Dissociation process of CH4/H2 gas mixture during EACVD

The dissociation process of CH₄/H₂ gas mixture during EACVD has been investigated using Monte Carlo simulation for the first time. The electron velocity distribution and H₂ dissociation were obtained over a wide range: 100<E/N<2000 Td. The variation of CH₄ dissociation with CH₄ concentration in the filling gas has been simulated. The electron velocity profile is asymmetric for the component parallel to the field. Most electrons possess non-zero velocity parallel to the substrate. The number of atomic H is a function of E/N. There are two peaks at E/N=177 Td and 460 Td. The appropriate E/N is suggested to be 500–800 Td for low temperature deposition. The main diamond growth precursor is proposed to be CH₃ and CH₃⁺.     

Carburization and decarburization kinetics of iron in CH4 — H2 mixtures between 1000 – 1100 °C

In this study the rate constants of the methane decomposition reaction on iron surfaces were determined in the 1000–1100°C temperature range, by grav? metric methods. Earlier works showed that the reaction velocity was given by The results indicate that the constant values vary from 2.72 × 10^?6 to $\text{16.74 × 10}{}^{\mathrm{?6}}\text{mol C/cm}{}^2\text{/sec/atm}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for k and 2.61 × 10^?8 to $\text{8.62 × 10}{}^{\mathrm{?8}}\text{mol C/cm}{}^2\text{/sec/atm}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ for k′ between 1000 and 1100°C.     

Two-step growth of high-quality nano-diamond films using CH4/H2 gas mixture

Diamond films with fine grain size and good quality were successfully deposited on pure titanium substrate using a novel two-step growth technique in microwave plasma-assisted chemical vapor deposition (MWPCVD) system. The films were grown with varying the methane (CH₄) concentration at the stage of bias-enhanced nucleation (BEN) and nano-diamond film deposition. It was found that nano-diamond nuclei were formed at a relatively high methane concentration, causing a secondary nucleation at the accompanying growth step. Nano-diamond film deposition on pure titanium was always very hard due to the high diffusion coefficient of carbon in Ti, the big difference between thermal expansion coefficients of diamond and Ti, the complex nature of the interlayer created during diamond deposition, and the difficulty in achieving very high nucleation density. A smooth and well-adhered nano-diamond film was successfully obtained on pure Ti substrate. Detailed experimental results on the synthesis, characterization and successful deposition of the nano-diamond film on pure Ti are discussed.     

甲烷/氢气在超微孔金属有机骨架中的吸附与分离性能研究

使用巨正则蒙特卡罗方法(GCMC)对CH₄和H₂在3种具有不同结构的超微孔金属有机骨架(UM-MOFs)中的吸附与分离性能进行了研究。获得了这3种材料对CH₄和H₂分子的单组分吸附。通过分析它们对CH₄/H₂二元混合物的吸附数据,获得了相应的吸附选择性分布曲线,探索了UM-MOFs对CH₄/H₂分子的吸附与分离机理。     

Preparation of SiC foams by CVI-R technique with SiCl4/H2/CH4 system

Silicon carbide foams were prepared by the chemical vapor infiltration-reaction (CVI-R) of SiCl₄/H₂/CH₄ with carbon foam derived from mesophase pitch (MP), which had not only high bending strength but also low bulk density. The influence of the CH₄/SiCl₄ ratio in reaction atmosphere on the properties of as-prepared silicon carbide foams was investigated in detail. As the CH₄/SiCl₄ ratio was 0.25, resultant foam possessed the highest bending strength of 17.13 MPa. At the same time, correlations between properties and microstructure are also discussed.     

Characteristics of nano-crystalline diamond films prepared in Ar/H2/CH4 microwave plasma

Characteristics of nano-crystalline diamond (NCD) thin films prepared with microwave plasma chemical vapor deposition (CVD) were studied in Ar/H₂/CH₄ gas mixture with a CH₄ gas ratio of 1-10% and H₂ gas ratio of 0-15%. From the Raman measurements, a pair of peaks at 1140 cm^− 1 and 1473 cm^− 1 related to the trans-polyacetylene components peculiar to nano-crystalline diamond films was clearly observed when the H₂ gas ratio of 5% was added in Ar/H₂/CH₄ mixture. With an increase of H₂ gas content up to 15%, their peaks decreased, while a G-peak at roughly 1556 cm^− 1 significantly increased. The degradation of NCD film quality strongly correlates with the decrease of C₂ optical emission intensity with the increase of hydrogen gas contents. From the surface analysis with atomic force microscopy (AFM), it was found that grain sizes of NCD films were typically of 10-100 nm in case of 5% H₂ gas addition.     

