Fraction Of Si Research Articles

Origin of diffuse C II 158 micron and Si II 35 micron emission in the Carina nebula

We present the results of mapping observations with ISO of (O  )6 3µm, 145 µm, (N ) 122 µm, (C ) 158 µm, (Si  )3 5µm, and H2 9.66 µm line emissions for the Carina nebula, an active star-forming region in the Galactic plane. The observations were made for the central 40 � × 20 � area of the nebula, including the optically bright H  region and molecular cloud lying in front of the ionized gas. Around the center of the observed area is the interface between the H  region and the molecular cloud which creates a typical photodissociation region (PDR). The (C ) 158 µm emission shows a good correlation with the (O  )6 3µm emission and peaks around the H -molecular region interface. The correlated component has the ratio of (C ) 158 µ mt o (O )6 3µm of about 2.8. We estimate from the correlation that about 80% of (C ) emission comes from the PDR in the Carina nebula. The photoelectric heating efficiency estimated from the ratio of the ((C ) 158 µm + (O  )6 3µm) intensity to the total far-infrared intensity ranges from 0.06 to 1.2%. (O ) 145 µm is detected marginally at 10 positions. The average ratio of (O ) 145 µ mt o (O )6 3µm of these positions is about 0.09 ± 0.01 and is larger than model predictions. The observed (C ) 158 µ mt o (O )6 3µm ratio indicates a relatively low temperature (<500 K) of the gas, while the large (O ) 145 µ mt o 63µm ratio suggests a high temperature (∼1000 K). This discrepancy cannot be accounted for consistently by the latest PDR model with the efficient photoelectric heating via polycyclic aromatic hydrocarbons (PAHs) even if absorption of (O  )6 3µm by foreground cold gas is taken into account. We suggest that absorption of (C ) 158 µm together with (O  )6 3µm by overlapping PDRs, in which the heating via PAHs is suppressed due to the charge-up effect, may resolve the discrepancy. Quite strong (Si  )3 5µm emission has been detected over the observed area. It shows a good correlation with (N ) 122 µm, but the correlation with (O  )6 3µm is very weak, indicating that (Si  )3 5µm comes mainly from the diffuse ionized gas rather than the PDR. The ratio of (Si  )3 5µ mt o (N) 122 µm is about 8 and Si of about 50% of the solar abundance relative to N should be present in the gas phase. The present results suggest that efficient dust destruction takes place and a large fraction of Si returns to the gas in the Carina star-forming region.

Influence of Si 1− xGe x interlayer on the initial growth of SiGeC on Si(1 0 0)

The initial growth of Si 1− x− y Ge x C y film with Si 1− x Ge x interlayer on Si(1 0 0) surface is investigated by scanning tunneling microscopy and reflection high energy electron diffraction. The increase in the Ge fraction of Si 1− x Ge x interlayers raises the critical thickness of the transition from two-dimensional (2D) to three-dimensional (3D) growth of Si 1− x− y Ge x C y layers, and is effective to suppress the surface-roughening of Si 1− x− y Ge x C y layers. The atomic-scale valley structure separating 2D-islands of the Si 1− x− y Ge x C y layers are observed on the surface, which is deduced to be the structure for the compressive-strain relaxation of Si 1− x− y Ge x C y layers on the Si substrate as well as missing dimmer rows.

Fabrication of SiGe-on-insulator by rapid thermal annealing of Ge on Si-on-insulator substrate

We report on fabrication of SiGe single crystal film on insulator by a simple approach including a growth of a thin Ge film on a commercially available SOI substrate, formation of a SiO 2 protective layer, and rapid thermal annealing (RTA) in an Ar atmosphere. Homogeneity of the local Si fraction in SiGe-on-insulator (SGOI) was found to be closely connected with the SiGe phase diagram, and RTA below the solidus line is required to obtain homogeneous SGOI. In spite of the high annealing temperature beyond the melting point of Ge, obtained SGOI was revealed to be single crystalline as evidenced by electron back scattering pattern analysis.

Site Preference and Si/B Mixing in Mixed‐Alkali Borosilicate Glasses: A High‐Resolution 11B and 17O NMR Study.

