Synthesis of multiwall carbon nanotubes by chemical vapor deposition of ferrocene alone

Multiwall carbon nanotubes (MWNTs) filled with Fe nanoparticles (NPs) have been synthesized by thermal chemical vapor deposition of ferrocene alone as the precursor. The MWNTs were grown at different temperatures: 980 and 800 degrees C. Characterization of as-prepared MWNTs was done by scanning and transmission electron microscopy, and X-ray diffraction. The transmission electron microscopy study revealed that Fe NPs encapsulated in MWNTs grown at 980 and 800 degrees C are spherical and rod shaped, respectively. Room-temperature vibrating sample magnetometer studies were done on the two samples up to a field of 1T. The magnetization versus magnetic field loop reveals that the saturation magnetization for the two samples varies considerably, almost by a factor of 4.6. This indicates that Fe is present in different amounts in the MWNTs grown at the two different temperatures. (C) 2009 Elsevier Ltd. All rights reserved.

Chemical vapor detection using nonlinear electrical properties of carbon nanotube bundles

We demonstrate the electrical transport behavior of carbon nanotubes (CNTs) upon exposure to organic analytes (namely ethanol, benzene, acetone and toluene). The resulting nonlinear current-voltage characteristics revealed a power law dependence of the differential conductivity on the applied bias voltage. Moreover, suppression of differential conductivity at zero bias is found to be dependent on different selective analytes. The power law exponent values have been monitored before, during and after exposure to the chemicals, which revealed a reversible change in the number of electron conducting channels. Therefore, the reduction in the number of conductive paths can be attributed to the interaction of the chemical analyte on the CNT surfaces, which causes a decrease in the differential conductivity of the CNT sample. These results demonstrate chemical selectivity of CNTs due to varying electronic interaction with different chemical analytes.

Growth and electron effective mass measurements of strained Si and Si0.94Ge0.06 on relaxed Si0.62Ge0.38 buffers grown by rapid thermal chemical vapor deposition

Abstract: We report the growth and the electron cyclotron resonance measurements of n-type Si/Si0.62Ge0.38 and Si0.94Ge0.06/Si0.62Ge0.38 modulation-doped heterostructures grown by rapid thermal chemical vapor deposition. The strained Si and Si0.94Ge0.06 channels were grown on relaxed Si0.62Ge0.38 buffer layers, which consist of 0.6 mu m uniform Si0.62Ge0.38 layers and 0.5 mu m compositionally graded relaxed SiGe layers from 0 to 38% Ge. The buffer layers were annealed at 800 degrees C for 1 h to obtain complete relaxation. A 75 Angstrom Si(SiGe) channel with a 100 Angstrom spacer and a 300 Angstrom 2 X 10(19) cm(-3) n-type supply layer was grown on the top of the buffer layers. The cross-sectional transmission electron microscope reveals that the dense dislocation network is confined to the buffer layer, and relatively few dislocations terminate on the surface. The plan-view image indicates the threading dislocation density is about 4 X 10(6) cm(-2). The far-infrared measurements of electron cyclotron resonance were performed at 4 K with the magnetic field of 4-8 T. The effective masses determined from the slope of the center frequency of the absorption peak versus applied magnetic field plot are 0.203m(0) and 0.193m(0) for the two dimensional electron gases in the Si and Si0.94Ge0.06 channels, respectively. The Si effective mass is very close to that of a two dimensional electron gas in an Si MOSFET (0.198m(0)). The electron effective mass of Si0.94Ge0.06 is reported for the first time and is about 5% lower than that of pure Si.

Structural, optical and electrical properties of sulfur-incorporated amorphous carbon films

Amorphous carbon-sulfur (a-C:S) composite films were prepared by vapor phase pyrolysis technique. The structural changes in the a-C:S films were investigated by electron microscopy. A powder X-ray diffraction (XRD) study depicts the two-phase nature of a sulfur-incorporated a-C system. The optical bandgap energy shows a decreasing trend with an increase in the sulfur content and preparation temperature. This infers a sulfur incorporation and pyrolysis temperature induced reduction in structural disorder or increase in sp (2) or pi-sites. The presence of sulfur (S 2p) in the a-C:S sample is analyzed by the X-ray photoelectron spectroscopy (XPS). The sp (3)/sp (2) hybridization ratio is determined by using the XPS C 1s peak fitting, and the results confirm an increase in sp (2) hybrids with sulfur addition to a-C. The electrical resistivity variation in the films depends on both the sulfur concentration and the pyrolysis temperature.

Electronic-structures of h2o.bf3 and related n-v addition-compounds - a combined eels-ups study in vapor-phase

The detailed electronic structure of the n-v addition compound H2O·BF3 has been investigated for the first time by a combined use of electron energy loss spectroscopy (EELS) and UV photoelectron spectroscopy (UPS) augmented by MO calculations. The calculated molecular orbital energies of H2O·BF3 agree well with the UPS results and have been used to assign the electronic transitions obtained from EELS and to construct an orbital correlation diagram. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.

