Weak Si Research Articles

SN 2020udy: A New Piece of the Homogeneous Bright Group in the Diverse Iax Subclass

We present optical observations and analysis of the bright type Iax supernova SN 2020udy hosted by NGC 0812. The evolution of the light curve of SN 2020udy is similar to that of other bright type Iax SNe. Analytical modeling of the quasi-bolometric light curves of SN 2020udy suggests that 0.08 ± 0.01 M ⊙ of 56Ni would have been synthesized during the explosion. The spectral features of SN 2020udy are similar to those of the bright members of type Iax class, showing a weak Si ii line. The late-time spectral sequence is mostly dominated by iron group elements with broad emission lines. Abundance tomography modeling of the spectral time series of SN 2020udy using TARDIS indicates stratification in the outer ejecta; however, to confirm this, spectral modeling at a very early phase is required. After maximum light, uniform mixing of chemical elements is sufficient to explain the spectral evolution. Unlike in the case of normal type Ia SNe, the photospheric approximation remains robust until +100 days, requiring an additional continuum source. Overall, the observational features of SN 2020udy are consistent with the deflagration of a carbon–oxygen white dwarf.

Abundance stratification in type Ia supernovae – VII. The peculiar, C-rich iPTF16abc: highlighting diversity among luminous events

ABSTRACT Observations of Type Ia supernovae (SNe Ia) reveal diversity, even within assumed subcategories. Here, the composition of the peculiar iPTF16abc (SN 2016bln) is derived by modelling a time series of optical spectra. iPTF16abc’s early spectra combine traits of SNe 1999aa and 1991T known for weak Si ii λ 6355 and prominent Fe iii features. However, it differs with weak early Fe iii lines, and persistent C ii lines post-peak. It also exhibits a weak Ca ii H&K feature aligning it with SN 1991T, an observation supported by their bolometric light curves. The early attenuation of Fe iii results from abundance effect. The weakening of the Si ii λ 6355 line, stems from silicon depletion in the outer shells, a characteristic shared by both SNe 1999aa and 1991T, indicating a common explosion mechanism that terminates nuclear burning at around 12 000 km s−1 unseen in normal events. Beneath a thin layer of intermediate mass elements (IMEs) with a total mass of 0.18 M⊙, extends a 56Ni rich shell totaling 0.76 M⊙ and generating a bolometric luminosity as high as Lpeak = 1.60 ± 0.1 × 1043 ergs s−1. Inner layers, typical of SNe Ia, hold neutron-rich elements, (54Fe and 58Ni), totaling 0.20 M⊙. Stable iron, exceeding solar abundance, and carbon, coexist in the outermost layers, challenging existing explosion models. The presence of carbon down to v ≈ 9000 km s−1, totalling ∼0.01 M⊙ unprecedented in this class, links iPTF16abc to SN 2003fg-like events. The retention of 91T-like traits in iPTF16abc underscores its importance in understanding the diversity of SNe Ia.

Enhanced As extraction from paddy soils with high As contamination risk by rice plant upon Si fertilization

Owing to flooded growing conditions and specific physiological characteristics, rice plant is more efficient in As uptake and accumulation, which provides a cost-effective and time-efficient pathway to deplete bioavailable As from paddy soils. In the present study, the enhancing effect of silicon (Si) fertilization on As extraction from heavily contaminated paddy soils by rice was explored Upon incorporation of one weak acid Si fertilizer (AcSF), soil As solubility was significantly promoted by 1.3–1.4-fold, while a slightly increase in porewater As was observed with alkaline soluble Si fertilizer Na2SiO3 (AlSF). With both Si fertilizers applied before transplanting, a relatively low Si/As molar ratio (<100) in soil porewater was obtained, As a result, soil As uptake by rice plant with Si fertilizers was enhanced by 37.2%–171.7% compared to control (CK). Notably, up to 91.6% of the total As in rice plant retained in root with Si fertilization, suggesting the importance of root removal. By harvesting the whole rice plant including roots, soil bioavailable As measured by diffusive gradients in thin films (DGT) declined by 26.9%–31.3% in AlSF treatments relative to CK. Total soil As depletion by the whole rice plant was significantly enhanced from 2.8% in CK to 7.0%–11.2% in Si fertilizer treatments. In this way, 197.5 mg As m−2-232.5 mg As m−2 could be eliminated from soil following one rice-growth season, which was 2.3–2.7-fold higher compared to CK. These results identified the effectiveness of soluble Si fertilizer in enhancing soil As depletion by rice from paddy soils with high As contamination risk, which could serve as a cost-effective strategy with little technical-restriction.

