Coarsening dynamics of polymer droplets for a lubrication model with large slippage

We analyze the final stages of the dewetting process of nanoscopic thin polymer films on hydrophobized substrates using a lubrication model that captures the large slippage at the liquid-substrate interface. The final stages of this process are characterized by the slow-time coarsening dynamics of the remaining droplets. For this situation we derive a reduced system of equations from the lubrication model, using singular perturbation analysis. Such reduced models allow for an efficient numerical simulation of the coarsening process. The reduced model extends results of [2] for no-slip lubrication model. Apart from collapse and collision, we identify here some new coarsening dynamics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Experiments on the spreading of silicone oil droplets on horizontal rotating plates

The spreading of liquid films is involved in many coating processes, e.g. in the spin-coating process. To achieve a high quality of the coating, the spreading liquid layer should be thin and homogeneous. Instabilities at the wetting front may lead to an inhomogeneous thickness of the coating layer and to uncoated areas. In this article the spreading of perfectly-wetting silicone oil droplets with viscosity of 100 mPa s on rotating glass plates is discussed. A Schlieren system is set up to observe the wetted area and a traversed chromatic confocal distance sensor is used to measure the contour of the droplet. The experimental data are presented and compared to an analytical model which is derived from lubrication theory and valid for thin liquid layers. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Diamond nucleation on surface of C60 thin layers

Diamond nucleation on the surface of C₆₀ thin layers and intermediate layer of Si substrates are studied by scanning electron microscopy (SEM). The cross-section SEM images of diamond films show that diamond grains really nucleate on the surface of C₆₀ thin layers. The SEM images of diamond nucleating sites show the nucleating aggregation of diamond on C₆₀ surfaces. The preferential oriented diamond films are observed. The plasma pretreatment of C₆₀ sublimating layers is a key factor for diamond nucleation.     

A few typical delamination patterns of compressed thin films

In this paper we consider compressed flat thin films on rigid substrates. Residual compressive stresses arising e.g. from temperature loading are the driving quantities of the irreversible delamination process. A Reissner–Mindlin shell formulation is used as a model for the thin film, since small geometrical imperfections are considered to initiate buckling. For the interface we postulate the existence of a cohesive free energy as a function of the opening displacement vector and internal variables. The irreversible delamination process is described using a cohesive law of exponential type, where the parameters depend on the combination of the modes I, II and III. In order to analyse the delamination process exactly we use the energy criterion of the steady-state growth. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of ZnO: Al films deposited by r.f. magnetron-sputtering at low temperature

Transparent conducting ZnO: Al thin films with good adhesion and low resistivity have been prepared on organic substrates and Corning 7059 glass substrates by r.f. magnetron-sputtering technique at low substrate temperature (25–210°C). Structural and photoelectric properties of the deposited films are investigated. The deposited films are polycrystalline with hexagonal structure and a preferred orientation with the c-axis perpendicular to the substrate. Only the (002) peak is observed. High quality films with resistivity as low as 1.0 x 10^-3Ω·cm and 8.4 x 10^-4Ω·cm, the average transmittance over 74% and 85% in the wavelength range of the visible spectrum have been obtained on different substrates.     

Spreading of thin liquid droplets on rotating disks

In many industrial processes solids are coated to obtain specific surface properties, as e.g. corrosion resistance, mechanical, optical, or electrical properties. Even today many of such coating processes are not fully understood and the choice of parameters is mainly based on experience. Hence, a prediction of the complete hydrodynamic process in its dependency on the parameters appears highly desirable. This would e.g. allow for a precise prediction of the (liquid) layer thickness and shape and help to optimize the quality of the coating. A common coating technique is the so–called spin coating. The coating agent is dissolved or suspended in a liquid, brought onto the solid, spread by rotation, and the carrier liquid is finally removed by evaporation or by chemical reactions. In this article an evolution equation is derived from lubrication theory, valid for thin liquid layers. The model involves a dynamic contact angle, centrifugal, capillary, gravitational, and molecular (London–van–der–Waals) forces. The evolution equation without molecular forces can even be solved analytically, provided the capillary number is small. Otherwise a numerical integration of the governing equations is engaged. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of ZnO:AI films deposited by r.f.magnetron-sputtering at low temperature

Transparent conducting ZnO:AI thin films with good adhesion and Iow resistivity have been prepared on organic substrates and Coming 7059 glass substrates by r.f. magnetron-sputtering technique at Iow substrate temperature (25-210℃). Structural and photoelectric properties of the deposited films are investigated. The deposited films are polycrystalline with hexagonal structure and a preferred orientation with the c-axis perpendicular to the substrate. Only the (002) peak is observed.High quality films with resistivity as Iow as 1.0 x 10- 3Ω@ cm and 8.4 x 10- 4Ω@ cm, the average transmittance over 74% and 85% in the wavelength range of the visible spectrum have been obtained on different substrates.     

