In situ diagnostics of the decomposition of silacyclobutane on a hot filament by vacuum ultraviolet laser ionization mass spectrometry

The gas-phase reaction products of silacyclobutane (SCB) and 1, 1-dideuterio-silacyclobutane (SCB-d(2)) from a hot-wire chemical vapor deposition (HWCVD) chamber were diagnosed in situ using vacuum ultraviolet (VUV) laser single-photon ionization (SPI) coupled with time-of-flight (TOF) mass spectrometry. The SCB molecule was found to decompose at a filament temperature as low as 900 degrees C. Both Si- (silylene, methylsilylene, and silene) and C-containing (ethene and propene) species were produced from the SCB decomposition on the filament. Ethene and propene were detected by the mass spectrometer. It is demonstrated that the formation of ethene is favored over that of propene. The experimental study of hot-wire decomposition of SCB-d(2) shows that propene is most likely produced by a process that is initiated by a 1,2-H(D) migration to form n-propylsilylene, followed by an equilibration with silacyclopropane, which then decomposes to propene. The detection of ethene in our experiment indicates that a competitive route of fragmentation exists for SCB decomposition on the filament. It has been shown that this competitive route occurs without H/D scrambling. The highly reactive silylene, silene, and methylsilylene species produced from SCB decomposition underwent either insertion reactions into the Si-H bonds of the parent molecule or pi-type addition reaction across the double and triple CC bonds. The dimerization product of silene, 1,3-disilacyclobutane, at m/z = 88 was also observed.     

Improvement of interfacial adhesion performance of the kevlar fiber mat by depositing SiC/TiO2/Al2O3/graphene nanoparticles

Modern world seeks dramatic progress in composite materials use in numerous applications. Scientists worldwide are researching on fabricating new composites and attempting to have more applications using these materials. Serious attempts have also been taken to improve the properties of these materials. In this circumstance, a conscious attempt has been made in this present work that studies the effect of SiC/TiO₂/Al₂O₃/ graphene nanoparticles (NPs) deposition on Kevlar fiber. In this process, SiC/TiO₂/Al₂O₃/ graphene NPs have been deposited on Kevlar fiber by dip coating process. For the analysis, physical observation has been performed well at first which confirms nanoparticle deposition on the fiber and formation of adhesive bonding. SEM analysis followed by surface topography has been conducted to observe and further analysis of nanoparticle deposition. Atomic bonding mechanism shows how chemical bonding between fiber and nanoparticles. TGA analysis shows thermal improvement of the fiber by NPs deposition where graphene with binder makes 21.6% improvement in decomposition temperature. Tensile strength and young’s modulus of binder inclusion coated kevlar fabric are improved up to 26% and 5.7%, respectively. Finally, the IR-spectra confirms successful deposition of nanoparticles on the fiber.     

IR laser decomposition of 1,3-disilacyclobutane in presence of carbon disulfide: chemical vapour deposition of polythiacarbosilane

TEA CO₂ laser irradiation of gaseous mixtures of 1,3-disilacyclobutane - carbon disulfide affords chemical vapour deposition of solid polythiacarbosilane films that possess Si-S-X (X = Si, C), S-H and Si-H bonds and undergo slow hydrolysis in air to polyoxothiacarbosilanes containing Si-H, Si-O-Si and (C)S-H bonds. The formation of the polythiacarbosilane is proposed to take place via polymerization of transient silene and incorporation of CS₂ into growing polysilene network.     

Stereoselective Activation of Small Molecules by a Stable Chiral Silene

The reaction of the dilithium salt of the enantiopure (S)-BINOL (1,1’-bi-2-naphthol) with two equivalents of the amidinate-stabilized chlorosilylene [L^PhSiCl] (L^Ph=PhC(NtBu)₂) led to the formation of the first example of a chiral cyclic silene species comprising an (S)-BINOL ligand. The reactivity of the Si=C bond was investigated by reaction with elemental sulfur, CO₂ and HCl. The reaction with S₈ led to a Si=C bond cleavage and concomitantly to a ring-opened product with imine and silanethione functional groups. The reaction with CO₂ resulted in the cleavage of the CO₂ molecule into a carbonyl group and an isolated O atom, while a new stereocenter is formed in a highly selective manner. According to DFT calculations, the [2+2] cycloaddition product is the key intermediate. Further reactivity studies of the chiral cyclic silene with HCl resulted in a stereoselective addition to the Si=C bond, while the fully selective formation of two stereocenters was achieved. The quantitative stereoselective addition of CO₂ and HCl to a Si=C bond is unprecedented.     