Deciphering the structural origins of high sulfur solubility in vanadium-containing borosilicate glasses

The addition of V2O5 has been long known to increase the sulfur (as SO42-) solubility in borosilicate glasses. However, the mechanism governing this effect is still unknown. Although several studies have been published in the past two decades attempting to decipher the structural origins of increasing sulfur solubility as a function of V2O5 in borosilicate glasses, most of these studies remain inconclusive. The work presented in this paper attempts to answer the question, “Why does V2O5 increase sulfur solubility in borosilicate glasses?” Accordingly, a series of melt-quenched glasses in the system [30 Na2O – 5 Al2O3 – 15 B2O3 –50 SiO2](100-x) – xV2O5, where x varies between 0 – 9 mol.%, have been characterized for their short-to-intermediate range structure and the redox chemistry of vanadium using 11B, 27Al, 51V MAS NMR, Raman, and XPS spectroscopy. The impact of V2O5 on sulfur solubility in glasses has been followed by ICP-OES. The addition of ≤ 5 mol.% V2O5 results in a linear increase in sulfur solubility in the investigated glass system. Based on the results, we hypothesize that adding vanadium to the glasses increases their network connectivity, but reduces the network rigidity by replacing stronger Si–O–Si linkages with weaker Si–O–V linkages and forming (VO3)n-single chains. These modifications to the glass structure increase the flexibility of the network, thus making it possible to accommodate SO42− in their voids/open spaces.

Investigation on microstructure characteristics of tool wear and machined surface mechanisms while milling: kenaf vs glass fiber-reinforced composites

In composites' secondary/machining process, there is still a requirement for a comparative assessment of microstructure features of tool wear and machined surface mechanisms while machining natural fiber against glass fiber-based composites. This experimental study uniquely investigates the dry-end milling of two polypropylene (PP)-based composites made of 30 wt.% discontinuous reinforcements - kenaf and glass fibers (GF). Surprisingly, though, GF are much harder (GF:5.84 GPa > kenaf:0.15 GPa) and abrasive (silicon content, GF:24.16% > kenaf:0.57%) than kenaf inclusions, cutting GF/PP resulted in relatively lower tool wear (≈0.08 mm) but contrarily showed adverse machined surface finishes (>8 μm) depicting tearing-dragging mechanisms with fuzzy textures. This cautions on the appropriate consideration for the tool's life-determining criterion – i.e., whether it should be based on the tool wear or surface finish. While machining GF/PP material, the tool wear growth on the cutting edges was significantly restricted by the formations of continuous-robust microstructural transfer protective film (TPF) characterized by strong Si + O, Al + O, and Fe + O tribo-chemical reactions through the interesting wear mechanisms associated with tribological phenomena. However, thin-patch type microstructural TPFs consisting of weak Si + C bonds occurred on tool edge regions while machining kenaf/PP. Better mechanical properties and fiber-matrix adhesion of GF/PP influenced by fiber dimensions and their higher aspect ratios (GF:27.60 > kenaf:7.20) decisively seem to have a dominant effect on limiting the tool wear. Chip micrographs clarified the cutting of GF/PP and kenaf/PP occurred by predominant melt-extrusion and shearing respectively.

Enhanced Red Emission from Amorphous Silicon Carbide Films via Nitrogen Doping.

The enhanced red photoluminescence (PL) from Si-rich amorphous silicon carbide (a-SiCx) films was analyzed in this study using nitrogen doping. The increase in nitrogen doping concentration in films results in the significant enhancement of PL intensity by more than three times. The structure and bonding configuration of films were investigated using Raman and Fourier transform infrared absorption spectroscopies, respectively. The PL and analysis results of bonding configurations of films suggested that the enhancement of red PL is mainly caused by the reduction in nonradiative recombination centers as a result of the weak Si-Si bonds substituted by Si-N bonds.

