Strong Si Research Articles

How a Thermally Unstable Metal Hydrido Complex Can Yield High Catalytic Activity Even at Elevated Temperatures.

Despite their instability in ethereal solvents, organotitanium hydride catalysts are successfully employed in catalysis at moderate to high temperatures (110 °C), even in the presence of alcohols. It is shown computationally (bond dissociation energy (BDE) analysis and energetic profile for regeneration) and experimentally (EPR studies and kinetic studies), with the specific example of hydrodefluorination (HDF), that despite the long standing belief, regeneration of Ti-H bonds from Ti-F bonds using silanes is endergonic. The resulting low concentration of Ti-H species is crucial for the catalytic stability of those systems. The resting state in the catalysis is a Ti-F species. The most promising silanes for regeneration are not the ones that have the strongest Si-F bond, but the ones that show the largest difference in Si-F and Si-H BDEs.

Atomic Layer Deposition of Silicon Dioxide Using Aminosilanes Di-sec-butylaminosilane and Bis(tert-butylamino)silane with Ozone

In situ Fourier transform infrared (FTIR) spectroscopy is used to investigate silicon dioxide deposition on OH-terminated oxidized Si(100) surfaces using two aminosilanes, di-sec-butylaminosilane (DSBAS) and bis(tert-butylamino)silane (BTBAS), with ozone as the coreactant. Both DSBAS and BTBAS readily react at 100 °C with surface −OH groups (loss at 3745 cm–1) with formation of Si–O–SiH3 and Si–O–SiH2–(NHtBu), respectively, through elimination of secondary and primary amines. The (O−)SiH3 structure is characterized by a strong Si–O–Si band at 1140 cm–1, and sharp (O−)SiH3 stretch (2192 cm–1) and deformation (983 cm–1) bands. SiH3 remains stable up to 400 °C, at which point rearrangement into bidentate ((O−)2SiH2) and then tridentate ((O−)3SiH) bonding takes place through condensation reaction with neighboring OH or O groups. In contrast, the O–SiH2–(NHtBu) structure obtained from BTBAS exposure at 100 °C loses its NHtBu group at ∼350 °C, leading to a bidentate bonding ((O−)2SiH2) that remains stable up to...

EXTENSIVE SPECTROSCOPY AND PHOTOMETRY OF THE TYPE IIP SUPERNOVA 2013ej

We present extensive optical ($UBVRI$, $g'r'i'z'$, and open CCD) and near-infrared ($ZYJH$) photometry for the very nearby Type IIP SN ~2013ej extending from +1 to +461 days after shock breakout, estimated to be MJD $56496.9\pm0.3$. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive $UBVRIJHK$ bolometric calibrations from $UBVRI$ and unfiltered measurements that potentially reach 2\% precision with a $B-V$ color-dependent correction. We observe moderately strong Si II $\lambda6355$ as early as +8 days. The photospheric velocity ($v_{\rm ph}$) is determined by modeling the spectra in the vicinity of Fe II $\lambda5169$ whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives $v_{\rm ph} = 4500\pm500$ km s$^{-1}$ at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10--12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be $9.0_{-0.6}^{+0.4}$ Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be $94\pm7$ days long, yields an explosion energy of $0.9\pm0.3\times10^{51}$ ergs, a final pre-explosion progenitor mass of $15.2\pm4.2$~M$_\odot$ and a radius of $250\pm70$~R$_\odot$. We observe a broken exponential profile beyond +120 days, with a break point at +$183\pm16$ days. Measurements beyond this break time yield a $^{56}$Ni mass of $0.013\pm0.001$~M$_\odot$.

