Concentration Of Nitrogen Atoms Research Articles

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 & Co. KGaA, Weinheim)

Surface Modification of Polymers with 3-Aminopropyltriethoxysilane as a General Pretreatment for Controlled Wettability

Various polymer surfaces were analyzed for reactivity toward 3-aminopropyltriethoxysilane (APTES). Results indicate that the method described here is useful as a general surface-selective modification technique for polar polymers such as polyesters, polyamides, polycarbonates, polyimides, cellulosics, polyacrylics, etc. X-ray photoelectron spectroscopy (XPS) showed an average of 10% silicon and nitrogen atomic concentrations at 75° takeoff for all successfully modified surfaces. The APTES multilayers were subsequently hydrophobized with perfluorinated chlorosilanes giving 40% fluorine atomic concentration by XPS and 120°/90° (advancing/receding) dynamic contact angle averages. APTES modifications were successful in all solvents with the exception of protic solvents. On the basis of these and other observations, a new model for the reaction pathway is proposed. We propose the reaction proceeds by initial APTES adsorption (likely through hydrogen bonding by the amine) to the substrate, lateral bond formation, and subsequent multilayer formation. The model is thus analogous to silane multilayer formation on silica.

Study of local concentration of single substitutional nitrogen atoms in microdiamonds from the Kokchetav massif

In this communication we present an estimation of the concentration of single substitutional nitrogen atoms (P1 centre) from EPR data in Kokchetav diamonds. We first performed an analysis of local P1 centre concentrations using van Wyk’s treatment (van Wyk et al ., 1997) of the line width of the resolved EPR spectrum. Also by analysing the dependence of the line-width of the broad exchange line on the P1 concentration in range higher than 1000 ppm in synthetic diamonds, we obtained a calibration curve allowing the estimation of the local P1 centre concentration higher than 1000 ppm and the local volumes occupied by substitutional nitrogen atoms without taking measurements of microcrystalline volume. In addition to the development of a method for calculating high local nitrogen concentrations, the aggregation process in P,T-treated Kokchetav diamonds has been given considerable attention and it was shown that the rate of nitrogen aggregation in these diamonds is consistent with data given in Evans (Evans & Qi, 1982).

Nitrogen-Doping of Polycrystalline 3C-SiC Films Deposited by Low Pressure Chemical Vapor Deposition

This paper reports the effect of deposition temperature on the deposition rate, residual stress, and resistivity of in-situ nitrogen-doped (N-doped) polycrystalline 3C-SiC (poly-SiC) films deposited by low pressure chemical vapor deposition (LPCVD). N-doped poly-SiC films were deposited in a high-throughput, resistively-heated, horizontal LPCVD furnace capable of holding up to 150 mm-diameter substrates using SiH2Cl2 (100%) and C2H2 (5% in H2) precursors, with NH3 (5% in H2) as the doping gas. The deposition rate increased, while the residual stress decreased significantly as the deposition temperature increased from 825oC to 900°C. The resistivity of the films decreased significantly from 825°C to 850°C. Above 850°C, although the resistivity still decreased, the change was much smaller than at lower temperatures. XRD patterns indicated a polycrystalline (111) 3C-SiC texture for all films deposited in the temperature range studied. SIMS depth profiles indicated a constant nitrogen atom concentration of 2.6×1020/cm3 in the intentionally doped films deposited at 900°C. The nitrogen concentration of unintentionally doped films (i.e., when NH3 gas flow was zero) deposited at 900°C was on the order of 1017/cm3. The doped films deposited at 900°C exhibited a resistivity of 0.02 -cm and a tensile residual stress of 59 MPa, making them very suitable for use as a mechanical material supporting microelectromechanical systems (MEMS) device development.

Optoelectronic properties of nitrogenated amorphous carbon films synthesized by microwave surface wave plasma chemical vapor deposition system

The n-type nitrogen doped amorphous carbon (a-C:N) thin films have been grown by microwave (MW) surface wave plasma (SWP) chemical vapor deposition (CVD) system on silicon, quartz and ITO substrates at different nitrogen flow rates (1 to 4 sccm). The effects of nitrogen doping on chemical, optical, structural and electrical properties were studied through X-ray photoelectron spectroscopy, Nanopics 2100/NPX200 surface profiler, UV/VIS/NIR spectroscopy, Raman spectroscopy and solar simulator measurements. Argon, acetylene and nitrogen are used as plasma sources. Optical band gap decreased and nitrogen atomic concentration (%) increased with increasing nitrogen flow rate as a dopant. The a-C:N/p-Si based device exhibits photovoltaic behavior under illumination (AM 1.5, 100 mW/cm 2), with a maximum open-circuit voltage ( V oc), short-circuit current ( J sc) and fill factor of 4.2 mV, 7.4 μA/cm 2 and 0.25 respectively.

