Electrochemical Integration of Graphene with Light-Absorbing Copper-Based Thin Films

We present an electrochemical route for the integration of graphene with light-sensitive copper-based alloys used in optoelectronic applications. Graphene grown using chemical vapor deposition (CVD) transferred to glass is found to be a robust substrate on which photoconductive CuxS films of 1-2 mu m thickness can be deposited. The effect of growth parameters on the morphology and photoconductivity of CuxS films is presented. Current-voltage (I-V) characterization and photoconductivity decay experiments are performed with graphene as one contact and silver epoxy as the other.

Atomic layer deposition of ZrO2 thin films: Study of growth kinetics and dielectric behaviour

Thin films of ZrO2 have been deposited by ALD on Si(100) and SIMOX using two different metalorganic complexes of Zr as precursors. These films are characterized by X-ray diffraction, transmission and scanning electron microscopies, infrared spectroscopy, and electrical measurements. These show that amorphous ZrO2 films of high dielectric quality may be grown on Si(100) starting about 400degreesC. As the growth temperature is raised, the films become crystalline, the phase formed and the microstructure depending on precursor molecular structure. The phase of ZrO2 formed depends also on the relative duration of the precursor and oxygen pulses. XPS and IR spectroscopy show that films grown at low temperatures contain chemically unbound carbon, its extent depending on the precursor. C-V measurements show that films grown on Si(100) have low interface state density, low leakage current, a hysteresis width of only 10-250 mV and a dielectric constant of similar to16-25.

Compositionally modulated Pb(Mg1/3Nb2/3)O-3-PbTiO3 relaxor thin films deposited by pulsed excimer laser ablation technique

Thin films of (1-x)Pb(Mg1/3Nb2/3)O-3 - xPbTiO(3) (x = 0.1 to 0.3)(PMN-PT) were deposited on the platinum coated silicon substrate by pulsed excimer laser ablation technique. A template layer of LaSr0.5Co0.5O3 (LSCO) was deposited on platinum substrate prior to the deposition of PMN-PT thin films. The composition and the structure of the films were modulated via proper variation of the deposition parameter such as substrate temperature, laser fluence and thickness of the template layers. We observed the impact of the thickness of LSCO template layer on the orientation of the films. A room temperature dielectric constant varying from 2000 to 4500 was noted for different composition of the films. The dielectric properties of the films were studied over the frequency range of 100 Hz - 100 kHz over a wide range of temperatures. The films exhibited the relaxor- type behavior that was characterized by the frequency dispersion of the temperature of dielectric constant maxima (T-m) and also diffuse phase transition. C1 Indian Inst Sci, Mat Res Ctr, Bangalore, Karnataka 560012 India.

A comparative study of erbium oxide and gadolinium oxide high-k dielectric thin films grown by low-pressure metalorganic chemical vapour deposition (MOCVD) using beta-Diketonates as precursors

In this paper, a comparative study of thin films of Er2O3 and Gd2O3 grown on n-type Si(100) by low-pressure metalorganic chemical vapour deposition (MOCVD) under the identical conditions has been presented. beta-Diketonate complex of rate earth metals was used as precursor. Description on the evolution of the morphology, structure, optical, and electrical characteristics of films with respect to growth parameters and post-deposition annealing process has been presented. As-gown Gd2O3 films grow with <111> texture, whereas the texture of Er2O3 films strongly depends on the growth temperature (either <100> or <111>). Compositional analysis reveals that the Gd2O3 films grown at or above 500degreesC are carbon free whereas Er2O3 films at upto 525degreesC show the presence of heteroatoms and Er2O3 films grown above 525degreesC are carbon five. The effective dielectric constant is in the range of 7-24, while the fixed charge density is in the range - 10(11) to 10(10) CM-2 as extracted from the C-V characteristics. DC I-V study was carried out to examine the leakage behaviour of films. It reveals that the as-grown Gd2O3 film was very leakey in nature. Annealing of the films in oxidizing ambient for a period of 20 min results in a drastic improvement in the leakage behaviour. The presence of heteroatoms (such as carbon) and their effect on the properties of films are discussed.

