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Spatially resolved trace rare gases optical emission spectroscopy was used to analyze the electron energy-distribution function (EEDF) in low-pressure argon plasma columns sustained by surface waves. At frequencies >1 GHz, in the microwave-sustained region, the EEDF departs from a Maxwellian, characterized by a depletion of low-energy electrons and a high-energy tail, whereas in the field-free zone, the EEDF is Maxwellian. Abnormal behavior of the EEDF results from the acceleration of low-energy electrons due to the conversion of surface waves into volume plasmons at the resonance point where the plasma frequency equals the wave frequency and their absorption by either collisional or Landau damping.

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RESUMEN

We report a new method for studying surface reactions and kinetics at moderately high pressures (<10 Torr) in near real time. A cylindrical substrate in a reactor wall is rotated at up to 200,000 rpm, allowing the surface to be periodically exposed to a reactive environment and then analyzed by a triple-differentially pumped mass spectrometer in as little as 150 micros thereafter. We used this method to study oxygen plasma reactions on anodized aluminum. When the substrate is spun with the plasma on, a large increase in O2 signal at m/e = 32 is observed with increasing rotation frequency, due to O atoms that impinge and stick on the surface when it is in the plasma, and then recombine over the approximately 0.7 to 40 ms period probed by changing the rotation frequency. Simulations of O2 signal versus rotation frequency indicate a wide range of recombination rate constants, ascribed to a range of O-binding energies.

RESUMEN

We have studied the recombination of O atoms on an anodized Al surface in an oxygen plasma, using a new "spinning wall" technique. With this method, a cylindrical section of the wall of the plasma reactor is rotated and the surface is periodically exposed to an oxygen plasma and then to a differentially pumped mass spectrometer (MS). By varying the substrate rotation frequency (r), we vary the reaction time (t(r)), that is, the time between exposure of the surface to O atoms in the plasma and MS detection of desorbing O(2) (t(r) = 1/2r). As t(r) is increased from 0.7 to 40 ms, the O(2) desorption signal decreases by a factor of 2 for an O-atom flux of 1 x 10(16) cm(-2) s(-1) and by a factor of 6 when the O flux is 1 x 10(17) cm(-2) s(-1). The O(2) signal decay is highly nonexponential, slowing at longer times and reaching zero signal as r --> 0. A model of O-atom recombination is compared with these time-dependent results. The model assumes adsorption occurs at surface sites with a range of binding energies. O can detach from these sites, become mobile, and diffuse along the surface. This leads to desorption of O, reattachment at free adsorption sites, and recombination to form O(2) that promptly desorbs. With several adjustable parameters, the model reproduces the observed shapes of the O(2) desorption decay curves and the lack of detectable desorption of O and predicts a high O-atom recombination coefficient on anodized aluminum.

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Trace rare gases optical emission spectroscopy (TRG-OES) is a new, nonintrusive method for determining electron temperatures (T(e)) and, under some conditions, estimating electron densities (n(e)) in low-temperature, low-pressure plasmas. The method is based on a comparison of atomic emission intensities from trace amounts of rare gases (an equimixture of He, Ne, Ar, Kr, and Xe) added to the plasma, with intensities calculated from a model. For Maxwellian electron energy distribution functions (EEDFs), T(e) is determined from the best fit of theory to the experimental measurements. For non-Maxwellian EEDFs, T(e) derived from the best fit describes the high-energy tail of the EEDF. This method was reported previously, and was further developed and successfully applied to several laboratory and commercial plasma reactors. It has also been used in investigations of correlations between high-T(e) and plasma-induced damage to thin gate oxide layers. In this paper, we provide a refined mechanism for the method and include a detailed description of the generation of emission from the Paschen 2p manifold of rare gases both from the ground state and through metastable states, a theoretical model to calculate the number density of metastables (n(m)) of the rare gases, a practical procedure to compute T(e) from the ratios of experimental-to-theoretical intensity ratios, a way to determine the electron density (n(e)), a discussion of the range of sensitivity of TRG-OES to the EEDF, and an estimate of the accuracy of T(e). The values of T(e) obtained by TRG-OES in a transformer-coupled plasma reactor are compared with those obtained with a Langmuir probe for a wide range of pressures and powers. The differences in T(e) from the two methods are explained in terms of the EEDF dependence on pressure.

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Many children are at risk for developing serious and costly health problems because they are not adequately immunized. This descriptive correlational study explored the relationship between social support, parental knowledge of vaccine-preventable diseases, and the immunization status of preschool children. A convenience sample of 153 parents and guardians of children aged 6 to 24 months completed Procidano and Heller's Perceived Social Support Scales, a questionnaire on immunization knowledge, and a demographics questionnaire. Data indicating completeness of immunizations were obtained from the children's health records. Point-biserial statistical analysis revealed a positive relationship between immunization status and social support (r = .29; p = .0003). This finding supports those of past studies that identified a positive relationship between social support and preventive health practices. No relationship was found between immunization status and parental knowledge of vaccine-preventable diseases. Assessment of social support can assist nurses in identifying children at risk for incomplete immunizations and in isolating potential reasons for the deficiency.

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