Study of chemical bonds and element composition of silicon oxycarbonitride films by the methods of XP-, IR-, and energy-dispersive spectroscopy

The element composition and chemical bonds of nanocomposite films of hydrogenated silicon oxycarbonitride fabricated through high-frequency plasma-chemical deposition from initial gas mixtures of 1,1,3,3-tetramethyldisilazane with nitrogen and oxygen in the temperature range 373–973 K depending on the synthesis conditions is studied. The effect of changes in the temperature and chemical composition of the initial gas mixtures on the element composition and types of chemical bonds in SiC _x N _y O _z :H films is investigated.     

Synthesis of silicon carbonitride dielectric films with improved optical and mechanical properties from tetramethyldisilazane

Films of silicon carbonitride have been obtained by the plasma chemical decomposition of a gaseous mixture of helium and a volatile organic silicon compound 1,1,3,3-tetramethyldisilazane (TMDS) in the temperature range of 373–973 K. The modeling of the processes of deposition from a gaseous mixture (TMDS + He) in the temperature range of 300–1300 K and pressures of P _total ⁰ = 10^?2–10 Torr has shown that it is possible to vary the equilibrium composition of the condensed phase depending on the synthesis temperature and the initial gaseous mixture composition. The chemical and phase compositions, as well as physicochemical and functional properties, of the films obtained in the range of 373–973 K have been studied using a complex of modern techniques, including Fourier transformed infrared (FTIR) Raman, X-ray photoelectron (XPS) and energy-dispersive spectroscopy (EDS), scanning electron (SEM) and atomic-force microscopy (AFM), X-ray diffraction using synchrotron radiation (XRD-SR), ellipsometry, and spectrophotometry. The electrophysical parameters are determined using the C-V and I-V characteristics, and the microhardness and Young’s modulus are determined by the nanoindentation method. It is established that the chemical composition of low-temperature (373–673 K) films of silicon carbonitride corresponds to a gross formula of SiC _x N _y O _z : H, while that of high-temperature films corresponds to SiC _x N _y . The presence of nanocrystals with the phase composition close to the standard phase α-Si₃N₄ is detected in the films. It is shown that all of the films are perfect dielectrics (k = 3.8–6.4, ρ = 2.2 × 10¹⁰?1.3 × 10¹¹ Ohm · cm), possess high transparency (～98%) in a wide spectral range of 280–2500 nm, and have a high microhardness (3.8–36 GPa) and Young’s momentum (125–190 GPa).     

Effects of oxygen on the thermal stability of silicon nitride fibers

Two types of Si₃N₄ fibers with different oxygen contents were annealed in a nitrogen atmosphere at 1500 °C for 1 h. After annealing, the fiber (SN-L) containing 0.5 wt% oxygen crystallized to α-Si₃N₄ but lost its strength, whereas the fiber (SN-H) containing 4.2 wt% oxygen was amorphous and retained 63.6% of its strength. The phase transition in these fibers was mainly influenced by the oxygen level. The lower oxygen content in the SN-L favored the precipitation of an almost stoichiometric composition of α-Si₃N₄ initially at ~1450 °C with an activation energy (Ea) of 663.357 kJ/mol. Nanopores existing naturally in the fiber promoted crystallization via heterogeneous nucleation. SN-H precipitated as an amorphous SiN_xO_y metaphase preferentially at ~1400 °C with an Ea of 440.434 kJ/mol, owing to the higher oxygen content approaching that of Si₂N₂O. SiN_xO_y inhibited the crystallization of α-Si₃N₄, making SN-H more thermally stable than SN-L at temperatures above 1500 °C.     

Bonding characterization and nano-indentation study of the amorphous SiCxNy films with and without hydrogen incorporation

The hardness and effective modulus of hydrogen-containing and hydrogen-free amorphous SiC_xN_y films were studied by nano-indentation. Amorphous SiC_xN_y films with and without hydrogen were deposited by electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD) using a SiH₄–CH₃NH₂–N₂–H₂ gas mixture and hydrogen-free ion-beam sputtering deposition (IBSD), respectively. Fourier-transform infrared spectroscopy (FTIR) studies were used to investigate the bonding states of the SiC_xN_y materials. SiH, CH and NH bonds were detected by FTIR in ECR-CVD, but not in IBSD, films. The incorporation of hydrogen led to a reduction in both the hardness and modulus of the amorphous SiC_xN_y films. From nano-indentation measurements, the hardness and effective modulus of the IBSD coated, hydrogen-free amorphous SiC_xN_y films were 27–30 and 211–258 GPa, respectively. The corresponding values for the ECR-CVD coated, hydrogen-containing amorphous SiC_xN_y were 22–26 and 115–144 GPa, respectively.     

