Strong Si Research Articles

Visible-light photoredox-catalyzed selective carboxylation of C(sp3)−F bonds with CO2

Visible-light photoredox-catalyzed selective carboxylation of C(sp3)−F bonds with CO2

New Constraints on the Physical and Biological Controls on the Silicon Isotopic Composition of the Arctic Ocean

The silicon isotope composition of silicic acid, δ30Si(OH)4, in the deep Arctic Ocean is anomalously heavy compared to all other deep ocean basins. To further evaluate the mechanisms leading to this condition, δ30Si(OH)4 was examined on US GEOTRACES section GN01 from the Bering Strait to the North Pole. Isotope values in the polar mixed layer showed a strong influence of the transpolar drift. Drift waters contained relatively high [Si(OH)4] with heavy δ30Si(OH)4 consistent with the high silicate of riverine source waters and strong biological Si(OH)4 consumption on the Eurasian shelves. The maximum in silicic acid concentration, [Si(OH)4], within the double halocline of the Canada Basin formed a local minimum in δ30Si(OH)4 that extended across the Canada Basin, reflecting the high-[Si(OH)4] Pacific source waters and benthic inputs of Si(OH)4 in the Chukchi Sea. δ30Si(OH)4 became lighter with the increase in [Si(OH)4] in intermediate and deep waters; however, both Canada Basin deep water and Eurasian Basin deep water were heavier than deep waters from other ocean basins. A preliminary isotope budget incorporating all available Arctic δ30Si(OH)4 data confirms the importance of isotopically heavy inflows in creating the anomalous deep Arctic Si isotope signature, but also reveals a surprising similarity in the isotopic composition of the major inflows compared to outflows across the main gateways connecting the Arctic with the Pacific and the Atlantic. This similarity implies a major role of biological productivity and opal burial in removing light isotopes entering the Arctic Ocean from rivers.

Interactions, space presentations, blocks and cross products

Physics counts four basic forces, the electromagnetic EMI, weak WI, strong SI interactions and gravity GR. The first three are provided with a unified theory which partly needs revision and has the symmetry U(1)xSU(2)xSU(3). In this article their space presentations are described in order to inlcude a theory for gravity which cannot be added directly to the standrd model. There are many instances of gravitational actions which are different from the other three interactions. Gravity uses geometrical models beside spactime, often projective, including stereographic and spiralic orthogonal subspace projections. Real and complex cross products, symmetries which belong to the complex Moebius transformation subgroups, complex cross ratios, Gleason frame GF measures, dihedrals nth roots of unity with symmetris are some new tools (figure 14) for a new gravity model. The basic vector space is 8-dimensional, but beside the usual vector addition and calculus there are different multiplications added. The author uses complex multiplications in the complex 4-dimensional space C4 for calculus. The SU (3) multiplication of GellMann 3x3-matrices is used for C³ and its three 4-dimensional C² projections. Projective spaces are CP² for nucleons and a GR Higgs plane P² and projective measuring GF‘s which have 3-dimensional, orthogonal base vectors like spin. The doubling of quaternionic spacetime to octonians has a different multiplication and seven GF‘s which partly occur in physics as cross product equations. Beside the real, the complex cross product extends the spacetime dimensions from 4 to 8. Consequences are that there are many 3-dimensional, many 4-dimensional, some 6-dimensional and also projective 5-dimensional spaces in which the actions of gravity can then be described. Spacetime is for this not sufficient. No symmetry can be muliplied to the standard model since the new symmetries belong to different geometries and are not directly related to a set of field quantums like one photon for EMI, three weak bosons (or four) for WI, eight gluons for SI. GR has graviton waves similar to EMI waves and in quasiparticle form rgb-graviton whirls, for mass Higgs bosons, maybe also solitons (density as mass per volume changing). They attribute to a distance metric between two points (kept fixed) an amplitude density (operator} which changes the metrical diameter of the volume, but not the mass.

