Si-N Bonds Research Articles

Electronic structure, stability, and mechanism of the decohesion and shear of interfaces in superhard nanocomposites and heterostructures

Electronic structure of interfaces, their stability and the mechanism of decohesion in tension as well as of ideal shear have been studied by means of ab initio density-functional theory for heterostructures consisting of a few nanometer thick fccNaCl-TiN slabs with one monolayer of pseudomorphic SiN interface. It is found that the SiN interface sandwiched between fcc001-TiN slabs is unstable in its symmetric fcc structure, but it stabilizes by distortion of the Si-N bonds, which lowers the symmetry. Significant strengthening of the SiN interface occurs due to partial transfer of valence charge to the Si containing interface which induces damped valence charge-density oscillations propagating into the TiN bulk. As a consequence of these oscillations, decohesion, and ideal shear does not occur within the SiN interface, but in the TiN slabs between the Ti-N planes parallel to that interface. We provide a detailed study of this mechanism of decohesion and ideal shear on the atomic scale. The results are discussed in the context of the experimentally found hardness enhancement in heterostructures and superhard nanocomposites.

Ion induced formation of Silicon nitride substrate and GaN overlayer growth at room temperature on Si (111) surface

AbstractGaN and related nitride semiconductors have attracted great attention in view of their wide applications in photonics and high temperature & high power electronic devices. Among other issues, reduction of defect densities by forming these interfaces at lower temperature and on novel substrates has been the motivation for several researchers. In the present study ion-induced conversion of Si (111) surface into silicon nitride at room temperature is optimized and used as substrate for the growth of Ga films. These Ga films are again nitrided by optimal N+ ion bombardment. Experiments have been performed in-situ in an ultra high vacuum chamber equipped with a Ga source and X-ray photoelectron spectrometer (XPS) at base pressure of 2×10-10 torr. The energy dependence of the nitridation is carefully performed at constant flux. The results clearly demonstrate the Si-N bond formation after a energy of 2 keV and the formation of GaN layer after 800eV of ion bombardment on Si (111) 7×7 surface and Ga adsorbed silicon nitride surface, respectively. The FWHM and chemical shifts in the core-level spectra of Si(2p), Ga(2p) and N(1s) have been analyzed to probe the interface reactions. The results demonstrate a possible novel and low temperature approach towards the integration of III-nitride & silicon technologies, since silicon nitride bonds can act as barriers to dislocation propagation.

Low-Temperature Growth of N-doped SiO2 Layer Using Inductively-Coupled Plasma Oxidation and Its Effect on the Characteristics of Thin Film Transistors

Silicon dioxide as gate dielectrics was grown at <TEX>$400^{\circ}C$</TEX> on a polycrystalline Si substrate by inductively coupled plasma oxidation using a mixture of <TEX>$O_2$</TEX> and <TEX>$N_2O$</TEX> to improve the performance of polycrystalline Si thin film transistors. In conventional high-temperature <TEX>$N_2O$</TEX> annealing, nitrogen can be supplied to the <TEX>$Si/SiO_2$</TEX> interface because a NO molecule can diffuse through the oxide. However, it was found that nitrogen cannot be supplied to the Si/<TEX>$SiO_2$</TEX> interface by plasma oxidation as the <TEX>$N_2O$</TEX> molecule is broken in the plasma and because a dense Si-N bond is formed at the <TEX>$SiO_2$</TEX> surface, preventing further diffusion of nitrogen into the oxide. Nitrogen was added to the <TEX>$Si/SiO_2$</TEX> interface by the plasma oxidation of mixtures of <TEX>$O_2/N_2O$</TEX> gas, leading to an enhancement of the field effect mobility of polycrystalline Si TFTs due to the reduction in the number of trap densities at the interface and at the Si grain boundaries due to nitrogen passivation.

First-principles study of the electonic structure of nitrogen-doped silicon carbide nanotubes

The electronic structures of the intrinsic and nitrogen-doped silicon carbide nanotubes （SiCNTs） have been calculated by first-principles approach based on the density functional theory. The intrinsic （8, 0） SiCNT is a direct band-gap semiconductor with a gap value of 0.94 eV. The band-gap of the SiCNT with the doping concentration of nitrogen being 1.56% and 3.12％ is narrowed to 0.83 eV and 0.74 eV， respectively. The narrowing of the band-gap is the result of the weakening of the Si-N bonds compared with the corresponding Si-C bonds, which can be seen by comparing the charge density difference of the intrinsic SiCNT with that of the nitrogen-doped nanotube.

