Concentration Of Nitrogen Atoms Research Articles

Thermal stability of copper nitride thin films: The role of nitrogen migration

The atomic composition, structural, morphological, and optical properties of N-rich copper nitride thin films have been investigated prior to and after annealing them in vacuum at temperatures up to 300 °C. Films were characterized by means of ion-beam analysis (IBMA), X-ray diffraction (XRD), atomic force microscopy (AFM), and spectroscopic ellipsometry techniques (SE). The data reveal that even when the total (integrated over the whole thickness) atomic composition of the films remains constant, nitrogen starts to migrate from the bulk to the film surface, without out-diffusing, at temperatures as low as 100 °C. This migration leads to two chemical phases with different atomic concentration of nitrogen, lattice parameters, and crystallographic orientation but with the same crystal structure. XRD experimental and Rietveld refined data seem to confirm that nitrogen excess accommodates in interstitial locations within the anti-ReO3 crystal lattice forming a solid solution. The influence of nitrogen migration on the optical (electronic) properties of the films will be discussed.

Nitrogen and Luminescent Nitrogen‐Vacancy Defects in Detonation Nanodiamond

An efficient method to investigate the microstructure and spatial distribution of nitrogen and nitrogen-vacancy (N-V) defects in detonation nanodiamond (DND) with primary particle sizes ranging from approximately 3 to 50 nm is presented. Detailed analysis reveals atomic nitrogen concentrations as high as 3 at% in 50% of diamond primary particles with sizes smaller than 6 nm. A non-uniform distribution of nitrogen within larger primary DND particles is also presented, indicating a preference for location within the defective central part or at twin boundaries. A photoluminescence (PL) spectrum with well-pronounced zero-phonon lines related to the N-V centers is demonstrated for the first time for electron-irradiated and annealed DND particles at continuous laser excitation. Combined Raman and PL analysis of DND crystallites dispersed on a Si substrate leads to the conclusion that the observed N-V luminescence originates from primary particles with sizes exceeding 30 nm. These findings demonstrate that by manipulation of the size/nitrogen content in DND there are prospects for mass production of nanodiamond photoemitters based on bright and stable luminescence from nitrogen-related defects.

Estrutura e propriedades do aço inoxidável austenítico AISI 316L Grau ASTM F138 nitretado sob plasma à baixa temperatura

Os aços inoxidáveis austeníticos possuem restrições para a nitretação nas temperaturas convencionais, próximas de 550ºC, devido à precipitação intensa de nitretos de cromo na zona de difusão. Essa precipitação eleva a dureza, mas deteriora as propriedades de corrosão. O uso do processo de nitretação sob plasma permite introduzir nitrogênio em temperaturas inferiores a 450ºC, levando à formação de uma fina camada de austenita expandida pelo nitrogênio (gN). Essa fase possui uma estrutura cristalina mais bem representada pelo reticulado triclínico, com elevada concentração de nitrogênio em solução sólida supersaturada, a qual promove um estado de tensões residuais de compressão capaz de elevar a dureza do substrato de 4 GPa para valores próximos de 14 GPa. O Módulo de Elasticidade mantém-se próximo de 200 GPa após a nitretação.

Influence of oxygen on the formation of cubic boron nitride by r.f. magnetron sputtering

Formation of cubic boron nitride by r.f. magnetron sputtering has been studied with O 2 addition to the common working gas Ar/N 2. The chemical and the phase composition were determined with Auger electron spectroscopy sputter depth profiling and Fourier transform infrared spectroscopy. The result shows that oxygen hinders the formation of cBN in sufficient nitrogen-supply, but facilitates the growth of cBN in insufficient nitrogen-supply. With insufficient nitrogen-supply, there exists an optimal oxygen-supply in the working gas that promoted the establishment of the stoichiometric condition in the growing film. O-concentration in the film increases with oxygen-supply in the working gas. cBN forms only when the oxygen concentration is below 5% and c N/ c B (ratio of concentration of nitrogen atoms and boron atoms) is 1 in the film.

