Spatial distributions of neutral radicals CH3 and CH2 in a capacitively coupled rf glow discharge of methane were measured by threshold ionization mass spectrometry. A strong asymmetry of the density profile was found for the CH2 radical in the high-pressure (∼100 mTorr) discharge. In addition, comprehensive measurements of electron energy distribution, ionic composition, and radical sticking coefficient were made to use as inputs to theoretical modeling of radicals in the methane plasma. The model predictions agree substantially with the measured radical distributions.

The absolute cross sections for electron-impact dissociation of octafluoro-cyclobutane (C4F8) into the neutral radicals CF, CF2, CF3 and C3F5 are measured from the threshold to 250 eV. This measurement was accomplished by appearance mass spectrometry in a dual electron beam device. The threshold energies for the neutral dissociation into CF, CF2 and CF3 are 14.5, 10.5 and 12.8 eV, respectively. The cross sections for dissociation from C4F8 into CF2 and CF are much larger than those from CF4. Besides the neutral dissociation, the cross sections for the dissociative ionization of C4F8 are extensively measured for formation of CF+, CF2 +, CF3 +, C2F3 +, C2F4 + and C3F5 +.

Neutral CH3 radicals in a capacitively coupled rf discharge in methane have been detected with a quadrupole mass spectrometer utilizing a threshold ionization technique. The absolute density of CH3 radicals was measured at pressures from 0.5 to 20 mTorr, together with the ionic composition of the methane plasma. The principal ionic species were CH+5 and C2H+5 , except in the low-pressure region, suggesting the importance of ion-molecule reactions in the plasma. The lifetime of CH3 radicals in the afterglow of pulsed rf discharges was measured and explained in terms of the recombination reaction CH3 +CH3 →C2 H6.

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Microwave bubble plasma in water is a novel plasma applicable to the processing of materials in liquid. An electromagnetic simulation of slot excitation of microwaves reveals that the electric field at a slot antenna is significantly influenced by the size of the bubble existing in front of the antenna. To improve the power efficiency and the plasma stability, a bubble control plate is installed adjacent to the antenna, the effect of which on the electric field enhancement is confirmed in the simulation. Furthermore, three slot antennas are newly developed. According to these modifications of the microwave excitation system, a dramatic increase in the decomposition efficiency of an organic solute by a factor of 20 is found in the experiment.

The electron energy dependence of partial cross sections for dissociation of methane into CH3 and CH2 radicals has been reported in part I of this paper. In order to assign absolute values to these relative cross sections, two additional experiments were carried out. One was cross-section measurement for electron-impact nitrogen dissociation (N2→N+N, N+N+) using threshold-ionization mass spectrometry. The other was the measurement of sticking coefficients of CH3, CH2, and atomic nitrogen. According to these measurements, the absolute partial cross sections for neutral dissociation were determined: maximum cross section is 1.4×10-20 m2 at 24 eV for CH3 radical and 0.72×10-20 m2 at 18 eV for CH2 radical.

The abundances of primary neutral radicals CH3 and CH2 resulting from electron-impact dissociation of methane have been measured. This was accomplished with threshold-ionization mass spectrometry in a differentially pumped dual-electron-beam device. The relative partial cross sections for dissociation into CH3 and CH2 are reported for electron energies between 10 and 100 eV. A maximum cross section is found at 20-30 eV for both CH3 and CH2 radicals. At higher energies, the cross section decreases rather sharply, in particular for dissociation into the CH2 radical.

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