Effect of H2/Ar plasma on growth behavior of ultra-nanocrystalline diamond films: The TEM study

Incorporation of H₂ species into Ar plasma was observed to markedly alter the microstructure of diamond films. TEM examinations indicate that, while the Ar/CH₄ plasma produced the ultrananocrystalline diamond films with equi-axed grains (~ 5 nm), the addition of 20% H₂ in Ar resulted in grains with dendrite geometry and the incorporation of 80% H₂ in Ar led to micro-crystalline diamond with faceted grains (~ 800 nm). Optical emission spectroscopy suggests that small percentage of H₂-species (< 20%) in the plasma leads to partially etching of hydrocarbons adhered onto the diamond clusters, such that the C₂-species attach to diamond surface anisotropically, forming diamond flakes, which evolve into dendrite geometry. In contrast, high percentage of H₂-species in the plasma (80%) can efficiently etch away the hydrocarbons adhered onto the diamond clusters, such that the C₂-species can attach to diamond surface isotropically, resulting in large diamond grains with faceted geometry. The field needed to turn on the electron field emission for diamond films increases from E₀ = 22.1 V/μm (J_e = 0.48 mA/cm² at 50 V/μm applied field) for 0% H₂ samples to E₀ = 78.2 V/μm (J_e < 0.01 mA/cm² at 210 V/μm applied field) for 80% H₂ samples, as the grains grow, decreasing the proportion of grain boundaries.     

Trapping of CH3O formed from CO + H2

Methoxy formed on Al₂O₃ from¹³CO and H₂ coadsorption on Ni/Al₂O₃ was trapped by C₂H₅OH adsorption and temperature-programmed reaction (TPR). The presence of excess C₂H₅OH significantly increases the rate of¹³CH₃OH and (¹³CH₃)₂O formation. The¹³CH₃OH forms by the reaction of C₂H₅OH with¹³CH₃O on Al₂O₃. In the absence of C₂H₅OH,TPR following¹³CO and H₂ coadsorption did not produce significant amounts of¹³CH₃OHor(¹³CH₃)₂O.     

High resolution transmission electron microscopy study of the initial growth of diamond on silicon

A polycrystalline diamond film grown by hot filament CVD was ion-milled and thinned to the diamond/silicon-substrate interface and the structures formed during the initial stages of diamond nucleation were studied by high resolution transmission electron microscopy (HRTEM). At the interface, isolated polycrystalline islands (15–35 nm) consisting primarily of mixed phase β-SiC and nanocrystalline diamond could be observed. The β-SiC phase occurred mainly as isolated nano-sized domains with no evidence of a larger micron-scale coalescence. In addition to co-existing with β-SiC in the polycrystalline islands, nanocrystalline diamond was also observed to nucleate in the amorphous carbon matrix. The density of the nanocrystalline diamond in the amorphous carbon matrix was observed to be at least an order of magnitude higher than that in the polycrystalline β-SiC phase. The total nanocrystalline diamond nucleation density was found to be several orders of magnitude higher than the growth density of the micron-sized diamond crystallites that ultimately evolved from the interface at longer growth times.     

Reactions of adsorbed CH3 species with CO2 on Rh/SiO2 catalyst

Methyl radicals, produced by the high temperature pyrolysis of azomethane, were adsorbed on Rh/SiO₂. The reaction between adsorbed CH₃ and gaseous CO₂ has been followed by determining the intensity changes of the asymmetric stretch of CH₃ and the composition of the gas phase. It was found that adsorbed CH₃ reacts with CO₂ at and above 373 K. It is assumed that similar processes may also take place in the dry reforming of methane, and that they are responsible for the lack of carbon deposition on supported Rh catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of adsorbed impurities on the crystal growth of poorly soluble salts from slightly supersaturated solutions

A model explaining the nonlinear dependence of crystal growth on the concentration of the impurity to be adsorbed in solution, impurity particle size, and surface coverage for poorly soluble salts at low supersaturations is proposed. The hypothesis about the adsorption of impurity particles on the terraces of crystals makes it possible to describe the evolution of growth steps using the model of crystallization at the potential relief. Analysis of the potential relief allows us to determine the critical surface coverage and the critical inhibitor concentration at which the crystallization is completely terminated. When the values of the surface coverage are lower than critical, the model predicts the near-exponential dependence of the crystallization rate on the surface coverage and impurity concentration, which agrees with the experimental data reported in the literature.     

