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Abstract: The kinetics of a low pressure pulsed DC discharge in dry air is experimentally studied using simultaneous measurements of the concentrations of NO and NO2 downstream the plasma region. The measurements have been performed via infrared tunable diode laser absorption spectroscopy. The gas pressure was 3.95mbar and the pulse duration and frequency range from 20μs to 3ms and from 50 to 1000Hz, respectively. The peak current was varied from 10 to 80mA. It is shown that the NO and NO2 densities depend only on the averaged current. In order to explain this feature a simplified analytical calculation has been developed which considers about 30 kinetic reactions involved in the NO x formation. The calculations lead to a fair agreement with the experimental results. [Copyright &y& Elsevier]

Relative transition probabilities of spontaneous emission in the R and P branches of the A1Π→X1Σ+ (0–0) band of BH molecule have been obtained for the first time. It was observed that measured ratios of the line strengths are in agreement with corresponding ratios of Ho¨nl–London factors. Thus, the non-adiabatic effect of perturbations is negligibly small and Ho¨nl–London formulas may be used for derivation of rovibronic population densities from measured line intensities of the (0–0)R branch of BH. The (0–0)P branch is less prospective because too much overlapping by other BH emissions cannot be avoided with the moderate resolution spectrometers usually used in plasma spectroscopy. General considerations are illustrated on the example of a low-pressure plasma of a planar microwave discharge in a H2–Ar–B2H6 (64:33:3) gas mixture (total pressure 1–2.5 mbar, power 1.2–2.4 kW). The values of the rotational temperatures obtained directly for the excited electronic-vibrational states d3Πu−, v′=2 (Td2rot(H2)) and A1Π+, v′=0 (TA0rot(BH)) and those calculated in the framework of excitation-deactivation models for the ground X1Σu+, v=0 vibronic states (TX0rot(H2) and TX0rot(BH)) have been analysed. It has been observed that TX0rot(H2) and TX0rot(BH) are in excellent agreement, while compared to these values TA0rot(BH) is noticeably higher and Td2rot(H2) is about two times lower. Thus, the simultaneous measurements of intensity distributions in the rotational structure of BH and H2 emission bands can be used as a prospective method for determination of gas temperature in non-equilibrium boron and hydrogen containing plasmas. [Copyright &y& Elsevier]

Infrared laser absorption spectroscopy (IRLAS) and laser-induced fluorescence spectroscopy (LIF) are applied in the present study for online in-situ characterization of volatiles products in the close vicinity of a single pyrolysing wood sphere. These advanced analytical techniques are combined with online measurements of temperature and mass evolutions in order to gain further insight into the complex processes occurring during slow pyrolysis of thermally thick wood particles. Three different heating rates (5, 10, 20 °C/min) and two wood types (beech, pine) were used. Time-resolved absolute concentrations of the main permanent gases CO 2 , CO, CH 4 and H 2 O were measured applying IRLAS. From the LIF measurements the qualitative temporal release of polycyclic aromatic hydrocarbons (PAHs) could be deduced. Different behaviors regarding the release of volatiles, temperature evolution and conversion rates were observed for both wood species, which could not be ascribed only to the different content of cellulose, hemicellulose and lignin. According to the measured volatiles evolution an enhancement of heterogeneous catalytic tar cracking seemed to be present with higher heating rates for both wood types. However, the evolution of exothermicity and PAH release differed for both wood types indicating different reaction pathways. An analysis of possible reaction pathways including secondary reactions is performed taking into account all experimental findings about the in-situ composition of the volatiles and the evolution of the PAHs as well as the exothermicity. The differences in the pyrolytic behavior of both species can be related to both the chemical and physical properties of the raw materials. [ABSTRACT FROM AUTHOR]

The introduction of room temperature continuous wave external-cavity quantum cascade lasers (EC-QCLs) with narrow linewidths has greatly facilitated high resolution spectroscopy over wide spectral ranges in the mid-infrared (MIR) region. Using the wide tuning range of an EC-QCL we have measured the absolute line strengths of many P-branch transitions of the stretching dyad of the ν 3 fundamental band of 28 SiH 4 between 2096 and 2178 cm −1 . Furthermore, the high spectral resolution available has enabled us to resolve and measure representative examples of the tetrahedral splittings associated with each component of the P-branch. The positions of these components are in excellent agreement with spherical top data system (STDS) predictions and theoretical transitions from the TDS spectroscopic database for spherical top molecules. These are the first measurements of these line strengths of 28 SiH 4 and are an example of the applicability of high-powered, widely tunable EC-QCLs to high resolution spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: Low pressure pulsed DC N2–H2 plasmas with admixtures of CH4 used for active screen plasma nitriding (ASPN) have been studied by time resolved Langmuir probe and optical emission spectroscopy (OES) techniques (f=1kHz, 60% duty cycle, p=1mbar). The temporal behavior of parameters of the electrons inside the process volume of the ASPN reactor was at the center of interest. Based on probe diagnostics the electron density and temperature as well as the plasma potential could be determined in dependence (i) on time in the discharge pulses and (ii) on parameters of the gas mixture including the N2–H2 ratio. Electron temperatures between 0.13 and 0.31V and electron densities in the order of 109 cm−3 could be measured. In addition OES has been used to receive complementary information about neutral and charged nitrogen molecules from the glow discharge between the active screen and the outer reactor wall. It was found, that the ratio of hydrogen to nitrogen content in the feed gas mixture influences the emission characteristics of the plasma at the active screen considerably, i.e. the intensity ratio of the N2 +-(0–0)- band to the N2-(0–2)-band. Another focus was the analysis of differences of the electron parameters in pure N2–H2 discharges compared to feed gas mixtures containing methane and the influence on outer electrical parameter of the ASPN reactor. Finally the results of nitriding experiments showed a correlation to the findings of the plasma diagnostic studies. [Copyright &y& Elsevier]