Frictionless elliptical contact of thin viscoelastic layers bonded to rigid substrates

A three-dimensional unilateral contact problem for thin viscoelastic layers bonded to rigid substrates shaped like elliptic paraboloids is considered. Two cases are studied: (a) Poisson’s ratios of the layer materials are not very close to 0.5 and (b) the layer materials are incompressible with Poisson’s ratio of 0.5. Poisson’s ratios are assumed to be time independent. In the present paper we derive the general solutions to the problems of elliptical contact between thin compressible or incompressible layers of arbitrary viscoelastic materials. The approach is based on the analytical method developed by the authors for the elliptical contact of thin biphasic cartilage layers. The obtained analytical solution is valid for monotonically increasing loading conditions.     

Dynamic susceptibility computations for thin magnetic films

This paper deals with the dynamic modelling of thin ferromagnetic layers, based on the coupling of Maxwell's equations with the nonlinear Landau–Lifschitz–Gilbert law. A 2-D micromagnetic model is described which involves a FDTD code to determine equilibrium configurations and a finite element method to compute magnetostatic fields. Finally, after linearization, the susceptibility spectra of films supporting a weak-stripe-domain structure are computed and successfully compared to existing measurements without introducing any fitting parameter.     

3D FEA of Size Effects in Deformation of Thin Metallic Films

The purpose of this work is to analyze size effects in the deformation occurring during nanoindentation-tests of thin metallic films on ceramic substrates. It is well known that classical phenomenological theories of plasticity are hardly applicable in cases of very small dimensions of a body [1]. Thus, the dependency of the mechanical behavior of thin films on the thickness can not be studied in the framework of classical theories. In order to simulate numerically the deformation, a specific material model has been chosen which is able to account for size effects. It bases on the theory of ”Mechanism Strain Gradient” (MSG) plasticity [2] in conjunction with the deformation theory of plasticity. The material model has been implemented via the user defined element subroutine (UEL) in the commercial FE code ABAQUS/Standard as a ten-node tetrahedron-element. With the developed subroutine the deformation of thin copper films on Si substrates during nanoindentation-tests has been simulated. Different material models of the indentor (rigid and elastic) as well as different friction conditions between the film and the pyramidal indentor were tested. Furthermore, the influence of an additional oxide layer on the films surface has been analysed. In order to verify the numerical investigations, results from nanoindentation experiments have been used for comparison [4]. The FE simulations for different thicknesses in the range of 100-600nm showed a very good agreement with the experiments. In particular, the size dependency of the force-displacement curves, calculated by using the developed subroutine, is in rather good agreement with experiments. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Opérateurs différentiels magnétiques : stabilité des trous dans le spectre,invariance du spectre essentiel et applications

We study here the problem of geometry optimization for a crystal in the Thomas–Fermi–Von Weizsäcker (TFW) solid-state setting, i.e., the problem of minimizing the TFW energy with respect to the periodic lattice defining the positions of the nuclei. We show the existence of such a minimum, and use for that purpose the TFW models of polymers and thin films defined in a previous work (X. Blanc and C. Le Bris, Adv. Differential Equations, 5, 977–1032, 2000).     

Microscale mechanics for metal thin film delamination along ceramic substrates

The metal thin film delamination along metal/ceramic interface in the case of large scale yielding is studied by employing the strain gradient plasticity theory and the material microscale effects are considered. Two different fracture process models are used in this study to describe the nonlinear delamination phenomena for metal thin films. A set of experiments have been done on the mechanism of copper films delaminating from silica substrates, based on which the peak interface separation stress and the micro-length scale of material, as well as the dislocation-free zone size are predicted.     

