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Octa-vinyl polyhedral oligomeric silsesquioxane (V-POSS) and octa-(methacryloxy) propyl polyhedral oligomeric silsesquioxane (M-POSS) were incorporated into PMMA to prepare POSS/PMMA hybrid materials at molecular level via in situ polymerization. The resulting hybrid materials showed only swelling instead of solution in ethyl acetate, while pristine PMMA completely dissolved in ethyl acetate; moreover, the M-POSS/PMMA hybrid materials exhibited more excellent resistance to solvent stress cracking. An excellent transparency was observed for all hybrid materials. Incorporation of V-POSS and M-POSS significantly improved thermal properties of PMMA. The thermal decomposition temperature of hybrid materials was enhanced except a slightly compromised initial decomposition temperature. The hybrid materials prepared with 0.2-0.6 mol% M-POSS or V-POSS improved the reinforcing and toughening properties in comparison to pristine PMMA. Also, the incorporation of POSS decreased the dielectric constant and dielectric loss of the hybrid materials with more voids introduced into the composites no matter the structure of POSS. POLYM. ENG. SCI., 55:565-572, 2015. © 2014 Society of Plastics Engineers, INTRODUCTION Poly(methyl methacrylate) (PMMA) is an important thermoplastic with excellent transparency, high modulus, relative easy processing, and excellent dimensional stability which is widely used in various fields [1]. However, the [...]

Abstract A series of poly(trifluoropropylmethyl)-siloxane-block-polyurethanc-urea (FSPUU) films is prepared through moisture curing based on a three-step process. First, prepolymers are produced from poly(tetramethylene oxide) and toluenediisocyanate. Second, the prepolymers are [...]

A comprehensive study of the gas barrier properties of hybrid organic-inorganic coatings formed by polyvinyl alcohol (PVOH) and Si-[SiO.sub.2], obtained via sol-gel technique, was carried out. It has been shown that the oxygen, nitrogen and carbon dioxide transfer rates of barrier polymers such as poly(ethylene terephthalate) and oriented polypropylene can be further reduced, by up to two orders of magnitude, with a thin coating (1-2 μm) of PVOH/Si-[SiO.sub.2]. More notably, it has been observed that the material maintains this feature even after a prolonged contact with water, which is a strong solvent for PVOH. Direct moisture sorption measurements show that silica lowers the water uptake of PVOH and inhibits sorption-induced swelling and plasticization of the polymer. Correlations between the gas transport properties of the hybrid coatings and factors such as the silica content, the type of polymeric substrate, the nature of penetrant and the temperature have been found, providing guidelines for the selection and design of multilayer materials for packaging applications. POLYM. ENG. SCI., 50:144-153, 2010. [C]2009 Society of Plastics Engineers, INTRODUCTION A new class of transparent organic-inorganic nanocomposite materials can be prepared with the sol-gel methodology, through the incorporation of oligomeric or polymeric molecules into a solution formed by a [...]

We have formed compositionally abrupt interfaces in silicon-germanium (Si-Ge) and Si-SiGe heterostructure nanowires by using solid aluminum-gold alloy catalyst particles rather than the conventional liquid semiconductor--metal eutectic droplets. We demonstrated single interfaces that are defect-free and close to atomically abrupt, as well as quantum dots (i.e., Ge layers tens of atomic planes thick) embedded within Si wires. Real-time imaging of growth kinetics reveals that a low solubility of Si and Ge in the solid particle accounts for the interfacial abruptness. Solid catalysts that can form functional group IV nanowire-based structures may yield an extended range of electronic applications. 10.1126/science.1178606

A prism coupler is used for examining the polarization-dependent optical properties of slab waveguide films, which are composed on nanoparticles dispersed in a Si[O.sub.2] matrix. The optical spectra of the nanocomposite films are compared with those of cosputtered films and the optical anisotropy of the films are modeled and analyzed based on an effective medium theory with Maxwell-Garnett geometry and layer-by-layer photonic band-gap structures.