Growth of silicon carbide thin films by hot-wire chemical vapor deposition from SiH4/CH4/H2

Silicon carbide (SiC) thin films were prepared by hot-wire chemical vapor deposition from SiH₄/CH₄/H₂ and their structural properties were investigated by X-ray diffraction, Fourier transform infrared absorption and Raman scattering spectroscopies. At 2 Torr, Si-crystallite-embedded amorphous SiC (a-Si_1 − xC_x:H) grew at filament temperatures (T_f) below 1600 °C and nanocrystalline cubic SiC (nc-3C-SiC:H) grew above T_f = 1700 °C. On the other hand, At 4 Torr, a-Si_1 − xC_x:H grew at T_f = 1400 °C and nc-3C-SiC grew above T_f = 1600 °C. When the intakes of Si and C atoms into the film per unit time are almost the same and H radicals with a high density are generated, which takes place at high T_f, nc-3C-SiC grows. On the other hand, at low T_f the intake of Si atoms is larger than that of C atoms and, consequently, Si-rich a-Si_1 − xC_x:H or Si-crystallite-embedded a-Si_1 − xC_x:H grow.     

Effect of doping elements on ZnO etching characteristics with CH4/H2/Ar plasma

Effect of doping elements on the etching characteristics of doped-ZnO (Ag, Li, and Al) thin films, etched with a positive photoresist (PR) mask, and an etch process window for infinite etch selectivity were investigated by varying the CH₄ flow ratio and self-bias voltage, V_dc, in inductively coupled CH₄/H₂/Ar plasmas. Increased doping of ZnO films decreased the etch rates significantly presumably due to lower volatility of reaction by-products of doped Li, Ag, and Al in CH₄/H₂/Ar plasmas. The etch rate of AZO (Al-doped ZnO) was most significantly decreased as the doping concentration is increased from 4 to 10 wt%. It was found that process window for infinite etch selectivity of the doped ZnO to the PR is closely related to a balance between deposition and removal processes of a-C:H (amorphous hydrogenated carbon) layer on the doped-ZnO surface. Measurements of optical emission of the radical species in the plasma and surface binding states by optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS), respectively, implied that the chemical reaction of CH radicals with Zn atoms in doped-ZnO play an important role in determining the doped-ZnO etch rate together with an ion-enhanced removal mechanism of a-C:H layer as well as Zn(CH_x)_y etch by-products.     

Influence of gas pressure on low-temperature preparation and film properties of nanocrystalline 3C-SiC thin films by HW-CVD using SiH4/CH4/H2 system

We investigated an influence of gas pressure on low-temperature preparation of nanocrystalline cubic silicon carbide (nc-3C-SiC) films by hot-wire chemical vapour deposition (HW-CVD) using SiH₄/CH₄/H₂ system. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra revealed that the films prepared below 1.5 Torr were Si-nanocrystallite-embedded hydrogenated amorphous SiC. On the other hand, nc-3C-SiC films were successfully prepared at gas pressure above 2 Torr. The high gas pressure plays two important roles in low-temperature preparation of nc-3C-SiC films: (1) leading to sufficient decomposition of CH₄ molecules through a gas phase reaction and an increase in the incorporation of carbon atoms into film and (2) promoting a creation of H radicals on the heated filament, allowing the sufficient coverage of growing film surface and a selective etching of amorphous network structure and/or crystalline-Si phase. It was found that total gas pressure is a key parameter for low-temperature preparation of nc-3C-SiC films.     

Deep etch-induced damage during ion-assisted chemical etching of sputtered indium-zinc-oxide films in Ar/CH4/H2 plasmas

Plasma etch damage to sputtered indium-zinc-oxide (IZO) layers in the form of changes in the film stoichiometry was investigated using Auger Electron Spectroscopy (AES). While damage resulting from pure chemical etching processes is usually constrained to the surface vicinity, ion-assisted chemical etching of IZO in Ar/CH₄/H₂ plasmas produces a Zn-rich layer, whose thickness (∼ 50 nm) is well-above the expected stopping range of Ar ions in IZO (∼ 1.5 nm). Based on AES depth profiles as a function of plasma exposure time, it is concluded that the observed Zn enrichment and In depletion deep into the IZO film are driven by the implantation of hydrogen atoms.     

