Tailoring the optical properties of amorphous heavily Er3+-doped Ge-Ga-S thin films

This study deals with the influence of Er-doping level and thermal annealing on the optical properties of amorphous Ge-Ga-S thin films. Nominal compositions of (GeS2)(75)(Ga2S3)(25) doped with high concentrations of 2.1 and 2.4 mol% Er2S3 (corresponding to 1.2 and 1.4 at% Er, respectively) have been chosen for this work. The results have been related to those obtained for the un-doped samples. The values of the refractive index, the absorption coefficient and optical band gap have been determined from the transmittance data. It has been found that the optical band gap of un-doped and 2.1 mol% Er2S3-doped films slightly increases with annealing temperature, whereas at 2.4 mol% Er2S3-doping level it is decreased. The dependences of the optical parameters on the erbium concentration and effect of annealing in the temperature range of 100-200 degrees C have been evaluated and discussed in relation to possible structural changes.

Metal doped nanosized titania used for the photocatalytic degradation of rhodamine B dye under visible-light

Metal-doped anatase nanosized titania photocatalysts were successfully synthesized using a sal gel process. Different amounts of the dopants (0.2, 0.4, 0.6, 0.8 and 1.0%) of the metals (Ag, Ni, Co and Pd) were utilized. The UV-Vis spectra (solid state diffuse reflectance spectra) of the doped nanoparticles exhibited a red shift in the absorption edge as a result of metal doping. The metal-doped nanoparticles were investigated for their photocatalytic activity under visible-light irradiation using Rhodamine B (Rh B) as a control pollutant. The results obtained indicate that the metal-doped titania had the highest activity at 0.4% metal loading. The kinetic models revealed that the photodegradation of Rh B followed a pseudo first order reaction. From ion chromatography (IC) analysis the degradation by-products Rhodamine B fragments were found to be acetate, chloride, nitrite, carbonate and nitrate ions.

Ultranarrow and Widely Tunable Mn2+-Induced Photoluminescence from Single Mn-Doped Nanocrystals of ZnS-CdS Alloys

Extensively studied Mn-doped semiconductor nanocrystals have invariably exhibited photoluminescence over a narrow energy window of width <= 150 meV in the orange-red region and a surprisingly large spectral width (>= 180 meV), contrary to its presumed atomic-like origin. Carrying out emission measurements on individual single nanocrystals and supported by ab initio calculations, we show that Mn PL emission, in fact, can (i) vary over a much wider range (similar to 370 meV) covering the deep green-deep red region and (ii) exhibit widths substantially lower (similar to 60-75 meV) than reported so far, opening newer application possibilities and requiring a fundamental shift in our perception of the emission from Mn-doped semiconductor nanocrystals.

Characteristics of Photo Electrodes Based on TiO2 Nanoparticles, Nanotubes and Microspheres for Dye Solar Cell

We have analyzed the characteristics of electrodes made of TiO2 nanotubes, microspheres and commercially available nanoparticles for dye sensitized solar cell. The morphology of the electrodes and the formation of aggregates have been analyzed by scanning electron microscopy and surface profiling technique. The concentration of Ti3+ type impurity state on the surface of these electrodes is quantified by X-ray photoelectron spectroscopy. Micro structural properties have been characterized by Brunauer, Emmett and Teller method The optical properties of the electrodes such as band gap energy, the type of band formation and the diffuse reflectance are evaluated by UV-Visible spectroscopy. The photovoltaic characteristics of dye solar cell made of these electrodes have been evaluated and it is found that the characteristics of the TiO2 film alone can alter the overall conversion efficiency to a great extent. Additional analysis using electrochemical impedance spectroscopy has been carried out to probe the electron transport properties and charge collection efficiency of these electrodes.

