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The impurity composition of natural and isotopically enriched silane obtained from magnesium silicide and silicon tetrafluoride is studied by gas chromatography–mass-spectrometry. The impurities characteristic of silane with natural and isotopically enriched composition are atmospheric gases; carbon dioxide; hydrides; saturated, unsaturated, and aromatic hydrocarbons; halogenated hydrocarbons; alkyl derivatives and silane homologues, siloxanes. The impurity content of high-purity silane does not exceed 10–7–10–5 mol % After synthesis, the concentrations of impurities in the silane and fractions isolated by its distillation purification lie in the range n × 10–6 − n × 10 mol % The limits of detection for impurities are 1 × 10–8–9 × 10–4 mol %

It is for the first time that the method of gas chromatography was used for the determination of silicon fluoride-chlorides SiСl n F 4-n ( n = 0 ÷ 4) which are the initial, intermediate and final substances while producing silicon tetrachloride from silicon tetrachloride and aluminum chloride (III). The analysis of samples taken during this reaction was carried out using the "Tsvet - 800" gas chromatographer. The samples were injected into the instrument using a vacuum dosing system. To separate the components, a chromatographic column made of molybdenum glass with a length of 5 m and an internal diameter of 3 mm was used. It was filled with a Chromatone N-AW-HMDS (grain size 0.250-0.315 mm) with 15% methylsilicon elastoplastic E-301. The registration of silicon fluoride-chlorides was implemented using a thermal conductivity detector. The identification of SiF 4 and SiCl 4 in the mixture was conducted by comparing the times of holding the chromatographic peaks with the times of holding these individual substances. The times of holding not available for SiClF 3 , SiCl 2 F 2 , SiCl 3 F in the individual states were determined using the dependence of the logarithm of the corrected holding time on their molecular mass. The concentrations of silicon fluoride-chlorides were determined using the internal normalization method. The data were obtained on the changes in the concentrations of these substances during the synthesis of silicon tetrachloride. The confirmation of the correctness of the analysis results was made using the method of varying the size of the sample. Key words: silicon fluoride-chlorides, gas chromatography, identification, calibration factor, correctness (Russian) DOI: http://dx.doi.org/10.15826/analitika.2019.23.4.011 Т .G. Sorochkina, О .Yu. Chernova, О .Yu. Troshin, А .Yu. Sozin, А .D. Bulanov, А . А . Ermakov G.G. Devyatykh Institute of Chemistry of High-Purity Substances of the Russian Academy of Sciences, ul. Tropinina 49, Nizhny Novgorod, 603950, Russian Federation

The nature of the interactions between silicon tetrafluoride and series of nitrogen bases, including nitriles (RCN, with R > CH3), pyridine, and various fluoro-substituted pyridines, has been investigated via quantum-chemical computations, low-temperature IR spectroscopy, and bulk reactivity experiments. Using (primarily) M06 with the 6-311+G(2df,2pd) basis set, we obtained equilibrium structures, binding energies, harmonic frequencies, and N–Si potentials in the gas-phase and in bulk dielectric media for an extensive series of 1:1 molecular complexes, including: C6H5CH2CN–SiF4, CH3CH2CN–SiF4, (CH3)3CCN–SiF4, C5H5N–SiF4, 4-FC5H4N–SiF4, 3,5-C5F2H3N–SiF4, 2,6-C5F2H3N–SiF4 and 3,4,5-C5F3H2N–SiF4. In addition, for the analogous 2:1 complexes of pyridine and 3,5-difluororpyridine, we obtained equilibrium structures, binding energies, and harmonic frequencies. The N–Si distances in the 1:1 nitrile complexes are fairly long, ranging from 2.84 A to 2.88 A, and the binding energies range from 4.0 to 4.2 kcal/mol (16.7–17.6 kJ/mol). Also, computations predict extremely anharmonic N–Si potentials, for which the inner portions of the curve are preferentially stabilized in dielectric media, which predict an enhancement of these interactions in condensed-phases. However, we see no evidence of bulk reactivity between C6H5CH2CN, CH3CH2CN, or (CH3)3CCN and SiF4, nor any significant interaction between (CH3)3CCN and SiF4 in low temperature IR spectra of solid, (CH3)3CCN/SiF4 thin films. Conversely, the interactions in four of the five 1:1, pyridine-SiF4 complexes are generally stronger; binding energies range from 5.7 to 9.6 kcal/mol (23.8–40.2 kJ/mol), and correspondingly the N–Si distances are relatively short (2.12–2.25 A). The exception is 2,6-C5F2H3N–SiF4, for which the binding energy is only 3.6 kcal/mol (15.1 kJ/mol), and the N–Si distance is quite long (3.12 A). In addition, both pyridine and 3,5-difluororpyridine were found to form stable reaction products with SiF4; but no analogous product was obtained with 2,6-difluororpyridine and SiF4, nor was any significant interaction indicated in low-temperature IR spectra of 2,6-difluororpyridine/SiF4 films. By contrast, low temperature spectra of pyridine/SiF4 and 3,5-difluororpyridine/SiF4 thin films are consistent with the presence of a distinct 2:1 reaction product. Moreover, the observed frequencies agree reasonably well with those predicted for the cis, octahedral coordination isomers of the 2:1 molecular complexes, in which the N–Si bonds are compressed slightly relative to those in the predicted gas-phase structures.

