Temperature gradient induced phase transitions and morphological changes in diamond thin film

The diamond films were deposited onto a wurtzite gallium nitride (GaN) thin film substrate using hot-filament chemical vapor deposition (HFCVD). During the film deposition a lateral temperature gradient was imposed across the substrate by inclining the substrate. As grown films predominantly showed the hexagonal phase, when no inclination was applied to the substrate. Tilting the substrate with respect to the heating filament by 6 degrees imposed a lateral temperature gradient across the substrate, which induced the formation of a cubic diamond phase. Diamond grains were predominantly oriented in the (100) direction. However, a further increase in the substrate tilt angle to 12 degrees, resulted in grains oriented in the (111) direction. The growth rate and hence the morphology of diamond grains varied along the inclined substrate. The present study focuses on the measurements of dominant phase formation and crystal orientation with varying substrate inclination using orientation-imaging microscopy (OIM). This technique enables direct examination of individual diamond grains and their crystallographic orientation. (C) 2012 Elsevier B.V. All rights reserved.

Bioactivity and mechanical properties of nickel-incorporated hydrogenated carbon nanocomposite thin films

In this paper, the influence of nickel incorporation on the mechanical properties and the in vitro bioactivity of hydrogenated carbon thin films were investigated in detail. Amorphous hydrogenated carbon (a-C : H) and nickel-incorporated hydrogenated carbon (Ni/a-C : H) thin films were deposited onto the Si substrates by using reactive biased target ion beam deposition technique. The films' chemical composition, surface roughness, microstructure and mechanical properties were investigated by using XPS, AFM, TEM, nanoindentation and nanoscratch test, respectively. XPS results have shown that the film surface is mainly composed of nickel, nickel oxide and nickel hydroxide, whereas at the core is nickel carbide (Ni3C) only. The presence of Ni3C has increased the sp(2) carbon content and as a result, the mechanical hardness of the film was decreased. However, Ni/a-C : H films shows very low friction coefficient with higher scratch-resistance behavior than that of pure a-C : H film. In addition, in vitro bioactivity study has confirmed that it is possible to grow dense bone-like apatite layer on Ni/a-C : H films. Thus, the results have indicated the suitability of the films for bone-related implant coating applications. Copyright (C) 2011 John Wiley & Sons, Ltd.

Variation in glass transition temperature of polymer nanocomposite films driven by morphological transitions

We report the variation of glass transition temperature in supported thin films of polymer nanocomposites, consisting of polymer grafted nanoparticles embedded in a homopolymer matrix. We observe a systematic variation of the estimated glass transition temperature T-g, with the volume fraction of added polymer grafted nanoparticles. We have correlated the observed T-g variation with the underlying morphological transitions of the nanoparticle dispersion in the films. Our data also suggest the possibility of formation of a low-mobility glass or gel-like layer of nanoparticles at the interface, which could play a significant role in determining T-g of the films provided. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4773442]

Low-thermal-budget solution processing of thin films of zinc ferrite and other complex oxides

Further miniaturization of magnetic and electronic devices demands thin films of advanced nanomaterials with unique properties. Spinel ferrites have been studied extensively owing to their interesting magnetic and electrical properties coupled with stability against oxidation. Being an important ferrospinel, zinc ferrite has wide applications in the biological (MRI) and electronics (RF-CMOS) arenas. The performance of an oxide like ZnFe2O4 depends on stoichiometry (defect structure), and technological applications require thin films of high density, low porosity and controlled microstructure, which depend on the preparation process. While there are many methods for the synthesis of polycrystalline ZnFe2O4 powder, few methods exist for the deposition of its thin films, where prolonged processing at elevated temperature is not required. We report a novel, microwave-assisted, low temperature (<100°C) deposition process that is conducted in the liquid medium, developed for obtaining high quality, polycrystalline ZnFe2O4 thin films on technologically important substrates like Si(100). An environment-friendly solvent (ethanol) and non-hazardous oxide precursors (β-diketonates of Zn and Fe in 1:2 molar ratio), forming a solution together, is subjected to irradiation in a domestic microwave oven (2.45 GHz) for a few minutes, leading to reactions which result in the deposition of ZnFe2O4 films on Si (100) substrates suspended in the solution. Selected surfactants added to the reactant solution in optimum concentration can be used to control film microstructure. The nominal temperature of the irradiated solution, i.e., film deposition temperature, seldom exceeds 100°C, thus sharply lowering the thermal budget. Surface roughness and uniformity of large area depositions (50x50 mm2) are controlled by tweaking the concentration of the mother solution. Thickness of the films thus grown on Si (100) within 5 min of microwave irradiation can be as high as several microns. The present process, not requiring a vacuum system, carries a very low thermal budget and, together with a proper choice of solvents, is compatible with CMOS integration. This novel solution-based process for depositing highly resistive, adherent, smooth ferrimagnetic films on Si (100) is promising to RF engineers for the fabrication of passive circuit components. It is readily extended to a wide variety of functional oxide films.