Diamond-Like Amorphous Carbon Films Deposited for Field-Emission Use by Upper-Electrode-RF-Power-Controlled Supermagnetron Plasma

Nitrogenated and hydrogenated diamond-like amorphous carbon (DAC:N and DAC:H) films were synthesized using i-C4H10/(N2 and H2) supermagnetron plasma, respectively. The upper- and lower-electrode rf powers (UPRF/LORF) were controlled to be 100–800/100 W, and N2 and the H2 concentrations were selected to be 25 and 20%, respectively. In the DAC:N layer deposited at 300/100 W, the nitrogen atom concentration was measured to be 1.7 mass %. In the case of DAC:N film, the lowest threshold electric field intensity (ETH) was observed to be 12 V/µm at the growth condition of 300/100 W. In the case of a DAC:H planar structure, the lowest ETH was 13 V/µm for 800/100 W deposition. In both types in the films with the lowest ETH, we observed the same optical band gap of approximately 1.2 eV. The optimum distribution and size of sp2 CC nanoclusters formed in both the DAC layers probably caused the ETH to decrease.

Control of Nitrogen Depth Profile near Silicon Oxynitride/Si(100) Interface Formed by Radical Nitridation

Depth profiles of composition and chemical structures in radical nitrided silicon oxynitride films formed with Ar/N2, Xe/N2, or Ar/NH3 plasma excited by microwave have been investigated by X-ray photoelectron spectroscopy combined with step etching in HF solution. The relationship between the intensities of emission from N2+ radical in these plasmas and the concentration of nitrogen atoms forming Si3≡N configuration near the silicon oxynitride film/Si substrate interface nitrided using these plasmas was studied. The emission intensities from N2+ radical generated in Xe/N2 or Ar/NH3 plasma are a quarter or one-sixth of that from N2+ radical generated in Ar/N2 plasma respectively. However, the emission from NH radical is also detected in Ar/NH3 plasma. Although the nitrogen concentration of Xe/N2 plasma is smaller than that of Ar/N2 plasma at the film/substrate interface, that of Ar/NH3 plasma is larger than that of Ar/N2 plasma at the interface. It is important for the reduction of the nitrogen concentration near the film/substrate interface to use Xe/N2 plasma in which both of the generation efficiencies of N2+ and NH radicals are low.

Shock-Tube Measurement of Nitridation Coefficient of Solid Carbon

The coefficient of reaction of nitrogen atoms with solid carbon to form gaseous cyanogen CN is measured in a shock tube. A stream of highly dissociated nitrogen is produced in a shock tube and passed over a grid of metal wire coated with carbon. The radiation emitted by the wake of the wire grid is observed with a monochromator set at 386 nm, where CN is known to radiate strongly. From the intensity of the CN radiation, the concentration of CN in the wake is determined. The concentration of nitrogen atoms in the stream are calculated by integrating conservation equations. From these concentration values, the fraction of the collisions of nitrogen atoms producing CN, that is, the reaction coefficient, is deduced. The results show that the reaction coefficient is about 0.3 at both 300 and 1100 K. The uncertainties in the results are described, and improvements are proposed.

Si‐oxide/Si and Si‐oxynitride/Si interfaces analysed by ultra‐low energy SIMS

AbstractDepth profile analyses of silicon oxides and oxynitrides are compared using SIMS (Secondary Ion Mass Spectrometry) technique with ultra low energy of primary Ar+ ion beam. SiO2 (5–80 nm thick) layers on p‐Si 〈100〉 were formed by thermal heating of silicon wafers in oxygen flow. SiOx Ny (2–4 nm thick) layers on p‐Si 〈100〉 were obtained by nitrogen implantation followed by plasma oxidation process. The nitrogen implantation was performed with NH3 and N2 plasma sources in 350 °C. The influence of r.f. power, used during implantation on the oxynitride layer properties, was studied.SIMS measurements were done using ultra‐low energy 880 eV Ar+ beam and quadrupole mass spectrometer. Quantitative atomic concentrations of nitrogen and oxygen were calculated basing on Si2N+, Si2O+ and Si2+ secondary ion currents. The obtained layers were also characterised by X‐ray Photoelectron Spectroscopy, ellipsometry and electrical tests. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Properties of an atmospheric pressure radio-frequency argon and nitrogen plasma

An atmospheric pressure capacitive discharge source has been developed that operates at power densities over 100 W cm−3. The ground state nitrogen atom concentration was measured at the exit of the source by titration with NO, and it was found to reach a maximum of 3.0 ± 0.8 × 1017 cm−3 at 6.0 vol% N2 in argon, 250 °C and 150 W cm−3. This is equivalent to 2.3 vol% of N atoms in the afterglow. At these conditions, the electron density and temperature are estimated to be 3.1 × 1012 cm−3 and 1.2 eV. A plug-flow model of the plasma and afterglow was developed, and it was determined that the maximum N atom concentration achievable is limited by three body recombination.

