Argon Nitrogen Research Articles

Influence of substrate bias voltage on structure and properties of hard Si–B–C–N films prepared by reactive magnetron sputtering

We systematically investigated the effect of the rf induced negative substrate bias voltage, U b, on characteristics of novel quaternary Si–B–C–N films. The films were deposited on Si(100) or glass substrates by reactive dc magnetron co-sputtering of silicon, boron and carbon from a single C–Si–B or B 4C–Si target in nitrogen–argon gas mixtures at substrate temperatures of 180–350 °C. Elemental compositions of the films, their surface bonding structure, and mechanical and electrical properties were primarily controlled by the U b values, varied from a floating potential (being between − 30 and − 40 V) to U b = − 700 V. The energy and flux of ions bombarding the target and the growing films were evaluated on the basis of the measured discharge characteristics. The films were found to be amorphous with thickness up to 5 μm and density around 2.4 g/cm 3. They exhibited hardness up to 44 GPa, modified Young's modulus between 170 and 280 GPa, elastic recovery up to 82% and good adhesion to substrates at a low compressive stress (0.6–1.8 GPa). The results of stress measurements were compared with predictions of the model developed by Davis and a beneficial role of silicon in reducing the compressive stress in the films was proved. Electrical conductivity of the semiconductive Si–B–C–N films with a high (approximately 40 at.%) carbon content was controlled by the nitrogen–argon gas mixture composition and the U b values.

Optical emission characteristics of glow discharge in the N 2–H 2–Sn(CH 3) 4 and N 2–Ar–Sn(CH 3) 4 mixtures

Optical emission spectroscopy (OES) and optical actinometry were used to investigate 100 kHz low-pressure discharge in nitrogen–hydrogen–tetramethyltin and nitrogen–argon–tetramethyltin mixtures. High energy species have been identified in plasma phase. The emission intensities of main species were monitored as a function of plasma composition. The influence of reactive gases on the decomposition of tetramethyltin was investigated and plasma processes were discussed. Glow discharge plasma was characterized by optical temperatures (the electron excitation temperatures of Sn, Ar, H, vibrational temperatures of CN, N 2, N 2 + and rotational temperature of N 2 +) and by the electron number density. The obtained results revealed a strong deviation of plasma from LTE state for both analyzed mixtures. The X-ray diffraction method was applied to investigate the structure of deposited materials, being solid products of the tetramethyltin decomposition.

Photoisomerizations of N4-Hydroxycytosines

A series of N4-hydroxycytosines, unsubstituted or substituted with methyl groups at N3 or C5 atoms of the heterocyclic ring, was studied using the matrix-isolation method. Depending on the absence or presence of the methyl substituent at N3 or C5 atoms (or at both of them) the syn or anti form of the compounds (or a mixture of both forms) was trapped from the gas phase into a low-temperature matrix. Upon UV (lambda > 295 nm) irradiation of the matrixes the syn --> anti as well as the anti --> syn photoisomerization reactions were observed. The syn and anti isomers of N4-hydroxycytosines were identified by comparing their experimental IR spectra with the theoretical spectra calculated at the DFT(B3LYP)/6-31G(d,p) level. For the majority of the studied compounds, the UV induced reactions led to a photostationary state. The position of the final photostationary state was found to be a sensitive function of weak interactions of a studied N4-hydroxycytosine with the matrix environment: solid argon or solid nitrogen. However, not all of the studied photoisomerizations led to a classical photostationary state. For some of the investigated N4-hydroxycytosines, the position of the photostationary state was shifted very strongly in favor of the photoproduct, whereas for some others the position was shifted so strongly in favor of the starting isomer that no photoisomerization was observed. These experimental findings were elucidated by theoretical investigations of the potential energy surfaces of the ground (S0) and first excited (S1) electronic states of N4-hydroxycytosine. The crucial result of these calculations (carried out at the CASSCF level) was the localization of a conical intersection between S0 and S1 at a structure with perpendicular orientation of the hydroxylimino group with respect to the heterocyclic ring.

