New and versatile minature microwave plasma source (original) (raw)
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Development of a Microwave-Induced Nitrogen Discharge at Atmospheric Pressure (MINDAP)
Applied Spectroscopy, 1985
A microwave-induced plasma has been sustained with the use of nitrogen as the nebulizer and plasma supporting gas. A concentric tube torch was constructed so the plasma could be easily ignited and maintained. This new plasma emission source has a flame-like appearance and extends I0 cm beyond the cavity, at an applied power of 250 W. The nitrogen plasma readily accepts aerosol samples and is compatible with sample introduced from a conventional nebulizer system. The radial (side-on) optical viewing configuration was found to have lower background emission than the more commonly employed axial (end-on) configuration. Optimum operating conditions were established from the effects of applied power, flow rate, and signal-to-background noise on the intensity of both atom and ion transitions. A discussion of the background spectral features and the analytical potential of this new source is presented.
Optical characterization of a novel miniature microwave ICP plasma source in nitrogen flow
Plasma Sources Science and Technology, 2018
A Miniature Microwave (MMW) Inductively Coupled Plasma Source (ICP) is characterized by optical emission spectroscopy and by optical imaging of nitrogen plasma. The MWW source operates in two different modes (Hmode and hybrid-E/H mode) with different plasma parameters and different emission morphologies, depending on the absorbed microwave (MW) power (Pabs). The measured spectra of the second positive system (N2(C-B)) and of the first negative system (N2 + (B-X)) of nitrogen reveal an electron density ne = (6.4±1.7)×10 18 m-3 and a gas temperature of Tg = (650±20)K for Pabs = 13 W at a pressure of 1000 Pa. By increasing the absorbed power to Pabs = 78 W the parameters increase to ne = (3.5±1.7)×10 19 m-3 and Tg = (1600±100) K. The discharge morphology in hybrid and Hmode is different. While in the H-mode the plasma resembles a "donuts" shape, the hybrid mode has a very narrow shape close to the walls and to the gap capacitor of the resonator. For our discharge conditions the power absorption is limited to 158 W, above which the discharge spontaneously switches from Hmode to hybrid mode.
High-resolution optical emission spectroscopy and automated Langmuir probe are applied to examine the production of active species in the pure nitrogen plasma excited by single (40.68 MHz) and dual high-frequency (HF) radio frequency (RF) power sources (40.68/2.1 MHz). The emission intensities of the spectral bands correspond to the (0, 2) transition of the second positive system (SPS) of N2 (λ =380.50 nm) and (0, 0) transition of the first negative systems (FNSs) of N2+ (λ =391.40 and 427.81 nm have been measured and compared with plasma parameters using the Langmuir probe to investigate the dependence of their radiative states on operating conditions for both single and dual HF RF capacitively coupled plasma (CCP) discharge. It was found that the high power of the low-frequency (LF) source and the gas pressures are the most effective parameters in dual RF CCP discharge system. Thus, both SPS intensity decreases and FNS intensity increases with the increasing LF power at constant pressure. Furthermore, the emission intensity of the first negative band heads increases at least four times in dual RF mode in comparing with the single RF CCP discharge. In contrast, the intensity of the second band heads decreases dramatically to its half values. Likewise, it was found that the transition pressures for the electron heating mode (with increasing the gas pressure) and the transition from α to γ mode (with increasing the RF power) is close to 0.3 torr in single RF mode, but these transitions are about 0.5 torr for dual RF CCP mode.
Capacitively coupled radio-frequency discharges in nitrogen at low pressures
Plasma Sources Science and Technology, 2012
This paper uses experiments and modelling to study capacitively coupled radio-frequency (rf) discharges in pure nitrogen, at 13.56 MHz frequency, 0.1-1 mbar pressures and 2-30 W coupled powers. Experiments performed on two similar (not twin) setups, existing in the LATMOS and the GREMI laboratories, include electrical and optical emission spectroscopy (OES) measurements. Electrical measurements give the rf-applied and the direct-current-self-bias voltages, the effective power coupled to the plasma and the average electron density. OES diagnostics measure the intensities of radiative transitions with the nitrogen second-positive and first-negative systems, and with the 811.5 nm atomic line of argon (present as an actinometer). Simulations use a hybrid code that couples a two-dimensional time-dependent fluid module, describing the dynamics of the charged particles (electrons and positive ions N + 2 and N + 4 ), and a zero-dimensional kinetic module, describing the production and destruction of nitrogen (atomic and molecular) neutral species. The coupling between these modules adopts the local mean energy approximation to define space-time-dependent electron parameters for the fluid module and to work out space-time-averaged rates for the kinetic module. The model gives general good predictions for the self-bias voltage and for the intensities of radiative transitions (both average and spatially resolved), underestimating the electron density by a factor of 3-4.