In a series of mono and mixed-alkali borosilicate glasses (∼0.7M2O·B2O3·2SiO2, M = Li, Na, K, (1/2Li2O + ∼1/2Na2O), (1/2Li2O + 1/2K2O), and (∼1/2Na2O + 1/2K2O)), we have applied triple-quantum magic-angle spinning (3QMAS) and 11B and 17O NMR to obtain high-resolution information about short-range structure and the connections among various network structural units, to study the effect of mixed cations on the glass structure, and to explore the distribution and mixing of these modifier cations. For a Li-containing glass, a lower fraction of [4]B, a lower fraction of Si−O−B, and a higher fraction of nonbridging oxygen than those found in Na- and K-containing glasses suggests that there is a significant heterogeneity in terms of Si/B mixing in the former. For Li−Na and Li−K mixed cation glasses, anomalously high fractions of nonbridging oxygen were also observed along with smaller fractions of [4]B and Si−O−B, again indicating significant chemical heterogeneity. For Na−K mixed cation glasses, the populations...

Characterization of 7-nm-thick strained Ge-on-insulator layer fabricated by Ge-condensation technique

A strained Ge-on-insulator (GOI) structure with a 7-nm-thick Ge layer was fabricated for applications to high-speed transistors. The GOI layer was formed by thermal oxidation of a strained SiGe layer grown epitaxially on a silicon-on-insulator (SOI) wafer. In transmission electron microscopy measurements, the obtained GOI layer exhibited a single-crystal structure with the identical orientation to an original SOI substrate and a smooth Ge/SiO2 interface. The rms of the surface roughness of the GOI layer was evaluated to be 0.4 nm by atomic force microscopy. The residual Si fraction in the GOI layer was estimated to be lower than the detection limit of Raman spectroscopy of 0.5% and also than the electron energy loss spectroscope measurements of 3%. It was found that the obtained GOI layer was compressively strained with a strain of 1.1%, which was estimated by the Raman spectroscopy. Judging from the observed crystal quality and the strain value, this technique is promising for fabrication of high-mobility strained Ge channel of high-performance GOI metal–insulator–semiconductor (MIS) transistors.

Site Preference and Si/B Mixing in Mixed-Alkali Borosilicate Glasses: A High-Resolution 11B and 17O NMR Study

In a series of mono and mixed-alkali borosilicate glasses (∼0.7M2O·B2O3·2SiO2, M = Li, Na, K, (1/2Li2O + ∼1/2Na2O), (1/2Li2O + 1/2K2O), and (∼1/2Na2O + 1/2K2O)), we have applied triple-quantum magic-angle spinning (3QMAS) and 11B and 17O NMR to obtain high-resolution information about short-range structure and the connections among various network structural units, to study the effect of mixed cations on the glass structure, and to explore the distribution and mixing of these modifier cations. For a Li-containing glass, a lower fraction of [4]B, a lower fraction of Si−O−B, and a higher fraction of nonbridging oxygen than those found in Na- and K-containing glasses suggests that there is a significant heterogeneity in terms of Si/B mixing in the former. For Li−Na and Li−K mixed cation glasses, anomalously high fractions of nonbridging oxygen were also observed along with smaller fractions of [4]B and Si−O−B, again indicating significant chemical heterogeneity. For Na−K mixed cation glasses, the populations...

Structural-phase transformations in SiOx films in the course of vacuum heat treatment

A thermally stimulated structural transformation of the Si-O phase in the SiOx layers, which leads to the formation of Si nanoinclusions, was investigated using gravimetry, infrared spectroscopy, multiple-angle ellipsometry, and atomic-force microscopy. It is demonstrated that vacuum heat treatment leads to an increase in the concentration of O bridges in the structural network of oxide. Oxide is compacted, and its surface roughness is smoothened. Silicon and SiO2 phases are precipitated due to the transfer of O atoms from lightly oxidized molecular clusters (SiOSi3) to heavily oxidized ones (SiO3Si). An analysis of ellipsometry data in the context of the effective medium model made it possible to estimate the fractions of the precipitated Si and SiO2 phases.

Formation of Minor‐Ion Charge States in the Fast Solar Wind: Roles of Differential Flow Speeds of Ions of the Same Element

