P. Veis

Study of oxygen atom recombination on a Pyrex surface at different wall temperatures by means of time-resolved actinometry in a double pulse discharge technique

The surface recombination probability of oxygen atoms as a function of wall temperature is studied by using a double pulse discharge technique. The main discharge pulse dissociates molecular oxygen and the second pulse, shorter than the main one, excites atoms during the stationary afterglow. The recombination probability is determined from the atomic oxygen density decay during the stationary afterglow of the main pulse (MP). The oxygen atoms are detected by time-resolved optical emission spectroscopy. In order to correlate the oxygen emission lines with the oxygen atom density, argon is used as an actinometer. To scan the whole afterglow of the main discharge pulse, the delay of the probe pulse is uniformly increased in every period following the MP. The evolution of the relative O atom density is deduced from the O emission lines at 777 and 844?nm and from the Ar actinometry line at 750?nm. The wall recombination probability ? on a Pyrex surface ranges from 4.0 ? 10?4 to 1.6 ? 10?2 for wall temperatures from 77 to 460?K.

Characterization and properties of the copolymer of dipyrido-[3,2-a; 2′,3′-c]-thien-[3,4-c]azine with 3-dodecylthiophene

Abstract The method of chemical oxidative polymerization with FeCl 3 was used to synthesize the copolymer of dipyrido-[3,2-a; 2′,3′-c]-thien-[3,4-c]azine (DPTA) and 3-dodecylthiophene (DDT). The copolymer was characterized by UV–VIS, Raman, 1 H and 13 C NMR and EPR spectroscopy. It has been found that the DPTA/DDT copolymer exhibits properties of the low-band-gap polymer ( E g

Time resolved O2(b

This paper deals with a simple and quick method for the determination of rotational temperature from a low-resolved (0-0) A-band of the atmospheric system O2 (b (X . A classical comparison method of simulated and measured spectra was used to determine the temperature of the pulsed oxygen discharge and of the time afterglow at pressures in the range 0.5-3 Torr. The proposed new method has been used to determine the temperature in a late time afterglow.

^1\Sigma^+_g

Optical emission spectroscopy, ranging from visible to near infrared, is used to determine densities and rotational temperatures of N2(B?3?g) and N2(C?3?u) states in a nitrogen?argon (0?95% Ar) discharge, under moderate pressures (200?400?Pa). The plasma is sustained by a helical cavity with an excitation frequency of 27?MHz and power fixed to 28?W. Firstly, in the case of a pure N2 discharge, the two states turn out to have a similar rotational temperature, which approximates the gas temperature reasonably well. With a gradual increase in the Ar concentration up to 95%, the rotational temperature of N2(C?3?u) roughly doubles while that of N2(B?3?g) stays unchanged at 430???50?K regardless of the gas composition. Secondly, as observed, the densities of the N2(B?3?g) and N2(C?3?u) states increase with increasing Ar percentage in the gas mixture. The increase in the emission intensity values is less marked for positions corresponding to both ends of the cavity. In fact, the difference in the emission level between the power input and helix middle positions is reduced, revealing that the total discharge is more uniform along the cavity for large argon concentrations. The experimental results show a strong dependence of temperatures and densities on the Ar amount in the gas mixture. A kinetic model is developed to explain this phenomenon, which is then used in modelling density evolutions versus relative abundance of Ar and versus the position along the cavity axis. The model indicates the importance of the role of electron and metastable species in the above-described discharge.

) rotational temperature measurements in a low-pressure oxygen pulsed discharge. Simple and quick method for temperature determination

Standard H2∕CH4∕B2H6 plasmas (99% of H2 and 1% of CH4, with 0–100ppm of B2H6 added) used for doped diamond film growth are studied by optical emission spectroscopy in order to gain a better understanding of the influence of boron species on the gas phase chemistry. Only two boron species are detected under our experimental conditions (9∕15∕23Wcm−3 average microwave power density values), and the emission spectra used for studies reported here are B(S1∕22−P1∕2,3∕202) and BH[AΠ1‐XΣ+1(0,0)]. Variations of their respective emission intensities as a function of the ratio B∕C, the boron to carbon ratio in the gas mixture, are reported. We confirmed that the plasma parameters (Tg, Te, and ne) are not affected by the introduction of diborane, and the number densities of B atoms and BH radical species were estimated from experimental measurements. The results are compared to those obtained from a zero-dimensional chemical kinetic model where two groups of reactions are considered: (1) BHx+H↔BHx−1+H2 (x=1–3) by ana...

Spectroscopic diagnostics and modelling of a N2–Ar mixture discharge created by an RF helical coupling device: I. Kinetics of N2(B 3Πg) and N2(C 3Πu) states

