Si-N Bonds Research Articles

Synthesis and structural characterization of amido scorpionate rare earth metals complexes

The reactivity of hybrid scorpionate/cyclopentadienyl ligands in the form of the protio derivatives as a mixture of two regioisomers, namely bpzcpH [1-{2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl}-1,3-cyclopentadiene and 2-{2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl}-1,3-cyclopentadiene] and bpztcpH [1-{2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethyl}-1,3-cyclopentadiene and 2-{2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethyl}-1,3-cyclopentadiene], with the tris(silylamide) precursors [M{N(SiHMe2)2}3(thf)x] of rare earth metals (including the group 3 metals scandium and yttrium) is related to the atomic radii of the metal centres. The reaction with the precursor containing the smallest ion, [Sc{N(SiHMe2)2}3(thf)], did not proceed even heating at reflux temperature in toluene. The reaction with the precursors that contain a medium-sized metal ion, i.e., [M{N(SiHMe2)2}3(thf)2] (M = Y, Lu), proceeded only at high temperature and gave good yields of the silylenediamide-containing derivatives [M{κ(2)-NN-Me2Si(NSiHMe2)2}(bpzcp)] (M = Y , Lu ) and [M{κ(2)-NN-Me2Si(NSiHMe2)2}(bpztcp)] (M = Y , Lu ) by an double activation of Si-H and Si-N bonds. However, the reaction with the precursors that contained the largest metal ions, i.e., [M{N(SiHMe2)2}3(thf)2] (M = Nd, Sm), proceeded rapidly at room temperature to afford the bis(silylamide) complexes [M{N(SiHMe2)2}2(bpzcp)] (M = Nd , Sm ) and [M{N(SiHMe2)2}2(bpztcp)] (M = Nd , Sm ). Additionally, the alkyl heteroscorpionate yttrium and lutetium complexes [M(CH2SiMe3)2(NNCp)] (M = Y, Lu) reacted with an excess of HN(SiHMe2)2 to give the mixed alkyl/amide derivatives [M{N(SiHMe2)2}(CH2SiMe3)(bpzcp)] (M = Y , Lu ) and [M{N(SiHMe2)2}(CH2SiMe3)(bpztcp)] (M = Y , Lu ). The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structures of , and were also established.

A new assisted molecular cycloaddition on boron doped silicon surfaces: a predictive DFT-D study.

In the framework of the Density Functional Theory (DFT-D), we investigate the phthalocyanine (H2Pc) molecule adsorption on SiC(0001)3 × 3 and Si(111)√3 × √3R30°-B (SiB) surfaces, and particularly compare the involved molecular adsorptions. In the H2Pc-SiC(0001)3 × 3 system, the molecular adsorption can be ascribed to a [10+2] cycloaddition. The H2Pc-SiB system is considered in three cases: defectless SiB surface (denoted SiB-0D) and SiB surfaces presenting one or two boron defects (denoted SiB-1D and SiB-2D respectively). The SiB-0D surface is passivated by a charge transfer from the Si adatoms to the boron atoms and therefore no chemical bond between the molecule and the substrate is observed. A similar molecular adsorption as already evidenced in the H2Pc-SiC(0001)3 × 3 system is involved in the SiB-2D case. In the case of the SiB-1D surface, two Si-N bonds (Si1-N1 and Si2-N2) are observed. One of them, Si1-N1, is nearly similar to that found in the H2Pc-SiB-2D system, but the Si2-N2 bond is unexpected. The Bader charge analysis suggests that, in the presence of the H2Pc molecule, the boron atoms behave like an electron reservoir whose availability varies following the involved molecular adsorption process. In the SiB-1D case, charges are transferred from the substrate to the molecule, allowing the Si2-N2 bond formation. Such a kind of molecular adsorption, not yet observed, could be designed by "assisted pseudo cycloaddition".

