This set of slides consists of a collec on of short presenta ons on different topics, all related to plasma diagnos cs. During my presenta on I will use the first ‘introductory’ presenta on as a guideline. I will discuss some diagnos cs in more detail, and make a selec on of the applica ons of diagnos cs, depending on the audience.
Plasma Diagnostics - how to study molecule formation in plasma ? -
Richard Engeln Introduction
“ your working gas mixture ≠ input gas mixture” (at high dissociation degree)
quote from Prof. J. Winter during his lecture during the 2005 Summer School on Low Temperature Plasma Physics: Basics and Applications Introduction Molecule Formation in Plasma
Plasma source substrate
O2 plasma expansion
O2 plasma impinging on a substrate taken from: A. Lebéhot et al. in ‘Atomic and Molecular Beams’, ed. R. Campargue Introduction Molecule Formation in Plasma
3 2 2 O( P)atm + NOads → NO2{ B1} → NO2{ A1} + hν
N2 plasma with O2 injected in the background Introduction Molecule Formation in Plasma
over-population
r, v - H2 detection via QMS detection of H - H2 + e --> H + H Introduction Molecule Formation in Plasma
Diffuse (translucent) clouds ! 40-100 K / 100 part./cm3 ! Unknown absorption features
Dark (dense) clouds ! 10-30 K / 104-108 part./cm3 ! Universal molecule factory
(from: H. Linnartz, CRD meeting (2004)) Introduction Questions when studying molecule formation in plasma ? (when in contact with a surface)
" What particles are arriving at the surface ?
" In which state are the particles arriving ?
" New molecules are generated: - electronically and/or ro-vibrationally Excited NO 2 excited ? - substrate material and temperature dependence ?
" Is there flux dependence on the generation process ?
Shuttle glow Introduction Questions when studying molecule formation in plasma ? (when in contact with a surface)
" What particles are arriving at the surface ?
" In which state are the particles arriving ? What is needed to answer " New molecules are generated: these questions ? - electronically and/or ro-vibrationally Excited NO 2 excited ? - substrate material and temperature dependence ?
" Is there flux dependence on the generation process ?
Shuttle glow Introduction Gas-phase optical diagnostics for the detection of stable molecules and atomic/molecular radicals
" (VUV) Laser Induced Fluorescence
- relative densities, + spatial resolution " Fourier Transform IR/UV absorption
- line of sight, + absolute densities, + large λ-range (overview spectrum ) " (Cavity Ring Down) absorption
- line of sight, + (very) high sensitivity " (spontaneous) Raman spectroscopy
- ‘low’ sensitivity, + every molecule Raman active, + spatial resolution Plasma Diagnostics (optical)
Optical diagnostic Parameters Examples
Doppler LIF w, T, n Ar-metastable
Two-photon LIF w, T, n H atom
r, v VUV LIF n(v,J), T H2
IR absorption n(v,J), T NO, N2O, NO2
Cavity Ring Down absorption n(v,J), T NH, NH2, NH3
Literature
On diagnostics (general):
! H R Griem, Plasma Spectroscopy (McGraw-Hill Book Company, New York, 1964)
! W Demtröder, Laser Spectroscopy,Basic Concepts and Instrumentation edited by F P Schäfer (Springer-Verlag, Berlin, Heidelberg, New York, 1981)
! K Muraoka, K Uchino, M D Bowden, Plasma Physics and Controlled Fusion 40, 1221 (1998)
! J-P E Taran, CARS spectroscopy in Applied Laser Spectroscopy, edited by W Demtröder and M Inguscio (Plenum, New York, 1990)
! G Berden, R Peeters, G Meijer, Int. Rev. Phys. Chem. 19, 565 (2000)
