To study the effect of an Si-Si bond on gas-phase reaction chemistry in the hot-wire chemical vapor deposition (HWCVD) process with a single source alkylsilane molecule, soft ionization with a vacuum ultraviolet wavelength of 118 nm was used with time-of-flight mass spectrometry to examine the products from the primary decomposition of hexamethyldisilane (HMDS) on a heated tungsten (W) filament and from secondary gas-phase reactions in a HWCVD reactor. It is found that both Si-Si and Si-C bonds break when HMDS decomposes on the W filament. The dominance of the breakage of Si-Si over Si-C bond has been demonstrated. In the reactor, the abstraction of methyl and H atom, respectively, from the abundant HMDS molecules by the dominant primary trimethylsilyl radicals produces tetramethylsilane (TMS) and trimethylsilane (TriMS). Along with TMS and TriMS, various other alkyl-substituted silanes (m/z = 160, 204, 262) and silyl-substituted alkanes (m/z = 218, 276, 290) are also formed from radical combination reactions. With HMDS, an increasing number of Si-Si bonds are found in the gas-phase reaction products aside from the Si-C bond which has been shown to be the major bond connection in the products when TMS is used in the same reactor. Three methyl-substituted 1,3-disilacyclobutane species (m/z = 116, 130, 144) are present in the reactor with HMDS, suggesting a more active involvement from the reactive silene intermediates.

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.

The effect of the Si-H bond on the gas-phase reaction chemistry of trimethylsilane in the hot-wire chemical vapor deposition (HWCVD) process has been studied by examining its decomposition on a hot tungsten filament and the secondary gas-phase reactions in a reactor using a soft laser ionization source coupled with mass spectrometry. Trimethylsilane decomposes on the hot filament via Si-H and Si-CH(3) bond cleavages. A short-chain mechanism is found to dominate in the secondary reactions in the reactor. It has been shown that the hydrogen abstractions of both Si-H and C-H occur simultaneously, with the abstraction of Si-H being favored. Tetramethylsilane and hexamethyldisilane are the two major products formed from the radical recombination reactions in the termination steps. Three methyl-substituted disilacyclobutane molecules, i.e., 1,3-dimethyl-1,3-disilacyclobutane, 1,1,3-trimethyl-1,3-disilacyclobutane, and 1,1,3,3-tetramethyl-1,3-disilacyclobutane are also produced in reactor from the cycloaddition reactions of methyl-substituted silene species. Compared to tetramethylsilane and hexamethyldisilane, a common feature with trimethylsilane is that the short-chain mechanism still dominates. However, a more active involvement of the reactive silene intermediates has been found with trimethylsilane.

The decomposition of 1,1-dimethyl-1-silacyclobutane (DMSCB) on a heated tungsten filament has been studied using vacuum ultraviolet laser single photon ionization time-of-flight mass spectrometry. It is found that the decomposition of DMSCB on the W filament to form ethene and 1,1-dimethylsilene is a catalytic process. In addition, two other decomposition channels exist to produce methyl radicals via the Si-CH(3) bond cleavage and to form propene (or cyclopropane)/dimethylsilylene. It has been demonstrated that both the formation of ethene and that of propene are stepwise processes initiated by the cleavage of a ring C-C bond and a ring Si-C bond, respectively, to form diradical intermediates, followed by the breaking of the remaining central bonds in the diradicals. The formation of ethene via an initial cleavage of a ring C-C bond is dominant over that of propene via an initial cleavage of a ring Si-C bond. When the collision-free condition is voided, secondary reactions in the gas-phase produce various methyl-substituted 1,3-disilacyclobutane molecules. The dominant of all is found to be 1,1,3,3-tetramethyl-1,3-disilacyclobutane originated from the dimerization of 1,1-dimethylsilene.

The perfect hemostatic material should be capable of rapidly controlling substantial hemorrhaging from visceral organs, veins, and arteries. Ideally, it should be biodegradable, biocompatible, easily applied, and inexpensive. Herein, taking advantages of sodium alginate (SA), carboxymethyl chitosan (CMC), and collagen, a degradable powdery hemostatic composite (SACC) was synthesized using emulsification and cross-linking technology. The morphology and structure of SACC were determined using Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). This hemostatic material exhibited a typical generic sphere shape with narrow size distribution, rough surface, and satisfactory water absorption. Using in vitro bleeding and in vivo bleeding models (rat liver injury model and rat tail amputation model), it was shown that SACC had superior hemostatic actions compared to CMC and SA. Excellent cytocompatibility was proven during cytotoxicity tests and SEM observations. Histomorphological evaluation during the wound healing process proved the superior biocompatibility of SACC in a rat liver injury model. Biodegradability of SACC was demonstrated by immunofluorescence techniques both in vitro and in vivo. In summary, we have demonstrated the enormous potential of SACC, which has excellent hemostatic activity, biodegradability, and biocompatibility properties for use in clinical hemostasis applications.

The alloying of tungsten filament when using 1,1,3,3-tetramethyl-1,3-disilacyclobutane (TMDSCB) in a hot-wire chemical vapor deposition reactor was systematically studied by scanning electron microscopy, Auger electron spectroscopy, analysis of the power consumed by the filament, and in situ mass spectrometric measurements of the gas-phase species produced in the process. Only carburization of the W filament was observed. The carburization is mainly caused by the interaction of methyl radicals with the filament. Graphite as well as both WC and W2C alloys can form on the filament surface, depending on the filament temperatures and source gas pressures. Both WC and graphite are converted to W2C with the diffusion of C into the filament. It is shown that filament carburization affects the consumption rate of the source gas and the intensities of gas-phase reaction products. Gas-phase reactions dominate at T < or = 1400 degrees C. The carburization rate increases with increasing filament temperatures and dominates at T > or = 1800 degrees C.

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The tungsten filament aging when using silacyclobutane (SCB) as a source gas in a hot-wire chemical vapor deposition reactor was systematically studied by the characterization of surface morphology using scanning electron microscopy and the chemical composition analysis of the filament surfaces using Auger electron spectroscopy. It is shown that filament aging involves the formation of silicides and under more severe conditions, a pure silicon deposit. At low pressures of SCB samples, e.g., 0.06 and 0.03Torr, only Si3W5 alloy was formed. Silicon-rich silicide, Si2W, was found when using a higher pressure of SCB at 0.12Torr. At the high SCB pressure of 0.12Torr and low temperatures, pure silicon was deposited on the W filament surface. It is also demonstrated that H2 can etch the aged filament at high temperatures above 1900°C. The etching products detected by the 10.5eV vacuum ultraviolet laser single photon ionization∕time-of-flight mass spectrometer include SiH4, SiCHx (x=2–5), and SiC2Hy (y=4–7).