F4280 Technologie depozice a povrchovych uprav:    7.3.2 Cold Atmospheric Pressure Discharges
ka Zajíčková
1 /18
7.3.2 Cold Atmospheric Pressure Discharges
Plate-to-plate configuration (a)_
Up to ± 30kV
High-voltage pulsed DC or AC or RF
Streamers
(b)
m uiei
T i
Dielectric
barrier ...... Plasma
(c) Substrate
—i——■:—*:—n—«:——i.   K \—^—T\
T
> >  í I i   -t   ■< <
> >  > i :<<<<<<<<<
:- :■ <  <  < < >   >   >   > 9
Plasma jet configuration HE
[
uW or RF
_f
I1!
Substrate
At low p, the collision frequency is low electron energies remain high compared to ion neutral energies    non-equilibrium (cold) plasma.
At high p, the collision frequency is high plasma tends to equilibrate temperatures formation of streamers (fast-moving ionization fronts in the form of filaments) - precursors of sparks (hot plasmas)
Suppression of sparks using:
► high-frequency AC fields or short-pulsed DC power
► dielectric barriers on AC electrodes
► high gas flow rates
► special electrode shapes with multiple structures
► suitable gas, e.g. He.
Tuner Dielectric
L. Bärdos, H. Baränkovä, Thin Solid Films
F4280 Technologie depozice a povrchových úprav:
Filamentary x Homogeneous AP-DBDs
ka Zajíčková
2/18
Atmospheric Pressure DBD (AP-DBD;
Two forms of dielectric barrier discharges (DBDs) with parallel plate electrodes:
► filamentary
► homogeneous
Stabilization of homogeneous DBDs requires suppression of filament formation.
Important role of
metal foil
U.V.
-----ľ
----I
silicone film
ceramics
metal mesh
0 0 35 329»
► structure and material of electrodes
e.g. M. Kogoma, S. Okazaki, JPD (1994) 27 1985
► higher frequencies of power supply
T. Nozaki et al., Plasma Process. Polym. (2008) 5 300)
► gas mixture (He, Ne, N2, Ar + NH3 etc.):
► homogeneous DBD in He, Ar/NH3 and N2
F. Massines et al. Surf. Coat. Technol. 174-175, 8 (2003); Plasma Phys. Controlled Fusion 47, B577 (2005).
► PECVD in HMDSO/N2 and HMDSO/N2/synthetic air mixtures
D. Trunecetal. J. Phys. D: Appl. Phys. 37 (2004) 2112; J. Phys. D: Appl. Phys. 43 (2010) 225403
► PECVD in Ar/C2H2
M. Elias etal. J. Appl. Phys. 117(10) (2015) 103301
F4280 Technologie depozice a povrchových úprav:    Filamentary x Homogeneous AP-DBDs Lenka Zajíčková 3/18
Homogeneous Dielectric Barrier Discharges
Two different forms of homogeneous discharges were classified by Massines et al. Both start with Townsend breakdown initiating a Townsend discharge but
► in He, during the current increase, the discharge transits to a glow discharge (ne « 1011) having a cathode fall and a positive column if gas gap is > 2 mm - atmospheric pressure glow discharge (APGD)
► in N2, the ionization level is too low (ne « 108) to allow formation of cathode fall and the glow regime cannot be achieved - atm. pressure Townsend discharge (APTD).
Visualisation of a Townsend Avalanche
Electric field
i Key
C    Ionisation even!
- ionising electron path
- Liberated electron path.
■---------
Anode
y	DC Voltage
i	Source
Original ionization event
Cathode
1000
800 -
>
tu 600 ■§ 400
1    1    1    .    .    1    1    1    1 1 Dark Discharge	1    1    1    1    1   11    1    1 1 Glow Discharge,    Arc -
1........	i .   . i
10
-15
-10
10"iU 10" Current (A)
101
C: avalanche Townsend discharge
► D: self-sustained Townsend discharges
► F: sub-normal glow discharge
► G: normal glow discharge
F4280 Technologie depozice a povrchových úprav:    Filamentary x Homogeneous AP-DBDs Lenka Zajíčková 4/18
Homogeneous DBD (APGD) in Ar/acetylene
filamentary DBD in Ar
filamentary DBD in Ar/CH4
homogeneous DBD in Ar/C2H2
(80 /is (one half-period) exposure time)
► difference caused by possibility of Penning ionization of C2H2 in Ar
► Ar 1 s5 metastable -11.55 eV,
C2H2 ionization potential 11.40eV butCH4 12.61 eV
>
>
>
0.3
0.1 0.2 t(ms)
(a) DBD in pure Ar, (b) DBD in Ar/( (c) APGD in Ar/C2H2
M. Eliáš etal., J. Appl. Phys. 117(10) (2015) 103301
F4280 Technologie depozice a povrchových úprav:
Filamentary x Homogeneous AP-DBDs
ka Zajíčková
5/18
Why to Use Homogeneous DBD for Deposition?