Optical and structural properties of nanostructured oxide thin films by sol‐gel technique

TiO2 and Al2O3 are commonly used materials in optical thin films in the visible and near‐infrared wavelength region due to their high transparency and good stability. In this work, TiO2 and Al2O3 single, and nano composite thin films with different compositions were deposited on glass and silicon substrates at room temperature using a sol‐gel spin coater. The optical properties like reflectance, transmittance and refractive index have been studied using Spectrophotometer, and structural properties using X‐Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM).

Polyvinylbutyral based hybrid organic/inorganic films as a moisture barrier material

Flexible and thermally stable, freestanding hybrid organic/inorganic based polymer-composite films have been fabricated using a simple solution casting method. Polyvinylbutyral and amine functionalized mesoporous silica were used to synthesize the composite. An additional polyol-''tripentaerythritol''-component was also used to increase the -OH group content in the composite matrix. The moisture permeability of the composites was investigated by following a calcium degradation test protocol. This showed a reduction in the moisture permeability with the increase in functionalized silica loadings in the matrix. A reduction in permeability was observed for the composites as compared to the neat polymer film. The thermal and mechanical properties of these composites were also investigated by various techniques like thermogravimetric analysis, differential scanning calorimetry, tensile experiments, and dynamic mechanical analysis. It was observed that these properties detonate with the increase in the functionalized silica content and hence an optimized loading is required in order to retain critical properties. This deterioration is due to the aggregation of the fillers in the matrix. Furthermore, the films were used to encapsulate P3HT (poly 3 hexyl thiophene) based organic Schottky structured diodes, and the diode characteristics under accelerated aging conditions were studied. The weathered diodes, encapsulated with composite film showed an improvement in the lifetime as compared to neat polymer film. The initial investigation of these films suggests that they can be used as a moisture barrier layer for organic electronics encapsulation application.

Development of uniformly grown ZnO NPs films using single precursor solution by pulsed spray pyrolysis technique

In this article, we have reported the controlled synthesis of uniformly grown zinc oxide nanoparticles (ZnO NPs) films by a simple, low-cost, and scalable pulsed spray pyrolysis technique. From the surface analysis it is noticed that the as-deposited films have uniformly dispersed NPs-like morphology. The structural studies reveal that these NPs films have highly crystalline hexagonal crystal structure, which are preferentially orientated along the (001) planes. The size of the NPs varied between 5 and 100 nm, and exhibited good stoichiometric chemical composition. Raman spectroscopic analysis reveals that these ZnO NPs films have pure single phase and hexagonal crystal structure. These unique nanostructured films exhibited a low electrical resistivity (5 Omega cm) and high light transmittance (90 %) in visible region.