The structures of dicyclopentadienylsilenes and related compounds

The most stable form, according to MNDO calculations, of the silene (C₅H₅)₂Si is the bis-monohapto isomer, in which the angle (CSiC) is 105.4°, and the conformation is such that the dihedral angles δ (HCSiC) are zero. The bis-pentahapto isomer is of comparable energy, and has minimum energy for a structure of D_5d symmetry: this isomer does not represent a genuine energy minimum. Entirely similar conclusions result from calculations on the isoelectronic (C₅H₅)₂P⁺, but for (C₅H₅)₂Al^?, although the lowest energy form is again (η⁵-C₅H₅)₂Al^? , the (η⁵-C₅H₅)₂Al^? isomer has only C_2v symmetry with angle (XAlX) 151.5°. In the silene derivatives (η¹-C₅H₅)SiCY₂, the unique SiC interaction is a genuine SiC double bond and the molecular skeleton C₂SiCY₂ is planar: however in the isomeric species (η⁵-C₅H₅)₂SiCY₂, which do not represent genuine energy minima, the unique SiC interaction is a long, highly polar bond in a twisted X₂SiCY₂ skeleton in which the X₂SiC and SiCY₂ planes are perpendicular.     

Anharmonic force field and spectroscopic constants of silene: an ab initio study

High-level ab initio calculations with large basis sets are reported for silene, H₂C=SiH₂. Correlated harmonic force fields are obtained from coupled cluster CCSD(T) calculations with the cc-pVQZ basis (cc-pVTZ for H) while the anharmonic force fields are computed at the MP2/TZ2Pf level. There is excellent agreement with the available experimental data, in particular the equilibrium geometry and the fundamental vibrational frequencies. Many other spectroscopic constants are predicted for the C _{2 v} isotopomers of silene. Received: 27 May 1998 / Accepted: 23 July 1998 / Published online: 9 October 1998     

Highly selective 13C separation by CO2-laser-induced IRMPD of CF2Cl2/HI and CF2ClBr/HI mixtures

The CO₂-laser-induced IRMPD of CF₂CL₂/HI and CF₂ClBr/HI mixtures produced ¹³C-enriched CF₂HCl. In CF₂Cl₂/HI mixtures, the CF₂HCl underwent secondary IRMPD in the continuing pulse irradiation at the same wavenumber and fluence, yielding CF₂H₂ with a ¹³C content of 97%. Because of efficient decomposition at relatively low fluences, CF₂ClBr seems to be a promising starting molecule in two-step ¹³C enrichment.     

Single and double IR laser multiphoton decomposition of trifluoromethylsilane

Single and double IR laser multiphoton decomposition of trifluoromethylsilane have been studied at 0.1 and 0.3 mbar. The IRMPD products FSiH₃ and C₂H₄ form independently of the wavelength of the laser pulses both in the single and double laser experiments. The decomposition rate is however very sensitive to both the wavenumber of the irradiation and the time delay between the two laser pulses at different wavenumbers.     

Spectroscopic evidence for mobilization of amide position protons during CID of model peptide ions

Infrared multiple photon dissociation (IRMPD) spectroscopy was used to study formation of b ₂⁺ from nicotinyl-glycine-glycine-methyl ester (NicGGOMe). IRMPD shows that NicGGOMe is protonated at the pyridine ring of the nicotinyl group, and more importantly, that b ₂⁺ from NicGGOMe is not protonated at the oxazolone ring, as would be expected if the species were generated on the conventional b _n ⁺ /y _n ⁺ oxazolone pathway, but at the pyridine ring instead. IRMPD data support a hypothesis that formation of b ₂⁺ from NicGGOMe involves mobilization and transfer of an amide position proton during the fragmentation reaction.     

Effect of CO2-induced side reactions on the deposition in the non-aqueous Li-air batteries

This paper presents a non-aqueous Li-air battery model that considers the side reactions of lithium carbonate (Li₂CO₃) formation from both electrolyte decomposition and carbon dioxide (CO₂) in the ambient air. The deposition and decomposition behaviors of discharge products, the voltage, and capacity evolutions during the cycling operation of the Li-air batteries are investigated. The deposition behavior analysis implies that the Li₂CO₃ generated by electrolyte decomposition is mainly distributed near the separator side, while it is dominantly generated by Li-O₂/CO₂ reaction near the air side. The formation of Li₂CO₃ by side reactions makes the Li-air batteries exhibit a peak discharge deposition inside the cathode. Moreover, Li₂CO₃ is difficult to decompose and gradually accumulates with cycles, especially near the air side. The severe accumulation of Li₂CO₃ near the air side significantly reduces the O₂ diffusion into the electrode, which induces severe cycling performance decay of the Li-air batteries. According to the distribution and evolution of the deposition, three simple hierarchical cathode structures with high porosities near the air side are finally studied. The simulation results indicate that the increase of the local porosity near the air side substantially improves the cycling performance of the Li-air batteries.

