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Two types of fluoride ion-catalyzed desilylative-defluorination (intermolecular and intramolecular versions) have been reported. The intermolecular desilylative-defluorination consists of sequential reactions: generation of a nucleophile by fluoride ion-promoted desilylation, its reaction with a fluorinated electrophile, and simultaneous formation of a final product and regeneration of fluoride ion. Precursors of nucleophiles used in the catalytic reaction system involve disilane, silyl ethers, CF 3 -TMS, and FSO 2 CF 2 CO 2 TMS. The intramolecular version is quite useful for the preparation of gem -difluoroalkenes including α-substituted 2,2-difluorostyrenes, 2-trimethylsilyloxy-3,3-difluoroacrylate, tetrafluoroquinodimethane, which arise from 1,2-, 1,4- and 1,6-desilylative-defluorination, respectively. The potential advantages for both types of the desilylative-defluorinations are (1) effective preparation of base or nucleophile-sensitive products, (2) very mild and essentially neutral conditions, and (3) use of a catalytic amount of fluoride ion.

Non-volatile memory devices are realized using CVD and ALD of all active layers in a cluster tool. The floating gate consists of silicon nanocrystals. A high nanocrystal density was obtained through an enhanced nucleation rate by using disilane (Si2H6) as well as trisilane (Si3H8, known as Silcore®) as precursors for low-pressure chemical vapor deposition (instead of silane). The deposition temperature was 300–325 °C and the deposition pressure ranged between 0.1 and 10 mbar. To prevent oxidation of the nanocrystals, they were encapsulated directly after deposition with a 10-nm thick ALD-grown Al2O3 layer (blocking oxide). The deposition of Si-nanocrystals as a function of substrate temperature, precursor flow rate and total gas pressure was explored. Appreciable retention and endurance were measured on realized Al/TiN/Al2O3/Si-nanocrystal/SiO2/ Si(100) floating-gate capacitor structures.

Hydrogenated nanocrystalline silicon germanium thin films (nc-SiGe:H) is an interesting alternative material to replace hydrogenated nanocrystalline silicon (nc-Si:H) as the narrow bandgap absorber in an a-Si/a-SiGe/nc-SiGe(nc-Si) triple-junction solar cell due to its higher optical absorption in the wavelength range of interest. In this paper, we present results of optical, structural investigations and electrical characterization of nc-SiGe:H thin films made by hot-wire chemical vapor deposition (HW-CVD) with a coil-shaped tungsten filament and with a disilane/germane/hydrogen gas mixture. The optical band gaps of a-SiGe:H and nc-SiGe:H thin-films, which are deposited with the same disilane/germane/hydrogen gas mixture ratio of 3.4 : 1.7 : 7, are about 1.58 eV and 2.1 eV, respectively. The nc-SiGe:H thin film exhibits a larger optical absorption coefficient of about 2–4 in the 600–900 nm range when compared to nc-Si:H thin film. Therefore, a thinner nc-SiGe:H layer of ∼500 nm thickness may be sufficient for the narrow bandgap absorber in an a-Si based multiple-junction solar cell. We enhanced the transport properties as measured by the photoconductivity frequency mixing technique. These improved alloys do not necessarily show an improvement in the degree of structural heterogeneity on the nanometer scale as measured by smallangle X-ray scattering. Decreasing both the filament temperature and substrate temperature produced a film with relatively low structural heterogeneity while photoluminescence showed an order of magnitude increase in defect density for a similar change in the process.

The synthesis and structure of zirconium and titanium complexes containing the chelating disilane-1,2-diolate ligand rac - [ Me ( Me 3 Si ) 3 SiSiO ] 2 2 - ( 1 )-2H are reported. The compounds ( E )-[Me(Me 3 Si) 3 SiSiO] 2 TiCl 2 ( 3a ) and ( E )-[Me(Me 3 Si) 3 SiSiO] 2 ZrCl 2 · THF ( 3b ) were prepared by the reactions of MCl 4 (M = Ti, Zr) with {( E )-[Me(Me 3 Si) 3 SiSiO] 2 } 2 Ti ( 2a ) and {( E )-[Me(Me 3 Si) 3 SiSiO] 2 } 2 Zr · HNEt 2 ( 2b ), which are derived from the reaction of 1 with Zr(NEt 2 ) 4 and Ti(OEt) 4 , respectively. Upon treatment with 3 equiv. of TiCl 4 , 2a undergoes a ring opening reaction to yield the dinuclear complexes ( E )-[Me(Me 3 Si) 3 SiSiO] 2 Ti 2 Cl 6 ( 4 ) and ( E )-[Me(Me 3 Si) 3 SiSiO] 2 Ti 2 OCl 4 ( 5 ). The solid state structures of 2a , 5 and TiCl 4 · 2THF- d 8 have been determined by X-ray crystallography.

report-ed that the photolysis of 4-(trifluoromethyl)phenylpenta-methyldisilane in ethanol-hexane mixture affords 4-(tri-fluoromethyl)phenyldimethylsilane, (trimethylsilyl)[(eth-oxydimethyl)silyl](trifluoromethyl)cyclohexadienes, and 4-(trifluoromethyl)phenyl(ethoxydimethyl)silane in 24, 41,and 15% yields, respectively. In this reaction, it wasconcluded that 4-(trifluoromethyl)phenyldimethylsilane wasformed through the nucleophilic attack of ethanol at the β-silicon atom of the disilane moiety. In the photolysis of