Enhanced interfacial reaction of silicon carbide fillers onto the metal substrate in carbon nanotube paste for reliable field electron emitters

Adhesion of carbon nanotube (CNT) onto a cathode substrate is very crucial for field electron emitters that are operating under high electric fields. As a supporting precursor of CNT field emitters, we adopted silicon carbide (SiC) nano-particle fillers with Ni particles and then enhanced interfacial reactions onto Kovar-alloy substrates through the optimized wet pulverization process of SiC aggregates for reliable field electron emitters. As-purchased SiC aggregates were efficiently pulverized from 20 to less than 1 micro-meter in a median value (D50). CNT pastes for field emitters were distinctively formulated by a mixing process of the pulverized SiC aggregates and pre-dispersed CNTs. X-ray photoelectron spectroscopy studies showed that the optimally pulverized SiC-CNT paste-emitter had a stronger Si 2p3/2 signal in the Ni2Si phase than the as-purchased one. The Si 2p3/2 signal would represent interfacial reaction of the SiC nano-particle onto Ni from the CNT paste and the Kovar substrate, forming the supporting layer for CNT emitters. The optimal paste-emitter even in a vacuum-sealed tube exhibited a highly reliable field emission current with a high current density of 100 mA cm−2 for over 50 h along with good reproducibility. The enhanced interfacial reaction of SiC filler onto the metal substrates could lead to highly reliable field electron emitters for vacuum electronic devices.

Chemoselective Amide-Forming Ligation Between Acylsilanes and Hydroxylamines Under Aqueous Conditions.

We report the facile amide-forming ligation of acylsilanes with hydroxylamines (ASHA ligation) under aqueous conditions. The ligation is fast, chemoselective, mild, high-yielding and displays excellent functional-group tolerance. Late-stage modifications of an array of marketed drugs, peptides, natural products, and biologically active compounds showcase the robustness and functional-group tolerance of the reaction. The key to the success of the reaction could be the possible formation of the strong Si-O bond via a Brook-type rearrangement. Given its simplicity and efficiency, this ligation has the potential to unfold new applications in the areas of medicinal chemistry and chemical biology.

Chemoselective Amide‐Forming Ligation Between Acylsilanes and Hydroxylamines Under Aqueous Conditions

AbstractWe report the facile amide‐forming ligation of acylsilanes with hydroxylamines (ASHA ligation) under aqueous conditions. The ligation is fast, chemoselective, mild, high‐yielding and displays excellent functional‐group tolerance. Late‐stage modifications of an array of marketed drugs, peptides, natural products, and biologically active compounds showcase the robustness and functional‐group tolerance of the reaction. The key to the success of the reaction could be the possible formation of the strong Si−O bond via a Brook‐type rearrangement. Given its simplicity and efficiency, this ligation has the potential to unfold new applications in the areas of medicinal chemistry and chemical biology.

Functional Possibilities of Strong Compensated Leggier Si with the different Deep Energetic Levels Impurities in Electronics

Functional Possibilities of Strong Compensated Leggier Si with the different Deep Energetic Levels Impurities in Electronics

Modelling spectra of MN112

ABSTRACT MN112 is a Galactic luminous blue variable (LBV) candidate with a circumstellar nebula. P Cygni was the first LBV discovered, and was recorded during major eruptions in the 17th century. The stars have similar spectra with strong emission hydrogen lines, He i, N ii, Si ii, and Fe iii lines. We present the results of spectroscopic analysis and modelling of MN112 spectra. We obtained the main stellar parameters and chemical abundances of MN112 and compared them with those of P Cygni. Atmosphere models were calculated using the non-local thermodynamic equilibrium radiative transfer code cmfgen. We have used spectra of MN112 obtained with the 3.5-m telescope at the Observatory of Calar Alto and 3.5-m ARC telescope at the Apache Point Observatory. P Cygni spectra were taken with the 6-m BTA telescope. We have found the best fit of the observed spectrum with the model at temperature $T_{\text{eff}}= 15\, 200$ K, clumping-corrected mass-loss rate $\dot{M}f^{-0.5}=5.74 \times 10^{-5}\, \mathrm{M}_{\odot }\text{yr}^{-1}$, filling factor f = 0.1, luminosity $L=5.77 \times 10^5\, \mathrm{L}_{\odot }$ for MN112. The ratio of helium to hydrogen He/H is 0.27 (by the number of atoms) with nitrogen overabundance (XN/X⊙ = 6.8) and an underabundance of carbon (XC/X⊙ < 0.1).