Effect of substitutional N on the diamond CVD growth process: A theoretical approach

For both (111) and (100) diamond surface orientations, one C atom within the first or second surface carbon layer has substitutionally been replaced by an N atom. The effects of this impurity on CH₃ adsorption and H abstraction from a newly adsorbed CH₃ have been carefully investigated by using ultra-soft pseudo-potential density functional theory (DFT) under periodic boundary conditions. The effects of N at various positions within the two atomic layers were especially studied. It was generally found that nitrogen in the first atomic layer will never affect the initial growth reactions. An exception exist for the dopant in one of the three studied positions within the (100) surface, where a β-scission rearrangement is observed. When N is positioned within the second carbon layer for both surface orientations with all surface carbons H-terminated (i.e. no surface radicals), nitrogen is moving off-site and one of the N–C bonds is thereby broken. On the other hand, when a radical is present on the surface (formed by the abstraction of one surface H), N move back on-site and one electron is transferred from N to the surface C radical with a resulting electron lone pair formation. When CH₂ is bonded to the surface as a result of gaseous H abstraction from the adsorbed CH₃ species and with N directly bonded to the surface carbon onto which CH₃ is initially adsorbed, a β-scission rearrangement is also observed.     

In situ study of the initial stages of diamond deposition on 3C–SiC (100) surfaces: Towards the mechanisms of diamond nucleation

The mechanisms involved in the diamond nucleation on 3C–SiC surfaces have been investigated using a sequential in situ approach using electron spectroscopies (XPS, XAES and ELS). Moreover, diamond crystals have been studied by HRSEM. The in situ nucleation treatment allows a high diamond nucleation density close to 4 × 10¹⁰ cm^− 2. During the in situ enhanced nucleation treatment under plasma, a negative bias was applied to the sample. The formation of an amorphous carbon phase and the roughening of the 3C–SiC surface have been observed. The part of these competing mechanisms in diamond nucleation is discussed.     

Effect of different dopants on porous calcium silicate composite bone scaffolds by 3D gel-printing

Porous CaSiO₃ composite scaffolds with different dopants, such as MgSiO₃, MgCl₂ and CaSO₄, were successfully prepared by 3D gel-printing (3DGP). (m, n) is proposed to describe the filament geometry features. The results show that doping can improve the strength of porous composite scaffolds and MgCl₂-doped composite scaffolds had the highest modulus of elasticity of 1241 MPa. The shrinkage rate range of the composite scaffolds was 11.44–13.16%, and their porosity was all about 60%. When porous composite scaffolds were soaked in SBF for 28 days at 37°С, the degradation rate was 2.7% (pure), 0.3% (MgSiO₃), 0.2% (MgCl₂), 5.27% (CaSO₄), respectively. It explains that MgSiO₃ and MgCl₂ inhibited the in vitro degradation of CaSiO₃, while CaSO₄ promoted. It is obviously that doped MgCl₂ can improve the mechanical properties of porous scaffolds, and doped CaSO₄ can improve the degradation of scaffolds, which play an important role in bone repair engineering.     

Effect of ion beam nitriding on diamond nucleation and growth onto steel substrates

Ion beam nitriding was successfully employed to overcome the difficulty of diamond growth on ferrous base substrates. Commercial steels were pretreated by an ion beam method in an ambient environment of nitrogen gas, diamond was then deposited by hot filament chemical vapor deposition (CVD). The deposited films were characterized by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Continuous diamond films with a sharp characteristic Raman peak of 1337.7 cm⁻¹ were grown and adhered well on the nitrided region of the steel substrates. On the other hand, a mixture of diamond crystallites, amorphous carbon and graphitic carbon was loosely deposited on the unnitrided region. A thin layer of iron and chromium nitrides, formed on the steel surface by ion beam nitriding, enabled the subsequent nucleation and growth of high-quality CVD diamond.     

Synthesis and structure of a mixed valence metal carbitoxide complex: Eu3[O(CH2CH2O)2CH2CH3]4(OC6H3iPr2-2,6)3

The direct reaction of europium metal with HO(CH₂CH₂O)₂CH₂CH₃ followed by treatment with 2,6-ⁱPr₂C₆H₃OH leads to the crystallographically-characterizable, mixed valent carbitoxide product Eu₃[O(CH₂CH₂O)₂CH₂CH₃]₄(OC₆H₃ⁱPr₂-2,6)₃ (1), which contains bridging alkoxide ligands and both terminal and bridging aryloxide ligands.     

Effect of gas composition on the growth and electrical properties of boron-doped diamond films

Boron-doped diamond films are synthesized by the hot-filament chemical vapor deposition (HFCVD) method via introduction of the gas mixtures of methane and hydrogen, as well as the boron precursor carried by H₂ through a B(OCH₃)₃ liquid, into the chamber. Boron-doping level in as-grown diamond films can be well controlled in the range from 10¹⁹ to 10²¹ cm^? 3 by adjusting the B/C ratios of gas mixtures. The morphology, structure and resistivity of as-grown diamond films are investigated with scanning electron microscopy (SEM), X-ray diffraction (XRD) and Hall measurement system. The results show that the crystal quality and carrier concentration and resistivity of the as-grown films are obviously dependent on the B/C ratio of the gas mixtures during the deposition process. A critical B/C ratio of 3:4 is found to correspond to the highest crystal quality, highest carrier concentration and smallest film resistivity of as-grown boron-doped diamond films, which should be mainly related with the effective doping ability. In addition, based on the growth kinetics of the diamond films, the effect of the boron-doping on the growth process is discussed in detail.     