Synthesis and Properties of Thin Films Formed by Vapor Deposition from Tetramethylsilane in a Radio-Frequency Inductively Coupled Plasma Discharge

Thin films of hydrogenated silicon carbide (SiC_x:H) and carbonitride (SiC_xN_y:H) are synthesized in a reactor with inductively coupled RF plasma with the introduction of tetramethylsilane vapors and additive gases—argon and/or nitrogen. The process is carried out at different synthesis temperatures, plasma power, and partial pressure of tetramethylsilane and additive gases in the reactor. The dependences on the synthesis conditions of the films’ growth rate, chemical composition, and properties such as the light transmission coefficient, refractive index, optical band gap, and dielectric constant are obtained. The weak dependence of the films’ composition and properties on the preset synthesis conditions is a characteristic feature of the studied process within the investigated range of conditions. The possible reasons of this phenomenon and the results of in situ studies of the gas phase composition in the plasma are examined.     

Mechanical Properties and Microstructural Characterization of Amorphous SiCxNy Thin Films After Annealing Beyond 1100°C

The effect of thermal annealing on structure and mechanical properties of amorphous SiC_xN_y (y ≥ 0) thin films was investigated up to 1500°C in air and Ar. The SiC_xN_y films (2.2–3.4 μm) were deposited by reactive DC magnetron sputtering on Si, Al₂O₃ and α‐SiC substrates without intentional heating and at 600°C. The SiC target with small excess of carbon was sputtered at various N₂/Ar gas flow ratios (0–0.48). The nitrogen content in the films changes in the range 0–43 at.%. Hardness and elastic modulus (nanoindentation), change in film thickness, film composition, and structure (Raman spectroscopy, XRD) were investigated in dependence on annealing temperature and nitrogen content. All SiC_xN_y films preserve their amorphous structure up to 1500°C. The hardness of all as‐deposited and both air‐ and Ar‐annealed SiC_xN_y films decreases with growth of nitrogen content. The annealing in Ar at temperatures of 1100°C–1300°C results in noticeable hardness growth despite the ordering of graphite‐like structure in carbon clusters in nitrogen free films. Unlike the SiC, this graphitization leads to hardness saturation of SiCN films starting above 900°C, especially for films with higher nitrogen content (deposited at higher N₂/Ar). This indicates the practical hardness limit achievable by thermal treatment for SiC_xN_y films deposited on unheated substrates. The ordering in carbon phase is facilitated by the presence of nitrogen in the films and its extent is controlled by the N/C atomic ratio. The suppression of graphitization was observed for N/C ranging between 0.5–0.7. Films deposited at 600°C show higher hardness and oxidation resistance after annealing in comparison with those deposited on unheated substrates. Hardness reaches 40 GPa for SiC and ~28 GPa for SiC_xN_y (35 at.% of nitrogen). Such a high hardness of SiC film stems from its partial crystallization. Annealing of SiC_xN_y film (35 at.% of N) in Ar at 1400°C is accompanied by formation of numerous hillocks (indicating heterogeneous structure of amorphous films) and redistribution of film material.     

β-SiAlON-TiN/TiB<Subscript>2</Subscript>-BN composites by infiltration-mediated SHS under high pressure of nitrogen gas

Infiltration-mediated SHS of β-Si_6–z Al _z O _z N_8–z –TiN/TiB₂–BN composites was explored upon variation in applied nitrogen pressure, amount of combustible and inert components in green mixture, sample size, and BN content of resultant composites. Synthesized ceramics of different density and phase composition were characterized by their strength parameters, tribological behavior, electrical resistance, and thermal shock resistance.     

Alkali-thermal gasification and hydrogen generation potential of biomass

Generating hydrogen gas from biomass is one approach to lowering dependencies on fossil fuels for energy and chemical feedstock, as well as reducing greenhouse gas emissions. Using both equilibrium simulations and batch experiments with NaOH as a model alkaline, this study established the technical feasibility of converting various biomasses (e.g., glucose, cellulose, xylan and lignin) into H₂-rich gas via catalyst-free, alkalithermal gasification at moderate temperatures (as low as 300 °C). This process could produce more H₂ with less carbon-containing gases in the product than other comparable methods. It was shown that alkali-thermal gasification follows C _x H _y O _z + 2xNaOH + (x–z)H₂O = (2x + y/2–z)H₂ + xNa₂CO₃, with carbonate being the solid product which is different from the one suggested in the literature. Moreover, the concept of hydrogen generation potential (H₂-GP)—the maximum amount of H₂ that a biomass can yield, was introduced. For a given biomass C _x H _y O _z , the H₂-GP would be (2x + y/2–z) moles of H₂. It was demonstrated experimentally that the H2-GP was achievable by adjusting the amounts of H₂O and NaOH, temperature and pressure.