The molecular structure of plasma polymerized thiophene and pyrrole thin films produced by double discharge technique

Production of polythiophene (PTH) and polypyrrole (PPY) thin films via double discharge plasma system has been studied. The double discharge system is a superposition of an ordinary low-pressure dc glow discharge and a high-current pulsed one. The glass substrates were located simultaneously at three different positions in the reactor and the thin films were synthesized at constant plasma parameters to evaluate the influence of the position on the molecular structure. And, the as-grown and iodine doped thin films were investigated to find out the correlation between molecular structure variation of the iodine–film interactions, too. The PTH (C 4H 4S) and PPY (C 4H 5N) monomers without using any carrier gases have been used as plasma precursors, each at 1 mbar operating pressure. The thin films were compared by using Fourier transform infrared (FTIR), X-ray photoelectron (XPS), and UV–visible absorption spectroscopy. It is found that the thin films obtained at the pulsed plasma region where the gas phase polymerization is dominated resemble to conventional polymeric structure. The XPS depth profiles revealed that while the stoichiometry of the monomer was almost preserved with the successive depth of PTH samples, but at the PPY one was not preserved. Moreover, the atomic concentration of oxygen and nitrogen observed at the surface of the films significantly drops down beneath the surface which indicates that they could be employed as anti-corrosive materials. It is found that chemical bonding with iodine take place after doping and the value of the optical band gap of polymers ( E g) are reduced proportionally with doping time.

Stress induced preferred orientation and phase transition for ternary WC xN y thin films

We deposit ternary WC x N y thin films on Si (1 0 0) substrates at 500 °C using direct current (DC) reactive magnetron sputtering in a mixture of CH 4/N 2/Ar discharge, and explore the effects of substrate bias ( V b) on the intrinsic stress, preferred orientation and phase transition for the obtained films by virtue of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and selective area electron diffraction (SAED). We find that with increasing the absolute value of V b up to 200 V the carbon ( x) and nitrogen ( y) atom concentrations of WC x N y films keep almost constant with the values of 0.75 and 0.25, respectively. The XPS and SAED results, combined with the density-functional theory (DFT) calculations on the electronic structure of WC 0.75N 0.25, show our obtained WC x N y films are single-phase of carbonitrides. Furthermore, we find that the compressive stress sharply increases with increasing the absolute value of V b, which leads to a pronounced change in the preferred orientation and phase structure for the film, in which a phase transition from cubic β-WC x N y to hexagonal α-WC x N y occurs as V b is in the range of −40 to −120 V. In order to reveal the relationship between the stress and phase transition as well as preferred orientation, the DFT calculations are used to obtain the elastic constants for β-WC x N y and α-WC x N y . The calculated results show that the preferred orientation is dependent on the competition between strain energy and surface energy, and the phase transition can be attributed to a decrease in the strain energy.

Post-Discharge Nitriding: Mathematical Modeling and Numerical Simulation of the Layer Growth

Nitriding by microwave post-discharge process involves molecular nitrogen dissociation. It has been observed that nitrogen flux from surface to solid during the early stage does not follow a parabolic regime and that the growth rate of concomitant nitride layers is sensitive to atomic nitrogen concentration on the surface. In this work a mathematical model has been developed in order to describe the kinetics of the compound layer formation during a post-discharge nitriding process. The model is related to a moving boundary value problem and considers different stages: diffusion process, formation of the layers, layer growth and quasi-stabilization of the layer growth. Natural conditions on the nitrogen concentration consistent with the mass transfer mechanism are assumed. An analytical approximate solution of Goodman’s type is sought and numerical simulation is conducted to study the nitride layer growth.

Mathematical simulation of the layer growth kinetics during post-discharge nitriding: From early stage to quasi-steady stage

Nitriding by microwave post-discharge process involves molecular nitrogen dissociation. It has been observed that nitrogen flux from surface to solid during the early stage does not follow a parabolic regime and that the growth rate of concomitant nitride layers is sensitive to atomic nitrogen concentration on the surface. In this work a mathematical model has been developed in order to describe the kinetics of the compound layer formation during a post-discharge nitriding process. The model is related to a moving boundary value problem and considers different stages: diffusion process, formation of the layers, layer growth and quasi-stabilization of the layer growth. An analytical approximate solution of Goodman's type is sought and representations of the motion of the interfaces and the nitrogen concentration profiles are analyzed.

