Chemical Vapor Reaction Research Articles

SiC/SiC minicomposites with (PyC/TiC)n interphases processed by pressure-pulsed reactive CVI

(Pyrocarbon/titanium carbide) n multilayered interphases were prepared within SiC/SiC minicomposites by a new method: pressure-pulsed reactive chemical vapour infiltration (P-RCVI). This method combines P-CVI with reactive chemical vapour deposition (RCVD). Minicomposite tensile tests with unload-reload cycles have shown that the interfacial shear stress depends on the number of TiCl4 gas pulses used for the processing of TiC sub-layers. TEM observations have shown, that with a few gas pulses, the carbide nucleates as isolated grain islands which disturbs the structural anisotropy of the pyrocarbon. This structure results in a good mechanical fibre/matrix load transfer. By increasing the number of gas pulses, the TiC sub-layers become continuous and it is possible to partially consume the highly ordered pyrocarbon sub-layers, but, in that case, the load transfer is poor. The specimen behaviour in air at 700°C under a constant tensile loading was assessed. Compared with a pure pyrocarbon reference interphase, the interphases containing TiC significantly improve the lifetime of the SiC/SiC minicomposites.

気相反応を用いるフッ素系有機薄膜の生成と性質

A SUS316 substrate surface was modified with fluoroalkylsilane (FAS) by a chemical vapor reaction with the aim to form fluoride thin layers on the metal surface. The water repellency of the substrate surface increased with the reaction time. When the reaction temperature was 150ºC and the reaction time was over 1 hour, the water contact angle of the substrate surface reached 110º. Furthermore, a random multi layer formed when the reaction time increased and the reaction temperature was raised. The increasing the amount of FAS in the reaction stage reinforced the durability of this layer. And the layer that formed on the SUS316 substrate was stronger than that which formed on the glass. X-ray photoelectron spectra (XPS) analysis revealed C-F covalent bonds on the treated substrate. On the basis of these results, the formation mechanism of fluoride thin layers was discussed.

Chemical preparation and characterization of nitrogen-rich carbon nitride powders

Creamy white powders were obtained by the chemical vapor reaction of carbon tetrachloride and ammonia at 1000 °C, followed by washing with boiling water. The composition of the material was C 3N 5.5O 0.5H 5.4, having a nitrogen content greater than that of the hypothetical hard material C 3N 4. The powders were harder than quartz whose Mohs hardness is 7, but were not as hard as sapphire (Mohs hardness: 9). The hardness could be explained by the C–N single bond observed in the ESCA C1s spectrum. The material washed with boiling water showed photoluminescence, which was mostly bright and white-blue in color to the naked eye.

Ni-seeding effects on the properties of polycrystalline silicon–germanium grown at low temperature

We have investigated the Ni-seeding effects on the low-temperature growth of the polycrystalline silicon–germanium (poly-SixGe1−x) films by reactive thermal chemical vapor deposition with Si2H6 and GeF4. Very thin Ni films (<2 nm) were deposited on the glass substrates by electron beam evaporation in prior to poly-SixGe1−x deposition. The crystallinity and electrical performance of the poly-SixGe1−x films were characterized. p-channel bottom-gate thin-film transistors (TFTs) were also fabricated with these films to evaluate the effect of Ni seeding on device performance. We found that a certain amount of Ni, i.e., less than 0.5 nm, impacts upon the grain size and crystallinity without additional degradation of electrical properties due to the incorporation of Ni in the film. A 0.2 nm equivalent thickness of Ni gives the best crystallinity and the largest grain size (135 nm) and results in the highest mobility (31 cm2/V s) in p-channel TFTs fabricated on SiO2/Si substrates.

SiC nanowire networks

Novel 2-D semiconductor SiC nanonetworks have been synthesized at relatively low-temperature via a new method (chemical vapor reaction approach) in a homemade graphite reaction cell. The mixture of milled Si and SiC powder and C 3H 6 were chosen as the starting materials. EDX, XRD and HRTEM indicated that the nanonetworks are formed by interconnecting nanowires. The nanowires with diameter of about 20–70 nm are single crystalline β-SiC and the growth direction is along [111]. A growth mechanism of β-SiC nanowire networks is discussed.

