Excimer emission from cathode boundary layer discharges

Abstract

The excimer emission from direct current glow discharges between a planar cathode and a ring-shaped anode of 0.75 and 1.5 mm diameter, respectively, separated by a gap of 250 m, was studied in xenon and argon in a pressure range from 75 to 760 Torr. The thickness of the ''cathode boundary layer'' plasma, in the 100 m range, and a discharge sustaining voltage of approximately 200 V, indicates that the discharge is restricted to the cathode fall and the negative glow. The radiant excimer emittance at 172 nm increases with pressure and reaches a value of 4 W/cm 2 for atmospheric pressure operation in xenon. The maximum internal efficiency, however, decreases with pressure having highest values of 5% for 75 Torr operation. When the discharge current is reduced below a critical value, the discharge in xenon changes from an abnormal glow into a mode showing self-organization of the plasma. Also, the excimer spectrum changes from one with about equal contributions from the first and second continuum to one that is dominated by the second continuum emission. The xenon excimer emission intensity peaks at this discharge mode transition. In the case of argon, self-organization of the plasma was not seen, but the emission of the excimer radiation ͑128 nm͒ again shows a maximum at the transition from abnormal to normal glow. As was observed with xenon, the radiant emittance of argon increases with pressure, and the efficiency decreases. The maximum radiant emittance is 1.6 W/cm 2 for argon at 600 Torr. The maximum internal efficiency is 2.5% at 200 Torr. The positive slope of the current-voltage characteristics at maximum excimer emission in both cases indicates the possibility of generating intense, large area, flat excimer lamps.

Microdischarges for use as microthrusters: modelling and scaling

“…They are being investigated for possible use as, for example, excimer lighting sources [6], hydrogen production [7,8] and diamond deposition [9]. Radio frequency (rf) excited MDs are also being studied for use in lighting and surface modification [10][11][12].…”

“…MDs based on cathode boundary layer [6] or hollowcathode excitation [7,8] leverage pd (pressure × distance) scaling to operate as dc discharges at pressures of hundreds of Torr to 1 atm and characteristic dimensions of tens to hundreds of micrometres. They are being investigated for possible use as, for example, excimer lighting sources [6], hydrogen production [7,8] and diamond deposition [9].…”

Modelling cathode spots in glow discharges in the cathode boundary layer geometry

“…A range of experimental reports have since been published [1][2][3][4][5][6][7][8][9][10]. Modelling of the phenomenon [9,[11][12][13][14][15] has revealed, in agreement with the general theory of cathode spots and patterns in arc and DC glow discharges [16], the existence of multiple steady-state solutions for a given value of discharge current, which comprise modes of current transfer associated with different cathode spot patterns.…”

“…The vast majority of the experiments [1][2][3][4][5][6][7][8][9][10] have been performed in a discharge device comprising a flat cathode and a ring-shaped anode, separated by a dielectric (cf., e.g., figure 1 of [10]); this discharge configuration is called cathode boundary layer discharge (CBLD) by the authors of the experiment. However, the modelling has been performed up to date for discharges with parallel-plane electrodes only [9,[11][12][13][14][15].…”

Microplasmas: A Review

“…(1) shows the typical configuration of a CBL discharge [29][30][31]. It is a DC glow discharge and consists of a planar cathode and a ring-shaped anode.…”