Oxidation of Amorphous Carbon Films by Ultraviolet Light Irradiation and Thermal Annealing

Using polymer-like amorphous carbon films deposited using supermagnetron plasma, ultraviolet light irradiation and thermal annealing effects in air were studied. Upper and lower electrode rf powers (UPRF/LORF) were selected to be 5/5 W, and such films were deposited using i-C4H10, and N2 or H2 plasma chemical vapor deposition (CVD). For comparison, polymer-like amorphous carbon films were deposited using Ar magnetron sputtering. By X-ray fluorescence spectroscopy (XFS), an increase in oxygen atom concentration and a small change in nitrogen atom concentration were observed under both ultraviolet (UV) light exposure and thermal annealing.

Anomalous dependence of the magnetic resonance signal of cesium atoms in the afterglow in an N2-Ar mixture

The investigation of spin-exchange collisions between optically oriented cesium atoms in the ground 2 S 1/2 state and nitrogen atoms in the ground 4 S 3/2 state reveals an anomalous behavior of the magnetic resonance signal of cesium atoms in the afterglow in an N2-Ar mixture, namely, the magnetic resonance signal is slowly enhanced during the time interval between the high-frequency pulses exciting a discharge in the absorption cell. It is found that such a behavior of the magnetic resonance signal is explained by a slow change in the concentration of nitrogen atoms in the absorption cell, which affects the magnetic resonance of cesium atoms via efficient spin exchange.

Polyurethane cationomers synthesised with 4,4′-methylenebis(phenyl isocyanate), polyoxyethylene glycol and N-methyl diethanolamine

Polyurethane cationomers with increased contents of ions were synthesised in the reaction of 4,4′-methylenebis(phenyl isocyanate) (MDI) with polyoxypropylene glycol (M = 450) and N-methyl diethanolamine (N-MDA). Amine segments were built-in to the urethane–isocyanate prepolymer in the reaction with formic acid and then they were converted to alkyl-ammonium cations. The obtained isocyanate prepolymers were then extended in the aqueous medium with the use of 1,6-hexamethylenediamine. That yielded stable aqueous dispersions, which were applied on the surfaces of test poly(tetrafluoroethylene) samples. After evaporation of water, the dispersions formed thin polymer coatings. 1H and 13C NMR spectral methods were employed to confirm chemical structures of synthesised cationomers and to modify their quantitative composition in relation to that assumed on the basis of the stoichiometry of the reactions, which were conducted on successive stages of the polyaddition process. Furthermore, the GPC method was used to learn the sizes and distributions of mean molecular weights of those cationomers. Based on 1H NMR spectra, the factor κ was calculated which represented the polarity level of the obtained cationomers. Good correlation was found between that factor and the free surface energy γS (increasing in the range 38–42 mJ/m2) as well as its polar and acid-base components, as determined from the van Oss–Good model on the basis of measured wetting angles between the coatings and model liquids with various polarities. The values of κ and γS parameters resulted principally from the increasing amounts of cations NH+, which were evaluated on the basis of the concentrations of tertiary nitrogen atoms increasing within 1.37–2.66 wt%. Those concentrations and amounts resulted, in turn, from the amounts of amine N-MDA which could be built into cationomers. The effects were discussed of chemical structures and polarity specifications of polyurethane cationomers on the viscosities of produced aqueous dispersions and on the sizes of their colloidal particles, on the values of free surface energy and on its polar and acid-base components, and on the glass transition temperatures Tg2 of the rigid segments as found by the differential scanning calorimetry (DSC) method.

Complete prevention of reaction at HfO 2/Si interfaces by 1 nm silicon nitride layer

When hafnium oxide (HfO 2) is directly deposited on Si by the RF sputtering method, Hf silicide is formed and post-deposition anneal (PDA) at 400 °C transforms Hf silicide to Si suboxide plus Hf suboxide. The leakage current density for the 〈aluminum (Al)/HfO 2/Si(1 0 0)〉 diodes without PDA is high due to the high density interface states near the Fermi level (0.86 eV above the Si valence band maximum, VBM) and minute conduction channels. PDA at 400 °C eliminates the interface states and the conduction channels, and improves the characteristics of the HfO 2 layer, but interface states are newly formed at 0.53 eV above the VBM, resulting in still high leakage current density. Silicon nitride (SiN) layers formed by Si nitridation using N 2-plasma generated by the low energy electron impact method possess a high nitrogen atomic concentration ratio, N/(N + O) of 0.65. When a 1.0 nm SiN layer is inserted between HfO 2 and Si, interfacial reaction is completely prevented, resulting in a smaller effective oxide thickness, EOT of 1.4 nm. In spite of the smaller EOT, the leakage current density is nearly the same as that with no SiN layer, possibly due to the prevention of the formation of the conduction channels. PDA at 400 °C improves HfO 2 characteristics without causing the interfacial reaction, leading to a decrease in the leakage current density.