     

Gas-phase formation of SiSe in IR laser-co-decomposition of dimethyl selenide and 1,3-disilacyclobutane

A LIF excitation spectrum of SiSe obtained upon IR laser irradiation of gaseous mixture of 1,3-disilacyclobutane and dimethyl selenide reveals that the previously reported infrared multiple photon co-decomposition of both compounds involves formation of SiSe. The SiSe formation is explained in terms of reaction of Se atoms with RHSi: silylenes (R = CH₃, H) and silene, and elimination of RH from silaneselones (RHSiSe, R = CH₃, H).     

Short time deposition of TiO2 nanoparticles on SiC as photocatalysts for the degradation of organic dyes

The deposition of TiO₂ nanoparticles on SiC was carried out by mechanical milling under different conditions. SiC–TiO₂ samples were used as photocatalysts for the degradation of organic dyes such as methylene blue and rhodamine B. A short time deposition of TiO₂ nanoparticles was observed during mechanical milling (2 min at 200 rpm) to cover the SiC particles. The presence of SiC and TiO₂ (anatase and rutile) was confirmed by means of X-ray diffraction after thermal treatment at 450 °C. The deposition of TiO₂ on SiC was corroborated by scanning electron microscopy analysis; the thickness of the thin layer of TiO₂ deposited on SiC increases as the proportion of TiO₂ increases. The energy band gap values obtained for these compounds were around 3.0 eV. SiC–TiO₂ photocatalysts prepared by mechanical milling exhibited better activity under UV-light irradiation for the degradation of methylene blue and rhodamine B than commercial TiO₂ powder (titania P25).     

Improvement of stability of a Fe/Mg/Al2O3 catalyst for the decomposition of methane in the presence of O2/CO2

The stability of an Fe/Al₂O₃ catalyst in the methane decomposition in the presence of O₂/CO₂ was found to be improved by the addition of Mg into the catalyst (Mg/Fe=1/1 wt ratio), probably due to suppression of carbon deposition even under CH₄/ O₂/CO₂ (80/10/5 vol. ratio) conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Preparation of thin films of platinum group metals by pulsed MOCVD. II. Deposition of Ru layers

In situ high-temperature mass spectrometry is used to analyze the thermal decomposition of Ru(acac)₃ and Ru(nbd)(allyl)₂ vapor and possible schemes of thermal transformations on the heated surface. By pulsed MOCVD with in situ mass spectrometric control of deposition processes ultrathin Ru layers with a thickness of several nanometers are obtained. The role of the reaction medium, precursor nature, and deposition temperature in the formation of a nanocrystalline structure of the films is revealed. Ruthenium films with a compact continuous structure are formed from Ru(acac)₃ and hydrogen at a deposition temperature of 340°C and below; an increase in the temperature results in the growth of nanogranular Ru layers. Regardless of deposition conditions, from Ru(nbd)(allyl)₂ granular nanocrystalline Ru layers are formed     

Ce0.5Zr0.5O2修饰的Ni/SiC、Fe/SiC和Co/SiC催化燃烧甲烷性能

以铈锆固溶体（Ce_0.5Zr_0.5O₂）修饰的高比表面积SiC为载体,采用两步浸渍法制备了Ni、Fe和Co基催化剂,研究了其在煤层气催化燃烧脱氧中的催化活性和稳定性. 利用X射线衍射（XRD）、X射线光电子能谱（XPS）、电感耦合等离子体质谱（ICP-MS）、高分辨透射电子显微镜（HRTEM）、比表面积（BET）、热重分析（TGA）和H₂程序升温还原（H₂-TPR）对催化剂进行了表征. 分析结果表明,Ni、Fe和Co部分进入Ce_0.5Zr_0.5O₂固溶体晶格内部,导致催化剂体相形成更多的缺陷;同时Ce_0.5Zr_0.5O₂固溶体有助于加速金属氧化物和金属之间氧化还原过程的进行,促进了氧吸附、传输和对甲烷的活化. 另外,SiC和Ce_0.5Zr_0.5O₂固熔体良好的抗积碳性能,有效避免了催化剂在富甲烷反应气氛中因积碳而失活,从而使三种催化剂均具有优良的催化燃烧脱氧活性和稳定性. 其中,Co/Ce_0.5Zr_0.5O₂/SiC活性最高,可在320 ℃活化催化甲烷,并在410 ℃实现完全脱氧.     