.. to eliminate unwanted surface structures and non-uniformities
D. Trunec, Z. Navrátil, P. Sťaheletal. J. Phys. D: Appl. Phys. 37(2004)2112:
deposition in APTD (HMDSO/N2) and in filamentary discharge
0 u,rti  0 |_im
H. Caquineauet. all Phys. D:Appl. Phys. 42(2009) 125201:
Local increased of the deposition rate, "deposition spots", due to non-uniform power dissipation in micro-filaments.
a deposition
2 deposition areas
F4280 Technologie depozice a povrchových úprav:    Filamentary x Homogeneous AP-DBDs Lenka Zajíčková 6/18
Why to Use Homogeneous DBD for Deposition?
modification of temperature sensitive and porous polymer nanofibers
Interesting novel material, polymer nanofibers, can be prepared by electrospinning but it requires further modification of surface properties (as usually with polymers)
Classical nozzle electrospinning:
Taylor «Ad
?.\v.nnh y Up
Cunvcttivc flow
-tiniriLtry rf-cünt k-tgoYLrriLd I by (he «L*C-frf iurÍBMlwitofi 1
tO.*lříEPM[aN£ fřfUliiOíi !
iLini- if Ir.irisiliftn hriivii.'ii
liquid and sol id
i
iLQW *ÍCELEfl*TIOřr
RflPIDflCCELEPATION
target
Nozzle-less electrospinning by Nanospider™ from ELMARCO:
Substrate
A
Fibers
I Rotating cylinder^™ ^^^^
Tank with polymer solution
a) polycaprolactone electrospun nanofibers b) coated by plasma polymerization in homogeneous DBD
F4280 Technologie depozice a povrchovych uprav:    Film Uniformity? Gas Dynamics Modelling
ka Zajíčková
roblem of Film Uniformity
Amospheric-pressure plasmas are characterized by high collision frequencies of particles (several orders of magnitude higher compared to low pressure)
=>- Delivery of active species to the substrate is much more advection than diffusion-driven (opposed to low-pressure).
High electron-neutral collision frequency =>- fast monomer conversion
Basic gas delivery set-ups
Gas flow
Gas flo*
Gas flow
i—^![I^^Q^[p[g aSĚÍ3
J. *    4    <|r    T    T V
T
are modified for optimization of flow patterns by gas dynamics simulations
P. Cools et ai, Plasma Process. Polym. H. Caquineau et al. J. Phys. D: Appl.
2015, 12, 1153-1163 Phys. 42(2009) 125201
IFigures Schematic representation of the four different in let set-ups: a) Sideway inlet, b) ring inlet c) porous glass inlet, and d) microplasma-electrode.
gas i: i Iii. hü i
grounded 4 «Kodes
■.i ili.Ir.IV:
F4280 Technologie depozice a povrchovych uprav:    Film Uniformity? Gas Dynamics Modelling
as Dynamics Simulations in Our Set-up
ka Zajíčková
Solving the Navier-Stokes equations (laminar flow) in full 3D geometry for pure Ar (results are shown for 1550 seem):
Surface: Velocity magnitude (m/s) Arrow Surface: Velocity field
0.03 0.025 „ 0.02
- 0.015
m
ro 0.01 c
P 0.005 o
° 0 N -0.005 -0.01 -0.015
▲ 2.49
2
1.5 1
0.5
-0.04 -0.03 -0.02 -0.01     0     0.01   0.02   0.03   0.04 "0 y-coordinate [m] y o
Surface: Velocity magnitude (m/s) Arrow Surface: Velocity field
▲ 2.49
-0.015 -0
04  -0.03  -0.02   -0.01     0      0.01   0.02    0.03 0.04"0 x-coordinate [m] ▼ 0
=>- Complex flow patterns inside the buffer chamber make the flow through the slit relatively even but better designs of the buffer chamber can be found!