! G. Berden and R. Engeln, Cavity Ring-Down Spectroscopy, Techniques and Applications, Blackwell Publishing Ltd, United Kingdown (2009) Laser Induced Fluorescence spectroscopy Laser Induced Fluorescence (LIF)
Ø number of laser photons na absorbed in unit volume and time: laser na = σli I L nl V IL
Ø number of fluorescence photons Nf (λik) originating from V:
Aik N f = na V q f = σli I L nl V ⋅ Ai + R i Ø signal Sf: R j Sf = N f ⋅Ω / 4π ⋅T ⋅qph (λ)⋅Gph σli.IL Aik k
Ail S f ∝ nl l Laser Induced Fluorescence (LIF)
Advantages Disadvantages
Ø sensitive Ø not quantitative
Ø extra info from time behaviour Ø depending on gas composition
Ø experimentally straightforward (quenching) Ø possibility of 2D-imaging
LIF on ground-state atoms: ü ground-state atoms have large energy spacings Howe.g. H: toE(n=2) detect - E(n=1) the = 10.2 hydrogen eV atom ü species selectivity requires high energetic photons (H: λ <121.6 nm) experimentallyin the demandinggroundstatewith techniques LIF ? with for VUV-generation LIF ? 2 photon LIF
H excitation schemes
4 i R j 3 486 486 486 656 195 Aik 656 (2) 2 k 2 σli .IL
Ail 122 193 2 x 205 nm 2 x 243 nm 2 x 243 nm l n=1
Advantages Disadvantages
Ø no demanding VUV-generation Ø low 2-photon cross sections require Ø non-resonant fluorescence detection high laser intensities possible Ø 2-photon cross sections often not
Ø self-absorption can be avoided known Laser Induced Fluorescence (LIF)
Quantities deduced from LIF
~ v 500 Δν νlif Ø integrated intensity: n
400 Ø Doppler width: T
300 Δν 1 8ln2⋅kT D = 200 δν ~ T ν c M
100 Ø Doppler shift ν - ν0: v Fluorescence signal (a.u.) signal Fluorescence νth Area ~ n 0 97490 97492 97494 97496 97498 97500 97502 Frequency (cm-1) 2 photon LIF on atoms
monitoring H monitoring N
3s,d 3p 656 nm 745 nm 205 nm 207 nm Hα 2p 3s
205 nm 207 nm
1s 2p
Applications: Applications: Ø fast deposition of a-Si:H Ø deposition of a-C:N Ø H-source Ø plasma etching (photo-resist) Ø surface passivation
(VUV) LIF on H2 molecules
Excitation from H2(X, v=0) to H2(B)
Photons with energy ≅ 11 eV (λ ≅ 110 nm, Vacuum UV)
Fluorescence of H2 in B-state
λ in the Vacuum UV Absorp on spectroscopy absorption
Absorption spectroscopy
Sample Light Source
I(ν ) l I ( ) 0 ν
Lambert-Beer : I( ) I ( )exp[ l] ν = 0 ν −κν
Absorption: n(v, J ) κν = σν
ΔI If κ l is small: = κ l ν I ν 0 IR absorption
IR laser absorption
spectroscopy IR absorption
IR laser absorption
spectroscopy
Trace gas detection 1.0
0.9
CH 4 0.8 N O 2 H O 0.7 2
1306.0 1306.2 1306.4 1.0
Transmission 0.9
0.8 0.7 1306.0 1306.2 1306.4 Wavenumber [cm-1] FTIR absorption
Fourier Transform absorption spectroscopy
interferogram
0.020
0.015
0.010
0.005
0.000 intensity (a.u.) intensity -0.005
-0.010
-0.015
189500 190000 190500 191000 mirror position (cm-1) FTIR absorption
O2 FTIR measurement in a vessel
vessel
0.036 arc
window
interferometer 0.034
glowbar detectors
sample compartiment 0.032 intensity (a.u.) intensity
background sample 0.030
13120 13125 13130 13135 13140 13145 13150 13155 13160 13165 13170 -1 frequency (cm ) vesselfinalabsorption / graph 3 FTIR absorption
O2 FTIR measurement in a vessel
vessel
0.030
arc
window 0.025
interferometer 0.020
glowbar 0.015 detectors
sample compartiment 0.010 absorption
0.005
0.000
-0.005 13120 13130 13140 13150 13160 13170 frequency (cm-1) absorption
IR laser absorption FT IR absorption
+ ü Very high wavelength resolution ü Multiplex advantage ü High sensitivity ü Very large wavelength range
- ü Very small wavelength range ü Low wavelength resolution ü Sensitivity
Homo-nuclear diatomic species not detectable in IR absorption
Sensitivity
ΔI ≥10 − 3 (pulsed lasers) I 0
−3 è l 10 κν ≥
