Layered Film Structures Research Articles

Self-assembled 3D biocompatible and bioactive layer at the macro-interface via graphene-based supermolecules

Research on the interface self-assembly of functional layers is fuelled by diverse biomedical needs, like drug encapsulation and release, stem cell proliferation and differentiation, cell and tissue cultures, as well as artificial organs. In this study, a novel and biocompatible 3D composite layer is fabricated on a membrane substrate by the layer-by-layer (LBL) self-assembly of graphene-based 2D supermolecules. The graphene-based 2D supermolecules are prepared by grafting poly(styrenesulfonate) (PSS, polyanion) and poly(acrylamide) (PAM, polycation) onto graphene oxide (GO) through free radical polymerization. Then, the prepared graphene-based supermolecules are taken to construct a 3D porous thin film layer through a LBL process. Polyethersulfone (PES) membrane is chosen as the model substrate. The chemical composition, surface morphology, water contact angle, surface zeta-potential, blood compatibility and the cell compatibility are systematically investigated. The results indicate that the 2D graphene-based supermolecules are successfully assembled into a 3D porous thin film layer structure on the membrane surface. The assembled layer shows increased hydrophilicity, suppressed platelet adhesion, and a limited hemolysis ratio and complement activation compared to the pristine substrate. The cell morphology observation and cytotoxicity assays demonstrate that the 3D graphene layer shows superior performance both in endothelial and hepatocyte cells proliferation and morphology differentiation. In addition, the excellent anticoagulant bioactivities indicate that the 2D graphene-based supermolecules have heparin-mimicking biological activity. In general, the protocol of interface thin film layer self-assembly confers the modified substrates with integrated blood compatibility, cell proliferation and biological activity; which may forward the fabrication of multi-functional biomedical devices by using the 2D graphene-based supermolecules.

Surface Heating Fuser with Roller Structure

The surface heating fuser structure has low energy consumption and high heating speed due to its low heat capacity and simple structure. The authors have introduced a surface heating fuser system in NIP 29. The heating material is composed of carbon nano tube and silicon rubber composite, and fabricated with thin film layer structure in order to minimize the heat capacity. A nip supporting member is applied to the heating tube inside slide along the surface of heating tube. But the high friction between the nip support member and the heating tube caused to the limitation of fusing speed and failure of electrical supply unit due to leaked lubricant. In this study, the roller type surface heating fuser structure is proposed. The fusing performance has been predicted by numerical simulation and verified by fabricated proto sample. The high fusing speed and durability of structure is confirmed through the evaluation of fusing system.

태양열 집열기에 사용될 선택흡수막의 성능 평가

Metal-metal oxide (M-M oxide) cermet solar selective coatings with a double cermet layer film structure were deposited on the Al-deposited glass substrate by using a directed current (DC) magnetron sputtering technology. M oxide (CrO and ZrO) was used as the ceramic component in the cermets, and Cr and Zr used as the metallic components. In addition, black Cr (Cr- cermet) solar selective coatings were deposited on the Ni-plated Cu substrate by using a electroplating method for comparison. The thermal stability tests were carried out for performance evaluation of solar coatings. Reflectance measurements were used to evaluate both solar absorptance() and thermal emittance () of the solar coatings before and after thermal testing by using a spectrometer. Optical properties of optimized cermet solar coatings were and (). The results of thermal stability test of M-M oxide solar coatings showed that the Cr-CrO cermet solar selective coatings were more stable than the Zr-ZrO cermet selective coatings at temperature of both in air and in vacuum. The black Cr solar selective coatings were degraded in air at temperature of . The main optical degradation modes of these coatings were diffusion of metal atoms, and oxidation.

Layered structure of friction films revealed by the comparison between multi-energy X-ray microanalysis and Monte Carlo simulations

Multi-energy X-ray spectra were acquired on friction films formed on semi-metallic brake pads rubbed against grey cast iron discs in friction tests at low and high speed, performed in a full scale bench dynamometer. The amount of X-rays generated with electrons in the same energy range as in the experimental measurements was calculated with Monte Carlo simulations performed with CASINO software, on structures of multi-layered and mixed phase films. The comparison of the qualitative behavior of the experimental peaks with results from the simulations enabled conclusions on layering, mixing, and thickness of the measured structure and revealed a layered structure on some friction films.