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Use of hexamethylcyclotrisilazane for preparation of transparent films of complex compositions

This paper reports on the results of the thermodynamic modeling of chemical vapor deposition of SiC _x N _y silicon carbonitride films with the use of the volatile organosilicon compound hexamethylcyclotrisilazane (HMCTS) over a wide temperature range 300–1300 K at low pressures of 10^?2?10 Torr. It is demonstrated that there are ranges of conditions under which the gas phase is in equilibrium with a mixture of solid phases SiC + Si₃N₄ + C with the total composition represented in the form of the ternary compound SiC _x N _y . Transparent silicon carbonitride films of different compositions are experimentally obtained under conditions in the above range through plasma-enhanced chemical vapor deposition at a pressure of 5 × 10^?2 Torr and temperatures of 373–1023 K with the use of the initial gaseous mixture of hexamethylcyclotrisilazane and helium. The chemical and phase compositions of the films are determined and their properties are investigated using ellipsometry, IR and Raman spectroscopy, spectrophotometry, energy-dispersive spectroscopy, and synchrotron X-ray powder diffraction. It is shown that the films synthesized at low temperatures of 373–573 K contain a considerable amount of hydrogen. The results obtained ftom atomic-force and scanning electron microscopy indicate that the films involve nanograins.     

Amorphous carbon nitride deposition by nitrogen radical sputtering C+N+O+H

Amorphous carbon nitride films a-CN_x were prepared by a nitrogen radical sputtering of a carbon target. A-CN_x films were treated by atomic hydrogen or by an oxygen plasma, using a layer-by-layer method, forming LLa-CN_x or LLa-CN_xO_y. These a-CN_x films show large photosensitivity, high resistivity and low dielectric constants. Possible applications are also discussed briefly.     

Effects of niobium doping site and concentration on the phase structure and oxygen permeability of Nb-substituted SrCoOx oxides

Niobium doping effect on phase structure, phase stability and electrical conductivity of SrCoO_x oxides and oxygen permeability of the corresponding membranes were systematically investigated. Niobium was successfully incorporated into A-site, B-site or simultaneously A and B double sites of SrCoO_x oxide and stabilized the perovskite structure with a cubic symmetry in air down to room temperature at a proper doping amount. However, the A-site doping could not stabilize the cubic structure under a more reducing atmosphere of nitrogen, as to SrCo_1?yNb_yO_3?δ, y ≥ 0.1 is necessary to sustain the cubic perovskite structure. Simultaneous doping of Nb at A and B sites is the most effective way to stabilize the perovskite structure under nitrogen atmosphere. Irrespective of doping site, the electrical conductivity decreased monotonously with Nb-doping amount. Both Nb_xSr_1?xCoO_3?δ and Nb_zSr_1?zCo_1?zNb_zO_3?δ envisaged a decrease in oxygen permeation flux with Nb-doping amount while SrCo_1?yNb_yO_3?δ reached the maximum flux at y = 0.1. Among all the membranes, SrCo_0.9Nb_0.1O_3?δ and Nb_0.05Sr_0.95Co_0.95Nb_0.05O_3?δ show the highest oxygen fluxes of 3.5 and 2.7 ml cm^?2 min^?1 at 900 °C under an air/helium gradient, respectively.     

Parameters of luminescence and the local structure of Eu<Superscript>3+</Superscript> centers in fluorogermanate glasses

The influence of the chemical nature of the local environment of Eu³⁺ ions on the parameters of luminescence of these centers in glasses of the (BaGeO₃)_{1 ? x ? y} (Al₂O₃) _x (0.45CaF₂ · 0.55MgF₂) _y (x = 0.25, y = 0; x = 0.17, y = 0.17; x = 0.15, y = 0.22; x = 0.07, y = 37.00; x = 0, y = 0.45) system is investigated. The oxidation state of europium atoms and the degree of homogeneity of their local environment in the glasses are determined using ¹⁵¹Eu Mössbauer spectroscopy.     

