Modeling Nonlinear Peeling of Ductile Thin Films-Critical Assessment of Analytical Bending Models Using FE Simulations

Three analytical double-parameter criteria based on a bending model and a two-dimensional finite element analysis model are presented for the modeling of ductile thin film undergoing a nonlinear peeling process. The bending model is based on different governing parameters: (1) the interfacial fracture toughness and the separation strength, (2) the interfacial fracture toughness and the crack tip slope angle, and (3) the interfacial fracture toughness and the critical Mises effective strain of the delaminated thin film at the crack tip. Thin film nonlinear peeling under steady-state condition is solved with the different governing parameters. In addition, the peeling test problem is simulated by using the elastic-plastic finite element analysis model. A critical assessment of the three analytical bending models is made by comparison of the bending model solutions with the finite element analysis model solutions. Furthermore, through analyses and comparisons for solutions based on both the bending model and the finite element analysis model, some connections between the bending model and the finite element analysis model are developed. Moreover, in the present research, the effect of different selections for cohesive zone shape on the ductile film peeling solutions is discussed.

Surface Stability of Epitaxial Elastic Films by Casimir Force

We investigate the morphological stability of epitaxial thin elastic films on a substrate by the Casimir force between the film surface and a flat plate. Critical undulation wavelengths are derived for two different limit conditions. Consideration of the Casimir force in both limit cases decreases the critical wavelength of the surface perturbation.

Low Temperature Properties of PI/SiO_2 Nanocomposite Films

In this paper, the mechanical properties of PI/Si_O, nanocomposite hybrid films with different silica doping levels are experimentally studied at low temperature. Experimental results show that the coefficient of thermal expansion (CTE) of the PI/Si_O, nanocomposite hybrid films gradually reduces when the ambiance temperature is decreased. At the liquid nitrogen temperature (77 K), the CTE value is about five times less than that at room temperature (287 K). The measured CTEs of hybrid films greatly decrease when doped with inorganic silica, especially when the silica doping level is more than 1 wt.%. However, too high silica contents (more than 10 wt.%) can cause problem to disperse effectively and the specimens become quite opaque. Experimental results also show that the effects of the pre-applied stress levels can be neglected on the CTE testing. When the ambient temperature changes from 287 to 77 K, the measured average values of the films' ultimate tensile strength (UTS) and Young's modulus increase about 60 and 90%, respectively, while the breaking elongation decreases about 42%.

The Nonlinear Phenomena Of Thin Polydimethylsiloxane (Pdms) Films In Electrowetting

Electrowetting (EW) is an effective way to manipulate small volume liquid in micro- and nano-devices, for it can improve its wettability. Since the late 1990s, electrowetting-on-dielectric (EWOD) has been used widely in bio-MEMS, lab-on-a-chip, etc. Polydimethlsiloxane (PDMS) is extensively utilized as base materials in the fabrication of biomedical micro- and nano-devices. The properties of thin PDMS films used as dielectric layer in EW are studied in this paper. The experimental results show that the thin PDMS films exhibit good properties in EWOD. As to PDMS films with different thicknesses, a threshold voltage and a hysteresis were observed in the EIWOD experiments.

Piezoelectricity Of Zno Films Prepared By Sol-Gel Method

ZnO piezoelectric thin films were prepared on crystal substrate Si(111) by sol-gel technology, then characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy (AFM). The ZnO films characterized by X-ray diffraction are highly oriented in (002) direction with the growing of the film thickness. The morphologies, roughness and grain size of ZnO film investigated by AFM show that roughness and grain size of ZnO piezoelectric films decrease with the increase of the film thickness. The roughness dimension is 2.188-0.914 nm. The piezoelectric coefficient d(33) was investigated with a piezo-response force microscope (PFM). The results show that the piezoelectric coefficient increases with the increase of thickness and (002) orientation. When the force reference is close to surface roughness of the films, the piezoelectric coefficient measured is inaccurate and fluctuates in a large range, but when the force reference is big, the piezoelectric coefficient d(33) changes little and ultimately keeps constant at a low frequency.