Curved surface effect and characteristic emission of silicon nanostructures

Some bonds on the curved surface (CS) of silicon nanostructures can produce localized electron states in the band gap. Calculated results show that different curvature can form the characteristic electron states for some special bonding on nanosilicon surface, which are related to a series peaks in photoluminescience (PL), such as LN, LO1 and LO2 lines in PL spectra due to SiN, Si=O and SiOSi bonds on the curved surface, respectively. In the same way, SiYb bond on the curved surface of Si nanostructures can manipulate the emission wavelength into the window of optical communication by the CS effect, which is marked as LYb line near 1550 nm in the electroluminescience (EL).

Hydrometallation of amino-trialkynylsilanes--intramolecular M-N interactions (M = Al, Ga) and potential activation of Si-N bonds.

Hydrometallation of a pyrrolidyl functionalised trialkynylsilane, H8C4N-Si(C≡C-CMe3)3, with equimolar quantities of H-M(CMe3)2 (M = Al, Ga) resulted in the formation of mixed alkenyl-dialkynylsilanes (3a, 3b) which have a Lewis-acidic Al or Ga atom in the geminal position to the Si atom and form four-membered M-N-Si-C heterocycles by a strong interaction of the amine N atoms with the Lewis-acidic metal atoms. This interaction results in a concomitant lengthening and weakening of the Si-N bonds. Dual hydrometallation afforded alkynyl-dialkenylsilanes (4a, 4b) with two Lewis-acidic metal atoms. Al-N and Ga-N interactions to one of the Lewis-acidic centres led again to the formation of M-N-Si-C heterocycles. The second Al atom of 4a interacted with C-H bonds of the vinylic tert-butyl group, while the Ga atom of 4b was coordinated to the α-C atom of the remaining alkynyl substituent. Dual hydrometallation of the corresponding pyrrolyl-trialkynylsilane resulted in compounds with different structures (5a, 5b) due to the delocalisation of the lone pair of electrons at nitrogen in the aromatic ring. One metal atom is coordinated to the α-C atom of the alkynyl group, and the other has close contact to a C-H bond of the pyrrole ring. The synthesis of 4b gave an unprecedented bicyclic by-product (6) which has a Ga-H-Ga 3c-2e bond. It was formally formed by hydrogallation of the trialkyne with the sesquihydride [H2Ga-CMe3]2[H-Ga(CMe3)2]2 and was also obtained by the selective reaction with this starting material.

Stereoselective Synthesis of Silicon‐Stereogenic Aminomethoxysilanes: Easy Access to Highly Enantiomerically Enriched Siloxanes

A route towards the synthesis of N,O-functionalized silicon-stereogenic organosilanes with excellent optical purities has been developed. Investigations into the stereoconvergence and configurational stability of an aminomethoxysilane suggest a kinetically controlled multistep substitution mechanism. Selective exchange of the Si-N bond by a second Si-O bond builds the basis for the controlled formation of chiral siloxane units with different oxygen-containing functional groups. Subsequent reactions of the chiral aminomethoxysilanes with hydroxy groups support a general inversion mechanism at the asymmetrically substituted silicon atom of N,O-functionalized organosilanes.

Elastic properties of tensile nitrogen-plasma-treated multilayer silicon nitride films

Highly stressed silicon nitride thin films are used in gate first complementary metal oxide semiconductors to improve mobility in the silicon channel. Compressive stresses improve hole mobility in p-type MOS transistors while tensile stresses increase electron mobility in n-type MOS devices. High levels of compressive stress are easily reached in plasma enhanced chemical vapor deposited films by using the plasma power setting at a temperature compatible with the integration flow. Tensile stresses are more difficult to obtain with a plasma process because of the low temperatures required. Nevertheless, some post-treatments have been developed based on desorption of hydrogen that has been incorporated during the deposition step. The present study concerns one of those treatments consisting in a sequential deposition/nitrogen plasma treatment of elementary layers. Both nano-indentation and picosecond ultrasonic methods are used to measure the Young's modulus of the obtained silicon nitride thin films. The effect of the plasma treatment on the change in elastic modulus is investigated through the relationship with other properties like mass density and the concentration of SiN bonds.