The impurity composition of 28SiF4 has been studied for the first time by gas chromatography/mass spectrometry using gas-adsorption capillary columns. For identification and determination of impurity substances by gas chromatography/mass spectrometry, we have proposed using cryogenic preconcentration of the impurities from 28SiF4. The presence of C2–C4 hydrocarbon impurities and sulfur hexafluoride has been confirmed. We have identified 35 impurity substances in 28SiF4, including linear and branched C5–C8 saturated hydrocarbons, aromatic hydrocarbons, chlorine- and fluorine-containing hydrocarbons, and silicon- and sulfur-containing substances, of which 28 have been detected for the first time.

In the present article, the performance of heterojunction silicon solar cells with intrinsic thin buffer layers (HIT) has, for the first time, been improved via a fluorinated microcrystalline silicon oxide (µc-SiO:F:H) emitter layer. Using silicon tetrafluoride (SiF 4 ) in the deposition process of µc-SiO:F:H causes the formation of better crystallinity. µc-SiO:F:H has shown better properties in comparison with a-Si:H and µc-SiO:H in the emitter layer of HIT. Such properties include lower recombination rate and higher electrical conductivity cause of better crystallinity, because of SiF 4 that remove dangling bonds to have better passivation, other ones are better refractive index and extinction coefficient which lead to better absorption of incoming photons and increase in current and efficiency. As a result, through assessment and analysis of the three materials of a-Si:H, µc-SiO:H, and µc-SiO:F:H in the emitter layer, we found that the cell with the µc-SiO:F:H possesses a higher short circuit current (36.12mA/cm2) and an increase in short circuit current has caused an increase in the efficiency of the cell.

We present a procedure for the determination of the isotopic ratios of silicon and oxygen from the same aliquot of anhydrous silicate material. The sample is placed in a bromine pentafluoride atmosphere as it is heated with a CO2 laser system releasing silicon tetrafluoride and oxygen gasses. The oxygen gas is then purified to remove other reaction by-products through several liquid nitrogen traps before being captured onto a molecular sieve and transferred to an isotope ratio mass spectrometer. The silicon tetrafluoride gas is then purified using a supplementary line by repeatedly freezing to -196°C with liquid nitrogen and then thawing with an ethanol slurry at -110°C through a series of metal and Pyrex traps. The purified gas is then condensed into a Pyrex sample tube before it is transferred to an isotope ratio mass spectrometer for silicon isotope ratio measurements. This system has silicon yields of greater than 90% for pure quartz, olivine, and garnet standards and has a reproducibility of ±0.1‰ (2σ) for pure quartz for both oxygen and silicon isotope measurements. Meteoritic samples were also successfully analyzed to demonstrate this system's ability to measure the isotopic ratio composition of bulk powders with precision. This unique technique allows for the fluorination of planetary material without the need for wet chemistry. Though designed to analyze small aliquots of meteoritic material (1.5 to 3 mg), this approach can also be used to investigate refractory terrestrial samples where traditional fluorination is not suitable.

A new generation of silicon crystals even further enriched in (28)Si (x((28)Si)0.999 98 mol/mol), recently produced by companies and institutes in Russia within the framework of a project initiated by PTB, were investigated with respect to their isotopic composition and molar mass M(Si). A modified isotope dilution mass spectrometric (IDMS) method treating the silicon as the matrix containing a so-called virtual element (VE) existing of the isotopes (29)Si and (30)Si solely and high resolution multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) were applied in combination. This method succeeds also when examining the new materials holding merely trace amounts of (29)Si (x((29)Si) ≈ 5 × 10(-6) mol/mol) and (30)Si (x((30)Si) ≈ 7 × 10(-7) mol/mol) extremely difficult to detect with lowest uncertainty. However, there is a need for validating the enrichment in (28)Si already in the precursor material of the final crystals, silicon tetrafluoride (SiF4) gas prior to crystal production. For that purpose, the isotopic composition of selected SiF4 samples was determined using a multicollector magnetic sector field gas-phase isotope ratio mass spectrometer. Contaminations of SiF4 by natural silicon due to storing and during the isotope ratio mass spectrometry (IRMS) measurements were observed and quantified. The respective MC-ICP-MS measurements of the corresponding crystal samples show-in contrast-several advantages compared to gas phase IRMS. M(Si) of the new crystals were determined to some extent with uncertainties urel(M)1 × 10(-9). This study presents a clear dependence of the uncertainty urel(M(Si)) on the degree of enrichment in (28)Si. This leads to a reduction of urel(M(Si)) during the past decade by almost 3 orders of magnitude and thus further reduces the uncertainty of the Avogadro constant NA which is one of the preconditions for the redefinition of the SI unit kilogram.

Deposition of Si films is done in a high power 24 GHz gyrotron-based electron-cyclotron resonance plasma enhanced chemical vapour deposition setup. The possibility of high-rate (2.5 nm/s) deposition of thin silicon films from SiF4 + H2 plasmas in an electron-cyclotron resonance reactor with gyrotron microwave plasma source at the frequency of 24 GHz is demonstrated. The analysis with spectroscopic ellipsometry and Raman scattering shows that films have large crystalline fraction (75%) with an average size of silicon grains of 3 nm. The use of gyrotron with high microwave power opens up the possibility to make depositions from high density plasmas at pressures of tens of pascals, which results in high deposition rates (tens nm/s).

