Modeling of nitrogen/diborane/methane/hydrogen plasma for nanocrystalline diamond growth: Comparison with experimental data

Gas phase thermodynamic equilibrium calculations involving N₂/B₂H₆/CH₄/H₂ mixtures were performed to investigate the chemical interactions leading to boron incorporation and microstructure variations in microwave plasma assisted chemical vapor deposition of diamond films. Molecular fractions of several BH_x (x = 1–3) species were calculated to study the incorporation mechanism of boron atom into diamond structure. A strong influence of the BH in causing the boron incorporation level in diamond lattice is confirmed by the correlation of its modeled equilibrium composition in the gas phase with boron content as determined experimentally. Nitrogen addition leads to nanocrystallinity and a reduction in boron incorporation due to a decrease in BH as additional B/N/H radicals are formed in the gas phase. We also obtained a good degree of agreement between the theoretically predicted CH₃/CN gas phase ratio and the experimental surface roughness trends as measured for all samples.     

EPR studies of a nickel–boron centre in synthetic diamond

Possible models are discussed for a new EPR centre (NOL1) observed in a diamond grown from a nickel-containing solvent catalyst with a titanium nitrogen getter. Nickel and boron are the most prevalent impurities in the diamond. The centre has trigonal (C_3v) symmetry about 〈111〉, S=1, g_∣∣=2.0235(5), g_⊥=2.0020(10) and D=−171(1) GHz. The EPR lineshape is unusual and we tentatively attribute this to partially resolved ¹¹B hyperfine structure. This centre may be the same as NIRIM-5, observed in boron doped synthetic diamond. The most likely structure for this centre is an interstitial Ni²⁺ with a substitutional B⁻ ion at the nearest neighbour site along 〈111〉.     

Excimer laser-induced photochemical modification and adhesion improvement of a fluororesin surface

Modification of a selective area of a fluororesin surface was accomplished by using ArF excimer laser radiation and a boron complex with oleophilic or hydrophilic functional groups. The chemical stability of fluororesin is attributed to the presence of C-F bonds. The F atoms were abstracted by B atoms selectively from the area irradiated with excimer laser radiation and were replaced with the desired functional groups. In this modification, B(CH₃)₃ and B(OH)₃ were used: a boron compound with methyl groups to generate an oleophilic surface, and one with hydroxyl groups to generate a hydrophilic surface. As a result, the resin surface exposed to ArF laser radiation becomes oleophilic or hydrophilic. Both samples were bonded to stainless steel plates with an epoxy bonding agent and the tensile shear strength was 1.2 x 10⁷ Pa in both cases.     

Role of platinum surface morphology on hydrogen adsorption isotherms—IV

The changing characters of hydrogen quasi-equilibrium adsorption isotherms on high surface area platinum electrocatalyst crystallites in 1 M H₂SO₄ were examined as a function of the average crystallite sizes. On varying the platinum crystallite sizes (28–460 A dia), the relative concentrations of surface atoms identified with edges, vertices and crystallite faces are changed and are compared to the changing surface concentrations of the adsorbed hydrogen species. Model crystallite calculations assume a cubo-octahedral structure with (111) and (100) faces to give the lowest surface energy.The heterogeneity parameter, g, in the hydrogen quasi-equilibrium isotherms is an extrinsic factor, specifically associated with the adsorbed species and not an intrinsic function of the platinum crystallite surface. Also, interstitial B₅ sites are not important as specific hydrogen adsorption locations. Crystallite edge atoms (or Pt atoms with low coordination numbers) have been identified as having a specific adsorbed hydrogen species, θ_3a, and weakly and strongly bonded adsorbed hydrogen are associated with the (111) and (100) crystallite faces, respectively.     

