Photoelectron spectroscopy of silicon doped gold and silver cluster anions

Photoelectron spectra of low temperature silicon doped gold cluster anions Au(n)Si(-) with n = 2-56 and silver cluster anions Ag(n)Si(-) with n = 5-82 have been measured. Comparing the spectra as well as the general size dependence of the electron detachment energies to the results on undoped clusters shows that the silicon atom changes the apparent free electron count in the clusters. In the case of larger gold clusters (with more than about 30 gold atoms) the silicon atom seems to consistently delocalize all of its four valence electrons, while in the case of the silver clusters a less uniform behavior is observed. Here the silicon atoms act partly as electron donors, partly as electron acceptors, without following an obvious simple principle. Additionally some structural information can be obtained from the measured spectra: while Ag(54)Si(-) seems to adopt an icosahedral structural motif, Au(54)Si(-) seems to take on a low symmetry structure, much like the corresponding pure 55 atom clusters. This indicates that for such larger clusters the incorporation of a single silicon atom does not change the ground state geometry significantly.     

In situ STM investigation of gold reconstruction and of silicon electrodeposition on Au(111) in the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide

The electrodeposition of silicon on Au(111) was investigated by cyclic voltammety (CV) and by in situ scanning tunneling microscopy (STM) in the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide with a SiCl(4) concentration of 0.1 mol/L. A main reduction process begins in the cyclic voltammogram at about -1800 mV versus ferrocene/ferrocinium, which is correlated to the electrodeposition of elemental semiconducting silicon. It has been found that at an electrode potential more negative than the open circuit potential (OCP), the Au(111) surface is subject to a restructuring/reconstruction both in the case of the pure ionic liquid and in the presence of SiCl(4). The first STM-probed silicon islands with 150-450 pm in height appear at about -1700 mV versus ferrocene/ferrocinium. Their lateral and vertical growth leads to the formation of a rough layer with silicon islands of up to 1 nm in height. At about -1800 mV the islands merge and form silicon agglomerates. In situ I/U tunneling spectroscopy reveals a band gap of 1.1 +/- 0.2 eV for layers of about 5 nm in height, a value that has to be expected for semiconducting silicon.     

An indirect spectrophotometric method for the determination of silicon in serum, whole blood and erythrocytes.

An indirect method for the determination of silicon in blood samples has been developed. The proposed method overcame interference from a large amount of salts and phosphate in blood samples, and enabled us to determine the silicon contents in serum and whole blood by the same operation. After blood samples were digested by microwave heating, silicon, present as silicate in the sample solution, was reacted with molybdate to form a silicomolybdate complex. The complex was then separated from unreacted molybdate by a cation-exchange resin column. The molybdate liberated from the complex was spectrophotometrically determined in place of silicon. Since the method is not affected the composition of matrices between serum and whole blood, it could achieve good precision and accuracy, and could also estimate the silicon contents in erythrocytes from those in serum and whole blood. The sensitivity of the method was almost equal to that of the conventional silicomolybdenum blue method, and the calibration curve was linear up to 50 micromol l(-1) of silicon with a detection limit of 1.1 micromol l(-1) in whole blood. The mean concentrations of silicon in five healthy subjects were 11 micromol l(-1) for serum, 28 micromol l(-1) for whole blood and 50 micromol l(-1) for erythrocytes. Thus, the obtained distribution ratio between serum and erythrocytes was in the range of 0.15-0.39, and was found to be included in a narrow range.     

Effects of antimony on the surface tension of molten silicon

The effect of antimony concentration (C(Sb)/mass%) on the surface tension of molten silicon has been determined with the sessile drop method in the temperature range from 1693 to 1773 K and in the range of the oxygen partial pressure, Po(2), in an Ar atmosphere from 10(-23) to 10(-21) MPa. The results show that the surface tension of molten silicon decreases with increasing Sb concentration in the range of C(Sb)<0.9 mass%, which indicates positive adsorption of Sb in molten silicon and can be fairly described with the Szyszkowski's equation. The maximum decrease rate of surface tension is about 65 mN m(-1) (mass% C(Sb))(-1), and the temperature coefficient of surface tension, (partial differential sigma/ partial differential T)C(Sb), increases with increasing C(Sb). The evaporation of the systems was only observed between the melting points of antimony (904 K) and silicon (1683 K), and the surface tension presents no dependence on measuring time above the melting point of silicon.     