Measurement of nitrogen depth profile in steel

The characterization of nitridated steel samples, in special the depth profile of nitrogen, aims to help improving the quality of the surface and to increase the durability of the steel pieces. In this work we used ERDA and NRA to determinate the profile of nitrogen in different sets of stainless steel samples. An incident beam of 35Cl of 56MeV was used for ERDA analysis of a first set of samples. Results indicated an homogeneous distribution for most of the identified elements, with atomic nitrogen concentrations around 2% in the analyzed depth range (0.2μm) and the presence of thin films on the surface (about 50×1015at/cm2), one of C and the other of iron oxide. In a second set of samples, 4.43MeV gamma rays produced from 15N(H,αγ)12C reaction, using an external proton beam of 1.3 MeV, were used to quantify nitrogen concentration. N concentrations of about 0.47% were obtained comparing the gamma production rate of the samples with a referenced material (Stainless steel CRM298 – 0.236% of N in mass) irradiated in the same conditions. Also PIXE analyses were done on both sets of samples in order to identify main elements in the matrix.

Practical sensor for nitrogen in direct current glow discharges

This paper presents a method for precise measurement of atomic and molecular nitrogen in an oxygen-nitrogen dc plasma. This is achieved by monitoring the intensities of the atomic nitrogen spectral line at 821.6 nm and the molecular nitrogen bandhead at 337.1 nm, relative to the atomic oxygen spectral line at 844.7 nm. Oxygen is one of the most frequently used gases for surface chemical treatment, including deposition and etching, therefore the ability to measure and control the process and chemical composition of the process is essential. To validate this oxygen actimometry method for N2-xO2 (where x varies from 0 to 1) dc plasmas, threshold tests have been performed with Ar actinometry. The optical measurements have been performed using two methods. The first approach uses a USB2000 fiber optic spectrometer, calibrated with a Gigahertz–Optik BN-0102-1 reference standard source, to record the desired spectral lines. The second approach uses narrow bandwidth optical filters (∼0.7–0.07 nm) with central wavelengths of 821.6, 337.1, and 844.69 nm and photodiodes to detect the emission intensity, also calibrated with the same standard source. Optical data are collected for a range of experimental conditions in a flowing glow discharge of N2-xO2 mixture. The maximum dc voltage is 2.2 kV and maximum chamber pressure is 266 Pa. Data from both optical methods are compared and used to interpret the relative atomic and molecular nitrogen concentrations under various operating conditions.

Density Functional Theory Modeling of (001)Si–Oxynitride Interfaces

Four interface models for crystalline oxynitride on (001)Si substrates are proposed and investigated. All four models are proposed to model thin oxynitride films on Si substrates, according to experimental findings and theoretical studies on amorphous oxynitride films and nitrogenated SiO2. State-free insulating interfaces were obtained by expanding the bulk oxynitride cell by approximately 12% and 1% along the [100] and [010] axes, respectively, and interfacing it with (001)Si. Results demonstrate state-free insulating interfaces for all models with, however, valence-band offsets slightly above or below 1 eV. The significant decrease in the valence-band offsets is mainly attributed to the significant expansion of the oxynitride’s lattice constant to lattice-matched (001)Si, as well as to the high concentration of nitrogen atoms in the oxynitride bulk.