Neutron-irradiation effect on the electrical characteristics of amorphous silicon carbide and nitrogen-doped silicon carbide films prepared by PECVD technology

Silicon carbide (SiC) and nitrogen-doped silicon carbide (SiC(N)) films were deposited on p-type Si(100) substrates at various deposition conditions by means of plasma-enhanced chemical vapor deposition (PECVD) technology using silane (SiH4), methane (CH4), and ammonia (NH3) gas as precursors. The concentration of elements in the films was determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analytical method simultaneously. Chemical composition was analyzed by Fourier transform infrared spectroscopy (FT-IR). The films contain a small amount of oxygen. IR results showed the presence of SiC, SiN, SiH, CH, CN, NH, and SiO bonds. The current–voltage (I–V) characteristics of samples before and after neutron irradiation were measured. The measured current increases after irradiation with neutrons.

Microstructure and the dielectric properties of SiCN–Si3N4 ceramics fabricated via LPCVD/CVI

SiCN–Si3N4 ceramics were fabricated by infiltrating SiCN into porous Si3N4 ceramics with different flux ratio of precursor gases via low-pressure chemical vapor deposition/infiltration (LPCVD/CVI). Several methods of characterization were employed to discuss the effects of different precursor gases ratio on the microstructure and dielectric properties of fabricated SiCN–Si3N4 ceramics. The deposition product is amorphous and mainly consists of SiN, CC and SiC bonds. In SiCN–Si3N4 ceramics, free carbon disperses uniformly in the amorphous and low-conductivity SiCN, which results in suitable dielectric properties. The mean real part (ε′) and imaginary part (εʺ) of permittivity increase from 3.82 and 0.05 to 7.71 and 6.94, respectively. The dielectric loss (tanδ) can be controlled from 0.014 to 0.899 by changing the flux ratio of C3H6.

Investigation of the Flatband Voltage (<I>V</I><SUB>FB</SUB>) Shift of Al<SUB>2</SUB>O<SUB>3</SUB> on N<SUB>2</SUB> Plasma Treated Si Substrate

The relationships between the physical and electrical characteristics of films treated with N2 plasma followed by forming gas annealing (FGA) were investigated. The Si substrates were treated with various radio frequency (RF) power levels under a N2 ambient. Al2O3 films were then deposited on Si substrates via remote plasma atomic-layer deposition. The plasma characteristics, such as the radical and ion density, were investigated using optical emission spectroscopy. Through X-ray photoelectron spectroscopy, the chemical-bonding configurations of the samples treated with N2 plasma and FGA were examined. The quantity of Si-N bonds increased as the RF power was increased, and Si--O--N bonds were generated after FGA. The flatband voltage (VFB) was shifted in the negative direction with increasing RF power, but the VFB values of the samples after FGA shifted in the positive direction due to the formation of Si--O--N bonds. N2 plasma treatment with various RF power levels slightly increased the leakage current due to the generation of defect sites.

XPS Studies on Nanocomposite Si–C–N Coatings Deposited by Magnetron Sputtering

A systematic X-ray photoelectron spectroscopy (XPS) investigation on silicon-carbon-nitride (Si-C-N) nano-composite thin films deposited at varying deposition parameters has been carried out. X-ray photoelectron spectroscopy analyses revealed the presence of C-N and Si-N bonds in the harder films. The hardness of the film was found to vary within the range similar to 2400 to 3300 Hv. The harder film had higher C-N/Si-N intensity ratio confirming that C-N bond formations contribute in increasing hardness value.

Bede's Liberation Philology: Releasing the English Tongue

In his tale of the miraculous healing of a mute youth inThe Ecclesiastical History of the English People(bk. 5, ch. 2), Bede figures language pedagogy as poetic emancipation. The tongue's loosening is an escape from physical disability and a figurative deliverance from the bonds of pagan sin through baptismal gesture. It also signifies liberation from the desolation of being trapped in one's own consciousness, a freeing into communion with other people. Bede uses the figure of a linguistically disabled youth to explore the grammatical underpinnings of all language, spoken or written. While he depicts the sacramental aspects of Latinate language learning, he also makes a startling move, hinting that English, a tongue ideologically and geographically peripheral, can adopt the pedagogies of Latin for its own secular uses. The story is an interpretative capstone to Bede's accounts of Cædmon, Imma, and Gregory I's encounter with English slaves in a Roman marketplace.

