1. 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@tue.nl web page www.phys.tue.nl/EPG/w.w.stoffels@tue.nl

2. RF electrode Trapping ring Magnetron sputter head Particle cloud Light source Manipulator arm with particle sieve 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. SETUP

3. 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. 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.

4. Problem:There 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 Problem:There 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 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. 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.

5. Particles coated with sputtered aluminium.

6. (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. 2-D VOID FORMATION

7. 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 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 VOID EVOLUTION IN ARGON

8. 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. 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.

9. 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 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