Variation of ferroelectric properties in (Bi,Pr)(Fe,Mn)O3/SrRuO3-Pt/CoFe2O4 layered film structure by applying direct current magnetic field

We report the preparation of (Bi,Pr)(Fe,Mn)O3(BPFM)/SrRuO3 (SRO)-Pt/CoFe2O4(CFO) layered film structure on (100) SrTiO3 substrate by pulsed laser deposition method and their structural and electrical properties. Favorable ferroelectric properties of BPFM were observed in the layered film structure with (100)-oriented growth of BPFM, SRO, and CFO. Variation of polarization vs electric field loops of BPFM by applying DC magnet field was observed, and the remnant polarization was found to increase by 3% with increasing the applied magnetic field from 0 to 10 kOe. The magnetoelectric coefficient in the present structure was estimated to be 1.5 V/(cmOe).

Optical characteristics of Bi4-xEuxTi3O12 ferroelectric thin films on fused silica substrates

Bi4-xEuxTi3O12 (BEuT) ferroelectric thin films were prepared on fused silica substrates by using chemical solution deposition technique. The attained samples had a polycrystalline bismuth-layered perovskite structure, and their optical properties were composition dependent. The thin film samples had good optical transmittance above 500 nm wavelength. A blue shift of the optical absorption edge was observed in the BEuT thin films with increasing Eu3+ concentration. The optical band gaps of BEuT thin films were estimated to be about 3.57, 3.60, 3.61, 3.63, and 3.69 eV for the samples with x = 0.25, 0.40, 0.55, 0.70, and 0.85, respectively. Photoluminescence measurements showed that two emission peaks of BEuT thin films originated from two transitions of 5 D 0 → 7 F 1 (594 nm) and 5 D 0 → 7 F 2 (617 nm) had maximum intensities when Eu3+ concentration was x = 0.40. The relatively high quenching concentration of Eu3+ content was thought to be related to the layered structure of BEuT thin films. These results suggested that multifunctional BEuT thin film materials could have promising applications in optoelectronic devices.

Lubricant evolution and depletion under laser heating: a molecular dynamics study

Understanding the performance of polymeric perfluoro-lubricants under femtosecond laser irradiation is of great fundamental importance in enhancing the stability and durability of micro- and nano-devices. In this paper, molecular dynamics simulations of perfluoropolyether are carried out to investigate the evolution and depletion of molecularly thin lubricants when subjected to laser heating. Ultrathin perfluoropolyether lubricant films are modeled by the coarse-grained bead-spring model and are coated on an inert substrate. Periodical surface morphology and layered film structure are formed in the equilibrium lubricant system due to the polar interaction of functional beads. It is found that the lubricant undergoes severe depletion with an increase in laser heating duration, resulting in aggravated lubricant evaporation and raised ridges. A temperature gradient is formed in the radial direction due to the heat transfer between the heated beads and the surrounding lubricants. During the cooling process, the strong functional interaction between end-beads and the substrate layer hinders the recovery and redistribution of depleted lubricant beads, resulting in an undersaturated film. The mechanism of lubricant depletion under laser heating is further demonstrated by analyzing the temperature dependence of surface tension. The detailed analyses of lubricant depletion provided in the present work are expected to be guidelines to design novel perfluoropolyether lubricants.