Abundance stratification in Type Ia supernovae – VI. The peculiar slow decliner SN 1999aa

ABSTRACT The abundance distribution in the ejecta of the peculiar slowly declining Type Ia supernova (SN Ia) SN 1999aa is obtained by modelling a time series of optical spectra. Similar to SN 1991T, SN 1999aa was characterized by early-time spectra dominated by Fe iii features and a weak Si ii 6355 Å line, but it exhibited a high-velocity Ca ii H&amp;K line and morphed into a spectroscopically normal SN Ia earlier. Three explosion models are investigated, yielding comparable fits. The innermost layers are dominated by ∼0.3 M⊙ of neutron-rich stable iron-group elements, mostly stable iron. Above that central region lies a 56Ni-dominated shell, extending to $v \approx 11\, 000$–$12\, 000$ km s−1, with mass ∼0.65 M⊙. These inner layers are therefore similar to those of normal SNe Ia. However, the outer layers exhibit composition peculiarities similar to those of SN 1991T: The intermediate-mass elements shell is very thin, containing only ∼0.2 M⊙, and is sharply separated from an outer oxygen-dominated shell, which includes ∼0.22 M⊙. These results imply that burning suddenly stopped in SN 1999aa. This is a feature SN 1999aa shares with SN 1991T, and explains the peculiarities of both SNe, which are quite similar in nature apart from the different luminosities. The spectroscopic path from normal to SN 1991T-like SNe Ia cannot be explained solely by a temperature sequence. It also involves composition layering differences, suggesting variations in the progenitor density structure or in the explosion parameters.

Artificial Neurons and Synapses Based on Al/a-SiNxOy:H/P+-Si Device with Tunable Resistive Switching from Threshold to Memory.

As the building block of brain-inspired computing, resistive switching memory devices have recently attracted great interest due to their biological function to mimic synapses and neurons, which displays the memory switching or threshold switching characteristic. To make it possible for the Si-based artificial neurons and synapse to be integrated with the neuromorphic chip, the tunable threshold and memory switching characteristic is highly in demand for their perfect compatibility with the mature CMOS technology. We first report artificial neurons and synapses based on the Al/a-SiNxOy:H/P+-Si device with the tunable switching from threshold to memory can be realized by controlling the compliance current. It is found that volatile TS from Al/a-SiNxOy:H/P+-Si device under the lower compliance current is induced by the weak Si dangling bond conductive pathway, which originates from the broken Si-H bonds. While stable nonvolatile MS under the higher compliance current is attributed to the strong Si dangling bond conductive pathway, which is formed by the broken Si-H and Si-O bonds. Theoretical calculation reveals that the conduction mechanism of TS and MS agree with P-F model, space charge limited current model and Ohm’s law, respectively. The tunable TS and MS characteristic of Al/a-SiNxOy:H/P+-Si device can be successfully employed to mimic the biological behavior of neurons and synapse including the integrate-and-fire function, paired-pulse facilitation, long-term potentiation and long-term depression as well as spike-timing-dependent plasticity. Our discovery supplies an effective way to construct the neuromorphic devices for brain-inspired computing in the AI period.

New SIMS method to characterize hydrogen in polysilicon films

A new analysis protocol for profiling the hydrogen (H) concentration depth distributions in polysilicon (poly-Si) thin films on Si oxide was developed by using secondary ion mass spectrometry (SIMS). Traditional SIMS determination of H concentrations in poly-Si films is to monitor and collect the atomic H−, but this analysis method presents some challenges for providing stable and repeatable H depth profiles, especially, for shallow profiling in thinner poly-Si films on thicker Si oxide films. In this paper, we present a thorough study of the SIMS characterization of H levels in poly-Si thin films on Si oxide. We describe an approach for the use of cluster SiH− instead of atomic H− to determine the H concentrations. The utilization of the SiH− cluster ion minimizes both H adsorption effects on the film surface regions and sample surface charging effects arising from the Si oxide layer underneath, thus enhancing the secondary ion signal stability in poly-Si films, as discussed with secondary ion energy distribution on the samples. This method differs from the conventional SIMS analysis of H in thin films and significantly improves the data quality and accuracy. Fourier transform infrared spectroscopy analysis was used to study the Si–H chemical bonding information for investigating the nature of the SIMS collected SiH− cluster ions. Both the H implant sample with no significant Si–H bonding and the poly-Si samples with high levels of H and the weak Si–H bonding exhibited strong SiH− secondary cluster ion intensities in our studies. This indicates the cluster ion signals arise from either the combination of Si and H ions through the physics formation process or weak chemically bonded Si and H.