Abstract: Reactive ion etch processes for modern interlevel dielectrics become more and more complex, especially for further scaling of interconnect dimensions. The materials will be damaged within such processes with the result of an increase in their dielectric constants. The capability of selected additives to minimize the low-k sidewall damage during reactive ion etching (RIE) of SiCOH materials in fluorocarbon plasmas was shown in different works in the past. Most of the investigated additive gases alter the fluorine to carbon ratio as well as the dissociation of the parent gas inside the etch plasma. The result is a changed etch rate, a modified polymerization behavior and other characteristics of the process induced SiCOH damage. Heavy inert ions like argon will be accelerated to the sample surface in the cathode dark space and enhance therewith the sputter yield on the SiCOH network . In this paper the additives Ar, O2, C4F8, H2, N2 and CO were added to a conventional CF4 etch plasma. We try to provoke different changes in the plasma conditions and therewith in the process results. Contact angle measurements, spectroscopic ellipsometry, Hg-probe analysis, FTIR measurements and SEM cross-sections were used to overview the additive induced modifications. To understand the influences of the additives gases more exactly, changes in the physical and chemical plasma behavior must be analyzed. Therefore quadrupole mass spectrometry (QMS) and quantum cascade laser absorption spectroscopy (QCLAS) were used. [Copyright &y& Elsevier]

Abstract: A hot filament plant for chemical vapor deposition of crystalline diamond featuring new operating stages has been built. It allows (i) a separate methane feed locally at substrate position and (ii) supplying a forced gas flow towards the substrate. To understand the effect of these two features on diamond growth, the results of systematic diamond growth experiments are discussed. To reveal the effects of these features on the gas phase, infrared tunable diode laser absorption spectroscopy (IR-TDLAS) was employed. Using a forced gas flow showed a remarkable increase in the diamond growth rate of a factor >6 compared to standard coating setups. By lowering the methane content in the forced flow diamond quality factors >95% were achieved. IR-TDLAS showed an increase of all measured carbon-containing species CH4, C2H2, CH3 and CO when applying the forced flow. The mass transport dominated by diffusion in the standard setup shifts to a convective gas transport in the forced flow setup. The induced laminar flow causes a more effective transport of the growth species to the substrate and leads to higher growth rates. Application of feeding methane locally at substrate position leads to exceptionally high growth rates (0.68μm/h) at correspondingly high diamond quality (91%). For this, the methane content has to be lowered, though, which at the same time leads to a more homogenous deposition lateral on the surface. From the IR-TDLAS gas phase measurements, a more effective precursor dissociation, a higher CH3 density and a rise in the CH3⧸C2H2 ratio above the substrate surface can be derived. [Copyright &y& Elsevier]

Abstract: In hot-filament CVD the gas-phase composition is a vital parameter for diamond coating results. Concentrations of carbon-containing species have significant influence on growth rate, quality and morphology of deposited diamond. To learn more about the correlations between process parameters and gas species concentrations we applied the highly sensitive infrared tunable diode laser absorption spectroscopy (IR-TDLAS) technique. With a sophisticated compact IR-TDLAS unit, relative and absolute concentrations of CH4, C2H2 and CO were simultaneously measured. Also, the absolute concentration of the methyl radical was determined in dependence on process parameters. Concentrations of CO2, C2H6 and HCN were investigated but found to be lower than the detection limit. The influence of the typical diamond CVD-process parameters on various species concentrations is discussed. The applicability of IR-TDLAS for hot-filament process monitoring is evaluated. In context with diamond growth results, information for CVD process refinement was deducted from the IR-TDLAS measurements. [Copyright &y& Elsevier]

Rotationally resolved spectra of the fundamental band of the CN free radical in four isotopic forms have been measured using tunable diode laser absorption spectroscopy. The source of the radical was a microwave discharge in a mixture of isotopically selected methane and nitrogen diluted with argon. The lines were measured to an accuracy of 5×10-4 cm-1 and fitted to the formula for the vibration rotation spectrum of a diatomic molecule, including quartic distortion constants. The band origins of each of the isotopomers from the five parameter fits were found to be 12C14N: 2042.42115(38) cm-1, 13C14N: 2000.08479(23) cm-1, 12C15N: 2011.25594(25) cm-1, 13C15N: 1968.22093(33) cm-1 with one standard deviation from the fit given in parenthesis. Some of the lines showed a resolved splitting due to the spin rotation interaction. This was averaged for fitting purposes. The average equilibrium internuclear distance derived from the v=0 and 1 rotational constants of the four isotopomers is 1.171800(6) Å which is in good agreement with the value determined from microwave spectroscopy. [Copyright &y& Elsevier]