Capillary condensation of an adsorbate in the cylindrical channels of MSM-41 mesoporous adsorbent

Exact direct calculations of adsorption of model argon atoms and nitrogen molecules in cylindrical proes of a MSM-41-type material were performed with the use of the fragment method over a wide temperature range. It was demonstrated that, in pores with a diameter of about 2 nm, no phase transitions occur, and, therefore, no hysteresis loops are observed. Topological and geometric criteria of the quasi-one-dimensional behavior of the adsorbate in pores with diameters of from 2 to 10 nm were introduced and examined. The geometric criteria predict the appearance of a hysteresis loop for pores with a diameter of 4 nm, in agreement with the available experimental data.

Influence of the carrier gas on the luminescence of ZnO tetrapod nanowires

ZnO tetrapod nanowires were prepared by thermal evaporation of Zn in the flow of different carrier gases (argon, nitrogen, humidified argon and humidified nitrogen). The optical properties of the tetrapod nanowires were investigated by low-temperature photoluminescence measurements, reflectance measurements and X-ray photoelectron spectroscopy (XPS). It was found that the type of gas significantly affects the optical properties of the fabricated tetrapod nanowires. The origin of the differences in the photoluminescence spectra of tetrapod nanowires fabricated with different carrier gases is discussed. The addition of water vapor to the carrier gas affected the photoluminescence and XPS spectra for both N 2 and Ar carrier gases, and the changes observed in the XPS spectra indicated possible incorporation of hydrogen in these samples.

Multiple electron loss by structured heavy ions in fast collisions with complex atoms

A nonperturbative theory of multiple ionization of heavy structured ions in fast collisions with complex neutral atoms is developed. Cross sections are calculated for multiple loss of electrons (up to 15) in collisions of U10+ and U28+ with argon atoms and nitrogen molecules. The results are compared with experimental data.

A hybrid particle-continuum method applied to shock waves

A hybrid numerical scheme designed for hypersonic non-equilibrium flows is presented which solves the Navier–Stokes equations in regions of near-equilibrium and uses the direct simulation Monte Carlo method where the flow is in non-equilibrium. Detailed analysis of each stage of the hybrid cycle illustrates the difficulty in defining physically correct DSMC boundary conditions in regards to both macroscopic state and velocity distribution. However, results also show that DSMC boundary conditions have little effect on a previously initialized interior particle domain. A sub-relaxation technique capable of determining macroscopic, hydrodynamic properties in a DSMC simulation is used to determine low-scatter boundary conditions for the NS domain. Particle and continuum domains adapt during the hybrid simulation through application of a continuum breakdown parameter based on the gradient-length Knudsen number. The hybrid code reproduces experimental results and full DSMC simulations in half the time for a large range of 1D shock waves in argon and diatomic nitrogen gas.

Nitrogen dissociation in a low pressure cylindrical ICP discharge studied by actinometry and mass spectrometry

A cylindrical inductively coupled plasma source (ICPS) is optimized for nitrogen atom production. How to operate in the bright mode (H-mode) in pure nitrogen at relatively low applied power is explained. Actinometry is developed for a quantitative determination of the nitrogen dissociation fraction in the ICPS. These results are compared with those obtained outside the ICPS by modulated beam mass spectrometry. A qualitative agreement is obtained between the nitrogen dissociative fraction inside and outside the ICPS. The higher magnitude of the dissociation fraction given by mass spectrometry compared with that derived from actinometry is explained by the contribution of dissociative recombination of near the exit hole of the ICPS. A dissociation fraction of up to 0.7 is observed by mass spectrometry. Some results are also reported for argon–nitrogen gas mixtures.

Study of the structural and optical properties of GaPN thin films grown by magnetron RF sputtering

GaP 1− x N x thin films were deposited on glass substrates by RF sputtering employing a nitrogen–argon atmosphere in a partial pressure of 2×10 −2 Torr. We varied the growth temperature in the range 420–520 °C. The film's optical properties were studied by transmittance and absorbance spectroscopy. Characterization by scanning electron microscopy in cross-sectional view, atomic force microscopy, and X-ray diffraction was performed to determinate the film thickness, surface morphology, and crystal structure, respectively. Raman spectroscopy was employed to analyze the structural properties of samples. The GaP 1− x N x films presented a cubic polycrystalline structure with a preferential orientation along the [1 1 1] direction. By varying the growth conditions we were able to change the band gap energy between 1.35 and 1.98 eV.