The solubility mechanism of silica in a fluoride-chloride melt has been determined in situ using Raman spectroscopy. The spectroscopy data revealed that the silica solubility process involved Si-O bond breakage and Si-F bond formation. The process results in the formation of silicate complexes, fluorine-bearing silicate complexes, and silicon tetrafluoride in the melt. Mass spectrometry of the vapor phase over the KF-KCl-K2SiF6 and KF-KCl-K2SiF6-SiO2 melts and differential scanning calorimetry coupled with thermal gravimetric analysis of these melts were performed to verify the silica solubility mechanism.

The process of plasma-chemical conversion of silicon tetrafluoride in a radiofrequency (13.56 MHz) discharge has been studied. The dependence of the yield of silicon on the specific energy input and the H2/SiF4 molar ratio has been examined in the pressure range of 0.1–0.3 Tort. The maximum yield of silicon is 60%, and the optimal specific energy consumption is 44.6 MJ per mole of Si. A mechanism has been proposed for the plasma-assisted reduction of silicon tetrafluoride under the given experimental conditions.

Ion chromatography (IC) method was applied to detection of fluorine in the atmosphere calm wind conditions at the area around the yellow phosphorus enterprise. The results indicated that the recovery of standard addition of Fluroide is 96.7%~100.6%. It gives a linear response of chromatographic peak height with respect to the fluoride in the range of 1~25 μg/mL, and the coefficient correlations R value is 0.9994. The concentration of Fluorine in the surrounding of yellow phosphorus enterprise ranging from 100~1500 m varies from 0.641~0.070 mg/m3. The relative standard deviation (RSD) of this method is between 2.10%~0.50%. This method is sensitivity and selectivity, low disturbance, and it is considered as a promising method for the detection of Fluorine surrounded yellow phosphorus enterprise.

Glasses in the PbF2-PbO-SiO2 system doped with 1 mol % of rare-earth elements (Nd3+, Er3+, or Yb3+) are synthesized and studied. The glasses were heat-treated in order to obtain glass ceramics with a fluoride crystalline phase. The changes in the structure and spectral optical properties of glass ceramics with respect to initial glasses were determined by using X-ray diffraction analysis and by studying the luminescent characteristics of dopant ions.

In this contribution the gas-phase measurements of 19 F and 29 Si chemical shifts and scalar spin–spin couplings in SiF 4 and (SiF 3 ) 2 O have been reported. The density dependence of silicon and fluorine nuclei chemical shifts is strictly linear for both compounds. An extrapolation of gaseous data to the zero-density limit permitted the measurements of 19 F and 29 Si absolute nuclear magnetic shielding of isolated molecules at 300 K. They were referenced against general accepted standards and are as follows: σ 0 (Si F 4 ) = 362.87 ppm, σ 0 ( Si F 4 ) = 488.15 ppm, σ 0 ((Si F 3 ) 2 O) = 356.50 ppm, and σ 0 (( Si F 3 ) 2 O) = 487.95 ppm. The direct measurements of shielding constants on the basis of NMR frequencies were also performed. Indeed, we have successfully demonstrated the equivalence of both shielding values refinements. Careful investigation of 19 F spectra shows isotope effects connected with the presence of three naturally occurring silicon isotopes: 28 Si (92.19%), 29 Si (4.70%) and 30 Si (3.09%). The isotope effect measured on 19 F nuclei does not exceed 0.01 ppm. The 1 J (Si, F) indirect spin–spin coupling constants in both molecules were extracted from an experimental spectra of gaseous samples. The intermolecular effects in the gaseous state as well as in coming from gas to organic solutions were also observed. The new experimental results were used for verification of the theoretical evaluations presented earlier.

In this paper, we present results on microcrystalline silicon solar cells that are deposited from SiF 4 /H 2 /Ar mixtures, on which efficiencies exceeding 9% have already been obtained. Structural characterizations of the cells indicate a fully crystalline material with no preferential crystallographic orientation. This suggests that, as opposed to microcrystalline silicon cells deposited using silane, an amorphous phase is not required to passivate defects at column boundaries. These results are discussed in light of the specific growth mechanism and structural properties associated with film deposition using SiF 4 . They pave the way toward low-cost, high-performance polycrystalline cells on glass.

Silicon tetrafluoride SiF4 reacted with aliphatic alcohols ROH to form liquid complex compounds SiF4 · 2ROH. The gas-liquid SiF4(g) -SiF4 · 2ROH(l) systems can be used for separating silicon isotopes. The hydrodynamics and mass transfer of the separation of silicon isotopes in a countercurrent column were studied using SiF4-SiF4 · 2ROH systems based on butanol-1, pentanol-1, and hexanol-1 at 293 K. Corrections were applied to the empirical coefficients in the equations of the dependence of the total holdup of a helical prismatic packing (HPP) and its specific pressure drop on a load in an isotope exchange column. The height equivalent to the theoretical plate (HETP) increased more than twofold in the butanol-1-hexanol-1 homologous series (the flow rate in the column was (3.4 ± 0.2) mmol SiF4/(cm2 min) for the working gas). It was shown using pentanol-1 as a complex-forming agent that the limiting stage of mass transfer during the separation of silicon isotopes was the isotope exchange between SiF4 and the SiF4 · 2ROH complex.