Optical emission spectroscopy in vacuum ultraviolet and UV spectral ranges is applied to study densities, and vibrational and rotational temperatures of the N2 molecule in a nitrogen–argon (0–95% Ar) plasma sustained at a pressure of 400 Pa by a helical cavity supplied with a power of 28 W and an excitation frequency of 27 MHz. The spatial investigation of all emission systems from UV to NIR shows a minimum situated in the middle of the helical structure and two maxima located at the positions where the RF power is transmitted to the gas and at the end of the helix. The minimum was deepest for emission of the first positive (1+) nitrogen system. This hollow shaped density profile due to the presence of a non-linear phenomenon in the discharge is constant whatever the gas composition. The emissions related to Lyman–Birge–Hopfield and the second positive (2+) systems of molecular nitrogen, and N(2P) atoms, are analyzed versus the Ar percentage. Additionally, the NO(A 2Σ+ → X 2Π) and OH(A 2Σ+ → X 2Π) emission systems coming from impurities are investigated. All the densities of the considered species increase with Ar amount. The rotational and vibrational temperatures of the emitter species are determined through the comparison between experimental and simulated spectra. In the case of a N2 discharge, all the rotational temperatures deduced through the nitrogen emission systems are equal and can be assimilated to the gas temperature. With the increase in the Ar amount, only the rotational temperature obtained from the 1+ system is close to the gas temperature. The rotational and vibrational temperatures related to the NO(A 2Σ+) species are constant whatever the gas composition. The vibrational distribution function of N2(a 1Πg) state presents a Boltzmann law with a vibrational temperature in the range 5600–8000 K (±1000 K) for the N2–x% Ar mixture with x < 75%. When the Ar percentage increases above this limit, we observe strong deviations from the Boltzmann law and no temperature can be deduced. Some kinetic considerations, where the nitrogen and argon metastables play an important role, are discussed to explain the strong dependence of the temperatures and density species toward the Ar amount in the gas mixture.

Optical emission study of a doped diamond deposition process by plasma enhanced chemical vapor deposition

Oxygen atoms recombination at the wall is studied by time-resolved Optical Emission Spectroscopy in a pulsed discharge. In order to observe the atomic oxygen emission after discharge pulse, it is indispensable to re-excite O atoms because the lifetime of O* atoms is short. Here is proposed a technique based on a double pulse excitation. Atomic oxygen, created during the main discharge pulse, is probed in a time after-glow with a diagnostic pulse. This diagnostic pulse is as short as possible to only repopulate the atomic excited states, without significant production of supplementary atoms. The intensities of the emission lines O(3P-3S) at 844.6 nm and O(5P-5S) at 777.4 nm, measured during diagnostic pulse, are observed in the whole time after-glow as a function of delay after main pulse. The decrease of line intensities is related to the recombination of O atoms at the wall. For a “Pyrex” wall at 300 K, the obtained recombination probability γ is 10−3. This value is in agreement with previous results.

Vacuum UV and UV spectroscopy of a N2–Ar mixture discharge created by an RF helical coupling device

Laser-induced breakdown spectroscopy (LIBS) for composition analysis of polymer materials results in optical spectra containing atomic and ionic emission lines as well as molecular emission bands. In the present work, the molecular bands are analyzed to obtain spectroscopic information about the plasma state in an effort to quantify the content of different elements in the polymers. Polyethylene (PE) and a rubber material from tire production are investigated employing 157nmF2 laser and 532nm Nd:YAG laser ablation in nitrogen and argon gas background or in air. The optical detection reaches from ultraviolet (UV) over the visible (VIS) to the near infrared (NIR) spectral range. In the UV/VIS range, intense molecular emissions, C2 Swan and CN violet bands, are measured with an Echelle spectrometer equipped with an intensified CCD camera. The measured molecular emission spectra can be fitted by vibrational-rotational transitions by open access programs and data sets with good agreement between measured and fitted spectra. The fits allow determining vibrational-rotational temperatures. A comparison to electronic temperatures Te derived earlier from atomic carbon vacuum-UV (VUV) emission lines show differences, which can be related to different locations of the atomic and molecular species in the expanding plasma plume. In the NIR spectral region, we also observe the CN red bands with a conventional CDD Czerny Turner spectrometer. The emission of the three strong atomic sulfur lines between 920 and 925nm is overlapped by these bands. Fitting of the CN red bands allows a separation of both spectral contributions. This makes a quantitative evaluation of sulfur contents in the start material in the order of 1wt% feasible.

STUDY OF OXYGEN RECOMBINATION WITH A DOUBLE PULSE DISCHARGE

The vacuum UV (VUV)-near Infrared (NIR) laser induced breakdown spectroscopy (LIBS) technique was applied to investigate the composition of W-based samples with a protective carbon layer. The sample was analyzed under pressures from 5 to 105 Pa and atmosphere (air, He). The spectra were recorded with three spectrometers at delays from 200 ns to 10 μs at atmospheric pressures and from 100 to 500 ns at low pressures. The electron density was determined from the measured spectra using Stark broadening and the electron temperature from the W I–W III Saha–plot in the VUV–NIR spectral range. The better precision was achieved due to usage W III spectral lines of tungsten. The achieved results are more reliable than results obtained without W III spectral lines. The calibration free LIBS method was then applied to determine the W and C contents of the analyzed sample.

Laser-induced optical breakdown spectroscopy of polymer materials based on evaluation of molecular emission bands

ITER plans foresee the quantitative diagnostics of fuel retention in reactor walls at near-atmospheric pressures. Using laser induced breakdown spectroscopy (LIBS) for this purpose assumes a reliable resolving of Balmer α-lines of hydrogen isotopes in spectra of plasma produced by focused laser radiation onto the target surface. To develop LIBS for quantitative diagnostics of fuel retention during the maintenance breaks of ITER, the effect of background gas pressure on the laser-induced plasma characteristics has been studied. The background pressure limits the expansion rate of plasma and as a result it leads to higher plasma concentrations. At the same time the limiting factor of the resolving of hydrogen isotope lines is the lines broadening by Stark effect, which is the function of electron concentration. The resolving of lines become possible recording spectra at longer delay times after the laser pulse. On the other hand, at longer delays the signal-to-noise ratio decreases. As a compromise, we found that at atmospheric pressure and at delay times >2000 ns, a fitting of H α and D α lines by Voigt contours allows a reliable discrimination of these lines.