16 -3 Example: l = 0. 1 m è n(v, J) ≥10 m σ =10 −18 m2
N = n(v, J) ≥1018 m-3 tot ∑ v,J
Alternative schemes: Fourier Transform spectroscopy (multiplex, but low sensitivity) Cavity Ring Down spectroscopy (high sensitivity) CRD absorption
Sensitive direct absorption technique
(A. O’Keefe and D.A.G. Deacon, Rev. Sci. Instrum. 59 (1988) 2544)
ü absorption per unit of pathlength (cavity loss): 1/ cτ = (1− R + nσL) / d ü non-intrusive and remote ü high sensitivity due to effective multipassing ü directabsorption absorption per unit –> of line of sight measurement CRD absorption
Basic scheme of the pulsed CRD spectrometer
Ring-down time Cavity loss d 1 1-R nσL τ = = + c(1-R+nσL) cτ dd CRD absorption
Performing a pulsed CRD experiment
Ring-down transient CRD spectrum
1500
1000
500 Intensity (a.u.) (a.u.) Intensity Ring-down time (ns) Ring-down time (ns) 0 0 1000 2000 3000 4000 13100 13101 13102 time (ns) frequency (cm-1) CRD absorption
Performing a pulsed CRD experiment
CRD absorption spectrum Cavity loss (1/cm)
1 1-R nσL 5 1 1-R+ nσL == + 1/cm) 4 ccττ dddd -5 3
baseline 2 If cavity length is 45 cm, determine R. 1 absorption spectrum 1. R = 99 % loss (10 Cavity 0 2. R = 99.9 % 13100 13101 13102 -1 3. R = 99.99 % frequency (cm ) 4. Not enough information CRD absorption
+ optical technique
+ independent of intensity
+ direct absorption measurement: -- but: line-of-sight
+ high sensitivity due to effective multipassing
+ pulsed light sources: spectral range into the UV
+ experimentally straightforward (tunable laser, highly reflecting mirrors, PMT, ‘fast’ and ‘deep’ digitizer)
high potential for diagnostics in plasmas ETP setup
Plasma created at high pressure (~400 mbar) in cascaded arc plasma source
Expansion into low-pressure chamber (0.2 mbar)
+ injection of e.g. SiH4
Plasma in interaction with surface, leading to e.g. deposition or etching CRD absorption during deposition
CRD for the detection of SiH during a:Si-H deposition
Ar
oscilloscope
cascaded arc plasma source precursor injection expanding plasma filter PMT
R R laser pulse (tunable dye-laser)
protection flow (Ar) substrate holder CRD absorption during deposition
CRD spectrum of SiH measured during a:Si-H deposition CRD absorption during deposition
CRD spectrum of SiH measured during a:Si-H deposition
nσL/d
(1-R)/d CRD absorption on SiH
2 2 SiH detection: A Δ à X Π, 405 – 430 nm
T = 3000K vibr line width T (v=0) = 1800K rot Q 2 Q 150 1
) Simulated (LIFBase) Q (11.5) temperature -6 1 Q (14.5) 100 1 absorption + 50 R (14.5) cross-section Experimental 2 Absorption (x10
0 density 412,5 413,0 413,5 414,0 414,5 Wavelength (nm) TALIF spectroscopy on H atoms Ar/H2 plasma expansion
stationary shock wave anodeanode cathodescathode (× (3)3) (nozzle) (nozzle) subsonic flow M < 1 supersonic flow gasgas M > 1 inlet Mach disk M = 1 Cascaded arc arc Plasma expansion Rayleigh scattering on H/H2 plasma expansion
1022 ) -3 1/z2 1021 density (m 2 H 20 Pa 100 Pa 1020 1 10 100 axial position (mm) TALIF detection of H atoms
ion 13.6 3s2S 3p2P 3d2D Ø produce 205 nm via THG of a Nd:YAG 12.1 Hα 656.5 nm pumped dye laser 10.2 2s2S 2p2P Ø from spectral scans data on: n,T,v,f(v)
121.56 nm Lyman α 205.14 nm energy (eV) energy
0 1s2S
cascaded arc 205 nm 3.5 slm H2 I=40A, V=150V 205 nm
slitmask fliter gates PMT H atom density along the jet axis (TALIF)
100 Pa 1021 20 Pa ) -3
1020 Density (m
1019 1 10 100 z (mm) Effect of nozzle-length on H density
1021 ) -3
1020
H density (m H density nozzle length 6 mm 19 10 14 mm
1 10 100 axial position (mm) Effect of nozzle-length on H flux