Kinetics of Chemical Vapor Deposition

A generalized mass transport model is developed for predicting the rate ofdeposition in chemical vapor deposition (CVD) systems. This combines thegeneralized method of obtaining equilibrium composition, with elemental fluxbalance expressions. This procedure avoids the usual problems encountered incalculating the rates in multicomponent systems, like writing overall reactionschemes. The dependence of multicomponent diffusivities on the fluxes is accountedin this model using an iterative procedure. The model developed isapplied to the deposition of titanium carbide on cemented carbide tool bitsfrom a gas mixture of titanium tetrachloride, toluene, and hydrogen. Experimentaldeposition rates were obtained using a thermogravimetric assembly.Mass transport controlled rates give an order of magnitude estimates of theobserved rates.

A novel investigation of vapor-phase charge-transfer complexes of halogens with n-donors by electron energy loss spectroscopy

Complexes of I2 with diethyl ether and triethylamine and of Br, with diethyl ether have been investigated in the vapor phase for the first time by employing electron energy loss spectroscopy. Besides the CT bands, blue-shifted vacuum-UV bands of the halogens have been assigned; the amine-I, system appears to exhibit two CT bands,associated with two different excited states of the complex.

Electron-Energy Loss Spectroscopy (Eels) Of Organic-Molecules In Vapor-Phase - Design And Fabrication Of An Indigenous Eel Spectrometer

An indigenous electron energy loss spectrometer has been designed and fabricated for the study of free molecules. The spectrometer enables the recording of low-resolution electronic spectra of molecules inthe vapour phase with ready access to the vacuum ultraviolet region. Electron energy loss spectra of aliphatic alcohols and carbonyl compounds as wellas of benzene derivatives have been recorded with the indigenous spectrometer and the electronic transitions in these molecules discussed.

Kinetics of oxidation of pseudocumene in the vapor phase

The kinetics of pseudocumene oxidation in the vapor phase with tin vanadate as catalyst have been studied over the following ranges of the variables: Oxygen concentration, 0.909 to 2.857 mole/m3; pseudocumene concentration, 0.071 to 0.125 mole/m3; temperature, 260 to 320°C; space time, 22.5 to 90 × 104 g. catalyst/mole sec. Oxidation-reduction models have been found to describe the kinetics adequately. The mechanism is found to remain the same throughout the temperature range covered.

Vapor phase oxidation of ethanol over thorium molybdate catalyst

Ethanol oxidation in the vapor phase was studied in an isothermal flow reactor using thorium molybdate catalyst in the temperature range 220–280 °C. Under these conditions the catalyst was highly selective to acetaldehyde formation. The rate data were well represented by a steady state two-stage redox model given by the equation: View the MathML source The parameters of the above model were estimated by linear and nonlinear least squares methods. In the case of nonlinear estimation the sum of the squares of residuals decreased. The activation energies and preexponential factors for the reduction and oxidation steps of the model, estimated by nonlinear least squares technique are: 9.47 kcal/mole, 9.31 g mole/ (sec) (g cat) (atm) and 9.85 kcal/mole, 0.17 g mole/(sec) (g cat) (atm)0.5, respectively. Oxidations of ethanol and methanol over thorium molybdate catalyst were compared under similar conditions.

Catalytic vapor-phase oxidation of p-xylene over tin vanadate

Rates of oxidation of p-xylene were measured in the temperature range 320 to 420 °C using tin vanadate as catalyst in an isothermal differential flow reactor. The amounts of p-xylene converted were determined by analyzing the main products (p-tolualdehyde, maleic anhydride, p-toluic acid and traces of terephthalic acid). Negligible amounts of products of complete combustion were formed. The reaction rates obtained for p-xylene followed the relation, Image based on the redox model. The mechanism of the reaction was determined by conducting different sets of experiments and it was found that the reaction followed the parallel-consecutive mechanism, in which p-tolualdehyde and maleic anhydride were formed from the parallel route whereas p-toluic acid was formed from the consecutive route.

Electrochromic, magnetotransport and AC transport properties of vapor phase polymerized PEDOT(VPP PEDOT)

Poly(3,4-ethylenedioxy)thiophene (PEDOT) doped with tosylate ion (PEDOT-tosylate or VPP PEDOT) was synthesized by vapor phase polymerization (VPP) technique on glass as well as on glass/ITO and the electrochromic properties were investigated. Compared with that of PEDOT-PSS spin-coated on glass/ITO, the studies showed that VPP PEDOT has a lower work function and better electrochromic properties. The magneto and AC transport properties studies were done on VPP PEDOT coated on glass substrate. The system shows 2-dimensional variable range hopping and wave function shrinkage of charge carriers.