Electron energy distributions in plasmas IV. Oxygen and nitrogen

Abstract

The Druyvesteyn method of measuring electron energy distributions in low pressure plasmas has been applied to cold-cathode direct current glow discharges in oxygen and nitrogen at pressures in the range 0.010 to 0.050 mm Hg. Two discharge modes occurred in both gases. Mass spectrometer measurements showed that in nitrogen only N 2 + was present but in oxygen the ions O - , O 2 - , O + , O 2 + , were all present. O - and O 2 + concentrations were about equal in magnitude and formed over 90 % of the ions present. Electron energy distributions in the positive column showed three groups in oxygen and nitrogen. The data available from the oxygen discharge are consistent with the lowest energy peak being a manifestation of a large negative ion concentration ( n - / n e = 20).

Laser induced photo-detachment of O2 in DC discharge

“…-In some oxygen plasmas, where mass spectroscopy and laser methods were applied, ratio of O O 2 --/ of 0.66 were found [30][31][32][33] with similar power dependency as those reported in the present work.…”

“…Recombination reaction between positive and negative ions O − +O 2 + →O 2 +O can also be of importance, considering the fact that detachment is the most significant loss process [30][31][32]…”

“…Nevertheless it was pointed out [35] that it is generally assumed, that the processes are similar in DC and RF, while it is recognized that different mechanisms do set the electron temperature, density and even the distribution of charged particles leading to serious differences in the obtained negative ions number densities. Also it was stated [30], that detachment processes on O( 3 p) atoms and a O 2 1 g D ( ) molecules strongly influence the discharge electrodynamics and determine the electric field in a wide range of the pL parameters, where p is the pressure and L is the reactor electrodes separation in [33]. Equally [39] indicated the importance of detachment in oxygen plasma in a comparable range of pressure and reactor plate separation.…”

Desarrollo de superficies nanoestructuradas para biosensores ópticos y sensores biomiméticos

“…181 Normalmente existe una proporción muy superior de iones moleculares respecto a iones atómicos (aproximadamente 30:1). 182 Además, los iones positivos predominan debido a que los negativos son más pesados y existen en bajas concentraciones con respecto a los electrones, por lo que normalmente quedan confinados a la región del plasma, teniendo un efecto muy pequeño sobre la superficie de reacción. Sin embargo, la composición y distribución de las especies químicas generadas a partir de moléculas diatómicas de oxígeno son tan complejas que el grado de disociación puede variar desde una pequeña fracción hasta el 20%, dependiendo de la potencia y de la presión.…”