The effect of copper precipitation on the formation of denuded zone (DZ) in Czochralski silicon is examined by using scanning infrared microscopy (SIRM) and optical microscopy. The formation of DZ is affected by the copper precipitation mechanism, which is controlled by the annealing temperature and point defects.

The small signal gain measurements of optically excited terahertz Si:P and Si:Bi lasers are presented. It is found that the silicon lasers are optically excited with radiation from a free electron laser or a C[O.sub.2] laser.

An easy-to-implement capillary coating strategy based on polymer entrapment in the network of polymerized silicate is described. In this manner, cationic polymers are tightly fixed onto the inner wall of the capillary for electroosmotic flow control without necessitating complex surface modification chemistries. The resulting coated capillary exhibited good stability over a wide range of pH, good reproducibility, strong endurance in more than 300 electrophoretic runs, and tolerance of commonly employed organic solvent additives in CE. Applications in CE-MS analysis of biologically important anions as well as sample enrichment are shown. Additionally, it was used as a durable base for attachment of multiple layers of charged polymers on the wall, via electrostatic interaction with the preceding layer. Thus, two novel types of highly stable coated capillaries, one with anodic EOF and the other cathodic, were developed.

Using [sup.29]Si, [sup.1]H, and [sup.2]H magic-angle spinning (MAS) and [sup.29]Si{[sup.1]H} heteronuclear correlation (HetCor) nuclear magnetic resonance (NMR) spectroscopy the tetrahedral sheets of the 10 [Angstrom] phase are shown to contain [Q.sup.2]-type Si bonded to silanol groups that donate hydrogen bonds to interlayer [H.sub.2]O. [sup.29]Si NMR spectra of 10 [Angstrom] phase samples synthesized from oxide and from crystalline talc starting materials contain a peak near -87 ppm for [Q.sup.2] Si, in addition to the main peak at -98 ppm for the talc-like [Q.sup.3] of the tetrahedral sheet. The [sup.1]H MAS NMR spectra of the 10 [Angstrom] phase contain two distinct peaks, at chemical shifts of +7.8 and +3.2 ppm, in addition to a narrow peak near +0.9 ppm from the talc-like hydroxyl groups. [sup.29]Si{[sup.1]H} HetCor data indicate that the +7.8 ppm [sup.1]H resonance corresponds to silanol groups and that at +3.2 ppm arises from interlayer [H.sub.2]O. Comparison of the observed data with correlations of [sup.1]H NMR chemical shift and [sup.2]H quadrupolar coupling indicates that the silanol groups donate moderate hydrogen bonds to interlayer [H.sub.2]O, d(O ... O) [approximately equal to] 2.8 [Angstrom], whereas most interlayer [H.sub.2]O donate only very weak or no hydrogen bonds at ambient conditions. Our results suggest that formation of the 10 [Angstrom], phase involves formation of vacancies, which allow favorable hydrogen bond interaction between interlayer [H.sub.2]O and the normally hydrophobic talc-like 2:1 layers. Keywords: NMR, l0 [Angstrom] phase, talc, silanol, hydrogen bond

Growth of [Si.sub.1?x][Ge.sub.x] nanodots on Si substrates is accomplished using single source gaseous precursors. It is found that on the nanodots they are relaxed and their compositions correlate with the molecular ratios in the precursors used in their fabrication.

Large-scale aligned silicon carbonitride (SiCN) nanotube arrays are synthesized by microwave-plasma-assisted chemical vapor deposition by using Si[H.sub.4], C[H.sub.4], and [N.sub.2] as precursors. With the increasing Si concentration, the SiCN nanotube has displayed favorable oxidation resistance, suggesting that SiCN nanotube is a promising candidate as stable field emitter.