Effect of dopants on microwave dielectric properties of Ba(Zn1/3Nb2/3)O3 ceramics

Ba(Zn_1/3Nb_2/3)O₃ (BZN) has been prepared with various amounts of different dopants such as oxides of monovalent, divalent, trivalent, tetravalent, pentavalent and hexavalent elements. Effect of these dopants on microwave dielectric properties of BZN is investigated. Some of the dopants are found to increase quality factor Q × f and slightly alter the temperature coefficient of resonant frequency (τ_f). Annealing undoped BZN increased the quality factor. Small amounts of dopants such as oxides of Ni, In, Al, Ga, Zr, Ce, Sn, Ti, Sb, and W increased the quality factor. The doped ions substitute for the ordered B ions decreasing the order parameter. Annealing increased the quality factor for all doped BZN samples. Doping BZN with In₂O₃, Al₂O₃, WO₃ and SnO₂ decreased the order parameter but at the same time increased the quality factor indicating that order parameter alone is a poor indicator of quality factor. The quality factor is found to depend on the dopant ionic radii and its concentration. The quality factor increased when the ionic radius of the dopant is close to the ionic radius of the B site ions Zn or Nb. Microstructure studies using SEM showed that the doped high Q ceramics contained large grains.     

Effect of initial compositions on boron carbide synthesis and corresponding growth mechanism

ABSTRACT

The yield of boron carbide (B₄C) synthesised by carbothermal reduction (CTR) is low (40–50%) owing to the inappropriate initial composition. In this paper, thermodynamic equilibrium simulations for effects of initial compositions on B₄C synthesis were performed, while initial compositions on the quality and yield of B₄C synthesised by CTR from B₂O₃-C mixture at atmospheric pressure were systemically investigated. The reaction mechanisms for B₄C synthesis process were thermodynamically analysed. Moreover, growth mechanisms for B₄C particles were speculated based on the thermodynamic and experimental results. The results show that the simulations agree well with experimental results, and optimal initial composition is 1.906 (B₂O₃/C weight ratio). Under optimal condition, B₄C powder prepared at 1973?K is high-quality with well crystallinity, purity of 93.58% and yield of 90.05%. Additionally, the prepared B₄C particles show two types of morphologies, aggregate of small equiaxed particles and needle-like particle, which are formed through different reaction mechanisms, respectively.     

Effect of bias treatment in the CVD diamond growth on Ir(001)

The effect of bias treatment (BT) on direct-current plasma CVD diamond growth has been studied in situ by X-ray photoelectron diffraction (XPD) together with LEED and XPS. It was found that C 1s XPD patterns from the sample after BT are similar to those of diamond (001). Coverage of carbon after BT is several tens of ML when BT is very successful. However, LEED shows no diamond (001) spots for the sample after BT. These apparently contradictory findings are explained by the sizes of the diamond (001) crystallites, which, after BT, are large enough to produce C 1s XPD patterns of diamond, but too small to have coherent interference spots in LEED. It is concluded from this and other information that BT in a DC plasma creates hetero-epitaxial diamond crystallites a few nm or less. These diamond crystallites may be related to the atomically abrupt diamond/Ir interfaces of DC plasma CVD-grown samples revealed by TEM [A. Sawabe, H. Fukuda, T. Suzuki, Y. Ikuhara, T. Suzuki, Surf. Sci. 467 (2000) L845].     

Understanding the chemistry of low temperature diamond growth: an investigation into the interaction of chlorine and atomic hydrogen at CVD diamond surfaces

The interaction of chlorine with CVD diamond surfaces has been studied using Auger and photoelectron spectroscopy techniques, with reference to the development of low temperature growth models for diamond using halogen-based precursors. Chlorine is found to adsorb on the clean CVD surface with a sticking probability of ∼0.001 at 300 K, although this can be enhanced by prehydrogenation of the surface and by raising the substrate temperature. Adsorbed chlorine desorbs from the surface over a wide temperature range below 500°C, and is also very efficiently etched away by atomic hydrogen. Chlorine has therefore little tendency to poison the growth surface, and thus is capable of acting as a catalyst for low temperature growth.     

