No abstract

A model is presented of the positive column of a dc glow discharge in argon with small admixtures of hexamethyldisiloxane (HMDS). The axial electric field, the ion production rates for direct-, stepwise-, pair-, and Penning ionization, the densities of metastable Ar atoms and of electrons, and the wall current of HMDS ions are calculated in dependence on HMDS admixture and discharge current density. For the calculations particle balance equations were used for a diffusion determined plasma in a mixture of two gaseous components. The reaction rates for the electron collision processes were determined applying the electron distribution function calculated for pure argon. Taking into account PENNING ionization of HMDS molecules by metastable argon atoms the decrease of electric field for increasing HMDS admixtures is according to the experimentally measured values. Also ion wall currents and electron densities are compared with experimental values for thin film formation rate and results of probe measurements.

The time-averaged probe current is calculated by using a sampling method for sinusoidal and sawtooth-like oscillations of the space potential. The effect of oscillations on the meiisured plasma parameters obtained with the aid of the single probe method, double probe method and the method of the second derivative of the p r o b characteristic is discuseed, with the electronsaturation current being taken into account. In the ion current the values rp/AD, A]rp and MI characterizing the working regime are varied. The cnlcnlated results are checked by corresponding measurements in a beam generated plasma. 1.Probe measurements in plasmas with oscillations and waves where time-resolved meeaurements are not practicable. 2. RF-dischargea. Here the plasma parameters are subjected to sinusoidal oscillations of the same frequency as that of the generating rf-field and the probe current receives a component produced by the rf-field. 3. Heated probes. If the probe is heated by a direct current in order to ensure a homogeneous w?rk function or to obtain an emitting probe characteristic [S], the heating voltage drop amounts to double the value of the amplitude of a sawtooth voltage superposing the probe potential. 4. Inhomogeneities of work function [7]. The influence of the inhomogeneity of the work function (e.g. caused by contamination) on the measured plasma parameters can i i = ii = Sniedc(kT,/Mi)ll*, dc = 1.22, cf. [ll],

The influence of the beam energy and beam current density on the parameters of the plasma is investigated. The efficiency of carrier generation by collective interactions (Langmuir-oscillations) is compared with that by the single collision mechanism. The additional negative charging of the static probe caused by the beam electrons is used for the determination of the beam electron density. , IntroductionAboiit 15 or 20 pears ago the beam generated plasma got importance as a means of generating high frequency oscillations. Another interesting feature of this plasma is the possibility of plasma heating by the beam plasma interaction. For about 5 years attempts have been made to use the anisothermal plasma produced by passing an electron beam through a working gas for substance transformation.The construction and modes of operation of the plasmachemical reactor "MINI-PLAST", used in our experiments, are described in [l]. As working gases we used air and argon. Our paper deals with the spatial distribution of such parameters as plasma potential, mean energy of plasma electrons, number density and energy distribution of the electron gas. From this, statements are to be deduce .-about the range of existence of a working regime favourable to the beam plasma energy input, -about the relations between beam intensiby and plasma properties, and between number density of plasma elect.rons and number density of beam electrons,-about the efficiency of carrier generation by collective interactions as compared to the single ionization by collisions and -about the comparison between inert gas and molecular gas concerning the energy capacity of the electron component of the plasma for argon and air respectively.Several probe techniques were used in our investigations. The systematic error of results and the influence of the weak magnetic field existing in the reactor on the probe characteristic and its 2nd derivative are discussed. fj Beitr. P!asmsphys., Bd. 32, H. 2

Probe measurements were carried out in the positive column of an argon glow discharge in a flow system wit& different admixtures of hexamethyldisiloxane (HMDS). From, this the mean electron energy U,, number density n, and gradient E were determined. Some results concerning the predominant ionization mechanism and the ion distribution in the gas phase could be obtained.By means of probes i t is also possible to get some information about the deposition mechanism in polymerizing plasmas.