Si Bridging Bonds Research Articles

Tribological behavior of polycrystalline diamond based on photo-Fenton reaction

Polycrystalline diamonds (PCD) has high thermal conductivity and as heat sinks in semiconductor power devices. However, PCD exhibits high hardness and strong chemical inertness lead to lower processing efficiency and increase processing costs. Hence, achieving efficiently obtain high-quality PCD surfaces is crucial. In this study, we investigated the tribological behavior of PCD in different environments (deionized water, H2O2 + UV, Fenton, and photo-Fenton) and under different photo-Fenton conditions (pH, light intensity, Fe3O4 concentration, and H2O2 concentration) via Si3N4 ball-disk friction and wear experiments. The photo-Fenton reaction improved the material removal rate of PCD, which was the highest (285.4 μm3/min) under optimized conditions of pH = 3, 100 mW/cm2 light intensity, 2 wt% Fe3O4 concentration, and 10 wt% H2O2 concentration. Based on the friction and wear experimental results and X-ray photoelectron spectroscopy, we propose a material removal mechanism for PCD. The hydroxyl radical (·OH) produced by the photo-Fenton reaction oxidize the PCD surface to form CO, CO, and C–OH groups, which are converted into C–O–Si bridge bonds on the PCD surface, resulting in material removal. Our study findings provide theoretical support for the photo-Fenton reaction -assisted CMP of PCD.

Phase evolution and mechanical-hydroscopic properties of alkali-silica reaction gels modified by magnesium nitrate

Alkali-silica reaction (ASR)'s destructiveness is governed by the compositions and properties of ASR products, while methods of converting these hygroscopic-expansive gel-like products into innocuous phases remain unexploited. In this study, the influence of magnesium nitrate on the evolutions of phase, molecular structure, hydroscopic and mechanical properties of ASR gels with varying Mg/Si ratios from 0.1 to 1.1 was investigated. The results indicate that the primary phases of ASR products, tobermorite-type calcium silicate hydrate (C–S–H) and alkali kanemites, can be suppressed into brucite and eventually converted into magnesium-silicate-hydrate (M-S-H) in the presence of increasing Mg/Si ratios and the consequent decreasing pH. The Si–O–Si bridging bonds and Si–O symmetric stretching in the Q3 sites of ASR products can be suppressed. The phase and structure modifications resulted in a 93.5% reduction in hydroscopic swelling, a 94.7% decrease in strength, and a 152.3% drop in modulus of elasticity rendering the ASR products less destructive.

Manipulating the Spin State of Fe Sites via Fe-O-Si Bridge Bonds for Enhanced Polysulfide Redox Kinetics in the Li-S Battery.

Transition metals with 3d unoccupied orbitals have superior catalytic activity, but inherent high spin suppresses their adsorption capability, leading to sluggish polysulfide conversion kinetics for Li-S batteries. Herein, we provide Fe-O-Si bridge bonds to manipulate eg filling and induce a high-to-medium spin transition of Fe3+ sites, which enhances polysulfide adsorption and facilitates sulfur redox reaction kinetics. The resultant cathodes exhibit outstanding performances under high sulfur loading, which can deliver a high battery specific energy of 1061 mA h·g-1 even after 100 cycles in Li-S pouch batteries. This work provides new insights into the kinetic and multi-step conversion mechanism of the sulfur redox reaction process, helping in the understanding and design of spin-dependent catalysts.

Odd aromatic Si4 ring stabilized by VV bond passing through it: May π‐bonding form without σ‐bonding as precondition?

AbstractThis work theoretically presents a type of inverse sandwiches [VCl]2[Si4R4] (RH, CH3, SiH3), of which VV, VSi, and SiSi bonding modes are very odd. [VCl]2[Si4R4] has the tetragonal dipyramid structure of two V atoms bridged by Si4 ring. The eight VSi edges mainly consist of four 3c‐2e VSiV and two 4c‐2e VSiVSi bridge bonds. A VV bond passes through the square aromatic Si4 ring. The oddest phenomenon is that no apparent SiSi σ‐bonding is found in the 4c‐6e aromatic Si4 ring, indicating that π‐bonding may form without σ‐bonding as precondition. The orbital and bond order analyses prove the phenomenon. The odd aromatic π system may be stabilized by bridge bonds and the unique VV bond passing through the center ligand, because such phenomena are not available for [TiCl]2[Si4R4]. Since π‐bondings are not so stronger than σ‐bondings, it is easy to perform interconversion between the aromatic/non‐cyclic 4c‐6e π systems of [VCl]2[Si4R4].