Enthalpic interaction promotes the stability of high elastic Cu-Ni-Sn alloys

Enthalpic interaction between the elements determines the stability of the local structures in the alloy system. Multicomponent synergistic effect is expected to improve the thermal stability and the relevant properties by regulating the enthalpic interaction. In this work, the composition of Cu-Ni-Sn alloys is explained by introducing the cluster-plus-glue-atom mode, and the strong and weak enthalpic interaction elements Si and Zn, respectively, are chosen for multi-componentization of Cu-Ni-Sn alloys. The results demonstrate that the synergistic effect of Zn and Si improves the stability of both the Cu matrix and D022 or L12-γ′ phase, inhibits the discontinuous precipitation effectively and gains a notable higher strength-over-resistivity ratio (HR / ρR) than the Cu-15Ni-8Sn (wt. %) (C72900) alloy. After adding Si and Zn, the reinforcing enthalpic interaction between the elements is the crucial factor for the stability enhancement of the alloys, and it is embodied by two aspects: (a) the reducing elastic strain energy in the solution treated alloys; (b) the more homogeneous surface potential and the higher work function in the age treated alloys. Additionally, Compared with the Cu80Ni15Sn5 alloy that based on the ideal cluster formula, the Cu79.68Ni15.63Sn4.69 alloy, based on the modified cluster formula: {[Cu-CuxNi12-x]Cu3}a{[Sn-NiyCu12-y]Sn3}16-a, possesses a preferable thermal stability whatever solution treated or age treated state, and exhibits a decreasing amount of discontinuous precipitation although has a slightly lower HR / ρR, which is beneficial to the improvement of the workability of the alloys. The modified cluster formula is more suitable for the compositional design of Cu-Ni-Sn alloys. The work provides an effective theoretical and experimental basis for the composition design of high stability Cu-Ni-Sn alloys.

Ru‐Catalyzed Cross Dehydrogenative Coupling Leading to Si−O and Si−S Bond Formations and Also Stimulating an Alternative Scope for Hydrogenation of C=O, C=N and N=N Bonds

AbstractReaction pathways involved in catalytic Cross Dehydrogenative Coupling (CDC) reactions leading to formation of Si−O and Si−S bonds have been formulated and explored theoretically using Density Functional Theory (DFT). The advantage of the weak Si−H bond has been exploited to carry out coupling with water, alcohol and thiol, along with H2 release. Ru complex, [K(dme)2][Ru(H)(trop2dad)] when reacts with water generates a neutral complex, [Ru(trop2dad)]. This neutral complex has been employed to act as a catalyst in CDC reactions. It has also been found that the complex, [Ru(H2)(trop2dad)] formed within the catalytic cycle may also be used for hydrogenation of C=O, C=N and N=N bonds. The optimized geometries of all the complexes and transition states have been obtained using wB97xd functional in conjunction with 6‐31++G(d,p) basis set. The whole assisting phenomena in solvent medium has been investigated through the implementation of conductor‐like screening solvation model (COSMO) considering tetrahydrofuran as the bulk solvent medium. The Turnover frequency (TOF) has been calculated by Energetic Span Model. The theoretical investigation extends the role of the ruthenium catalyst to the regime of ‘element to element’ bond formation, along with H2 release, which may be significant in the field of energy storage, and also triggers an alternative possibility of hydrogenation of carbonyls, imines and diazo compounds.