Growth-temperature dependent physical properties of SnS nanocrystalline thin films

In this article we have demonstrated the influence of growth-temperature on the morphology and orientation of SnS films deposited by thermal evaporation technique. While increasing the growth-temperature, the morphology of SnS films changed from flakes-like nanocrystals to regular cubes, whereas their orientation shifted from <111> to <040> direction. The chemical composition of SnS films gradually changed from sulfur-rich to tin-rich with the increase of growth-temperature. The structural analyzes reveal that the crystal structure of SnS films probably changes from orthorhombic to tetragonal at the growth-temperature of about 410 degrees C. Raman studies show that SnS films grown at all temperatures consist of purely SnS phase, whereas the optical studies reveal that the direct optical bandgap of SnS films decreased with the increase of growth-temperature. From these results it has been emphasized that the morphology and orientation along with electrical and optical properties of nearly stoichiometric SnS films strongly depend on their growth-temperature.

Selenium adsorption on Au(111) and Ag(111) surfaces: adsorbed selenium and selenide films

Results of a high resolution photoemission and electrochemistry study of Se adsorption Au(111) and Ag(111) surfaces performed by immersion of pristine samples into an aqeuous solution of Na2Se are presented. Cyclic voltammetry on Au shows formation of selenium adsorbed species and the structures observed in reductive desorption are to the atomic and polymeric species observed in XPS. In the case of Au(111) XPS spectra in the Se(3d) region indeed show two main features attributed to Se chemisorbed atomically and polymeric Se-8 features.' Smaller structures due to other types of Se conformations were also observed. The Au(4f) peak line, shape does not show core level, shifts: indicative of Au selenide formation the case of silver, XPS spectra for the Ag(3d) show a broadening of the peak and a deconvolution into Ag-B bulk like Ag-Se components shows that the Ag-Se is located at a lower binding energy, an effect similar to oxidation and sulfidation of Ag. The Se(3d) XPS spectrum is found to be substantially different from the Au case and dominated by atomic type Se due to the selenide, though a smaller intensity Se structure at an energy similar to the Se-8 structure for Au is also observed. Changes in the valence band region. related to Se adsorption are reported.

Investigation of Magnon Assisted Resistivity in Permalloy Thin Films

Magnon contribution to the resistance of ferromagnetic film like Permalloy is investigated by magnetotransport measurements. We are able to observe and distinguish Anisotropic-Magnetoresistance(AMR)(1) and Magnon Magnetoresistance(MMR)(2) contributions clearly in PLD grown Permalloy films. A linear non-saturating longitudinal MR observed in high field regime for permalloy films could never be explained using AMR but only MMR can account for it.

Albumin-mediated incorporation of water-insoluble therapeutics in layer-by-layer assembled thin films and microcapsules

The present study demonstrates a method to deliver hydrophobic drugs by incorporation into thin films and microcapsules fabricated via a layer-by-layer assembly approach. The hydrophobic molecule binding properties of albumin have been exploited for solubilization of a water-insoluble molecule, pyrene (model drug), by preparation of non-covalent conjugates with bovine serum albumin (BSA). Conjugation with BSA renders a highly negative zeta potential to the previously uncharged pyrene which favors the assembly formation by electrostatic interaction with a positively charged polyelectrolyte, chitosan (at acidic pH). The growth of the assembly was followed by monitoring pyrene absorbance with successive layer deposition. The thin film assembly was demonstrated to be capable of releasing its hydrophobic cargo under physiological conditions. We demonstrated the applicability of this approach by encapsulating a water-insoluble drug, curcumin. These assemblies were further loaded with the anti-cancer drug Doxorubicin. Biocompatible calcium carbonate microparticles were used for capsule preparation. The porous nature of the microparticles allows for the pre-encapsulation of therapeutic macromolecules like protein. The fabrication of protein encapsulated stable microcapsules with hydrophobic molecules incorporated into the shell of the microcapsules has been demonstrated. The microcapsules were further capable of loading hydrophilic molecules like Rhodamine B. Thus, using the approach described, a multi-agent carrier for hydrophobic and hydrophilic drugs as well as therapeutic macromolecules can be envisioned.