Interfacial coupled design of epitaxial Graphene@SiC Schottky junction with built-in electric field for high-performance anodes of lithium ion batteries

Abstract In-situ epitaxial graphene (EG) strategy is adopted to activate the electrochemically inactive silicon carbide (SiC) by constructing Schottky junction for high-performance anode of lithium-ion battery (LIB). Raman and Hall measurements confirm the high quality and electronic mobility of EG. Refined structural characterization (XPS and XANES) and theoretical analysis indicate that the interfacial coupled structure exhibits Schottky junction with an inherent built-in electric field, and the strong interfacial Si–C interaction could reinforce the interfacial coupling. This prototype can systematically comprehend interfacial electronic properties and transport mechanisms. As a proof-of-concept study, this interfacially designed Schottky junction is demonstrated to promote both the surface electron densities and charge carriers transportation efficiency for LIB anodes. Even at 10.0 A g−1, the EG@SiC anode can still deliver a capacity of 322.1 mA h g−1. The ex-situ XRD, HRTEM, and XPS analysis confirm the reversible intercalation reaction mechanism and excellent structural stability. The proposed strategy of constructing Schottky junction through interlayer engineering can construct advanced SiC-based electrodes for high-performance rechargeable batteries.

Latent (Pro)Nucleophiles in Enantioselective Lewis Base Catalyzed Allylic Substitutions

The use of latent nucleophiles, which are molecules that are not nucleophilic but can be activated to act as a nucleophile at an opportune time during the reaction, expands the scope of Lewis base catalyzed reactions. Here, we provide an overview of the concept and show examples of applications to N- and C-centered nucleophiles in allylic substitutions. N- and C-silyl compounds are superior latent (pro)nucleophiles in Lewis base catalyzed reactions with allylic fluorides in which the formation of the strong Si–F bond serves as the driving force for the reactions. The latent (pro)nucleophiles ensure high regio­selectivity in these reactions and enable enantioselective transformations of Morita–Baylis–Hillman adducts by the use of common chiral Lewis base catalysts.1 Introduction2 Substitution of MBH Carbonates3 The Concept of Latent (Pro)Nucleophiles4 Enantioselective Allylation of N-Heterocycles5 Enantioselective Phosphonyldifluoromethylation of Allylic Fluorides6 Conclusion

Interface defect engineering for high-performance MOSFETs with novel carrier mobility model: Theory and experimental verification

As the conventional hydrogen-termination method has a limited ability to improve the interface quality between SiO2 and its Si substrate, an alternative termination method to reduce the influence of interface states is necessary. Interface engineering using first-principles calculations to suppress the influence of interface states is proposed based on the findings that silicon with dangling bonds is their primary origin. First-principles calculations indicate that the interface states can be terminated with oxygen when incorporated into the SiO2/Si interface without additional oxidation, which generates other interface states from an appropriate oxygen-anneal process. It is experimentally shown that such an oxygen termination can be realized in slow and low-temperature annealing, and the oxygen-termination method is a promising alternative for hydrogen termination. The stronger Si–O bond introduced from the oxygen termination compared with the Si–H bonds from hydrogen termination ensures a better interface quality. As one oxygen atom terminates two silicon atoms, the oxygen-termination method can efficiently suppress the number of interface defects compared with hydrogen and fluorine termination. The mobility degradation due to the interface states was improved more from oxygen termination than from hydrogen termination because the strength of Coulomb scattering due to Si–O dipoles is reduced from the heavier oxygen mass. Theoretical predictions were verified using experiments, indicating that the oxygen-termination method under appropriately optimized annealing conditions (speed and temperature) is a promising candidate to improve the interface quality by reducing the influence of interface states.