Evanescent-wave cavity ring-down spectroscopy has been applied to a planar fused-silica surface covered with crystal violet (C[V.sup.+]) cations to characterize the silanol groups indirectly. A radiation-polarization dependence of the adsorption isotherm of C[V.sup.+] at the C[H.sub.3]CN/silica interface is measured and fit to a two-site Langmuir equation to determine the relative populations of two different types of isolated silanol groups. C[V.sup.+] binding at type I sites yields a free energy of adsorption of -29.9 [+ or -] 0.2 kJ/mol and a saturation surface density of (7.4 [+ or -] 0.5) x [10.sup.12] [cm.sup.-2], whereas the values of -17.9 [+ or -] 0.4 kJ/mol and (3.1 [+ or -] 0.4) x [10.sup.13] [cm.sup.-2] are obtained for the type II sites. The C[V.sup.+] cations, each with a planar area of ~120 [[Angstrom].sup.2], seem to be aligned randomly while lying over the SiO-type I sites, thereby suggesting that this type of site may be surrounded by a large empty surface area (> 480 [[Angstrom].sup.2]). In contrast, the C[V.sup.+] cations on a type II sites are restricted with an average angle of ~400 tilted off the surface normal, suggesting that the C[V.sup.+] cations on these sites are grouped closely together. The average tilt angle increases with increasing concentration of crystal violet so that C[V.sup.+] cations may be separated from each other to minimize the repulsion of nearby C[V.sup.+] and SiOH sites.

Simple techniques involving electro- and electroless deposition from a 0.05 mM Au[Cl.sub.3] and 0.1 M NaCl[O.sub.4] solution were employed to grow dome-shaped gold nanoparticles with an average diameter of 10.5 nm on H-terminated Si(100) substrates. The results show that the deposited Au nanoparticles belong to the fcc phase with the relative intensity of the (220) plane for Au nanoparticles obtained by electroless deposition found to be notably larger than that by electrodeposition.

The density functional study of the activation of X-H (X = H, Si, B, C) bonds was carried to get an insight into the factors that dictate the heterolytic cleavage pathways for X-H (X = H, Si, B, C) bonds. The experimental reactivity demonstrated that the activation barriers for the heterolysis of the H-H, the Si-H, and the B-H bonds are low whereas that for the C-H bond is quite high.

The x-ray absorption fine structure (XAFS) spectroscopy was used to study the microstructure and electronic structure of epitaxially grown GaN which was subjected to high-dose Si implantation. The analysis of the extended XAFS spectra reveals that implantation with 100 keV Si ions with a fluence equal to 1 * [10.sup.18][cm.sup.-2] renders the material amorphous and promotes the formation of Si-N bonds with a bond length equal to that corresponding in S[i.sub.3][N.sub.4].

A silicon carbide layer is synthesized by the implantation of a p-type (100) Si waver at an elevated temperature and the crystallinity is enhanced by subsequent MeV low fluence heavy ion irradiation. The results have shown an enhancement of the crystallinity using higher energies, higher substrate temperatures of the high-energy heavy ion bombardment, indicating that electronic stopping plays a vital role in modifying the SiC crystal.

A combination of a molten Al flux technique and single-crystal diffraction is employed to analyze the structure and thermoelectric characterization of the [A.sub.x][Ba.sub.8-x][Al.sub.14][Si.sub.31] (where A = Sr, Eu) single crystals. The analysis reveals that such compounds exhibit low thermal conductivity, strong metallic behavior, as well as various transport processes dominated by electrons as carriers.

The sequential rhodium-catalyzed silycarbocyclization followed by palladium-catalyzed cross-coupling reactions is described to synthesize functionalized cyclopentanes with a highly substituted exocyclic double bond. The reaction that involved 1,6-enynes and underwent silylcarbocyclization, found that if the enyne bears an electron-deficient double bond then the major side reaction, silyformation, can be suppressed by carrying out reaction under a substochiometric amount of CO.