Photoluminescences and structrue performances of Si-rich silicon nitride thin films containing Si quantum dots

Silicon-rich silicon nitride (SiNx) thin films are deposited at 220 ℃ on n-type monocrystalline silicon substrates by plasma enhanced chemical vapor deposition using NH3 and SiH4 as the reaction gases. The samples are annealed at temperature in a range of 500-1100 ℃ in N2 atmosphere. We analyze the crystalline states of silicon quantum dots (Si-QDs) and calculate the crystalline ratios of samples under different annealing conditions according to the Raman spectra. The crystalline ratio is less than 18% when the annealing temperature is lower than 950 ℃, when the temperature reaches 1100 ℃, the crystalline ratio is increased to 53%, which indicates that most of the Si-QDs have been converted into crystallines. Fourier transform infrared spectra are measured at room temperature to investigate the evolutions of the bonding structures within the SiN_x matrix. We find that the wavelengths of Si-N and Si-H bond shift toward higher wavelength, which manifests the formation of near stoichiometric silicon nitride. Photoluminescence generated from all samples is investigated in detail. We find five luminescence peaks, whose origins are analyzed. We conclude that the obvious green luminescence (centred at 500-550 nm) oringinates from Si-QDs and the others come from different defects in the films. The effects of sizes and distribution of Si-QDs on the shift of the luminescence peak are discussed. We acquire that the sizes of Si-QDs are in a rang from 1.6 nm to 3 nm, which have an obvious confinement effect. These results are useful for fabricating contronllable Si-QDs and achievement of luminescent devices based on Si-QDs.

Tailored amorphous silicon carbide barrier dielectrics by nitrogen and oxygen doping

The effects of N or O doping into hydrogenated amorphous silicon carbide (a-SiC:H) films on molecular structure and resulting material properties with particular attention to elastic constant, cohesive fracture energy, and moisture-assisted cracking were investigated. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy characterizations demonstrated that doped N primarily formed SiN and NH bonds, and doped O formed SiO suboxide bonds. The elastic constant of both N-doped a-SiC:H (a-SiCN:H) and O-doped a-SiC:H (a-SiCO:H) films increased with increasing N and O atomic concentrations (at.%). The cohesive fracture energy, Gc, of the a-SiCN:H and a-SiCO:H films also increased with increasing N and O at.%. These increases in the mechanical properties of the films were attributed to film densification with increasing N and O at.%. The a-SiCN:H films exhibited a greater increase in Gc than the a-SiCO:H films, which was due to the moisture-insensitivity of the a-SiCN:H films as opposed to the a-SiCO:H films. The a-SiCN:H films exhibited no moisture-assisted fracture behavior, which was attributed to moisture-insensitivity of SiN bonds due to their less polar nature.

Hard and relaxed a-SiNxHy films prepared by PECVD: Structure analysis and formation mechanism

Amorphous hydrogenated silicon nitride (a-SiNxHy) films were prepared by plasma-enhanced chemical vapor deposition (PECVD). Their chemical structures and mechanical properties were investigated. Results reveal that there are four kinds of SiN groups, involving Si3N4, HSiN3, H2SiN2, and Si3SiN, in the a-SiNxHy films. Deposition at 300°C and flow ratio of SiH4/NH3=30/30sccm leads to the yield of special a-SiNxHy films, in which per two high-N-coordinated SiN groups (Si3N4 or HSiN3) are distributed with one inter-buffer group (Si3SiN). Such a-SiNxHy films exhibit ultralow residual stress (−0.17MPa), high elastic modulus (206.9GPa) and high uniformity, holding great potential for device fabrications. The chemical reactions for the formation of a-SiNxHy films were proposed, and the thermodynamic calculations indicate that the utilization ratio of NH3 reagent in the chemical reactions increases significantly with the increase of SiH4 flow, but the utilization ratio of SiN bonds in the a-SiNxHy formation decreases inversely. This work discloses valuable information on the chemical reactions and structures for a-SiNxHy films, and suggests a route to the preparation of a-SiNxHy films with high hardness and low stress by conventional PECVD.