Low-energy high-flux ion bombardment-induced interfacial mixing during Al2O3 plasma-enhanced atomic layer deposition

We investigated the formation mechanism of interfacially mixed AlSiOx films on Si surfaces under low-energy (&amp;lt;15 eV), high-flux (&amp;gt;4 × 1015 cm−2 s−1) O2+ ion bombardment during Al2O3 plasma-enhanced atomic layer deposition. When high-dose O2+ ions (&amp;gt;1 × 1017 cm−2 cycle−1) were incident on the growing film surface during the oxidation steps in Al2O3 atomic layer deposition (ALD), interfacially mixed films with thin (∼0.8 nm) SiOx interlayers were formed on Si surfaces. The deposited films possessed a layered structure of Al2O3/AlSiOx/AlOx layers. In order to reveal the formation mechanism, films deposited during the early stages of ALD were evaluated using an angle-resolved x-ray photoelectron spectroscope. In the first oxidation step, thin, low-density SiOx films with weak Si–O bonds containing excess oxygen were formed on the Si surface. In subsequent oxidation steps, adsorbed Al atoms on the surface were knocked on by the energetic ions and penetrated into the SiOx film. As a result, Al atoms were taken into SiOx. Some of the Al atoms accumulated near the interface. After several tens of cycles, ordinary Al2O3 films were deposited on the Si-rich layers. Thus, the films with a layered structure of Al2O3/AlSiOx/AlOx layers were formed on the Si substrate.

Structure, stability, MEP, NICS, reactivity, and NBO of Si–Ge nanocages evolved from C20 fullerene at DFT

We have performed systematic theoretical studies of C20 and its SinGenC20-2n heterofullerenic derivatives with n = 1–10, at the density functional theory. Vibrational frequency analysis confirms that except for Si5Ge5C10, Si8Ge8C4, and Si10Ge10, other systems are true minima and none of the 12 computed heterofullerenes collapses to open deformed as segregated nanocage. Isolating the Si–Ge hetero bonds through C=C double bond and/or one carbon atom is an appropriate approach for reaching highly substituted stable heterofullerenes, since it prevents weak Si–Si and Ge–Ge homo bonds. The calculated band gap, ionization potential, and atomization energy of Si1Ge1C18 shows it as the best insulated heterofullerene. Binding energy, and absolute values of heat of atomization of computed heterofullerene decrease as number of substituting Si–Ge unit increases. Henceforth, in contrast to the common belief that thermodynamically stable species are not always kinetically stable, here isolable or extractable Si1Ge1C18 heterofullerene is stable from both viewpoints. Contrary, Si10Ge10 that unfortunately suffers from lack of carbon participation, is revealed as the most chemically reactive heterofullerene and the best optically active via increasing its hyperpolarizability. Exclusive of Si10Ge10, substitutional doping of other heterofullerenes leads to a high NBO charge distribution upon their surfaces. We are very pleased to state that isolating the Si–Ge single bonds by intermediation of only one carbon atom is an applicable strategy for obtaining the highest atomic charge distributions on C, Si, and Ge atoms of Si6Ge6C8 as suitable hydrogen storage. Evaluating nucleus independent chemical shift (NICS) values at the cage centers clearly show the highest aromatic character of Si1Ge1C18 species followed by Si2Ge2C16 (− 48.76 and − 35.42 ppm compared to − 19.61 for the pure carbon cage, C20).

Search for transient optical counterparts to high-energy IceCube neutrinos with Pan-STARRS1

In order to identify the sources of the observed diffuse high-energy neutrino flux, it is crucial to discover their electromagnetic counterparts. To increase the sensitivity of detecting counterparts of transient or variable sources by telescopes with a limited field of view, IceCube began releasing alerts for single high-energy (Eν &gt; 60 TeV) neutrino detections with sky localisation regions of order 1° radius in 2016. We used Pan-STARRS1 to follow-up five of these alerts during 2016–2017 to search for any optical transients that may be related to the neutrinos. Typically 10–20 faint (miP1 ≲ 22.5 mag) extragalactic transients are found within the Pan-STARRS1 footprints and are generally consistent with being unrelated field supernovae (SNe) and AGN. We looked for unusual properties of the detected transients, such as temporal coincidence of explosion epoch with the IceCube timestamp, or other peculiar light curve and physical properties. We found only one transient that had properties worthy of a specific follow-up. In the Pan-STARRS1 imaging for IceCube-160427A (probability to be of astrophysical origin of ∼50%), we found a SN PS16cgx, located at 10.0′ from the nominal IceCube direction. Spectroscopic observations of PS16cgx showed that it was an H-poor SN at redshiftz = 0.2895 ± 0.0001. The spectra and light curve resemble some high-energy Type Ic SNe, raising the possibility of a jet driven SN with an explosion epoch temporally coincident with the neutrino detection. However, distinguishing Type Ia and Type Ic SNe at this redshift is notoriously difficult. Based on all available data we conclude that the transient is more likely to be a Type Ia with relatively weak Si IIabsorption and a fairly normal rest-framer-band light curve. If, as predicted, there is no high-energy neutrino emission from Type Ia SNe, then PS16cgx must be a random coincidence, and unrelated to the IceCube-160427A. We find no other plausible optical transient for any of the five IceCube events observed down to a 5σlimiting magnitude ofmiP1 ≈ 22 mag, between 1 day and 25 days after detection.