Growth Behavior and Thermal Stability of CoSi2 Layer on Poly-Si Substrate Using Reactive Chemical Vapor Deposition

Uniform polycrystalline <TEX>$CoSi_2$</TEX>layers have been grown in situ on a polycrystalline Si substrate at temperature near <TEX>$625^{\circ}C$</TEX> by reactive chemical vapor deposition of cyclopentadienyl dicarbonyl cobalt, Co(η<TEX>$^{5}$</TEX> -C<TEX>$_{5}$</TEX> H<TEX>$_{5}$</TEX> )(CO)<TEX>$_2$</TEX>. The growth behavior and thermal stability of <TEX>$CoSi_2$</TEX>layer grown on polycrystalline Si substrates were investigated. The plate-like CoSi<TEX>$_2$</TEX>was initially formed with either (111), (220) or (311) interface on polycrystalline Si substrate. As deposition time was increasing, a uniform epitaxial <TEX>$CoSi_2$</TEX>layer was grown from the discrete <TEX>$CoSi_2$</TEX>plate, where the orientation of the<TEX>$ CoSi_2$</TEX>layer is same as the orientation of polycrystalline Si grain. The interface between <TEX>$CoSi_2$</TEX>layer and polycrystalline Si substrate was always (111) coherent. The growth of the uniform <TEX>$CoSi_2$</TEX>layer had a parabolic relationship with the deposition time. Therefore we confirmed that the growth of <TEX>$CoSi_2$</TEX>layer was controlled by diffusion of cobalt. The thermal stability of <TEX>$CoSi_2$</TEX>layer on small grain-sized polycrystalline Si substrate has been investigated using sheet resistance measurement at temperature from <TEX>$600^{\circ}C$</TEX> to <TEX>$900^{\circ}C$</TEX>. The <TEX>$CoSi_2$</TEX>layer was degraded at <TEX>$900^{\circ}C$</TEX>. Inserting a TiN interlayer between polycrystalline Si and <TEX>$_CoSi2$</TEX>layers improved the thermal stability of <TEX>$CoSi_2$</TEX>layer up to <TEX>$900^{\circ}C$</TEX> due to the suppression of the Co diffusion.

Synthesis process and growth mechanism of Y′-Fe4N nanoparticles by phase- transformation

Multiphase Fe/N nanoparticles were synthesized by means of chemical vapor reaction, the influence of the preparing parameters on the properties of particles was studied carefully during the first nitriding process. The optimum process was determined. Single phase γ ′-Fe 4 N was prepared by twice-nitriding. Multiphase iron-nitride really transforms γ ′-Fe 4 N nanoparticle of single-phase and uniform. Moreover, the mechanism of nanoparticle nucleation and growth, including phase-transformation, was revealed. In addition, the mircograph, particle size, physical phases, schemical constituents and magnetic properties before and after phase-transformation were characterized initially.

Low temperature poly-Si xGe 1− x deposited by reactive thermal CVD for thin film transistor application

We have prepared a highly silicon-rich polycrystalline silicon–germanium (poly-Si x Ge 1− x , x=0.98) film at 450 °C by the reactive thermal chemical vapor deposition (RTCVD) from a gaseous mixture of disilane (Si 2H 6) and germanium tetrafluoride (GeF 4) under He dilution. We fabricated inverted-staggered bottom-gate n-channel thin-film transistors (TFTs) with films of 200 nm thickness deposited directly on SiO 2/Si substrates. The TFT characteristics are influenced by the grain size of the poly-Si x Ge 1− x films and carrier mobility was increased significantly after hydrogenation. The fairly high mobility of 36 cm 2/ V s and a low threshold voltage of 1.8 V have been achieved in the TFT prepared with the film having the largest grain size of 100 nm. We discuss the effect of crystallinity and defects in the films in conjunction with the TFT characteristics.

Simulation of Silicon Carbide Converted Graphite by Chemical Vapor Reaction Method

Simulation of Silicon Carbide Converted Graphite by Chemical Vapor Reaction Method

Improved Morphological Stability of CoSi2 Layer by In Situ Growth on Polycrystalline Silicon Using Reactive Chemical Vapor Deposition

layers have been grown in situ on undoped polycrystalline silicon by reactive chemical vapor deposition of at and their stability has been investigated in the temperature range from 800 to The layers grown by the in situ method had grains with a strong (111) orientation, while no (111) orientation appeared in the layers grown by the conventional two-step method where CoSi formed first and transformed to The stability of the layers grown by the in situ process was improved by over that of the layers grown by the conventional two-step process. The layers grown in situ on a large-grained polycrystalline silicon were stable up to The effect of stability improvement by the in situ growth was more pronounced when the grains of the polycrystalline silicon had a small size. The improved stability of the layers grown in situ may be mainly due to the formation of a uniform layer with the grains of (111) orientation. © 2001 The Electrochemical Society. All rights reserved.

Field emission characteristics of CoSi2/TiN-coated silicon emitter tips

A CoSi2/TiN bilayer was coated on Si emitter tips and the emission characteristics of the tips were investigated. The CoSi2 layer was grown in situ by a reactive chemical vapor deposition of cyclopentadienyl dicarbonyl cobalt at 650°C and then the TiN was deposited on the CoSi2 layer at 550°C by a reactive sputtering of Ti with N as a reactive gas. The CoSi2 layer was conformally coated on the Si tips and the TiN layer adhered well to the CoSi2 layer. The CoSi2/TiN-coated emitters showed a low turn-on voltage due to the low work function by TiN and a steep current increase caused by CoSi2. The current fluctuation of the CoSi2/TiN-coated Si emitter was smaller than that of the TiN-coated emitter. The long-term emission stability of the CoSi2/TiN-coated Si emitter was also greatly improved compared to the CoSi2-coated emitter because of the superior high temperature stability of the TiN layer.