激光烧蚀硅酸盐的材料产生氧化硅氧化铝复合团簇

采用习飞行时间质谱技术,用308nm准分子激光烧蚀不同硅铝比的ZSM-5沸石,产生了氧化硅氧化铝复合团簇.在负离子通道测得含铝的新团簇系列[(SiO~2)~n~-~1(ALO~2)]^-和[(SiO~2)~nOAl]^-,讨论了这些系列的丰度分布和样品硅铝比之间的关系.由于AlO~2有较高电负性,激光烧蚀产生的团簇负离子系列[(SiO~2)~n~-~1(AlO~2)]^-具有以AlO~2为生长核心的生长机理。     

Effect of boron on the surface tension of molten silicon and its temperature coefficient

The influence of boron concentration (C(B)/mass%) on the surface tension of molten silicon has been investigated with the sessile drop method under oxygen partial pressure P(O(2))=1.62x10(-25)-2.63x10(-22) MPa, and the results can be summarized as follows. The surface tension increases with C(B) in the range below 2.09 mass%, and the maximum increase rate of the surface tension is about 30 mN m(-1)(mass% C(B))(-1). The temperature coefficient of the surface tension, ( partial differential sigma/ partial differential T)C(B), was found to increase with the boron concentration in molten silicon. At the interface between molten silicon and the BN substrate, a discontinuous Si(3)N(4) layer was reckoned to form and the layer might prevent BN from dissolving into the molten silicon. Since dissolved boron from the BN substrate into the molten silicon is below 0.054 mass% and the associated increase in surface tension is below 1.5 mN m(-1), the contamination from the BN substrate on the surface tension can be ignored. The relation between the surface tension and C(B) indicates negative adsorption of boron and can be well described by combining the Gibbs adsorption isotherm with the Langmuir isotherm.     

XPS study on early stages of heat deterioratin of silicon-containing aromatic polymide film

Early stages of heat deterioration of some siliconcontaining aromatic polyimide thin films with disiloxane groups (I) in their main chains were studied with XPS. It was found that the thermal decomposition of silicon-containing aromatic polyimides takes place at lower temperatures than those not modified with silicon. The low thermal stabilities observed are explained by the easier decomposition of silicon–carbon bonds (e.g. silicon–methylene, silicon–aryl) than other bonds (e.g. carbon–carbon, carbon–oxygen). Particularly, silicon–methylene bonds (II) readily undergo thermal oxidative decomposition and start to decompose at 350°C under aerobic conditions. This starting temperature of thermal decomposition is lower by 100°C than that of the corresponding polyimide not modified with silicon. In the case of polyimide incorporating silicon–aryl bonds (III) instead of silicon–methylene bonds, the decrease in the thermal decomposition temperature is as small as 50°C, and decomposition under aerobic conditions starts at 400°C.      

Quantitative determination of silicon in silica dust by FT-Raman spectroscopy

Silicon was quantitatively determined in respirable silica dusts and silica fume by FT-Raman spectroscopy using barium sulfate as an internal standard. Barium sulfate was selected as the standard as its Raman spectrum does not overlap with that of silicon and its scattering cross-section is significantly lower. This allowed silicon admixed with barium sulfate in ratios as low as 0.00003 to be detected. The laser beam was defocussed to cover the sample area. 128 scans at 4 cm(-1) resolution with 600 mW of power at the sample achieved a detection limit of 0.1 mug of silicon in a 5 mg sample. Silicon to BaSO(4) ratios in the range 0.00003-0.06 showed a near linear response with any decade change being linear. The RSD for this analytical method was +/-2%. Silica fume and respirable silica dust showed silicon concentrations to be in the range 2.6-51.5 ppm and 0.05-0.7 mg m(-3) respectively.     