Applied Physics Letters, 2006
In this letter, atmospheric-pressure glow discharges in ␥ mode with argon/nitrogen as the plasma-forming gas using water-cooled, bare copper electrodes driven by radio-frequency power supply at 13.56 MHz are achieved. The preliminary studies on the discharge characteristics show that, induced by the ␣-␥ coexisting mode or ␥ mode discharge of argon, argon-nitrogen mixture with any mixing ratios, even pure nitrogen, can be employed to generate the stable ␥ mode radio-frequency, atmospheric-pressure glow discharges and the discharge voltage rises with increasing the fraction of nitrogen in the argon-nitrogen mixture for a constant total gas flow rate.
Plasma Processes and Polymers, 2007
Densities of N, H and O atoms have been determined in flowing microwave discharges by optical actinometry and by NO titration for N atoms in the post-discharge. Two N2–xH2 and N2–xO2 gas mixtures have been separately studied in the same discharge conditions: 0<x<5%, N2 gas pressure of 530 Pa (4 Torr), flow rate of 1 Slm (Standart litre per minute), microwave power of 100 W, quartz discharge tube of 5 mm internal diameter. The relative densities of N, H and O atoms in the discharges are obtained by optical actinometry by adding 5% Ar in the N2–xH2 and N2–xO2 gas mixtures. After calibration by NO, the N atom density in the post-discharge is followed by the intensity of the N2, 580 nm peak emission. It is observed in with the N2–xO2 gas mixture the same decrease with x(O2) of the N atom relative densities in the discharge and of the absolute value of N-atom density in the post-discharge. Also with N2–xH2 discharge the decrease in the N-atom relative density with x(H2) is in the same way as for the N2–xO2 gas mixture. But in the post-discharge, the absolute density of N atoms in N2–xH2 decreased more slowly than in the N2–xO2 post-discharge. These results are interpreted from kinetics reactions in the discharges and post-discharges. In particular, the recombination of NH radicals could be a source of N and H atoms in the N2–H2 post-discharge.
The European Physical Journal Applied Physics, 2009
Flowing microwave N2 afterglows at reduced pressure are studied as a source of N-atoms. It is presently reported results obtained by pulsing the nitrogen gas flow with an electromagnetic (EM) valve before the plasma, starting with discharge conditions of continuous flow around 1 Torr. By keeping the microwave power tuned on as in continuous flow, it is obtained two successive plasmas: the first one at a pressure of 2-3 Torr when the flow gas is on and the second one at lower pressure (0.4−0.5 Torr) when the flow gas is off. The gas pressures were measured in a 5 L post-discharge chamber. The two plasmas are here analysed by emission spectroscopy and the transmitted powers are deduced from the N + 2 /N2 intensity ratio for both cases. It is obtained about the same power as for continuous flow when the flow gas is on with a negligible reflected power. The transmitted power is lower and thus the reflected power is important when the flow gas is off. The emission of the N2 1st positive system at 580 nm, signature of the N-atom recombination in the afterglow, is observed in the reactor after the gas pressure rise, with a maximum intensity obtained for a duty cycle of 0.5 at a period of 2 s, corresponding to a maximum N-atom density of about 10 15 cm −3 and a pressure variation Δp in the range 2.3−0.5 Torr.
Plasma Science and Technology, 2011
Optical emission spectroscopic measurement of trace rare gas is carried out to determine the density of nitrogen (N) atom, in a nitrogen plasma, as a function of filling pressure and RF power applied. 2% of argon, used as an actinometer, is mixed with nitrogen. In order to normalize the changes in the excitation cross section and electron energy distribution function at different operational conditions, the Ar-I emission line at 419.83 nm is used, which is of nearly the same excitation efficiency coefficient as that of the nitrogen emission line at 493.51 nm. It is observed that the emission intensity of the selected argon and atomic nitrogen lines increases with both pressure and RF power, as does the nitrogen atomic density.