To investigate the possibility of differential flow speeds between ions of the same element and their roles in the determination of ionic fractions, this paper extends our latest minor-ion model to a five-fluid model, describing the behavior of five species of minor ions of one given element in the fast solar wind. We solve the five sets of mass, momentum, and energy equations simultaneously to include the effects of ionization, recombination, and heating. The five species of minor ions are taken as test particles flowing in a background plasma consisting of electrons, protons, and alpha particles. The parameters of the background gas are calculated using a previous three-fluid wave-driven magnetohydrodynamic model for the fast solar wind. These background parameters are modeled as closely as possible to observed values. Using this background of fast solar wind parameters, the five-fluid minor-ion model has no problem reproducing the frozen-in charge-state distributions observed in the fast solar wind for C and O ions, while the modeled ionic fractions of Si, Mg, and Fe show significant shifts to lower charge states compared with the observed values. It is found that the majority of C and O ions are frozen-in below 1.2 solar radii, while most Si, Mg, and Fe ions are frozen-in beyond 1.3-1.5 solar radii. Comparing the cases with and without differential flows shows that even though differential flow speeds between ions of the same element do develop beyond a certain heliocentric distance (e.g., 1.2 solar radii for Si ions), they cannot account for the high ion charge states observed in situ.

Preparation of SiN x and composite SiN x–TiN films from alkoxide solutions by liquid injection plasma CVD

Monolithic SiN x and composite SiN x –TiN films were prepared on a Si wafer at 700 °C by a plasma chemical vapor deposition technique designed to inject ethanol solution of alkoxides (hexa-methyl-disiloxane and titanium tetra-ethoxide) at a feed rate of 0.05–0.3 ml min −1 into a thermal Ar/H 2/N 2 plasma. The films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy, electrical resistivity, and Vickers micro-hardness. The silicon nitride was found to be amorphous, designated as SiN x , by XRD. SiN x films obtained at a feed rate of 0.05 ml min −1 exhibited the composition near Si 3N 4 with densely packed particles of 0.1 μm in size. In composite SiN x –TiN films, the N content was 30–35 and 40–45 at.% at a Si fraction of 0.1–0.5 and above 0.5, respectively, and the Ti and Si contents changed linearly and complementarily with the solution composition. SEM showed that films are 1–1.5 μm thick, possessing particle size of 300–400 nm at a Si fraction of 0.1, which increases to 1–2 μm at fractions higher than 0.3. The resistivity and microhardness of the monolithic TiN and composite SiN x –TiN films were measured.

Microstructure and conductivity of large area nanocrystalline silicon films grown by specially designed thermal-assisted chemical vapor deposition

Large-area thin films of silicon consisting of an amorphous matrix with embedded silicon nanocrystallites were deposited on glass substrates using a specially-designed thermal-assisted chemical vapor deposition technique that is compatible with the mature silicon technology. Under this way, the typical nanocrystalline silicon film was grown at 660 °C with crystallization ratio of over 50% and average silicon crystallite size approximately 8–12 nm. The deposition temperature and the post-annealing procedure determine the nanocrystalline Si fraction in the amorphous matrix, which affects the room-temperature dark conductivity of the film. The thermal-assisted tunneling of carriers between neighboring silicon nanocrystallites embedded in amorphous matrix was suggested, which coincides with the theory of hetero-quantum dots.

Influence of nitrogen–argon gas mixtures on reactive magnetron sputtering of hard Si–C–N films

Si–C–N films were deposited on p-type Si(100) substrates by dc magnetron co-sputtering of silicon and carbon using a single sputter target with variable Si/C area ratios in nitrogen–argon mixtures. The film characteristics were primarily controlled by the argon concentration (0–75%) in the gas mixture at a fixed 40% silicon fraction in the magnetron erosion track area. The total pressure and the discharge current on the magnetron target were held constant at P=0.5 Pa and I m=1 A, the substrate temperature was adjusted at T s=600 °C by an ohmic heater and the rf-induced negative substrate bias voltage, U b was −500 V. Mass spectroscopy was used to explain differences between sputtering of carbon and silicon in nitrogen–argon discharges. The films, typically 1.0–1.5 μm thick, were found to be amorphous with a very smooth surface ( R a≤0.8 nm). It was shown that the nitrogen–argon gas mixture composition is an important process parameter in a reproducible production of Si–C–N compounds with controlled properties by dc magnetron co-sputtering using a composed C–Si target with variable Si/C area ratios. With a rising argon concentration in the gas mixture, the Si content in the films rapidly increases (from 19 to 34 at.% for a 40% Si fraction in the erosion target area), while the C content decreases (from 34 to 19 at.%) at an almost constant (39–43 at.%) N concentration. An intensified bombardment of growing films by argon leads to its subplantation into the films (up to 5 at.%) and to a decrease in a volume concentration of hydrogen (from 5 to 1 at.%). As a result, the NSi and SiN bonds dominate over the respective NC and SiO bonds, preferred in a pure nitrogen discharge, and the film hardness increases up to 40 GPa. The effect of the negative substrate bias voltage (from a floating potential of −18 to −500 V) on characteristics of the films prepared in a 50% N 2+50% Ar gas mixture is not too marked at T s=600 °C. A decrease in the T s values to 135–210 °C leads to a higher incorporation of hydrogen into the films (up to 6 at. %) and to a stronger influence of the negative substrate bias voltage.

