Scattering length density profile of Ni film under controlled corrosion: A study in neutron reflectometry

We report the density depth profile of an as-deposited Ni film and density profile for the same film after controlled electrochemical corrosion by chloride ions, measured by unpolarized neutron reflectometry. The neutron reflectometry measurement of the film after corrosion shows density degradation along the thickness of the film. The density profile as a function of depth, maps the growth of pitting and void networks due to corrosion. The profile after corrosion shows an interesting peaking nature.      

Thick films of viscous fluid coating a plate withdrawn from a liquid reservoir

We consider the deposition of a film of viscous liquid on a flat plate being withdrawn from a bath, experimentally and theoretically. For any plate speed U, there is a range of "thick" film solutions whose thickness scales like U{1/2} for small U. These solutions are realized for a partially wetting liquid, while for a perfectly wetting liquid the classical Landau-Levich-Derjaguin film is observed, whose thickness scales like U{2/3}. The thick film is distinguished from the Landau-Levich-Derjaguin film by a dip in its spatial profile at the transition to the bath. We calculate the phase diagram for the existence of stationary film solutions as well as the film profiles and find excellent agreement with experiment.     

Resonant x-ray reflectivity measurements of a Ni/Fe alloy thin film: A composition profile

We have measured the composition profile of a Ni/Fe permalloy (0.8 Ni/0.2 Fe) thin film using glancing incidence X-ray reflectivity. Resonant reflectivity measurements were carried out by tuning the X-ray energy below and above, close and away from the respective K-edges of Fe and Ni. The information obtained using this method allows a determination of not only the electron density but also the composition profiles of the Ni/Fe alloy thin film. This non-destructive technique is a promising tool for the determination of the chemical composition of thin film. We used a matrix formalism to describe the wave propagation in a continuous medium. In our calculations, we used linear segments to approach the local electron density profile at the interfaces and Gaussian factors to account for the rms(root mean squre) roughness due to irregularities in the boundary position. We were able to obtain excellent fits to the data and get consistent geometry and composition parameters from the reflectivity measurements at five different X-ray energies. We detected oxidation layers on the top surface and between the alloy thin film and the substrate. We observed also that the Ni/Fe composition at the interfaces deviate from that of the bulk of the thin film sample.     

Surface polaritons on metal films with grating surface

We obtained the dispersion relation for surface polaritons propagating across a metal film upon which a periodic grating has been impressed in one face. We employed the method of reduced Rayleigh equations, and found that the surface polariton dispersion curve has an infinite number of branches. Assuming a dielectric function of a free-electron metal for the film and a sinusoidal profile function, numerical solutions were obtained for films with different thicknesses. We observed that the convergence of the method depends on the film thickness.     

周期性多层膜合金化制取的TiNi形状记忆薄膜的室温微结构特征

用掠入射X射线衍射及X射线反射对磁控溅射制取的等原子比Ni／Ti周期性多层膜晶化热处理 后的TiNi形状记忆薄膜室温微结构进行了研究.TiNi形状记忆薄膜在深度方向的相分布和元 素分布是不均匀的，都是一种多层结构.室温下其微结构特征为最外层是Ti氧化膜，再下层 是Ti₃Ni₄,B19’马氏体相和少量的B2奥氏体相的三相混合物，靠近 基体为主要相成分马氏体，最后是Ni和Si界面反应层.X射线反射率的拟和结果显示薄膜微结 构的分析是合理的.薄膜中相深度分布的不均匀性主要是动力学因素决定的. 关键词： 相深度分布 形状记忆 TiNi 多层膜     

New slip regimes and the shape of dewetting thin liquid films

We compare the flow behavior of liquid polymer films on silicon wafers coated with either octadecyl-(OTS) or dodecyltrichlorosilane (DTS). Our experiments show that dewetting on DTS is significantly faster than on OTS. We argue that this is tied to the difference in the solid/liquid friction. As the film dewets, the profile of the rim advancing into the undisturbed film is monotonically decaying on DTS but has an oscillatory structure on OTS. For the first time we can describe this transition in terms of a lubrication model with a Navier-slip condition for the flow of a viscous Newtonian liquid.     

Development of surface magneto-optical imaging method

We have observed single vortices in a NbTiN thin film by using magneto-optical (MO) imaging method, in which the light reflected from the surface of the sample produces MO contrasts. The gap between the sample and the indicator film is estimated by the Newton ring and curve fitting to the flux density profile of single vortices.     