LINE IDENTIFICATIONS OF TYPE I SUPERNOVAE: ON THE DETECTION OF Si II FOR THESE HYDROGEN-POOR EVENTS

ABSTRACT Here we revisit line identifications of type I supernovae (SNe I) and highlight trace amounts of unburned hydrogen as an important free parameter for the composition of the progenitor. Most one-dimensional stripped-envelope models of supernovae indicate that observed features near 6000–6400 Å in type I spectra are due to more than Si ii λ6355. However, while an interpretation of conspicuous Si ii λ6355 can approximate 6150 Å absorption features for all SNe Ia during the first month of free expansion, similar identifications applied to 6250 Å features of SNe Ib and Ic have not been as successful. When the corresponding synthetic spectra are compared with high-quality timeseries observations, the computed spectra are frequently too blue in wavelength. Some improvement can be achieved with Fe ii lines that contribute redward of 6150 Å; however, the computed spectra either remain too blue or the spectrum only reaches a fair agreement when the rise-time to peak brightness of the model conflicts with observations by a factor of two. This degree of disagreement brings into question the proposed explosion scenario. Similarly, a detection of strong Si ii λ6355 in the spectra of broadlined Ic and super-luminous events of type I/R is less convincing despite numerous model spectra used to show otherwise. Alternatively, we suggest 6000–6400 Å features are possibly influenced by either trace amounts of hydrogen or blueshifted absorption and emission in Hα, the latter being an effect which is frequently observed in the spectra of hydrogen-rich, SNe II.

Formation of lateral nanowires by Ge deposition on Si(111) at high temperatures

The lattice strain is the main factor which governs the surface morphology formation during the Si/Ge heteroepitaxial growth. Its influence becomes significantly weakened at high growth temperatures due to strong Si–Ge intermixing, giving an advantage of other factors which may produce unusual effects. We observed the formation of lateral SiGe nanowires (NWs) after Ge deposition on Si(111) at 830–860°С using solid-source molecular beam epitaxy. An additional factor to the strain minimization is associated with an energy barrier for the misfit dislocation network introduction at the NW/substrate interface, which causes the NWs to be straight. However, the requirement to attain a certain SiGe composition provides the formation of winding NWs, reflecting the subtle aspects of the growth process.

Fire enhances solubility of biogenic silica

Changing fire regimes in response to climate change are likely to have significant effects on terrestrial ecosystems and biogeochemical cycles. While effects of fire on some nutrient cycles have been quite well-studied, little attention has been paid to the silicon cycle. We used an alkaline continuous extraction to examine changes in the quantity and characteristics of alkaline extractable Si (AlkExSi) after applying two burning treatments (no heating, 350°C and 550°C) to three types of organic soil material (from spruce forest, beech forest and a commercial peat). The total AlkExSi measured was 25.1±2.1mgg−1 and 15.4±0.9mgg−1 for spruce and beech respectively, and 1.2±0.5mgg−1 for peat. The alkaline extraction parameters confirm a purely biogenic AlkExSi source in untreated spruce and beech organic soil material samples. Organic soil material of beech forest had two biogenic silica pools, differing in reactivity during alkaline extraction. Burning severely alters the alkaline dissolution parameters suggesting a significant crystallization of biogenic Si (BSi) with increased burning severity. Additionally, dissolution experiments carried out in rain water showed that fire increased the solubility of BSi by a factor of 40 and 20 in the case of the spruce and beech organic soil material respectively. The extent of enhanced Si solubility appears to be a trade-off function between organic matter losses and degree of crystallization. The burned soils could provide a strong and immediate Si source for the environment. In situ ecosystem characteristics that affect the uptake-leaching balance will determine the fate of the dissolved Si. Ecosystems low in BSi, like Sphagnum peatland, will not show drastic alteration in the Si cycle due to fire.

Si(111)7×7 表面再構成過程のストレス変位

We have focused on stress measurements of the reconstructed Si(111) 7×7 and the hydrogen (H)-terminated Si(111) 1×1 surfaces. In order to obtain information on both the surface stress and the surface structure simultaneously, we have combined the surface-curvature and the reflection high-energy electron-diffraction instrumentations in an identical ultrahigh vacuum system. The surface stress behaviors during desorption and adsorption processes of hydrogen on the Si(111) surfaces reveal that the Si(111) 1×1 surface releases 1.6∼1.7 N/m (= J/m2), or 1.3∼1.4 eV/ (1×1 unit cell), of the surface energy from the strong tensile Si(111) 7×7 reconstruction.