Adsorption of vinyl trimethoxysilane and formation of vinyl siloxane nanolayers on zinc surface from aqueous solution

The method of quartz crystal microbalance is used to study adsorption of vinyl trimethoxysilane (VS) on the surface of zinc from an aqueous solution. Adsorption isotherms are obtained. Approaches corresponding to the known adsorption isotherms are used for interpretation of adsorption data: Langmuir, BET, Flory–Huggins, Langmuir multicenter, Temkin, and Langmuir–Freundlich. It is shown that silanes are adsorbed on the surface of thermally deposited zinc from aqueous solutions and displace adsorbed water from the surface by occupying more than six adsorption sites on the surface. It is found that monolayer coverage of the zinc surface is reached at a concentration of the VS solution of 1 × 10–4 M. The neighboring adsorbate molecules can interact, forming siloxane dimers and trimers bound to the metal surface by either covalent or hydrogen bonds. Adsorption heats are calculated using different adsorption models. It is shown that VS is chemosorbed on the surface of zinc. An increase in the concentration of the VS solution up to 0.1 M results in formation of polycondensed siloxane oligomers on the surface with polycondensation degree n = 8–12. Oligomer surface fragments are connected with each other by hydrogen bonds and are connected with the surface by Zn–O–Si bridge bonds. The overall thickness of such a layer is 10–12 nm or ten molecular layers.

Atomic insight into tribochemical wear mechanism of silicon at the Si/SiO2 interface in aqueous environment: Molecular dynamics simulations using ReaxFF reactive force field

In this work, the atomic mechanism of tribochemical wear of silicon at the Si/SiO2 interface in aqueous environment was investigated using ReaxFF molecular dynamics (MD) simulations. Two types of Si atom removal pathways were detected in the wear process. The first is caused by the destruction of stretched Si–O–Si bonds on the Si substrate surface and is assisted by the attachment of H atoms on the bridging oxygen atoms of the bonds. The other is caused by the rupture of Si–Si bonds in the stretched Si–Si–O–Si bond chains at the interface. Both pathways effectively remove Si atoms from the silicon surface via interfacial Si–O–Si bridge bonds. Our simulations also demonstrate that higher pressures applied to the silica phase can cause more Si atoms to be removed due to the formation of increased numbers of interfacial Si–O–Si bridge bonds. Besides, water plays a dual role in the wear mechanism, by oxidizing the Si substrate surface as well as by preventing the close contact of the surfaces. This work shows that the removal of Si atoms from the substrate is a result of both chemical reaction and mechanical effects and contributes to the understanding of tribochemical wear behavior in the microelectromechanical systems (MEMS) and Si chemical mechanical polishing (CMP) process.

Structural analysis of the interface of silicon nanocrystals embedded in a Si3N4 matrix

The structure and interface states of thin nanocomposite layers containing Si nanocrystals embedded in an amorphous nitride matrix have been analyzed by Raman spectroscopy and x-ray photoelectron spectroscopy (XPS). The Si 2p core-level spectrum of the nanocomposite layer was deconvoluted by using five Gaussian–Lorentzian contributions corresponding to the different nitride states of Si. It was shown that the Si-ncs/Si3N4 interfaces formed during annealing are composed of a high density of Si2+ subnitrides. These subnitrides are more likely to be responsible for the shoulder at 494 cm−1 on the Raman spectra. Considering the proportion of Si2+ subnitrides with respect to Si0 states, an abrupt transition from the crystalline to the amorphous phase due to Si2=N–Si bridge bonds is suggested.

IR reflectance characterization of glass–ceramic films obtained by high pressure impregnation of SnO 2 nanopowders on float glass

Glass–ceramic thin films of tin dioxide on float glass surfaces were obtained using a method based on high pressures and temperatures below the glass transition temperature. SnO 2 thin films were confirmed using XRD, SEM and XRF techniques. These thin films were identified using IR reflectance due to a shift induced by Sn ion content of about ∼100 cm −1 in the main maximum peak position which is typical of stretching vibration intensities of a ν Si −O–Si bridging bonds, or a ν Si – O − nonbridging bonds.