The process of plasma chemical deposition of silicon from inductively coupled plasma of the mixture of high-purity SiF4 and H2 sustained by RF discharge at 13.56 MHz in amount sufficient for subsequent growth of crystal by Czochralski method was investigated. The structure and impurity content of the produced layers as well as of the grown crystal have been studied (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This article presents a study of the characteristics of radicals in high-aspect-ratio deep Si etching by continuous-type SF6/O2 plasmas. A parametric study of etched depths clearly shows that the Si etch rates are dependent on concentrations of F atoms but independent of ion energy and substrate temperature. Results of Monte Carlo simulation based on a Knudsen transport model provide a remarkably good fit for experimental results on aspect-ratio-dependent etching. Comparison of the experimental data and results of simulation shows that the probability of a F atom reacting with the Si surface is 0.4–0.45 if the probability of loss at sidewall surfaces for F atoms is negligible. Results also indicate that the latter probability is, in fact, extremely small (

In this article, the authors focus on the profiles formed by high-aspect-ratio deep Si etching with SF6/O2 plasma mixtures. One of the most serious problems for deep Si etching processes is lateral etching in the upper regions of sidewalls. This lateral etching seems to depend on time (or etched depth) rather than aspect ratio (depth/width). Reducing the SF6:O2 ratio and lowering the temperature not only reduced the scope of lateral etching but also produced features that were more strongly tapered with depth. Results of simulation indicated that the distribution of radicals during the formation of a hole plays a significant role in determining the characteristics of the hole. In fact, the addition of SiFx radicals from the top of the hole is markedly effective in reducing lateral etching without sacrificing shape in the vicinity of the bottom of the hole. However, the distribution of radicals alone cannot explain the time dependence of lateral etching. The results of experiments with masks having various...

The effect of adding of silicon tetrafluoride (SiF4) to silane (SiH4) hydrogen gas mixture on the properties of highly crystallized microcrystalline silicon (μc-Si:H) films was studied. We found that the addition of a small amount of SiF4, with a ratio to SiH4 not exceeding 1/10, has almost no effect on deposition rate and does not affect the structure of the μc-Si:H films, but strongly reduces oxygen incorporation into the films. Reduction of oxygen content to values below 1019 cm-3 results in intrinsic character of the films with ratio of photo to dark conductivity about 103 in whole studied range of deposition temperatures from 175 to 250 °C in contrast to films, deposited without SiF4 addition, which show strong decrease of photosensitivity with increase of deposition temperature above 200 °C (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Matrix isolation Fourier transform IR spectroscopy has been used for studying the products and mechanism of the silicon tetrafluoride reaction with water at various component ratios and reaction durations. Assignment of new bands in the spectrum confirms the earlier assumptions of first the formation of a molecular complex with water and later of trifluorosilanol, which finally condenses to give hexafluorodisiloxane.

The data on fabrication of silicon layers on various substrates by plasma enhanced chemical vapor deposition from the (silicon tetrafluoride)-hydrogen system are reported. The emission spectra of the plasma in the system are recorded. The samples were studied by the X-ray diffraction and secondary ion mass spectrometry techniques. The morphologic properties of the surface are examined, and the Raman spectra, the transmittance spectra in the infrared region, and photoluminescence spectra are recorded. The phase composition of the layers corresponds to nanocrystalline silicon, in which the dimensions of coherent-scattering grains vary with the conditions of the preparation process in the range from 3 to 9 nm. The layers exhibit intense photoluminescence at room temperature.

Properties of microcrystalline silicon (μc-Si) films produced by standard radio frequency glow discharge from SiH4 or SiF4 precursors were studied. Spectroscopic ellipsometry (SE), Raman spectroscopy and time resolved microwave conductivity (TRMC) were used for their characterisation. Although modelling of SE spectra shows that μc-Si films with crystalline fractions up to 100% can be deposited from both types of precursors, we have found that SiF4 allows obtaining films with improved electronic properties. A detailed analysis of the SE data reveals that such improvement relates to the larger grain size for films deposited from SiF4 in comparison with the ones deposited from SiH4. Interestingly, the deposition rate, the fraction of large grains, and the mobility of carriers for the films grown from SiF4 display close dependencies on the product of pressure and inter-electrode distance. These results are discussed with respect to the contribution of the plasma-synthesised nanocrystals to deposition.

The permeabilities, diffusivities and solubilities of He, Ne, A, O2, N2, Kr, CO2, H2S, and H2O in poly(ethyl methacrylate) have been measured above and below the glass temperature. Water showed a small increase in solubility when the polymer was heated above the glass temperature. Water also showed anomalous behavior in that the solubilities calculated from the permeability constants and the time-lag diffusion constants are much less than those measured by direct weighing. The behavior had been found previously with other polymers and has been interpreted in terms of the clustering of water molecules in the polymer. The Arrhenius plots of the permeability and diffusion constants for water showed the change in slope at the glass temperature reported to occur with many gases and vapors through other polymers. The gases, however, showed no change in slope even with large molecular size gases such as silicon tetrafluoride and sulfur hexafluoride. The results found with water are interpreted as due to the plasticizing effect of the penetrant when the polymer is above the glass temperature. In the case of the gases, the lack of a transition effect is interpreted in terms of the relative sizes of the gas molecule and the average hole she of the polymer. The energies of activation for diffusion were found to be proportional to the 1.6 power of the molecular diameter of the; penetrants, i.e., intermediate between that found for rubber and for both poly(vinyl acetate) and poly(ethylene terephthalate).