Effects of process parameters on ultrafine SiC synthesis using induction plasmas

A study is reported of the formation of ultrafine SiC powder through the reaction of elemental silicon and CH₄ in an induction plasma. The reaction route used involved in the first place the vaporization of a fine elemental silicon powder axially injected into the center of the discharge followed by the carburization reaction through the coinjection of CH₄. The powder obtained was composed of a mixture of α- and β-SiC with varying amounts of free carbon and free silicon. The particle size distribution was typically in the range of 40–60 nm with a corresponding specific surface area of 30–50 m²/g. A parametric study showed that the quality of the powder obtained varied with the plasma plate power and the position of the injection probe. The plasma gas composition employed was found to influence the proportions of α- and β-SiC in the synthesized SiC powder. With an Ar/N₂ mixture as the plasma gas, the ratio of the α to β phases was less than 1.0, whereas the ratio was greater than 1.5 when using a mixture of Ar/H₂ as plasma gas. The Si powder feed rate and the input C/Si molar ratio in the injected reactants significantly affected both the formation of the SiC and the free Si and free C content in the synthesized powder. Lining the cylindrical reactor wall with graphite resulted in improved conversion of Si to SiC. The weight fraction of the powder collected at different sections of the reactor system varied with the reactor operating conditions. The experimental results support the view that the formation mechanism for ultrafine SiC is dominated by the reaction of Si vapor with the thermal decomposition products of CH₄.     

Carbon-13 Separation by IRMPD of mixtures of C2F6 and Br2

The infrared multiple-photon decomposition of mixtures of C₂F₆ and Br₂ has been examined as functions of various experimental parameters. Carbon-13 was found to be enriched in the main product CF₃Br; the maximum enrichment factor was 35. The combination of this process with the IRMPD of CF₃Br provides a closed chemical cycle for efficient carbon isotope separation     

Theoretical studies on the structures and isomerization of methylene lithium‐chlorosilylenoid H2CSiLiCl

The methylene lithium‐chlorosilylenoid H₂C?SiLiCl was studied with ab initio calculations at the G2(MP2) level. Its four equilibrium structures, p‐complex, three‐membered ring, σ complex and silene, and three isomerization transition states were located. The calculations show that the nonplanar p‐complex structure is the lowest in energy among four equilibrium structures of H₂C?SiLiCl and should be experimentally detectable. The silene and σ complex structures with high energies are unstable and easy to isomerize to the most stable p‐complex structure via three‐membered ring one. Also, the geometric characteristics and bonding properties of various structures were analyzed and discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Structure of sodiated octa-glycine: IRMPD spectroscopy and molecular modeling

The structure of the sodiated peptide GGGGGGGG-Na⁺ or G₈-Na⁺ was investigated by infrared multiple photon dissociation (IRMPD) spectroscopy and a combination of theoretical methods. IRMPD was carried out in both the fingerprint and N—H/O—H stretching regions. Modeling used the polarizable force field AMOEBA in conjunction with the replica-exchange molecular dynamics (REMD) method, allowing an efficient exploration of the potential energy surface. Geometries and energetics were further refined at B3LYP-D and MP2 quantum chemical levels. The IRMPD spectra indicate that there is no free C-terminus OH and that several N—Hs are free of hydrogen bonding, while several others are bound, however not very strongly. The structure must then be either of the charge solvation (CS) type with a hydrogen-bound acidic OH, or a salt bridge (SB). Extensive REMD searches generated several low-energy structures of both types. The most stable structures of each type are computed to be very close in energy. The computed energy barrier separating these structures is small enough that G₈-Na⁺ is likely fluxional with easy proton transfer between the two peptide termini. There is, however, good agreement between experiment and computations in the entire spectral range for the CS isomer only, which thus appears to be the most likely structure of G₈-Na⁺ at room temperature.     

Production and characterization of nitrided CVD-SiC films

Silicon Carbide (SiC) and SiC with free silicon [SiC(Si)] thin films were prepared by chemical vapor deposition (CVD) using a CH₃SiCl₃-H₂-Ar gas mixture at a temperature of 1223 K. Afterwards these layers were gas nitrided in an ammonia-hydrogen-argon mixture at 1273 K. The solid product is an extremely thin film of silicon nitride on SiC or SiC(Si)-basic layers. These ultra thin silicon nitride films were investigated by glow discharge optical spectroscopy (GDOS) and x-ray photoelectron spectroscopy (XPS). The thickness of the layers was determined to a maximum value of 30 nm.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday