Atomistic simulation of thermally activated glide of dislocations in Fe---Ni---Cr---N austenite

Thermally activated glide of edge and screw dislocations with the Burgers vector b = a/2110 in Fe---Ni---Cr austenite without and with nitrogen has been analyzed using the conjugate gradient method to minimize the potential energy of the crystal (subject to appropriate constraints) and the embedded-atom method to quantify the atomic interactions. The results of the analyses were compared with their experimental counterparts. In austenite without nitrogen, the variation of the crystal energy with the dislocation position gives rise to a Peierls frictional stress. However, the magnitude of this stress is relatively low and both edge and screw dislocations can readily overcome it by the assistance of thermal activation. The presence of nitrogen, on the other hand, causes the core of a screw dislocation to dissociate onto two {111} planes containing the dislocation line. This renders the screw dislocation sessile. Such changes in the core structure of an edge dislocation were not observed. Instead, the interaction of nitrogen with edge dislocations was found to give rise to both an athermal (long-range) and a thermal (short-range) component of the frictional stress. A detailed analysis of the interactions between the nitrogen atoms and the edge dislocations suggests that the athermal component of the frictional stress observed in the present work is most likely responsible for the experimentally observed athermal flow stress in Fe---Ni---Cr polycrystalline austenite. On the other hand, with a possible exception of very low temperature, the contribution of the thermal frictional stress associated with the interaction of edge dislocations with nitrogen to the strength of Fe---Ni---Cr polycrystalline austenite is small.     

Investigation of reactively sputtered TiN films for diffusion barriers

Two groups of reactively sputtered TiN films, gold-yellow films (G films) with low resistivity and high compressive internal stress and brown-black films (B films) with high resistivity, which are formed with and without a negative substrate bias, were examined as potential diffusion barriers.The microstructures and compositions were investigated by Auger electron spectroscopy, electron probe microanalysis and X-ray diffraction. The G films and the B films have a fine-grained and a columnar-arranged morphological structure respectively. Both films exhibit the cubic NaCl-type crystallographic structure strongly oriented towards the (111) plane which is parallel to the substrate surface. They also exhibit a superstoichiometric composition having excess nitrogen atoms. In addition, the B films contain a large number of oxygen atoms.The compressive internal stress in the G film originates from lattice expansion which is probably due to the incorporation of the excess nitrogen atoms. Using the experimental value of the Young's modulus, the expanded lattice parameter in this film was calculated from the corrected interplanar spacing after the silicon substrate had been removed.The superior diffusion barrier capability of the B film is demonstrated through the application of the TiN films to an Au/Pt/TiN/Ti metal system on thick polysilicon. It is assumed that the higher diffusion barrier capability of the B film is due to the reduction of grain boundary diffusion by the oxygen atoms located in the intercolumnar layers. This is supported by film analysis, the peculiar etching behaviour and hardness studies.     

Structure-dependent response of a chemiluminescence nitrogen detector for organic compounds with adjacent nitrogen atoms connected by a single bond

High-throughput screening (HTS) of chemical libraries is indispensable for drug discovery research. However, the HTS data quality for lead discovery, lead optimization, and quantitative structure activity relationship studies has been severely compromised due to the uncertain compound concentrations in screening plates. In order to address this issue, we compared various high-throughput technologies for quantification of compounds in microtiter plate format without the need for authentic compounds as standards and identified the chemiluminescence nitrogen detector (CLND) as the method of choice at the present time. However, the structure dependence of this detector has not been well studied. A proposed rule suggested that the only exception to equimolar response is for compounds that contain adjacent nitrogen atoms. The response should be zero when the adjacent nitrogen atoms are connected by a double bond and 0.5 when they are connected by a single bond. In this investigation, we studied a broad range of compounds with isolated and adjacent nitrogen atoms. We confirmed that compounds with isolated nitrogen atoms produce an equimolar response with a 15-20% variation depending on structures and compounds with adjacent nitrogen atoms connected by a double bond giving nearly zero response. We discovered that the CLND response for compounds containing adjacent nitrogen atoms that are connected with a single bond is highly structure dependent. Substitutions on the nitrogen atoms or nearby in the molecule can increase the CLND response to approach a value higher than the predicted value 0.5 (maximal value 0.82/nitrogen atom). Without substitution, much lower values than predicted (minimal value 0.0-0.08/nitrogen atom) are obtained. Therefore, the prediction of response of 0.5/nitrogen atom for compounds with adjacent nitrogen atoms connected by a single bond should be abandoned. Compounds with similar structures should be used to generate calibration curves for quantification of this class of compounds.     