Optical and UV studies of type Ia supernovae SN 2009ig and SN 2012cg

Abstract We present an extensive optical–ultraviolet photometry and analysis of a series of optical spectra of type Ia supernovae SN 2009ig and SN 2012cg. The observations range from −15 to +185 d for SN 2009ig and from −14 to 316 d for SN 2012cg, with respect to maximum light in B band. Both SN 2009ig and SN 2012cg exhibit similar properties. They have similar decline rate parameter (Δm15(B)true = 0.92 ± 0.04 for SN 2009ig and 0.93 ± 0.06 for SN 2012cg) and B band peak absolute magnitude (−19.45 ± 0.40 mag for SN 2009ig and −19.50 ± 0.31 mag for SN 2012cg). Their early spectra show high-velocity features in Si ii and Ca ii lines. The strong Fe iii, Si iii, and weak Si ii λ5972 line during pre-maximum phase are indicative of hot photosphere. The post-maximum velocity evolution shows a plateau like phase with velocities ∼13 000 km s−1 for SN 2009ig and ∼10 000 km s−1 for SN 2012cg. Both events show spectral evolution similar to normal SNe Ia and fall in LVG and Core Normal subgroup. Both have smaller strength ratio [$\cal R$(Si ii) = 0.17 for SN 2009ig and 0.20 for SN 2012cg] consistent with smaller Δm15(B). Peak bolometric luminosities ($\log L_\text{bol}^\text{max}$) of these events are estimated as 43.17 ± 0.16 and 43.24 ± 0.11 erg s−1 suggesting that 0.60 ± 0.20 M⊙ of 56Ni was synthesized in the explosion of SN 2009ig and 0.72 ± 0.31 M⊙ in SN 2012cg.

Effects of Silicon on the Growth, Photosynthesis and Chloroplast Ultrastructure of Oryza sativa L. Seedlings under Acid Rain Stress

Silicon (Si) is a beneficial element for plants and can increase plant resistance. In the present work, a hydroponic experiment was carried out to study the effects of Si on the growth and photosynthesis of rice (Oryza sativa L.) seedlings under simulated acid rain (SAR) stress. The growth, photosynthesis and chloroplast ultrastructure of rice seedlings treated with combined or single weak SAR (pH 4.0) and/or Si (1, 2 or 4 mM) were improved. Spraying with moderate or severe SAR (pH 3.0 or 2.0) significantly inhibited the growth and photosynthesis and severely damaged the chloroplast ultrastructure of rice seedlings. The incorporation of exogenous Si increased the growth and photosynthesis and improved the chloroplast ultrastructure of rice seedlings treated with moderate or severe SAR (pH 3.0 or 2.0). The 2.0 mM Si treatment had more significant promoting or alleviating effects than the 1 and 4 mM Si treatments. The stomatal conductance (Gs), chlorophyll content, maximum quantum efficiency of PSII photochemistry (Fv/Fm), actual photochemical quantum efficiency of PSII photochemistry (Y) and chloroplast ultrastructure were improved with the addition of Si to the SAR treatment, which indicated that the positive effect of Si on photosynthesis was partly associated with stomatal and non-stomatal factors. Thus, Si fertilization improves rice resistance to acid rain.