A variety of arylethynylsilanes (Ar-C[triple bond]C-C6H4-C[triple bond]C)(n)SiMe(4-n) were prepared successfully by reaction of the corresponding chlorosilanes Me(4-n)SiCl(n) with Ar-C[triple bond]C-C6H4-C[triple bond]CM (M = Li, MgBr), which was prepared by treatment of ethynyl(diarylethyne)s Ar-C[triple bond]C-C6H4-C[triple bond]CH with BuLi or MeMgBr. The ethynyl(diarylethyne)s were readily prepared in good yields by the double-elimination method: addition of lithium hexamethyldisilazide to a mixture of ArCH2SO2Ph, TMS-C[triple bond]C-C6H4-CHO, and ClP(O)(OEt)2, followed by desilylation. In the tetrakis(arylethynyl)silanes (Ar-C[triple bond]C-C6H4-C[triple bond]C)4Si thus prepared, through-space conjugation of four triple bonds on the silicon atom emerges as a result of participation of the silicon orbitals in the acetylenic pi orbitals. This participation enhances the emissive quantum yields of arylethynylsilanes with an increase in the number of arylethynyl moieties on silicon: quantum yields of emission (phiF) of 0.72 for (MeOC6H4-C[triple bond]C-C6H4-C[triple bond]C)4Si, 0.53 for (MeOC6H4-C[triple bond]C-C6H4-C[triple bond]C)2SiMe2, and 0.47 for MeO-C6H4-C[triple bond]C-C6H4-C[triple bond]CSiMe3 were obtained. Although this enhancement effect was also observed in the phenylethynylarylsilane (MeOC6H4-C[triple bond]C-C6H4)2SiMe2, the bis(arylethynyl)disilane (MeOC6H4-C[triple bond]C-C6H4-C[triple bond]C-SiMe2)2 exhibited non-enhanced emission.

The lowest frequency perpendicular fundamental band ν 9 of disilane has been analyzed to investigate torsion mediated vibrational interactions. We report here a three-band analysis involving torsional levels built on the ground state, the ν 9 vibrational fundamental, and ν 3 fundamental. This analysis includes transitions from the far-infrared torsional bands, ν 4 , 2 ν 4 − ν 4 , 3 ν 4 − 2 ν 4 , two perturbation-allowed rotational series from the overtone band 3 ν 4 and transitions restricted to −21 ⩽ k Δ k ⩽ 21 in the ν 9 fundamental band. An excellent fit to the included data was obtained. Two interactions are identified in this fit, a resonant Coriolis interaction between the ν 9 torsional stack and that of the ground vibrational state and a Fermi interaction between the ν 3 fundamental and the gs. The introduction of the Fermi interaction causes a large change in the barrier height for the ground vibrational state and makes the barrier shape parameter redundant, indicating that the vibrational contributions to the experimental barrier shape are dominant. Such effects have also been observed for ethane and other similar molecules.

Silicon nanowires SiNWs) on a {100} silicon wafer coated with a gold film were formed by thermal cracking of disilane at 473-573 K. The SiNWs were single-crystalline with 10-100 nm in diameter and a (111) crystal orientation. The optimum conditions for obtaining long SiNWs that are several hundred μm long include a disilane flow rate of 0.017 cm 3 /s, an argon gas flow rate of 0.33 cm 3 /s, and a total pressure of 0.67 kPa. The low-temperature formation of SiNWs was explained by lowering the melting point of Au-Si eutectic particles. Self-wiring of SiNWs between gold square dots placed 15 μm from each other was successfully conducted.

Liquid Si ditertiarybutyl silane (DTBSi) metal-organic source was used as the Si dopant source for the growth of n-type GaN by metal-organic chemical vapor deposition (MOCVD) for the first time to replace the conventional gaseous Si sources like silane SiH 4 [K. Pakula, R. Bozek, J.M. Baranowski, J. Jasinski, Z. Liliental-Weber, J. Crystal Growth 267 (2004) 1] and disilane Si 2 H 6 [L.B. Rowland, K. Doverspike, D.K. Gaskill, Appl. Phys. Lett. 66 (1995) 1495]. Electrical, structural, optical, and surface properties of the samples doped by DTBSi as well as an undoped control sample are determined by Hall, high resolution X-ray diffraction (HRXRD), photoluminescence (PL), and atomic force microscopy (AFM) measurements respectively. A constant doping efficiency for GaN is obtained with carrier concentration up to 10 18 cm −3 . The typical HRXRD full-width at half-maximum values of symmetric (0 0 2) and asymmetric (1 0 2) planes are 284 and 482 arcsec, respectively. The near band edge PL intensity is found to be increased proportional to the doping concentration. Dark spot density is also determined from AFM measurement.

The molecular structure of the title compound, C22H38Si2, features atransarrangement of the cyclopentadienyl rings to avoid steric strain [C—Si—Si—C torsion angle = −179.0 (5)°]. The Si—Si bond length is 2.3444 (4) Å. The most notable intermolecular interactions in the molecular packing are C—H...π contacts that lead to the formation of wave-like supramolecular chains along thebaxis.

