Presentation is loading. Please wait.

Presentation is loading. Please wait.

Alex.A. Samarian and Brian.W. James School of Physics, University of Sydney, NSW 2006, Australia Sheath edge location The charge of dust particles in sheath.

Similar presentations


Presentation on theme: "Alex.A. Samarian and Brian.W. James School of Physics, University of Sydney, NSW 2006, Australia Sheath edge location The charge of dust particles in sheath."— Presentation transcript:

1 Alex.A. Samarian and Brian.W. James School of Physics, University of Sydney, NSW 2006, Australia Sheath edge location The charge of dust particles in sheath region Dust Motion in rf-Discharge Plasma

2 2 Sheath model Different features of the sheath and plasma areas Sheath edge location is one of the most important parameters in many sheath models Plasma Sheath Electrode n e (z) n i (z)  (z) zeze zbzb Cross section of sheath in z-dir perpendicular to electrode E(z)

3 3 Charging of dust particle Ion and electron fluxes a) electrons b) ions

4 4 Equilibrium of dust particles F Gr av F El ec F Ion Drag F Thermoph oretic F Neut Drag Force Diagram F Grav F Elec F Ion Drag F Thermophoretic F Neut Drag Force Diagram Temperature Gradient Temperature Gradient Neutral Flux is the screening length Where and z Electric Field Gradient Electric Field Gradient Ion Flux

5 5  (z) E(z) zeze zbzb Electrode Plasma Sheath for  i =10 7 s -1 for  i = 5x10 6 s -1 for  i = 10 6 s -1 Normalised difference between grain equilibrium position & sheath edge position as a function of grain radius for different values of ion plasma frequency  

6 6 Front View Experimental setup

7 7 Back View Experimental setup

8 8 Experimental Setup Experimental chamber and image of test dust particles levitated above the electrode The test grains are generated in the discharge (power up to 200W, pressure up to 1 torr) by electrode sputtering.

9 9 Main parameters RF discharge 15 MHz Pressure from 10 to 400 mTorr Input power from 15 to 200 W Self-bias voltage from 5 to 180V Carbon (C) particles’ diameter ~ 1 μm Melamine formaldehyde μm ± 0.06 μm Melamine formaldehyde μm ± 0.10 μm Argon plasma T e ~ 2 eV, V p =50 V & n e ~ 10 9 cm -3

10 10 Result of Measurements Measured electron temperature T e (points with error bars) and discharge emission I (solid line) for P = 90m Torr, W = 80 W. The dashed line shows the equilibrium position (h eq =10.8 mm) of test grains (a~350 nm). Rf-compensated single Langmuir probe Electron temperature T e Ocean optics spectrometer PC2000 discharge emission I

11 11 Result of Measurements Position of sheath edge (h b ) vs pressure at different rf-input powers – 35W – 60W – 100W

12 12 Result of Measurements Estimation of dust charge from vertical equilibrium hqhq E E eq h eq hbhb 2(V b -V p )/h b V(h)=h 2 V b /h b 2 +V p -V b E=2(V p -V b )(h b -h eq )/h b 2 Z d =2  a 3 h b 2 /3e (V p -V b )(h b -h eq ) Dust particle radius, (  m) Charge on dust particle (e) From vertical equilibrium From probe data x x x x x x10 4 hbhb

13 13 Summary Spatial location of sheath edge in planar rf- discharge has been determined using test dust grains. The diagnostic technique is based on measurement of the equilibrium position of fine (<500nm) dust grains levitated above the powered electrode of the rf-discharge. Using the resulting value of sheath dimension the charge on dust particles in the sheath region has been estimated.


Download ppt "Alex.A. Samarian and Brian.W. James School of Physics, University of Sydney, NSW 2006, Australia Sheath edge location The charge of dust particles in sheath."

Similar presentations


Ads by Google