给出一些修正公式．结果表明,成核速率正比于衬底表面未被覆盖面积的平方．而薄膜理论认为成核速率是时间常量,似显得粗糙． 关键词：     

Pulsed laser deposition of hydroxyapatite film on laser gas nitriding NiTi substrate

A hydroxyapatite (HA) film was deposited on laser gas nitriding (LGN) NiTi alloy substrate using pulsed laser deposition technique. TiN dendrite prepared by LGN provided a higher number of nucleation sites for HA film deposition, which resulted in that a lot number of HA particles were deposited on TiN dendrites. Moreover, the rough LGN surface could make the interface adhesive strength between HA film and substrate increase as compared with that on bare NiTi substrate.     

Rigorous Generalization of Young's Law for Heterogeneous and Rough Substrates

We consider a SOS type model of interfaces on a substrate which is both heterogeneous and rough. We first show that, for appropriate values of the parameters, the differential wall tension that governs wetting on such a substrate satisfies a generalized law which combines both Cassie and Wenzel laws. Then in the case of an homogeneous substrate, we show that this differential wall tension satisfies either the Wenzel's law or the Cassie's law, according to the values of the parameters.     

Effect of the wall roughness on slip and rheological properties of hexadecane in molecular dynamics simulation of couette shear flow between two sinusoidal walls

Molecularly thin liquid films of alkanes in extreme conditions in a boundary lubrication regime have been investigated. The wall is modeled as a rough atomic sinusoidal wall. The effect on the boundary condition of the roughness characteristics, given by the period and amplitude of the sinusoidal wall, is studied here. The effect of the molecular length of the lubricating fluid is also examined here. The results show that the relative size of the fluid molecules and wall roughness determines the slip or nonslip boundary conditions. The effect of wall roughness characteristics on the rheological properties of the lubrication film is also studied.     

Anisotropic laser-induced evaporation of graphite films

An experimental investigation of the effect of linearly polarized high-energy pulsed laser light, normally incident on a carbon thin film, is reported. The material under study consists of platelike graphite crystallites with basal crystallographic planes mostly oriented perpendicular to the substrate surface. An increase is revealed in the fraction of the graphite crystallites oriented perpendicular to the polarization plane. Laser light is found to cause significant anisotropy in diffuse scattering by the film surface. Experimental observations are explained by a model of anisotropic evaporation of graphite-like carbon material due to polarization dependence of the absorption and reflection coefficients for a rough surface.     

含咔唑与偶氮分散红共聚物的表面增强共振拉曼光谱研究

借助于表面增强共振拉曼光谱散射(SERRS)技术,研究了一种新型的偶氮聚合物材料侧链含咔唑与偶氮分散红共聚物(CAP)在化学沉积法制备的银膜表面的拉曼峰增强和吸附行为。实验结果显示,CAP在银表面的状态为: 聚合物通过咔唑单体中咔唑基团和偶氮单体中硝基与银膜衬底发生物理吸附,而聚合物的主链与衬底相距较远没有相互作用。可以推测,聚合物在衬底表面的这种状态将对偶氮光存储器件的稳定性和工作效率产生不良影响。     

Large Eddy Simulation of Turbulent Channel Flow with 3D Roughness Using a Roughness Element Model

Large eddy simulation of turbulent channel flow with dense and small 3D roughness elements is carried out using a roughness element model Profiles of mean Reynolds stress, mean velocity and rms velocity as well as turbulent structures near the wall are obtained. The shear stress in the rough wall is larger than that in the smooth wall side and the rough wall has a larger influence on the channel flow. Profiles of mean streamwise velocity near the wall have logarithmic velocity distributions for both smooth and roughness walls, while there is a velocity decrease for the rough wall due to larger fractional drag. All the three components of rms velocities in the rough wall region are larger than that in the smooth wall region, and the roughness elements on the wall increase turbulent intensity in all directions. The s~reak spacing and average diameter of near wall quasi-s~reamwise vortices increase with the presence of roughness elements on the wall and it is shown that the rough wall induces complex and strong streamwise vortices. Results of dense and small 3D roughness elements in both turbulent statistics and structure, obtained with a relatively simple method, are found to be comparable to related experiments.     

Magnetization distribution in magneto-optical medium on patterned substrate

A micromagnetic calculation of magnetization in a ferromagnetic thin film with a perpendicular magnetic anisotropy fabricated on a patterned substrate is carried out. The domain wall energy of pinning of domain walls between up and down magnetized domains is shown to be determined by geometry of substrate. Estimations of regions of stability of two different domain structures in the hexagonal lattice of circle patches are given.     

Characterization of gold films by surface plasmon spectroscopy: Large errors and small consequences

Evaporated gold films have a smooth interface with their substrate and a rougher top surface. We investigate the optical response of such a film by excitation of surface plasmons both on the rough and on the smooth side. The smooth side, although polycrystalline, has an optical response that is very similar to a monocrystalline surface. The film can be modeled as two-layers with significantly different optical constants. For investigations on thin dielectric films though, this heterogeneity introduces only a negligible error.     

The surface cracking behavior in air plasma sprayed thermal barrier coating system incorporating interface roughness effect

The objective of this work is to understand the effect of interface roughness on the strain energy release rate and surface cracking behavior in air plasma sprayed thermal barrier coating system. This is achieved by a parameter investigation of the interfacial shapes, in which the extended finite element method (XFEM) and periodic boundary condition are used. Predictions for the stress field and driving force of multiple surface cracks in the film/substrate system are presented. It is seen that the interface roughness has significant effects on the strain energy release rate, the interfacial stress distribution, and the crack propagation patterns. One can see the completely different distributions of stress and strain energy release rate in the regions of convex and concave asperities of the substrate. Variation of the interface asperity is responsible for the oscillatory characteristics of strain energy release rate, which can cause the local arrest of surface cracks. It is concluded that artificially created rough interface can enhance the durability of film/substrate system with multiple cracks.     