Steady and Unsteady Jet Wiping Processes

The jet wiping process is widely used in continuous coating applications to remove the excess amount of liquid entrained by a sheet moving out of a liquid bath. Typical fields of applications are hot dip galvanization of metal strips and coating of photographic films. The process is based on the impact of a gas jet onto the liquid film carried by the solid substrate. In the present study the process is investigated for the case of strictly two‐dimensional flow. It is assumed that inertia effects on the film flow can be neglected, whereas the effects of the pressure gradient and the shear stress distribution of the impinging jet and the surface tension of the liquid film are taken into account. As a result it is possible to derive a single kinematic wave equation which governs the distribution of the film thickness. Numerical results for representative steady and unsteady processes including the formation of shock discontinuities are presented.     

Atomic scale epitaxial growth of BaTiO3 thin films by laser molecular beam epitaxy

By using laser molecular beam epitaxy (L-MBE), atomic scale epitaxid growth of BaTiO₃(BTO) thin films on SrTiO₃ (STO) substrates is achieved. Measurements of reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy reveal that the BTO films arec-axis oriented single crystals with smooth surface. The multi-layer ferroelectric/superconducting heterostructures are also prepared and the ferroelectric properties of BTO films are studied. The results show that by using L-MBE technique, high quality BTO films and improved device performance can be obtained. Project supported by the National Natural Science Foundation of China, the National Department of Finance, and the National Center for R and D on Superconductivity of China.     

缫丝工程中不同茧层的茧粒数分布模型及其应用

在定粒缫丝工程中采用粗细茧丝搭配的方法进行配茧缫丝时,需要根据落绪茧及茧丝粗细搭配状况选择适当的接绪茧接绪,以保持厚薄茧型的搭配,减小生丝纤度方差.本文对该缫丝动态过程进行数学建模,给出差微分方程组及其平衡状态下不同茧层茧粒数的分布.通过对定粒缫丝动态过程的计算机模拟,对获得的理论结果及其在缫丝工程管理中的应用问题进行了讨论.     

Stability of a thin liquid layer,spreading on a quasi–rotating disk

In many industrial processes solids are coated to obtain specific surface properties, as e.g. corrosion resistance, mechanical (wear) resistance, optical, or electrical properties. Even today many coating processes are not fully understood and the choice of parameters is largely based on experience. Hence, a prediction of the complete hydrodynamic process and the appearance of instabilities in its dependency on the parameters appears highly desirable. This would serve to optimize the quality of the coating. A common coating technique is the so-called spin coating. The coating agent is dissolved or suspended in a liquid, brought onto the solid, spread by rotation, and the carrier liquid is finally removed by evaporation or by chemical reactions. In this article an evolution equation is derived from lubrication theory, valid for thin liquid layers. The model involves a dynamic contact angle, centrifugal, capillary, and gravitational forces. The evolution equation can be solved analytically, provided the capillary number is small. Then a coupled linear stability analysis of the contact line and the free interface is performed. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Epitaxial growth and electrical transport properties of La0.5Sr0.5Co03 thin films prepared by pulsed laser deposition

Epitaxial growth of the La_0.5Sr_{0.5 3}(LO) thin films has been realized on Lin3, SrTiC₃ and MgO substrates by pulsed laser deposition. The epitaxial growth behavior and the electrical transport properties of these films were studied systematically. The temperature dependencies of the resistivity of the film have been determined. Studies indicate that close dependencies exist between the crystal structures and the electrical transport properties of the epitaxial LSCO films, and that the epitaxial thin films are of low resistivity and metallic conductive features. The epitaxial films deposited on the LaA10₃ substrates at about 700 °C possess the optimal properties compared with the others. Discussions of the dependencies and the mechanisms of the epitaxial structures on the electrical transport properties of the LSCO films have been made. Project supported by the National Natural Science Foundation of China (Grant No. 19574003 and No. 19674001).     

Specific quantum mechanical solution of difference equation of hyperbolic type

Difficulties connected to solving difference equations of hyperbolic type were analyzed in this work and discussed in detail. The results are compared to those of the standard wave equation and certain similarities were established. The method of solving the equation is generalized by means of kernel expanded into separable polynomials. The analysis was inspired by some new ideas concerning quantization of time. Two examples are given: excitons and phonons in thin crystalline films. The advanced methodology of Green’s function method and the application of this new methodology resulted in a set of interesting conclusions concerning thin film properties. The significance of the obtained spatial dependence of exciton concentration was discussed and it was concluded, on the basis of the found spatial dependence of exciton concentration, that such boundary conditions of a thin molecular film which lead to high exciton concentrations can be determined. It was also concluded that thin films possess high superconductive properties, that physical characteristics of thin films are spatially dependent and that the spatial dependence can be the basis for widening the field of application of nanostructures.