Effect of AC&DC field on the dielectric response of (Pb,La)TiO3 thin films

Lanthanum doped lead titanate thin films are the potential candidates for the capacitors, actuators and pyroelectric sensor applications due to their excellent dielectric, and ferroelectric properties. Lanthanum doped lead titanate thin films are grown on platinum coated Si substrates by excimer laser ablation technique. A broad diffused phase transition with the maximum dielectric permittivity (ϵmax) shifting to higher temperatures with the increase of frequency, along with frequency dispersion below Tc, which are the signatures of the relaxor like characteristics were observed. The dielectric properties are investigated from −60°C to 200°C with an application of different dc fields. With increasing dc field, the dielectric constant is observed to reduce and phase transition temperature shifted to higher temperature. With the increased ac signal amplitude of the applied frequency, the magnitude of the dielectric constant is increasing and the frequency dispersion is observed in ferroelectric phase, whereas in paraelectric phase, there is no dispersion has been observed. The results are correlated with the existing theories.

Antimicrobial Properties of Nanostructured TiO2 Plus Fe Additive Thin Films Synthesized by a Cost-Effective Sol-Gel Process

We prepared thin films composed of pure TiO2 or TiO2 with an Fe additive (at concentrations of 0.2-0.8 wt%) via a simple and cost effective sol gel process, and tested their antifungal properties (against Candida albicans (MTCC-1637), Candida tropicalis (MTCC-184), Candida parapsilosis (MTCC-2509), and Candida glabrata (MTCC-3019) and antibacterial properties (against Staphylococcus faecalis (NCIM-2604) Staphylococcus epidermidis (NCIM-2493), Staphylococcus aureus (NCIL-2122), and Bacillus subtilis (NCIM-2549)). The films were deposited on glass and Si substrates and subjected to annealing at 400 degrees C for 3 h in ambient air. The film structural and morphological properties were investigated by X-ray photoelectron spectroscopy profilometry and scanning electron microscopy, respectively. Antifungal and antibacterial tests were conducted using the drop test method. Among the species examined, Candida albicans (MTCC-1637), and Staphylococcus aureus (NCIL-2122) showed complete colony formation inhibition after exposure for 4 h for the TiO2 loaded with 0.8 wt% Fe thin films. These results indicate that increasing the Fe concentration increased the antimicrobial activity, with complete inhibition of colony formation after 4 h exposure.

Compositionally and structurally modulated Pb(Mg1/3Nb2/3)O3-PbTiO3 relaxor thin films for microactuator application

Thin films of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3(x = 0.1 to 0.3) (PMN-PT) were successfully grown on the platinum coated silicon substrate by pulsed excimer laser ablation technique. A thin template layer of LaSr0.5Co0.5O3 (LSCO) was deposited on platinum substrate prior to the deposition of PMN-PT thin films. The composition and the structure of the films were modulated via proper variation of the deposition parameter such as substrate temperature, laser fluence and thickness of the template layers. We observed the impact of the thickness of LSCO template layer on the orientation of the films. The crystallographic structure and compositional variation were confirmed with x-ray diffraction and energy diffraction x-ray (EDX) analysis. A room temperature dielectric constant varying from 2000 to 4500 was noted for different composition of the films. The dielectric properties of the films were studied over the frequency range of 100 Hz - 100 kHz over a wide range of temperatures. The films exhibited the relaxor-type behavior that was characterized by the frequency dispersion of the temperature of dielectric constant maxima (Tm) and also diffuse phase transition. This relaxor nature in PMN-PT thin films was attributed to freezing of the dipole moment, which takes place below a certain temperature. This phenomenon was found to be very similar to spin glass system, where spins are observed to freeze after certain temperature.

Optical, electrical and structural characterization of ZnO:Al thin films prepared by a low cost sol-gel method

ZnO:Al thin films were prepared on glass and silicon substrates by the sol-gel spin coating method. The x-ray diffraction (XRD) results showed that a polycrystalline phase with a hexagonal structure appeared after annealing at 400 degrees C for 1 h. The transmittance increased from 91 to about 93% from pure ZnO films to ZnO film doped with 1 wt% Al and then decreased for 2 wt% Al. The optical band gap energy increased as the doping concentration was increased from 0.5 wt% to 1 wt% Al. The metal oxide semiconductor (MOS) capacitors were fabricated using ZnO films deposited on silicon (100) substrates and electrical properties such as current versus voltage (I-V) and capacitance versus voltage (C-V) characteristics were studied. The electrical resistivity decreased and the leakage current increased with an increase of annealing temperature. The dielectric constant was found to be 3.12 measured at 1 MHz. The dissipation value for the film annealed at 300 degrees C was found to be 3.1 at 5 V. (C) 2011 Elsevier Ltd. All rights reserved.

