DC Nitrogen Plasma Research Articles

Modification of 40X13 steel at high-intensity nitrogen ion implantation

This paper presents the results of the formation of deep modified layers in 40X13 steel using a high-intensity repetitively pulsed nitrogen ion beam with a current density up to 0.25 A/cm2. An arc generator with a hot cathode provided the DC nitrogen plasma flow. A plasma immersion approach was used for high-frequency, short-pulse very intense nitrogen ion beam formation. A grid hemisphere with radii of 7.5 cm was immersed in the plasma. Negative bias pulses with an amplitude of 1.2 kV, a pulse duration of 4 μs, and a pulse repetition rate of 105 pulses per second were applied to the grid. The substrates were implanted at the temperature of 500 °C and various processing times ranging from 20 to 120 minutes with 1.2 keV nitrogen ions using a very-high current density up to 0.25 A/cm2 ion beams. The work explores the surface morphology, elemental composition, and mechanical properties of deep-layer modified 40X13 steel after low ion energy, very-high-intensity nitrogen ion beam implantation.

High intensity, low ion energy implantation of nitrogen in AISI 5140 alloy steel

This paper presents the results of the formation of deep modified layers in AISI 5140 alloy steel using a high-intensity repetitively pulsed nitrogen ion beam. An arc generator with a hot cathode provided the DC nitrogen plasma flow. A plasma immersion approach was used for high-frequency, short-pulse very intense nitrogen ion beam formation. A grid hemisphere with radii of 7.5 cm was immersed in the plasma. Negative bias pulses with an amplitude of 1.2 kV, a pulse duration of 4 μs, and a pulse repetition rate of 105 pulses per second were applied to the grid. The substrates were implanted at various temperatures ranging from 450 to 650 °C with 1.2 keV nitrogen ions using a very-high current density up to 0.5 A/cm2 ion beams. The work explores the surface morphology, elemental composition, and mechanical properties of deep-layer modified AISI 5140 alloy steel after 60 min of low ion energy, very-high-intensity nitrogen ion beam implantation.

Nanomechanical properties of TiN/ZrN multilayers prepared by pulsed laser deposition

The ability to control matter at the range of micron as well nanometer is crucial for material science and engineering. In the domain of material science, the transition metal (TM) nitrides find a unique place owing to their excellent properties such as wear resistance, high hardness and etc. These excellent properties recommended TM nitrides to be used as hard and protective coatings. Further improvements of the mechanical properties were reported by using either ternary compounds such as TiSiC, TiSiN, TiAlN, multilayer or bilayers structures. Here we report the preparation of of multilayer with no of layers of 2,4,10 of titanium nitride (TiN)/zirconium nitride (ZrN) thin films on single crystal Si(100) substrate by using pulsed laser deposition with Nd-YAG laser operating at a wavelength of 1064 nm, pulsed duration 6 ns and repetition rate 10 Hz. The multilayers are grown by ablating from the targets of Zr and Ti in reactive DC nitrogen plasma at a substrate temperature of 673 K at a nitrogen partial pressure of 2x10-3mbar. We investigated the mechanical properties and roughness analysis by Nanoindentation and Atomic force microscopy. Grazing incidence X ray diffraction was used to identify the phase presence in multilayers of TiN/ZrN and cross sectional scanning electron microscopy was used to examine the microstructures and thickness of bilayers. The nanoindentation results showed that peak in hardness was observed in (TiN/ZrN) 2 about 18 Gpa and young’s modulus 250 Gpa

Investigation of 50 Hz Pulsed DC Nitrogen Plasma with Active Screen Cage by Trace Rare Gas Optical Emission Spectroscopy

Optical emission spectroscopy is used to investigate the nitrogen-hydrogen with trace rare gas (4% Ar) plasma generated by 50 Hz pulsed DC discharges. The filling pressure varies from 1 mbar to 5 mbar and the current density ranges from 1 mA·cm−2 to 4 mA·cm−2. The hydrogen concentration in the mixture plasma varies from 0% to 80%, with the objective of identifying the optimum pressure, current density and hydrogen concentration for active species ([N] and [N2]) generation. It is observed that in an N2-H2 gas mixture, the concentration of N atom density decreases with filling pressure and increases with current density, with other parameters of the discharge kept unchanged. The maximum concentrations of active species were found for 40% H2 in the mixture at 3 mbar pressure and current density of 4 mA·cm−2.