甲烷浓度对金刚石薄膜(100)织构生长的影响

以H2和CH4的混合气体为气源,用微波等离子体辅助化学气相沉积法(MPECVD)在1 cm×1 cm S i(100)基体上沉积了金刚石薄膜。研究了不同的甲烷浓度对金刚石薄膜(100)织构生长趋势的影响。分别采用扫描电子显微镜(SEM),Ram an光谱对金刚石膜的表面形貌、质量进行了分析。结果表明,当基体温度为750℃,气压为4.8×103Pa,甲烷浓度为1.4%时,薄膜表面为(100)织构。     

醇对络合物TpRu(PPh3)(CH3CN)H催化氢化二氧化碳生成甲酸的影响

研究了络合物TpRu(PPh3)(CH3CN)H 在甲醇溶液中催化氢化CO2生成甲酸的最佳条件,进一步研究了甲醇、乙醇、正丙醇、异丙醇、特丁醇为溶剂时对该络合物催化氢化CO2生成甲酸的影响,提出可能的催化反应机理.     

Single crystal structure of a heterometallic one-dimensional polymer: [{Cu(1,10-phen)}2(V2O4)(O3PCH2CH2CH2CH2PO3H)2(H2O)]n

A heterometallic one-dimensional polymer [{Cu(1,10-phen)}₂(V₂O₄)(O₃PCH₂CH₂CH₂CH₂PO₃H)₂(H₂O)]_n 1 (1,10-phen=1,10-phenanthroline) has been synthesized under hydrothermal conditions. The structure of 1 shows a stepped chain with two parallel 1,4-butylenediphosphonate ligands as linking units.     

The Effect of CO2 and H2O on the Kinetics of NO Reduction by CH4 Over Sr-Promoted La2O3

The influence of CO₂ and H₂O on the activity of 4% Sr-La₂O₃ mimics that observed with pure La₂O₃, and a reversible inhibition of the rate is observed. CO₂ causes a greater effect, with decreases in rate of about 65% with O₂ present and 90% in its absence, while with H₂O in the feed, the rate decreased around 35-40% with O₂ present or absent. The influence of these two reaction products on kinetic behavior can be described by assuming competitive adsorption on the surface, incorporating adsorbed CO₂ and H₂O in the site balance, and using rate expressions previously proposed for this reaction over Sr-promoted La₂O₃. In the absence of O₂, the rate expression is $$r_{N_2 } = \frac{{k'P_{{\text{NO}}} P_{{\text{CH}}_{\text{4}} } }}{{{\text{(1 + }}K_{{\text{NO}}} P_{{\text{NO}}} {\text{ + }}K_{{\text{CH}}_{\text{4}} } P_{{\text{CH}}_{\text{4}} } {\text{ + }}K_{{\text{CO}}_{\text{2}} } P_{{\text{CO}}_{\text{2}} } {\text{ + }}K_{{\text{H}}_{\text{2}} {\text{O}}} P_{{\text{H}}_{\text{2}} {\text{O}}} {\text{)}}^{\text{2}} }},$$ which yields a good fit to the experimental data and gives optimized equilibrium adsorption constants that demonstrate thermodynamic consistency. With O₂ in the feed, nondifferential changes in reactant concentrations through the reactor bed were accounted for by assuming integral reactor behavior and simultaneously considering both CH₄ combustion and CH₄ reduction of NO, which provided the following rate law for total CH₄ disappearance: $$(r_{{\text{CH}}_{\text{4}} } )_{\text{T}} = \frac{{k'_{{\text{com}}} P_{{\text{CH}}_{\text{4}} } P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} + k'_{{\text{NO}}} P_{{\text{NO}}} P_{{\text{CH}}_{\text{4}} } P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} }}{{{\text{(1 + }}K_{{\text{NO}}} P_{{\text{NO}}} {\text{ + }}K_{{\text{CH}}_{\text{4}} } P_{{\text{CH}}_{\text{4}} } {\text{ + }}K_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} {\text{ + }}K_{{\text{CO}}_{\text{2}} } P_{{\text{CO}}_{\text{2}} } {\text{ + }}K_{{\text{H}}_{\text{2}} {\text{O}}} P_{{\text{H}}_{\text{2}} {\text{O}}} {\text{)}}^{\text{2}} }}.$$ The second term of this expression represents N₂ formation, and it again fit the experimental data well. The fitting constants in the denominator, which correspond to equilibrium adsorption constants, were not only thermodynamically consistent but also provided entropies and enthalpies of adsorption that were similar to values obtained with other La₂O₃-based catalysts. Apparent activation energies typically ranged from 23 to 28 kcal/mol with O₂ absent and 31-36 kcal/mol with O₂ in the feed. With CO₂ in the feed, but no O₂, the activation energy for the formation of a methyl group via interaction of CH₄ with adsorbed NO was determined to be 35 kcal/mol.