Unveiling the first post-graphene member of silicon nitrides: A novel 2D material

We have theoretically predicted a new two-dimensional allotrope of the silicon nitrides family, being found during our effort to construct a nanosheet from the unit cell of hexagonal β-Si3N4. Electronic structure calculations at the DFT-PBE level of theory have revealed that this new material is an insulator with a band gap of about 4 eV. Finite-temperature density functional molecular dynamics simulations applied at the unit-cell level have also verified that the new compound is thermodynamically more stable than the layered form of hexagonal β-Si3N4 due to having both stronger Si–N bonds and a more compact crystal structure. Furthermore, phonon dispersion calculations have tested and proved the dynamic stability of the new monolayer to a great accuracy with accordingly no soft modes being observed. Results obtained within the quasi-harmonic approximation also demonstrate that our predicted material is indeed a Debye solid with a low-temperature specific heat proportional to T2 as a consequence of its two-dimensional nature, possessing a Debye temperature of about 860 K considerably higher than those of α,β, and γ phases of Si3N4.

Rapid Shifts in Chemical and Isotopic Compositions of Sediment Pore Waters in the Amami Sankaku Basin in Response to Initial Arc Rifting in the Mid‐Oligocene

AbstractPore waters were recovered from the sediment cores drilled in the back‐arc Amami Sankaku Basin (ASB) during the International Ocean Discovery Program Expedition 351. The sediment sequence is composed of the recent mud and ooze from late Oligocene/early Miocene accumulated at 7 m/Ma and rapid deposition of thick volcaniclastic sequence at 50 m/Ma. Such variations are reflected in the evolutions of chemical and isotopic compositions of pore waters. Cl and Ca concentrations in pore waters increased rapidly with depth and became enriched in the deep portion. Before arc rifting, extremely high deposition rates of volcaniclastic gravity‐flow sediments from the nearby Kyushu‐Palau arc into the ASB resulted in strong alteration, removing Mg and Si from pore waters. Mg concentrations were initially almost zero but abruptly shifted to substantial increases after ~29.5 Ma, indicating extended rifting of the active volcanic axis from the ASB. The δ18O and δD values of pore waters also evolved from more depleted and wide range to more positive and narrow range as a response to reduced alteration and increasing influence of seawater. Concentrations of Si and Mn in pore waters rapidly increased since ~29.5 Ma but suddenly declined at ~17.5 Ma due to the cessation of input of volcaniclastic materials. Covariations of Ca and Mg in pore waters are very similar to those in the back‐arc West Philippine Basin but significantly different from those in the Izu‐Bonin fore‐arc basin. Variations in chemical and isotopic compositions of pore waters can assist the reconstruction of tectonic activities.

Structural and mechanical properties of ternary MgCaSi phase: A study by density functional theory

The structural, elastic, and electronic properties of multi-performance ternary phase MgCaSi have been investigated by density functional theory. The present results show that MgCaSi is thermodynamically and mechanically stable. The derived elastic constants indicate that the c axis is the easiest to compress, followed by the a and b axes. The bulk, shear, and Young’s moduli of MgCaSi are higher than these of the mother phase Ca2Si, demonstrating that the hardness of MgCaSi has been favorably improved. The higher Debye temperature of MgCaSi also indicates stronger interatomic interactions and better thermal conductivity. Although MgCaSi exhibits less brittleness based on Pugh’s empirical formula, Poisson’s ratio, and the Cauchy pressure, orthorhombic MgCaSi possesses lower anisotropy than Ca2Si based on several criteria. To reveal the bonding nature of MgCaSi, the electronic structures are further investigated. It is found that the strong Si−Si bond plays a significant role for structural stability and elastic properties.