We present results from first-principles calculations on silane (SiH4) under pressure. We find that a three dimensional P-3 structure becomes the most stable phase above 241 GPa. A prominent structural feature, which separates the P-3 structure from previously observed/predicted SiH4 structures, is that a fraction of hydrogen leaves the Si-H bonding environment and forms segregated H2 units. The H2 units are sparsely populated in the system and intercalated with a polymeric Si-H framework. Calculations of enthalpy of formation suggest that the P-3 structure is against the decomposition into Si-H binaries and/or the elemental crystals. Structural stability of the P-3 structure is attributed to the electron-deficient multicenter Si-H-Si interactions when neighboring silicon atoms are linked together through a common hydrogen atom. Within the multicenter bonds, electrons are delocalized and this leads to a metallic state, possibly also a superconducting state, for SiH4. An interesting outcome of the present study is that the enthalpy sum of SiH4 (P-3 structure) and Si (fcc structure) appears to be lower than the enthalpy of disilane (Si2H6) between 200 and 300 GPa (for all previously predicted crystalline forms of Si2H6), which calls for a revisit of the stability of Si2H6 under high pressure.

A new class of aluminum homocatenated compounds (LinAlnH2n+2) is proposed based on quantum chemical calculations. In these compounds, Al abstracts an electron from Li, becoming valence isoelectronic with C, Si, and Ge, thus mimicking respective structural features of Group 14 hydrides. Using the Coalescence Kick search program coupled with density functional theory calculations, we investigated the potential energy surfaces of Li2Al2 H6 and Li3Al3H6 . Then single-point-energy coupled-cluster calculations were performed for the lowest energy structures found. Indeed, the global minima established for Li2 Al2 H6 and Li3 Al3 H6 contain the Al2 H6(2-) and Al3H6(3-) kernels, which are isostructural with ethane (C2H6), disilane (Si2H6), digermane (Ge2 H6) and propane (C3H8), trisilane (Si3H8), trigermane (Ge3H8) molecules, respectively. Structural, energetic, and electronic characteristics of the Li2 Al2 H6 and Li3 Al3 H8 compounds are presented and the viability of their synthesis is discussed.

Hydrogenation of Cp*SiCl2SiCl3 (A) (Cp*=C5Me5) with diisobutylaluminum hydride (DIBAL-H) gave partially hydrogenated disilane Cp*SiCl2SiH3 (1) with 45% yield, whereas the reaction with lithium aluminum hydride (LiAlH4) provided the well-known Cp*SiH2SiH3. The symmetric disilane Cp*SiH2SiH2Cp* (2) is accessible either by hydrogenation of Cp*SiCl2SiCl2Cp* (B) with DIBAL-H or LiAlH4 but attempts to partially hydrogenate the disilane B failed. The reaction of B with 1 eq. DIBAL-H afforded a mixture of five different molecules of the type Cp*SiR1R2SiR3R4Cp* (D, R1-R4=H, Cl) which co-crystallize in a single crystal with a H/Cl ratio of 1/3. Characterization by 1H and 29Si NMR, ATR IR spectroscopy, EI mass spectrometry and for 1 and the co-crystal D the single crystal X-ray diffraction analysis is presented. Compounds 1 and 2 are thermally stable in the solid state and do not decompose prior to evaporation.

A series of disilane-bridged donor-acceptor architectures 1-9 containing strong electron-donating and -withdrawing substituents were designed and synthesized in acceptable yields. The substituents substantially affected the fluorescence and nonlinear optical properties of the compounds. In the solid state, the compounds showed purple-blue fluorescence (λ(em) = 360-420 nm) with high quantum yields (up to 0.81). Compound 3, which had p-N,N-dimethylamino and o-cyano substituents, exhibited optical second harmonic generation (activity 2.9 times that of urea, calculated molecular hyperpolarizability β = 1.6 × 10(-30) esu) in the powder state. Density functional theory calculations for the ground and excited states indicated that both the locally excited state and the intramolecular charge transfer excited state make important contributions to the luminescence behavior.

Strained Si 1−y C y epilayers with up to 1.48% C content have been grown on Si(001) by RP-CVD using the low-cost precursors disilane and trimethylsilane. These epilayers, with higher C content, were found to form point defects throughout growth resulting in amorphous hillocks forming on the epilayer surface. The size and density of these surface defects increases with C content and epilayer thickness. With substitutional C compositions above 1.48% the hillocks fuse on the surface and subsequent amorphous growth occurs.

An imine−amine-substituted disilane (NN)MeSi−SiMe(ONO) [(NN) ≡ PhN(CH2)2NPh; (ONO) ≡ o-O-p-MeO−C6H3−C(Ph)N−C6H4-o-O] involving a penta- as well as a tetracoordinate silicon atom was synthesized. This ligand combination gives rise to a stable disilane with a hypercoordinate silicon atom by the imine donor action, while a 1,1-dichlorosilane (MeCl2Si)−SiMe(ONO) is not available due to Si−Si bond cleavage with formation of the pentacoordinate monosilane SiClMe(ONO).