Atomic structure, electronic and optical properties of Si nanocrystals embedded in [formula omitted]-cristobalite and [formula omitted]-quartz

We use DFT calculations to study the atomic structures, the optical and electronic properties of silicon nanocrystals (nc-Si) embedded in β-cristobalite and in α-quartz matrix. We show that the optical properties are influenced by the matrix type. The energy range of the absorption spectrum of nc-Si in α-quartz matrix is more extended than that of nc-Si in β-cristobalite. The presence of Si–O–Si bridge bonds at the nc-Si/β-cristobalite interface favours the stability of the system. The energy gap of nc-Si with interface defects is larger than that of nc-Si without interface defects.

Ab initio study of dissolution and precipitation reactions from the edge, kink, and terrace sites of quartz as a function of pH

In this study, the fundamental concept of mineral surface roughness and the role it plays on the dissolution and precipitation processes using ab initio density functional theory calculations, have been investigated. To understand the topological contribution to the dissolution and precipitation rates of quartz, a systematic study was designed to determine the reaction mechanisms and barrier heights of the forward reaction of hydrolysis of–Si(OH)3 group from underlying edge, kink, and terrace sites. The edge and kink sites are topological features on mineral surfaces that are bound to the bulk with fewer Si–O–Si bridge bonds than a terrace site, a factor that can be significant in the dissolution process. In this work, the local arrangement of atoms on the underlying sites is included by systematically increasing the Si–O–Si bridging to represent the edge, kink, and terrace sites under ambient conditions in the neutral, deprotonated, and protonated states. Nine reaction profiles were studied using the M05-2X density functional with 6–31 + G(d,p) basis set. The results show that hydrolysis of the–Si(OH)3 group and the back reactions are not too sensitive to the underlying edge, kink, and terrace site. The barrier height data also explain the experimentally observed dissolution rate over the entire pH range, especially the tremendously high dissolution rate below pH 2.

Ultralow k using a plasma enhanced chemical vapor deposition porogen approach: Matrix structure and porogen loading influences

To improve integrated circuit performance, microelectronic chip interconnections need dielectric materials with ultralow k (ULK) values. Porous a-SiOCH, an ULK material, can be created using a two step strategy called a porogen approach. The first step consists of a hybrid film deposition, which is an a-SiOCH matrix containing an organic sacrificial phase. Afterwards, the organic phase is removed during a post-treatment to generate the porosity. In this work, hybrid deposition was performed by plasma enhanced chemical vapor deposition and the post-treatment was a thermal annealing. Firstly, hybrid films with different a-SiOCH matrix structures were created using two matrix precursors [decamethylcyclopentasiloxane (DMCPS) and diethoxymethylsilane (DEMS)] and an O2 addition in a plasma gas feed. For the same porogen loading, the shrinkage behavior during the porogen removal is correlated to the matrix structure. Fourier transform infrared spectroscopy and Si29 solid nuclear magnetic resonance are both used to determine the structure. The O3SiMe1 is favorable to prevent high film shrinkage and the O2SiMe2 leads to high film shrinkage and absence of porosity generation. To prevent the existence of this type of structure, DEMS+O2 appears more appropriate as a matrix precursor than DEMS only or DMCPS. Secondly, using the appropriate matrix structure, the influence of the porogen loading on the porosity creation is studied. Hybrids with different porogen loadings are achieved by changing the porogen precursor ratio in the plasma gas feed. The porogen conversion into porosity is studied for different porogen loadings and the results indicate the existence of a porogen loading threshold. Above it, there is no more porosity generation because of the too high film shrinkage during the porogen removal. This behavior is explained by a too low matrix ratio in the hybrid film. For the high porogen loadings, the matrix skeleton (mainly constituted by SiOSi bridging bonds) is not in sufficient quantity to prevent such film shrinkage. The porous a-SiOCH created with the most favorable matrix structure and porogen loading has the ultralow k value of 2.3.

Interplay of EnE‘3-nC Valence Isomers (E, E‘ = Si, Ge): Bicyclo[1.1.0]butanes with Very Short Bridging Bonds and Their Isomerization to Alkyl-Substituted Cyclopropenes

1,2,3-Trisila- and 1,3-disila-2-germabicyclo[1.1.0]butane derivatives 7a,b were synthesized in high yields by the reduction of the appropriate precursors, 1,3-dichloro[1,2,3]trisiletane and 1,3-dichloro[1,3,2]disilagermetane, with KC8. The X-ray analysis of 7a revealed an exceedingly short Si−Si bridging bond of 2.2664(9) A, which is much shorter than the normal Si−Si single bond of 2.34 A. The nature of such an unusual bridging bond is discussed in terms of both electronic and steric effects of the methylene bridge. The thermolysis of bicyclo[1.1.0]butanes 7a,b unexpectedly resulted in the formation of their valence isomers, alkyl-substituted 1H-trisilirene 8a and 1H-disilagermirene 8b, representing a new type of E4 valence isomer (E = group 14 element). The germanium versions, 1H-siladigermirene 8c and 1H-trigermirene 8d, were also prepared.