Computational methods are used to study the reaction mechanism for the oxidative cyclization by clavaminic acid synthase. It is suggested that the biosynthesis of the oxapenam bicyclic structure could involve a 1,3-dipolar cycloaddition.

The density functional approach was used to systematically investigate the behaviors of the bimetal Mo-Mo doped cagelike silicon clusters [Mo.sub.2][Si.sub.n] at the size of n = 9-16. The results have shown that the dominant growth patterns of the bimetal Mo-Mo doped on opened cagelike silicon clusters (n = 9-13) are based on pentagon prism Mo[Si.sub.10] and hexagonal prism Mo[Si.sub.12] clusters, while the [Mo.sub.2] encapsulated [Si.sub.n] (n = 14-16) frames are dominant growth behaviors for the large-sized clusters.

A series of archetypal [S.sub.N]2@C and [S.sub.N]2@Si reactions are analyzed by using the ADF program. The results have shown that by simple increasing the steric demand of the substituents R around the silicon atom, the [S.sub.N]2@Si mechanisms changes from its regular single-well potential energy surfaces (PES), via a triple-well PES, to a double-well PES, which is normally encountered for [S.sub.N]2@C reactions.

Static absorption and fluorescence spectroscopy and ultrafast transient absorption measurements are used to investigate the contrasting photophysical properties of two silicon (IV) tetraphenylporphyrins (Si(Tpp)[(py).sub.2] and Si(Tpp)[Cl.sub.2]). The results have shown that the connection between structural distortions and the presence of low-energy excited states have given rise to ultrafast nonradiative deactivation of the photoexcited molecule to the ground electronic state.

The surface chemistry of pristine, 6-nm silicon nanoparticles is investigated by using Fourier transform infrared spectroscopy (FTIR) and static time-of-flight secondary ion mass spectroscopy (ToF-SIMS). ToF-SIMS measurements have suggested that hydrogen has desorbed from the particles surfaces over the same temperature range that the particles shrink.

The temperature dependent Hall effect (TDH), thermal and optical admittance spectroscopies and secondary ion mass spectroscopy (SIMS) are used to study the deep levels in high purity semi-insulating 4H-SiC. The results have shown that the compensation in the material is a complex process that has involved multiple deep levels.

Refocused MAS-J-INEPT NMR experiments in the solid state for the characterization of crystalline silicophosphate phases and amorphous gels are described. It is shown that [super 2][J.sub.P-O-Si] coupling constants are strongly dependent on the crystallographic chemical paths and on the number of (-OP) bonds around the Si atoms.

Asymmetric reduction of ketimines with trichlorosilane, which could be catalyzed by N-methylvaline-derived Lewis-basic formamides, is described. The results reveal that appending a fluorous tag simplifies the isolation procedure, while preserving high enantioselectivity.

A study was conducted to investigate AlGaN potential barrier heights of AlGaN/GaN heterostructures with and without SiN passivation. Catalytic chemical vapor deposition (Cat-CVD) SiN passivation lowered the AlGaN potential barrier height more significantly than plasma-enhanced CVD (PECVD) SiN passivation, suggesting that the passivation method could influence the AlGaN potential barrier height.

Boron [delta] doping in the Si spacer is used to show the broadband absorption of metal-oxide-semiconductor SiGe/Si quantum dot infrared photodetectors. Broadband detection is feasible using this device because the atmospheric transmission windows are located at 3-5.3 and 7.5-14 [micro]m and it should be noted that the detector should be operated in the inversion bias region to reduce dark current.

Fabry-Perot (FP) effects found in InGaN/GaN heterostructures and quantum wells epitaxially grown on Si(111) substrates have resulted from the high refractive index contrasts at the GaN/Si and the Air/InGaN interfaces. A three-layer FP model is used to describe the cavity and optically pumped lasing in nitride vertical-cavity surface-emitting laser is shown at room temperature.