Electromechanical Response of Multilayered Polymer Films for High Energy Density Capacitors

ABSTRACTMultilayered films comprising alternating layers of polycarbonate (PC) and poly(vinylidene fluoride-hexafluoropropylene) (P[VDF-HFP]) show an enhanced dielectric strength (EB> 750 kV/mm) and an increased energy storage density (Ud ~ 13.5 J/cm3) compared to monolithic PC and P[VDF-HFP] films. Here the role of electromechanical effects in the breakdown of multilayer films is explored both by imaging the changes in the layer structure caused by electrical fields below the breakdown field and by a direct measurement of the strain in multilayer PC/ P[VDF-HFP] films subjected to similar fields. Focused Ion Beam (FIB)/ Scanning Electron Microscopy (SEM) images of the layer structure in films subjected to repeated cycles at near-breakdown fields showed local changes in the thickness of individual layers, suggesting that mechanical forces arising from field-induced compression may play a role in the steps preceding the breakdown. The directly measured field induced strain showed evidence for both an elastic and a flow component to the strain. The mechanical responses of films with ≤ 50 vol% P[VDF-HFP] were modeled as simply the sum of an elastic and viscous flow. The observed electromechanical properties vary with the layer structure. This suggests that multilayering polymers may provide a means to mitigate deleterious electromechanical effects in low modulus, high dielectric materials.

OPTIMAL SYNTHESIS OF C-AXIS ORIENTED ALN THIN FILMS

ABSTRACT C-axis oriented AlN thin films have been deposited by reactive sputtering at room temperature. The crystallographic properties of layered film structures consisting of a piezoelectric layer, aluminum nitride (AlN), synthesized on fused silica as well as on single crystal silicon substrates, have been examined. Aluminum nitride thin films were deposited by reactive pulsed-DC magnetron sputtering using an aluminum target in an Ar/N2 gas mixture. The influence of the most critical deposition parameters on the AlN thin film crystallography has been investigated by means of X-ray diffraction (XRD) analysis of the Full Width at Half Maximum (FWHM) of the rocking curve of the AlN (0002) peak. The relationship between the deposition conditions and the crystallographic orientation of the films is discussed and a guide is given on how to optimize these conditions to obtain highly c-axis oriented AlN thin films without substrate heating.

Synthesis of c-axis oriented AlN thin films on different substrates: A review

Abstract Highly c-axis oriented AlN thin films have been deposited by reactive sputtering on different substrates. The crystallographic properties of layered film structures consisting of a piezoelectric layer, aluminum nitride (AlN), synthesized on a variety of substrates, have been examined. Aluminum nitride thin films have been deposited by reactive pulsed-DC magnetron sputtering using an aluminum target in an Ar/N2 gas mixture. The influence of the most critical deposition parameters on the AlN thin film crystallography has been investigated by means of X-ray diffraction (XRD) analysis of the rocking curve Full-Width at Half Maximum (FWHM) of the AlN-(0 0 0 2) peak. The relationship between the substrate, the synthesis parameters and the crystallographic orientation of the AlN thin films is discussed. A guide is provided showing how to optimize these conditions to obtain highly c-axis oriented AlN thin films on substrates of different nature.

Lateral shift effect on the spatial interference of light wave propagating in the single-layered dielectric film

Under the oblique incidence condition, the multiple reflection of wave packets in a layered film structure will have a lateral shift increasing with the film thickness. In the analysis of the spatial interference with consideration of the lateral shift effect, a set of new analytic formulae to normalize the intensity of the s-and p-polarized wave packet was obtained to reduce the error of the ellipsometry parameters significantly as the optical path difference delta is close to mpi. The principle and method developed in this work also can be applied to other film structures in more general applications.

Coverage dependence and surface atomic structure ofMn/Si(111)−3×3studied by scanning tunneling microscopy and spectroscopy

Thin manganese silicide films of different thicknesses on Si(111) have been studied in detail by low-energy electron diffraction (LEED), scanning tunneling microscopy, and scanning tunneling spectroscopy (STM/STS). Up to a Mn coverage of 3--4 monolayers (ML), island formation is favored. For higher Mn coverages up to 12 ML uniform film growth is found. The silicide film morphology at low coverages supports a layered Mn-Si film structure. The silicide surfaces displayed a $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ LEED pattern. STM images recorded from the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ surfaces mostly show a hexagonal pattern but a honeycomb pattern has also been observed. A surface atomic structure based on chained Mn triangles is proposed. Our STM results are in good agreement with a recent theoretical model. The high-quality STS spectra recorded from the different surfaces show a clear metallic character at 1.5 ML and higher coverages. The filled-state features in the STS spectra at surfaces with 3--4 ML Mn coverages are similar to earlier published angle-resolved photoelectron spectroscopy data.