Novel co-evaporation approach for the growth of Sb doped SnO2 nanowires

Antimony doped tin oxide (Sb:SnO2) nanowires were grown by thermal and e-beam assisted co-evaporation of Sb and Sn in the presence of oxygen at a low substrate temperature of 450 degrees C. The field emission scanning electron microscopy study revealed that the nanowires had a length and diameter of 2-4 mu m and 20-60 nm respectively. Transmission electron microscopy study revealed the single crystalline nature of the nanowires; energy dispersive X-ray spectroscopy (EDS) and EDS mapping on the nanowires confirmed the presence of Sb doping in the nanowires. UV light detection study on the doped SnO2 nanowire films exhibited fast response and recovery time compared to undoped SnO2 nanowire films. This is an innovative and simple method to grow doped SnO2 nanowires.

MECHANISM OF CELL LYSIS IN MICROFLUIDIC CHANNEL WITH INTEGRATED NANOCOMPOSITE ELECTRODES

This paper reports on the characterization of an integrated micro-fluidic platform for controlled electrical lysis of biological cells and subsequent extraction of intracellular biomolecules. The proposed methodology is capable of high throughput electrical cell lysis facilitated by nano-composite coated electrodes. The nano-composites are synthesized using Carbon Nanotube and ZnO nanorod dispersion in polymer. Bacterial cells are used to demonstrate the lysis performance of these nanocomposite electrodes. Investigation of electrical lysis in the microchannel is carried out under different parameters, one with continuous DC application and the other under DC biased AC electric field. Lysis in DC field is dependent on optimal field strength and governed by the cell type. By introducing the AC electrical field, the electrokinetics is controlled to prevent cell clogging in the micro-channel and ensure uniform cell dispersion and lysis. Lysis mechanism is analyzed with time-resolved fluorescence imaging which reveal the time scale of electrical lysis and explain the dynamic behavior of GFP-expressing E. coli cells under the electric field induced by nanocomposite electrodes. The DNA and protein samples extracted after lysis are compared with those obtained from a conventional chemical lysis method by using a UV-Visible spectroscopy and fluorimetry. The paper also focuses on the mechanistic understanding of the nano-composite coating material and the film thickness on the leakage charge densities which lead to differential lysis efficiency.

Proposal for Graphene-Boron Nitride Heterobilayer-Based Tunnel FET

We investigate the gate-controlled direct band-to-band tunneling (BTBT) current in a graphene-boron nitride (G-BN) heterobilayer channel-based tunnel field effect transistor. We first study the imaginary band structure of hexagonal and Bernal-stacked heterobilayers by density functional theory, which is then used to evaluate the gate-controlled current under the Wentzel-Kramers-Brillouin approximation. It is shown that the direct BTBT is probable for a certain interlayer spacing of the G-BN which depends on the stacking orders.

Large-area Piezoceramic Coating with IDT Electrodes for Ultrasonic Sensing Applications

In the present paper, the ultrasonic strain sensing performance of large-area piezoceramic coating with Inter Digital Transducer (IDT) electrodes is studied. The piezoceramic coating is prepared using slurry coating technique and the piezoelectric phase is achieved by poling under DC field. To study the sensing performance of the piezoceramic coating with IDT electrodes for strain induced by the guided waves, the piezoceramic coating is fabricated on the surface of a beam specimen at one end and the ultrasonic guided waves are launched with a piezoelectric wafer bonded on another end. Often a wider frequency band of operation is needed for the effective implementation of the sensors in the Structural Health Monitoring (SHM) of various structures, for different types of damages. A wider frequency band of operation is achieved in the present study by considering the variation in the number of IDT electrodes in the contribution of voltage for the induced dynamic strain. In the present work, the fabricated piezoceramic coatings with IDT electrodes have been characterized for dynamic strain sensing applications using guided wave technique at various different frequencies. Strain levels of the launched guided wave are varied by varying the magnitude of the input voltage sent to the actuator. Sensitivity variation with the variation in the strain levels of guided wave is studied for the combination of different number of IDT electrodes. Piezoelectric coefficient e(11) is determined at different frequencies and at different strain levels using the guided wave technique.

