PIIM, UMR 6633 CNRS - Aix-Marseille Université
GROWTH OF CARBONACEOUS NANOPARTICLES IN A GLOW DISCHARGE A. Mouberi1, C. Arnas1, X. Bonnin2 UMR 6633 CNRS- Aix Marseille Université, 13331 Marseille, France 2 LIMHP, UPR 1311 CNRS, Université Paris 13 - Institut Galilée, 93430 Villetaneuse, France 1 LPIIM,
Object: To understand the growth mechanisms of carbonaceous nanoparticles in plasma from graphite target sputtering
Experimental setup 1
Formation mechanism of carbonaceous nanoparticles
Par= 0.6 mbar - Cathode sputtering by Ar+ ions and fast charge-exchange Ar atoms.
ID= 80 mA (constant)
- Carbon cathode sputtering : C, C2, C3 injection, sputtering threshold ~70 eV 1.
VD= - 600 V 6
- Thermalization with gas atoms : d = 6 mm from cathode with Tg ~ 100 °C
• Optical spectroscopy
- Condensation : formation of Cn clusters.
• Laser extinction and
- Coagulation : formation of solid particles of nanometric size by cluster collisions
4
2
diffusion
5
3 1- Thermocouple
4- Glass tube
Vacuum pump
5- Nanoparticules collector 6- Graphite cathode
Description of agglomeration Two successive agglomeration processes: 1) Agglomeration of nuclei of 2-3 nm size which leads to the formation of nanoparticles of 8 -15 nm . 2)These later also agglomerate to form bigger particles. Charge fluctuations SEM Image @ 180 s 8 nm 1)
2)
48 nm
0.4 Charge (e)
Charge distribution (a.u.)
3- Anode
1
Charging mechanism
Np/Ni = 0.01 Te = 3eV, Tg = Ti = 400 K
0.2 0 50 Siz
40 e (n
30 m)
20
10
0 -60 -50
-40
-10 -30 -20
0
e) r ge ( Cha
50 40 30 20 10 0 0.1 0.08 Ra 0.06 tio N / 0.040.02 p N
0
50 60 30 40 10 20ize (nm) S
0
0.02 0 0.1 R0.08 ati0.06 o N 0.04 p /N 0.02
b)
0.25
0.4
Size frequency (a.u.)
Size frequency (a.u.)
Size (nm)
0.04
50 30 40
10 20
m)
Size histograms 1s 30 s 90 s
0.5
0.2
0.1
0.05
0.1 0 0
180 s 540s
0.2
0.15
0.3
a)
10
20
30
40
50
Size (nm)
60
70
0 0
80
10 20 30 40 50 60 70 80 90 100
Size (nm)
a) Growth by agglomeration and carbonaceous clusters deposition : growth rate ~ 13 nm/min2. b) Growth by clusters deposition : growth rate ~ 2,3 nm/min. - Size histograms are fitted by log normal distributions
Discharge duration (s)
Characteristics of discharge
b) Optical spectroscopy
10
2V0/dc
10
NG 4) 3)
FDS
PC
e-
VD Ratio
Ar+
800,6 nm/763,5nm 2) C2 516,5 nm dc / NG : Negative glow / FDS : Faraday dark space / PC : Positive column S : Sheath 3 1)Trapped electrons , 2) Electric field reversal : electric field is confining charging of nanoparticles , 3) Ions acceleration, 4) Electron acceleration .
Prospects Determination of plasma parameters, localization of nanoparticles in discharge, to improve calculation of charge mechanism by regarding the charge and size as discrete variables.
6 0
10
8
6
15
20
growth law 0
4
10
15
20
4 2 0
2
ID = 80 mA, PAr = 0,6 mbar 100
200
300
400
500
600
0 -3
100
3 x 10
200 3
x 10
-3
300
400
500
600
2.5
2.5
Intensity (ua)
- Modification of lines intensity emitted by plasma : modification of plasma parameters + important injection of carbon in plasma during ~1s Formation of primary particles. -Increase in intensity of lines Reduction of line trapping by the plasma Reduction in the lifespan of level Overpopulation of level 3p54s Emission of radiation by transfer excitation4. - Absorption of radiation by nanoparticles . Competition between absorption by nanoparticles and emission by radiation trapping.
ID = 10 mA, PAr = 1 mbar
5
8
2
0.1
0.1
1.5
2 0.05
1
1.5
0.05 0 12
0
100
200
Voltage (V)
Ar*r 800,6 nm
5
Voltage (V)
Intensity (ua)
1)
8
10
Ar*m 763,5 nm
S
V ,E
0.06
(n i 0 0 Size - Charge distribution equation : - The first four terms represent the rate of change due to the acquisition or the loss of a unit elementary charge and size. The term Pq represents the production rate of charge q particles and the last term accounts for other losses. - Model: charge and size are treated like continuous variables to facilitate calculations5. - The small particles (1-5 nm) have a given probability to be positively charged whereas the largest ones have always a negative charge the agglomeration mechanism by Coulomb attraction. - When dust reaches a critical diameter, its charge becomes negative and it collects less electrons : charge saturation. However, when Np/Ni~ 0, the charge evolves linearly dust explosion. - Charges of small dust fluctuate quickly: small dust is the source of agglomeration. The load of large dust does not fluctuate. i
Growth law
a) Region of glow discharge
Charge time fluctuation (s)
2- Langmuir probe
14
300
16
18
400
Discharge duration (s)
20
500
10
15
20
1
600
0
100
200
300
400
500
Discharge duration (s)
References: [1] C. Dominique and C. Arnas, J. Appl. Phys. 101, 123304 (2007) [2] C. Arnas, A. Mouberi, K. Hassouni, A. Michau, G. Lombardi, X. Bonnin, F. Bénédic and B. Pégourié, J. Nucl. Mater. 390-391, 140 (2009) [3] V. I. Kolobov and L. D. Tsendin, Phys. Rev. A 46 7837 (1992) [4] Methods of experimental physics, volume 7 part A: Atomic and electron physics (1968) [5] B. F. Gordiet and M. Ferreira, J. Appl. Phys. 84, 1231 (1998)
600