Reaction of pentamethylcyclopentadienyl(pentachloro)disilane (2), prepared from hexachlorodisilane and potassium pentamethylcyclopentadienide (Cp*K), with a further equivalent of Cp*K leads selectively to the title compound Cp* 2 Si 2 Cl 4 (3) which was characterized by NMR and X-ray structural data. Dehalogenation of 3 with four equivalents of sodium naphthalenide offers an alternative route for the synthesis of decamethylsilicocene (1).

A zinc porphyrin–fullerene dyad with a disilane as a σ-conjugated linker has been newly synthesized to evaluate the electron transfer ability of the oligosilane chain. Its photoinduced processes ha...

The thermolysis of 1,2-di(adamantoyl)tetrakis(trimethylsilyl)disilane (1a) with diphenylacetylene at 140 °C for 24 h afforded 1-[(E)-1,2-diadamantyl-2-(trimethylsiloxy)ethenyloxy]-2,3-diphenyl-1-[tris(trimethylsilyl)silyl]-1-silacycloprop-2-ene (2a) and 3,4-diadamantyl-2,2-bis(trimethylsiloxy)-1,1-bis(trimethylsilyl)-1,2-disilacyclobut-3-ene (3a) in 43% and 41% yields, respectively. Similarly, the cothermolysis of 1,2-di(pivaloyl)tetrakis(trimethylsilyl)disilane (1b) with diphenylacetylene gave 1-[(E)-1,2-di(tert-butyl)-2-(trimethylsiloxy)ethenyloxy]-2,3-diphenyl-1-[tris(trimethylsilyl)silyl]-1-silacycloprop-2-ene (2b) in 52% yield, along with a mixture of unidentified products. The reaction of 1a with bis(trimethylsilyl)acetylene under the same conditions produced 1-[(E)-1,2-diadamantyl-2-(trimethylsiloxy)ethenyloxy]-2,3-bis(trimethylsilyl)-1-[tris(trimethylsilyl)silyl]-1-silacycloprop-2-ene and 3a in 54% and 23% yield, while 1b with bis(trimethylsilyl)acetylene gave 1-[(E)-1,2-di(tert-butyl)-2-(trimethy...

The functionalized disilane (PhSCH2)Me2SiSiMe2(CH2SPh) (1) has been prepared and coordinated as a dithioether ligand on [PtCl2(PhCN)2] to afford the fluxional seven-membered chelate complex cis-[Pt...

Reaction of the thermally stable silylene Si[(NCH 2 Bu t ) 2 C 6 H 4 -1,2] ( 1 ) [abbrev. as Si(NN)] with SiX 4 (X = Cl or Br) afforded the disilanes (NN)SiX(SiX 3 ) and [(NN)SiX] 2 (X = Br only), the trisilane (NN)SiX-[(SiX 3 )Si(NN)] and the monosilane (NN)SiX 2 (X = Br only), whereas treatment of 1 with MCl 4 (M = Ge or Sn) yielded (NN)SiCl 2 and MCl 2 . [(NN)SiBr] 2 and (NN)SiBr 2 were also obtained by reaction of 1 with Br 2 . Reaction of 1 with PhSiCl 3 yielded the disilane (NN)SiCl(SiCl 2 Ph) and trisilane [(NN)SiCl] 2 SiClPh, whereas the disilane (NN)SiCl(SiCl 2 Me) was obtained with MeSiCl 3 . The trisilane (NN)SiCl-[(SiCl 3 )Si(NN)] was thermally labile and converted to [(NN)SiCl] 2 SiCl 2 .

Mesoporous phenylene–silica materials with three-dimensional-cage structures were synthesized from a phenylene-bridged disilane precursor [(EtO)3–Si–C6H4–Si–(OEt)3] using various surfactants. Compared to 1D-channel type materials, the 3D-cage mesoporous materials have an advantage of easy access and diffusion of molecules inside the pores. The materials obtained using hexadecyltrimethylammonium bromide (C16TMA+Br−) or hexadecylpyridinium chloride (C16Py+Cl−) show spherical morphology with a 3D-cage pore architecture and cubic symmetry. The use of triblock copolymer F88 [(EO)100–(PO)39–(EO)100] resulted in a 3D-cage type mesoporous material with microporosity in the pore walls. All the materials have high thermal stability of up to 773 K.

An efficient new method for the silylation of p‐nitrobenzyl‐2‐diazoacetoacetate using hexamethyl disilane and iodine is presented.

Kinetic aspects of the thermal decomposition of monosilane at 690–830 K and initial pressures of 0.1–3.7 MPa in a free-space reactor are considered. Neglecting the preparatory initiation period for the reaction (which is difficult to evaluate under the present dynamic conditions), the onset temperature for the decomposition is stipulated to some 700–710 K, independent of the initial monosilane pressure. The overall reaction appears to be of first order throughout the progressing decomposition process. We observe considerably lower reaction rates under the high-pressure conditions than existing models in the literature suggest. A modified model is proposed that simulates the observed reaction rates within ±1% and moreover predicts credible concentrations of the involved gaseous species. A key feature of the modified model is incorporation of two third-body assisted surface reactions, which generate monosilane from disilane and disilane from trisilane. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 309–321, 2006