Formation of Cone-Shaped Inclusions and Line Defects on the Cz-Si Wafer Surface by the Helium Implantation and DC Nitrogen Plasma Treatment

The general goal of this work is to investigate the defects formed on the surface of the Cz-Si wafers subjected to helium implantation, vacuum annealing and nitrogen plasma treatment. The performed scanning electron microscopy study has shown that in the general case two types of surface defects can be formed: cone-shaped inclusions with the base diameter of 0.2–2 μm and the ratio of diameter to height of approximately 1:1, as well as crystallographically oriented line defects with the length equal to 0.2–2 μm. The concentration of these defects depends on the conditions of implantation and plasma treatment.

Effects of Microfilaments on DC Plasma Torches and Afterglows

In this paper, we investigate the effects of microfilaments on the operation of direct-current (dc) atmospheric-pressure nitrogen plasma torches. We measure the roto-vibrational temperatures of the first negative and second positive systems of the N2 and N2 + species, as well as the electron energy distribution function (EEDF) in the plasma plume and at several distances away from the source. The EEDF is measured using both planar and double-point Langmuir probes. We found that the operation of a dc nitrogen plasma torch in a mixed glow/microfilament regime results in the ejection of high-energy electron bullets from the torch nozzle. The frequency of these electron bullets outside the plasma coincides with the microfilament frequency. Furthermore, the microfilament frequency is shown to have a direct correlation with the N2 + roto-vibrational temperature. The electron bullets possess a highly non-Maxwellian EEDF and maintain their nonequilibrium energies while contained within the N2 substrate gas.

Synthesis of silicon carbide in a nitrogen plasma torch: rotational temperature determination and material analysis

Experiments on silicon carbide synthesis were performed using a dc nitrogen plasma torch. Measurements of rotational temperature of nitrogen molecules by emission spectroscopy were performed, based on the band (0, 1) of the first negative system of nitrogen for the R branch. Three different plasma torch powers were studied in order to optimize the production of silicon carbide with our experimental set-up. The synthesized products were characterized by x-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy.

Optical actinometry of the N-atom density in nitrogen plasma

Trace-rare-gas optical actinometry is used to measure the N-atom density in 50 Hz pulsed dc nitrogen plasma as functions of the discharge parameters. The excited-state population density of N atoms is extracted from their respective optical transitions and is related to the ground-state population density by considering the changes in the electron energy distribution function. This technique provides reliable information on the atomic N concentration in the gas discharge, which is vital in the synthesis of nitrides owing to its high chemical reactivity.

Continuous Monitoring of Toxic Metals in Gas Flows Using Direct-Current Plasma Excited Atomic Absorption Spectroscopy

A measurement apparatus employing direct current (dc) plasma excited atomic absorption spectroscopy was developed and demonstrated for continuous measurement of toxic metals in process gases. Process gas is continuously sampled along a heated sample line. Metal compounds contained in the gas are thermally decomposed by mixing the gas with a plasma jet produced with a dc nitrogen plasma torch. Transmission of monochromatic light is measured through the gas jet, and absorbance caused by metal atoms is distinguished from the background by means of the Zeeman effect. The metal concentration in the sample gas is calculated from the measured absorbance with the known dilution and decomposition factors taken into account. The detection limits of the current prototype are 0.04 mg/m3 for cadmium and 0.4 mg/m3 for lead. The measurement accuracy is better than 20%, and the maximum measurement rate is about 100 values per minute. The instrument was designed to withstand wet, corrosive, and particulate-laden flue gases at temperatures up to 1100 °C. The instrument can also be used, after minor modification, for measurements at pressurized conditions. The performance of the instrument was demonstrated in connection with a real fluidized bed combustor.

