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Abstract A dust particle immersed in a glow-discharge plasma has long been known to have a charge that isnegative, while the plasma is powered. However, in the afterglow, following the stopping of the plasma power, a largepositivecharge can collect on the particle, as was shown recently for particles in a cathodic sheath. While that outcome of positive charging in the afterglow may be common, an experimental discovery reported here reveals that the opposite outcome is also possible: a particle can develop anegativecharge in the afterglow, if the plasma had previously been operated with a modulated power. Before stopping the plasma power off altogether, in a run with power modulated at a low duty cycle of 4.5 , the particle’s residual charge was negative, but it was positive in a control run without modulation. This result points to a way of controlling the charge of dust particles in a decaying plasma, which can be useful for mitigating defects in semiconductor manufacturing.
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Controlling the charge of dust particles in a plasma afterglow by timed switching of an electrode voltage
Abstract A method is demonstrated for controlling the charge of a dust particle in a plasma afterglow, allowing a wider range of outcomes than an earlier method. As in the earlier method, the dust particles are located near an electrode that has a DC voltage during the afterglow. Here, that DC voltage is switched to a positive value at a specified delay time, instead of maintaining a constant negative voltage as in the earlier method. Adjusting the timing of this switching allows one to control the residual charge gradually over a wide range that includes both negative and positive values of charge. For comparison, only positive residual charges were attained in the earlier method. We were able to adjust the residual charge from about −2000 eto +10 000 e, for our experimental parameters (8.35 µm particles, 8 mTorr argon pressure, and a DC voltage that was switched from −150 V to +125 V within the first two milliseconds of the afterglow). The plasma conditions near the dust particles changed from ion-rich to electron-rich, when the electrode was switched from cathodic to anodic. Making this change at a specified time, as the electrons and ions decay in the afterglow, provides this control capability. These results also give insight into the time development of a dust particle’s charge in the afterglow, on a sub-millisecond time scale.
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- Award ID(s):
- 1740379
- PAR ID:
- 10422196
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Journal of Physics D: Applied Physics
- Volume:
- 56
- Issue:
- 37
- ISSN:
- 0022-3727
- Page Range / eLocation ID:
- Article No. 375202
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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