基于槽形函数拟合的刻划光栅衍射特性分析方法

作为对光栅刻划工艺的理论指导，提出了一种基于槽形函数拟合的机械刻划光栅衍射特性分析方法，解决了高刻线密度光栅衍射效率测量值与理论值偏差较大的问题.以刻线密度为1200l/mm的紫外光栅为例，对光栅主截面上的实际槽形纵横坐标扫描取值，进而拟合出槽形函数，经理论计算找到了导致衍射效率偏低的原因，并通过改进工艺，使光栅衍射效率提高了约20%. 关键词： 刻划光栅 槽形函数拟合 衍射特性 分析方法     

Spatial mode control of a diode-pumped Nd:YAG laser by use of an intracavity holographic phase plate

We present a new method of realizing phase plates by phase-volume holography on a photopolymer film. We implement such a component in a diode-pumped Nd:YAG oscillator to control the output spatial beam profile. Flattop super-Gaussian and square-shaped beams are obtained.     

Hindered and enhanced coalescence of drops in stokes flows

We analyze axisymmetric near-contact motion of two drops under the action of an external force or imposed flow. It is shown that hydrodynamic stresses in the near-contact region that are associated with the outer (drop-scale) flow can qualitatively affect the drainage of the thin fluid film separating the drops. If this far-field stress acts radially inward, film drainage is arrested at long times; exponential film drainage occurs if this stress acts outward. An asymptotic analysis of the stationary long-time film profile is presented for small-deformation conditions, and the critical strength of van der Waals attraction for film rupture is calculated. The effect of an insoluble surfactant is also considered. Hindered and enhanced drop coalescence are not predicted by the current theories, because the influence of the outer flow on film drainage is ignored.     

Thickness dependent surface microstructure evolution of bismuth thin film prepared by molecular beam deposition method

The evolution of surface microstructure on bismuth thin film deposited by molecular beam deposition method is investigated. Morphological, topographical, structural, and electrical property changes of the film with various thicknesses are studied by means of AFM, XRD, XRR, and 4-point probe. Drastic change of surface grain in shape, which transforms from round shape to polyhedral shape, is detected around 13–18 nm film thickness. Abrupt horizontal profile change of surface grain is verified with power spectral density (PSD) function. At this threshold thickness, the film shows very low roughness value and surface area ratio. Then both increase steeply as the film thickness surpasses the thickness. As the bismuth film is deposited thicker, it has textured structure and high roughness on surface. With increment of the thickness, the electrical sheet resistance of the films is significantly decreased. We explain this surface microstructure evolution on the bismuth film with the evolutionary selection model.     

Magnetic nonuniformity and thermal hysteresis of magnetism in a manganite thin film

We measured the chemical and magnetic depth profiles of a single crystalline (La(1-x)Pr(x))(1-y)Ca(y)MnO(3-δ) (x=0.52±0.05, y=0.23±0.04, δ=0.14±0.10) film grown on a NdGaO(3) substrate using x-ray reflectometry, electron microscopy, electron energy-loss spectroscopy, and polarized neutron reflectometry. Our data indicate that the film exhibits coexistence of different magnetic phases as a function of depth. The magnetic depth profile is correlated with a variation of chemical composition with depth. The thermal hysteresis of ferromagnetic order in the film suggests a first-order ferromagnetic transition at low temperatures.     

Direct measurement of the triplet exciton diffusion length in organic semiconductors

We present a new method to measure the triplet exciton diffusion length in organic semiconductors. N,N'-di-[(1-naphthyl)-N,N'-diphenyl]-1,1'-biphenyl)-4,4'-diamine (NPD) has been used as a model system. Triplet excitons are injected into a thin film of NPD by a phosphorescent thin film, which is optically excited and forms a sharp interface with the NPD layer. The penetration profile of the triplet excitons density is recorded by measuring the emission intensity of another phosphorescent material (detector), which is doped into the NPD film at variable distances from the injecting interface. From the obtained triplet penetration profile we extracted a triplet exciton diffusion length of 87±2.7 nm. For excitation power densities >1 mW/mm(2) triplet-triplet annihilation processes can significantly limit the triplet penetration depth into organic semiconductor. The proposed sample structure can be further used to study excitonic spin degree of freedom.     