Monitoring A Micromechanical Process In Macroscale Carbon Nanotube Films And Fibers

The evaluation of mechanical properties of carbon nanotube (CNT) fibers is inherently difficult. Here, Raman scattering-a generic methodology independent of mechanical measurements-is used to determine the interbundle strength and microscopic failure process for various CNT macroarchitectures. Raman data are used to predict the moduli of CNT films and fibers, and to illustrate the influences of the twisting geometries on the fibers' mechanical performances.

Structural, Electrical, And Optical Properties Of Inasxsb1-X Epitaxial Films Grown By Liquid-Phase Epitaxy

The InAsxSb1-x films were grown on (100) GaSb substrates by liquid-phase epitaxy, and their structural, electrical, and optical properties were investigated. The high-resolution x-ray diffraction results reveal that the single crystalline InAsxSb1-x films with a midrange composition are epitaxially grown on the GaSb substrates. Temperature dependence of the Hall mobility was theoretically modeled by considering several predominant scattering mechanisms. The results indicate that ionized impurity and dislocation scatterings dominate at low temperatures, while polar optical phonon scattering is important at room temperature (RT). Furthermore, the InAsxSb1-x films with the higher As composition exhibit the better crystalline quality and the higher mobility. The InAs0.35Sb0.65 film exhibits a Hall mobility of 4.62x10(4) cm(2) V-1 s(-1). The cutoff wavelength of photoresponse is extended to about 12 mu m with a maximum responsivity of 0.21 V/W at RT, showing great potential for RT long-wavelength infrared detection. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2989116]

The Key Factors In Fabrication Of High-Quality Ordered Macroporous Copper Film

The template-directed fabrication of highly-ordered porous film is of significant importance in implementation of the photonic band gap structure. The paper reports a simple and effective method to improve the electrodeposition of metal porous film by utilizing highly-ordered polystyrene spheres (PSs) template. By surface-modification method, the hydrophobic property of the PSs template surfaces was changed into hydrophilic one. It was demonstrated that the surface modi. cation process enhanced the permeability of the electrolyte solution in the nanometer-sized voids of the colloidal template. The homogeneously deposited copper film with the highly-ordered voids in size of less than 500 nm was successfully obtained. In addition, it was found that large defects, such as microcracks in the template, strongly influenced the macroporous films quality. An obvious preferential growth in the cracked area was observed. (C) 2008 Elsevier B. V. All rights reserved.

Thickness And Component Distributions Of Yttrium-Titanium Alloy Films In Electron-Beam Physical Vapor Deposition

Thickness and component distributions of large-area thin films are an issue of international concern in the field of material processing. The present work employs experiments and direct simulation Monte Carlo (DSMC) method to investigate three-dimensional low-density, non-equilibrium jets of yttrium and titanium vapor atoms in an electron-beams physical vapor deposition (EBPVD) system furnished with two or three electron-beams, and obtains their deposition thickness and component distributions onto 4-inch and 6-inch mono-crystal silicon wafers. The DSMC results are found in excellent agreement with our measurements, such as evaporation rates of yttrium and titanium measured in-situ by quartz crystal resonators, deposited film thickness distribution measured by Rutherford backscattering spectrometer (RBS) and surface profilometer and deposited film molar ratio distribution measured by RBS and inductively coupled plasma atomic emission spectrometer (ICP-AES). This can be taken as an indication that a combination of DSMC method with elaborate measurements may be satisfactory for predicting and designing accurately the transport process of EBPVD at the atomic level.

Large Scale Fabrication Of Periodical Bowl-Like Micropatterns Of Single Crystal Zno

Nanostructured ZnO materials are of great significance for their potential applications in photoelectronic devices, light-emitting displays, catalysis and gas sensors. In this paper, we report a new method to produce large area periodical bowl-like micropatterns of single crystal ZnO through aqueous-phase epitaxial growth on a ZnO single crystal substrate. A self-assembled monolayer of polystyrene microspheres was used as a template to confine the epitaxial growth of single crystal ZnO from the substrate, while the growth morphology was well controlled by citrate anions. Moreover, it was found that the self-assembled monolayer of colloidal spheres plays an important role in reduction of the defect density in the epitaxial ZnO layer. Though the mechanism is still open for further investigation, the present result indicates a new route to suppress the dislocations in the fabrication of single crystal ZnO film. A predicable application of this new method is for the fabrication of two-dimensional photonic crystal structures on light emitting diode surfaces.