Doubly and triply differential ionization studies using positrons and electrons

Methods and results from experimental studies of single and multiple ionization of atoms induced by positron and electron impact are discussed. Coincidences between recoil ions, forward scattered projectiles and electrons ejected into a cone of angles are measured. From these data, doubly and triply differential cross-sections are extracted. Comparisons of the differential cross-sections and/or differential charge state fractions are being used to extract information about projectile charge effects on the collision dynamics as well as about the importance of various ionization mechanisms. Examples for ionization of argon and krypton atoms and nitrogen molecules are presented.

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.

Nitrogen: a possible substitute for mercury as a UV-emitter for mercury-less low-pressure discharge fluorescent lamps using Penning-like energy transfer

Nitrogen is well known as a UV-emitter because of its 2nd positive band lying around 350 nm. However, it is a molecular gas and when energy is stored in rotational or vibrational levels, the gas temperature can become high enough to melt even the glass tube. To avoid such problems the authors tried to use the Penning-like effect between the argon metastables and nitrogen C 3Πu states with very low partial pressure of nitrogen compared with that of the argon. By adding a very small amount of nitrogen to argon, the discharge changes drastically. Though pure argon discharge and pure nitrogen discharge are both unstable and easy to constrict, a small amount of nitrogen improves the stability of the discharge and emits the nitrogen 2nd positive band UV light by energy transfer from the argon metastable to the nitrogen molecule C 3Πu state. Nitrogen-added argon fluorescent lamps operated at 30 kHz of alternative square voltage wave achieve about 4500 cd m−2 at 3.75 W and at 9.3 kPa of pressure with good dimming characteristics. The maximum luminance should be higher than this because the input power is limited by the power supply. At this condition the luminous efficacy achieves 7.1 lm W−1. These results show a possibility of argon–nitrogen fluorescent lamps as mercury-less fluorescent lamps.

Cotton fabric graft copolymerization using microwave plasma. II. Physical properties

AbstractMicrowave plasma treatments were applied to lightweight cotton fabric with oxygen, nitrogen, and argon at various microwave power levels and exposure times. The results showed significant effects from the type of plasma, microwave power, and treatment time on the fabric weight loss. Oxygen plasma treatment generates higher weight loss than argon plasma and nitrogen plasma. The breaking strength of the treated fabric was affected mainly by longer exposure time to the plasma. The active centers created within the cellulose macromolecules were used to initiate copolymerization reactions with the vinyl laurate monomer [CH3(CH2)10COOCHCH2]. The grafted cotton fabric showed excellent water repellency properties. Repeated home laundering of the treated cotton fabrics revealed no significant effect on the water contact angle or on the quantity of grafted vinyl laurate monomer as determined by universal attenuated total reflectance Fourier transform IR, demonstrating the good durability of the treatment that was applied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 896–902, 2005

Do the Differential Enthalpies of Adsorption Vary Between 77 K and 302 K? An Experimental Case Study of Argon and Nitrogen on Two Faujasite Type Zeolites

Adsorption microcalorimetry of non-polar argon and quadrupolar nitrogen gases was carried out at 77 K and 302 K on two chemically different faujasite type zeolites (DAY and NaX). Considering absolute quantities adsorbed, the differential enthalpies of adsorption at zero coverage obtained with each system do not vary with temperature. Similarities in the differential enthalpies with increasing coverage are observed only if one considers non-specific adsorption phenomena either with a non-polar probe or on a non-polar surface. Where “specific” polar interactions occur for the nitrogen-NaX system, significant differences are observed. This experimental study is the first to compare microcalorimetric measurements of adsorption in such a wide range of temperature.

PECVD of h-BN and c-BN films from boranedimethylamine as a single source precursor

Boron nitride (BN) thin films have been successfully synthesised via low pressure plasma enhanced chemical vapour deposition (PECVD) by using boranedimethylamine, BH 3NH(CH 3) 2, as a single source precursor in the temperature range 280–550 °C in a nitrogen–argon atmosphere. The plasma power was optimised with the aim of obtaining suitable cubic/hexagonal phase ratios. The annealing of the h-BN films at temperatures up to 1000 °C in a nitrogen atmosphere, at normal pressure, gave rise to a complete transformation into the cubic phase. FTIR measurements provided a suitable method for identifying the structure of BN films. UV–vis spectroscopy was carried out in order to investigate the optical behaviour of the films.