Study of O2 and OH adsorption energies on Pd-Cu alloys surface with a quantum chemistry approach

Variation of the intrinsic metal surface properties (lattice parameter, binding energy, work function (W_f), d-band filling and d-band center ?_d) and O₂ and OH adsorption energies of on (1 1 1) Pd-Cu surface alloys were determined using ab initio program. Calculations of these parameters were based on plane waves approach on slab system with density functional theory (DFT) using the Vienna ab initio simulation program (VASP). It was shown that insertion of Cu atoms in Pd lattice affects geometric and electronic properties of Pd. These changes influence significantly O₂ and OH adsorption. Indeed, the highest OH adsorption energy and the lowest O₂ adsorption energy were found with 30 at.% in Cu. The volcano shape of the O₂ and OH adsorption with composition in Cu was explained, respectively, by firstly the highest bond distance that reduces adsorption energy of oxygen and the compromise between low DOS(E_f) and secondly, low band width (W) reach for Pd₃Cu which leads to the highest OH adsorption energy. O₂ and OH adsorption energies tendency could explain effect of the transition metal (TM) on kinetic current of the oxygen reduction reaction.     

Kinetic isotope effect in the reaction of NOads and COads on the Pt(100) surface

The reaction of CO with ¹⁵NO and ¹⁴NO mixtures in a co-adsorption layer on the Pt(100)-(hex) surface was studied by TPR. The kinetic isotope effect (KIE) manifests itself in the variation of the temperature of the maximum of the N₂ desorption peak depending on the isotopic composition: T_max(¹⁴N₂)<T _max(¹⁴N¹⁵N)≈ T_max(¹⁵N₂). The KIE observed is consistent with the assumption that the NO_ads dissociation is the rate-determining step of the reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Importance of activated carbon's oxygen surface functional groups on elemental mercury adsorption

The effect of varying physical and chemical properties of activated carbons on adsorption of elemental mercury (Hg⁰) was studied by treating two activated carbons to modify their surface functional groups and pore structures. Heat treatment (1200 K) in nitrogen (N₂), air oxidation (693 K), and nitric acid (6N HNO₃) treatment of two activated carbons (BPL, WPL) were conducted to vary their surface oxygen functional groups. Adsorption experiments of Hg⁰ by the activated carbons were conducted using a fixed-bed reactor at a temperature of 398 K and under N₂ atmosphere. The pore structures of the samples were characterized by N₂ and carbon dioxide (CO₂) adsorption. Temperature-programmed desorption (TPD) and base-acid titration experiments were conducted to determine the chemical characteristics of the carbon samples. Characterization of the physical and chemical properties of activated carbons in relation to their Hg⁰ adsorption capacity provides important mechanistic information on Hg⁰ adsorption. Results suggest that oxygen surface complexes, possibly lactone and carbonyl groups, are the active sites for Hg⁰ capture. The carbons that have a lower carbon monoxide (CO)/CO₂ ratio and a low phenol group concentration tend to have a higher Hg⁰ adsorption capacity, suggesting that phenol groups may inhibit Hg⁰ adsorption. The high Hg⁰ adsorption capacity of a carbon sample is also found to be associated with a low ratio of the phenol/carbonyl groups. A possible Hg⁰ adsorption mechanism, which is likely to involve an electron transfer process during Hg⁰ adsorption in which the carbon surfaces may act as an electrode for Hg⁰ oxidation, is also discussed.     

Template-free method for synthesizing sponge-like graphitic carbon nitride with a large surface area and outstanding nitrogen photofixation ability induced by nitrogen vacancies

Nitrogen fixation is the second most important chemical process in nature next to photosynthesis. Herein, we report a convenient template-free method for synthesizing sponge-like graphitic carbon nitride (g-C₃N₄) with a large surface area and outstanding nitrogen photofixation ability under visible light. X-ray diffraction (XRD), N₂ adsorption, UV–vis spectroscopy, N₂-Temperature programmed desorption (N₂-TPD), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), and photocurrent measurements were used to characterize the prepared catalysts. The results indicate that solvent species (alcohols) play the most important role in the formation of the porous structure. Methanol-treated g-C₃N₄ exhibits the highest surface area and nitrogen photofixation ability, which are 15.2-fold and 27.2-fold greater, respectively, than that of untreated g-C₃N₄. Nitrogen vacancies could activate N₂ and promote interfacial electron transfer, thereby significantly improving the nitrogen photofixation ability.     