Langevin dynamics of an interface near a wall

We study dynamical contact angles and precursor films using Langevin dynamics for SOS type models, near a wall which favors spreading. We first solve exactly the Gaussian model and discuss various asymptotic regimes. This is only appropriate to partial wetting. We then consider more general models. Using local equilibrium and scaling arguments, we derive the shape of the dynamical profile and the speed of the precursor film which exists when the spreading coefficient is strictly positive. Long-range potentials lead to a layered structure of the precursor film. We also consider the case of a meniscus in a capillary.     

Long ranged correlations at a solid-fluid interface A signature of the approach to complete wetting

We have investigated the behaviour of the pairwise distribution function for Sullivan's model of a gas adsorbed on a solid substrate. We show that in the approach to complete wetting, when a thick film of liquid density is adsorbed on the substrate, long ranged transverse correlations (parallel to the surface) develop at the edge of the film where the density profile of the fluid resembles that of a liquid-gas interface. The long ranged correlations can be attributed to damped capillary-wave-like fluctuations; for a class I wetting situation the damping decreases and the range of the correlations increases and ultimately diverges as the bulk gas pressure approaches the saturated vapour pressure.

Our analysis provides a physical explanation of the long ranged transverse correlations calculated by Foiles and Ashcroft in their recent study of a model of argon at a carbon dioxide substrate. We also predict that long range transverse correlations will occur for the case of adsorption from a dense liquid provided the solid-fluid potential is such that a thick film of gas forms between the substrate and the bulk liquid.     

Monte Carlo simulations of biaxial structure in thin hybrid nematic film based upon spatially anisotropic pair potential

Hybrid nematic films have been studied by Monte Carlo simulations using a lattice spin model, in which the pair potential is spatially anisotropic and dependent on elastic constants of liquid crystals. We confirm in the thin hybrid nematic film the existence of a biaxially nonbent structure and the structure transition from the biaxial to the bent-director structure, which is similar to the result obtained using the Lebwohl--Lasher model. However, the step-like director's profile, characteristic for the biaxial structure, is spatially asymmetric in the film because the pair potential leads to K₁ ≠ K₃. We estimate the upper cell thickness to be 69 spin layers, in which the biaxial structure can be found.     

Origins of nanoscale heterogeneity in ultrathin films

A key challenge in thin-film growth is controlling structure and composition at the atomic scale. We have used spatially resolved electron scattering to measure how the three-dimensional composition profile of an alloy film evolves with time at the nanometer length scale. We show that heterogeneity during the growth of Pd on Cu(001) arises naturally from a generic step-overgrowth mechanism relevant in many growth systems.     

Structure and morphology of Cu/Ni film grown by electrodeposition method: A study of neutron reflectivity and AFM

We present detailed study of structure and interface morphology of an electrodeposited Cu/Ni film using X-ray diffraction, X-ray reflectivity, neutron reflectivity and atomic force microscopy (AFM) techniques. The crystalline structure of the film has been determined by X-ray diffraction, which suggest polycrystalline growth of the film. The depth profile of density in the sample has been obtained from specular X-ray and neutron reflectivity measurements. AFM image of the air-film interface shows that the surface is covered by globular islands of different sizes. The AFM height distribution of the surface clearly shows two peaks and the relief structure (islands) on the surface in the film, which can be treated as a quasi-two-level random rough surface structure. We have demonstrated that the detailed morphology of air-film interfaces, the quasi-two-level surface structure as well as morphology of the buried interfaces can be obtained from off-specular neutron reflectivity data. AFM and off-specular neutron reflectivity measurements also show that the morphologies of electrodeposited surface is distinctively different as compared to that of sputter-deposited surfaces in the sample.     

Enhancing the phase profile and contrast of an interferogram by polarization recording in bacteriorhodopsin

Interferometry is a technique for reconstructing the profiles of phase objects. We present a novel interferometric setup for generating interferograms with doubled phase profile and enhanced contrast compared with the standard interferogram. The proposed system consists of a two-beam interferometer in which the reference and test waves are circularly polarized orthogonally to each other. They are superposed upon a bacteriorhodopsin film, creating a polarization grating that is distorted by the phase of the test object. This polarization pattern is read by a polarized He-Ne beam. We show analytically and experimentally that, when the zero diffraction order is removed, an interferogram with doubled phase profile and enhanced contrast is obtained.     

Nonlinear waves guided by graded-index films

We derive both the dispersion relation and the power flow for waves guided by a linear graded-index film in contact with an arbitrary nonlinear cladding. For an exponential-like graded-index profile and a Kerr-like nonlinearity we present numerical results and compare them with those familar from the step-index profile.