Nanostructured CexZn1-xO thin films: Influence of Ce doping on the structural, optical and electrical properties

Thin films of CexZn1-xO thin films were deposited on glass substrates at 400 degrees C by nebulizer spray pyrolysis technique. Ce doping concentration (x) was varied from 0 to 10%, in steps of 2.5%. X-ray diffraction reveals that all the films have polycrystalline nature with hexagonal crystal structure and high preferential orientation along (002) plane. Optical parameters such as; transmittance, band gap energy, refractive index (n), extinction coefficient (k), complex dielectric constants (epsilon(r), epsilon(i)) and optical conductivity (sigma(r), sigma(i)) have been determined and discussed with respect to Ce concentration. All the films exhibit transmittance above 80% in the wavelength range from 330 to 2500 nm. Optical transmission measurements indicate the decrease of direct band gap energy from 3.26 to 3.12 eV with the increase of Ce concentration. Photoluminescence spectra show strong near band edge emission centered similar to 398 nm and green emission centered similar to 528 nm with excitation wavelength similar to 350 nm. High resolution scanning electron micrographs indicate the formation of vertical nano-rod like structures on the film surface with average diameter similar to 41 nm. Electrical properties of the Ce doped ZnO film have been studied using ac impedance spectroscopy in the frequency range from 100 Hz-1 MHz at different temperatures. (C) 2013 Elsevier B.V. All rights reserved.

Electrical switching behavior of amorphous Ge15Te85 Si--x(x) thin films with phase change memory applications

Amorphous Ge15Te85-xSix thin film switching devices (1 <= x <= 6) have been deposited in sandwich geometry, on glass substrates with aluminum electrodes, by flash evaporation technique. These devices exhibit memory type electrical switching, like bulk Ge15Te85-xSix glasses. However, unlike the bulk glasses, a-Ge15Te85-xSix films exhibit a smooth electrical switching behavior. The electrical switching fields of a-Ge15Te85-xSix thin film samples are also comparable with other chalcogenide samples used in memory applications. The switching fields of a-Ge15Te85-xSix films have been found to increase with increasing Si concentration. Also, the optical band gap of a-Ge15Te85-xSix films is found to increase with Si content. The observed results have been understood on the basis of increase in network connectivity and rigidity with Si addition. (C) 2013 Elsevier Ltd. All rights reserved.

Control of magnetization reversal in oriented strontium ferrite thin films

Oriented Strontium Ferrite films with the c axis orientation were deposited with varying oxygen partial pressure on Al2O3(0001) substrate using Pulsed Laser Deposition technique. The angle dependent magnetic hysteresis, remanent coercivity, and temperature dependent coercivity had been employed to understand the magnetization reversal of these films. It was found that the Strontium Ferrite thin film grown at lower (higher) oxygen partial pressure shows Stoner-Wohlfarth type (Kondorsky like) reversal. The relative importance of pinning and nucleation processes during magnetization reversal is used to explain the type of the magnetization reversal with different oxygen partial pressure during growth. (C) 2014 AIP Publishing LLC.

Near-infrared photoactive Cu3BiS3 thin films by co-evaporation

Semiconducting Cu3BiS3 (CBS) thin films were deposited by co-evaporation of Cu, Bi elemental metallic precursors, with in situ sulphurisation, using a quartz effusion cell. Cu3BiS3 thin films were structurally characterized by XRD and FE-SEM. The chemical bonding of the ions was examined by XPS. As deposited films were demonstrated for metal-semiconductor-metal near IR photodectection under lamp and laser illuminations. The photo current amplified to three orders and two orders of magnitude upon the IR lamp and 60 m W cm(-2) 1064 nm IR laser illuminations, respectively. Larger grains, made up of nano needle bunches aided the transport of carriers. Transport properties were explained based on the trap assisted space charge conduction mechanism. Steady state detector parameters like responsivity varied from 1.04 AW(-1) at 60 m Wcm(-2) to 0.22 AW(-1) at 20 m Wcm(-2). Detector sensitivity of 295 was found to be promising and further could be tuned for better responsivity and efficiency in utilization of near infra-red photodetector. (C) 2014 AIP Publishing LLC.