Diamond-like carbon thin films grown by large-area surface-wave mode microwave plasma CVD: Effects of stage distance to microwave window

Diamond-like carbon (DLC) thin films were grown on silicon and quartz substrates by using large-area surface-wave mode microwave plasma chemical vapor deposition at different distances from microwave quartz window. The chemical, optical, bonding and structural properties of the films were characterized by X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. Nitrogen atomic concentration (%) of the films increased with decreasing the distance of substrate to microwave quartz window. Optical band gap of the films decreased from 2.7 to 2.4 eV when the substrate to microwave quartz window decreased from 12 to 3 cm. The FT-IR absorbance peaks of the DLC films in the region 2800–3000 cm − 1 became more and more prominent as the distance of substrate to the microwave quartz window increased from 3 to 12 cm, suggesting the formation of crystalline structure in the films. The increase of sp 2 fraction with decreasing the distance of substrate to the microwave quartz window (i.e. increasing the electron density of the plasma) was conformed by Raman spectra of the films.

The effective mass issues in light nitride silicon oxide

On the basis of the first-principle calculations, the band-structure properties of light nitride silicon oxide are studied. The average effective electron mass near the bottom of the conduction band is observed to increase exponentially with nitrogen atom concentration. The defect-like energy levels are also observed within the band gap. Due to these levels, the leakage current caused by defect-like states within the band gap may make a larger contribution to the gate leakage current. And thus interpreting the experimental tunnelling current with a single leakage mechanism is not practical. The results also show that a silicon oxynitride dielectric film with a special nitrogen atom concentration can greatly extend the oxide-equivalent thickness.

Nitrogen-doped porous carbon microspherules as supports for preparing monodisperse nickel nanoparticles

N-doped porous carbon microspherules were developed through controlled carbonization of the copolymer of vinylidene chloride and acrylonitrite. The carbon precursors were prepared by an inorganic–organic hybrid route. Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS) analysis showed the formation of N-doped carbon spherules. N 2 sorption analysis showed that the resultant carbon materials have a BET surface area of 692 m 2/g. Nickel nanoparticles supported over them are kept in a well-dispersed state. Electron Probe Microanalysis (EPMA) and Transmission Electron Microscopy (TEM) showed nickel nanoparticles are quite monodisperse. Analysis of XPS spectra of the samples with different surface nitrogen atomic concentration demonstrated that nitrogen species on the carbon surfaces have a great impact on the dispersion state of the mounted metal nanocrystals.

Determination of atomic nitrogen concentrations using titration with molecular oxygen

For the determination of the concentration of atomic nitrogen at atmospheric pressure and temperature, chemical titration with molecular oxygen has been studied by spectroscopic experiments and chemical simulations. The formation of oxygen atoms (by the reaction between nitrogen atoms and molecular oxygen) leads to the rapid production of ozone which can be easily observed and quantified using its strong ultraviolet absorption. Chemical simulations indicate that, although the amount of produced ozone provides only a lower limit of the atomic nitrogen concentrations, the observed ozone concentrations are only 10–15% below the atomic nitrogen concentrations over several orders of magnitude.

Microstructure, composition and oxidation resistance of nanostructured NiAl and Ni–Al–N coatings produced by magnetron sputtering

Nanostructured NiAl and Ni–Al–N thin films were RF magnetron sputtered from a NiAl compound target in different argon–nitrogen atmospheres. The structure and stoichiometry of as-deposited coatings were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Differential thermal analysis (DTA) was also conducted to study the oxidation kinetics of the films at high temperatures. Microstructural and compositional changes of the coatings after isothermal oxidation were investigated using XRD, SEM, and Rutherford backscattering spectrometry (RBS). The results show that: (1) denser and more completely crystallized Ni–Al–N thin films can be tailored through controlled ion bombardment during deposition, (2) nano-composite NiAl–AlN thin films were synthesized with nitrogen atomic concentrations up to 30%, and (3) the NiAl and Ni–Al–N coatings exhibited good oxidation resistance even at temperatures above 1273 K. The addition of AlN to NiAl resulted in decreased activation energies for oxidation. The oxidation study also revealed different rate controlling mechanisms for NiAl and Ni–Al–N (21.4 at.% N) films isothermally oxidized in air at 1273 K.