FT IR spectroscopy of silicon oxide layers prepared with perchloric acid

Chlorine oxidation is important methods for improvement of many properties such as passivation of mobile oxide charge, breakdown strength or enhancement of the minority-carrier lifetime in the underlying silicon. In this study we consider effects influencing the density of SiO2 layers formed by three different methods: thermal oxidation at 850°C, low temperature oxidation method by use of nitric acid – HNO3 (NAOS) and HClO4 afterward passivated with KCN/HCN solutions. Thicknesses of SiO2 layers determined by both capacitance–voltage (C–V) and XPS revealed fast oxidation rate compared with samples prepared by thermal oxidation. FT IR measurement showed that all absorption spectra are almost similar. Higher absorption of the sample prepared in HClO4 was observed. No SiCl bonds were visible. Calculated atomic density of the SiO2 layer obtained from IR measurements was lowest for sample formed in HClO4. Chlorine oxidation results in higher oxidation rate (higher thickness) and formation of stoichiometric SiO2 layer with lower density. Following KCN/HCN passivation causes formation of SiN, SiO and SiOH bonds at the expense of SiCl bonds.

PECVD based silicon oxynitride thin films for nano photonic on chip interconnects applications

Thin silicon oxynitride (SiOxNy) films were deposited by low temperature (∼300°C) plasma enhanced chemical vapour deposition (PECVD), using SiH4, N2O, NH3 precursor of the flow rate 25, 100, 30sccm and subjected to the post deposition annealing (PDA) treatment at 400°C and 600°C for nano optical/photonics on chip interconnects applications. AFM result reveals the variation of roughness from 60.9Å to 23.4Å after PDA treatment with respect to the as-deposited films, favourable surface topography for integrated waveguide applications. A model of decrease in island height with the effect of PDA treatment is proposed in support of AFM results. Raman spectroscopy and FTIR measurements are performed in order to define the change in crystallite and chemical bonding of as-deposited as well as PDA treated samples. These outcomes endorsed to the densification of SiOxNy thin films, due to decrease in SiN and SiO bonds strain, as well the OH, NH bonds with in oxynitride network. The increase in refractive index and PL intensity of as deposited SiOxNy thin films to the PDA treated films at 400°C and 600°C are observed. The significant shift of PL spectra peak positions indicate the change in cluster size as the result of PDA treatment, which influence the optical properties of thin films. It might be due to out diffusion of hydrogen containing species from silicon oxynitride films after PDA treatment. In this way, the structural and optical, feasibility of SiOxNy films are demonstrated in order to obtain high quality thin films for nano optical/photonics on chip interconnects applications.

Wide variations of SiCxNy:H thin films optical constants deposited by H2/N2/Ar/hexamethyldisilazane microwave plasma

SiCxNy:H thin film growth has been achieved in N2/H2/Ar/hexamethyldisilazane microwave plasma induced chemical vapor deposition process. Depending on the N2 and H2 flow rates, film composition can be changed from “SiCx:H-like” to “SiNx:H-like”. Therefore, refractive index (n) and Tauc's optical gap (Eg) are modified over a wide range of values (1.75≤n≤2.15 and 3.5eV≤Eg≤5eV). In addition, n and Eg values are closely related to SiC bonding density. N2 addition to the plasma leads to the substitution of SiC by SiN bonds in the film and results in important composition and optical constants variations. This “silane free” process appears as an interesting plasma induced chemical vapor deposition process for silicon-based coating synthesis in the field of optical applications.

Density functional study of the intramolecular proton transfer and conformations in hydroxyaminosilanethione

