Growth and Characterization Studies of ABi2ta2o9 (A = Ba, Sr and Ca) Ferroelectric Thin Films

Thin films of ferroelectric ABi2Ta2O9 bismuth-layered structure, where A = Ba, Sr and Ca, were prepared by pulsed laser deposition technique on Pt/TiO2/SiO2/Si(100) substrates. The influence of substrate temperature between 500 to 750°C, and oxygen partial pressure 100-300 mTorr, on the structural and electrical properties of the films was investigated. The films deposited above 650°C substrate temperature showed complete Aurivillius layered structure. Films annealed at 750°C for 1h in oxygen atmosphere have exhibited better electrical properties. Atomic force microscopy study of surface topography shows that the films grown at lower temperature has smaller grains and higher surface roughness. This paper discusses the pronounced influence of A-site cation substitution on the structural and ferroelectric properties with the aid of Raman spectroscopy, X-ray diffraction and electrical properties. The degradation of ferroelectric properties with Ba and Ca substitution at A-sites is attributed to the higher structural distortion caused by changing tolerance factor. A systematic proportionate variation of coercive field is attributed to electronegativity difference of A-site cations.

The effect of electrochemical lithiation on physicochemical properties of RF-sputtered Sn thin films

Thin films of Sn were deposited on Pt/Si substrates by sputtering technique and subjected to electrochemical lithiation studies. Electrochemical lithiation of Sn resulted in the formation of Sn-Li alloys of different compositions. Charging of Sn-coated Pt/Si electrodes was terminated at different potentials and the electrodes were examined for physicochemical properties. The scanning electron microscopy and atomic force microscopy images suggested that the Sn films expanded on lithiation. Roughness of the film increased with an increase in the quantity of Li present in Sn-Li alloy. Electrochemical impedance data suggested that the kinetics of charging became sluggish with an increase in the quantity of Li in Sn-Li alloy.

Indium flux, growth temperature and RF power induced effects in InN layers grown on GaN/Si substrate by plasma-assisted MBE

In the present work, we report the growth of wurtzite InN epilayers on GaN/Si (1 1 1) substrate by plasma-assisted molecular beam epitaxy (PAMBE). The growth parameters such as indium flux, substrate temperature and RF power affect the crystallographic and morphological properties of InN layers, which were evaluated using high resolution X-ray diffraction (HRXRD) analysis and atomic force microscopy (AFM). It is found that excess indium (In) concentrations and surface roughness were increased with increase in In flux and growth temperature. The intensity of HRXRD (0 0 0 2) peak, corresponding to c-axis orientation has been increased and full width at half maxima (FWHM) has decreased with increase in RF power. It was found that highly c-axis oriented InN epilayers can be grown at 450 degrees C growth temperature, 450 W RF power and 1.30 x 10(-7) mbar In beam equivalent pressure (BEP). The energy gap of InN layers grown by optimizing growth conditions was determined by photoluminescence and optical absorption measurement. (C) 2011 Elsevier B.V. All rights reserved.

Graphene as a Nanocarrier for Tamoxifen Induces Apoptosis in Transformed Cancer Cell Lines of Different Origins

A cationic amphiphile, cholest-5en-3 beta-oxyethyl pyridinium bromide (PY(+)-Chol), is able to efficiently disperse exfoliated graphene (GR) in water by the physical adsorption of PY(+)-Chol on the surface of GR to form stable, dark aqueous suspensions at room temperature. The GRPY(+)-Chol suspension can then be used to solubilize Tamoxifen Citrate (TmC), a breast cancer drug, in water. The resulting TmCGRPY(+)-Chol is stable for a long time without any precipitation. Fluorescence emission and UV absorption spectra indicate the existence of noncovalent interactions between TmC, GR, and PY(+)-Chol in these suspensions. Electron microscopy shows the existence of segregated GR sheets and TmC ribbons in the composite suspensions. Atomic force microscopy indicates the presence of extended structures of GRPY(+)-Chol, which grows wider in the presence of TmC. The slow time-dependent release of TmC is noticed in a reconstituted cell culture medium, a property useful as a drug carrier. TmCGRPY(+)-Chol selectively enhanced the cell death (apoptosis) of the transformed cancer cells compared to normal cells. This potency is found to be true for a wide range of transformed cancer cells viz. HeLa, A549, ras oncogene-transformed NIH3T3, HepG2, MDA-MB231, MCF-7, and HEK293T compared to the normal cell HEK293 in vitro. Confocal microscopy confirmed the high efficiency of TmCGRPY(+)-Chol in delivering the drug to the cells, compared to the suspensions devoid of GR.