Analysis of high purity graphite and silicon carbide by direct solid sampling electrothermal atomic absorption spectrometry

Solid sampling electrothermal atomic absorption spectrometry using the boat technique and a transversely heated graphite tube was applied to direct analysis of graphite and silicon carbide powders for 14 and 12 impurity elements, respectively. With graphite, for all analytes under investigation, a very effective in-situ analyte/matrix separation was achieved. That was the case also for analytes in silicon carbide requiring atomization temperatures below 2400 degrees C. At higher atomization temperatures, the decomposition products of silicon carbide give rise to significant background, which can still be corrected. Sample amounts of up to 4 mg graphite and 8 mg silicon carbide per analysis cycle were applied. For all analytes in both materials, limits of detection at the lower ng g(-1) and sub-ng g(-1) level were achieved, excluding arsenic for which they were 50 ng g(-1) and 23 ng g(-1) for graphite and silicon carbide, respectively. Quantification was performed using calibration curves measured with aqueous standard solutions. The accuracy was checked by comparison of the results with those obtained by instrumental neutron activation analysis and by other independent methods.     

Neutral hexa- and pentacoordinate silicon(IV) complexes with SiO(6) and SiO(4)N skeletons

The neutral heteroleptic hexacoordinate silicon(IV) complexes 4 and 5 (SiO(6) skeletons) and the neutral pentacoordinate silicon(IV) complexes 7-9 (SiO(4)N skeletons) were synthesized, starting from the hexacoordinate precursor 2 and the pentacoordinate precursor 6, respectively. In these reactions, two monoanionic cyanato-N ligands are replaced by one dianionic bidentate O,O-chelate ligand. Compounds 4, 5, and 7-9 were characterized by single-crystal X-ray diffraction and solid-state and solution NMR spectroscopy. The chiral silicon(IV) complexes 4, 5, 7, and 8 were obtained as racemic mixtures, whereas 9 was isolated as a cocrystallizate consisting of the two diastereomers, (C,S)-9 and (A,S)-9 (ratio 1:1). The stereodynamics of 5 and 8 were studied by variable-temperature (1)H NMR experiments.     

Effect of silicon precursor on silicon incorporation in SAPO-11 and their catalytic performance for hydroisomerization of n-octane on Pt-based catalysts

SAPO-11 molecular sieves were synthesized using silica sol, hydrophilic fumed silica, and tetraethyl orthosilicate(TEOS) as silicon precursors. Their physicochemical properties were characterized using XRD,SEM, nitrogen adsorption-desorption, Py-IR, NH_3-TPD, EDS, and ~(27)Al,~(31)P,~(29)Si MAS NMR techniques. The catalytic performance was assessed in the hydroisomerization of n-octane. The results showed that the silicon precursors influenced the physicochemical properties and catalytic performance of SAPO-11. SAPO-11 synthesized using hydrophilic fumed silica as silicon precursor showed higher silicon distribution and had more medium acid sites. SAPO-11 synthesized using TEOS as silicon precursor had more silicon content, but more silicon islands formed in its framework. The depolymerization of silicon precursors might affect the silicon content and distribution in SAPO-11. In the hydroisomerization of n-octane, the catalytic activity strongly depended on the number of medium acid sites instead of the number of total acid sites.SAPO-11 synthesized using hydrophilic fumed silica as silicon precursor exhibited higher catalytic activity than the other samples because it has more medium acid sites.     

(29)Si NMR shifts and relative stabilities calculated for hypercoordinated silicon-polyalcohol complexes: role in sol-gel and biogenic silica synthesis