A study of electron drift velocity in Ar---CO2 and Ar---CO2---CF4 gas mixtures

We have measured the electron drift velocity as a function of electric field in Ar---CO₂ mixtures. Measurements are made for mixtures containing 8% to 20% CO₂ in 1% increments. Effects of air and nitrogen contamination on Ar---CO₂ mixtures are investigated. These results are useful for determining the correct mixing ratio of the Ar---CO₂ mixture in drift chamber applications. We have also measured the electron drift velocity in several Ar---CO₂---CF₄ mixtures.     

Crystal structure of K4[H2J2O10].8H20

Crystals of K₄ [H₂J₂O₁₀] 8H₂O belong to the triclinic system, space group P 1 with a = 7.161 (2) $\text{A}\text{?}\text{, b}\text{= 10,553}$ (5) $\text{A}\text{?}\text{, c}\text{= 7,081}$ (2) $\text{A}\text{?}\text{, α = 98°1′}$, β = 117°8′, γ = 90°6′ and Z = 1. The crystal structure has been determined on the basis of photographic data from 877 independent reflections, with the final R value of 6,6%. The iodine atoms are surrounded by a distorted octahedra consisting of five oxygen atoms and one OH group. The average J-O distance is 2.03 Å. There are 2 independent K atoms in the structure. K(1) has a coordination number of eight, while K(2) is surrounded by 6 (5 water molecules + one OH group) nearest neighbours.     

Deposition process of Si-B-C ceramics from CH3SiCl3/BCl3/H2 precursor

Si-B-C coatings have been prepared by chemical vapour deposition (CVD) from CH₃SiCl₃/BCl₃/H₂ precursor mixtures at low temperature (800-1050 °C) and reduced pressures (2, 5, 12 kPa). The kinetics (including apparent activation energy and reaction orders) related to the deposition process were determined within the regime controlled by chemical reactions. A wide range of coatings, prepared in various CVD conditions, were characterized in terms of morphology (scanning electron microscopy), structure (transmission electron microscopy, Raman spectroscopy) and elemental composition (Auger electron spectroscopy). On the basis of an in-situ gas phase analysis by Fourier transform infrared spectroscopy and in agreement with a previous study on the B-C system, the HBCl₂ species was identified as an effective precursor of the boron element. H_xSiCl_(4−x), SiCl₄ and CH₄, derived from CH₃SiCl₃, were also shown to be involved in the homogeneous and the heterogeneous reactions generating silicon and carbon in the coating. A correlation between the various experimental approaches has supported a discussion on the chemical steps involved in the deposition process.     

Nanocrystalline chemically modified CdIn2O4 thick films for H2S gas sensor

CdIn₂O₄ sensor with high sensitivity and excellent selectivity for H₂S gas was synthesized by using sol-gel technique. Structural, electrical and gas sensing properties of doped and undoped CdIn₂O₄ thick films were studied. XRD revealed the single-phase polycrystalline nature of the synthesized CdIn₂O₄ nanomaterials. Since the resistance change of a sensing material is the measure of its response, selectivity and sensitivity was found to be enhanced by doping different concentrations of cobalt in CdIn₂O₄ thick films. The sensor exhibits high response and selectivity toward H₂S for 10 wt.% Co doped CdIn₂O₄ thick films. The current-voltage characteristics of 10 wt.% Co doped CdIn₂O₄ calcined at 650 °C shows one order increase in current with change in the bias voltage at an operating temperature of 200 °C for 1000 ppm H₂S gas.     

Charge transfer in blends of P3HT and colloidally prepared CuInS2 nanocrystals

CuInS₂ (CIS) is a suitable semiconductor for thin film photovoltaics and also a promising candidate to replace CdSe in hybrid polymer/nanoparticle solar cells, advantages being the lower toxicity and the better absorption properties. In this work, crystalline nanoparticles of CuInS₂ were successfully synthesized with uniform size and shape by means of colloidal chemistry. Photo-induced absorption spectroscopy was used to study charge transfer between poly(3-hexylthiophene) (P3HT) and the CIS nanoparticles. The appearance of signals corresponding to positive polarons provides evidence that charge transfer is possible in the P3HT/CIS system.     