非平整基底上受热液膜流动稳定性研究

本文研究了二维黏性流体薄膜沿非平整不均匀加热基底流动时非线性表面波的演化及其流动稳定性.利用长波摄动法推导出非平整线性加热基底上非线性表面波的零阶和一阶演化方程,基于所得演化方程,绘制出正弦波纹基底上液膜的表面波形图,并研究液膜流动的线性稳定性,分析了各无量纲参数对液膜线性稳定性的影响.分析结果表明:在正弦波纹基底上,液膜自由表面随同壁面作相同频率的正弦型波动,且液膜厚度沿流动方向逐渐变小;Marangoni数为稳定影响因素,随Marangoni数的增大,液膜稳定区域增大;Peclet数和倾角θ均为不稳定影响因素,随Peclet数和倾角θ的增大,液膜稳定区域减小;在非平整基底的波峰和波谷处,Peclet数、Marangoni数和倾角θ对稳定性的影响趋势一致,但基底波谷处的液膜稳定区域小于波峰处区域,流动更易失稳.     

Effects of substrate shape, curvature and roughness on thin heteroepitaxial films of Pt on Au(1 1 1)

The growth of thin (1–10 nm) films of Pt on Au(1 1 1) was studied in order to understand and clarify differences in growth mode observed in ultra-high vacuum (UHV) studies and in electrochemical deposition studies. It was found that on flat Au(1 1 1), Pt grows in a layer-by-layer growth mode, but if the gold substrate is exposed to an acidic environment prior to Pt deposition, then the substrate becomes nanoscopically rough (islanded) and Pt growth follows a pseudo-Stranski–Krastanov (SK) growth mode in which an initially thin wetting layer becomes rougher with increasing film thickness. An analysis of curvature effects on epitaxial growth mode shows that thermodynamic curvature effects involving surface stress are negligible for the Pt/Au(1 1 1) system. Rather, the apparent SK growth is linked to kinetic effects associated with inhomogeneous in-plane elastic relaxation of Pt films on rough surfaces that drive Pt atoms from pits to the tops of islands in the early stages of growth. Implications for the control of epitaxial film roughness are discussed.     

Theoretical estimate of errors in ellipsometric measurement of thin films of water on slightly rough quartz surfaces

The simple Fenstermaker-McCrackin method has been used to estimate possible errors that may be incurred on interpretation of the ellipsometric measurement of the thickness of thin water films on model rough surfaces of quartz. Two different methods are used to interpret the results expected from such a system. Both give very nearly the same result which indicates large errors for systems where the quartz substrate roughness is of the same magnitude as the thickness of the water film.     

Detection of a small defect on a rough surface

We report experimental results that show that the far-field correlation function is sensitive to a small local change in rough-surface geometry, where the speckle spatial correlation rather than the sample ensemble average is adopted. The angular cross-correlation function of the far-field speckles scattered by one-dimensional random rough surfaces is measured when a polarized beam of light is incident upon the rough surface from vacuum, where one part of the surface used is a thin dielectric film deposited upon a glass substrate and the other part is identical to the first except for a localized defect. We envisage application of this sensitivity property to inspection of a sample with a defect by means of speckle mapping.     

Thickness-dependent coercivity of ultrathin Co films on a rough substrate: Cu-buffered Si(111)

The hysteresis loops, of Co films with thicknesses ranging from 12- to 80-monolayer-equivalent (MLE) coverages grown by thermal evaporation on a Cu-covered Si(111) surface, were measured in situ by the surface magneto-optic Kerr effect (SMOKE) technique. The hysteresis loops were measured as a function of Co coverage under an external sinusoidal magnetic field at fixed driving frequency. The coercivity H_c of the Co film versus thickness t followed a power law t⁻ⁿ with n=0.4±0.1 between 12 and 44 MLE, and stabilized after 44 MLE, up to the 80 MLE studied. The surface morphology of the 80-MLE Co film was imaged ex situ by atomic force microscopy (AFM) and scanning tunneling microscopy (STM), revealing cauliflower-like islands that were rough both in the short and long range. Analysis of the height–height correlation function for the largest image gave measurements of the effective roughness exponent (0.8), the vertical interface width w(2500 Å), and the lateral correlation length ξ(10 000 Å). We suggest that the coercivity changed in part due to changes in roughness of the Co films, deposited on a rough substrate; the spatial roughness would create an additional surface anisotropy, contributing to a fluctuation in the domain wall energy, resulting in a roughness-dependent coercivity.     

Non-homogeneous SiGe-on-insulator formed by germanium condensation process

Ge condensation process of a sandwiched structure of Si/SiGe/Si on silicon-on-insulator （SOI） to form SiGe-on- insulator （SGOI） substrate is investigated. The non-homogeneity of SiGe on insulator is observed after a long time oxidation and annealing due to an increased consumption of silicon at the inflection points of the corrugated SiGe film morphology, which happens in the case of the rough surface morphology, with lateral Si atoms diffusing to the inflection points of the corrugated SiGe film. The transmission electron microscopy measurements show that the non-homogeneous SiGe layer exhibits a single crystalline nature with perfect atom lattice. Possible formation mechanism of the non-homogeneity SiGe layer is presented by discussing the highly nonuniform oxidation rate that is spatially dependent in the Ge condensation process. The results are of guiding significance for fabricating the SGOI by Ge condensation process.