Optical properties and residual stress in aluminum nitride films prepared by alternating-current dual reactive magnetron sputtering

Aluminum nitride films were deposited by alternating-current dual reactive magnetron sputtering. The influence of different nitrogen flow and working pressures at a sputtering power of 5 kW on the refractive index, extinction coefficient, crystalline structure, residual stress, and surface roughness of aluminum nitride films was discussed. The aluminum nitride film would have high refractive index, low extinction coefficient and small residual stress at suitable nitrogen flow rate and low working pressure.     

Controlled surface modification of boron nitride nanotubes

Controlled surface modification of boron nitride nanotubes has been achieved by gentle plasma treatment. Firstly, it was shown that an amorphous surface layer found on the outside of the nanotubes can be removed without damaging the nanotube structure. Secondly, it was shown that an oxygen plasma creates nitrogen vacancies that then allow oxygen atoms to be successfully substituted onto the surface of BNNTs. The percentage of oxygen atoms can be controlled by changing the input plasma energy and by the Ar plasma pre-treatment time. Finally, it has been demonstrated that nitrogen functional groups can be introduced onto the surface of BNNTs using an N(2) + H(2) plasma. The N(2) + H(2) plasma also created nitrogen vacancies, some of which led to surface functionalization while some underwent oxygen healing.     

The effect of noble gas bombarding on nitrogen diffusion in steel

The low energy (∼50–350 eV) noble gases ion bombardment of the steel surface shows that the pre-treatments increase nitrogen diffusion by modifying the outermost structure of the material. The surface microstructure and morphology of the studied samples were characterized by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The crystalline and chemical structures in the outermost layers of the surface were analyzed by grazing angle X-ray diffraction (GAXRD) and photoemission electron spectroscopy (XPS). Temperature effusion studies of the implanted ions are used to elucidate the noble gases site localization in the network. The local compressive stress induced by the nearby iron atoms on the core level electron wave functions of the trapped noble gases are studied by photoemission electron spectroscopy (XPS) and interpreted considering a simple mechanical model. Nano-hardness measurements show the dependence of the material elastic constant on the energy of the implanted noble gases. Although the ion implantation range is about few nanometers, the atomic attrition effect is larger enough to modify the material structure in the range of micrometers. Two material stress zones were detected where the outermost layers shows compressive stress and the underneath layers shows tensile stress. The implanted noble gases can be easily removed by heating. A diffusion model for polycrystalline-phase systems is used in order to discuss the influence of the atomic attrition on the N diffusion coefficient. The concomitant effect of grain refining, stress, and surface texture on the enhancing nitrogen diffusion effect is discussed.     

Heat Transfer in Subsonic Flows of Dissociated Nitrogen: HF Plasmatron Experiment and Numerical Simulation

Experiments on heat transfer in subsonic jets of dissociated nitrogen have been carried out on a IPG-4 induction plasmatron. The heat fluxes to copper, stainless steel, nickel, graphite, and quartz surfaces at the stagnation point of a water-cooled cylindrical flat-faced model 20 mm in diameter and dynamic pressures have been measured at a pressure of 50 hPa in the test chamber and a power of 35–65 kW of the HF generator. The experiments showed the influence of surface catalytic properties on the heat flux in relation to the nitrogen atom recombination. In the conditions of the experiments, a numerical simulation of nitrogen plasma flows in the discharge channel of plasmatron and the subsonic dissociated nitrogen jet flow around the cylindrical model has been carried out. The experimental and calculated data on heat fluxes to cooled copper, stainless steel, nickel, graphite, and quartz surfaces are compared. The quantitative catalyticity scale of the studied materials in relation to the heterogeneous recombination of nitrogen atoms is established.     