Optical and Thermal Characteristics of Zr-O Solar Selective Coatings

Zr-O (Zr-ZrO2) cermet solar selective coatings with a double cermet layer film structure on Al-coated glass substrates for solar collectors used at in high temperatures were prepared by using direct-current magnetron sputtering technology. The typical film structure from the surface to the bottom substrate was an Al2O3 anti-reflection layer on a double Zr-O cermet layer on an Al-metal infrared reflection layer. The deposited Zr-O cermet solar selective coatings had a solar absorptance of α = 0.94 – 0.96 and a thermal emittance of e = 0.07 – 010 (100 ◦C), depending on the sputtering conditions. The absorption layers of the Zr-O cermets coatings on glass and silicon substrates were identified as being amorphous by using X-ray diffraction. Surface roughness measurements of coating layers by using atomic force microscopy showed that the cermet films were very smooth and that their root-mean-square roughness (rms) was approximately 0.1 nm. The composition of the cermet coatings was determined by using X-ray photoelectron spectroscopy. A chemical shift of the photoelectron binding energy occurred due to a change in the structure of the deposited Zr-O cermet coating with increasing oxygen flow rate. The results of the thermal stability test for the thermal characteristics analysis showed that solar selective coating of the Zr-O cermet was stable at temperatures under 350 ◦C.

Magnetization dynamics in the presence of pure spin currents in magnetic single and double layers in spin ballistic and diffusive regimes

In this paper we study the spin transport by using the spin-pumping effect in epitaxial magnetic single and double layer film structures. For the magnetic single layer sample we show the spin-pumping-induced interface damping increases and saturates with the Au capping layer thickness. In addition magnetic double layer structures allowed us to investigate both the spin-pump and spin-sink effects. Coupling of pure spin currents to the magnetization via spin-sink effect is studied using time-resolved magneto-optical Kerr effect. These measurements were used to study the propagation of pure spin currents across a Au spacer layer between the two ferromagnets. The propagation of spin momentum density through the Au spacer layer was well described by spin-diffusion equation, which takes into account electron momentum and spin-flip scattering. The spin-diffusion theory was integrated into modified Landau-Lifshitz equations accounting in self-consistent manner for spin-pump/sink mechanism and spin momentum density propagation. Good agreement between theory and experimental data was found.

Second sound in bursting freely suspended smectic-Afilms

We describe the bursting of macroscopic spherical bubbles formed by smectic liquid crystals. During rupture, strong light scattering is observed. It is suggested here that peristaltic undulations of the films are responsible for this scattering. This phenomenon distinguishes bursting smectic films from bursting soap films. The dynamics of these mechanical waves are strongly influenced by the internal layered structure of the smectic films, viz. by the elasticity of the molecular layers, expressed by the smectic layer compression modulus B. We study experimentally the optical properties of bursting smectic films by means of optical transmission measurements and laser scattering. The typical wavelength range of the propagating peristaltic waves is in the micrometer range. The wavelength spectrum rather is independent of the initial film thickness delta, but the scattering intensity strongly depends on delta.

APPLYING SURFACE ACOUSTIC WAVES TECHNIQUE FOR FILM ADHESIVENESS DETERMINATION

Layered film structures are widely applied. The adhesiveness of thin layer, which controls the product quality, is a key factor to be known. The possibility of applying the surface acoustic waves (SAWs) technique to determine the adhesiveness quality of film and substrate is explored by a theoretical approach, where the interface adhesiveness is modeled by the spring model. Numerical results show that the proposed SAWs technique has a high resolution on determining the interface adhesiveness. Meanwhile, SAWs can also be applied to detect the parameters of film such as the elastic modulus, thickness, density, and Poisson's ratio nondestructively.