From Hexagonally Arrayed Nanorods To Ordered Porous Film Through Controlling The Morphology Of Zno Crystals

The macrostructure can be changed by changing the morphology of its units. In this article, we use a colloidal template route, combined with hydrothermal growth method, to get the hexagonally arrayed ZnO nanorods on the polycrystalline ZnO substrate. More significantly, through controlling the morphology of ZnO crystals by adding structure-directing agent in the precursor solution, the highly ordered porous ZnO films were obtained instead of ZnO nanorods. This templated solvent-thermal method has great potential in micro/nano-fabrication. (C) 2008 Elsevier B.V. All rights reserved.

Peeling Experiments Of Ductile Thin Films Along Ceramic Substrates - Critical Assessment Of Analytical Models

Two types of peeling experiments are performed in the present research. One is for the Al film/Al2O3 substrate system with an adhesive layer between the film and the substrate. The other one is for the Cu film/Al2O3 substrate system without adhesive layer between the film and the substrate, and the Cu films are electroplated onto the Al2O3 substrates. For the case with adhesive layer, two kinds of adhesives are selected, which are all the mixtures of epoxy and polyimide with mass ratios 1:1.5 and 1:1, respectively. The relationships between energy release rate, the film thickness and the adhesive layer thickness are measured during the steady-state peeling process. The effects of the adhesive layer on the energy release rate are analyzed. Using the experimental results, several analytical criteria for the steady-state peeling based on the bending model and on the two-dimensional finite element analysis model are critically assessed. Through assessment of analytical models, we find that the cohesive zone criterion based on the beam bend model is suitable for a weak interface strength case and it describes a macroscale fracture process zone case, while the two-dimensional finite element model is effective to both the strong interface and weak interface, and it describes a small-scale fracture process zone case. (C) 2007 Elsevier Ltd. All rights reserved.

Anisotropic Deformation Of Polystyrene Particles By Mev Au Ion Irradiation

MeV An irradiation leads to a shape change of polystyrene (PS) and SiO2 particles from spherical to ellipsoidal, with an aspect ratio that can be precisely controlled by the ion fluence. Sub-micrometer PS and SiO2 particles were deposited on copper substrates and irradiated with Au ions at 230 K, using an ion energy and fluence ranging from 2 to 10 MeV and 1 x 10(14) ions/cm(2) to 1 x 10(15) ions/cm(2). The mechanisms of anisotropic deformation of PS and SiO2 particles are different because of their distinct physical and chemical properties. At the start of irradiation, the volume of PS particles decrease, then the aspect ratio increases with fluence, whereas for SiO2 particles the volume remains constant. (C) 2008 Elsevier B.V. All rights reserved.

Structural and magnetic properties of insulating Zn1-xCoxO thin films

Cobalt-doped ZnO (Zn1-xCoxO) thin films were fabricated by reactive magnetron cosputtering. The processing conditions were carefully designed to avoid the occurrence of Co precipitations. The films are c-axis oriented, and the solubility limit of Co in ZnO is less than 17%, determined by x-ray diffraction. X-ray photoemission spectroscopy measurements show Co ions have a chemical valance of 2+. In this paper, hysteresis loops were clearly observed for Zn1-xCoxO films at room temperature. The coercive field, as well as saturation magnetization per Co atom, decreases with increasing Co content, within the range of 0.07films are nonconductive as x is no more than 17%. Our results clearly demonstrate that ferromagnetism can be realized in Zn1-xCoxO without carrier incorporation. (C) 2004 American Institute of Physics.

Laser-induced wavy pattern formation in metal thin films

Laser-induced well-ordered and controllable wavy patterns are constructed in the deposited metal thin film. The micrometer-sized structure and orientation of the wavy patterns can be controlled via scanning a different size of rectangle laser spot on the films. Ordered patterns such as aligned, crossed, and whirled wave structures were designed over large areas. This patterning technique may find applications in both exploring the reliability and mechanical properties of thin films, and fabricating microfluidic devices. (C) 2004 American Institute of Physics.