Growth of in situ CoSi2 layer by metalorganic chemical vapor deposition on Si tips and its field-emission properties

We prepared Si emitters coated with a metalorganic chemical vapor deposited CoSi2 layer to improve emission properties. The CoSi2 layer was grown in situ by reactive chemical vapor deposition of cyclopentadienyl dicarbonyl cobalt at 650 °C. The CoSi2 layer was conformally deposited on the Si emitter tips and had a twinned structure at the epitaxial CoSi2/Si interface in the partial region. The CoSi2-coated Si emitters showed an enhanced emission due to the increase in the number of emitting sites from the Fowler–Nordheim plot. The fluctuation of emission current was reduced by the CoSi2 coating. But the long-term stability was not much improved, which may be due to the decrease of the field enhancement factor and the number of emitting sites of the CoSi2-coated Si tip.

Poly-SiGe TFTs Fabricated by Low Temperature Chemical Vapor Deposition at 450°C

AbstractLow temperature growth of poly-SiGe has been investigated by reactive thermal chemical vapor deposition technique, which is a newly developed technique for preparing polycrystalline materials with using redox reactions in a set of source materials, Si2H6 and GeF4.. In order to prepare high uniformity and reproducibility of Si-rich poly-SiGe, total pressure, gas flow ratio, and residence time are optimized at 450°C of substrate temperature. Through optimizing the conditions, poly-Si1−xGex (x&lt;0.04) films have been prepared in the reproducibility more than 90% and uniformity more than 88%. Bottom gate type of n-channel thin film transistors has been fabricated in various grain size of poly-Si1−xGex on SiO2 (100nm)/Si substrates. 5-36 cm2/Vs of field effect mobility of thin film transistors (L/W = 50μm/50μm) have been achieved after hydrogenation, whose threshold voltage is around 2±0.5V, and on/off ratio is more than 104.

High thermal conductivity SiC/SiC composites for fusion applications

SiC/SiC composites offer excellent potential for fusion energy as well as numerous commercial applications. High manufacturing cost and very low through-the-thickness (transverse) thermal conductivity (below 15 W/m K) hinders wider applications of SiC/SiC composites. To overcome these obstacles, a low cost chemical vapor reaction (CVR) process was developed to fabricate crystalline, high-purity SiC fibers. Several variations of the CVR process were used to fabricate SiC/SiC composites. An unirradiated, 4-mm thick SiC/SiC composite was completely CVR-converted from a converted SiC fiber preform with a pitch graphite matrix, and exhibited a bulk density of 2.65 g/cc, 10% open porosity, room temperature (RT) and 1000°C thermal conductivity values of 70 and 35 W/m K, respectively, and an RT bend strength of 200 MPa.

Effect of ZrCl 4 addition on ZrB 2 film synthesis in flowing Ar–BCl 3 post-discharges

Zirconium diboride films are synthesized on Zircaloy-4 substrates at 733 K by reactive chemical vapor deposition enhanced by a flowing microwave Ar–BCl 3 post-discharge. The ZrB 2 growth mechanism consists of a diffusion step of zirconium from the substrate to the gas–film interface. Zirconium atoms react with boron chlorides to synthesize a zirconium diboride thin film. Zirconium chlorides, which are by-products of this reaction, are evacuated by the gas flow. Consequently, a substrate weight loss is noted during the ZrB 2 film growth. ZrCl 4 addition in the reactive gas mixture significantly lowers this weight loss by decreasing the rate of zirconium chloride formation. The zirconium diboride growth mechanism occurs even if no zirconium tetrachloride is introduced in the reactor. However, the use of a ZrCl 4 flow rate modifies the film composition. Indeed, oxygen concentration in the coating is constant when no ZrCl 4 is used. It decreases along the substrate when ZrCl 4 is added to the reactive gas mixture. This decrease is due to a homogeneous gas phase reaction between zirconium tetrachloride and the oxygen-containing molecules. The use of a ZrCl 4 flow rate improves the adhesion of the films. Tin accumulation at the film–substrate interface, which is induced by diffusion of zirconium atoms, slows down when ZrCl 4 is added to the gas mixture. Thus, the use of a zirconium tetrachloride flow enables the synthesis of thicker ZrB 2 films without the coating peeling off.

