Mechanisms of Dust Formation and Growth in a Complex Plasma Blake Churton Supervised by Lénaïc Couëdel and Dr Alex Samarian

Plasma A plasma is a state of matter in which atoms are partially ionised.

Complex Plasma A complex plasma has an additional component, dust. This dust may be injected into the plasma or may be grown inside the chamber.

Discharge Chamber This is a Capacitively Coupled Radio Frequency Sputtering Discharge

Discharge chamber

Dust Formation 1.Chemically Active Discharge: Nucleation, Coagulation and Accretion. 2.Sputtering Discharge: Current research suggests the mechanisms are similar.

Sputtering High speed ions accelerated by the electric field impact the electrodes causing parts to be ejected. The electrodes may be covered to sputter this covering instead, in my experiment it is Melamine Formaldehyde powder that is sputtered.

L. Boufendi and A. Bouchoule “Particle Nucleation and Growth in a low Pressure Argon-Silane Discharge” Plasma Sources Sci. Technol. 3 (1994) Chemically Active PlasmaSputtering Plasma D. Samsonov and J. Goree Redone based on: “Particle growth in a sputtering discharge”, J. Vac. Sci. Technol.

Techniques Electrode Self Bias From Cavarroc et al 2006 it is know that the self bias increases (more positive) when there is dust in the chamber. It further increases as the dust grows. Scanning Electron Microscopy Discharge run for different lengths of time to measure the size for a given position on the self bias graph. Figure 7 “Self-excited instability occurring during the nanoparticle formation in an Ar–SiH4 low pressure radio frequency plasma” M. Cavarroc, M. C. Jouanny, K. Radouane, M.Mikikian, and L. Boufendi © J. Appl. Phys. 99, (2006)

Aim of Project Overall project: Study the Mechanisms of Dust growth. My part: Find a correlation between the electrode self bias and dust growth. Future Work: This can be used to match the timing of the dust growth to the laser extinction.

Typical display for a long discharge run Time (Seconds) Data point every 0.01 seconds Input Voltage Arbitrary Scale Display shows the last 50 seconds of input Electrode Self Bias

Scanning Electron Microscopy Sample Point

Scanning Electron Microscopy Sample Point

Scanning Electron Microscopy Sample Point 3 050

Scanning Electron Microscopy Sample Point 4 Greater than 2 minutes.

Conclusions Whilst the particles are small, about 20nm, they do not affect the self bias greatly. When they start to coagulate the self bias increases rapidly, near vertically. Once coagulation ends the self bias stabilises to a new higher value. Self bias continues to increase slowly as the dust grows.

Conclusion ~20nm ~300nm ~30nm ~300nm ~100nm

These are the various instruments I needed to learn how to use to complete my project.

Plasma

Dust Formation in a Chemically Active Plasma Image from L. Boufendi and A. Bouchoule in their article: “Particle Nucleation and Growth in a low Pressure Argon-Silane Discharge” Plasma Sources Sci. Technol. 3 (1994) Nucleation, Coagulation and Accretion.

Dust formation in a sputtering discharge D. Samsonov and J. Goree studied graphite particle formation. Their work is only preliminary and further research is required. Redone based on: “Particle growth in a sputtering discharge”, J. Vac. Sci. Technol.

Sample Point 2