The luminescent properties of concentration dependence are found in Ba[Mg.sub.2][Si.sub.2][O.sub.7]:[Eu.sup.2+], [Mn.sup.2+] red phosphor. The analysis of the energy transfer from [Eu.sup.2+] to the two [Mn.sup.2+] centers has indicated that the number ratio of [Mn.sup.2+](II) to [Mn.sup.2+](I) has increased with increasing [Mn.sup.2+] concentration.

A molecular dynamics (MD) model is used to examine both the deposition and etching steps during the layer-by-layer etching of Si and Si[O.sub.2]. The results have shown that fluorocarbon passivation films can be grown in a self-limiting manner on both Si and Si[O.sub.2] by using low-energy C[F.sub.2.sup.+] and C[F.sub.3.sup.+] ions.

A study demonstrates that desilication in alkaline medium of large ZSM-5 crystals, presenting a homogeneous distribution of framework aluminum, originates in an accessible interconnected network of intracrystalline mesopores and preserved crystallinity. The substantial mesoporosity and the high degree of accessibility make desilication an advantageous approach towards manufacturing hierarchically structured micro- and mesoporous ZSM-5 zeolites for improved gas transport properties.

A study obtained high-resolution [sup.17.O]/[sup.1.H] double resonance nuclear magnetic resonance (NMR) spectra for two zeolites, one with a low Si/Al ratio (zeolite HY) and another with a high Si/Al ratio (HZSM-5), to investigate their local structure and Bronsted acidity. Results show that the [sup.17.O], one-pulse NMR spectra of H-form zeolites are dominated by the signals due to the framework Si-O-Si and Si-O-Al sites.

Large-scale amorphous silicon oxide nanowires (SiONWs) are synthesized from silicon monoxide powder under supercritically hydrothermal conditions. The [triple bond] Si-OH can reduce the adsorption activity of the SiONW surface that might be in favor of preventing the growth from the cross section and assisting the growth along the axial direction of the SiONWs.

The density functional theory (DFT) ab initio calculation of Fe-silicon hybrid redox potentials is reported. It is suggested that the hydrosilylation activated by visible light proceeds through a mechanism, which is not yet described, thus indicating that saturations are preserved during the addition.

The synthesis, characterization, and growth rates of aluminum- and germanium,aluminum-substituted silicalite-1 (Al-silicalite-1, Ge,Al-silicalite-1) materials grown from clear solutions are presented. The results have provided insights about how one can design silicalite-1 nanoparticles with sufficient heteroatom content to be drelevant for catalysis.

The covalent modification of Si surfaces through a two-step chlorination-methylation method is described to introduce kinetically stable C[H.sub.3]-Si bonds onto Si(111) surfaces. The results have provided strong evidence that the energetics of chemically modified Si interfaces can be fixed with respect to pH and have shown that the band-edge energies of Si can be tuned independently of pH-derived variations in the electrochemical potential of the solution redox species.

Single crystals of the type 1 clathrate compound Ba8Al14Si31 are grown using a molten Al flux method. Single-crystal neutron diffraction of Ba8Al14Si31 confirms that the Al partially occupies all of the framework sites.

Ab initio based configuration interaction calculations are conducted to explore the low-lying electronic states and spectroscopic properties of the heaviest nonradioacitve silicon chalcogenide molecule and its monopositive ion. The calculated dissociated energies of SiTe and [SiTe.sup.} are 4.41 and 3.52 eV, respectively and the spin-orbit splitting between the two components of the ground state of [SiTe.sup.} is found to be 1880 [cm.sup.-1].