Magnesiothermic reduction of SiO2f/SiO2 composites for brazing with Nb using AgCuTi

Brazing SiO2f/SiO2 composites is always associated with the problem of poor wettability, and directly brazing SiO2f/SiO2 to Nb with AgCuTi cannot obtain the high strength joints. To overcome the problem, strong binding Si layer was synthesized on SiO2f/SiO2 surface by magnesiothermic reduction method. Results show that the content of Si raised to twice higher than original composites. The contact angle of AgCuTi on SiO2f/SiO2 composites was decreased from 95.9° to 34.7° via reducing SiO2 into Si. Due to the reaction of Si and Mg, SiO2 matrix were corroded to some extent inducing the zigzag reaction layer in the joints. With the increasing of Si content, O contained compounds in reaction layer were replaced by Ti-Si phase. And low thermal expansion Ti5Si3 particles would disperse near the reaction layer to maintain the stability of reaction layer. The highest shear strength reached 38.3 MPa with 4 h reducing treatment.

Topological analysis on structure and dynamics of SiO2 liquid with the help of Si-particle and O-particle statistics

A large model of silica liquid has been produced at temperature of 3000 K and ambient pressure by molecular dynamics (MD) simulation. We propose a topological analysis based on shell-core particles. Our result shows that the dynamics is spatially sparse due to the SiO4 ↔ SiO5 and OSi2 ↔ OSi3 transformations happen non-uniformly in the network structure. The simulation reveals Si-particles having 2 Si and O-particles containing up to 14 O. The network structure comprises clusters of particles which occupy micro-regions with pure compositions. The number of atoms in a Si-cluster varies from 2 to 7, and the O-cluster contains up to 63 atoms. We also found particles and clusters of particles which are stable for a long time. The stable particle and cluster of particles occupy micro-regions where the atoms of the same ion type are confined. The strong chemical Si–O bonds between core and shell atoms prevent those particles from breaking apart. The atoms of rigid SiO4 tetrahedrons are not uniformly distributed in the network structure, but instead they gather into domains containing the rigid Si–O subnets, stable particles and clusters of stable particles.

Facile preparation of hyperbranched polysiloxane‐grafted carbon fibers with improved interfacial strength of silicone resin composites

AbstractNew hybrid carbon fibers (CFs) were facilely prepared via in situ synthesizing hyperbranched polysiloxane with epoxy groups onto the fiber surface with the aim to enhance interfacial strength of composites. CFs were grafted with phenyl amine groups through an aryl diazonium reaction, and then modified with hyperbranched polysiloxane obtained by the sol‐gel polymerization of γ‐glycidyloxypropyltrimethoxysilane. Surface structures of different CFs were characterized by Raman spectroscopy and X‐ray photoelectron spectroscopy, indicating the successful modification. The introduced hyperbranched polysiloxane enhanced fiber roughness, polarity, wettability, and surface free energy. Hence, the interfacial shear strength and impact toughness of polysiloxane modified composites (CF‐g‐Polysiloxane) increased sharply compared with those of untreated composites. Moreover, Interfacial reinforcing and toughening mechanisms have also been studied, and polysiloxane modification maintained fiber tensile strength. The obvious improvement of anti‐hydrothermal aging behaviors after modification could be due to the introduction of strong SiOSi bonds at the interface.

Syngas production via CO2 reforming of CH4 over Ni-based SBA-15: Promotional effect of promoters (Ce, Mg, and Zr)