Role of substrate temperature on the properties of Na-doped ZnO thin film nanorods and performance of ammonia gas sensors using nebulizer spray pyrolysis technique

Sodium doped zinc oxide (Na:ZnO) thin films were deposited on glass substrates at substrate temperatures 300,400 and 500 degrees C by a novel nebulizer spray method. X-ray diffraction shows that all the films are polycrystalline in nature having hexagonal structure with high preferential orientation along (0 0 2) plane. High resolution SEM studies reveal the formation of Na-doped ZnO films having uniformly distributed nano-rods over the entire surface of the substrates at 400 degrees C. The complex impedance of the ZnO nano-rods shows two distinguished semicircles and the diameter of the arcs got decreased in diameter as the temperature increases from 170 to 270 degrees C and thereafter slightly increased. (c) 2013 Elsevier B.V. All rights reserved.

Facile synthesis of carbon doped TiO2 nanowires without an external carbon source and their opto-electronic properties

The present study demonstrates a simple protocol for the preparation of one dimensional (1D) oxidized titanium carbide nanowires and their opto-electronic properties. The oxidized titanium carbide nanowires (Ox-TiC-NW) are prepared from TiC nanowires (TiC-NW) that are in turn synthesized from micron sized TiC particles using the solvothermal technique. The Ox-TiC-NW is characterized by X-ray diffraction, UV-Vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman spectroscopy. Thermal oxidation of TiC-NW yields carbon doped TiO2-NW (C-TiO2-NW), a simple methodology to obtain 1D C-TiO2-NW. Temperature dependent Raman spectra reveal characteristic bands for TiO2-NW. Electrical characterization of individual C-TiO2-NW is performed by fabricating a device structure using the focused ion beam deposition technique. The opto-electronic properties of individual C-TiO2-NW demonstrate visible light activity and the parameters obtained from photoconductivity measurements reveal very good sensitivity. This methodology opens up the possibility of using C-TiO2-NW in electronic and opto-electronic device applications.

NiS - An unusual self-doped, nearly compensated antiferromagnetic metal

NiS, exhibiting a text-book example of a first-order transition with many unusual properties at low temperatures, has been variously described in terms of conflicting descriptions of its ground state during the past several decades. We calculate these physical properties within first-principle approaches based on the density functional theory and conclusively establish that all experimental data can be understood in terms of a rather unusual ground state of NiS that is best described as a self-doped, nearly compensated, antiferromagnetic metal, resolving the age-old controversy. We trace the origin of this novel ground state to the specific details of the crystal structure, band dispersions and a sizable Coulomb interaction strength that is still sub-critical to drive the system in to an insulating state. We also show how the specific antiferromagnetic structure is a consequence of the less-discussed 90 degrees and less than 90 degrees superexchange interactions built in to such crystal structures.

Platinum Ion-Doped TiO2: High Catalytic Activity of Pt2+ with Oxide Ion Vacancy in Ti1-x4+Ptx2+O2-x Compared to Pt4+ without Oxide Ion Vacancy in Ti1-x4+Ptx4+O2