Self assembly of bivalent glycolipids on single walled carbon nanotubes and their specific molecular recognition properties

Solubilization of single walled carbon nanotubes (SWNTs) in aqueous milieu by self assembly of bivalent glycolipids is described. Thorough analysis of the resulting composites involving Vis/near-IR spectroscopy, surface plasmon resonance, confocal Raman and atomic force microscopy reveals that glycolipid-coated SWNTs possess specific molecular recognition properties towards lectins.

Photocatalytic degradation of dimethoate using LbL fabricated TiO2/polymer hybrid films

Degradation of dimethoate under UV irradiation using TiO2/polymer films prepared by the layer-by-layer (LbL) method was investigated. The thin films were fabricated on glass slides and the surface morphology and roughness of the thin films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effect of lamp intensity, catalyst loading in the layers, number of bilayers, pH and initial dimethoate concentration on the degradation of dimethoate was systematically studied. The degradation was monitored using high performance liquid chromatography (HPLC) analysis and total organic carbon (TOC) measurements as a function of irradiation time, to see the change in concentration of dimethoate and mineralization, respectively. Complete degradation of dimethoate was achieved under TiO2 optimum loading of 4 g/L at an UV irradiation time of 180 min. Increase in the lamp intensity, catalyst loading and number of bilayers increased the rate of degradation. At a pH of 4.62, complete degradation of dimethoate was observed. The degradation efficiency decreased with increase in initial dimethoate concentration. The degradation byproducts were analyzed and confirmed by gas chromatography-mass spectra (GC-MS). Toxicity of the irradiated samples was measured using the luminescence of bacteria Vibrio fischeri after 30 min of incubation and the results showed more toxicity than the parent compound. Catalyst reusability studies revealed that the fabricated thin films could be repeatedly used for up to ten times without affecting the photocatalytic activity of the films. The findings of the present study are very useful for the treatment of wastewaters contaminated with pesticides. (C) 2011 Elsevier B.V. All rights reserved.

Growth of rutile TiO2 nanorods on TiO2 seed layer deposited by electron beam evaporation

Dense rutile TiO2 nanorods were grown on anatase TiO2 seed layer coated glass substrate by solution technique. The crystalline nature of nanorods has confirmed by transmission electron microscopy. The band gap of the TiO2 seed layer and nanorods were calculated using the UV-vis absorption spectrum and the band gap value of the anatase seed layer and rutile nanorods were 3.39 eV and 3.09 eV respectively. Water contact angle measurements were also made and showed that the contact angle of rutile nanorods was (134 degrees) larger than the seed layer contact angle (93 degrees). The RMS surface roughness of the TiO2 seed layer (0.384 nm) and nanorods film (18.5 nm) were measured by an atomic force microscope and correlated with their contact angle values. (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.

