Structural evaluation of polycrystalline silicon thin films by hot-wire-assisted PECVD

Tungsten wires were introduced into a plasma-enhanced chemical vapor deposition (PECVD) system as a catalyzer: we name this technique 'hot-wire-assisted PECVD' (HW-PECVD). Under constant deposition pressure (p(g)), gas flow ratio and catalyzer position, the effects of the hot wire temperature (T-f) on the structural properties of the poly-Si films have been characterized by X-ray diffraction (XRD), Raman scattering and Fourier-transform infrared (FTIR) spectroscopy. Compared with conventional PECVD, the grain size, crystalline volume fraction (X-e) and deposition rate were all enhanced when a high T-f was used. The best poly-Si film exhibits a preferential (220) orientation, with a full width at half-maximum (FWHM) of 0.2 degrees. The Si-Si TO peak of the Raman scattering spectrum is located at 519.8 cm(-1) with a FWHM of 7.1 cm(-1). The X-c is 0.93. These improvements are mainly the result of promotion of the dissociation of SiH4 and an increase in the atomic H concentration in the gas phase. (C) 2001 Elsevier Science B.V. All rights reserved.

Effect of core structure on the fluorescence properties of hyperbranched poly(phenylene sulfide)

We functionalize the focal group of hyperbranched poly(phenylene sulfide) (HPPS) with benzyl, phenyl, and naphthyl group, respectively. DSC analysis shows that T-g of HPPS is increased from 55 to 93 degrees C by functionalization of the focal group with a conjugated naphthyl group. The fluorescence properties of the three core-functionalized HPPS' are studied under the comparison with the original HPPS.

Multilayered core-shell structure of the dispersed phase in high-impact polypropylene

The multiphase morphology of high impact polypropylene (hiPP), which is a reactor blend of polypropylene (PP) with ethylene-propylene copolymer, was investigated by transmission electron microscopy, selected area electron diffraction, atomic force microscopy, and field-emission scanning electron microscopy techniques in conjunction with an analysis of the hiPP composition and chain structure based on solvent fractionation, C-13-NMR, and differential scanning calorimetry measurements.

Selective oxidation of cyclohexane with hydrogen peroxide in the presence of copper pyrophosphate

Liquid phase oxidation of cyclohexane was carried out under mild reaction condition over copper pyrophosphate catalyst in CH3CN using hydrogen peroxide as an oxidant at the temperature between 25 and 80 degrees C. The copper pyrophosphate catalyst was characterized by means of XRD, FT-IR and water contact angle measurement. It was found that appropriate surface hydrophobicity is the key factor for the excellent performance of the catalyst. In addition, a significant improvement for the cyclohexane conversion in the presence of organic acid was observed.

Effect of Copolymerization Time on the Microstructure and Properties of Polypropylene/Poly(ethylene-co-propylene) In-Reactor Alloys

Three Polypropylene/Poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys produced by a two-stage slurry/gas polymerization had different ethylene contents and mechanical properties, which were achieved by controlling the copolymerization time. The three alloys were fractionated into five fractions via temperature rising dissolution fractionation (TRDF), respectively. The chain structures of the whole samples and their fractions were analyzed using high-temperature gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), C-13 nuclear magnetic resonance (C-13 NMR), and differential scanning calorimetry (DSC) techniques. These three in-reactor alloys mainly contained four portions: ethylenepropylene random copolymer (EPR), ethylene-propylene (EP) segmented and block copolymers, and propylene homopolymer. The increased copolymerization time caused the increased ethylene content of the sample. The weight percent of EPR, EP segmented and block copolymer also became higher.

Effect of different VOPO4 phase catalysts on oxidative dehydrogenation of cyclohexane to cyclohexene in acetic acid

alpha(1)-VOPO4, alpha(II)-VOPO4 and beta-VOPO4 have been investigated as catalysts for the gas phase oxidative dehydrogenation (ODH) of cyclohexane to cyclohexene with the addition of acetic acid (HOAc) in the feeds in a fixed bed reactor. Different VOPO4 phases showed different acidity and reducibility. beta-VOPO4 phase is more active than alpha(I)-VOPO4 and alpha(II)-VOPO4 in the ODH without acetic acid addition. In the presence of acetic acid, the acidity of the catalyst may play an important role in the ODH process. Due to higher acidity, alpha(I)-VOPO4 phase catalyst gives better catalytic performances than alpha(I)-VOPO4 and beta-VOPO4 for the ODH of cyclohexane by adding of acetic acid in the reactants.

Effects of acetic acid on product selectivity in gas phase oxidative dehydrogenation of cyclohexane

The effect of adding acetic acid on the product distribution in gas phase oxidative dehydrogenation of cyclohexane over alpha(1)-VOPO4 catalyst was investigated. The role of acetic acid in the reaction process was put forward. The proposed mechanism is that acetic acid take precedence of cyclohexane adsorbing on the active sites of alpha(1)-VOPO4 catalyst to form isolated active site. Thus, cyclohexene species can desorb quickly from the active sites, avoiding its deep oxidation dehydrogenation. Almost 100% selectivity to cyclohexene could be obtained when the molar ratio of acetic acid to cyclohexane was 12.9:1 at 450 degrees C, the conversion of cyclohexane was 6.9%.