The impurity compositions of silicon tetrafluoride and silane prepared from it have been determined by high-resolution Fourier-transform IR spectroscopy. In the spectra of SiF4 samples differing in purity, we have identified rovibrational bands arising from Si2F6O, SiF3OH, HF, SiF3H, SiF2H2, SiH3F, CH4, CO2, and CO impurities. Their detection limits lie in the range 9 x 10(-5) (CO2) to 3 x 10(-3) mol % (Si2F6O). In the spectra of SiH4 samples of different purity, we have detected CH4, CO2, SiF3H, SiF2H2, and SiF4 impurities. Their detection limits lie in the range 8 x 10(-5) (CO2) to 1 x 10(-3) mol % (SiF4).

A procedure for the automated determination of isotopic abundances of silicon from biogenic and lithogenic particulate matter and from dissolved silicon in fresh or saltwaters is reported. Samples are purified using proven procedures through the reaction of Si with acidified ammonium molybdate, followed by precipitation with triethylamine and combustion of the precipitate to yield silicon dioxide. The silicon dioxide is converted to cesium hexafluosilicate by dissolution in hydrogen fluoride and the addition of cesium chloride. Isotopic analysis is accomplished by decomposing the cesium hexafluosilicate with concentrated sulfuric acid to generate silicon tetrafluoride gas. Silicon tetrafluoride is purified cryogenically and analyzed on a gas source isotope ratio mass spectrometer. Yields of silicon tetrafluoride are >99.5%. The procedure can be automated by modifying commercial inlet systems designed for carbonate analysis. The procedure is free of memory effects and isotopic biases. Reproducibility is +/-0.03-0.10 per thousand for a variety of natural and synthetic materials.

A procedure was developed for the gas-chromatographic determination of hydrocarbons in silicon tetrafluoride of natural and isotopically enriched compositions. For improving the efficiency of the chromatographic determination of impurities, it was proposed that the major compound be removed from the test sample with the subsequent cryofocusing of impurity hydrocarbons. The detection limits of C1-C4 hydrocarbons were 2 × 10−6−6 × 10−6 vol %.

The spectral characteristics of the SiF4 molecule in the range 3100700 cm1, including the absorption range of the band 3, are studied in the gas phase at P = 0.47 bar and in solutions in liquefied Ar and Kr. In the cryogenic solutions, the relative intensities of the vibrational bands, including the bands of the isotopically substituted molecules, are determined. The absorption coefficients of the combination bands 23, 3 + 1, 3 + 4, and 34 are measured in the solution in Kr. In the gas phase of the one-component system at an elevated pressure of SiF4, the integrated absorption coefficient of the absorption band 3 of the 28SiF4 molecule was measured to be A(3) = 700 ± 30 km/mol. Within the limits of experimental error, this absorption coefficient is consistent with estimates obtained from independent measurements and virtually coincides with the coefficient A(3) = 691 km/mol calculated in this study by the quantum-chemical method MP2(full) with the basis set cc-pVQZ. ©2005 Pleiades Publishing, Inc.

The infrared multiphoton dissociation (IRMPD) of pure SiF4 and in mixtures with different gases was studied using a tunable CO2 TEA laser. The initial dissociation step of the IRMPD of SiF4 was found to be the decomposition into SiF3 and F. The gas phase reactions of trifluorosilyl, SiF3, with F and H2 was investigated. A kinetic scheme was proposed to explain the experimental results. The set of coupled differential equations associated to this scheme was numerically solved. The rate constants of the SiF3+F→SiF4 and SiF3+H 2→SiF3H+H reactions were determined. Fil: Alcaraz, A. N.. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina Fil: Codnia, Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas para la Defensa. Centro de Investigación en Láseres y Aplicaciones; Argentina Fil: Azcárate, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas para la Defensa. Centro de Investigación en Láseres y Aplicaciones; Argentina

The impurity contents of different silicon tetrafluoride samples (isotopically unmodified and enriched) are determined by optical emission spectroscopy with the preconcentration of nonvolatile impurities by distilling off SiF4 .

A new approach for producing high-purity silicon with isotopic enrichment of 28Si isotope is reported. The methods of centrifugal enrichment were modified to obtain the initial gaseous silicon tetrafluoride with a record-breaking enrichment of 0.99999664(11) with respect to 28Si. The effective conversion of silicon tetrafluoride into elementary silicon with minimal isotopic dilution was achieved in an electron cyclotron resonance discharge plasma, sustained by gyrotron microwave radiation with a frequency of 24 GHz. We have experimentally demonstrated the deposition of the layers of microcrystalline 28Si with enrichment of 0.999986 ± 0.000003, which is the best result at the present time.

We present results on self-consistent calculations of second pVT–virial coefficients B(T), viscosity data η(T), and diffusion coefficients ρD(T) for eleven heavy globular gases: boron trifluoride (BF3), carbon tetrafluoride (CF4), silicon tetrafluoride (SiF4), carbon tetrachloride (CCl4), silicon tetrachloride (SiCl4), sulfur hexafluoride (SF6), molybdenum hexafluoride (MoF6), tungsten hexafluoride (WF6), uranium hexafluoride (UF6), tetramethyl methane (C(CH3)4, TMM), and tetramethyl silane (Si(CH3)4, TMS). The calculations are performed mainly in the temperature range between 200 and 900 K by means of isotropic n−6 potentials with temperature-dependent separation rm(T) and potential well depth e(T). The potential parameters at T=0 K (e, rm, n) and the enlargement of the first level radii δ are obtained solving an ill-posed problem of minimizing the squared deviations between experimental and calculated values normalized to their relative experimental error. The temperature dependence of the potential is ...