Single step fabrication of N-doped graphene/Si3N4/SiC heterostructures

In-plane heteroatom substitution of graphene is a promising strategy to modify its properties. The ability to dope graphene with electron-donor nitrogen heteroatoms is highly important for modulating electrical properties of graphene. Here we demonstrate a transfer-free method to directly grow large area quasi free-standing N-doped graphene bilayers on an insulating substrate （Si3N4）. Electron-bombardment heating under nitrogen flux results in simultaneous growth of N-doped graphene and a Si3N4 layer on the SiC surface. The decoupling of N-doped graphene from the substrate and the presence of Si3N4 are identified by X-ray photoemission spectroscopy and low-energy electron diffraction. The substitution of nitrogen atoms in the graphene planes was confirmed using high resolution X-ray photoemission spectroscopy which reveals several atomic configurations for the nitrogen atoms： Graphitic-like, pyridine-like, and pyrrolic- like. Furthermore, we demonstrated for the first time that N-doped graphene could be used to efficiently probe oxygen molecules via nitrogen atom defects.     

The influence of interstitial impurity atoms on the recovery behaviour of cold-worked vanadium

Vanadium containing oxygen and nitrogen shows, after deformation at room temperature by rolling, two distinct recovery stages at annealing temperatures of about 450 and 550° K. Measurements of electrical resistivity and of low frequency damping were made. By variation of the gas content of the samples, it was established that the stage situated at 450° K is caused by the migration of oxygen atoms to dislocations, whereas at 550° K nitrogen atoms migrate to dislocations. Two small steps occurring at 340 and 400° K can be attributed to ordering of oxygen and nitrogen atoms in the dislocation stress fields.     

An in vivo probe based on mechanically strong but structurally small carbon electrodes with an appreciable surface area.

Physically small carbon electrodes were fabricated by pyrolyzing acetylene in a nitrogen atmosphere using pulled quartz capillaries as the supporting substrate. A carbon disk geometry was obtained when a parallel flow of acetylene (50 kPa) and nitrogen (10 mL min(-1)) was introduced into the system. Further, carbon was found to deposit at the tip and on the shank of the quartz capillaries when the nitrogen flow rate was increased (80 mL min(-1)), yielding an approximately cylindrical geometry. A series of electrochemical and spectroscopic analyses was carried out to examine the type of carbon surface obtained by pyrolysis of acetylene. The results suggested that a surface consisting of an almost defect-free highly oriented pyrolytic graphite type structure was formed by the pyrolyzed acetylene. However, this contradicts the kinetically reversible electron transfer observed for dopamine oxidation at these electrodes. Meanwhile, the nonpolar and relatively oxygen-free characteristics indicate that these electrodes also behave similarly to a hydrogenated carbon surface. The formation of a hydrogenated carbon-type surface may be plausible as a result of the attack on the carbon surface by a surplus of hydrogen produced by the pyrolysis of acetylene to form graphitic carbon. These characteristics are expected to aid in reducing electrode fouling, which is often encountered in electrochemical detection of neurotransmitters in vivo. In conjunction with a miniature physical dimension, their appreciable surface area and enhanced mechanical strength make these carbon electrodes well suited to the detection of neurotransmitters in vivo.     

