Tunable infrared diode laser absorption spectroscopy has been used to detect the methyl radical and nine stable molecules, CH 4 , CH 3 OH, C 2 H 2 , C 2 H 4 , C 2 H 6 , NH 3 , HCN, CH 2 O and C 2 N 2 , in H 2 -Ar-N 2 microwave plasmas containing up to 7% of methane or methanol, under both flowing and static conditions. The degree of dissociation of the hydrocarbon precursor molecules varied between 20% and 97%. The methyl radical concentration was found to be in the range 10 12 -10 13 molecules cm −3 . By analysing the temporal development of the molecular concentrations under static conditions it was found that HCN and NH 3 are the final products of plasma chemical conversion. The fragmentation rates of methane and methanol (R F (CH 4 ) = (2-7) × 10 15 molecules J −1 , R F (CH 3 OH) = (6-9) × 10 15 molecules J −1 ) and the respective conversion rates to methane, hydrogen cyanide and ammonia (R Cmax (CH 4 ) = 1.2 × 10 15 molecules J −1 , R Cmax (HCN) = 1.3 × 10 15 molecules J −1 , R Cmax (NH 3 ) = 1 × 10 14 molecules J −1 ) have been determined for different hydrogen to nitrogen concentration ratios. An extensive model of the chemical reactions involved in the H 2 -N 2 -Ar-CH 4 plasma has been developed. Model calculations were performed by including 22 species, 145 chemical reactions and appropriate electron impact dissociation rate coefficients. The results of the model calculations showed satisfactory agreement between calculated and measured concentrations. The most likely main chemical pathways involved in these plasmas are discussed and an appropriate reaction scheme is proposed.
The recent availability of thermoelectrically cooled pulsed and continuous wave quantum and inter-band cascade lasers in the mid-infrared spectral region has led to significant improvements and new developments in chemical sensing techniques using in-situ laser absorption spectroscopy for plasma diagnostic purposes. The aim of this article is therefore two-fold: (i) to summarize the challenges which arise in the application of quantum cascade lasers in such environments, and, (ii) to provide an overview of recent spectroscopic results (encompassing cavity enhanced methods) obtained in different kinds of plasma used in both research and industry.
The long-term stability and γ-sterilisability of bioactive layers is the precondition for the application of implants. Thus, aging processes of a microwave deposited, plasma polymerized allylamine nanofilm (PPAAm) with positively charged amino groups were evaluated concerning physicochemical characteristics and cell adhesion capacity over the course of one year. XPS, FT-IR, surface free energy, and water contact angle measurements elucidated not only the oxidation of the PPAAm film due to atmospheric oxygen reacting with surface free radicals but also the influence of atmospheric moisture during sample storage in ambient air. Surprisingly, within 7 days 70% of the primary amino groups are lost and mostly converted into amides. A positive zeta-potential was verified for half a year and longer. Increasing polar surface groups and a water contact angle shift from 60° to 40° are further indications of altered surface properties. Nevertheless, MG-63 human osteoblastic cells adhered and spread out considerably on aged and additionally γ-sterilized PPAAm layers deposited on polished titanium alloys (Ti-6Al-4V_P). These cell-relevant characteristics were highly significant over the whole period of one year and may not be related to the existence of primary amino groups. Rather, the oxidation products, the chemical amide group, that is, seem to support the attachment of osteoblasts at all times up to one year.
The present work is concerned with the simulation analysis of a microwave plasma torch suitable for deposition applications prior to the admixture of any precursor. The self-consistent numerical model describes the electromagnetic field of the microwaves entering an R26 waveguide, the plasma generation, the gas flow through a tube crossing the waveguide, and the heat transfer in the gas. The plasma description avoids the assumption of quasi-neutrality and provides, therefore, a solution including the near-wall regions.The multiphysics model is applied to the source operated in argon at atmospheric pressure. Quasi-stationary solutions are obtained in a 2D Cartesian geometry and in a 3D geometry employing increasing degrees of complexity with respect to the physics, the reaction kinetics and the boundary conditions. The distribution of the electromagnetic field and the plasma parameters resulting from 2D fully coupled one-and two-ion models is analyzed for an incoming microwave power of 1 kW and a gas flow rate of 18 slm. The 2D model is capable of predicting the plasma parameters at a reasonable computational cost. The application of a 3D plasma-microwave model shows that the spatial distribution of the electromagnetic field and the plasma parameters is not, in general, axially symmetric. In the plane corresponding to the 2D work plane, the results of 3D one-ion plasma model show agreement with the 2D results, however, at significant computational costs. The 2D simulation analysis carried out allows us to draw up a decision-making with regard to the setup performance.
Tuneable infrared diode laser absorption spectroscopy at 16.5 µm and broadband ultraviolet absorption spectroscopy at 216 nm have both been used to measure the ground state concentrations of the methyl radical in two different types of non-equilibrium microwave plasmas (f = 2.45 GHz): (i) H 2 -Ar plasmas of a planar reactor with small admixtures of methane or methanol, at a pressure of 1.5 mbar, and (ii) H 2 -CH 4 plasmas of a bell jar reactor, at pressures of 25 and 32 mbar under flowing conditions. For the first time, two different optical techniques have been directly compared to verify the available data about absorption cross sections and line strengths of the methyl radical. It was found that application of the CH 3 absorption cross section of the B( 2 A 1 ) ← X( 2 A 2 ) transition at 216 nm, reported by Davidson
We have determined, in vivo and simultaneously, the tissue PO2 (Ptio2) and the oxidation-reduction (redox) state of cytochrome aa3 (cyt aa3) of cat cerebral cortex during and after a short period of N2 breathing. Thirteen cats were anesthetized, ventilated mechanically with room air, subjected to a limited bilateral craniotomy, and then injected with 25 mg/kg of pyrenebutyric acid (PBA) intravenously. Ptio2 was measured from PBA generated fluorescence, emitted by monitored cerebral cortical cells. The cyt aa3 redox state was measured from differential absorption of monochromatic light at 605 vs. 590 nm reflected from the same cortical cells. In response to a 1.5-min N2 ventilation (phase I) the increase in PBA fluorescence signal, indicating a decline in Ptio2, lagged behind the cyt aa3 reduction. When the animal was ventilated with room air (phase II), rapid reoxidation, followed by hyperoxidation of cyt aa3 occurred. The decrease in PBA fluorescence signal, indicating an increase in Ptio2, was seen to lag behind cyt aa3 reoxidation. These results indicate that hysteresis exists in the relation between Ptio2 and cyt aa3 redox state. This may be the result of the situation that 1) low tissue O2 concentration is partially compensated by accumulation of reduced cyt aa3, and 2) following brief periods of anoxia, the affinity of cyt aa3 to O2 is increased.
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.