Role of polydimethylsiloxane in properties of ternary materials based on polyimides containing zeolite Y

AbstractMixed matrix materials, containing poly(dimethylsiloxane), phosphine oxide-based polyimide, and zeolite Y were prepared by means of blending hybridisation. The thermal stability of the materials and the hydrophobic properties were enhanced. The decrease in the glass transition temperature of the materials with the increase in poly(dimethylsiloxane) content supported the polymer-chain flexibility. The pristine polyimide and the zeolite-filled polyimide exhibited the highest transparency. Fourier transform infrared (FTIR) spectroscopy confirmed that the increase in the amount of the lowest molecular mass poly(dimethylsiloxane) ingredient indicated strong alkyl and Si—O—Si stretching modes, whilst the alkyl and Si—O—Si stretching intensity decreased in the presence of the highest amount of and the highest molecular mass poly(dimethylsiloxane). The hydrophobic poly(dimethylsiloxane) moiety created an inverse relationship between the porosity of the materials (surface roughness) and the hydrophilicity. The nanocrystallite domain, identified by X-ray diffraction analysis (XRD) and possessing an exotherm crystallisation peak, occurred in the lowest amount of poly(dimethylsiloxane) with the highest molecular mass-based hybrid material. The nanocrystallite enhanced the storage modulus as determined by the dynamic mechanical analyser (DMA). The nanocrystalline formation resulted in a slight increase in the alkyl stretching and the Si—O—Si stretching of the lowest amount of and the highest molecular mass poly(dimethylsiloxane)-containing material over those of the lowest molecular mass poly(dimethylsiloxane) in the same amounts of material involved.

Photodegradation of Erythromycin antibiotic by γ-Fe2O3/SiO2 nanocomposite: Response surface methodology modeling and optimization

Efficient adsorbent γ-Fe2O3/SiO2 nanocomposites were synthesized using sol–gel method. The developed adsorbent was well characterized using various analytical techniques such as XRD, TEM, SEM, BET and DRS techniques. The obtained XRD pattern that revealed a strong Si (111) peak at 28.1°. On the other hand, the patterns of display representative γ-Fe2O3 peaks were centered at 2θ=31.2°, 33.9°, 44.1°, 52.5°, 57.6°, and 63.9°, due to (220), (311), (400), (422), (511), and (440) planes, respectively. The DRS analysis of γ-Fe2O3/SiO2 nanocomposite that shifted to a lower wavelength (blue-shift), reveals the high photocatalytic activity of the developed adsorbent. The central composite design superimposed with the response surface methodology (RSM) was used for the optimization of the influential parameters and photocatalytic removal of Erythromycin antibiotic. The obtained optimized values for the rapid removal of Erythromycin antibiotic were as follows: γ-Fe2O3/SiO2 nanocomposite dosage of 500mgL−1, initial RhB concentration of 6mgL−1, the irradiation time of 6min, and pH=8.

Influence of Si addition on the microstructure and mechanical properties of Ti–35Nb alloy for applications in orthopedic implants

In the development of new materials for orthopedic implants, special attention has been given to Ti alloys that show biocompatible alloy elements and that are capable of reducing the elastic modulus. Accordingly, Ti–Nb–Si alloys show great potential for application. Thus, this is a study on the microstructures and properties of Ti–35Nb–xSi alloys (x=0, 0.15, 0.35 and 0.55) (wt%) which were thermally treated and cooled under the following conditions: furnace cooling (FC), air cooling (AC), and water quenching (WQ). The results showed that Si addition is effective to reduce the density of omega precipitates making beta more stable, and to produce grain refinement. Silicides, referred as (Ti,Nb)3Si, were formed for alloys containing 0.55% Si, and its formation presumably occurred during the heating at 1000°C. In all cooling conditions, the hardness values increased with the increasing of Si content, as a result from the strong Si solid solution strengthening effect, while the elastic modulus underwent a continuous reduction due to the reduction of omega precipitates in beta matrix. Lower elastic moduli were observed in water-quenched alloys, which concentration of 0.15% Si was more effective in their reduction, with value around 65GPa. Regarding Ti–35Nb–xSi alloys (x=0, 0.15 and 0.35), the “double yield point” phenomenon, which is typical of alloys with shape memory effect, was observed. The increase in Si concentration also produced an increase from 382MPa to 540MPa in the alloys׳ mechanical strength. Ti–35Nb–0.55Si alloy, however, showed brittle mechanical behavior which was related to the presence of silicides at the grain boundary.

