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 SiCxNyOz:H films is investigated. 相似文献
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 Ptotal0 = 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 SiCxNyOz: H, while that of high-temperature films corresponds to SiCxNy. 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). 相似文献
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 SiNxOy metaphase preferentially at ~1400 °C with an Ea of 440.434 kJ/mol, owing to the higher oxygen content approaching that of Si2N2O. SiNxOy inhibited the crystallization of α-Si3N4, making SN-H more thermally stable than SN-L at temperatures above 1500 °C. 相似文献
The hardness and effective modulus of hydrogen-containing and hydrogen-free amorphous SiCxNy films were studied by nano-indentation. Amorphous SiCxNy 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 SiCxNy materials. SiH, CH and NH 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 SiCxNy films. From nano-indentation measurements, the hardness and effective modulus of the IBSD coated, hydrogen-free amorphous SiCxNy films were 27–30 and 211–258 GPa, respectively. The corresponding values for the ECR-CVD coated, hydrogen-containing amorphous SiCxNy were 22–26 and 115–144 GPa, respectively. 相似文献
Thin films of hydrogenated silicon carbide (SiCx:H) and carbonitride (SiCxNy: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. 相似文献
The effect of thermal annealing on structure and mechanical properties of amorphous SiCxNy (y ≥ 0) thin films was investigated up to 1500°C in air and Ar. The SiCxNy 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 SiCxNy films preserve their amorphous structure up to 1500°C. The hardness of all as‐deposited and both air‐ and Ar‐annealed SiCxNy 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 SiCxNy 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 SiCxNy (35 at.% of nitrogen). Such a high hardness of SiC film stems from its partial crystallization. Annealing of SiCxNy 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. 相似文献
Infiltration-mediated SHS of β-Si6–zAlzOzN8–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. 相似文献
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 CxHyOz + 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 CxHyOz, 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.
This paper reports on the results of the thermodynamic modeling of chemical vapor deposition of SiCxNy 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 SiCxNy. 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. 相似文献
Amorphous carbon nitride films a-CNx were prepared by a nitrogen radical sputtering of a carbon target. A-CNx films were treated by atomic hydrogen or by an oxygen plasma, using a layer-by-layer method, forming LLa-CNx or LLa-CNxOy. These a-CNx films show large photosensitivity, high resistivity and low dielectric constants. Possible applications are also discussed briefly. 相似文献
Niobium doping effect on phase structure, phase stability and electrical conductivity of SrCoOx 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 SrCoOx 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 SrCo1?yNbyO3?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 NbxSr1?xCoO3?δ and NbzSr1?zCo1?zNbzO3?δ envisaged a decrease in oxygen permeation flux with Nb-doping amount while SrCo1?yNbyO3?δ reached the maximum flux at y = 0.1. Among all the membranes, SrCo0.9Nb0.1O3?δ and Nb0.05Sr0.95Co0.95Nb0.05O3?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. 相似文献
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. 相似文献
The results of x-ray diffraction and IR-spectroscopic studies of samples of nonstoichiometric aluminomagnesium spinel Mg1?xAl2?yO4?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 Mg1?xAl2?yO4?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. 相似文献
This paper describes the impact of both Ar/N2 flow rate and rapid thermal annealing (RTA) on the structural properties and sensing characteristics of CoNxOy ceramic films formed through reactive sputtering and then used in extended-gate field-effect transistor (EGFET) pH sensors. The CoNxOy 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 CoNxOy ceramic films featured amorphous structures. X-ray photoelectron spectroscopy demonstrated that the Co3+ content of the CoNxOy 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 CoNxOy 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 CoNxOy 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 CoNxOy film having a rough surface, a high Co3+ ion content, and a low number of oxygen vacancies or defects. 相似文献
This article presents an overview on oxygen permeation, oxidative activation of light hydrocarbons and splitting of various molecules (H2O, N2O, NOx) containing oxygen in a hollow fiber catalytic membrane reactor made of BaCoxFeyZrzO3–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. 相似文献
Tantalum (oxy)nitrides (TaOxNy) have been investigated as new cathodes for polymer electrolyte fuel cells without platinum. TaOxNy 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 TaOxNy films were examined. The catalytic activity of the TaOxNy for the ORR increased with the increasing substrate temperature. The ORR current density at 0.4 V vs. RHE on TaOxNy prepared at 800 °C was approximately 20 times larger than that on TaOxNy prepared at 50 °C. The onset potential of the TaOxNy for the ORR was obtained at the ORR current density of −0.2 μA cm−2. The onset potential of the TaOxNy 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 TaOxNy which had Ta3N5 structure and lower ionization potential might have a definite catalytic activity for the ORR. 相似文献
Tests for the corrosion of β-Si6−zAlzOzN8−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. 相似文献
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. 相似文献
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, CcHhNnOoSs, 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 Ox, NxOy, NxSy and Nx, are partially removed. Compound classes with lower double bond equivalents or fewer CH2 groups are preferentially removed. Species that contain OxSy are fully removed by hydrotreatment. 相似文献