The (ν4 + ν6) − ν4, (ν4 + ν8) − ν4 and (ν4 + ν9) − ν4 hot infrared systems of disilane (Si2H6) have been analysed at high resolution, and the values of the relative vibration–rotation–torsion parameters have been determined. The torsional splitting is about 0.500 cm−1 in the ν4 and ν4 + ν6 states, and decreases strongly in the vibrationally degenerate upper states ν4 + ν8 (about 0.0272 cm−1 on average) and ν4 + ν9 (about 0.3019 cm−1), consistent with theoretical predictions. Comparison between the vibrational wavenumbers of cold transitions and hot transitions originating in the excited torsional state v4 = 1 allows one to determine the change of the fundamental torsional frequency ν4 caused by the excitation of small amplitude vibrations. A remarkable increase in ν4 of about 8.599 cm−1 is found in the v9 = 1 state (E1d SiH3-rocking mode, asymmetric to inversion in the staggered geometry), and this corresponds to an increase in the torsional barrier height in this excited fundamental vibrational state by ...

The atomic layer deposition (ALD) of tungsten can be accomplished using sequential exposures of WF6 and Si2H6 (disilane). In this paper, W ALD is explored using in situ quartz crystal microbalance (QCM) measurements as a function of the reactant exposure and deposition temperature. The QCM measurements revealed that the WF6 reaction is self-limiting. In contrast, W ALD growth rates exhibited a slow and continual increase for disilane exposures > 4 × 104 L. The W ALD growth rate was also weakly temperature-dependent with an activation energy of 1.5 ± 0.1 kcal/mol at T 275 °C. The QCM results and previous Auger results for W ALD yield the relationship between the silicon coverage deposited during the Si2H6 exposure and the tungsten coverage deposited during the WF6 exposure. The W/Si atomic ratio of ∼ 1:1 is consistent with earlier Auger investigations of the surface chemistry during W ALD at 200 °C. The QCM measurements are also consistent with silicon coverages of 1.7–2.1 monolayers after the Si2H6 exposures. These high silicon coverages are believed to result by silylene insertion from Si2H6 into surface Si–H bonds.

Low dielectric constant materials as interlayer dielectrics (ILDs) offer a way to reduce the RC time delay in high-performance ultra-large-scale integration (ULSI) circuits. Fluorocarbon films containing silicon have been developed for interlayer applications below 50-nm linewidth technology. The preparation of the films was carried out by plasma-enhanced chemical vapor deposition (PECVD) using gas precursors of tetrafluorocarbon as the source of active species and disilane (5 vol.% in helium) as a reducing agent to control the ratio of F/C in the films. The basic properties of the low dielectric constant (low-k) interlayer dielectric films are studied as a function of the fabrication process parameters. The electrical, mechanical, chemical, and thermal properties were evaluated including dielectric constant, surface planarity, hardness, residual stress, chemical bond structure, and shrinkage upon heat treatments. The deposition process conditions were optimized for film thermal stability while maintaining a relative dielectric value as low as 2.0. The average breakdown field strength was 4.74 MV/cm. The optical energy gap was in the range 2.2–2.4 eV. The hardness and residual stress in the optimized processed SiCF films were, respectively, measured to be in the range 1.4–1.78 GPa and in the range 11.6–23.2 MPa of compressive stress.

The electroreduction of dichloromethylphenylsilane was carried out in the presence of the disilane additives such as 1,1,1‐trimethyl‐2,2,2‐triphenyldisilane under constant current conditions by using Mg electrodes to give the corresponding polysilanes in 24–88% yield. The disilane additives were found to promote the electroreductive polymerization of dichloromethylphenylsilane and control the molecular weight distribution of the resulting polysilanes. The number average molecular weights of the resulting polysilanes were determined by GPC to be 2100–3800, and the molecular weight distributions, 1.05–1.25. The resulting polymers synthesized in the presence of the disilanes showed narrower molecular weight distributions than that synthesized without the additives. In particular, the resulting polymer prepared using an equal amount of the disilane additive to the dichlorosilane monomer, the number average molecular weight was 3200, the molecular weight distribution was 1.25, and the yield was found to be rem...

Surface modification of silicon-containing fluorocarbon (SiCF) films achieved by wet chemical treatments and through x-ray irradiation is examined. The SiCF films were prepared by plasma-enhanced chemical vapor deposition, using gas precursors of tetrafluoromethane and disilane. As-deposited SiCF film composition was analyzed by x-ray photoelectron spectroscopy. Surface modification of SiCF films utilizing n-lithiodiaminoethane wet chemical treatment is discussed. Sessile water-drop contact angle changed from 95°±2° before treatment to 32°±2° after treatment, indicating a change in the film surface characteristics from hydrophobic to hydrophilic. For x-ray irradiation on the SiCF film with a dose of 27.4kJ∕cm3, the contact angle of the sessile water drop changed from 95°±2° before radiation to 39°±3° after x-ray exposure. The effect of x-ray exposure on chemical bond structure of SiCF films is studied using Fourier transform infrared measurements. Electroless Cu deposition was performed to test the applic...