F4280 Technologie depozice a povrchovych uprav:    Film Uniformity? Gas Dynamics Modelling
ka Zajíčková
Variations of four different geometries tested
gas inlet
plastic tube
buffer chamber exit slit
bottom ceramics
[electrode underneath) HJfJfJcr
electrodes
V
0.02
-0.05
0,02
0.02
-0.05
xyJ
L. Zajíčková et al. Plasma Physics and Controlled Fusion 59(3) (2017) 034003
F4280 Technologie depozice a povrchových úprav:    Film Uniformity? Gas Dynamics Modelling Lenka Zajíčková 10/18
Variations of four different geometries tested
Velocity magnitude [m/s] and direction
Velocity magnitude [m/s] and direction
■ s\\ \ \ \ \ \
s ■
---/ / / / y /
■---' s / / / / / .
/ ,
' s / / / / S l
' s s ////// I
'////// / / / / / / /
mm
i í f f f í * f í í
!/!/// S / s r------.
/ / / / / s s s ^ ^Z. /////,-.-.--_-_--_
11
\ \ \ \ \ \ \
!!(!!!! »
s. ■ •.
v N
S N N
\ S X
\ \ \
\ \ \
í i i
WS1
- 2
0
x-coordinate [cm]
1.4 1.2 1
0.8 0.6 0.4 0.2
y
1
0.8 0.6 0.4 0.2
x-coordinate [cm]
Velocity magnitude [m/s] and direction
Velocity magnitude [m/s] and direction
o u
: \ \ \ . \ \ \
V \ \
V \ \
s \ \
v. V \
S N \
v. s, s.
I
s \ \ S \ N N X \ \ V V V V \
'   / / / / / /
S S S / / / /
I
s s////// t j
s / s / / / / / / 11
' í í í í Íí í í í Í ž í í í í í í U
ÍÍ
!   /  ?///// S S S\
■!  ' ' .-'    .-- .-- .■- .
- ---„ _
■-.     ■-. '•,---- — ■
N \ ^. ---
. s •-. x x x -» — ■
\ \\\\\\\\\\"
- 2
0
x-coordinate [cm]
\
1.4 1.2 1
0.8 0.6 0.4 0.2
0 u
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
x-coordinate [cm]
F4280 Technologie depozice a povrchovych uprav:    Film Uniformity? Gas Dynamics Modelling
Lenka Zajíčková
11/18
Does It Work in Real Life?
(case study for DBD co-polymerization of MA and C2H2 in Ar, no electrode movement)
igas inlet
plastic tube
buffer chamber exit slit
bottom ceramics _nr
[electrode underneath) COppcl
electrodes
xyJ
Interference colours are measured by imaging spectroscopy refractometry    fitting of optical data provides spatially resolved film thickness
f	I B	
		
		
0 mm 5     10    15    20 25
215 nm 200
180
160
140
120
100
F4280 Technologie depozice a povrchových úprav:
Atmospheric Pressure Plasma Jets
ka Zajíčková
12/18
Atmospheric Pressure Plasma Jets
► operating in local thermal equilibrium (LTE) Te ~ Tn, ne > 1015 cm-3 - transferred arc (torch), plasmatron
► translational plasmas (non-LTE but with a significant heating of the background gas 7"n ~ several thousand Kelvin - gliding arc, expanding sparks, non-transferred arc
► non-LTE "cold" plasma jets Te > Tn, Tn = 300 - 1000K, ne < 1013 cm"3
Geometry 1
Gas
		CM
Tube	I	
		
		
		
Tube	I	
		
Geometry 2
Geometry 3
Geometry 4
Geometry 7
Ti ha
Gas
Geometry 5
G.ir,
		
		
Tube		
	bo 2 J	
Gas
Geometry 6
Ar
Electrode 1 Electrode 2
Plasma Region (3 t    Gas flow B3I
(^) High Voltage Source (^^^ Microwave generator Q High Current Sou | |
Insulator or metal
J Insulator
Microwave resonator
AY*
J. Winter at al. Plasma Sources Sei. Technol. 24 (2015) 064001
F4280 Technologie depozice a povrchových úprav:
Translational Plasma Jets
Lenka Zajíčková
13/18
A. Fridman, Plasma Chemistry, Cambridge University Press 2008
Gas Output
v Non-Equilibrium r State
Gas Inlet
Equilibrium State
Breakdown