Silicon Tetrafluoride (SiF 4 ) is a dopant gas of choice for different silicon ion implantation processes used in semiconductor device engineering. It is a primary source of atomic dopants like Si and F, and a potential source of molecular dopants (e.g. Si 2 , SiF x , x=1–3). A significant challenge associated with the use of SiF 4 is that it can compromise ion source performance, resulting in poor beam stability and source life. This is primarily the result of the formation of a halogen cycle that takes place due to the presence of fluorine from the SiF 4 molecule along with tungsten materials that are present in the ion source (e.g. liners, walls). A second challenge associated with SiF 4 can be limited beam current. In order to improve implant tool performance when using SiF 4 , the following investigations have been performed: (1) Characterization of SiF 4 / H 2 mixtures: The addition of hydrogen co-gas can effectively mitigate the halogen cycle and improve source performance. Using the magnitude of the resulting WF x peaks as an indicator, the degree to which the halogen cycle is mitigated is shown as a function of H 2 flow rate. Also, in that single packages may impart various advantages, SiF 4 / H 2 co-mixture stability data are provided. (2) Characterization of enriched (en) 28SiF 4 : The additional enrichment can enable higher beam currents of 28Si+. The effect of En-28SiF 4 flow rate on beam current is presented, along with the resulting WF x spectra. (3) Initial observations of SiF 3 + beams are provided, along with the potential benefits that may be obtained in selecting this molecular ion.

Microcrystalline silicon deposited from SiF 4 /H 2 /Ar gas mixtures is used as active absorbing layer in thin film solar cells. Best solar cells are made from active layers deposited at the amorphous-to-microcrystalline transition where only a few percent of amorphous phase is present. Based on mass spectrometry measurements, we propose a simple model which accounts for the relevant features of the complex plasma chemistry: namely the depletion of H 2 , the formation of HF molecules and the amorphous to microcrystalline silicon transition. The specificity of SiF 4 /H 2 /Ar plasma is the ability to tightly tune the transition irrespective of the control of the deposition rate. A high crystalline fraction allows thicknesses above 3 µm with a high short-circuit current and no deterioration of the open-circuit voltage.

Layers of silicon with an isotope composition that differs from the native composition have been obtained by the method of plasma enhanced chemical vapor deposition from gaseous silicon tetrafluoride. The deposited layers possess an amorphous structure and high oxygen content. The Raman spectra and the spectra of optical transmission in the IR range are presented. The in-depth distribution of Si isotopes has been determined using the second ion mass spectrometry techniques.

The production of silicon layers using plasma enhanced chemical vapor deposition in the mixture of silicon tetrafluoride and hydrogen is reported. The samples have been analyzed by X-ray diffraction, Raman spectroscopy, and secondary ion mass spectrometry. The phase composition of the layers is nanocrystalline silicon with the crystalline-domain sizes from 3 to 9 nm in dependence of the conditions of the process. The samples are characterized by intense photoluminescence at room temperature.

The present work represents a thermal analysis study of topaz synthesis from kaolinite by its sintering with aluminium fluoride using a derivatograph. Also, it includes the study of the influence of aluminium fluoride on the thermal behaviour of kaolinite. The products of sintering were identified microscopically and by using a Siemens Crystalloflex diffractometer. The DTA and X-ray powder diffraction data show the beginning of the appearance of both topaz and mullite at 600°C and indicate that the reaction of kaolinite and aluminium fluoride of different amounts takes place in two distinct steps. The first is marked by a medium endothermic peak at 750–790°C, representing the intensive formation of topaz, and the second by a large and sharp or wide endothermic peak at 930–950°C, representing its subsequent dissociation with the formation of either mullite or (corundum and mullite) or corundum, depending on the amount of aluminium fluoride. This process is accompanied by a sharp decrease in weight, (TG curve), due to the volatilization of silicon tetrafluoride, water vapour and other gases. The synthesized topaz is colourless in thin sections and crystallizes in orthorhombic system in the form of elongated prismatic crystals, with perfect basal (0 0 1) cleavage; it is optically positive.

Reported is a method for the removal of silica for the direct analysis of solid geological samples high in silica content using slurry sampling electrothermal vaporization-inductively coupled plasma-mass spectrometry (ETV-ICP-MS). The ETV-ICP-MS vaporization curve for SiO2, sampled as a slurry, is reported for temperatures ranging from 810–2600 °C. This curve showed that silica was completely vaporized at a temperature of 2200 °C. The effect of using HF as a chemical modifier to remove silica as the tetrafluoride was studied. It was found that HF could completely remove any Si attributed to silica if sufficient modifier were added and an adequate reaction time allowed. At reaction hold times that were less than optimal, two Si signals were observed. The first signal, which appears at an earlier time and at a temperature less than 480 °C, is attributed to the volatilization of silicon tetrafluoride. The second signal, which appears at a later time and at a temperature of about 2500 °C, is attributed to the vaporization of residual unreacted SiO2 remaining in the graphite tube, or to the vaporization of a mixture of SiO2 and SiC. 20 µl of 50% HF is effective in completely removing 0.125 µg of SiO2. No adverse effects including corrosive degradation of the graphite tube were observed over the lifetime of the tube, which exceeded 200 firings. Hydrofluoric acid chemical modifier was successful in removing virtually all the silica content in natural silicate standard reference materials.