Arrayed Si/SiGe Nanowire Heterostructure Formation via Au-catalyzed Wet Chemical Etching Method

Aligned Si/SiGe nanowire heterostructures have been formed using Au-assisted top-down chemical etching method combined with nanosphere lithography. Since the nanowires are formed from the as-grown films, the heterostructures along the axial axis of the formed nanowires, i.e. axial heterostructures, are replica of the grown layered film structure. Thus SiGe nanowire heterostructures can be readily formed along the axis using an as-grown heterostructured film. By applying a nanosphere lithography technique, the space, diameter, and density of the nanowires can be controlled and readily formed at specifically defined area. Because of the flexibility and simplicity of this method, nanowires with embedded junctions of different doping characteristics and Si/Ge concentrations can be fabricated easily. Si and its Ge alloy nanowires and one dimensional heterostructures formed using this method may have great potential for vertical logic, photovoltaic and memory device applications.

Surface anchoring structure of a liquid crystal monolayer studied via dual polarization interferometry

The self-organization of liquid crystal molecules of 4- n -pentyl- 4' -cyanobiphenyl (5CB) forming an oriented monolayer by condensation from the vapor phase onto a silicon oxynitride surface has been observed using the evanescent wave dual slab waveguide dual polarization mode interferometry (DPI) technique. Two distinct stages to the layer formation are observed: After the formation of a layer of molecules lying prone on the surface, further condensation begins to densify the layer and produces a gradual mutual alignment of the molecules until the fully condensed, fully aligned monolayer is reached. At this limit the full coverage 5CB monolayer on this surface and at a temperature of 25 degrees C , is found to be anchored with an average molecular axis polar angle of 56+/-1 degrees and with a measured thickness of 16.6+/-0.5A . These results are in reasonable agreement with the molecular dimensions provided by molecular models. The apparent precision and accuracy of these results resolves some wide disparity between earlier studies of such systems. Previous difficulties in determining optogeometrical properties of such ultrathin birefringent films using ellipsometry or in the need for complex modeling of the film layer structure using x-ray reflectivity are overcome in this instance. We provide a technique for analyzing the dual polarization data from DPI such that the bulk refractive index values, when known, can be used to determine the orientation and thickness of a layer that is on the nanometer or subnanometer scale.

Hybrid ZnO/polymer thin films prepared by RF magnetron sputtering

Zinc oxide/poly(acrylic acid) (ZnO/PAA) multilayered hybrid films with different layer thicknesses were prepared by radio frequency magnetron sputtering. Zinc peroxide was used as precursor materials for the preparation of ZnO layers, since the zinc peroxide decomposes to ZnO during the film deposition. The films have a high transmittance in the visible region and exhibit visible photoluminescence emission. The band gap energy of the films—determined by the Tauc relationship—decreases with increasing layer thickness (3.40–3.36 eV) due to the increasing crystalline size of the ZnO particles. The morphological investigations showed that a real layered hybrid film structure formed.

Fabrication and photophysical property of Tb(III), Dy(III) and Eu(III) complex LB films containing double functional ligand of long chain mono docosyl phthalate

In this paper, new novel long chain amphiphillic monoester molecules were designed to afford double functions: film-formation and luminescent sensitization. Subsequently, organized molecular films of rare earth complexes with the functional ligands formulated as ML 2NO 3 were fabricated by the Langmuir–Blodgett film (LB) technology, where M denotes rare earth ions Eu 3+, Tb 3+ and Dy 3+; L denotes the long chain carboxylic ligands monodocosyl phthalate (22-Phth). The average molecular area was obtained according to the π-A isotherms. The LB film layer structure was demonstrated by low-angle X-ray diffraction and the average layer spacing were obtained according to the Bragg equation. UV absorbance intensity increases linearly with the number of LB films layers, which indicate that the LB films are homogeneously deposited. The fluorescence spectra of these LB films were quite different from those of their corresponding solid complexes. It reveals that the long chain esters ligands are suitable for those of the excited states of the luminescent Tb 3+ ion and Dy 3+ ion in the LB films as well as in the solid complexes, but not sensitize the europium ion effectively in the LB films.