The structure of the SiO2∕Si(100) interface from a restraint-free search using computer simulations

The structure of the interface between SiO2 and Si(100) is investigated using the replica-exchange method driven by classical molecular dynamics simulations based on ab initio-derived interatomic potentials. Abrupt interfaces are shown to be unstable, whereas a substoichiometric oxide forms at the transition between the two materials that exhibits Si atoms in all three intermediate oxidation states, in agreement with experiment. A number of physical characteristics are found to be consistent with experimental data, including the distribution of Si atoms with different oxidation states, the increase in atom density and the stability of a pseudo-cristobalite pattern at the interface as well as the presence of Si–O–Si bridge bonds between the substrate and the suboxide.

Photocatalytic performance of Ru doped anatase mounted on silica for reduction of carbon dioxide

Ru doped anatase supported on silica was prepared by solid-state dispersion method and examined for the photocatalytic reduction of carbon dioxide in aqueous medium at ambient conditions. To assist in interpreting the photocatalytic behaviour of Ru-TiO2/SiO2, reference systems consisting of Ru doped TiO2 and TiO2 supported on SiO2 were also analyzed and the conditions were optimized. Ru/TiO2 photocatalysts with metal loadings of 0.1, 0.3, 0.5 and 1.0wt% were prepared by impregnation method and a series of TiO2/SiO2 catalysts with low TiO2 (1, 3, 5 and 10wt%) contents were prepared by solid-state dispersion method. The photocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), UV–vis DRS, FT-IR and Raman spectroscopy. The results showed that TiO2 particles with Ru ions have higher photocatalytic activity than undoped TiO2 and the optimum Ru loading was found to be 0.5wt%. Nevertheless, the yield increased notably when TiO2 was supported on SiO2. This strong enhancement suggests that in 10wt% TiO2/SiO2 the efficiency of charge separation is strongly influenced through the presence of TiOSi bridging bonds. On the contrary, Ru-TiO2/SiO2 has no significant improvement in activity over TiO2/SiO2 except that it shows nearly quadruple times higher activity for the formation of methanol than Ru/TiO2. The difference in the photocatalytic activity is related to its physico-chemical properties.

Film strain and compositional changes in thermally nitrided silicon dioxide thin films

The nature of the Si–O bonds, composition, and film strain changes in thermally nitrided silicon dioxides in NH 3 at 1000 °C and 1 atm is investigated with Fourier transform infrared spectroscopy and spectroscopic ellipsometry. Shifts of the transverse optical and longitudinal optical phonons of O in Si–O–Si bridging bonds are the results of both compositional and strain within the silicon dioxide matrix. Red shifts during the initial nitridation period are followed by blue shifts at longer nitridation times. Red shifts can be explained by nitrogen incorporation and strain accumulation, while bulk film strain relaxation in nitrided oxides is most likely responsible for the blue shifts.

A molecular orbital study on the chemical interaction across the indomethacin/silica interparticle boundary due to mechanical stressing

A discrete variational-Xα (DV-Xα) method was applied to elucidate the formation of C–O–Si bridging bonds, produced when a silanol group of SiO 2 comes close enough to react with a carboxyl group of indomethacin (IM). A decrease in the coordination number (CN) of oxygen atoms per silicon atom at the SiO 2 surface increased the net charge (NC) of the silanolic hydrogen atom and decreased the bond overlap population (BOP) between the silanolic oxygen and hydrogen atoms. These changes favored the formation and stabilization of C–O–Si bridging bonds with simultaneous dehydration. The computational results agreed well with our previous experimental study of a ground indomethacin–SiO 2 mixture to obtain a better solid dispersion of the drug.