Acyl iodides in organic synthesis: XII. Reactions with organosilicon amines

Reactions were investigated between acyl iodides RCOI (R = Me, Ph) and organosilicon amines of two classes: trimethyl(diethylamino)silane, dimethyl-bis(diethylamino)silane, and hexamethyldisilazane on the one hand, and 3-aminopropyl(triorganyl)silanes H2N(CH2)3SiX3 (X = Et, EtO) on the other hand. The reaction of RCOI with trimethyl(diethylamino)silane Me3SiNEt2 occurred with a cleavage of the Si-N bond and the formation of N,N-diethylacet- or -benzamides and trimethyliodosilane separated in a mixture with hexamethyldisiloxane. At the reaction of acyl iodides RCOI (R = Me, Ph) with dimethyl-bis(diethylamino)silane in the ratio 2:1 in benzene solution both Si-N were ruptured leading to the diethylamide of the corresponding acid and dimethyldiiodosilane. The main product of the reaction of acetyl iodide with hexamethyldisilazane at the molar ratio 2:1 was diacetylimide (MeCO)2NH. This reaction can be recommended as a simple and convenient preparation procedure for diacylimides. The exothermal reaction of the acetyl iodide with 3-aminopropyl(triethyl)- and -(triethoxy)silanes at the molar ratio of the reagents 1:1 without solvent resulted in quaternary ammonium salts, hydroiodides of the corresponding acetylamides I−MeCON+H2(CH2)3SiX3 (X = Et, OEt).

N-Trimethylsilyl Amines for Controlled Ring-Opening Polymerization of Amino Acid N-Carboxyanhydrides and Facile End Group Functionalization of Polypeptides

We report a new strategy that uses N-trimethylsilyl (N-TMS) amine to mediate controlled ring-opening polymerization of amino acid N-carboxyanhydrides (NCAs). This polymerization proceeds via a unique, trimethylsilyl carbamate (TMS-CBM) propagating group that results from the cleavage of the Si-N bond of N-TMS amine followed by NCA ring opening. Propagation of the polypeptide chains proceeds through the transfer of the TMS group from the terminal TMS-CBM to the incoming monomer followed by the formation of a new TMS-CBM propagating group. Formation of the TMS-CBM was confirmed by MS and NMR. Polypeptides formed by the N-TMS amine-mediated polymerization have the expected molecular weights, narrow molecular weight distributions, and controlled functional groups at the C-termini of the polypeptides.

Lattice dynamics and thermodynamical properties of silicon nitride polymorphs

The lattice dynamics of three polymorphs of ${\text{Si}}_{3}{\text{N}}_{4}$, $\ensuremath{\alpha}$, $\ensuremath{\beta}$, and $\ensuremath{\gamma}$ phases, has been calculated by the real space force constant method combined with first-principles calculations. The thermodynamical properties of the three phases are evaluated from the vibrational density of states. The effect of thermal volume expansion is included by quasiharmonic approximation. The volume expansivity, bulk modulus, specific heat, and Helmholtz free energy of the three phases are computed as a function of temperature. All three phases are found to be dynamically stable. $\ensuremath{\beta}{\text{-Si}}_{3}{\text{N}}_{4}$ shows lower Helmholtz free energy than $\ensuremath{\alpha}{\text{-Si}}_{3}{\text{N}}_{4}$ in the temperature range from 0 to 2000 K. In other words, $\ensuremath{\alpha}{\text{-Si}}_{3}{\text{N}}_{4}$ is not a low-temperature phase but a metastable phase under the ordinary pressure. The presence of planer ${\text{N-Si}}_{3}$ units and their strong Si-N bonds in two hexagonal polymorphs, $\ensuremath{\alpha}$- and $\ensuremath{\beta}{\text{-Si}}_{3}{\text{N}}_{4}$, is the origin of the high-frequency phonon band at above 25 THz, which is absent in $\ensuremath{\gamma}{\text{-Si}}_{3}{\text{N}}_{4}$. It plays key roles for anisotropic local vibration of N atoms. The different temperature dependence of specific heat between $\ensuremath{\alpha}/\ensuremath{\beta}$ and $\ensuremath{\gamma}$ phases can also be ascribed to the structure. The transition pressure from $\ensuremath{\beta}$ to $\ensuremath{\gamma}$ phase is computed as a function of temperature. It is found to increase with the rise of temperature.