Silicon-rich amorphous hydrogenated silicon carbon (a-SiC:H) films with C content up to 23% have been grown on Si and Corning glass substrates using ArF laser induced chemical vapor deposition (ArF-LCVD). This technique allows tailoring film composition by controlling deposition parameters such as precursor gas mixture (disilane and ethylene diluted in helium) and substrate temperature (180–400 °C). The influence of both parameters on composition and bonding were studied by Fourier transform infrarred (FTIR) and X-Ray photoelectron spectroscopy (XPS). The optical gap of these semiconductors deposited at 250 °C varied from 1.6 to 2.4 eV and was determined by UV–vis spectroscopy. An additional analysis by profilometry and atomic force microscopy (AFM) have been done for determining the deposition rate and the roughness (rms

The effect of two reactive gases on the properties of bioactive glass thin films produced by pulsed laser deposition (PLD) was studied. The ablation of a bioactive silica-based glass was carried out by an ArF excimer laser ( λ = 193 nm, Φ = 4.2 J cm −2 , τ = 25 ns, f = 10 Hz) at various pressures of Si 2 H 6 /Ar and NH 3 /Ar reactive mixtures. The bonding configuration and chemical environment of the resulting coatings were followed by Fourier transform infrared spectroscopy (FT-IR). The composition and bond arrangement of bioactive glass films were tuned by varying the chamber atmosphere. The results show how to adjust film characteristics for osteointegration of implants.

Rate constants for the thermal dissociation of Si2H6 are predicted with a novel transition state model. The saddle points for dissociation on the Si2H6 potential energy surface are lower in energy than the corresponding separated products, as confirmed by high level ab initio quantum mechanical calculations. Thus, the dissociations of Si2H6 to produce SiH2 + SiH4 (R1) and H3SiSiH + H2 (R2) both proceed through tight inner transition states followed by loose outer transition states. The present "dual" transition state model couples variational phase space theory treatments of the outer transition states with ab initio based fixed harmonic vibrator treatments of the inner transition states to obtain effective numbers of states for the two transition states acting in series. It is found that, at least near room temperature, such a dual transition state model is generally required for the proper description of each of the dissociations. Only at quite high temperatures, i.e., above 2000 K for (R1) and 600 K for (R2), does a single fixed inner transition state provide an adequate description. Similarly, only at quite low temperatures (below 100 and 10 K for (R1) and (R2), respectively) does a single outer transition state provide an adequate description. Pressure dependent rate constants are obtained from solutions to the multichannel master equation. These calculations confirm that dissociation channel (R2) is negligible under conditions relevant to the thermal chemical vapor deposition (CVD) processes. Rate constants for the chemical activation reactions, SiH2 + SiH4 --Si2H6 (R-1) and SiH2 + SiH4 --H3SiSiH + H2 (R3), are also evaluated within the dual transition state model. It is found that reaction R3 is the dominant channel for low pressures and high temperatures, i.e., below 100 Torr for temperatures above 1100 K.

Gas source molecular beam epitaxy is used for the growth of SiGeC layers from disilane, germane and methylsilane precursors at low substrate temperatures. A systematic method of carbon concentration determination based on a combination of X-ray diffraction and X-ray reflectivity is examined. The grown layers were annealed using rapid thermal annealing and analysed with X-ray diffraction, X-ray reflectivity and secondary ion mass spectrometry. The recovery of compressive strain in the SiGeC layer is correlated to the loss of carbon through diffusion and indicates that the carbon atoms are incorporated substitutionally in the as-grown layers.

The SiC formation on a ordered Si(1 0 0) substrate at low temperatures (980–1180 K) and low total pressures (10 −6 mbar) has been investigated by in situ X-ray photoemission spectroscopy (XPS) and ex situ scanning tunneling microscopy (STM). SiC was grown by chemical vapor deposition (CVD) from C 2 H 2 and Si 2 H 6 as the precursor gases. At all the temperatures and in presence of both C 2 H 2 and Si 2 H 6 XPS data showed the formation of sub-stoichiometric Si 1− x C x alloys characterized by excess silicon. By exposing to C 2 H 2 only, stoichiometric SiC could be synthesized up to 1080 K. At 1180 K the formation of a Si 1− x C x alloy was observed. STM analysis has pointed out the role of silicon from the gas phase in the growth mechanisms and it has shown that uniform films with low roughness and small nanostructures can be obtained by tuning the acetylene/disilane ratios independently from the temperature selected in the investigated range.

We explored the deposition of hydrogenated amorphous silicon (a-Si: H) using trisilane (Si3H8) as a gas precursor in a radiofrequency plasma enhanced chemical vapour deposition process and studied the suitability of this material for photovoltaic applications. The impact of hydrogen dilution on the deposition rate and microstructure of the films is systematically examined. Materials deposited using trisilane are compared with that using disilane (Si2H6). It is found that when using Si3H8 as the gas precursor the deposition rate increases by a factor of similar to 1.5 for the same hydrogen dilution (R = [H-2]/[Si3H8] or [H-2]/[Si2H6])- Moreover, the structural transition from amorphous to nanocrystalline occurs at a higher hydrogen dilution level for Si3H8 and the transition is more gradual as compared with Si2H6 deposited films. Single-junction n-i-p a-Si: H solar cells were prepared with intrinsic layers deposited using Si3H8 or Si2H6. The dependence of open circuit voltage (V-oc) on hydrogen dilution was investigated. V-oc greater than 1 V can be obtained when the i-layers are deposited at a hydrogen dilution of 180 and 100 using Si3H8 and Si2H6, respectively.

