Processing of dust particles

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Processing of dust particles in low-pressure
plasmas   G. Paeva, R.P. Dahiya, E. Stoffels,
W.W. Stoffels, G.M.W. Kroesen, Department of
Physics, Eindhoven University of Technology, PO
Box 513, 5600 MB Eindhoven on leave from
Centre for Energy Studies, Indian Institute of
Technology, New Delhi - 110016, India. E-mail
w.w.stoffels_at_tue.nl web page www.phys.tue.nl/EPG/
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SETUP
A schematic view of the setup. Particles are
injected and trapped in the RF plasma. Coating is
performed using a magnetron sputter source at the
top. For the void formation experiment the
magnetron is replaced by a camera.
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Left The fluorescent spectrum of the BAM
particles in an Ar plasma. The fluorescence is
induced by the UV radiation from the
plasma. Right Optical spectrum during Cu coating
process in Ar using an external Hg lamp as a
light source. The broad band reflects the BAM
fluorescence from uncoated particles.
Simultaneously, Hg-lines are visible due to Mie
scattering.
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• Time dependence of scattering and fluorescence
  signal.
• The scattering signal reflects particle density.
• The fluorescence signal reflects uncoated
  particle surface.
• The faster decay of the fluorescence indicates
  particle coating.

• ProblemThere is some decrease in the
  fluorescence from the BAM particles even in pure
  Argon plasma. Probably due to VUV degradation of
  the BAM particles.
• ?Calibration in Ar needed
• ?Other fluorescent particles

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Particles coated with sputtered aluminium.
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2-D VOID FORMATION
(left) crystalline structure and (right) 7mm
diameter void in the dust cloud in RF plasma
sheath. Ring electrode (30 mm diameter) is
visible on the periphery. The pictures of 9.8 ?m
diameter MF are recorded by camera looking from
the top of the experimental system, which is
normal to the page.
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VOID EVOLUTION IN ARGON
Left Inner (ID) and outer diameter (OD) of
particle ring in argon RF plasma sheath and the
position of a single bigger size particle at
lower horizontal plane (right hand scale). Right
Surface of the particle cloud
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VOID EVOLUTION IN ARGON / OXYGEN
Variation of the void size (left) and cloud
surface(right) as a function of oxygen percentage
in Argon Oxygen mixture for RF power 40 W and
P 0.18 mbar. The void can be closed by adding
oxygen.
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• CONCLUSIONS
• Processing
• Particles can be trapped in an RF plasma and
  simultaneously coated by magnetron sputtering.
• Coating process is monitored using fluorescent
  particles.
• 2-D Void formation
• In 2-D Coulomb crystals voids can be created
  similarly to 3-D voids observed in micro gravity
  conditions.
• The driving force for void formation seems to be
  the ion drag force.
• Void diameter depends on plasma conditions
  (pressure, power).
• The void can be closed by using electronegative
  gases