laser-induced particle formation in a methane discharge eva stoffels, winfred stoffels, eindhoven...
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![Page 1: Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven](https://reader036.vdocuments.us/reader036/viewer/2022062421/56649d815503460f94a66c82/html5/thumbnails/1.jpg)
Laser-induced particle formation in a methane discharge
Eva Stoffels, Winfred Stoffels,
Eindhoven University of Technology,
PO Box 513, 5600 MB Eindhoven.
Giacomo Ceccone, Francois Rossi,
European Commission, Joint Research Center,
Ispra (VA), Italy.
![Page 2: Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven](https://reader036.vdocuments.us/reader036/viewer/2022062421/56649d815503460f94a66c82/html5/thumbnails/2.jpg)
• CH4 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 90o by photo-camera
Experimental setup
![Page 3: Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven](https://reader036.vdocuments.us/reader036/viewer/2022062421/56649d815503460f94a66c82/html5/thumbnails/3.jpg)
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250 450 650 850
power (mW)
time
(s)
Appearance of particles as a function of laser power
•Laser photon energy (ca. 3.5 eV) matches the bond energy of CH4.
•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
![Page 4: Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven](https://reader036.vdocuments.us/reader036/viewer/2022062421/56649d815503460f94a66c82/html5/thumbnails/4.jpg)
500 nm
SEM micrograph of particles
After nucleation, nanoparticles grow in the plasma until they reach a size of 100 nm.
![Page 5: Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven](https://reader036.vdocuments.us/reader036/viewer/2022062421/56649d815503460f94a66c82/html5/thumbnails/5.jpg)
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.
![Page 6: Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven](https://reader036.vdocuments.us/reader036/viewer/2022062421/56649d815503460f94a66c82/html5/thumbnails/6.jpg)
0.2 mm
SEM x2000 Optical microscope x7510 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
![Page 7: Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven](https://reader036.vdocuments.us/reader036/viewer/2022062421/56649d815503460f94a66c82/html5/thumbnails/7.jpg)
V-shape structures floating in plasma
1 cm
![Page 8: Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven](https://reader036.vdocuments.us/reader036/viewer/2022062421/56649d815503460f94a66c82/html5/thumbnails/8.jpg)
Forces on a single particle and on V-shaped conglomerate
Charge on a single particle of size a:
Ze = 40 a Vp, mass M = 4/3a
Charge on a linear string of N particles with size a:
Ze = 40 a Vp N/ln(4N), mass M = 4/3a
![Page 9: Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven](https://reader036.vdocuments.us/reader036/viewer/2022062421/56649d815503460f94a66c82/html5/thumbnails/9.jpg)
1 cm
Floating network above wafer
0.1 mmCoulomb 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.
![Page 10: Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven](https://reader036.vdocuments.us/reader036/viewer/2022062421/56649d815503460f94a66c82/html5/thumbnails/10.jpg)
SEM x50 Light microscope x50
0.5 mm 0.5 mm
Structure of floating network
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Growth on electrode
5 mmEventually, floating network collapses and deposits on the electrode.
![Page 12: Laser-induced particle formation in a methane discharge Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven](https://reader036.vdocuments.us/reader036/viewer/2022062421/56649d815503460f94a66c82/html5/thumbnails/12.jpg)
Overview of all phases