FTIR and XPS investigations of a-SiOxNy thin films structure

Amorphous silicon oxynitride (a-SiOxNy) thin films with large composition variation were deposited by reactive sputtering. Their structural study was carried out by mean of FTIR and XPS analysis. The IR absorption peak maximum was found to shift towards higher wavenumbers as the oxygen content increases and the absorption peaks of Si-O and Si-N bonds also appear. The Si 2p photoelectron peak was decomposed considering five tetrahedra of SiOvN4-v (where v = 0, 1, 2, 3 and 4) following the Random Bonding Model (RBM). But the comparison between RBM theoretical and experimental predictions and the non-linear behaviour of the modified Auger parameter (α) showed that the a-SiOxNy structure can be well described only considering a mixture of SiO2, Si3N4 and SiOxNy phases.

Study of pretreatment prior to silicon-oxycarbide deposition on Cu interconnect

A new approach using plasma self-alignment after chemical mechanical polishing in a Cu damascene process has been developed. The Cu and a low k dielectric surfaces were treated by a novel plasma treatment in which hydrogen plasma, silane soak, and ammonia plasma treatment were used sequentially. The Cu and low k surface roughness, characterized by atomic force microscope, increased after plasma treatment. The surface bonds of Cu after treatment were characterized by x-ray photoelectron spectroscopy. Si-N bonds were formed on the Cu surface after the new plasma treatment. The interface of copper and silicon oxycarbide with new plasma treatment sequences had the highest deobonding fracture energy at 9.6 J/cm2, which was measured by using the four-point bending test. The voltage breakdown of different plasma treatment conditions was evaluated by a single Cu damascene comb test structure capped with silicon oxycarbide. The new treatment had over 10 V improvement compared with others.

Thermal Stability of SiBCN Films

Silicon-Boron-Carbon-Nitride (SiBCN) thin films were deposited on Si (100) substrates by ECR-type ion beam sputtering at a substrate temperature of 200 oC, and thermal stability of SiBCN films were investigated at 600 oC, 700 oC and 800 oC in air. A composed Si-B-C (Si plate and B4C target) target was used for the film deposition. The composition and chemical bonding structure of the prepared films were investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. Si-N bonds increased with increasing silicon content. Surface roughness of SiBCN films decreased with increasing Si content. Hardness of SiBCN films exhibited up to 22 GPa with increasing silicon content. SiBCN films showed no changes in chemical bonds after heating at 600 oC. Even after heating at 700 oC, SiBCN films maintained relatively high hardness, whereas hardness of SiBCN films was quietly reduced after heating at 800 oC. Thermal stability of SiBCN films was improved with increasing Si content.

From lithium ketazides to isomeric silylketazine-rings – imine-enamine tautomerism

Di( tert-butylmethyl)ketazine ( I) reacts with n-BuLi in a 1:1 molar ratio to give a monolithium salt ( II). The reaction of II with t Bu 2SiF 2 in n-hexane leads, even in a 1:1 molar ratio, to the formation of the isomeric five- and four-membered ring compounds 1 and 2. Compound 1 has an endocyclic imine and an exocyclic enamine unit. The opposite is found for 2. The acyclic monosubstitution product, t Bu 2SiFCH 2–C t Bu N–N C t BuCH 3 ( III) could not be isolated. It reacts with the lithium ketazide to give 1 or 2. I is reformed. The reaction in THF yields only the four-membered ring 2. In a comparable reaction of the lithium ketazide and (H 3C) 2SiF 2, the substitution product 3 could be isolated. A possible formation mechanism for 2 includes an intermediate silene IV. Both compounds 1 and 2 react with H 3C–OH under cleavage of the endocyclic Si–N-bond to give the addition product 5. The reaction mechanism includes a hydrogen shift from a nitrogen atom to a carbon atom via an imine-enamine tautomerism. In a 2:1 molar ratio, n-BuLi and the di( tert-butylmethyl)-ketazine ( I) form the dilithium salt, 6. Compound 6 crystallizes from THF as trimer with four imine and two enamine units. A seven-membered ring ( 7) isomeric to 1 and 2 is the result of the reaction of 6 with t Bu 2SiF 2. Compound 7 contains one imine and one enamine unit in the ring skeleton. The comparable reaction of the (CH 3) 3Si-substituted dilithium-di( tert-butylmethyl)ketazide and t Bu 2SiF 2 yields the five-membered ring compound 8 with one endocyclic imine and one exocyclic enamine unit. Quantum chemical calculations of 1, 2, 7 and the intermediate silene IV have been carried out and show a low energy difference between the cyclic silyl-ketazine isomers.