Role of surface states in electrodeposition of Pb on n-Ge(111)

The influence of surface states on the kinetics of the initial stages of Pb electrodeposition on n-Ge(111) was studied by cyclic voltammetric and current transient measurements. The substrate surface was modified to n-Ge(111)H or n-Ge(111)OH applying appropriate experimental and polarization routines. In transient experiments, the driving force for nucleation, the supersaturation, was varied by both changing the electrode potential U at c_Pb²⁺=const and the concentration c_Pb²⁺ at U=const. The results obtained indicate that, under the experimental conditions used, the nucleation site density N₀ remains constant with the electrode potential and thus, does not influence the initial nucleation kinetics. The nucleation rate, the density of nucleation sites and the number of atoms N_crit in critical nuclei were obtained analyzing current transients on the basis of models for instantaneous and progressive nucleation. Nucleation kinetics were found to be more inhibited on n-Ge(111)OH. The experimental results show that the different nucleation behavior of H- and OH-terminated n-Ge(111) surfaces can be explained by different densities of Ge surface free radicals acting as nucleation sites. Problems connected with an application of electrodeposition for metallization of micro- and nanostructures are discussed.     

In situ characterization of interaction of ammonia with carbon surface in oxygen atmosphere

The adsorption and oxidation of ammonia over carbons differing in the chemical structure of surface functional groups have been investigated by FTIR spectroscopy. The reactions of NH₃ with carbons have been studied both in the presence and in the absence of oxygen. As a result of NH₃ chemisorption, in addition to ammonium salts, there are formed surface amide and imide structures. At the higher temperature surface isocyanate species are formed. Thermal stabilities of surface structures, formed as a result of NH₃ chemisorption have been determined by means of FTIR spectroscopy. The activity and selectivity of carbons for the selective catalytic oxidation (SCO) of NH₃ to N₂ with excess O₂ has been shown by microreactor studies at 295-623 K. Carbon catalysts are very active for NH₃ oxidation. Nitrogen is generally the predominant product of ammonia oxidation. The selectivity to N₂, N₂O and NO is determined by the surface oxygen coverage and reaction temperature. The data obtained indicate that the N₂ is formed via selective catalytic reduction (SCR) between NH_x surface species and NO formed from NH₄⁺ oxidation. This implies that ammonia is activated in the form of NH₄⁺ species for both SCR and SCO processes.     

Specific surface,pozzolanic activity and composition of pulverized-fuel ash

This paper describes a laboratory investigation into the relations between the specific surface—as determined by different methods—the chemical composition, and the pozzolanic activity of pulverized-fuel ash (PFA). It is shown that the values obtained for specific surfaces of ashes vary according to the method of determination. However, it is likely that the highest value, the specific surface determined by nitrogen adsorption (N_dry), is the most appropriate value. Positive and negative correlations were found between N_dry specific surface and the carbon content of the ash, and between N_dry specific surface and total silica and alumina contents, respectively. Ashes with high N_dry specific surface values are characterized by angular porous particles, whereas those with low N_dry specific surface values appear to be primarily composed of non-porousspherical particles. A negative correlation was found between pozzolanic activity and N_dry specific surface. However, there was little correlation between pozzolanic activity and chemical composition. It is recommended that an upper acceptable limit should be placed on the N_dry specific surface of PFA when it is to be used for purposes requiring high pozzolanic activity.     

An ab initio electronic structure study of methyl adsorption and reaction on cluster models for the diamond surface

Electronic structure calculations were carried out for a series of hydrogen-terminated carbon clusters designed to model the 100- and 111-diamond surfaces, C_d(100) and C_d(111). The subjects of the calculations were: (1) methyl radical (CH_3^·) adsorption on an activated diamond surface; and (2) hydrogen abstraction from adsorbed methyl via reaction with gas-phase atomic hydrogen. The largest clusters were treated at the MP2/6-31G*//HF/6-31G* level of theory. The results of higher level calculations on smaller clusters were used to estimate corrections to the MP2/6-31G*//HF/6-31G* energies. It is concluded that methyl adsorption is 6.8 kcal mol⁻¹ more exothermic on C_d(100) than on C_d(111). Also, the barrier for hydrogen abstraction from methyl adsorbed on C_d(100) is 2.4 kcal mol⁻¹ lower than that for abstraction from methyl adsorbed on the C_d(111) surface. Finally, the abstraction reaction energy is 0.8 kcal mol⁻¹ lower for methyl adsorbed on C_d(100) compared to methyl adsorbed on C_d(111).     