Penta- and hexa-coordinated silicon is rare, occurring as a transient species in some glasses, nonaqueous organosilicon solutions and organosilicon gels such as silicone, and is stable at high pressures within the earth in dense phases such as stishovite. The stable form expected in aqueous solution is quadra-coordinated silicon. A recent study proposed the existence of hypercoordinated silicon-polyalcohol complexes in aqueous solution, based on (29)Si NMR shifts at -102 to -103 ppm and -145 to -147 ppm. Here, we report ab initio molecular orbital calculations of (29)Si NMR chemical shifts and relative stabilities of silicon-polyalcohol monocyclic and spirocyclic complexes, from ethylene glycol (C(2)H(6)O(2)) to arabitol (C(5)H(12)O(5)) with Si in quadra-, penta- and hexa-coordination ((Q)Si, (P)Si, (H)Si), calculated at the HF/6-311+G(2d,p)//HF/6-31G* level. Calculated shifts are accurate with a 1-8% error for (Q)Si and 2-9% for (P)Si. Shifts calculated for the hypercoordinated silicon complexes having structures proposed in the literature are much more negative (-128 and -180 ppm for (P)Si and (H)Si) than observed. We propose that cyclic trimers complexed by polyalcohols can explain the -102 ppm shift, where the Si atoms are all (Q)Si, or where two silicons are (Q)Si and one is (P)Si with rapid exchange between the Si sites. The -145 ppm resonance results from structures similar to those proposed in the experimental NMR study for the -102 ppm peak. Our relative stability calculations indicate that structures proposed in the literature for hypercoordinated silicon complexes are thermodynamically unstable in aqueous solution at acidic to neutral conditions but may exist in degrading silicone-gel breast-implants. Thus, aqueous hypercoordinated silicon-polyalcohol complexes are unlikely to play an important role in biological silicon uptake and hold little promise for novel silica synthesis routes from aqueous solutions under nonextreme conditions.     

Analysis of crystalline phases in airborne particulates by grazing incidence X-ray diffractometry

Amounts of crystalline phases of airborne particulates collected on a silicon wafer (10 x 10 mm) using a high-volume air sampler were analyzed by grazing incidence X-ray diffractometry (GIXD). Airborne particulates were classified into five size ranges (1.09-10.5 microm) with a cascade impactor attached on the sampling ports of the high-volume air sampler. GIXD was used throughout this analysis to obtain better sensitivity for small amounts of airborne particulates on the silicon wafer. Calibration standards on the silicon wafer for the diffractometric determination were prepared by the suspension droplet method of the crystalline standards dispersed in cyclohexane. Analytical lines were (020) for gypsum, (101) for quartz, (104) for calcite, (200) for halite, and (110) for sal ammoniac. The sample and the calibrating standards were heated at 350 degrees C for 2 h to avoid mutual interference with gypsum (041 and 221) when calcite and halite were determined. The GIXD method enables us to determine 0.23-13.2 microg of gypsum, quartz, calcite, halite and sal ammoniac in 0.110-0.233 mg of airborne particulates on the silicon wafer.     

Tetrasilatetrahedranide: a silicon cage anion

The first silicon cage anion, tris{bis[bis(trimethylsilyl)methyl](methyl)silyl}tetrasilatetrahedranide (6-), has been synthesized by the reaction of tetrakis{bis[bis(trimethylsilylmethyl](methyl)silyl}tetrasilatetrahedrane with potassium graphite in diethyl ether by reductive cleavage of exocyclic Si-Si bond. The structural characterization of K+(18-crown-6).6- has been achieved by X-ray crystallography, showing that 6- is a separated ion pair and the tetrasilatetrahedranide moiety has a significantly distorted tetrahedrane skeleton containing one inverted tetrahedral (umbrella type) silicon atom. The four silicon atoms in the Si4 skeleton are equivalent on the NMR time scale due to the migration of the Dis2MeSi substituent.     

Synthesis of 1-organyl-1-(trimethylsiloxy)-2-(dimethylamino)ethenes and new hypervalent silicon compounds based thereon

1-Organyl-1-(trimethylsiloxy)-2-(dimethylamino)ethenes were synthesized for the first time, and their reactions with trichloro(methyl)silane and trifluoro(phenyl)silane afforded silicon bis-chelates, methylbis-[2-(dimethylamino)-1-(organyl)ethenolato-N,O]siliconium chlorides and bis[1-(dimethylamino)-3,3-dimethylbut-1-en-2-olato-N,O]fluoro(phenyl)silicon(IV), respectively.     

