Three continuous wave external cavity quantum cascade lasers (EC-QCLs) operating between 1305 and 2260 cm −1 (4.42-7.66 μm) have been tested as radiation sources for an absorption spectrometer focused on the analysis of physical and chemical phenomena in molecular plasmas. Based on the wide spectral tunability of EC-QCLs, multiple species detection has become feasible and is demonstrated in a study of low-pressure Ar/N 2 microwave plasmas containing methane as a hydrocarbon precursor. Using the direct absorption technique, the evolution of the concentrations of CH 4 , C 2 H 2 , HCN and H 2 O has been monitored depending on the discharge conditions at a pressure of p = 0.5 mbar and at a frequency of f = 2.45 GHz in a planar microwave plasma reactor. The concentrations were found to be in the range of 10 11 -10 14 molecules cm −3 . In addition, based on the analysis of the line profile of selected absorption lines, the gas temperature T g has been calculated in dependence on the discharge power. T g increased with the power values and was in the range between 400 and 700 K. Further, in a pure He/Ar microwave plasma, the wavelength modulation spectroscopy technique has been applied for the sensitive detection of transient plasma species with absorbencies down to 10 −5 . The typical spectral line width of an EC-QCL under the study was found to be in the range 24 to 38 MHz depending (i) on the chopping technique used and (ii) on a single or averaged measurement approach. Further, different methods for the modulation and tuning of the laser radiation have been tested. Varying the power values of an EC-QCL between 0.1 and 154 mW for direct absorption measurements under low pressure conditions, no saturation effects in determining the concentrations of methane, acetylene and carbon monoxide could be found under the experimental conditions used, i.e. for lines with line strengths between 10 −19 and 10 −22 cm molecule −1 .
In Ar and Ar/N 2 RF plasmas with admixtures of aluminum tri-isopropoxide (ATI) the fragmentation of this metal-organic precursor has been studied by means of infrared absorption spectroscopy (IR-AS) using an external-cavity quantum cascade laser (EC-QCL) arrangement. The experiments were performed in an asymmetric capacitively coupled reactor at a frequency of f = 13.56 MHz and a pressure of up to p = 10 Pa. The discharge power was in the range of P = 40 -100 W. Using EC-QCLAS the evolution of the concentrations of six stable molecules, CH4, C2H2, C2H4, H2O, HCN and HNO3, has been monitored in the plasma. The concentrations of these plasma chemical products were found to be in the range of about 7×10 12 -2×10 14 molecules cm −3 .
In Ar and He radio-frequency (RF) plasmas with admixtures of C 2 H 2 and CH 4 the hydrocarbon chemistry has been studied in relation to dust particle formation by means of infrared tunable diode laser absorption spectroscopy (TDLAS) combined with Fourier transform infrared (FTIR) spectroscopy. The experiments were performed in a RF capacitively coupled parallel plate reactor at a frequency of f = 13.56 MHz, a pressure of p = 0.1 mbar and a flow rate of = 8 sccm of Ar or He with admixtures of 0.5 sccm C 2 H 2 or 1 sccm CH 4 . The power was P = 15 W. Using TDLAS, the temporal evolution of the concentrations of the methyl radical and of four stable molecules, C 2 H 2 , CH 4 , C 2 H 4 and CO, was monitored in the plasma. Simultaneously, the growth process of the dust particles was analysed by FTIR spectroscopy. The degree of dissociation of the acetylene precursor was found to be nearly constant in the range of 96% under stabilized conditions for both the Ar and He plasmas. In contrast, the degree of dissociation of the methane precursor varied between 45% and 90% depending (i) on the appearance of dust particles in the reactor volume and (ii) on the Ar or He plasma conditions. The methyl radical concentration was found to be in the range of 10 11 molecules cm −3 . The concentrations of all hydrocarbon species were strongly correlated with the dynamic of the dust formation. Fragmentation efficiencies of acetylene (R F (C 2 H 2 ) = 3.2 × 10 16 molecules J −1 ) and of methane (R F (CH 4 ) = (0.16-2.5) × 10 16 molecules J −1 ) and conversion efficiencies to the produced hydrocarbons (R C = (0.23-8.5) × 10 14 molecules J −1 ) could be estimated in dependence on the discharge conditions in the RF plasma.
We synthesized chalcopyrite (CuFeS 2 ) nanoparticles by methods involving laser ablation and electrical discharge in water. The nanoparticles obtained were exposed to an oxygen/argon plasma of a microwave discharge. The synthesized material was studied by photometry, x-ray diffraction (XRD), and energy dispersive x-ray elemental analysis (EDX), IR spectroscopy, and atomic force electron microscopy (AFM). We have established that the nanoparticles are morphologically stable relative to exposure to plasma fluxes of power ≤1 kW, and can be used as a model system to study processes of interaction between a plasma and minerals.Keywords: nanoparticle, chalcopyrite, laser ablation, electrical discharge in a liquid, plasma treatment of minerals, froth flotation.Introduction. Plasma methods are quite effective in many modern technologies, including surface treatment of various minerals. A major problem in this technology is our insufficient basic knowledge about the mechanisms of interaction between the plasma and the surface of the minerals. In particular, detailed study of the interaction between the plasma and chalcopyrite (CuFeS 2 ) and pyrite (FeS 2 ) particles is needed for optimization of the technology for separating them, based on the froth flotation method (different wettabilities of the particles). The conventional approach uses an increase in the difference between the wettabilities, with the help of selective surfactants [1-6]. The surface of some particles in the mixture is hydrophobic (water-repellant). The hydrophobic particles, attaching to air bubbles introduced into the aqueous suspension of the mixture of minerals, are transported upward by the bubbles toward the froth layer on the surface of the suspension, thus separating them from the hydrophilic (wettable) particles. The new approach is based on treatment of the surface of the minerals with a non-thermal plasma under conditions leading to a change in wettability without a change in chemical composition. For optimization of the plasma treatment conditions, we need a detailed clarification of the basic mechanisms for interaction between the plasma fluxes and the indicated minerals. Due to the high surface/volume ratio and the reactivity of nanosized particles, they may be ideal model systems for studying processes leading to a change in surface wettability. In this case, laser ablation processes and electrical discharges in liquid media may be effectively used to obtain model CuFeS 2 nanoparticles.In this work, we have obtained nanosized chalcopyrite particles by laser and electrical-discharge spraying of a sample of the original mineral in water. The phase and elemental composition of the particles obtained were studied using x-ray diffraction (XRD) and energy dispersive x-ray elemental analysis (EDX). In order to determine the changes in the morphology of the particles due to plasma treatment, we used Fourier transform IR spectroscopy and atomic force electron microscopy (AFM).Experimental Section. Pure crystalline chalcopyrite (Alfa Easer, Germany...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.