Adsorption of graphene on an Fe3O4 surface: A molecular dynamics simulation study

A molecular dynamics (MD) simulation was used to investigate the adsorption of graphene oxide (GO) and graphene (G) onto an Fe₃O₄(111) surface. The MD simulation results indicated that the direction of the GO/G sheets introduced onto the Fe₃O₄(111) surface affected the morphologies of the GO/G sheets and the interface interaction energies. When the GO/G sheets were introduced onto the Fe₃O₄(111) surface from the parallel direction, a smooth, single-layered structure of the GO/G sheets formed, and the interface interaction energies were low. The interface interaction energy of GO-Fe₃O₄ interface was lower than that between G and Fe₃O₄(111) surfaces because of the strong interactions between the carboxyl groups on the GO edges and the iron atoms on the surface. The ideal distribution and lower interface interaction energies of the polymers (PEG and PEI) with GO/G indicated that the GO/G coated layer on the Fe₃O₄ surface could be further modified. According to results, GO, under specific stirring speeds, was adsorbed onto the Fe₃O₄ surface along the parallel direction and formed stable graphene-Fe₃O₄ composite microspheres suitable for drug carrier applications. Both GO and G covered the rough, grooved surface of Fe₃O₄(111), and the adsorption of GO was faster than that of G.     

Heteroepitaxy of Diamond on Cubic Boron Nitride

The epitaxial growth process of diamond from the gas phase on a cubic boron nitride (c-BN) {111} surface has been investigated. At the initial growth stage, carbon adsorption progressed on a boron-terminated surface of c-BN ({111}_B). The coordination of the carbon atoms was found to be the same as that observed in diamond, as confirmed by electron energy loss spectroscopy (EELS). The epitaxial growth of diamond particles has been observed after formation of the carbon layer. On the other hand, on the nitrogen-terminated surface ({111}_N), neither stable adsorption of carbon nor nucleation of diamond has been observed. The stability of adsorbed carbon atoms in the chemical vapor deposition (CVD) ambient, in which large amounts of atomic hydrogen are supplied to the substrate heated at high temperature, is quite important for the nucleation of diamond. Using cross-sectional transmission electron microscopy (TEM), numerous crystal defects were observed, both in c-BN and diamond. Formation of the epitaxial diamond particles has been observed especially at defect sites on c-BN. The misfit dislocation has been observed near the interface with the diamond particle. Even though there exist misfit dislocations that relieve the stress caused by the lattice mismatch between diamond and c-BN, the epitaxial film involved retains a tensile strain of about 0.29% for a film thickness of about 200 nm.     

Zn3N2 nanowires: growth,properties and oxidation

Zinc nitride (Zn₃N₂) nanowires (NWs) with diameters of 50 to 100 nm and a cubic crystal structure have been grown on 1 nm Au/Al₂O₃ via the reaction of Zn with NH₃ including H₂ between 500°C and 600°C. These exhibited an optical band gap of ≈ 3.2 eV, estimated from steady state absorption-transmission spectroscopy. We compared this with the case of ZnO NWs and discussed the surface oxidation of Zn₃N₂ NWs which is important and is expected to lead to the formation of a Zn₃N₂/ZnO core-shell NW, the energy band diagram of which was calculated via the self-consistent solution of the Poisson-Schrödinger equations within the effective mass approximation by taking into account a fundamental energy band gap of 1.2 eV. In contrast, only highly oriented Zn₃N₂ layers with a cubic crystal structure and an optical band gap of ≈ 2.9 eV were obtained on Au/Si(001) using the same growth conditions.     