Core level photoemission study of nitrided hafnium silicate thin films

We present a synchrotron radiation and Al K α core level study of ultra-thin nitrided hafnium silicate thins films, potential candidate for a high κ oxide to replace SiO 2. Nitriding the as deposited, uniform silicate results in the formation of Si-N and Hf-N bonds, with a nitrogen profile near the silicate/SiO 2 interface. Controlled etching reveals that the nitridation has proceeded beyond the silicate into the SiO 2 bottom oxide, without degrading the sharp silicate/SiO 2 interface. The 1.2 nm Hf 0.4Si 0.6O 2 nitrided silicate on 0.6 nm SiO 2 has an estimated equivalent oxide thickness of 1.1 nm.

Effect of the chemical structure of silyl derivatives of unsymmetrical dimethylhydrazine on the composition and structure of silicon carbonitride films: Theoretical and experimental studies

Quantum-chemical calculations are used to analyze the homolytic decomposition of 1,1-dimethyl-2-(dimethylhydrazino)silane (DMDMHS) and bis(2,2-dimethylhydrazino)dimethylsilane (bisDMHDMS)—precursors for the growth of silicon carbonitride films. The results indicate that the homolytic decomposition of DMDMHS is a highly endothermic process, whereas bisDMHDMS decomposition is almost thermally neutral, owing to the strong bond in the N2 molecule. This indicates that the probability of the breaking of the Si-N bond and the formation of volatile silanes, free of nitrogen, is higher in bisDMHDMS, and accounts for the absence of Si-C groups in films grown from this precursor at room temperature. The conclusions drawn from quantum-chemical calculations are supported by experimental data on the growth kinetics, chemical structure, and composition of layers grown from DMDMHS and bisDMHDMS.

Investigation of the structural transformations in nitrided layers of optical lead silicate glasses by infrared reflection spectroscopy

The IR reflection spectra of nitrided layers of the TF10, TF5, and TF8 glasses are analyzed. It is shown that thermal nitridation of the surface layers of the glass samples at a temperature of 375–495°C and a pressure of 0.1–1.0 MPa for 1–20 h brings about the breaking of the Si-O-Si bonds and the formation of the Si-N-Si and Si-N bonds. The degree of structural transformation in the surface layer depends on the conditions of thermal nitridation and on the chemical composition of the glass.

Crystal Structure and Electron Density of α-Silicon Nitride: Experimental and Theoretical Evidence for the Covalent Bonding and Charge Transfer

Crystal structure and electron-density distribution of alpha-silicon nitride (alpha-Si3N4, space group: P31c) have been investigated by a combined technique of the Rietveld method, the maximum-entropy method (MEM), and MEM-based pattern-fitting of high-resolution synchrotron powder diffraction data. In combination with density functional theory calculations, the present experimental electron-density distribution of the alpha-Si3N4 indicates covalent bonds between Si and N atoms and charge transfer from the Si to N atom. The triangular distribution around the N atoms, which is attributable to the nitrogen sp2 hybridization for the nearest silicon and nitrogen pairs, was found in both experimental and theoretical electron density distributions. The minimum electron density in an intralayer Si-N bond was a little lower than that in an interlayer bond, which would be responsible for the inequality between elastic constants, C33 > C11. The present work suggests that the high bulk modulus of the alpha-Si3N4 is attributable to the high minimum electron density of the Si-N bond.