Density Anomalies in Thin Liquid Films of Hydride Functional Siloxanes

Thin liquid films of polyfunctional poly(methylhydro-dimethyl)siloxane copolymers (PMDMS) have been investigated using X-ray reflectivity. The electron density of liquids within the films is altered significantly as a function of film thickness and fraction of Si−H groups in the PMDMS molecule. The density profile in the region next to the Si substrate is highly sensitive to the interaction between the liquid molecules and the substrate surface. Increasing the number of Si−H groups interacting with the surface leads to a more pronounced low-density region in the vicinity of the substrate. However, one-dimensional ordering normal to the surface is identical for all PMDMS films.

Pulsed laser crystallization of SiGe alloys on GaAs

We have investigated the crystallization of amorphous SiGe films deposited on crystalline GaAs (001) substrates using ns laser pulses. Analysis of the film structure using Raman spectroscopy indicates the formation of heteroepitaxial Si xGe1/GaAs structures for Si compositions up to x = 25%. Higher compositions lead to polycrystalline films. This is attributed to the increased lattice mismatch between Si xGe1 and GaAs as the Si fraction in the alloy increases

NMR Studies of Fluorine in Aluminosilicate–Lanthanum Fluoride Glasses and Glass‐Ceramics

NMR determinations of fluorine environments in transparent oxyfluoride glass‐ceramics were made to learn about the crystallization of LaF3, as well as to ascertain the structural role of fluorine in the surrounding glassy matrix. The fraction of fluorine in LaF3 was measured as a function of heat treatments, demonstrating significant differences between glasses modified with barium and those containing sodium. The results of these measurements showed that not all of the fluorine formed LaF3 in these glass‐ceramics, with resolution of additional fluoride sites at −135 and −185 ppm, due primarily to Si–F and Al–F bonding, respectively. Not only is the evidence of Si–F bonding unexpected, given the presence of aluminum, but the amount of Si–F bonding is sensitive to the type of modifier in the glass. Samples containing barium oxide as the modifier showed a higher fraction of Si–F bonding than those modified with sodium oxide.

Characterization of suspended solids in Lake Biwa by measuring their elemental composition of Al, Si, P, S, K, Ca, Ti, Mn, and Fe

We investigated the concentrations of particulate Al, Si, P, S, K, Ca, Ti, Mn, and Fe at various areas of Lake Biwa, such as the limnetic zone in the northern basin, the offshore zone, the dredged area and Akanoi Bay in the southern basin, and reed community areas in the shore. In the wide and deep northern basin, the density of suspended solids was low, and substantial fractions of particulate Si, P, S, and Ca were biogenic matter produced by phytoplankton. In the offshore zone in the narrow and shallow southern basin, the concentration ratios of particulate Si, K, Ca, Ti, and Fe against particulate Al were almost constant throughout the year and were similar to those found in crusts. Therefore, these elements are most likely derived from terrigenous clay matter. In the dredged area where the hypolimnion became anoxic during the stratification period, the concentrations of particulate Fe, Mn, P, S, and Ca increased because of the formation of hydrous Fe and Mn oxides and Fe sulfide. In Akanoi Bay, the ratios of Mn/Al and Fe/Al were high because of the stirring of sediments enriched with Mn and Fe oxides. In the reed community areas, the concentration of suspended solids correlated well with particulate Fe and P, but not with Al or chlorophyll a; therefore these areas seem to be rich in humic organic matter enriched with P and Fe due to microbial activity. Thus, the elemental composition of suspended solids reflects the chemical, biological, and physical processes in the lake and gives us useful indices of the characteristics of the water.

Characteristics of low-k and ultralow-k PECVD deposited SiCOH films.