Synthesis of nonstoichiometric aluminomagnesium spinel with a tetragonal lattice (review)

The results of x-ray diffraction and IR-spectroscopic studies of samples of nonstoichiometric aluminomagnesium spinel Mg_1?x Al_2?y O_4?z (OH)_z formed after treating aluminomagnesium spinel synthesized by the sol-gel method at temperatures of 800 and 1100°C with concentrated acids, are reported. It was found that three phases of nonstoichiometric aluminomagnesium spinel Mg_1?x Al_2?y O_4?z (OH)_z with tetragonal lattices and a different type of superstructure are formed. The x-ray patterns of the two phases correspond to body-centered lattices with parameters a = 5.712(3) Å, c = 8.092(3) Å, and a = 5.714(3) Å. The x-ray pattern of the third phase was indexed in a primitive tetragonal lattice: a = 5.718(3) Å, c = 24.261(27) Å.     

Structural properties and sensing performances of CoNxOy ceramic films for EGFET pH sensors

This paper describes the impact of both Ar/N₂ flow rate and rapid thermal annealing (RTA) on the structural properties and sensing characteristics of CoN_xO_y ceramic films formed through reactive sputtering and then used in extended-gate field-effect transistor (EGFET) pH sensors. The CoN_xO_y ceramic films were prepared under three different Ar/N₂ flow rates (20/5, 20/10, and 20/15) and then annealed at three different RTA temperatures (200, 300, and 400 °C). X-ray diffraction revealed that all of the CoN_xO_y ceramic films featured amorphous structures. X-ray photoelectron spectroscopy demonstrated that the Co³⁺ content of the CoN_xO_y film prepared at the 20/10 flow rate was higher than those of the films prepared at the other flow rates. Atomic force microscopy indicated that the surface roughnesses of the CoN_xO_y films obtained at flow rates of 20/10 and 20/15 were higher than that of the film prepared at 20/5. High pH-sensitivity (64.36 mV/pH), a small drift rate (0.27 mV/h), and a low hysteresis voltage (1.4 mV) were achieved for the CoN_xO_y EGFET sensor that had been fabricated at a flow rate of 20/10 with subsequent RTA at 300 °C. This high performance was due to its CoN_xO_y film having a rough surface, a high Co³⁺ ion content, and a low number of oxygen vacancies or defects.     

Catalytic Membrane Reactors – Chemical Upgrading and Pollution Control

This article presents an overview on oxygen permeation, oxidative activation of light hydrocarbons and splitting of various molecules (H₂O, N₂O, NO_x) containing oxygen in a hollow fiber catalytic membrane reactor made of BaCo_xFe_yZr_zO_3–δ (BCFZ, x+y+z = 1) which is used to separate oxygen from oxygen containing gases. Innovative reactor concepts are introduced and performances for the various applications are discussed. A detailed view is also given on the thermodynamic and kinetic background with regard to the above mentioned reactions. The potentials in terms of product intensification and energy saving by usage of the BCFZ hollow fibers as reaction vessels are evaluated. However, there are still technological challenges that prevent the described processes from being practiced on commercial scale by now.     

Tantalum (oxy)nitrides prepared using reactive sputtering for new nonplatinum cathodes of polymer electrolyte fuel cell

Tantalum (oxy)nitrides (TaO_xN_y) have been investigated as new cathodes for polymer electrolyte fuel cells without platinum. TaO_xN_y films were prepared using a radio frequency magnetron sputtering under Ar + O₂ + N₂ atmosphere at substrate temperatures from 50 to 800 °C. The effect of the substrate temperature on the catalytic activity for the oxygen reduction reaction (ORR) and properties of the TaO_xN_y films were examined. The catalytic activity of the TaO_xN_y for the ORR increased with the increasing substrate temperature. The ORR current density at 0.4 V vs. RHE on TaO_xN_y prepared at 800 °C was approximately 20 times larger than that on TaO_xN_y prepared at 50 °C. The onset potential of the TaO_xN_y for the ORR was obtained at the ORR current density of −0.2 μA cm⁻². The onset potential of the TaO_xN_y prepared at 800 °C was ca. 0.75 V vs. RHE. The X-ray diffraction patterns revealed that Ta₃N₅ structure grew as the substrate temperature increased. While, the ionization potentials of all specimens were lower than that of Ta₃N₅, and decreased with the increasing substrate temperature. The TaO_xN_y which had Ta₃N₅ structure and lower ionization potential might have a definite catalytic activity for the ORR.     