The polycrystalline silicon deposited by single-wafer rapid thermal chemical vapor deposition with both silane (SiH/sub 4/) and disilane (Si/sub 2/H/sub 6/) precursors have been characterized for across wafer uniformity, thickness repeatability, and basic material properties such as grain structure and surface topography. The results show that the disilane process greatly improves the manufacturability of the single-wafer polycrystalline silicon process. Specifically, a /spl sim/50% improvement in the thickness uniformity, /spl sim/25% improvement in surface roughness, and a significantly less sensitivity of the process to hardware have been achieved with similar particle performance. The grain structure of as-deposited and postimplant and anneal films have been compared by X-ray diffraction and transmission electron microscope. NMOS and PMOS capacitors have been fabricated with polycrystalline silicon using silane and disilane precursors. The grain structure and electrical parameters, such as gate leakage currents and gate capacitance, show no significant difference between these two precursors.

Growth rate of Si epitaxy on (1 0 0) and (1 1 0) Si surfaces was analyzed by a hydrogen coverage model assuming that the source disilane molecules adsorb and decompose only at the dangling bond site on the surface. The rate of each elementary process such as adsorption and decomposition of source molecules on the surface and desorption of hydrogen was evaluated from growth rate dependence on the temperature and the source gas pressure. It was revealed that the low sticking coefficient of the source molecule and low desorption rate of hydrogen on the (1 1 0) surface is responsible to the lower growth rate on the (1 1 0) surface than that on (1 0 0) surface.

Ceramic fibers with compositions in the system Si–C have a great potential for high-temperature applications. In recent years, our efforts have been dedicated to the development of polymers consisting of polysilanes suitable to spin fibers and build up matrices for CMC as well. The polysilanes are synthesized via disproportionation of the so-called disilane fraction [Richter, R., Roewer, G., Bohme, U., Busch, K., Babonneau, F., Martin, H.-P. et al., Appl. Organomet. Chem., 1997, 11, 71 (and references cited therein)]. A further thermal treatment yields materials which are soluble in organic solvents, and these solutions can be dry-spun to give fibers which are subsequently pyrolyzed. Solubility and high ceramic yield make this precursor a promising candidate for matrix infiltrations, too. The chemistry and the adjustment of viscosity and solubility to the requirements of the fiber processing as well as the conversion of the dried fibers to pure SiC fibers by thermal treatment will be reported.

Thermal, optical and electrochemical properties of phenyl-substituted disilanes have been investigated. Phase-transition temperature increased with increasing the number of phenyl substitutents. σ–π Conjugation effect by the introduction of phenyl-substitutents also strongly affected LUMO levels of disilanes with slight change of their HOMO levels.

N-p-n Si/SiGe/Si heterostructures have been grown by a disilane (Si2H6) gas and Ge solid sources molecular beam epitaxy system using phosphine (PH3) and diborane (B2H6) as n- and p-type in situ doping sources, respectively. Adopting an in situ doping control technology, the influence of background B dopant on the growth of n-Si emitter layer was reduced, and an abrupt B dopant distribution from SiGe base to Si emitter layer was obtained. Besides, higher n-type doping in the surface region of emitter to reduce the emitter resist can be realized, and it did not result in the drop of growth rate of Si emitter layer in this technology. (C) 2004 Elsevier B.V. All rights reserved.

An investigation of the stereochemical course of the reductive metallation of silyl chlorides with silicon-centred chirality has revealed two major events which are detrimental to stereoselection during silyl anion formation: (1) chloride-induced racemisation of silyl chlorides and (2) nonstereoselective formal dimerisation during metallation providing the corresponding disilane. In control experiments, the stereochemical course of these processes has been independently verified for the reductive metallation of the enantioenriched cyclic silyl chloride (SiS)-7a (R = H, er ⩾ 88:12). A screening of several related derivatives of (SiS)-7a led to the sterically encumbered silyl chloride (SiR)-7c (R = iPr, er ⩾ 94:6) which displays some unique features. This structural modification prevents racemisation by lithium chloride (T < −40 °C) as well as dimerisation (T < −100 °C) thus allowing for the first generation of an asymmetrically substituted silyl anion (SiS)-8c (er = 74:26) by reductive metallation of a silyl chloride with silicon-centred chirality. Moreover, the enantiospecificity of the preparation of (SiR)-7c by chlorination [(SiS)-9c (SiR)-7c] and its reduction with aluminium hydrides [(SiR)-7c (SiR)-9c] have been unambiguously determined by X-ray crystallography as retention (⩾99%) and inversion (⩾99%), respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The effect of various process parameters on the deposition rate of microcrystalline hydrogenated silicon is presented. The various pathways leading to high deposition rates involve the optimization of a combination of parameters, while maintaining the crystalline character of the film and avoiding the presence of particles. The deposition rate increases in conditions that enhance and at the same time “cool down” the electron population. Such conditions are: moderately higher frequencies, higher pressures, and the presence of larger molecules (like disilane) even in small quantities. There is an optimum pressure, determined by primary dissociation, for a certain silane fraction. In addition, silane fraction and power density must also increase up to the limit of transition to amorphous growth and before attachment becomes too important. In all of these cases, there is a need for optimizing the distance of the deposition substrate to the source of radical generation, especially at higher pressures, to further increase the already important contribution of higher silicon radicals. It is shown that similar deposition rates can be obtained via radical fluxes with very different compositions. In every case, there is a need for sufficient H atom fluxes to ensure crystalline growth.

