Self Assembly and Properties of C:WO3 Nano-Platelets and C:VO2/V2O5 Triangular Capsules Produced by Laser Solution Photolysis

Laser photolysis of WCl6 in ethanol and a specific mixture of V2O5 and VCl3 in ethanol lead to carbon modified vanadium and tungsten oxides with interesting properties. The presence of graphene’s aromatic rings (from the vibrational frequency of 1,600 cm−1) together with C–C bonding of carbon (from the Raman shift of 1,124 cm−1) present unique optical, vibrational, electronic and structural properties of the intended tungsten trioxide and vanadium dioxide materials. The morphology of these samples shows nano-platelets in WOx samples and, in VOx samples, encapsulated spherical quantum dots in conjunction with fullerenes of VOx. Conductivity studies revealed that the VO2/V2O5 nanostructures are more sensitive to Cl than to the presence of ethanol, whereas the C:WO3 nano-platelets are more sensitive to ethanol than atomic C

Thermally Induced Nano-Structural and Optical Changes of nc-Si:H Deposited by Hot-Wire CVD

We report on the thermally induced changes of the nano-structural and optical properties of hydrogenated nanocrystalline silicon in the temperature range 200–700 °C. The as-deposited sample has a high crystalline volume fraction of 53% with an average crystallite size of ~3.9 nm, where 66% of the total hydrogen is bonded as ≡Si–H monohydrides on the nano-crystallite surface. A growth in the native crystallite size and crystalline volume fraction occurs at annealing temperatures ≥400 °C, where hydrogen is initially removed from the crystallite grain boundaries followed by its removal from the amorphous network. The nucleation of smaller nano-crystallites at higher temperatures accounts for the enhanced porous structure and the increase in the optical band gap and average gap

Effect of Carbon Modification on the Electrical, Structural, and Optical Properties of TiO

Carbon-modified titanium dioxide nanoparticles (C:TiO2 NPs) have been synthesized by ultrasonic nebulizer spray pyrolysis (USP) and pneumatic spray pyrolysis (PSP) techniques. HRTEM on the NPs shows difference in lattice spacing in the NP structures prepared by the two methods—2.02 Å for the USP NPs and an average of 3.74 Å for the PSP NPs. The most probable particle sizes are 3.11 nm and 5.5 nm, respectively. Raman spectroscopy supported by FTIR confirms the TiO2 polymorph to be anatase with the intense phonon frequency at 153 cm−1 blue-shifted from 141 cm−1 ascribed to both carbon doping and particle size. A modified phonon confinement model for nanoparticles has been used to extract phonon dispersion and other parameters for anatase for the first time. Electronic measurements show “negative conductance” at some critical bias voltage, which is characteristic of n-type conductivity in the carbon-doped TiO2 NPs as confirmed by the calculated areas under the I-V curves, a property suited for solar cell applications. Practical solar cells built from carbon-doped TiO2 electrodes show up to 1.5 times improvement in efficiency compared to pure TiO2 electrodes of similar construction

Phase evolution of vanadium oxides obtained through temperature programmed calcinations of ammonium vanadate in hydrogen atmosphere and their humidity sensing properties

The possibility of obtaining vanadium dioxide (VO2) [wherein the vanadium ionic state is 4+] from a precursor of ammonium metavanadate (NH4VO3) bearing the ion V5+ is investigated. The reduction is carried out by calcining the NH4VO3 powders in similar concentrations of H2 flow at varying temperatures. The resulting powders have been studied by several techniques including XRD, Raman spectroscopy, FTIR, TEM, BET and DSC. It is found that remnants of bright yellow V5+ still exist up to calcination temperatures of 100 °C after which the sky-blue VO2 dominates at calcination temperatures of 150 °C-250 °C. There is a population surge of metastable dark-blue V6O13 (where V is in between V4+ and V5+ ionic states) between 250 °C and 300 °C. However above 350 °C the material reverts to the stable V5+ in the yellow-orange V2O5. XPS/EDS and VSM confirm the order of appearance to be VO2(150 °C) → V6O13(200 °C) → V2O5 (350 °C)

Ammonia gas sensing characteristics of V2O5 nanostructures: A combined experimental and ab initio density functional theory approach

A combined experimental and density functional theory of α-V2O5 for ammonia gas sensing have been investigated. The material was synthesized from hydrated NH4VO3 in CVD at 400 °C in N2 atmosphere for different time (12 h and 24 h). Highly crystalline orthorhombic α-V2O5 nano-rods with dominant (001) and (110) planes/facets nano-rods were observed from XRD, SEM and TEM characterizations. Using VSM technique, para-to ferro-magnetic transition was observed in the α-V2O5 nanoparticles synthesized at 24 h. Improved gas sensing was observed in case of the paramagnetic α-V2O5 nano-rods (nanoparticles synthesized at 12 h) compared with the one synthesized at 24 h. Additionally, significant rise in gas sensing response was observed around the metal to insulator transition temperature. Calculation of adsorption of NH3 molecule(s) on (001), (110), (200) and (400) facets showed that (001), (200) and (400) possessed more active sites than (110) surface. However, at higher concentration of NH3 molecules, the number of adsorbed molecules was found to be limited by the available adsorption sites in the case of (001) thereby causing the surface to be unstable. DFT calculations were also used to investigate NH3 adsorption on (110) surface of α-V2O5 with the analysis showing exponential decrease in the electronic band gap of the material's surface with the increasing numbers of NH3 loadings.</p

Optimization, Yield Studies and Morphology of WO₃Nano-Wires Synthesized by Laser Pyrolysis in C₂H₂and O₂Ambients&#8212;Validation of a New Growth Mechanism

<p>Abstract</p> <p>Laser pyrolysis has been used to synthesize WO₃nanostructures. Spherical nano-particles were obtained when acetylene was used to carry the precursor droplet, whereas thin films were obtained at high flow-rates of oxygen carrier gas. In both environments WO₃nano-wires appear only after thermal annealing of the as-deposited powders and films. Samples produced under oxygen carrier gas in the laser pyrolysis system gave a higher yield of WO₃nano-wires after annealing than the samples which were run under acetylene carrier gas. Alongside the targeted nano-wires, the acetylene-ran samples showed trace amounts of multi-walled carbon nano-tubes; such carbon nano-tubes are not seen in the oxygen-processed WO₃nano-wires. The solid&#8211;vapour&#8211;solid (SVS) mechanism [B. Mwakikunga et al., J. Nanosci. Nanotechnol., 2008] was found to be the possible mechanism that explains the manner of growth of the nano-wires. This model, based on the theory from basic statistical mechanics has herein been validated by length-diameter data for the produced WO₃nano-wires.</p