S. Abolmasov

Physics and engineering of crossed-field discharge devices

The physics of devices such as the Penning cell, anode layer ion source, and cylindrical and planar magnetrons is reviewed, with particular emphasis on new developments in the field. These crossed-field discharge devices are specially designed to operate at gas pressures below 10?2?Torr which makes them attractive for a wide range of applications. Due to effective electron confinement in crossed electric and magnetic fields some of these devices (e.g. inverted magnetron) can even run at pressures as low as 10?10?Torr. At such low pressures the electron confinement time is much longer than the ion transit time so that the discharge is practically pure electron plasma. The review covers not only the physics of the discharges themselves, but also their interactions with electromagnetic fields. The latter allow additional control over the discharge parameters. Important historical steps in development of E???B discharge devices as well as their characteristics and differences are described and some possible future research directions are discussed.

Probing dusty-plasma/surface interactions with a heat flux microsensor

Heat flux microsensor—a thermopile with millisecond response time—was employed for direct measurements of total energy flux to a floated surface in a dusty rf discharge. The measurements were performed in silane-hydrogen plasmas at discharge conditions close to those used for the growth of polymorphous silicon films. At rf power between 10 and 50 W, the measured energy flux was in the range of 20-250 mW/cm2. Due to fast time response, the thermopile was also capable of tracing the dynamics of nanoparticle growth. A significant decrease (about 30%) in the energy flux was observed during the agglomeration phase.

Negative corona discharge: application to nanoparticle detection in rf reactors

Negative corona discharges have been studied for their possible use to detect nanoparticles in capacitively coupled plasma (CCP) reactors. Silicon nanoparticles (below 20 nm in diameter) were produced in a pulsed CCP discharge in a silane–argon–hydrogen mixture. An emissive probe with a tungsten filament biased to a sufficient negative potential (in the range 350–450 V) was used to create a negative corona in the postplasma regime when the rf power was switched off. Due to surface contamination, the probe was operated in the regime of weak electron emission to allow stable operation. Nevertheless, the filament temperature was high enough for nanoparticle deceleration/acceleration by induced thermophoretic force. It appears that positively charged nanoparticles decelerated near the filament can switch the negative corona from a pulsed (subnormal) discharge mode into a normal glow discharge mode. Hence the negative corona may have potential for detecting nanoparticles in CCP reactors operating in silane-containing mixtures.

Strong visible and near-infrared electroluminescence and formation process in Si-rich polymorphous silicon carbon

We report here a strong and stable electroluminescence (EL) from Si-rich hydrogenated polymorphous silicon carbon thin films (pm-Si1-xCx : H) fabricated in a plasma-enhanced chemical vapor deposition system. We investigate an unusual forming process in the pm-Si1-xCx : H thin films, during initial EL stressing, and propose a current-stress-induced phase separation process for the formation of new Si nanoclusters, which give rise to strongly enhanced emissions in both visible and near infrared ranges at 1.8–2.1 eV and 0.8–1.2 eV, respectively. The sub-crystalline-Si-bandgap emission is particularly attractive to realize a Si-based multi-band light source for optical interconnection and telecommunication.

Negative corona in silane-argon-hydrogen mixtures at low pressures

Current pulses have been measured in negative corona discharges in argon‐hydrogen and silane‐argon‐hydrogen mixtures near the Paschen minimum. It was found that the current pulses appear only on the right branch of the Paschen curve and have shapes similar to those of subnormal oscillations in dc discharges between parallel‐plane electrodes. The effects of gas temperature and negative ions on the current pulse shape and size are examined. It appears that a small admixture of silane into an argon‐hydrogen discharge results in a more pronounced ion‐ion phase and doubles the pulse repetition frequency, while an increase in gas temperature acts in exactly the opposite way. The implications of these results on theories of current pulse formation are discussed.