Stable gases produced in SiH4 and H2-SiH4, capacitively coupled rf discharges operated at typical device-production conditions, were investigated by quadrupole mass spectrometry. The production of disilane and trisilane and the depletion of silane and pressure change were measured during consecutive short discharges. Dissociation rate constants and branching ratios for higher-silane production are obtained from the time-dependent densities. The influence of suspended Si particles on stable-gas production is found to be negligible, by changing the duration of individual discharges and thereby the particle densities and sizes. We have also observed pyrolitic decay of disilane and trisilane at 200°C, although this is negligible under normal reactor conditions.

(BGaIn)As and (InGa)(NAs) have been tested for the application in solar cells. Single layers have been grown lattice matched on GaAs using MOVPE at low growth temperatures. Optical properties, i.e. band-gap energies and optical constants have been determined with photoluminescence and spectroscopic ellipsometry. n- and p-Type doping have been achieved with disilane and diethylzinc as doping precursors, respectively. Corresponding free carrier properties are discussed based on Hall measurements. Different solar cell structures with n- and p-doped (BGaIn)As and (InGa)(NAs) as base layer have been grown and successfully tested.

The disilane derivative 2-(dichloromethylsilyl)-2-methyl-1,3-diphenyl-1,3,2-diazasilolidine was reacted with a salen-type tetradentate ligand to yield a pentacoordinate methylsilane with a silylated ligand. This surprising rearrangement reaction-with Si-Si bond cleavage and Si-C bond formation at 0 °C without a catalyst and without special external energy input such as irradiation-is confirmed by X-ray structure analysis as well as 1 H, 1 3 C, and 2 9 Si NMR spectroscopic data of this novel hypercoordinate silicon complex.

The gas phase infrared emission spectrum of the A 3 Σ − – X 3 Π electronic transition of SiC has been observed using a high resolution Fourier transform spectrometer. Three bands ν ′ − ν ″ = 0–1, 0–0, and 1–0 have been observed in the 2770, 3723, and 4578 cm −1 regions, where the 0–1 and 0–0 bands were observed for the first time. The SiC radical was generated by a dc discharge in a flowing mixture of hexamethyl disilane [(CH 3 ) 6 Si 2 ] and He. A total of 1074 rotational transitions assigned to the 0–1, 0–0, and 1–0 bands have been combined in a simultaneous analysis with previously reported pure rotational data to determine the molecular constants for SiC in the two electronic states. The principal equilibrium molecular constants for the A 3 Σ − state are: B e = 0.6181195(18) cm −1 , α e = 0.0051921(20) cm −1 , r e = 1.8020884(26) A, and T e = 3773.31(17) cm −1 , with one standard deviation given in parentheses. The effect of a perturbation was recognized between the ν = 4 level of X 3 Π and the ν = 0 level of A 3 Σ, and the analysis was carried out to determine the interaction parameter between the two states.

We report a direct, statistically significant calculation of the surface reactivity of the SiH 3 radical on hydrogenated amorphous silicon (a-Si:H) using molecular-dynamics simulations of repeated impingement of SiH 3 radicals on growth surfaces of smooth a-Si:H films over the temperature range 475–800 K. SiH 3 can either incorporate into the film by adsorbing onto a surface Si dangling bond or inserting into Si–Si bonds (sticking), or abstract surface H through Eley–Rideal (ER) or Langmuir–Hinshelwood (LH) pathways to produce SiH 4 gas, or react with another surface SiH 3 to desorb as Si 2 H 6 (recombination), or leave the film by reflection or desorption. The overall surface reaction probability, β , includes both radical sticking and recombination. In agreement with experimental measurements, β is almost constant over the temperature range studied, as are the probabilities for sticking and recombination, s and γ , respectively; the calculated mean value of β is 0.47 ± 0.03. Energetic analysis of the various surface reactions shows that radical adsorption, radical insertion, and ER abstraction are barrierless processes, which explains the measured temperature independence of β . LH abstraction is activated, but competes with disilane formation, yielding a temperature-independent γ . Also, LH abstraction leads to H elimination from a-Si:H during growth and can partly explain the experimentally measured temperature dependence of the H content in the a-Si:H film.

The meso form of (RMeSiOH)2 [R = Si(SiMe3)3] (2) was synthesized exclusively by hydrolysis of a diastereomeric mixture of (RMeSiCl)2 (1). The novel cyclic metal disiloxides (E)-(RMeSiO)2Ti(OEt)2 (3) and [(Z)-(RMeSiO)2]2Zr · HNEt2(4) are readily prepared from the reaction of meso-2 with Ti(OEt)4 and Zr(NEt2)4, respectively. The results of X-ray structure analyses reveal complexes 3 and 4 to be strained five-membered ring compounds forming a dimeric structure and an adduct with diethylamine.