The effect of the individual species of the N plasma on the characteristics of InAsN quantum dots grown by MBE

The influence of the different species which constitute N plasma, such as atomic nitrogen, diatomic nitrogen and ionized species, on the morphological and optical characteristics of the InAsN quantum dots (QDs) has been studied in this work. We have performed several sets of growths modifying in each one the concentration of these species. Atomic force microscopy (AFM) and photoluminescence (PL) techniques have been used to perform the surface characterization and the optical analysis of these samples, respectively. Clearly, we have found a strong correlation between the structural and optical characteristics of the InAsN QDs with the plasma composition used during the growth. Ionized species favour the high density of QDs, atomic nitrogen increase dimensions of the QDs and molecular nitrogen does not almost affect the characteristics of these nanostructures. An increment of ionized species in the plasma yields a higher density of QDs, an increase in the atomic nitrogen increases the dimensions of the QDs and the molecular nitrogen flux used does not almost affect the characteristics of these nanostructures. Also, we have found that there is not redshift of the peak wavelength of the PL emission as we increase the atomic nitrogen concentration during the growth. This may be due to equal nitrogen incorporation into the quantum dots. We supposed that the mechanism dominating in it is possible that the nitrogen incorporation in these types of nanostructures depend on another growth parameter.

Sputter-assisted plasma CVD of wide or narrow optical bandgap amorphous CN x:H films using i-C 4H 10/N 2 supermagnetron plasma

Amorphous hydrogenated carbon nitride (a-CN x :H) films were prepared on Si and glass (SiO 2) substrates using i-C 4H 10/N 2 supermagnetron plasma chemical vapor deposition. By controlling the rf power ratio (i.e., keeping the upper electrode rf power [UPRF] at 800 W but the lower electrode rf power [LORF] was varied in 0–100 W), wide or narrow optical bandgap a-CN x :H films were realized. At LORF > 25 W, the deposited a-CN x :H layers became hard and opaque. Optical bandgap of the films was below 0.8 eV, electrical resistivity was low, and hardness was above 20 GPa. At LORF < 20 W, however, deposited a-CN x :H layers became soft and transparent. Optical bandgap of the films was above 1.9 eV, electrical resistivity was high, and hardness was about 7 GPa. Nitrogen atom concentrations of all of the films were 12.5–13.4 mass% at LORF of 10–100 W.

Effects of nitrogen substitutional doping on the electronic transport of carbon nanotube

We have studied the effects of nitrogen substitutional doping on the transport properties of single-wall carbon nanotube (8, 0) using density functional theory and non-equilibrium Green's functions. The results reveal that the nanotube changes from the semiconducting to the quasi-metallic state because of the dopants, and their structures strongly dominate their electrical properties. Our calculations indicate that transport properties of the doped nanotubes are sensitive not only to the concentration of nitrogen atoms but also to their distribution. The doping effects on the electronic transport of the carbon nanotube are discussed.

Recent Progress in Studies of Nanostructured Impurity–Helium Solids

Impurity–helium (Im–He) solids are porous materials formed inside superfluid 4He by nanoclusters of impurities injected from the gas phase. The results of studies of these materials have relevance to soft condensed matter physics, matrix isolation of free radicals and low temperature chemistry. Recent studies by a variety of experimental techniques, including CW and pulse ESR, X-ray diffraction, ultrasound and Raman spectroscopy allow a better characterization of the properties of Im–He solids. The structure of Im–He solids, the trapping sites of stabilized atoms and the possible energy content of the samples are analyzed on the basis of experimental data. The kinetics of exchange tunneling reactions of hydrogen isotopes in nanoclusters and the changes of environment of the atoms during the course of these reactions are reviewed. Analysis of the ESR data shows that very large fraction of the stabilized atoms in Im–He solids reside on the surfaces of impurity nanoclusters. The future directions for studying Im–He solids are described. Among the most attractive are the studies of Im–He solids with high concentrations of stabilized atoms at ultralow (10–20 mK) temperature for the observation of new collective quantum phenomena, the studies of practical application of Im–He solids as a medium in neutron moderator for efficient production of ultracold (∼1 mK) neutrons, and the possibilities of obtaining high concentration of atomic nitrogen embedded in N2 clusters for energy storage.

Tunneling currents through lightly nitride silicon dioxide/oxide stacks

AbstractOxynitride has been used to decrease leakage current of thin film SiO2. Combining with the band structures obtained from first‐principles simulations, tunneling currents through SiO2/silicon oxynitride stacks were calculated. SiO2/silicon oxynitride stacks can reduce leakage current at low oxide field but will fail at higher field. The threshold oxide field, which means that SiO2/silicon oxynitride stacks can not reduce the tunneling current when oxide field is higher than it, decreases with increased nitrogen concentration while the effective oxide thickness remains constant. Direct tunneling and defect‐assisted tunneling will be dominant for lower and higher nitrogen atom concentrations, respectively. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)