Crystal Structure of (H3O)2[(UO2)2(SeO4)3(H2O)2](H2O)3.5

Crystals of (H₃O)₂[(UO₂)₂(SeO₄)₃(H₂O)₂](H₂O)_3.5 were prepared from aqueous solutions by evaporation. The crystal structure [monoclinic system, space group P2₁/m, a = 11.9402(11), b = 13.6452(14), c = 13.7271(12) Å, β = 109.436(7)°, V = 2109.1(3) ų] was solved by the direct method and refined to R ₁ = 0. 048 (wR ₂ = 0. 082) for 3677 reflections with |F _hkl |F _hkl |. The structure consists of [(UO₂)₂(SeO₄)₃(H₂O)₂]₂₋ layers arranged parallel to the (010) plane. The layers are formed by uranium and selenium coordination polyhedra sharing common vertices and are linked with each other by hydrogen bonds through the H₂O and H₃O⁺ groups arranged between the layers. __________ Translated from Radiokhimiya, Vol. 47, No. 5, 2005, pp. 412–414. Original Russian Text Copyright ? 2005 by Krivovichev, Kahlenberg.     

Deposition and characterization of smooth ultra-nanocrystalline diamond film in CH4/H2/Ar by microwave plasma chemical vapor deposition

The smooth ultra-nanocrystalline diamond (UNCD) films were prepared by microwave plasma chemical vapor deposition (MWCVD) using argon-rich CH₄/H₂/Ar plasmas with varying argon concentration from 96% to 98% and negative bias voltage from 0 to −150 V. The influences of argon concentration and negative bias voltage on the microstructure, morphology and phase composition of the deposited UNCD films are investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), atom force microscopy (AFM), and visible and UV Raman spectroscopy. It was found that the introduction of argon in the plasma caused the grain size and surface roughness decrease. The RMS surface roughness of 9.6 nm (10 micron square area) and grain size of about 5.7 nm of smooth UNCD films were achieved on Si(100) substrate. Detailed experimental results and mechanisms for UNCD film deposition in argon-based plasma are discussed. The deposited highly smooth UNCD film is also expected to be applicable in medical implants, surface acoustic wave (SAW) devices and micro-electromechanical systems (MEMS).     

Tetragonal-(Zr,Co)O2 solid solution: Combustion synthesis, thermal stability in air and reduction in H2, H2-CH4 and H2-C2H4 atmospheres

The synthesis of Co²⁺-stabilized zirconia by the nitrate/urea combustion route is investigated. Using seven times the so-called stoichiometric urea proportion allows to obtain for the first time the Zr_0.9Co_0.1O_1.9 solid solution fully stabilized in tetragonal form. The thermal stability in air and the reduction in H₂, H₂-CH₄ and H₂-C₂H₄ atmospheres are studied. The carbon forms obtained upon reduction are investigated. Reduction in H₂-CH₄ produces many carbon species including short carbon nanofibers, nanoribbons, hollow particles often forming bamboo structures, carbon-encapsulated Co particles and carbon nanotubes. Reduction in H₂-C₂H₄ produces 15-30 nm nanofibers.     

无烟煤制备颗粒活性炭及其PSA分离CH_4/N_2性能

为高效利用矿井煤层气,以重庆无烟煤为原料,采用简单的空气预氧化-碳化工艺制备了变压吸附（PSA）分离CH4和N2混合气体（CH4/N2）所用的颗粒活性炭（GAC）吸附剂,采用穿透和PSA实验研究了制备工艺条件对GAC分离CH4/N2的效果及其影响,利用低温液氮吸附和透射电镜（TEM）方法对GAC进行孔结构表征,利用傅立...     

Growth of nanocrystalline diamond films in CCl4/H2 ambient

We investigated the growth characteristics of the nanocrystalline diamond films using CCl₄/H₂ as gas sources in a hot-filament chemical vapor deposition (CVD) reactor. Successful growth of nanocrystalline diamond at typical growth condition of 1.5-2.5% CCl₄ and 550-730 °C substrate temperature has been demonstrated. Glancing angle X-ray diffraction (XRD) clearly indicated the formation of diamond in the films. Typical root-mean-square surface roughness of 10-15 nm and an optimal root-mean-square surface roughness of 6 nm have been achieved. Transmission electron microscopy (TEM) analyses indicated that nanocrystalline diamond film with an average grain size in the range of 10-20 nm was deposited from 2.5% CCl₄/H₂ at 610 °C. Effects of different source gas composition and substrate temperature on the grain nucleation and grain growth processes, whereby the grain size of the nanocrystalline film could be controlled, were discussed.