1. Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven. stoffels@discharge.phys.tue.nl Giacomo Ceccone, Francois Rossi, European Commission, Joint Research Center, Ispra (VA), Italy.

2. CH 4 radio-frequency plasma for diamond deposition pressure 0.2 - 1 Torr 3rd harm. Nd:YAG laser ( = 355 nm), 8 ns pulse, 10 Hz repetition frequency detection at 90 o by photo- camera Experimental setup

3. Appearance of particles as a function of laser power Laser photon energy (ca. 3.5 eV) matches the bond energy of CH 4. High radical densities are created locally by photodissociation. Nanoparticles (<10 nm) are nucleated. Nanoparticles are detected by the same laser, due to their fluorescence upon laser irradiation Time needed to nucleate carbon nanoparticles during laser irradiation, as a function of laser power

4. 500 nm SEM micrograph of particles After nucleation, nanoparticles grow in the plasma until they reach a size of 100 nm.

5. Coulomb crystal formation Formation of vertical strings First organised structures 100 nm particles have a permanent negative charge. Coulomb interactions lead to formation of organised structures.

6. 0.2 mm SEM x2000Optical microscope x75 10  m Vertical strings In the plasma-sheath transition electric fields are present Charged particles gain kinetic energy of about 1 eV, enough to overcome Coulomb repulsion Particle coalescence takes place

7. V-shape structures floating in plasma 1 cm

8. Forces on a single particle and on V-shaped conglomerate Charge on a single particle of size a: Ze = 4  0 a V p,mass M = 4/3  a   Charge on a linear string of N particles with size a: Ze = 4  0 a V p N/ln(4N), mass M = 4/3  a  

9. 1 cm Floating network above wafer 0.1 mm Coulomb repulsion Large structures in the plasma Deposited conglomerates Both charge and mass of a string increase with the string size N. Coulomb and gravitation forces remain balanced. Large strings are still floating.

10. SEM x50Light microscope x50 0.5 mm Structure of floating network

11. Growth on electrode 5 mm Eventually, floating network collapses and deposits on the electrode.

12. Overview of all phases