Gallium and indium co-doped ZnO thin films for white light emitting diodes

Ga and In co-doped ZnO (GIZO) thin films together with ZnO, In-doped ZnO (IZO), Ga-doped ZnO (GZO), and IZO/GZO multilayer for comparison, were grown on corning glass and boron doped Si substrates by PLD. The photoluminescence spectra of GIZO showed a strong white light emission and the current-voltage characteristics showed relatively lower turn-on voltage and larger forward current. The CIE coordinates for GIZO were observed to be (0.31, 0.33) with a correlated colour temperature of 6650 K, indicating a cool white light, and establishing a possibility of white light emitting diodes. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Optical properties change in Sb40S40Se20 thin films by light-induced effect

Thin films of Sb40Se20S40 with thickness 1000 nm were prepared by thermal evaporation technique. The amorphous nature of the thin films was verified by X-ray diffractometer. The chemical composition of the deposited thin films was examined by energy dispersive X-ray analysis (EDAX). The changes in optical properties due to the influence of laser radiation on amorphous thin films of Sb40Se20S40 glassy alloy were calculated from absorbance spectra as a function of photon energy in the wavelength region 450-900 nm. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It has been observed that laser-irradiation of the films leads to a decrease in optical band gap while increase in absorption coefficient. The decrease in the optical band gap is explained on the basis of change in nature of films due to disorderness. The optical changes are supported by X-ray photoelectron spectroscopy and Raman spectroscopy. (C) 2012 Elsevier B.V. All rights reserved.

Electrical switching and optical studies on amorphous GexSe35-xTe65 thin films

The electrical switching behavior of amorphous GexSe35-xTe65 thin film samples has been studied in sandwich geometry of electrodes. It is found that these samples exhibit memory switching behavior, which is similar to that of bulk Ge-Se-Te glasses. As expected, the switching voltages of GexSe35-xTe65 thin film samples are lower compared to those of bulk samples. In both thin film amorphous and bulk glassy samples, the switching voltages are found to increase with the increase in Ge concentration, which is consistent with the increase in network connectivity with the addition of higher coordinated Ge atoms. A sharp increase is seen in the composition dependence of the switching fields of amorphous GexSe35-xTe65 films above x = 21, which can be associated with the stiffness transition. Further, the optical band gap of a-GexSe35-x Te-65 thin film samples, calculated from the absorption spectra, is found to show an increasing trend with the increase in Ge concentration, which is consistent with the variation of switching fields with composition. The increase in structural cross-linking with progressive addition of 4-fold coordinated Ge atoms is one of the main reasons for the observed increase in switching fields as well as band gaps of GexSe35-xTe65 samples. (C) 2011 Elsevier B.V. All rights reserved.

Layer-by-Layer Assembled Thin Film of Albumin Nanoparticles for Delivery of Doxorubicin

Protein nanoparticles (NPs) have found significant applications in drug delivery due to their inherent biocompatibility, which is attributed to their natural origin. In this study, bovine serum abumin (BSA) nanoparticles were introduced in multilayer thin film via layer-by-layer self-assembly for localized delivery of the anticancer drug Doxorubicin (Dox). BSA nanoparticles (similar to 100 nm) show a high negative zeta potential in aqueous medium (-55 mV) and form a stable dispersion in water without agglomeration for a long period. Hence, BSA NPs can be assembled on a substrate via layer-by-layer approach using a positively charged polyelectrolyte (chitosan in acidic medium). The protein nature of these BSA nanoparticles ensures the biocompatibility of the film, whereas the availability of functional groups on this protein allows one to tune the property of the self-assembly to have a pH-dependent drug release profile. The growth of multilayer thin film was monitored by UV-visible spectroscopy, and the films were further characterized by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). The drug release kinetics of these BSA nanoparticles and their self-assembled thin film has been compared at a physiological pH of 7.4 and an acidic pH of 6.4.

Acenaphtho[1,2-b]quinoxaline based low band gap copolymers for organic thin film transistor applications

We report the synthesis of a novel class of low band gap copolymers based on anacenaphtho[1,2-b]quinoxaline core and oligothiophene derivatives acting as the acceptor and the donor moieties, respectively. The optical properties of the copolymers were characterized by ultraviolet-visible spectroscopy while the electrochemical properties were determined by cyclic voltammetry. The band gap of these polymers was found to be in the range 1.8-2.0 eV as calculated from the optical absorption band edge. X-ray diffraction measurements show weak pi-pi stacking interactions between the polymer chains. The hole mobility of the copolymers was evaluated using field-effect transistor measurements yielding values in the range 10(-5)-10(-3) cm(2)/Vs.

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.