Influence of ISSG tunnel oxide with decoupled plasma nitridation on erase characteristic of NOR-type floating-gate flash memories

This paper investigated the influence of ISSG (in situ steam generation) tunnel oxide layer with decoupled plasma nitridation (DPN) on the erase reliability of NOR-type floating-gate flash memory devices. The experimental results demonstrated that the tunnel oxide with ISSG process achieves better thickness uniformity and higher breakdown voltage than that with conventional dry oxidation process. However, the erase performance of flash cells was significantly degraded when DPN was applied to the ISSG oxide. The higher bulk nitrogen content from DPN process could lead to more bulk traps generation by substituting the strong Si–O bonds for the weak Si–N bonds in the tunnel oxide. During program/erase cycling, the more electrons trapped in the bulk tunnel oxide the less the FN erase electric field will be, which is responsible for the degradation of erase performance.

An NHC-Stabilized Silicon Analogue of Acylium Ion: Synthesis, Structure, Reactivity, and Theoretical Studies.

The silicon analogues of an acylium ion, namely, sila-acylium ions 2a and 2b [RSi(O)(NHC)2]Cl stabilized by two N-heterocyclic carbenes (NHC = 1,3,4,5-tetramethylimidazol-2-ylidene), and having chloride as a countercation were successfully synthesized by the reduction of CO2 using the donor stabilized silyliumylidene cations 1a and 1b [RSi(NHC)2]Cl (1a, 2a; R = m-Ter = 2,6-Mes2C6H3, Mes = 2,4,6-Me3C6H2 and 1b, 2b; R = Tipp = 2,4,6-iPr3C6H2). Structurally, compound 2a features a four coordinate silicon center together with a double bond between silicon and oxygen atoms. The reaction of sila-acylium ions 2a and 2b with water afforded different products which depend on the bulkiness of aryl substituents. Although the exposure of 2a to H2O afforded a stable silicon analogue of carboxylate anion as a dimer form, [m-TerSi(O)O]2(2-)·2[NHC-H](+) (3), the same reaction with the less bulkier triisopropylphenyl substituted sila-acylium ion 2b afforded cyclotetrasiloxanediol dianion [{TippSi(O)}4{(O)OH}2](2-)·2[NHC-H](+) (4). Metric and DFT (Density Functional Theory) evidence support that 2a and 2b possess strong Si═O double bond character, while 3 and 4 contain more ionic terminal Si-O bonds. Mechanistic details of the formation of different (SiO)n (n = 2, 3, 4) core rings were explored using DFT to explain the experimentally characterized products and a proposed stable intermediate was identified with mass spectrometry.

FUNCTIONALIZATION OF BIOMOLECULES WITH NANOSTRUCTURED POROUS SILICON FOR BIOMEDICAL APPLICATION

Porous silicon (PS) fabrication, changes in the optical properties and surface modification in the oxidized PS (dipped into the Glucose oxide) due to the infiltration of biomolecules using Luminescence Spectrophotometer [Photoluminescence (PL)], Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscope (SEM) were studied. The surface morphology of oxidized PS (OPS) and treated with Glucose have been studied by SEM. Spontaneous imbibition weight was calculated theoretically using imbibition equation for the porous medium using glucose solution as the wetting liquid. FTIR analysis revealed that, the strong Si–H, Si–O–Si bonds which covered most of the OPS surface. In the glucose treated PS layer, the amide I (C=O) stretch and amide II (C=N) stretch (1690 cm−1 and 1551 cm−1) groups were appeared in the spectrum which confirmed the coupling reaction. Efficient visible Photoluminescence was obtained at around 624 nm from glucose treated porous silicon. The functionalization of glucose with nano structured PS, changes light emission over the surface of OPS. It can be applied in optical biosensor and which can be used in biomedical applications.