Growth of GaP1–xNx thin films by rf sputtering

AbstractWe have deposited GaP1–xNx thin films on glass substrates by rf sputtering employing a nitrogen–argon atmosphere. The films properties were studied as a function of the growth temperature in the range of 420–520 °C. The films characterization was carried out by absorbance, X‐ray diffraction and Raman spectroscopy. The GaP1–xNx films have a cubic polycrystalline structure with a preferential orientation along the [111] direction; the structural properties of the films are improved by increasing the growth temperature up to 500 °C. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical emission spectra and ion energy distribution functions in TiN deposition process by reactive pulsed magnetron sputtering

In this study, a pulsed magnetron sputtering was employed to synthesize TiN films. We deal with pulse parameters such as pulse frequency and duty cycle in argon–nitrogen plasmas. Also, optical emission spectroscopy and energy resolved mass spectrometry as an integrated plasma diagnostics was employed during synthesis of thin films.The major emission lines and time-averaged ion energy distribution functions (IEDFs) corresponding to various titanium and gas discharge species are in situ surveyed in terms of frequency and duty cycles during deposition. The corresponding surface morphology was analyzed by atomic force microscopy (AFM).

Critical RF damage conditions for the plasma-assisted molecular beam epitaxy growth of GaInNAs with dilute N 2/Ar gas mix

In this work, we investigate the operating conditions for RF plasma sources that employ nitrogen–argon gas mixtures for the molecular beam epitaxy growth of dilute nitride, narrow-bandgap semiconductors. The effects of RF power and gas flow rate variations are discussed, wherein a ‘critical’ RF power level is identified at 300 W. Growths performed at RF powers below this critical setting resulted in noticeably better quality material, which was determined from a comparison of pre- and post-anneal room temperature photoluminescence measurements. In addition to the RF power, the gas flow rate directly influences the growth chamber pressure, which in turn also affects the material quality. A modified pumping configuration was used to decouple the chamber pressure from the gas flow rate. In all growths, lower chamber pressures resulted in better material quality, irregardless of the power setting used. These results suggest that operating the nitrogen RF plasma source at its lowest possible power setting and lowest gas flow rate, while still maintaining a stable plasma, will result in the best quality of dilute nitride materials.

Assessment of the application potential of the intensified glow discharge for industrial plasma nitriding of Ti-6Al-4V

The potential of the plasma nitriding process with an intensified glow discharge for industrial applications was examined. Investigations of nitriding layer growth were accomplished on disks, pistons and rotating bending specimens from the common α-β-alloy Ti-6Al-4V. By nitriding in argon–nitrogen plasmas with a low nitrogen content (less than 10 vol.%) it was possible to produce approximately 150 μm thick diffusion layers without compound layers at temperatures of about 500 °C within 6 h. The sliding wear of the nitrided disks was examined by a pin-on-disk test against Al2O3 balls. The calculated wear volume decreased from approximately 0.62 mm3 for the untreated substrates to approximately 0.07 mm3 for the nitrided substrates.

The effect of very large perturbation flows on a perturbation viscometer

A perturbation viscometer is a flux response technology device that measures gradients on the viscosity–composition curve of a binary mixture or more generally on the viscosity–composition surface. It provides a method of calculating relative gas viscosities very precisely. In conventional perturbation viscometry a small perturbation flow of one component of the gas mixture is added to a main flow of known composition flowing through a capillary. The pressure upstream of the capillary changes sequentially due to the change in flowrate and viscosity of the mixture. The ratio of these pressure changes gives the gradient of the viscosity–composition curve. Integration of the viscosity gradients across the composition range yields the relative viscosities of the mixtures. This present paper gives new theoretical treatments for large perturbation flows up to 150% of the main flowrate. Corrections to the theory for small finite perturbations are proposed that account for the differences observed when larger perturbations are used. These correction terms are used to demonstrate how the logarithmic viscosity gradient–composition curve can be found by adding progressively bigger perturbations to each of the two pure components. A second method is proposed which demonstrates how the viscosity ratios can be found directly from the large perturbation measurements. Experimental studies of the mixture argon–nitrogen at 25 ∘ C and 1.1 bar are used to validate the new theoretical treatments. Results using both large and small perturbation measurements permit direct comparison between the different methods. In addition, the large perturbation data are used to define the optimum perturbation size for use with conventional finite difference theory.