Doping by diffusion of dopants from the substrate: synthesis of doped ZnO nanowires

We report on the substrate assisted doping of ZnO nanowires grown by a vapor transport technique. The nanowires were grown non-catalytically on multiwalled carbon nanotubes (MWCNTs) and soda lime glass (SLG). Carbon from MWCNTs and sodium from SLG diffuse into ZnO during the growth and are distributed uniformly and provide doping. An advantage associated with the technique is that no conventional external dopant source is required to obtain doped ZnO nanowires. The diameter, length and hence the aspect ratio can easily be varied by changing the growth conditions. The transport studies on both carbon and sodium doped ZnO support the p-type nature of ZnO. The p-type nature of carbon doped ZnO is stable for at least eight months.

Room temperature synthesis of Mn2+ doped ZnS d-dots and observation of tunable dual emission: Effects of doping concentration, temperature, and ultraviolet light illumination

Mn2+ doped (0-50.0 molar %) ZnS d-dots have been synthesized in water medium by using an environment friendly low cost chemical technique. Tunable dual emission in UV and yellow-orange regions is achieved by tailoring the Mn2+ doping concentration in the host ZnS nanocrystal. The optimum doping concentration for achieving efficient photoluminescence (PL) emission is determined to be similar to 1.10 (at. %) corresponding to 40.0 (molar %) of Mn2+ doping concentration used during synthesis. The mechanism of charge transfer from the host to the dopant leading to the intensity modulated tunable (594-610 nm) yellow-orange PL emission is straightforwardly understood as no capping agent is used. The temperature dependent PL emission measurements are carried out, viz., in 1.10 at. % Mn2+ doped sample and the experimental results are explained by using a theoretical PL emission model. It is found that the ratio of non-radiative to radiative recombination rates is temperature dependent and this phenomenon has not been reported, so far, in Mn2+ doped ZnS system. The colour tuning of the emitted light from the samples are evident from the calculated chromaticity coordinates. UV light irradiation for 150 min in 40.0 (molar %) Mn2+ doped sample shows an enhancement of 33% in PL emission intensity. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4795779]

Nanostructured GdxZn1-xO thin films by nebulizer spray pyrolysis technique: Role of doping concentration on the structural and optical properties

Nanostructured GdxZn1-xO thin films with different Gd concentration from 0% to 10% deposited at 400 degrees C using the NSF technique. The films were characterized by structural, surface and optical properties, respectively. X-ray diffraction analysis shows that the Gd doped ZnO films have lattice parameters a = 3.2497 angstrom and c = 5.2018 angstrom with hexagonal structure and preferential orientation along (002) plane. The estimated values compare well with the standard values. When film thickness increases from 222 to 240 nm a high visible region transmittance (>70%) is observed. The optical band gap energy, optical constants (n and k), complex dielectric constants (epsilon(r), and epsilon(i)) and optical conductivities (sigma(r), and sigma(i)) were calculated from optical transmittance data. The optical band gap energy is 3.2 eV for pure ZnO film and 3.6 eV for Gd0.1Zn0.9-O film. The PL studies confirm the presence of a strong UV emission peak at 399 nm. Besides, the UV emission of ZnO films decreases with the increase of Gd doping concentration correspondingly the ultra-violet emission is replaced by blue and green emissions.

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.

Tuning the photoluminescence of ZnO thin films by indium doping

Zinc Oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown on p-type boron doped Si substrates by pulsed laser deposition (PLD). The effect of indium concentration on the structural, optical and electrical properties of the film was studied. XRD, XPS and Raman studies confirm the single phase formation and successful doping of In in to ZnO. We observed various photoluminescence emissions, ranging from UV to visible, with the incorporation of In into ZnO. Room temperature Current-Voltage (I-V) characteristics showed good p-n junction properties for n-type-undoped and In doped ZnO with p-type substrates. The turn on voltage was observed to be decreasing with increase in In composition.