Improving Subcritical Crack Growth Resistance for Alumina Glass Dental Composite

Abstract. The improvement of subcritical crack growth (SCG) resistance for alumina glass dental composites was explored in this study. The addition of nitrogen to the glass phases in the composite was found to increase the SCG resistance, where the SCG exponent n increases from 22 for the oxide glass composites to 30 for the composites containing 0.5 mol% nitrogen in the glass phases. The improvement was tentatively attributed to the nitrogen addition, which makes the glass network stronger through forming the non-flexible Si-N bonds and thus inhibits the hydrolysis reactions under the SCG conditions. Analyses demonstrated that the increase of the n value from 22 to 30 offers the potential to greatly extend the lifetime and improve the long-term reliability for the alumina glass dental composites.

Synthesis and Reactivity of (Silylamino)‐ and (Silylanilino)phosphines

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Organosilicon compounds containing carbofunctional biguanidine group

The reaction of triethoxysilylpropylamine (AGM-9) with dicyanodiamide was studied. The condensation of AGM-9 with dicyanodiamide occurs in the presence of a catalytic amount of CuCl2 at 125–145°C within 5–24 h; it involves both the amino group of AGM-9 and ethoxy substituents at the Si atoms, with an unusual exchange of a Si-O bond for a Si-N bond. The final reaction product is 1-N-(3-triethoxysilylpropyl)-2-N-[3-aminopropylsilyl(diethoxy)]biguanidine. Its hydrolytic polycondensation yields an organosilicon polymer, a polycondensate of AGM-9 with 1-N-(3-triethoxysilylpropyl)biguanidine, which is a highly efficient sorbent for Ag(I) (static sorption capacity 544 mg g−1).

Post-annealed silicon nanocrystal formation on substoichiometric SiOxNy(x&lt; 2,y&lt; 1) layers deposited in SiH4-N2O radiofrequency discharges

In this work is presented a detailed physicochemical, structural and optical characterization of SiO x N y thin films. The films deposited using PECVD in SiH 4 -N 2 O-He discharges were thermally annealed at 1273 K for 1 hour in ambient nitrogen. The film stochiometry was measured by Rutherford Backscattering Spectroscopy. The chemical composition was dominated by silicon suboxide containing some Si-N and Si-H bonds. Raman scattering measurements suggest the formation of nanocrystallite silicon in the annealed films. The Raman observation is strongly supported by Transmission Electron Microscopy analysis which shows a high density of silicon nanocrystals, having a mean radius ranging between 3 and 6 nm. Using Spectroscopic Ellipsometry, we discussed the dielectric function evolution as a function of the deposition parameters.

Supramolecular Template‐Directed Synthesis of Perfect Phenelenediimino‐Bridged Ladderlike Polyphenylsiloxanes

A template synthesis of the soluble, high molecular weight (Mw), and perfect p-phenylenediimino (p-PDA)-bridged ladderlike polyphenylsiloxane (PLPS) is reported. First, N,N'-bis(phenyldichlorosilyl)-p-PDA monomers were self-assembled into a perfect ladder superstructure (LS) by concerted interaction of aromatic pi-pi stacking and hydrogen bonding. Then the LS underwent a novel stoichiometric hydrolysis/dehydrochlorination-condensation reaction instead of the usual hydrolysis/dehydration-condensation reaction, leading to the PLPS. The perfect ladder structures of both the PLPS and, in particular, the unstable supramolecular LS were confirmed as follows. 1) There are two Bragg peaks in solid and/or solution X-ray diffraction (XRD) spectra representing the ladder width (w) and ladder thickness (t); these peaks were consistent with those calculated by molecular simulation. 2) Both the PLPS and LS have extremely sharp absorption peaks with small half-peak widths (Delta(1/2) < 0.3 ppm) in 29Si NMR spectra, suggesting the presence of the perfect ladder structure for PLPS and LS. 3) Moreover, no noticeable absorption peaks for the Si-OH and NH2 groups were observed in FT-IR and 29Si NMR spectra, indicating that the Si-N bond of the [triple bond]Si-NH-C6H4-NH-Si[triple bond] ladder rung of PLPS and LS is not cleaved. 4) Both PLPS and LS show similar emission peaks (in fluorescence spectroscopy) attributed to the excimer formed by face-to face pi-pi stacking of phenyl groups along the ladder chain rather than a branched direction. 5) Differential scanning calorimetry (DSC) measurements indicate a high glass temperature (Tg = 176.4 degrees C) for PLPS. As circumstantial evidence, this result further indicates very high stiffness of PLPSs ladder backbone as compared with flexible single-chain polyphenylmethylsiloxane with a low Tg = -69.4 degrees C.