The synthesis and characteristics of SiC nanopowder produced by chemical vapor reaction of SiH4–C2H4–H2 system

SiC nanometer powders were synthesized by the chemical vapor reaction of the SiH4–C2H4–H2 system in the temperature range between 1423 K and 1673 K. The effects of processing conditions such as reactive temperature, gas composition ratio, and total flow rate on powder characteristics were studied using transmission electron microscopy, x-ray diffraction, infrared, Brunauer–Emmett–Teller, and chemical analyses. A forming mechanism has been proposed for solid and hollow particles in different processing conditions. The experimental results concerning particle growth are discussed according to the model of G.D. Ulrich et al., which considers both collision and coalescence phenomena.

Corrosion resistance of the vacuum arc deposited Ti, TiN and TiO2 coatings on large area glass substrates

An industrial installation for vacuum arc deposition is presented. Its potential in the field of decorative coatings for large area glass sheets is demonstrated. In particular it is possible to deposit patterned coatings through a polymeric textile mask. The ability to deposit uniform multilayer coatings having interference colours onto large silicate glass sheets is shown. Titanium, titanium nitride and titanium dioxide coatings on silicate glass have been characterized in terms of composition and corrosion resistance. Depth profiling was achieved with the aid of Auger electron spectroscopy. The corrosion resistance of TiN coatings is higher than that of TiO2. The corrosion resistance of vacuum arc deposited TiN coatings on glass was higher than that of TiN coatings produced by direct current reactive sputtering and plasma assisted chemical vapour deposition. Mask-deposited TiN coatings do not show any signs of accelerated corrosion along the border between the coated and uncoated glass.

Low Temperature growth of poly-crystalline film of Silicon-rich Silicon-Germanium by Reactive Thermal Chemical Vapor Deposition

AbstractLow temperature growth of poly-SiGe has been investigated by reactive thermal chemical vapor deposition method, which is a newly developed technique for preparing poly-SiGe by using redox reactions in a set of source materials, i.e., Si2H6 and GeF4. In order to prepare silicon-rich poly-SiGe of high mobility, a series of experiment on total pressure, gas flow rates of the source materials and dilution gas of He, and residence time at 450°C has been investigated.At 0.45 Torr, high crystallinity films with high silicon content were prepared, however, homogeneity of film thickness and reproducibility of the film growth was quite low for device application. For overcoming this problem, the growth condition has been studied especially in higher-pressure range of 5-15 Torr. Appropriate choice of the residence time and the gas flow ratios lead to significant improvement in the Si content in the films. Finally, more than 95% of silicon-rich poly-SiGe films, which is p-type, has 7.5 cm2/Vs of Hall mobility and (220) orientation, have been prepared at 10 Torr and 450°C within ±2% fluctuation of reproducibility which is enough to fabricate devices.

Silicon Field Emission Arrays Coated with CoSi2 Layer Grown by Reactive Chemical Vapor Deposition

ABSTRACTWe prepared Si emitters coated with an MOCVD CoSi2 layer to improve the emission properties. The CoSi2 layer was grown in situ by reactive chemical vapor deposition of cyclopentadienyl dicarbonyl cobalt at 650 °C. The CoSi2 layer was conformally coated on the Si emitter tips and had a twinned structure at the epitaxial CoSi2/Si interface. The CoSi2-coated Si emitters showed an enhanced emission due to the increase of the number of emitting site from Fowler-Nordheim plot. The fluctuation of emission current was reduced by CoSi2 coating. But the long-term stability was not much improved.

Microstructural Characterization and Residual Stress Distribution of Chemical Vapor Reaction SiC Conversion Layers on the "Continuous" and "Discontinuous" Graphite.

β-SiC conversion layers have been prepared on two different graphites with the “continuous” and “discontinuous” pore size distribution by the solid-solid (SS) and vapor-solid (VS) reactions in SiO2-C system. X-ray diffraction patterns of converted specimens showed the noticeable differences in the conversion extent to SiC according to pore size distribution. It was thought that the high infiltration and high conversion rate of “continuous” (CBY) graphite were due to the continuous pore distribution in the range of 0.01-10.0μm. In cross-sectional morphology, the converted “continuous” graphites showed the SiC layer with the interlayer with the average SiC:C ratio of 1:3, but the converted “discontinuous” graphites showed the conversion layer and an interface boundary with the SiC:C ratio in the range of 1:3 to 1:4. The interlayer of converted “continuous” graphite seems to be responsible for the high SiO gas infiltration rate, the resultant active SiC nucleation behavior and the conversion behavior over limited volume of surface. The FEM stress field diagrams of the converted graphites revealed the residual stress fields associated with the thermal mismatch between the conversion layer and the substrate. It was assumed that the stress values of SiC conversion layers measured by X-ray method originated from the additional constraining effects by the stress relaxation across boundaries and the grain growth or grain combination effect in conversion area.