The possibility of combined application of gas chromatography, high-resolution IR spectroscopy, and transient microwave gas spectroscopy (TMGS) for investigation of the impurity composition of silicon tetrafluoride is studied. Using high-resolution IR Fourier spectroscopy, the lines of a number of impurities are observed in the region from 4500 to 550 cm−1. The absorption lines of some of the main well-known impurities in silicon tetrafluoride in the 2-mm wavelength range are analyzed. The advantages of the TMGS method for investigating the multicomponent SiF4-impurities system are demonstrated. Using the TMGS method, the freons CHF3, CH2F2, and CH3F are experimentally detected in silicon tetrafluoride.

The possibility of preparing high-purity silicon tetrafluoride by the thermal dissociation of pure grade Na2SiF6 was studied. The impurity composition of the product was studied by IR and atomic emission spectroscopy and by mass spectrometry.

Thin-film transistors were made using 50-nm-thick directly deposited nanocrystalline silicon channel layers. The transistors have a coplanar top gate structure. The nanocrystalline silicon was deposited from discharges in silane, hydrogen and silicon tetrafluoride. The transistors combine a high electron field effect mobility of ∼10 cm2 V-1s-1 with a low ‘off’ current of ∼10-14 A per μm of channel length and an ‘on’/‘off’ current ratio of ∼108. This result shows that transistors made from directly deposited silicon can combine high mobility with low ‘off’ currents.

A procedure for the purification, recovery, and determination of isotopic abundances of silicon from biogenic and lithogenic particulate matter and dissolved silicic acid is reported. Purification involves the reaction of acid molybdate with dissolved silicon in natural waters or that produced by the dissolution of particulate silica by hydrofluoric acid. The resulting silicomolybdic acid is then quantitatively precipitated by reaction with triethylamine hydrochloride. The silicon is recovered as silicon dioxide through stepwise combustion of the dried precipitate. Fluorination of the product for isotopic analysis is accomplished by laser heating under pure fluorine generated by the decomposition of a fluorine-based salt. The resulting silicon tetrafluoride is separated from hydrogen fluoride and other fluorination byproducts cryogenically using a variable-temperature cold trap. Yields for silicon recovery are 99.9% for precipitation and greater than 95% for the purification/fluorination procedure. Reproducibility of the isotopic composition for pure quartz granules processed through the procedure is ±0.1‰ for δ(30)Si.

高融点金属材料中の微量Siモリブドケイ酸青吸光光度法における試料分解法,フッ化ナトリウム溶液の添加によるヘキサフルオロケイ酸の生成及び四フッ化ケイ素の酸素ガス搬送について検討した.試料分解は硫酸と硫酸アンモニウム溶液を使用し,V,Zrは純水で,Nb,Taはシュウ酸アンモニウム溶液でそれぞれ希釈した.四フッ化ケイ素の発生条件は硫酸濃度を11M以上を必要とし,酸素流量は1000cm3min-1,通気時間は20分間で十分であった.この方法による各金属試料中のケイ素の回収率は98%以上であった.高純度鉄(JSS 002-2)を使用して正確さ及び精度を検討したところ,Si 0.0008%のRSDsは7.1%であった.又本法の検出限界(から試験値の3σ)は0.76μg,定量下限(から試験値の10σ)は試料量0.50gで5ppm(m/m)であった.

The infrared multiphoton dissociation (IRMPD) of SiF4 in the presence of CH4 has been studied using a tunable CO2 TEA laser. The siliconated reaction products have been identified. A kinetic scheme has been proposed to explain the experimental results. The reaction rate constant of the trifluorosilyl radical, SiF3, with CH4 has been obtained from the numerical solution of the differential equation system associated to the kinetic mechanism proposed as well as from non-linear regression methods. It has been additionally found that this reaction occurs through two channels. The relative importance of each and their reaction rate constants have been determined as well. Fil: Alcaraz, A. N.. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina Fil: Codnia, Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas para la Defensa. Centro de Investigación en Láseres y Aplicaciones; Argentina Fil: Azcárate, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas para la Defensa. Centro de Investigación en Láseres y Aplicaciones; Argentina

Phosphorus plays a key role in the fabrication of silicon-based electronic devices. The determination of phosphorus in silicon has been carried out by atomic absorption spectroscopy (AAS) using a bismuth phosphomolybdate complex. Bismuth and phosphorus are present in the stoichiometric ratio of 1:1 in the complex. The determination of bismuth has been carried out in the complex and correlated with phosphorus content. The silicon matrix does not cause interference in the method as most of it is volatilized as silicon tetrafluoride by treatment with a hydrofluoric acid and nitric acid mixture. In this paper conditions for the formation of the complex, its extraction with methyl isobutyl ketone, the determination of bismuth using a 223.06-nm resonance line, and its correlation with phosphorus have been described.

Silicon isotopes were separated by distilling silicon tetrafluoride in a 150-cm packed column at temperatures of 189–206 K. The data show a reverse isotope effect with heavy isotopes more volatile in this temperature range. At total reflux, the maximum column separations were 0.926 for 28/29Si and 0.872 for 28Si/30Si. Carbon monoxide was also distilled in the column to obtain an estimated number of separating stages. From an estimated HETP of 2 cm for the packing, the volatility of 28Si is 0.9990 relative to 29Si and 0.9982 relative to 30Si. The SiF4 isotope effect is the largest yet found in distilling silicon compounds, and the effect is opposite that seen for SiH4. The magnitude of the isotopic relative volatilities is large enough to consider SiF4 distillation as a practical method for silicon isotopic enrichment. This effect of higher mass isotopes being more volatile has analogues in isotope effects in SF4 and BF3.