Composition and chemical structure characteristics of CNx layers prepared by different plasma assisted techniques

CNx layers were grown on Si (100) wafers and cleaved NaCl (100) slices by reactive sputtering of graphite in DC nitrogen plasma, by DC and RF magnetron sputtering of graphite in N2 or N2+Ar mixture, and from C-containing precursors in nitrogen by plasma-enhanced chemical vapour deposition (PECVD). The chemical structure of the deposited layers was characterised by XPS and FT-IR spectroscopy. DC plasma deposition resulted in layers with high N content, close to CN stoichiometry (x≈1), as determined by XPS. The CNx layers deposited by DC or RF magnetron sputtering contained 22–32 at.% N (x≈0.3–0.5). For layers prepared by PECVD, N-content varying between 20 and 50 at.% was characteristic. The broad and asymmetric C1s and N1s XPS spectral lines manifested several chemical bonding states of the constituents. The proportions of the line components varied with the preparation conditions. Significant differences were also observed in the 1100–1700 cm−1 region of the FT-IR spectra. Assignment of the two major N1s photoelectron peak-components was proposed based on the established correlation between the FT-IR results, composition and binding energy values measured for magnetron-deposited CNx phases as follows: the N1 at 398.3 eV BE to NC double bonds and N2 at 400.2 eV BE to NC single bonds.

Detection of CN radicals in DC nitrogen plasma used for deposition of CN x layers

Emission spectra from a DC plasma discharge of nitrogen with a graphite cathode used for deposition of CN x layers were investigated in the visible range 350–900 nm. The spectra recorded at low and high resolution from both the negative glow and the positive column of the discharge were studied separately. All spectra are dominated by neutral and ionised N 2 emission. In the positive column the violet band of the cyanogen (CN) radical was identified and analysed for vibrational structure. From a computer simulation of the rotationally resolved violet band, vibrational temperatures were derived and found to be in the intensity distribution for the v=0, 1 and 2 levels from thermal equilibrium. In the negative glow the strong N 2 + features completely mask the spectral region of the violet band of CN. Conclusions were drawn concerning the CN formation by chemical sputtering, and the role of CN radicals in the formation of polymeric CN x layers of 1:1=C:N stoichiometry.

New Synthetic Method of Forming Aluminum Oxynitride by Plasma Arc Melting

A new synthetic method of forming the gamma‐phase of aluminum oxynitride (alon) has been proposed. alon has been successfully synthesized by the DC nitrogen plasma arc using alpha‐Al2O3 and AlN as starting materials. Alon rapidly forms in a liquid state under thermal plasma. The obtained lattice parameter of alon has been determined as a function of the concentration of Al2O3. Evaporation takes place during arc melting. The condensed alon from the vapor consists of nanoscale‐sized spherical particles, and these particles are in single crystals. The evaporation mechanism of alon during arc melting is discussed. Thus, arc plasma processing is a promising method for synthesizing alon and producing the ultrafine powder.

Influence of compensation on the luminescence of nitrogen-doped ZnSe epilayers grown by MOVPE

The luminescence of ZnSe grown by metalorganic vapour phase epitaxy and doped by a DC nitrogen plasma is investigated. With increasing N2 flux the donor-acceptor pair (DAP) band continuously develops into a structureless band peaking at 2.62 eV for highest doping levels. This broad band evolves back into a structured DAP band peaking at 2.698 eV with increasing excitation density. At high N concentrations and at large degree of compensation potential fluctuations become important for the spatially indirect DAP recombination. These fluctuations can easily be screened by optically excited carriers making the experimental conditions decisive for luminescence spectra of strongly doped ZnSe: N samples.

Doping of zinc-selenide-telluride

We investigate the doping behavior of ZnSe/ZnTe short period superlattices. p-type doping is achieved with a dc nitrogen plasma source, n-type doping with chlorine from a ZnCl2 Knudsen source. Even a small Te content has a strong positive effect on p doping: Doping levels in the upper 1019 cm−3 range are achieved, and ohmic contacts can be obtained even for low carrier concentrations. The data are in excellent agreement with a theory based on the amphoteric native defect model. The opposite is valid for n doping: At Te concentrations above 20% electron concentrations are below 1016 cm−3. As a possible way to get both good n- and p-type doping at the same lattice constant we propose the use of the quaternary compound Zn(1−y)Mg(y)Se(1−x)Te(x).