Reactive biased target ion beam deposited W-DLC nanocomposite thin films - Microstructure and its mechanical properties

Tungsten incorporated diamond like carbon (W-DLC) nanocomposite thin films with variable fractions of tungsten were deposited by using reactive biased target ion beam deposition technique. The influence of tungsten incorporation on the microstructure, surface topography, mechanical and tribological properties of the DLC were studied using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy. Atomic force microscope (AFM), transmission electron microscopy (TEM), nano-indentation and nano-scratch tests. The amount of W in films gets increases with increasing target bias voltage and most of the incorporated W reacts with carbon to form WC nanoclusters. Using TEM and FFT pattern, it was found that spherical shaped WC nanoclusters were uniformly dispersed in the DLC matrix and attains hexagonal (W2C) crystalline structure at higher W concentration. On the other hand, the incorporation of tungsten led to increase the formation of C-sp(2) hybridized bonding in DLC network and which is reflected in the hardness and elastic modulus of W-DLC films. Moreover, W-DLC films show very low friction coefficient and increased adhesion to the substrate than the DLC film, which could be closely related to its unique nanostructure of the W incorporated thin films. (C) 2011 Elsevier B.V. All rights reserved.

Dielectric properties of DC reactive magnetron sputtered Al2O3 thin films

Alumina (Al2O3) thin films were sputter deposited over well-cleaned glass and Si < 100 > substrates by DC reactive magnetron sputtering under various oxygen gas pressures and sputtering powers. The composition of the films was analyzed by X-ray photoelectron spectroscopy and an optimal O/Al atomic ratio of 1.59 was obtained at a reactive gas pressure of 0.03 Pa and sputtering power of 70 W. X-ray diffraction results revealed that the films were amorphous until 550 degrees C. The surface morphology of the films was studied using scanning electron microscopy and the as-deposited films were found to be smooth. The topography of the as-deposited and annealed films was analyzed by atomic force microscopy and a progressive increase in the rms roughness of the films from 3.2 nm to 4.53 nm was also observed with increase in the annealing temperature. Al-Al2O3-Al thin film capacitors were then fabricated on glass substrates to study the effect of temperature and frequency on the dielectric property of the films. Temperature coefficient of capacitance. AC conductivity and activation energy were determined and the results are discussed. (C) 2011 Elsevier B.V. All rights reserved.

Morphology dependent electrochemical performance of sputter deposited Sn thin films

This study deals with tailoring of the surface morphology, microstructure, and electrochemical properties of Sn thin films deposited by magnetron sputtering with different deposition rates. Scanning electron microscopy and atomic force microscopy are used to characterize the film surface morphology. Electrochemical properties of Sn thin film are measured and compared by cyclic voltammetry and charge-discharge cycle data at a constant current density. Sn thin film fabricated with a higher deposition rate exhibited an initial discharge capacity of 798 mAh g(-1) but reduced to 94 mAh g(-1) at 30th cycle. Film deposited with lower deposition rate delivered 770 mAh g(-1) during 1st cycle with improved capacity retention of 521 mAh g(-1) on 30th cycle. Comparison of electrochemical performances of these films has revealed important distinctions, which are associated with the surface morphology and hence on rate of deposition. (C) 2012 Elsevier Ltd. All rights reserved.

Study of n-ZnO/p-Si (100) thin film heterojunctions by pulsed laser deposition without buffer layer

ZnO/Si heterojunctions were fabricated by growing ZnO thin films on p-type Si (100) substrate by pulsed laser deposition without buffer layers. The crystallinity of the heterojunction was analyzed by high resolution X-ray diffraction and atomic force microscopy. The optical quality of the film was analyzed by room temperature (RT) photoluminescence measurements. The high intense band to band emission confirmed the high quality of the ZnO thin films on Si. The electrical properties of the junction were studied by temperature dependent current-voltage measurements and RT capacitance-voltage (C-V) analysis. The charge carrier concentration and the barrier height (BH) were calculated, to be 5.6x10(19) cm(-3) and 0.6 eV respectively from the C-V plot. The BH and ideality factor, calculated using the thermionic emission (TE) model, were found to be highly temperature dependent. We observed a much lower value in Richardson constant, 5.19x10(-7)A/cm(2) K-2 than the theoretical value (32 A/cm(2) K-2) for ZnO. This analysis revealed the existence of a Gaussian distribution (GD) with a standard deviation of sigma(2)=0.035 V. By implementing the GD to the TE, the values of BH and Richardson constant were obtained as 1.3 eV and 39.97 A/cm(2) K-2 respectively from the modified Richardson plot. The obtained Richardson constant value is close to the theoretical value for n-ZnO. These high quality heterojunctions can be used for solar cell applications. (C) 2012 Elsevier B.V. All rights reserved.