The glide arc can be operated in the transitional regime (combines the benefits of both equilibrium and non-equilibrium discharges):
► the discharge starts thermal
► becomes non-thermal during the space-time evolution
SurfaceTreat
f = 50 Hz
max. P = 500 W,
max. U= 10kV
typical operation conditions: 500 W, 10kV, (dry) air 11.8 slm
F4280 Technologie depozice a povrchových úprav:		Translational Plasma Jets	Len	ka Zajíčková 14/18
PlasmaTreat Jet				
Jet	Principle	Working gas	Working gas flow rate [slm]	Additive	Power [W]	Frequency	Treated area 0 [mm]
Plasmatreat rotating plasma jet (PT)	Electrical arc	Dry air	30	—	1000	21 kHz	33
AFS Plasmajet® (AFS)	Electrical arc	Dry air	5-10	—	200-500	16-31 kHz	8
SurfaceTreat gliding arc (GA)	Electrical arc	Dry air	11.8	Ar	550	50 Hz	27-36
RF plasma slit jet (RF)	CCP/ICP	Ar	50-100	N2	300-600	13.56 MHz	150-300
Working gas
PlasmaTreat Jets in general: non-transferred arc (DE10223865 A1, US2002179575, DE102008058783 A1), 1-100 kHz, airflow, plasma cleaning, activation, deposition
F4280 Technologie depozice a povrchových úprav:			Translational Plasma Jets		ka Zajíčková 15/18
					
Jet	Principle	Working gas	Working gas flow rate [slm]	Additive	Power [W]	Frequency	Treated area 0 [mm]
Plasmatreat rotating plasma jet (PT)	Electrical arc	Dry air	30	—	1000	21 kHz	33
AFS Plasmajet® (AFS)	Electrical arc	Dry air	5-10		200-500	16-31 kHz	8
SurfaceTreat gliding arc (GA)	Electrical arc	Dry air	11.8	Ar	550	50 Hz	27-36
RF plasma slit jet (RF)	CCP/ICP	Ar	50-100	N2	300-600	13.56 MHz	150-300
Turned to be not suitable for modification of polypropylene (too hot).
F4280 Technologie depozice a povrchových úprav:			Translational Plasma Jets		ka Zajíčková 16/18
	urfaceTreat Jet				
Jet	Principle	Working gas	Working gas flow rate [slm]	Additive	Power [W]	Frequency	Treated area 0 [mm]
Plasmatreat rotating plasma jet (PT)	Electrical arc	Dry air	30	-	1000	21 kHz	33
AFS Plasmajet® (AFS)	Electrical arc	Dry air	5-10	—	200-500	16-31 kHz	8
SurfaceTreat gliding arc (GA)	Electrical arc	Dry air	11.8	Ar	550	50 Hz	27-36
RF plasma slit jet (RF)	CCP/ICP	Ar	50-100	N2	300-600	13.56 MHz	150-300
F4280 Technologie depozice a povrchových úprav:    RF Plasma Jets
asma Jets
ka Zajíčková
17/1
"Cold" plasmas required for surface modification of thermosensitive materials (bonding, painting, printing) or plasma medicine/agriculture
Non-LTE atmospheric pressure plasma jets need to prevent the transition to arc pulsed or high f discharges, a dielectric barrier at one or both the electrodes
Earliest cold RF plasma jet     Development of cold RF jets in Brno, Masaryk University proposed by Koinuma et al.
APL60 (1992) 816
M. Klima et al. Czech Patent PV147698 (1998), US6,525,481 (2003) J. Janca et al. Surf. Coat. Technol. 116-119 (1999) 547
F4280 Technologie depozice a povrchových úprav:    RF Plasma Jets
ka Zajíčková
18/1!
cademic" RF	Plasma	Slit J	et				
Jet	Principle	Working gas	Working gas flow rate [slm]	Additive	Power [W]	Frequency	Treated area 0 [mm]
Plasmatreat rotating plasma jet (PT)	Electrical arc	Dry air	30	—	1000	21 kHz	33
AFS Plasmajeť® (AFS)	Electrical arc	Dry air	5-10	—	200-500	16-31 kHz	8
SurfaceTreat gliding arc (GA)	Electrical arc	Dry air	11.8	Ar	550	50 Hz	27-36
RF plasma slit jet (RF)	CCP/ICP	Ar	50-100	N2	300-600	13.56 MHz	150-300