AbstractWe have shown previously that the dielectric constants of PECVD prepared SiCOH dielectrics can be extended to ultralow-k values of k=2.0. The reduction in the dielectric constants has been achieved by adding an organic precursor to the tetramethylcyclotetrasiloxane (TMCTS) used for the preparation of the SiCOH dielectric and annealing the films to remove the thermally less-stable organic CHx fractions from the films, thereby adding porosity and reducing the density of the films. To assess the effects of the reduction of the dielectric constant on other physical properties of the material, the density and composition of the films have been determined by RBS and FRES and the porosity has been measured by PAS/PALS, SAXS and ellipsometric porosimetry. In addition the films have been characterized structurally and topologically by TEM and AFM.It has been found that addition of the organic precursor reduces the Si fraction in the films, however, there is no direct correlation between dielectric constant and film composition. The dielectric constant and density decrease with increasing porosity in the films, which reaches values of 30-39% for k values of 2.05. The pore size increases with decreasing k, however the diameter remains below 5 nm for k=2.05. This is significantly smaller than the pore size typically found in porous spin-on films and may provide an integration advantage compared to spin-on films having similar k values.

Effects of Si p size and volume fraction on properties of Al/Si p composites

Al–12 wt.% Si alloy matrix composites reinforced with high volume fraction of Si p were fabricated by squeeze infiltration. The effects of the compacting pressure on the volume fraction of Si p in preforms, and the influences of Si p size and volume fraction on the properties of Al/Si p composites were examined through this study. Si particles were compacted at different pressure of 40–130 MPa followed by sintered at 1000 °C for 7 h to obtain preforms containing 60–70 volume fraction (vol.%) of Si p. The sintered preforms were then infiltrated with Al–12 wt.% Si alloy at 750 °C under a 75 MPa squeeze infiltration pressure. It was found that lower coefficient of thermal expansion (CTE) and smaller density may be obtained with higher Si p volume fraction, yet increasing Si p volume fraction leads to higher amount of porosities in the composites and thus lowers the thermal conductivity (TC) and flexural strength. Besides, with the same Si p volume fraction, coarse Si particles result in higher CTE and TC, while finer Si particles may lower CTE and enhance the flexural strength of the composites effectively. From the results obtained in this study, it is expected that the high volume fraction Si p reinforced Al/Si p composites posses good potential in electronic packaging applications.

Raman scattering study of (GaAs)1−x(Si2)x alloys epitaxially grown on GaAs

(GaAs) 1−x (Si 2 ) x metastable alloys grown on (001), (110), (112), and (111) GaAs substrates, with Si fractions in the range 0⩽x⩽0.43, were studied by Raman scattering. Two modes near the LO and TO modes of GaAs, besides two local modes associated either with Si–As or Si–Ga and Si–Si bonds, are observed in the Raman spectra. The ratio of integrated intensities of TO-like and LO-like modes (ITO/ILO) is used to evaluate the short range order. It is observed that the zinc blende to diamond transition reported in the literature for these alloys does not influence the Si fraction dependence of the short range order.

Study of Ge 0.96Si 0.04 epilayers grown on Si (0 0 1) at high temperature

We have studied the properties of Ge 0.96Si 0.04 epilayers grown at high temperature on Si (0 0 1) substrates by X-ray diffraction, Raman spectra, and high-resolution transmission electron microscopy (TEM). Raman spectra show that there is an obvious transition region between the Ge 0.96Si 0.04 layer and the Si substrate. The thickness of this region is about 100 nm. Towards the Ge 0.96Si 0.04 layer, the Si fraction decreases rapidly from about 30 to 4%. In X-ray diffraction, there is a sharp peak of Ge 0.96Si 0.04 and a broad peak of the GeSi alloy region with lower Ge fraction. High resolution of cross-sectional TEM images show that the interface of GeSi/Si substrate is {1 1 1} faceted.

Non-detrital Si concentrations as an estimate of diatom concentrations in lake sediments and suspended material

This paper evaluates a method, based on normalization with Al, to estimate the concentration of diatoms in suspended and deposited sediments. Provided that Al exists primarily in the detrital phase, one can calculate the fraction of non-detrital Si (i.e. biogenic Si). Suspended matter and sediment in two lakes in northern Sweden have been analyzed. Results from the normalization method are compared with microscope count data. The results from the two methods differ somewhat. Partly dissolved diatom frustules may explain part of this discrepancy. These remnants can hardly be recognized as diatoms. Therefore, they are not counted during the microscopic analysis, although they contribute to the concentration of biogenic Si. Another factor is the differences in Si content among different types of diatoms. We show that the calculated concentrations of non-detrital Si are good estimates of the diatom concentrations. By using normalization as a tool, reasonable estimates of the stocks of biogenic Si can be obtained rapidly. Using these estimates as a guide, sites where considerable changes in diatom productivity and/or dissolution rates have occurred can be identified.