Amorphous silicon-germanium alloys (a-Si/sub 1-x/Ge/sub x/:H,F) have been deposited by glow-discharge decomposition of silicon tetrafluoride (SiF/sub 4/) and germane (GeH/sub 4/) in mixture with hydrogen. The effect of total RF power and deposition temperature on the characteristics of the gas phase and the grown material has been evaluated. Also, the effect of the dopant addition has been studied by adding PH/sub 3/ and B/sub 2/H/sub 6/ to the feeding mixture. Gas-phase characterization has been performed with optical emission spectroscopy for the analysis of the emitting species, mass spectrometry for the analysis of the stable species, and Langmuir electrical probes for the evaluation of electron density and temperature. The deposition rate has been measured in situ by laser interferometry. The deposited films have been analyzed with infrared and visible-range absorption spectroscopy and with X-ray microanalysis for the measurement of the chemical composition and optical properties. A kinetic analysis of the results points to a deposition model in which dissociative chemisorption of the gaseous reactants (SiF/sub 4/, GeH/sub 4/) plays a relevant role. There is also strong evidence that the chemisorption process is of the anionic type for SiF/sub 4/ and of the cationic type for GeH/sub 4/. >

Silicon tetrafluoride (SiF4) is observed in terrestrial volcanic gases and is predicted to be the major F - bearing species in low temperature volcanic gases on Io (Schaefer and Fegley, 2005b). SiF4 gas is also a potential indicator of silica-rich crust on Io. We used F/S ratios in terrestrial and extraterrestrial basalts, and gas/lava enrichment factors for F and S measured at terrestrial volcanoes to calculate equilibrium SiF4/SO2 ratios in volcanic gases on Io. We conclude that SiF4 can be produced at levels comparable to the observed NaCl/SO2 gas ratio. We also considered potential loss processes for SiF4 in volcanic plumes and in Io's atmosphere including ion-molecule reactions, electron chemistry, photochemistry, reactions with the major atmospheric constituents, and condensation. Photochemical destruction (tchem ~ 266 days) and/or condensation as Na2SiF6 (s) appear to be the major sinks for SiF4. We recommend searching for SiF4 with infrared spectroscopy using its 9.7 micron band as done on Earth., 16 pages, 2 figures, 1 table; Icarus, in press

Silicon tetrafluoride (SiF4) and sulfur hexafluoride (SF6) are widely used as sensitizing agents in photochemical experiments in the infrared region of the spectrum. These experiments include chemical vapor deposition, powder formation (for a review see Ref. 1), and kinetics. The energy of the Si-F bond is 610 kJ mol-1, whereas that of the corresponding S-F bond is 300 kJ mol-1. Therefore, SiF4 is expected to be a more versatile sensitizing agent than SF6, since the relatively high Si-F bond energy allows for greater radiative energy input and higher effective reaction temperatures. The high effective temperatures attained with the use of SiF4 (or SF6) necessitate the study of the absorptivities of these materials, since that quantity is known to be temperature dependent. Unfortunately, although some experimental results have been reported for SF6, such data are not generally available for SiF4. Moreover, in the case of laser-excited experiments, there is the potential for photochemical bleaching. Again, such data have been obtained for SF6, but only a limited amount of information is available for SiF4. In this study, we report on the absorptivity as a function of sample pressure (temperature) and as a function the continuous-wave (cw) laser power for conditions typically employed in sensitized infrared-driven chemical processes. It may be readily observed from the presented data that the absorptivity decreases with increasing laser power and that a limiting temperature is reached for increasing sample pressure at a constant laser power.

The microelectronic revolution has advanced at the expense of using materials which are potentially toxic to humans and damaging to the environment. The particularly reactive and hazardous nature of the dopants used during ion implant processes has generated concerns. Consequently, a number of preventive measures have been implemented to address environmental control and to minimize worker exposure risks. Delivery of dopants using SDS/sup (R)/ sources greatly reduced concerns related to gas handling issues. However, there is insufficient information about the nature and volume of gaseous emissions released by ion implanters to assess post-pump environmental and safety hazards. Effluent characterization could also provide an indirect measure of the performance of the implanter and crucial details necessary to customize an abatement solution. This paper summarizes the analyses performed at the exhaust of the ion source roughing pump and cryo pumps of an Applied Materials xR-80 ion implanter. Analyses were performed during standard implant processes using SDS arsine (AsH/sub 3/), phosphine (PH/sub 3/), boron trifluoride (BF/sub 3/), and silicon tetrafluoride (SiF/sub 4/) sources. The characterization study was performed in a quantitative, continuous, in-line mode using a Fourier transform infrared spectrophotometer (FTIR). Roughing pump exhaust streams generated using PH/sub 3/ and AsH/sub 3/ dopants contained no PH/sub 3/ and an average of 4% of the initially introduced AsH/sub 3/ respectively. Implant processes involving BF/sub 3/ and SiF/sub 4/, resulted in over 70% of the initially introduced dopants being released through the roughing pump. Characterization studies during cryo regeneration resulted in the identification and measurement of a number of gas species as a function of time.