The structure and reactivity of hydroxyaminosilanethione conformers were studied in the gas phase using density functional theory. Eight local minima were located, including two featuring pentacoordinate silicon atoms (2Z, S2) and one with a nitrososilanethiol structure (4Z). The global minimum at the B3LYP/6-31++G(dp)//B3LYP/6-31G(d) levels of theory is S2. Natural bond orbital (NBO) analysis reveals that there is a strong nS2→σN3Si1∗ interaction in the majority of isomers. The 3d orbitals of silicon are of minor importance in bonding for the isomers with the exception of those where the silicon is penta-coordinate (2Z and S2), where the occupancy of the 3d orbitals is 2.93, 4.34 respectively. The charge density and its Laplacian at the bond critical point (BCP), (ρ(r) and ∇2ρ(r)), indicate that all SiS, SiN and SiH bonds were constructed by ionic or electrostatic interactions, whereas NH and OH bonds are predominantly covalent. In addition, seven transition states connecting the various minima were located. TS7 has the highest energy (75.75kcal/mol) in the reaction coordinates and is therefore the rate-determining step in the conversion of 1Z–4Z. TS7, TS2 and TS3 have the highest energies (75.75, 66.50 and 57.92kcal/mol, respectively). The computed harmonic frequencies results were in good agreement with available experimental values. The spectra of S1 and 2Z have the lowest NH frequencies (3117 and 2965cm−1), this shift towards the lower frequency being attributable to the presence of intramolecular hydrogen bonding in S1 and 2Z.

Evolution of silicon nanoclusters and hydrogen in SiNx:H films: Influence of high hydrostatic pressure under annealing

Hydrogenated silicon-rich nitride (SRN) films of various stoichiometry (SiNx:H, 0.7<x≤1.3) were deposited on single-crystalline Si substrates with the use of plasma enhanced chemical vapor deposition at a temperature of 100°С. Furnace annealing for 5h in ambient Ar at 1130°С under atmospheric and enhanced hydrostatic pressure (HP — 11kbar, 1.1GPa) was applied to modify the structure of the films. The properties of as-deposited and annealed films were studied using ellipsometry, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, photoluminescence (PL), as well as high-resolution transmittance electron microscopy (HRTEM). According to the Raman data, the as-deposited film, in which the stoichiometry parameter x is below 1.0, contains amorphous silicon nanoclusters. Furnace annealing leads to crystallization of the nanoclusters. From the HRTEM and Raman data, the average size of the Si nanocrystals in the annealed films was 6–7nm. No silicon nanoclusters were observed in the as-deposited films with relatively low concentration of excessive silicon atoms (the case of SiNx:H, x>1); furnace annealing leads to segregation of the Si and Si3N4 phases, so, the amorphous Si clusters were observed in annealed films according to Raman data. Surprisingly, after annealing with such high thermal budget, according to the FTIR data, the SRN film with parameter x close to that of the stoichiometric silicon nitride contains hydrogen in the form of SiH bonds. From analysis of the FTIR data of the SiN bond vibrations one can conclude that silicon nitride is partly crystallized in the films with x>1 after annealing for 5h. No influence of HP on the structure of Si nanoclusters was observed in the case of SRN films with x≤1.1. Dramatic changes in the PL spectra of the SRN films with the x parameter close to that of the stoichiometric silicon nitride (x≈1.3), annealed under atmospheric pressure and HP, were observed. HP stimulates the formation of very small hydrogenated amorphous nanoclusters. The size of amorphous Si nanoclusters determined from the quantum size effect model describing the PL spectra, should be 2–4nm in this case.

Reactive ladder-like poly(p-decyl anilino)silsesquioxane for functional material’s precursor: Synthesis, characterization and functionalization

A well-defined polysilsesquioxane with reactive Si–N bonds, poly(p-decyl anilino)silsesquioxane (PASQ), was successfully prepared using supramolecular template polymerization. The monomers 1,3-bis-(p-decyl anilino)-1,1,3,3-tetrachloro-disiloxanes first self-assembled into ladder superstructures (LSs) primarily through the synergistic interactions of hydrogen bonding and the van der Waals interactions, and then polymerized by adding water and triethylamine to produce a well-defined PASQ. The LSs was fully characterized using vapor pressure osmometry (VPO), UV–vis spectroscopy and X-ray diffraction (XRD). NMR and XRD measurements revealed that the PASQ was a ladder polymer. The reactivity of PASQ was confirmed by its SiN bond reacting with trimethylsilanol to form a ladder-like trimethylsiloxysilicate (LMQ). The ladder structure of LMQ was also thoroughly characterized, which further verified the ladder structural regularity of PASQ.