Local bonding environment of plasma deposited nitrogen-rich silicon nitride thin films

Plasma deposited nitrogen-rich silicon nitride thin films were prepared at temperatures between 80 and 300 °C. The infrared transmission (400–4000cm−1) was measured, and selected absorption bands were quantified through a multiple Lorentzian oscillator parametric analysis. It is observed that the concentration of silicon-centered tetrahedra bonded together through nitrogen atoms increases monotonically with increasing deposition temperature. A qualitative model is presented to highlight the impact of the active adsorption site density on the degree of stepped (ordered) nucleation at the vapor-film interface. The importance of this growth profile, in particular for micro-systems-technology, is discussed in conjunction with measurements of the biaxial modulus and residual stress of the thin films. A mechanism for residual stress controllability is also presented. The atomic concentrations of silicon, nitrogen, and hydrogen in the thin films were calculated using infrared calibration factors derived from the deposition temperature dependent condensation processes. The results for silicon nitride thin films deposited at 300 °C were observed to be similar in composition to silicon diimide. Additional observations of the infrared transmission characteristics are reported, which include the identification of silazane bridge characteristics for the absorption feature around 610cm−1, which is typically associated with Si–H (bending) absorption.

Active nitrogen species dependence on radiofrequency plasma source operating parameters and their role in GaN growth

Radiofrequency (RF) nitrogen plasma sources are commonly used for the growth of III-nitrides by plasma-assisted molecular beam epitaxy. Their output mainly consists of a mixture of atomic nitrogen and metastable excited molecules. The relative concentration of these species as a function of RF power and nitrogen gas flow rate has been investigated by plasma optical emission spectroscopy. It is shown that the concentration of excited molecular nitrogen species is monotonically increasing with both parameters while the concentration of nitrogen atoms is almost independent of the nitrogen gas flow rate and increases monotonically with the coupled RF power. As a result of this functional dependence, the plasma source can be tuned to produce mainly excited nitrogen molecules or a mixture of excited molecules and atomic nitrogen. Comparison of the growth rates of gallium nitride films grown under different operating conditions of the RF source with the optical spectroscopy data shows that the metastable excited nitrogen molecules component of the source is the predominant factor contributing in the III-nitrides growth.

The role of N in the resputtering inhibition of Si in W–Si–N reactively sputtered thin layers

W–Si–N thin films were synthesized by reactive sputtering of W5Si3 target in an Ar∕N2 mixed atmosphere. The nitrogen atomic concentrations within the films ranged between 0 and 60at.%, as revealed by Rutherford backscattering measurements. At low nitrogen atom fluxes an intense Si resputtering was observed, leading to the formation of a W-rich layer with respect to target composition. The characterization of plasma parameters during the deposition, carried out with the help of a Langmuir probe, suggests that the Ar neutral atoms reflected by W atoms of the target are the main responsibilities of Si resputtering with respect to charged species, whose resputtering effect is less important. The inhibition of this phenomenon takes place with growing nitrogen concentration. The preferential formation of Si–N bonds with respect to W–N bonds was unveiled by both x-ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy. This also justifies the inhibition of Si resputtering. A comparison with literature data concerning W–Si–N systems sputtered at different plasma conditions was performed in order to highlight the influence of plasma parameters on the composition of the layers.

Effect of N doping on properties of diamond-like carbon thin films produced by RF capacitively coupled chemical vapor deposition from different precursors

In this paper, we report results concerning properties of diamond-like carbon (DLC) thin films obtained in different experimental conditions: various RF power values and different precursors (methane, acetone and toluene or in combination with nitrogen). The deposition rate of DLC thin films obtained from precursors with low ionizing energy and high number of carbon atoms in molecule as acetone and toluene was higher (142 nm/min for acetone and 607 nm/min for toluene as compared with 79 nm/min for methane at 400 W input power). The highest value of hardness was obtained from methane (18 GPa). In the case of acetone and toluene precursors, the hardness increased with input power to the highest values of 16.8 and 14.8 GPa. By utilizing nitrogen as doping element, the resistivity of DLC thin films obtained from methane and acetone decreased from values higher than 10 7 Ω cm to lower values of 12.5×10 3 Ω cm for 3.79% nitrogen atomic concentration in the case of films obtained from methane and 40×10 3 Ω cm for 4.26% nitrogen atomic concentration in the case of films obtained from acetone.