Surface stress measurement of Si(111) 7 × 7 reconstruction by comparison with hydrogen-terminated 1 × 1 surface

We have focused on measurements of the surface stress in Si(111) as a function of 7×7 reconstruction by comparison with the hydrogen (H)-terminated Si(111) 1×1 surface. In order to obtain information on both the surface stress and the surface reconstruction simultaneously, we have combined the surface-curvature and the reflection-high-energy-electron-diffraction instrumentations in an identical ultrahigh vacuum system. The stress evolution shows a decrease of tensile stress corresponding to the formation of H-termination at the beginning of the atomic H exposure of Si(111) 7×7 surface. After the above treatment, a complete transformation of the surface structure occurs from the reconstructed surface to the 1×1 one. As a result, we find the H-terminated Si(111) 1×1 surface releases 1.7N/m (=J/m2), or (1.4eV/(1×1 unit cell)), of the surface energy from the strong tensile Si(111) 7×7 reconstruction.

Global distribution of ionizing and recombining plasmas in the supernova remnant G290.1−0.8

We report on the Suzaku results of the mixed-morphology supernova remnant (SNR) G290.1−0.8 (MSH 11-61A). The SNR has an asymmetric structure extended to the south-east and the north-west. In the X-ray spectra of the center and the north-west regions, we discover recombining plasma features with a strong Si Lyα and radiative recombination continuum at ∼ 2.7 keV. These features are the most significant in the north-west region, and the spectra are well reproduced with a recombining plasma of kTe = 0.5 keV, whereas the spectra of other regions are expressed by an ionizing plasma of kTe = 0.6 keV. The recombining plasma has over-solar abundances, while the ionizing plasma has roughly solar abundances. Hence they are likely ejecta and of interstellar medium (ISM) origin, respectively. The recombining plasma in the north-west of G290.1−0.8 would be generated by a break-out of the supernova ejecta from a high density circumstellar medium to a low density ISM.

Silicene: A Promising Surface to Achieve Morphological Transformation in Gold Clusters

In recent years, gold clusters supported on solid materials have attracted considerable attention because of their various potential applications. With the objective of stabilizing the energetically less stable but catalytically more active planar form of finite sized gold clusters on some suitable solid support, we have theoretically investigated the morphological transformation of gold dimer, trimer, and Au20 clusters on pristine silicene/Ag(111) surface. In contrast to previous schemes which have been suggested for the stabilization of planar structures by appropriate surfaces, the present proposal does not require any external influence such as doping or application of external electric field. In fact, we have exploited the special characteristics of the silicene surface, namely, buckled nature and weak Si–Si π bonding, which enable this surface to make strong Si–Au covalent bonds resulting in the two-dimensional planar Au20 isomer being more stable than its three-dimensional tetrahedral structure. In...

Effect of Si additions on thermal stability and the phase transition sequence of sputtered amorphous alumina thin films

Si-alloyed amorphous alumina coatings having a silicon concentration of 0 to 2.7 at. % were deposited by combinatorial reactive pulsed DC magnetron sputtering of Al and Al-Si (90-10 at. %) split segments in Ar/O2 atmosphere. The effect of Si alloying on thermal stability of the as-deposited amorphous alumina thin films and the phase formation sequence was evaluated by using differential scanning calorimetry and X-ray diffraction. The thermal stability window of the amorphous phase containing 2.7 at. % of Si was increased by more than 100 °C compared to that of the unalloyed phase. A similar retarding effect of Si alloying was also observed for the α-Al2O3 formation temperature, which increased by more than 120 °C. While for the latter retardation, the evidence for the presence of SiO2 at the grain boundaries was presented previously, this obviously cannot explain the stability enhancement reported here for the amorphous phase. Based on density functional theory molecular dynamics simulations and synchrotron X-ray diffraction experiments for amorphous Al2O3 with and without Si incorporation, we suggest that the experimentally identified enhanced thermal stability of amorphous alumina with addition of Si is due to the formation of shorter and stronger Si–O bonds as compared to Al–O bonds.