Functionalization of silicon nanowires by iron oxide and copper for degradation of phenol

Research on Chemical Intermediates - Iron oxide (Fe3O4) and copper-functionalized silicon nanowires (SiNWs) from silicon powder mesh?&lt;?500 with a spherical structure have been...     

Surface morphology dependent photoluminescence from colloidal silicon nanocrystals

Monodisperse 1-2 nm silicon nanocrystals are synthesized in reverse micelles and have their surfaces capped with either allylamine or 1-heptene to produce either hydrophilic or hydrophobic silicon nanocrystals. Optical characterization (absorption, PL, and time-resolved PL) is performed on colloidal solutions with the two types of surface-capped silicon nanocrystals with identical size distributions. Direct evidence is obtained for the modification of the optical properties of silicon nanocrystals by the surface-capping molecule. The two different surface-capped silicon nanocrystals show remarkably different optical properties.     

Possibilities of low-level determination of silicon in biological materials by activation analysis

The capabilities of neutron and photon activation analysis (NAA and PAA, respectively) for low-level determination of silicon in biological materials have been examined. Sensitivities of a variety of modes of NAA and PAA with radiochemical separation have been evaluated. Results are presented for silicon in reference materials CSRM 12-2-03 Lucerne, Bowen's Kale, NIST SRM-1571 Orchard Leaves, and NIST SRM-1515 Apple Leaves. The results were obtained by employing the 29Si(n,p)29Al reaction with fast reactor neutrons and the radiochemical procedure developed for aluminium separation. Possibilities of further improvement of the silicon determination limit down to the microg g(-1) level by employing NAA and PAA with radiochemical separation are outlined.     

Rigiflex, spontaneously wettable polymeric mold for forming reversibly bonded nanocapillaries

We present a novel ultraviolet (UV)-curable mold that enables the formation of reversibly bonded nanocapillaries (500-50 nm) on a gold or silicon substrate. A sheet-type ( approximately 50 microm) polyethylene diacrylate (PEG-DA) mold was used for its rigiflex nature; it provides rigidity high enough for maintaining nanostructures (elastic modulus >70 MPa) and also flexibility good enough for intimate contact over a large area aided by weak electrostatic forces (zeta potential approximately -113.55 mW). The electrostatic charge is generated on a rigiflex PEG-DA mold upon peeling from an original engraved silicon master by mechanical friction, thereby assisting the formation of spontaneous contact with the gold or silicon substrate.     

Synthesis of dendron-protected porphyrin wires and preparation of a one-dimensional assembly of gold nanoparticles chemically linked to the pi-conjugated wires

A one-dimensional assembly of gold nanoparticles chemically bonded to pi-conjugated porphyrin polymers was prepared on a chemically modified glass surface and on an undoped naturally oxidized silicon surface by the following methods: pi-conjugated porphyrin polymers were prepared by oxidative coupling of 5,15-diethynyl-10,20-bis-((4-dendron)phenyl) porphyrin (6), and its homologues (larger than 40-mer) were collected by analytical gel permeation chromatography (GPC). The porphyrin polymers (>40-mer) were deposited using the Langmuir-Blodgett (LB) method on substrate surfaces, which were then soaked in a solution of gold nanoparticles (2.7 +/- 0.8 nm) protected with t-dodecanethiol and 4-pyridineethanethiol. The topographical images of the surface observed by tapping mode atomic force microscopy (AFM) showed that the polymers could be dispersed on both substrates, with a height of 2.8 +/- 0.5 nm on the modified glass and 3.1 +/- 0.5 nm on silicon. The height clearly increased after soaking in the gold nanoparticle solution, to 5.3 +/- 0.5 nm on glass and 5.4 +/- 0.7 nm on silicon. The differences in height (2.5 nm on glass and 2.3 nm on silicon) corresponded to the diameter of the gold nanoparticles bonded to the porphyrin polymers. The distance between gold nanoparticles observed in scanning electron microscopic images was ca. 5 nm, indicating that they were bonded at every four or five porphyrin units.