SiO 2/Si(100) interface characterization using infrared spectroscopy: estimation of substoichiometry and strain

The transverse optical (TO) and longitudinal optical (LO) phonons of the asymmetric stretch of the O in SiOSi bridging bond in thermal SiO 2 show red shift with decreasing oxide thickness. These shifts are primarily due to interface effects like strain and substoichiometric silicon oxides (suboxides). A method to isolate the contributions of strain and suboxide concentration towards the observed shifts is proposed. The procedure, which utilizes simple optical model and effective medium approximation, allows estimation of the average strain and suboxide concentration in films of different thickness. Analysis of infrared spectra shows that suboxide-rich layers in low temperature dry and wet oxides are confined to a distance of ∼1.5 nm from the interface; wet oxidation may generate lower stress near the interface.

An organosilyl derivative of trivacant tungstophosphate. Synthesis, characterization and crystal structure determination of α-A-[NBu n4] 3[PW 9O 34(C 2H 5SiO) 3(C 2H 5Si)

In the presence of NBu 4 n Br acting as phase-transfer reagent, organosilicon trichloride C 2H 5SiCl 3 reacts in acetonitrile with the trivacant tungstophosphate sodium salt β-A-Na 8H[PW 9O 34]·24H 2O to give hybrid organosilyl polyoxotungstate derivative α-A-[NBu 4 n ] 3[PW 9O 34(C 2H 5SiO) 3(C 2H 5Si)]. X-ray single crystal structural analysis indicates that the title compound is monoclinic, space group Cc, with lattice constants a=26.828(5), b=22.459(5), c=17.517(4) Å, β=103.19(3)°, V=10,276(4) Å 3, Z=4, R=0.0462. According to the result of X-ray single crystal diffraction and chemical analysis, the hybrid polyanion consists of one α-A-[PW 9O 34] 9− framework on which are grafted simultaneously three RSiO groups through six Si–O–W bridge bonds, each of which is attached to the fourth RSi group through three Si–O–Si bridge bonds. The hybrid polyanion becomes a partial saturated, closed cage structure and also has an assembly of virtual C 3 V symmetry.

Novel multicomponent silicate–poly(vinyl alcohol) hybrids with controlled reactivity

By a combination of inorganic and organic species at a molecular level, a new series of biomaterials having optimal controllable properties can be fabricated. The goal of this work is to determine how the reactivity of the composites (inorganic–organic hybrids) can be controlled by altering the nanostructure of the materials. Hybrids were synthesized by reacting poly(vinyl alcohol) (PVA) in acidic solution with either tetraethoxy silane (TEOS) or tetramethoxy silane (TMOS). The inorganic phase was also modified by incorporating calcium and phosphate compounds. The properties of the hybrids were determined by swelling experiments, infrared spectroscopy, and scanning electron microscopy/microprobe analysis. Transparent PVA–silicate hybrid free-standing films, having a range of compositions within the system, were produced by allowing the rate of hydrolysis of the alkoxide to be compatible with the kinetics of the dissolution processes of both the polymer and calcium-phosphate compounds. Results obtained from swelling experiments and infrared spectroscopy showed that the crosslink density can be increased when hybrids are prepared with larger concentrations of the inorganic component. Moreover, hybrids prepared at temperatures as high as 60°C have, among other properties, greater crosslink densities and inorganic phases with larger amounts of S–O–Si bridging bonds. Swelling experiments also showed that the obtained hybrids varied in their reactivities ranging from fast dissolution to hydrogel properties. We also demonstrate that the degree of reactivity can be controlled by manipulating structural factors of the hybrids such as the crosslink density, proportion of the phases and composition of the inorganic phase, among others.

Low temperature, plasma assisted oxidation of amorphous Si

A preliminary study of plasma assisted oxidation of amorphous, hydrogenated Si (a-Si:H) has been carried out using a microwave frequency, electron cyclotron resonance excited reactor. A ‘constant current through the substrate’ mode was used. Films up to several tens of nm were obtained at room temperature in a time of ⪡ 60 min. The growth kinetics of the SiO 2 on amorphous and crystalline Si substrates were similar and followed the predictions of a constant current, field assisted diffusion model. Infrared absorption spectroscopy on as-grown and chemically etched SiO 2 films suggests that they differ and are inhomogeneous compared to thermal oxides. The differences are attributed to a network having a smaller SiOSi bridging bond angle than that for thermal SiO 2 rather than density or stoichiometric differences. The latter has been confirmed by X-ray photoelectron spectroscopy measurements. Surface roughness in the form of macroscopic bubbles and peeling was observed in samples of a-Si:H following oxidation. This phenomenon, which we attribute to the release and nucleation of the H in the films, may severely limit the applicability of the method for producing low temperature oxides on a-Si.