Self-Assembly and Catalytic Activity of Metal Nanoparticles Immobilized in Polymer Membrane Prepared via Layer-by-Layer Approach

Densely packed nanoparticles distributed in a stable and robust thin film is a highly preferred system for utilizing the various applications of nanoparticles. Here, we report covalent bond mediated layer-by-layer (LbL) self-assembled thin films of nanoparticles embedded in polymer membrane. Polymer with complementary functional group is utilized for fabrication of thin film via covalent bonding. UV-visible spectroscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to monitor the growth of LbL thin film. Subsequently, the composite thin film is used for catalysis of an organic electron transfer reaction of p-nitrophenol to p-aminophenol by sodium borohydride. The catalytic activity of these composite films is assayed multiple times, proving its applicability as a catalyst. The kinetic data obtained by monitoring reduction of p-nitrophenol suggest that the reaction rates are directly related to the sizes of the nanoparticle and porosity of the membrane.

Multilayer assemblies of polyelectrolyte-gold nanoparticles for the electrocatalytic oxidation and detection of arsenic(III)

Multilayers of poly(diallyldimethylammonium chloride) (PDDA) and citrate capped Au nanoparticles (AuNPs) anchored on sodium 3-mercapto-1-propanesulfonate modified gold electrode by electrostatic layer-by-layer assembly (LbL) technique are shown to be an excellent architecture for the direct electrochemical oxidation of As(III) species. The growth of successive layers in the proposed LbL architecture is followed by atomic force microscopy, UV-vis spectroscopy, quartz crystal microbalance with energy dissipation, and electrochemistry. The first bilayer is found to show rather different physico-chemical characteristics as compared to the subsequent bilayers, and this is attributed to the difference in the adsorption environments. The analytical utility of the architecture with five bilayers is exploited for arsenic sensing via the direct electrocatalytic oxidation of As(III), and the detection limit is found to be well below the WHO guidelines of 10 ppb. When the non-redox active PDDA is replaced by the redoxactive Os(2,2'-bipyridine)(2)Cl-poly(4-vinylpyridine) polyelectrolyte (PVPOs) in the LbL assembly, the performance is found to be inferior, demonstrating that the redox activity of the polyelectrolyte is futile as far as the direct electro-oxidation of As(III) is concerned. (C) 2012 Elsevier Inc. All rights reserved.

Influence of annealing temperature on Raman and photoluminescence spectra of electron beam evaporated TiO2 thin films

Titanium dioxide (TiO2) thin films were deposited on fused quartz substrates by electron beam evaporation method at room temperature. The films were annealed at different temperatures in ambient air. The surface morphology/roughness at different annealing temperatures were analyzed by atomic force microscopy (AFM). The crystallinity of the film has improved with the increase of annealing temperature. The effect of annealing temperature on optical, photoluminescence and Raman spectra of TiO2 films were investigated. The refractive index of TiO2 films were studied by envelope method and reflectance spectra and it is observed that the refractive index of the films was high. The photoluminescence intensity corresponding to green emission was enhanced with increase of annealing temperature. The peaks in Raman spectra depicts that the TiO2 film is of anatase phase after annealing at 300 degrees C and higher. The films show high refractive index, good optical quality and photoluminescence characteristics suggest that possible usage in opto-electronic and optical coating applications. (C) 2012 Elsevier B.V. All rights reserved.