Single‐Site AuI Catalyst for Silane Oxidation with Water

Single‐site Au anchored on mpg‐C₃N₄ (519 ppm Au loading) is developed as a highly active, selective, and stable catalyst for the oxidation of silanes with water with a turnover frequency as high as 50 200 h^?1, far exceeding most known catalysts based on total gold content. Other hydrosilanes bearing unsaturated functional groups also lead to corresponding silanols under mild reaction conditions without formation of any side products in good or excellent yields. The spherical aberration correction electron microscopy and extended X‐ray absorption fine structure measurements both confirm the atomic dispersion of Au atoms stabilized by mpg‐C₃N₄. The coordination of the catalytically active Au^I by three nitrogen or carbon atoms in the tri‐s‐triazine repeating units not only prevents the Au atoms from aggregation, but also renders the surface Au^I highly active, which is completely different than homogeneous Au^I species.     

Surface layers produced by ion nitriding of austenitic Fe-Mn-Al alloys and the effects on hardness and corrosion resistance

Austenitic (fcc) Fe-Mn-Al alloys were nitrided in the temperature range 723 to 973 K by a glow discharge method using H₂-N₂ gas mixtures, and the microstructures and compositions of the nitrided layers were investigated in detail. A thin surface layer and a thick nitrogen-diffused layer (internal nitrided layer) were produced; the former consisted of both manganese nitrides and a ferritic (bec) phase, while the internal nitrided layer had an austenitic structure with the incorporated excess nitrogen atoms. X-ray photoelectron spectra revealed that the incorporated nitrogen atoms have a strong interaction with aluminium lattice atoms. By nitriding, hardness values of the Fe-Mn-Al alloys were increased fromH _v = 350 to ca. 1000, and the corrosion resistance to sulphuric acid solution was enhanced by a factor of 30. These improvements are associated with a uniform distribution of the incorporated nitrogen and also with the presence of nitride-like interactions between the nitrogen and aluminium atoms.     

超级电容器用含氮多孔炭电极材料的研究进展

概述了表面改性和本体富氮两种负载氮原子的方法及其优缺点,总结了经高温处理后炭材料表面含氮官能团(N-6、N-5、N-Q、N-X)的转化机制:氮原子最终以化学性质稳定的六圆环的形式出现(如N-6、N-Q、N-X),温度高于600℃时,N-5(Pyrrolic-N)通过扩环作用转变为N-6、N-Q、N-X。最后从法拉第氧化还原反应(产生赝电容)和电极的湿润性两方面归纳了表面含氮官能团对超级电容器电化学性能的影响,并展望了今后的研究方向。     

Characteristics of boron and nitrogen species on aluminum surface

The interactions of boron and nitrogen atoms with an aluminum (0 0 1) surface have been studied by means of density functional theory (DFT). Calculations of potential energy surfaces show that the nitrogen adsorption favors the formation of stronger bond with aluminum than the boron adsorption. This study indicates that a surface substrate of nitride as the first step in boron nitride deposition on aluminum would facilitate a good adhesion of the grown film with the substrate.     

Simultaneous determination of the recombination probability of nitrogen and oxygen atoms on quartz

The state of the problem of the heterogeneous recombination of nitrogen and oxygen atoms has been considered. A setup for measuring the probability of the heterogeneous recombination of atoms using resonance florescence spectroscopy has been described. The main feature of this method is the possibility of simultaneous registration of the concentration of N and O atoms in the air mixture in strictly controlled conditions. The temperature dependences of the probability of the recombination of nitrogen and oxygen atoms separately and in the combined recombination process on the quartz surface in the range of 300–600 K have been obtained. The proposed methodology also made it possible to start studying the mutual effect of the processes of the heterogeneous recombination of nitrogen and oxygen and to determine the fraction of the cross recombination.     

Room temperature formation of ammonia by oxidizing hydrogenated cerium nanoparticles in the air

Ammonia formation was observed when hydrogenated cerium nanoparticles prepared by hydrogen plasma-metal reaction (HPMR) were exposed to the air at room temperature. This novel phenomenon represents a successful example of room temperature cleavage of dinitrogen and may find application in low temperature synthesis of ammonia under thermodynamically favorable conditions. A possible mechanism is also proposed. We suggest that the oxidation of cerium hydride offers chemical force to drive the hydrogen atoms out of the lattice. The monoatomic H released to the surface is highly active and readily reacts with N2 to yield ammonia. Some surface processes, which we know little about at the moment, are likely to be involved so as to lower the energy barrier of nitrogen dissociation. Further investigation is required to elucidate the detailed mechanism.     