Corrosion of HIPed β-Si6−zAlzOzN8−z (z =0, 1, 2, 3) ceramics by NaCl vapor

Tests for the corrosion of β-Si_6−zAl_zO_zN_8−z (z =0, 1, 2, 3) (β-Si₃N₄ and β-SiAlON) ceramics were carried out at 1300 °C for 3–24 h in NaCl vapor of various concentrations (1.67 × 10⁻², 3.33 × 10⁻², 5.0 × 10⁻² g l⁻¹), which was carried by flowing Ar gas. The densified Si₃N₄ and SiAlON ceramics were fabricated by HIPing under N₂ of 150 MPa at 1700 °C. The corroded surface was observed by optical and scanning electron microscopy (OM and SEM). The phases produced during corrosion were identified by X-ray diffraction. The thickness of the corroded scale was determined by cross sectional SEM observation. The Si₃N₄ ceramics were hardly corroded by NaCl vapor, while the z=1 and 2 SiAlONs were slightly corroded with the formation of bubbles on the surface; the z=3 ceramics were severely corroded with the formation of Al₂O₃ needle crystals and fine mullite crystals, depending on the NaCl vapor concentration. Quantitative X-ray microanalysis showed that 2 at.% Na is contained in all the scales of the SiAlONs. The severe corrosion of the z=3 SiAlON was explained on the basis of the kinetic results for the thickness of the scale.     

Synthesis and Physicochemical Properties of Nanocrystalline Silicon Carbonitride Films Deposited by Microwave Plasma from Organoelement Compounds

Nanocrystalline films of a ternary compound, namely, silicon carbonitride SiC_xN_y, are prepared by plasma-enhanced chemical vapor deposition at temperatures of 473–1173 K with the use of a complex gaseous mixture of hexamethyldisilazane Si₂NH(CH₃)₆, ammonia, and helium. The chemical and phase compositions and the physicochemical properties of the films are investigated using IR, Auger electron, and X-ray photoelectron spectroscopy; ellipsometry; synchrotron X-ray powder diffraction; electron and atomic-force microscopy; microhardness measurements with a nanoindenter; and electrical measurements. Correlations of the composition of the initial gas phase and the synthesis temperature with a number of functional properties of the SiC_xN_y silicon carbonitride films are revealed.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Fainer, Kosinova, Rumyantsev, Maksimovskii, Kuznetsov, Kesler, Kirienko, Han Bao-Shan, Lu Cheng.     

The forming region and mechanical properties of CaO-Al2O3-SiO2 system

Glass system with compositions of 93.9% (xCaO-yAl₂O₃-zSiO₂)−5% MgO-1% B₂O₃−0.1% Fe₂O₃ has been prepared by a conventional melt-quenching technique, and the glass forming region and the mechanical properties of the derived glasses were investigated. The approximate glass forming region was found to be x = 10～35%, y = 10～35% and z = 50～80%, while the rest of the area was crystallization zone or crack zone. As x = 10%, y = 25% and z = 65% (Sample 13), the investigated glass possesses the optimum volume density, bending strength, compression strength and modulus, which are 2.572 g/cm³, 74.05 MPa, 312.84 MPa and 163.96 GPa, respectively. Compared to sample 13, samples with different compositions have reduced the volume density, lowered the Raman intensity and improved the optical band gap. For the mechanical properties, with decreasing the contents of SiO₂, the bending strength firstly increases, then decreases and finally shows a relatively small increasing trend. The dependence of compression strength and compression modulus on SiO₂ content shows a similar trend to the bending strength. Moreover, the optical band gap and Raman spectrum of the sample 13 indicate that the number of oxygen bonds in the bridge reach the maximum, which could further confirm a significantly improvement on the mechanical properties.     

Identification of hydrotreatment-resistant heteroatomic species in a crude oil distillation cut by electrospray ionization FT-ICR mass spectrometry

The diminishing clean oil reserve is driving the search for new or improved ways to reduce the level of NSO-containing species found in high abundance in heavy crude oils. Hydrotreatment is the currently preferred technique to remove those polar species. Unfortunately, nitrogen-containing compounds cause coke formation on the surface of the hydrotreatment catalyst, leading to partial or complete deactivation. Here, positive- and negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) identify those nitrogen compounds that resist hydrotreatment. ESI preferentially ionizes polar (e.g., heteroatom-containing) species: basic molecules are detected as positive ions and acidic/neutral molecules as negative ions. FT-ICR MS resolves thousands of species in a single mass spectrum, allowing for unambiguous determination of elemental composition, C_cH_hN_nO_oS_s, for identification of compound “class” (numbers of N, O, S heteroatoms, “type” (rings plus double bonds), and carbon number (revealing the extent of alkylation). We find that hydrotreatment-resistant compounds typically contain a single nitrogen atom, both pyridinic benzalogs and pyrollic benzalogs. Compounds with more than one heteroatom, such as O_x, N_xO_y, N_xS_y and N_x, are partially removed. Compound classes with lower double bond equivalents or fewer CH₂ groups are preferentially removed. Species that contain O_xS_y are fully removed by hydrotreatment.