H/D exchange reaction of cyclopropane derivatives in the ion system of CD3OD

The fragmentation properties of the product ions [M + 1](+), [M + 2](+) and [M + 3](+) formed by ion-molecule reaction of four cyclopropane derivatives with the ion system of CD3OD were investigated by using collision-induced dissocation technique. The experiment results indicated that the product ions were produced via the H/D exchange reaction between reactants and reactive reagent ions of CD3OD. There are two exchangable hydrogen atoms on the ring of compounds 1 and 2, and only one for compound 3 and 4.

Vibrational spectrum and luminescence properties of the system Al2O3-B2O3-Eu2O3

The system Al2O3-B2O3-Eu2O3, with Al/B ratio varying from 4.5 to 2 and Eu/(Al+B)=0.02, was synthesized by solid state reaction. The vibrational spectra of the system Al2O3-B2O3-Eu2O3 were investigated. It was found that no definite change in the regions of 1200 similar to 1000 cm(-1) due to the adsorption BO4 groups with decreasing Al/B ratio, indicating no Al3+ ion was substituted by Eu3+ ions and other changes revealed that there was an amorphous phase and Eu3+ ions may dope into the amorphous phase. The studies on the luminescent properties of the system Al2O3-B2O3 also show that Eu3+ ions dope into amorphous phase. The investigations on the phonon sideband of Eu3+ indicate that electron-phonon coupling strength decreases with Al/B ratio change from 3 to 2, leading to the non-radiative decay rate decreases and the Eu3+-emission intensity increase.

Gas-phase ion-molecule reactions of C-60 with methyl ethers CH3OCnH2n+1

Gas-phase ion-molecule reactions of buckminsterfullerene (C-60) with the ion systems generated from the self-chemical-ionization of alkyl methyl ethers(CH3OCnH2n+1, n =2 , 3, 4) were studied in the ion source of a mass spectrometer. The adduct cation [C60C2H5O](+) and protonated molecular ion [C60H](+) were observed as the major products, The former was produced by the reactions.of C-60 with the methoxymethyl ion [CH3O = CH2](+) , the latter corresponded to the proton transfer reactions from the protonated alkyl methyl ethers to C60 It is suggested that the [3+2] cycloadduct is the most favorable structure among the probable isomers with special chemical properties, Our investigation provides the guidance for the synthesis of this compound in condensed phase.

Gas-phase ion-molecule reactions of neutral C-60 with alkyl methyl ethers under chemical ionization conditions

Gas-phase ion-molecule reactions of buckminsterfullerene (C-60) with the ion systems generated from the self-chemical ionization of alkyl methyl ethers (CH3OR, R = n-C2H5, n-C3H7, n-C4H9) were studied in the ion source of a mass spectrometer. The adduct cation [C60C2H5O](+) and protonated molecule [C60H](+) were observed as the major products. The former adduct ion was produced by the reactions of C-60 with the methoxymethyl ion [CH3OCH2](+), and the latter resulted from the proton transfer reactions from protonated alkyl methyl ethers to C-60 It is suggested that the [3+2] cycloadduct to a 6-6 bond of C-60 (a C-C bond common to two annulated six-membered rings) is the most favorable structure among the probable isomers of [C60C2H5O](+). (C) 1998 John Wiley & Sons, Ltd.

Gas phase derivations of endohedral metallofullerenes by ion-molecular reactions

Gas phase ion-molecular reactions of endohedral metallofullerenes with the self-chemical ionization ion system of vinyl acetate, benzene and acetone in the ion source of the mass spectrometer have been studied. Several derivatized endohedral metallofullerene cations [M@C-82-C2H3O](+), [M-2@C-80-C2H3O](+), [M@C-82-C6H6](+) and [M@C-82-CO-CH3](+) are observed as the major products. The experimental results indicate that endohedral metallofullerenes have active gas phase reactivities and can be efficiently derivatized by some small organic cations.

Gas phase derivatization of endohedral metallofullerenes R@C-82 and R-2@C-80 (R = Nd, Ce)

Endohedral metallofullerenes Ce@C-82, Ce-2@C-80, Nd@C-82 and Nd-2@C-80 undergo gas phase ion/molecule reactions with the ion system from self-chemical ionization of vinyl acetate, and exohedral derivatives are thus generated, A new heterocycle is formed from metallofullerenes and a C2H3O+ cation, Endohedral metallofullerenes show much higher reactivities than empty fullerenes during the association and the charge and proton transfer processes, The strong electron-donating character of endohedral metallofullerenes is due to their unique super-atom-like electronic structures. (C) 1997 by John Wiley & Sons, Ltd.