Study of Dielectric properties for porous silicon prepared by Anodization

The nanostructure for porous silicon (PS) films is produced by anodization of p-type silicon chip with current consistency (15 mA/cm2), etching time about 10 min and HF concentration (32%) to the formation nanosized pore order with a dimension of around few hundreds nanometric. The films were featured by the measurement of atomic force microscopy (AFM) in the Baghdad university, X-Ray diffraction (XRD) and FTIR spectroscopy characteristics in the technological university. I am having appraising crystallites size from XRD about nanoscale for porous silicon and AFM proves the nanometric size. Chemical fictionalizations through the electrochemical etching clear on superficies chemical structure of PS. The etching possess disproportionate microstructures that include Si-H clusters in (Si3-SiH), sparse in amorphous silica matrix and Si-H2 scissor mode. From the FTIR testing appeared that the Si suspending bonds of the as- produced PS layer have massive quantities of Hydrogen to form weak Si–H bonds related to Si–H stretch (Si3-SiH) and Si-H stretch (Si2-SiH). The AC electrical properties were measured with LCR meter analyzer the frequency between 50 Hz and 5 MHz. for capacitance, dielectric and loss tangent (tan δD) to balk silicon and porous silicon have been done in the ministry of science and technology.

Hypercoordinated Oligosilanes Based on Aminotrisphenols.

The hypercoordinated silicon chlorides ClSi[(o-OC6H4)3N] (3) and ClSi[(OC6H2Me2CH2)3N] (5) were used for the synthesis of catenated derivatives (Me3Si)3SiSi[(o-OC6H4)3N] (9), (Me3Si)3SiSiMe2SiMe2Si(SiMe3)2Si[(o-OC6H4)3N] (11), and (Me3Si)3SiSi[(OC6H2Me2CH2)3N] (13) in reactions with (Me3Si)3SiK·THF (7) or (Me3Si)3SiK·[18-crown-6] (8). It was found that the nature of the (Me3Si)3SiK solvate determines the product of interaction, resulting in the formation of (Me3Si)3Si(CH2)4OSi[(OC6H2Me2CH2)3N] (12) or 13. Compounds obtained were characterized using multinuclear NMR and UV–vis spectroscopy and mass spectrometry. The molecular structures of 3, 9, and 11–13 were investigated by single-crystal X-ray analysis, featuring hypercoordinated Si atoms in a trigonal-bipyramidal coordination environment with O atoms in the equatorial plane. The structure of the side product [N(CH2C6H2Me2O)3Si]2O (6) was also studied, indicating highly tetrahedrally distorted trigonal-bipyramidal environment at the Si atoms, which was confirmed by crystal density functional theory calculations indicating the very weak Si ← N interaction. The Si···N interatomic distances span a broad range (2.23–2.78 Å). The dependence of structural and NMR parameters for hypercoordinated catenated compounds from the type of the ligand was established.

Exploring the structural stability and mechanical properties of TM5SiB2 ternary silicides

The improvement of the balance between ductility and strength is still a big dilemma for high-temperature materials. To improve the correlation between ductility and strength, we apply the ab-initio calculations to investigate the crystal structure, elastic properties and ductile-or-brittle behavior of TM5SiB2 ternary silicides. The calculated results show that Mo5SiB2, Cr5SiB2, W5SiB2 and Re5SiB2 are dynamically stable. In comparison to binary silicides, TM5SiB2 shows the strong volume deformation resistance and high elastic stiffness. In particular, TM5SiB2 exhibits better ductility. The calculated electronic structure reveals that the high elastic modulus of TM5SiB2 is attributed to the formation of TM‒B bond and B‒B covalent bond. However, the ductility of TM5SiB2 derives from the weak TM‒Si bond along the shear direction. Therefore, we propose that the adjustment of bond type, bond orientation and bond strength of ternary silicides by controlling the crystal structure is beneficial for improving the balance between strength and ductility.

Electronic structures of Al–Si clusters and the magic number structure Al8Si4

ABSTRACTThe low-energy structures of Al8Sim (m = 1–6) have been determined by using the genetic algorithm combined with density functional theory and the Second-order Moller-Plesset perturbation theory (MP2) models. The results show that the close-packed structures are preferable in energy for Al–Si clusters and in most cases there exist a few isomers with close energies. The valence molecular orbitals, the orbital level structures and the electron localisation function (ELF) consistently demonstrate that the electronic structures of Al–Si clusters can be described by the jellium model. Al8Si4 corresponds to a magic number structure with pronounced stability and large energy gap; the 40 valence electrons form closed 1S21P61D102S21F142P6 shells. The ELF attractors also suggest weak covalent Si–Si, Si–Al and Al–Al bonding, and doping Si in aluminium clusters promotes the covalent interaction between Al atoms.