Ti0.97Pt0.032+O1.97 and Ti0.97Pt0.034+O2 have been synthesized by a solution combustion method using alanine and glycine as the fuels, respectively. Both crystallize in anatase TiO2 structure with 15 nm average crystallite size. X-ray photoelectron spectroscopy (XPS) confirmed Pt ions are in the 2+ state in Ti0.97Pt0.03O1.97 (alanine) and 4+ state in Ti0.97Pt0.03O2 (glycine). The rate of CO oxidation occurring over Ti0.97Pt0.032+O1.97 (0.76 mu mol.g(-1).s(-1)) is similar to 10, times more than that over Ti0.97Pt0.034+O2 at 60 degrees C (0.08 mu mol.g(-1).s(-1)). A large shift in 100% hydrocarbons conversion to lower temperature was observed for Pt2+ ion-substituted TiO2 relative 10 that for Pt4+ ion-substituted TiO2. After reoxidation of the reduced compound by H-2 as well as CO, Pt ions are stabilized in mixed valences, 2+ and 4+ states. The role of oxide ion vacancy has been demonstrated by CO oxidation and H-2 + O-2 recombination reactions in the presence and absence of O-2. We analyze the activated lattice oxygens upon substitution of Pt2+ and Pt4+ ions in TiO2, using first-principles density functional theory (DFT) calculations with supercells of Ti31Pt1O63, Ti30Pt2O62, and Ti29Pt3O61 for Pt2+ ion substitution and Ti31Pt1O64, Ti30Pt2O62, and Ti29Pt3O61 for Pt4+ ion substitution in TiO2. We find that the local structure of Pt2+ ion has a distorted square planar geometry and that of Pt4+ ion has an octahedral geometry similar to that of Ti4+ ion in pure TiO2. The change in coordination of Pt2+ ion gives rise to weakly bonded oxygens, and these oxygens are involved in high rates of catalytic reaction. Thus, the high catalytic activity results from synergistic roles of Pt2+ ion and oxide ion vacancy and weakly bonded lattice oxygen.

Vertical electric field stimulated neural cell functionality on porous amorphous carbon electrodes

We demonstrate the efficacy of amorphous macroporous carbon substrates as electrodes to support neuronal cell proliferation and differentiation in electric field mediated culture conditions. The electric field was applied perpendicular to carbon substrate electrode, while growing mouse neuroblastoma (N2a) cells in vitro. The placement of the second electrode outside of the cell culture medium allows the investigation of cell response to electric field without the concurrent complexities of submerged electrodes such as potentially toxic electrode reactions, electro-kinetic flows and charge transfer (electrical current) in the cell medium. The macroporous carbon electrodes are uniquely characterized by a higher specific charge storage capacity (0.2 mC/cm(2)) and low impedance (3.3 k Omega at 1 kHz). The optimal window of electric field stimulation for better cell viability and neurite outgrowth is established. When a uniform or a gradient electric field was applied perpendicular to the amorphous carbon substrate, it was found that the N2a cell viability and neurite length were higher at low electric field strengths (<= 2.5 V/cm) compared to that measured without an applied field (0 V/cm). While the cell viability was assessed by two complementary biochemical assays (MTT and LDH), the differentiation was studied by indirect immunostaining. Overall, the results of the present study unambiguously establish the uniform/gradient vertical electric field based culture protocol to either enhance or to restrict neurite outgrowth respectively at lower or higher field strengths, when neuroblastoma cells are cultured on porous glassy carbon electrodes having a desired combination of electrochemical properties. (C) 2013 Elsevier Ltd. All rights reserved.

Laser receptive polyelectrolyte thin films doped with biosynthesized silver nanoparticles for antibacterial coatings and drug delivery applications

We report a simple method to fabricate multifunctional polyelectrolyte thin films to load and deliver the therapeutic drugs. The multilayer thin films were assembled by the electrostatic adsorption of poly (allylamine hydrochloride) (PAH) and dextran sulfate (DS). The silver nanoparticles (Ag NPs) biosynthesized from novel Hybanthus enneaspermus leaf extract as the reducing agent were successfully incorporated into the film. The biosynthesized Ag NPs showed excellent antimicrobial activity against the range of enteropathogens, which could be significantly enhanced when used with commercial antibiotics. The assembled silver nano composite multilayer films showed rupture and deformation when they are exposed to laser. The Ag NPs act as an energy absorption center, locally heat up the film and rupture it under laser treatment. The antibacterial drug, moxifloxacin hydrochloride (MH) was successfully loaded into the multilayer films. The total amount of MH release observed was about 63% which increased to 85% when subjected to laser light exposure. Thus, the polyelectrolyte thin film reported in our study has significant potential in the field of remote activated drug delivery, antibacterial coatings and wound dressings. (C) 2013 Elsevier B.V. All rights reserved.