Ar+ ion irradiation-induced reorganization of colloidal silica nanoparticles in Langmuir–Blodgett monolayers

The Ar+ ion irradiation-induced reorganization of Langmuir–Blodgett monolayers of colloidal silica nanoparticles with a diameter of 220nm and 450nm deposited on silicon substrate is investigated in a wide range of ion fluences. The cluster formation, average cluster size, ion beam-induced charging and discharging of particles, heating effects, the ion beam-induced viscous flow as well as the swelling of the Si substrate as a function of the ion fluence are discussed. Inhomogeneous particle distribution causes strong nonlinear Si swelling inside wide defect-channels between the clusters and linear Si swelling inside narrow channels between the particles. At low ion fluences particle charging and Coulomb repulsion forces govern the particle reorganization process, while at high ion fluences ion beam-induced viscous flow and hydrodynamic forces between the particles and the underlying substrate play major role. Two different types of patterns: smaller compact clusters of few particles and longer chain-like clusters of dozens of particles are observed. The dynamics of the reorganization process in both cases is treated analogous to the dynamics of colloidal suspensions based on the Tanaka–Araki model. The results of the model are comparable to the experimentally observed cluster characteristics.

Al‐Si‐Cu 주조합금의 이차 수지상 간격 및 공정 Si이 기계적 특성에 미치는 영향

The present study aims at investigating the effects of eutectic Si and Secondary dendrite arm spacing (SDAS) on mechanical properties of Al-Si-Cu alloy. Heat treatment and controlling of solidification rate affect to microstructure of Al-Si-Cu alloy. Al-Si-Cu alloy was dissolved in an electric furnace. The alloy cast in STD61 mold which had been pre-heated to 95 °C and 200 °C. Eutectic Si and SDAS were finer as cooling rate increased. Image analysis technique has been utilized to examine the microstructure. Microstructure observation results showed that T6 heat treatment has a strong influence eutectic Si particle morphology. The mechanical properties, such as tensile strength, yield strength, elongation, were improved by ASTM E8 standard. Tensile properties of the Al-Si-Cu alloys prepared by different cooling rates were the same as each other by T6 heat treatment. †(Received December 19, 2013)

Antireflective films with Si–O–P linkages from aqueous colloidal silica: Preparation, formation mechanism and property

The outdoor application of antireflective (AR) films requires not only high transmittance but also such mechanical properties as good abrasion-resistance, certain humidity resistance to resist the damage of the harsh environment. In the study, AR films with excellent performance were prepared by the dip-coating process in which aqueous colloidal silica (ACS) was used as the silica source and orthophosphoric acid as adhesion promoting agent. In the process of heat treatment of the films, the orthophosphoric acid in silica sols firstly transformed into the chain of metaphosphoric acid by the polycondensation reactions and then reacted with surface Si–OH groups from colloidal silica particles and the substrate, resulting in the formation of the numerous Si–O–P cross-linkings and 3SiO2·2P2O5 phase. Because colloidal silica particles were coated with 3SiO2·2P2O5 phase and linked by strong Si–O–P chemical bonds, abrasion-resistant property of films was markedly boosted. When the weight ratio of H3PO4 to silica sols was 2.71%, the pencil hardness grade of corresponding film had reached 6 H. Meanwhile, the average transmittance of the film in the visible spectrum was 97.9% and the weighted average transmittance (WAT) in the full spectrum range was as high as 97.2%, while that of the bare glass substrate was merely 89.6%. Moreover, the average transmittance still remained at around 97.9% after having been soaked in tap water for 30 days.