Aluminated hierarchical silicalite-2 particles: Catalyst with remarkably increased lifetime for methanol to hydrocarbons

Aluminated hierarchical silicalite-2 with both large particle size and high external surface area was prepared by aluminating silicalite-2 under the protection of TBA⁺ cations in a mild alkaline solution. The textural and acidic properties of thus formed material (Z11-meso) were characterized by SEM, TEM, XRD, N₂ adsorption, FTIR, NH₃-TPD, and ²⁷Al NMR spectroscopy. The resulting hierarchical Z11-meso contained mainly tetrahedral coordinated aluminum species with low Brønsted/Lewis ratio (B/L) while preserved the zeolitic structure. Owning to the high external surface area (S_ext), hierarchical porous structures and low B/L ratio, Z11-meso outperformed the microporous ZSM-11 counterparts in methanol to hydrocarbons in terms of both activity and stability.     

Doping-induced anisotropic lattice strain in homoepitaxial heavily boron-doped diamond

As a result of the larger covalent radius of boron (r_B = 0.88 Å) when compared to that of carbon (r_C = 0.77 Å), the introduction of substitutional boron into diamond leads to an expansion δa/a of the lattice parameter. This has been found previously to follow a linear interpolation (Vegard law) as long as the boron content is lower than about 0.5 at.% in MPCVD epilayers or 1.5 at.% in HPHT bulk crystals.Above those concentrations, the expansion is less pronounced than predicted by Vegard. In order to explain this effect, we have performed ab initio calculations on C:B substitutional alloys. The results show that the presence of interstitial boron and of boron clusters is not necessary to explain the experimental data available in the literature. Moreover, quantitative estimates are proposed for the deformation potential of the valence band maximum and for the steric effect associated to boron pairing. We then apply these conclusions to discuss the different variations of δa/a vs boron contents observed by high resolution XRD experiments performed on “insulating” and metallic (and superconducting) p⁺⁺ diamond epilayers grown by MPCVD on (100)- and (111)-oriented type Ib substrates, for which boron concentration profiles have been determined by Secondary Ion Mass Spectroscopy.     

Adsorption and corrosion inhibition behaviour of N-(phenylcarbamothioyl)benzamide on mild steel in acidic medium

Corrosion inhibition property of N-(phenylcarbamothioyl)benzamide (PCB) on mild steel in 1.0 M HCl solution has been investigated using chemical (weight loss method) and electrochemical techniques (potentiodynamic polarization and AC impedance spectroscopy). The inhibition efficiencies obtained from all the methods are in good agreement. The thiourea derivative is found to inhibit both anodic and cathodic corrosion as evaluated by electrochemical studies. The inhibitor is adsorbed on the mild steel surface according to Langmuir adsorption isotherm. The adsorption mechanism of inhibition was supported by spectroscopic (UV-visible, FT-IR, XPS), and surface analysis (SEM-EDS) and adsorption isotherms. The thermodynamic parameter values of free energy of adsorption (ΔG_ads) reveals that inhibitor was adsorbed on the mild steel surface via both physisorption and chemisorption mechanism.     

Carbothermal synthesis of boron nitride coating on PAN carbon fiber

Boron nitride (BN) thin coating has been formed on the surface of chemically activated polyacrylonitrile (PAN) carbon fiber by dip coating method. Dip coating was carried out in saturated boric acid solution followed by nitridation at a temperature of 1200 °C in nitrogen at atmospheric pressure to produce BN coating. Chemical activation improved surface area of PAN fiber which favours in situ carbothermal reduction of boric acid. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) have shown the formation of boron nitride. The X-ray photoelectron spectroscopy reveals that the coating forms a composite layer of carbon, BN/BO_xN_y and some graphite like BCN with local structure of B–N–C and B(N–C)₃. The oxidation resistance of the coated fiber was significantly higher than uncoated carbon fiber. Tensile strength measurement reveals that the BN coated fiber maintained 90% of its original strength. As compared to chemical vapor deposition (CVD), this process is simple, non-hazardous and is expected to be cost effective.