The effect of Se doping on spectroscopic and electrical properties of GeTe

Selenium doped thin films of GeTe alloys were investigated for their structural modifications by X-ray Diffraction, Fourier Transform Infrared Spectroscopy, X-ray photoelectron Spectroscopy (XPS) and Raman Spectroscopy. The band gap increase from 0.69 to 1.10 eV with increasing Se addition signifies the possibility of band gap tuning in the material. Disorder decreases, band widens and conductivity saturates about 0.20 at.% of Se addition. Structural changes are explained by the bond theory of solids. The as-deposited films are amorphous and 0.50 at.% Se alloy forms a homogeneous amorphous phase with a mixture of Ge-Se and Te-Se bonds. The XPS core level spectra and Raman spectra investigation clearly indicate the formation of Ge-Se, GeTe2 and Te-Se bonds with Se addition. Crystallization temperature is found to be increasing with Se and the 0.10 at.% Se alloy is found to have a higher resistance contrast compared to other Se concentration alloys. Up to 0.10 at.% of Se addition can enhance GeTe phase change memory properties. (C) 2013 Elsevier B.V. All rights reserved.

Anthracene-Containing Conjugated Polymer Showing Four Optical Transitions Upon Doping: A Spectroscopic Study

An anthracene-containing poly(arylene-ethynylene)-alt-poly(arylene-vinylene) (PAE-PAV) of general constitutional unit (PhCCAnthrCCPhCHCHAnthrCHCH)(n) bearing two 2-ethylhexyloxy solubilizing side chains on each phenylene (Ph) unit has been synthesized and characterized. The basic electrochemical characterization was done, showing the existence of two non-reversible oxidation and one reversible reduction peaks. The optical properties, the real and imaginary part of the dielectric function, were probed using spectroscopic ellipsometry (SE). The vibrational structure of the undoped/doped polymer was investigated using Fourier transformed infrared spectroscopy. A strong change in the polaronic absorption was observed during the doping, which after modeling revealed the existence of two separated transitions. The optical changes upon doping were additionally recorded using the SE technique. Similar to the results from FT-IR spectroscopy, two new in-the-gap absorptions were found. Moreover, the electrical conductivity as well as the mobility of positive carriers were measured. In the undoped state, the conductivity of the polymer was found to be below the detection limit (doping the conductivity increased to 0.69 S cm(-1). (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 338-346

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.

Doping a Correlated Band Insulator: A New Route to Half-Metallic Behavior

We demonstrate in a simple model the surprising result that turning on an on-site Coulomb interaction U in a doped band insulator leads to the formation of a half-metallic state. In the undoped system, we show that increasing U leads to a first order transition at a finite value U-AF between a paramagnetic band insulator and an antiferomagnetic Mott insulator. Upon doping, the system exhibits half-metallic ferrimagnetism over a wide range of doping and interaction strengths on either side of U-AF. Our results, based on dynamical mean field theory, suggest a new route to half metallicity, and will hopefully motivate searches for new materials for spintronics.

Effect Of Mo Doping On The Electrical Properties Of VO2 Phase

Solution combustion synthesis technique was adopted to synthesize V2O5, and Mo doped phases, The as-synthesized V2O5, has been reduced by a novel reduction technique to form VO2 typephase. The monophasic nature of the samples as revealed by XRD data and systematic shift in peak position indicated solid solubility up to 2 at % of Mo in VO2 lattice. The crystallite size was found to similar to 40 nm. Particle size measurement carried out using Transmission electron microscope ( TEM) agreed with XRD experiments. Scanning electron microscope revealed the morphology of the particles to be plate like and bimodal. Variation in the metal- insulator transition temperature as a function of doping was investigated by 4-probe electrical resistivity measurement on sintered ceramics.

Tailoring the Microstructural, Optical, and Electrical Properties of Nanocrystalline WO3 Thin Films Using Al Doping

We have studied the influence of Al doping on the microstructural, optical, and electrical properties of spray-deposited WO3 thin films. XRD analyses confirm that all the films are of polycrystalline WO3 in nature, possessing monoclinic structure. EDX profiles of the Al-doped films show aluminum peaks implying incorporation of Al ions into WO3 lattice. On Al doping, the average crystallite size decreases due to increase in the density of nucleation centers at the time of film growth. The observed variation in the lattice parameter values on Al doping is attributed to the incorporation of Al ions into WO3 lattice. Enhancement in the direct optical band gap compared to the undoped film has been observed on Al doping due to decrease in the width of allowed energy states near the conduction band edge. The refractive indices of the films follow the Cauchy relation of normal dispersion. Electrical resistivity compared to the undoped film has been found to increase on Al doping.