The promotional effect of different types of metals (Ce, Mg, and Zr) over Ni/SBA-15 which synthesized using ultrasonic co-impregnation technique were scientifically evaluated via CO2 reforming of CH4 (CRM). Characterizations including XRD, BET, FTIR, CO2-TPD were done to examine their physical attributes, metal-support interactions, and basicity properties. XRD results suggested that NiO particles were not distributed homogeneously within the confined framework of SBA-15 for Ni-Ce/SBA-15. Nevertheless, Mg and Zr promoters could effectively improve Ni dispersion over the SBA-15's siliceous framework and controlled the NiO crystallize sizes. The smallest NiO crystallite size of 9.3 nm was obtained by Ni-Zr/SBA-15. BET results verified the alteration of pore structure without changing the ordered structure of SBA-15 upon promoter addition. FTIR results suggested the partial transformation of Si–OH groups to the Si–O–X bond (X = Ce, Mg and Zr), whereas, CO2-TPD results confirmed the moderate basic sites present in Ni-Zr/SBA-15. H2-TPR evidenced the strongest metal-support interaction in Ni-Zr/SBA-15 owing to its high temperature reduction behaviour. At operating condition of P = 1.0 bar and WHSV = 15,000 mLg−1h−1, catalytic performance and stability ascended the trend of un-promoted < Ce-promoted < Mg-promoted < Zr-promoted Ni/SBA-15, in which Zr-promoted Ni/SBA-15 manifested the best catalytic activity (CO2 conversion = 93.8%; CH4 conversion = 88.3%; H2/CO ratio = 0.82). The ascendency catalytic activity and stability of Ni-Zr/SBA-15 catalyst were attributed to its favourable properties such as strong Si–O–Zr bond formation, smallest NiO crystallite size and a moderate amount of basic sites, which crucial for sintering restriction of NiO particles and carbon deposition, thus facilitated CRM reaction.

Role of Hydrogen Flow Rate on Microstructure of a-Si:H(n) Films: Spectroscopic Ellipsometry Studies

The influence of hydrogen flow rate on the microstructure and optical properties of phosphorous doped hydrogenated amorphous silicon (a-Si:H(n)) films is studied through spectroscopic ellipsometry (SE). A series of a-Si:H(n) films were deposited using radio frequency plasma enhanced chemical vapour deposition (RFPECVD) technique by varying the hydrogen flow rate (HFR) in the range of 30–80 SCCM. The SE measurements showed a shift in peak position of pseudo dielectric function of these films from 3.6 eV (for pure a-Si:H) to 4.1 eV with a shoulder peak at 3.4 eV (nanocrystallites embedded a-Si:H) as the hydrogen flow rate was increased. A systematic increase in crystalline fraction along with a decrease in void fraction was observed as HFR was increased up to 70 SCCM during deposition. The results confirm that hydrogen dilution helps in improving the microstructure of films and favours the formation of strong Si–H bonds. Beyond 70 SCCM of HFR, a large flux of hydrogen resulted in an increase in void fraction and disorder in the films.

Crystallization Products and Structural Characterization of CaO-SiO₂-Based Mold Fluxes with Varying Al₂O₃/SiO₂ Ratios.

During the casting of high aluminum steel, the dramatic increase in the Al2O3/SiO2 ratio is inevitable, resulting in significant changes of the crystallization behavior, which would result in heat transfer and lubrication problems. Crystallization products and structure characterization of glassy CaO-SiO2-based mold fluxes with different Al2O3/SiO2 ratios were experimentally investigated using a differential scanning calorimetry technique and Raman spectroscopy. With increasing Al2O3/SiO2 ratios, the following results were obtained. The crystallization temperature and the crystallization products are changed. With increasing Al2O3/SiO2 ratios from 0.088 to 0.151, the crystallization temperature first increases greatly from 1152 °C to 1354 °C, and then moderately increases. The crystallization ability of the mold flux is strengthened. The species of the precipitated crystalline phase change from two kinds, i.e., Ca4Si2O7F2 and Ca2SiO4, to four kinds, i.e., Ca4Si2O7F2, Ca2SiO4, 2CaO·Al2O3·SiO2 and Ca12Al14O32F2, the crystallization ability of Ca4Si2O7F2 is gradually attenuated, but other species show the opposite trend. The results of Raman spectroscopy indicate that Al3+ mainly acts as a network former by the information of [AlO4]-tetrahedral structural units, which can connect with [SiO4]-tetrahedral by the formation of new bridge oxygen of Al–O–Si linkage, but there is no formation of Al–O–Al linkage. The linkage of Al–O–Si increases and that of Si–O–Si decreases. The polymerization degree of the network and the average number of bridging oxygens decrease. Further, the relatively strong Si–O–Si linkage gradually decreases and the relatively weak Al–O–Si gradually increases. The change of the crystalline phase was interpreted from the phase diagram and structure.