Dependence of nitriding degree of Ti surface by non-LTE nitrogen plasma on various plasma parameters

Experiments of plasma nitriding of titanium are carried out by two plasma sources. One is a microwave discharge plasma source under several Torr, and the other is a nitrogen arc jet generated under atmospheric pressure followed by rapid expansion into a gas wind tunnel. The relationship between the surface density of nitrogen atoms in the α-Ti and various plasma parameters is systematically studied. For the microwave nitrogen plasma, it is found that the effect of the vibration temperature is the most essential for the surface nitriding, whereas the effect of electron temperature, density and rotation temperature is less remarkable. It is also found that the higher vibration temperature of the microwave discharge nitrogen plasma makes the target temperature higher, and consequently, the surface density of atomic nitrogen remarkably increased. However, the effect of target temperature is less remarkable for the arc jet nitrogen plasma.     

COMPUTATIONAL STUDY OF N@C60, P@C60, AND As@C60

Semiempirical and density functional theory structural calculations on Group V atom-endohedral complexes are reported. While reports, in some instances contradictory, on the structure of N@C₆₀ have appeared in the literature, this is the first computational study that includes both phosphorous and arsenic as endohedral atoms. Potential energy functions for all complexes are also reported. The calculations indicate that, as the atoms are translated towards the cages, weak covalent bonds external to the cage are possible. There is a significant difference between the potential surface for the nitrogen complex and that of either phosphorous or arsenic. The nitrogen surface is repulsive for movement of the endohedral atom off-center. The curves for the other atoms are essentially flat with displacement. The potential curves have also been calculated for the reaction products of the complexes with azides. Similar potentials, as a function of endohedral atom displacement, were observed. The relative experimental stabilities of the complexes are understood on the basis of these data.     

Stress behavior of FCC metallic thin films during thermal evaporation

The development of stress in metallic thin films, monitored by in-situ curvature measurements during deposition, is analyzed. Three distinct stress regions including initial compressive, broad tensile, and incremental compressive stress were reported in terms of the film thickness (deposition time) by F. Spaepen. An experimental set-up was assembled for the in-situ curvature measurements utilizing vacuum thermal evaporation and multi-beam laser reflection points arrayed in x- and y-axis. The change in the spacing of laser reflected points was converted to the curvature of specimen, in turn, to instantaneous stress levels in the growing films using Stoney's formula. To investigate the effect on the distinct stress regions, the flux of the depositing metallic atoms was used as an experimental variable in this study. For the lowest flux cases for Cu and Ag, an additional second compressive stress stages after tensile maximum stress was observed in this study. Initial compressive part and tensile maximum stress regions appeared in shorter period of time for the thin films deposited at higher flux of atoms. Thus the flux of depositing atoms may affect the mechanisms of each stage. The initial compressive stress is conjectured to stem from the state of thin film surfaces; dynamic and relaxed surface. A broad tensile region is reported from the fact that the reduction of excess volume associated with grain boundaries and/or the coalescence of grains for high mobility materials. The incremental compressive stress region may be related to surface state and atomic mobilities.     

Quantum states of he atoms adsorbed on surfaces of rare gas solids

Wave functions and energies for band states of helium atoms in the two-dimensional periodic potential at the surface of a semiinfinite rare gas solid have been studied. In the case of Kr and Ar substrates, the atoms are highly localized and, correspondingly, the band widths are small. In a third case, namely that of an argon crystal highly compressed to simulate the adsorption site density of the close-packed face of argon, much larger band widths were found. If this is a reasonable simulation, then band effects may be observable.