Abstract -- A procedure was proposed for the gas-chromatographic determination of impurity organic compounds in high-purity dichlorosilane with a detection limit of 0.1-0.2 ppm, which allows metrological control in the [...]

p-Si type electrodes modified with different organic monolayers were investigated by reaction with radical anion and cation electrogenerated at a microelectrode operating in the configuration of a scanning electrochemical microscope. The method proves to be a convenient tool for investigating both the quality and the redox properties of the layer as previously demonstrated on metallic electrodes especially when the sample cannot be electrically connected. Approach curves recorded with the different mediators were used to investigate the electron-transfer rates across alkyl monolayers bound to p-type silicon substrates. Preliminary results indicate that the interfacial electron transfer occurs via electron tunneling through the organic layer as generally described for SAMs grafted on gold electrodes.

Metal catalyzed, CVD-grown silicon nanowires decorated by chemical assembly of closely spaced Ag nanocrystals were modified with the well-known 'silver mirror' reaction and investigated as substrates for surface-enhanced Raman (SERS) and hyper-Raman (SEHRS) spectroscopy. Four chromophores were examined: Rhodamine 6G, crystal violet, a cyanine dye, and a cationic donor-acceptor substituted stilbene. After soaking the substrates overnight in [10.sup.-4] M aqueous chromophore solutions, all four chromophores gave good-quality SERS spectra in [less than or equal to] 60 s using < 1 [micro]W of 458-nm cw laser power, and SEHRS spectra are obtained in [less than or equal to] 120 s using < 1 mW of mode-locked 916-nm laser power. Results from this substrate are compared with those on colloidal silver nanoparticles deposited as a film, as well as surfaces grown by the silver mirror reaction.

Conventional and molecular beam Fourier transform microwave spectroscopy is used to measure the rotational spectra of the main isotopomer of the [.sup.29.Si] and of all [.sup.13.C] isotopologues of axial and equatorial forms of 1-fluoro-silacyclohexane. The rotational spectra of some, the most intense, vibrational satellites are measured and they are found to belong to the ring-puckering motions.

The enhancement of ultrathin silicon oxide/Si(100) films and the effect of fluorine on it is investigated by performing in situ pyrolytic-gas passivation (PGP) using N[F.sub.3] simultaneously with the previously proposed PGP using [N.sub.2]O. The results have shown that F passivation effectively contributes to compensate the inconsistent-state bonding sites near the interface that remain with N passivation.

A study was conducted to elucidate the structures and chemistry that occur on a dry silica gel surface when it is treated with P[Cl.sub.5] and moisture. The occurrence of phosphorous bridging between two adjacent silanols sites is seen and bridging structures based on Si-O-P-O-P-O-Si linkages are also seen.

A study of the mechanisms of the reaction of H2XN (X = C, Si) is conducted with NO at the level CCSD(T)/aug-cc-PVTZ/B3LYP/6-31++G(d,p). The results indicate that there are two favorable reaction pathways in the reaction H2CN + NO that have similar energy barriers.

The isotropic hyperfine coupling constants of silicon radical defects are calculated using density functional theory. It was found that changes in radical hybridization alongwith changes in first-nearest-neighbor composition are the main factors, which affects the calculated hyperfines.

We demonstrate that electrophoresis on a flat Si substrate is an effective method in separation of DNA with different configurations, e.g., linear, supercoiled, and relaxed or DNA of different length, e.g., supercoiled DNA ladder. The surface separation arises from the different number of contacts due to the conformational differences between adsorbed DNA chains. Imposing a Au nanopattern on the Si surface further improves the separation effect. The simulation of electric field on this patterned surface by the finite element method shows that Au nanodots act as local pinning points for DNA segments due to dielectrophoretic force. The results of molecular dynamics simulation showed that the conformational differences between adsorbed polymer chains were amplified on the patterned surface and enhanced separations were achieved, which are consistent with the experimental results.

Threshold photoelectron-photoion coincidence spectroscopy (TPEPICO) is used to study the dissociation kinetics and thermochemistry of [Me.sub.4]Si, [Me.sub.6][Si.sub.2] and [Me.sub.3]SiX, (X = Br, I) molecules. The accurate dissociative photoionization onsets for these species are measured from the breakdown diagram and the ion time-of-flight distribution.