Synthesis and photoluminescence properties of a novel Sr2CeO4:Dy3+ nanophosphor with enhanced brightness by Li+ co-doping

A series of Dy3+ (0.5-9 mol%) and Li+ (0.5-3 mol%) co-doped strontium cerate (Sr2CeO4) nanopowders are synthesized by low temperature solution combustion synthesis. The effects of Li+ doping on the crystal structure, chemical composition, surface morphology and photoluminescence properties are investigated. The X-ray diffraction results confirm that all the samples calcined at 900 degrees C show the pure orthorhombic (Pbam) phase. Scanning electron microscopy analysis reveals that the particles adopt irregular morphology and the porous nature of the product. Room temperature photoluminescence results indicate that the phosphor can be effectively excited by near UV radiation (290 to 390 nm) which results in the blue (484 nm) and yellow (575 nm) emission. Furthermore, PL emission intensity and wavelength are highly dependent on the concentration of Li+ doping. The emission intensity is enhanced by similar to 3 fold with Li+ doping. White light is achieved by merely varying dopant concentration. The colour purity of the phosphor is confirmed by CIE co-ordinates (x = 0.298, y = 0.360). The study demonstrates a simple and efficient method for the synthesis of novel nanophosphors with enhanced white emission.

Hexamethylenetetramine mediated simultaneous nitrogen doping and reduction of graphene oxide for a metal-free SERS substrate

We report a one-pot hydrothermal synthesis of nitrogen doped reduced graphene oxide (N-rGO) and Ag nanoparticle decorated N-rGO hybrid nanostructures from graphene oxide (GO), metal ions and hexamethylenetetramine (HMT). HMT not only reduces GO and metal ions simultaneously but also acts as the source for the nitrogen (N) dopant. We show that the N-rGO can be used as a metal-free surface enhanced Raman spectroscopy (SERS) substrate, while the Ag nano-particles decorated N-rGO can be used as an effective SERS substrate as well as a template for decorating various other nanostructures on N-rGO.

Enhancing the photocatalytic efficiency of sprayed ZnO thin films through double doping (Sn plus F) and annealing under different ambiences

Doubly (Sn + F) doped zinc oxide (ZnO:Sn:F) thin films were deposited onto glass substrates using a simplified spray pyrolysis technique. The deposited films were annealed at 400 degrees C under two different ambiences (air and vacuum) for 2 h. The photocatalytic activity of these films was assessed through photocatalytic decolorization kinetics of Methylene Blue (MB) dye and the decolorization efficiency of the annealed films was compared with that of their as-deposited counterpart. The photocatalytic studies reveal that the ZnO:Sn:F films annealed under vacuum environment exhibits better photocatalytic efficiency when compared with both air annealed and as-deposited films. The SEM and TEM images depict that the surface of each of the films has an overlayer comprising of nanobars formed on a bottom layer, having spherical grains. The studies show that the diameter of the nanobars plays crucial role in enhancing the photocatalytic activity of the ZnO:Sn:F films. The structural, optical and electrical studies substantiate the discussions on the photocatalytic ability of the deposited films. (C) 2014 Elsevier B.V. All rights reserved.

Effect of Pt doping on the gas sensing properties of porous chromium oxide films through a kinetic response analysis approach

The effect of doping trace amounts of noblemetals (Pt) on the gas sensing properties of chromium oxide thin films, is studied. The sensors are fabricated by depositing chromium oxide films on a glass substrate using a modified spray pyrolysis technique and characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The films are porous and nanocrystalline with an average crystallite size of similar to 30 nm. The typical p-type conductivity arises due to the presence of Cr vacancies, formed as a result of Cr non-stoichiometry, which is found to vary upon Pt doping. In order to analyze the effect of doping on the gas sensing properties, we have adopted a kinetic response analysis approach, which is based on Langmuir Adsorption isotherm (LA) theory. The sensor response is analyzed with equations obtained from LA theory and time constants as well as energies of adsorption-desorption are evaluated. It is seen that, Pt doping lowers the Schottky barrier height of the metal oxide semiconductor sensor from 222 meV to 172 meV. Subsequently the reduction in adsorption and desorption energies led to enhancement in sensor response and improvement in the kinetics of the sensor response i.e. the response time as well as recovery times of the sensor.