5 short nozzle short long nozzle (x5)
) 4 arc -1 s
-2 nozzle
m 3 25
long 2 arc
1 nozzle
H flux density (10 0
-6 -4 -2 0 2 4 6 radial position (mm) Effect of nozzle-width on H flux
large diam. nozzle 1.0 short nozzle 8
) arc -1 s -2 0.8 nozzle m 25 0.6
8 0.4 arc
0.2 nozzle
H flux density (10 0.0
-15 -10 -5 0 5 10 15 radial position (mm) Conclusions
1. Large influence of nozzle geometry on J H flux
H2 rv H rv 2H H 2H H 2. Loss of H atoms due to surface 2 H 2 association (volume association far too slow) nozzle
loss of H atoms = production of
rv 21 -1 H2 at the surface H flux: ΦH > 10 s Dissociation degree = 0.4
P. Vankan et al., Appl. Phys. Lett. 86 (2004) 101501 S. Mazouffre et al., Phys Rev. E 64 (2001) 066405 Doppler-LIF spectroscopy on Ar atoms Expanding Thermal Plasma (ETP)
Plasma creation
Plasma chemistry
+ dangling bond creation by Eley-Rideal H-abstraction
SiH3 reflection dangling bond ~85% SiH surface diffusion: creation by ion SiH reaction 3 3 strong bond formation + ~15%: with danling bond 5-fold bonded Si dangling bond surface diffusion
Material processing Doppler LIF
Ar plasma expansion Rayleigh scattering Ar density as function of distance from the exit of the source
1022 ) -3
1021 Ar density (m
42 Pa 100 Pa 1020 1 10 100 Axial position (mm) Doppler LIF
Doppler LIF experimental setup
chopper diode laser BS BS
z-axis
Fabry Argon Perot lamp
diodes
filter
PMT reference
Lock in trigger amplifier Doppler LIF
Typical result of a Doppler LIF measurement
1.0
Argon lamp
0.5 Fabry Perot intensity (a.u.) intensity
LIF signal 0.0 1 2 3 4 5 6 7 8 9 10 11 piezo voltage (a.u.) Doppler LIF Ar velocity distribution functions
0.5 z=59 mm
0.0
1.0 z=100 mm 0.5 0.0 intensity (a.u.) intensity 1.5 z=174 mm 1.0 0.5 0.0 -1 0 1 2 3 4 5 6 velocity (km/s) Doppler LIF
Ar atom velocity Ar atom temperature
20 Pa 1000 T (K) T velocity (m/s) 1000
100
-3 -2 -1 10-3 10-2 10-1 10 10 10 z (m) z (m)
calculated with: γ = 1.4 (theoretically: 5/3 for mono-atomic gas) zref = 0.0025 m T0 = 6000 K IR absorp on spectroscopy on
N2/O2 plasma N2/O2 plasma setup (IR diode laser absorption spectroscopy)
window retroreflector
I = 55 A
Ar
N2 window window pump
p = 20 Pa QMS
gas inlet window
Ar, N2 PMT
H2, O 2 pumps
diode laser
IRMA system Introduction Molecule Formation in Plasma
3 2 2 O( P)atm + NOads → NO2{ B1} → NO2{ A1} + hν
N2 plasma with O2 injected in the background
NO formation in an Ar-N2-O2 plasma Percentage of N (%) 2 100 90 80 70 60 50 40 30 20 10 0 6 20 Pa )
105 Pa 3.0 )
-3 5 -3 m m 19
4 20 2.0 10 3 (
2 1.0 1 NO densityNO (10 NO densityNO
0 0.0 0 10 20 30 40 50 60 70 80 90 100 Percentage of O (%) 2 N + NO → N2 + O N + NOads → N2O N2O formation in an Ar-N2-O2 plasma Percentage of N (%) 2 100 90 80 70 60 50 40 30 20 10 0 6 20 pa
) 105 Pa
-3 5 m
18 4
N2O only formed 3 at low O2 flow
2
O density (10 1 2 N 0
0 10 20 30 40 50 60 70 80 90 100 Percentage of O (%) 2 Time behavior of NO formation
in Ar-N2-O2 plasma
τres≅1s no O2 flow
O2 off after 3 min ⇓ )
-3 1.5 N2 off after 3 min no NO formation m 19 no N flow 1.0 2
⇓
NO formation >> τres 0.5 NO density (10 density NO 0.0 150 200 250 N on/in the surface Time (s) (no O storage) Time behavior of N2O formation in an N2-O2 plasma
τres≅1s 3 )
-4 O2 off after 1 min
O2 off after 5 min no O2 flow 2 ⇓
N2O formation >> τres
1 O mole fraction (10 fraction mole O 2 N NO on/in the surface 0 0 50 100 150 200 250 300 350 (depends upon O2 conditioning) Time [s] Conclusions
1. Input gas mixture, N2 and O2, changes into a
mixture of N2, O2 and NO, N2O and NO2. 2. Time-resolved measurements show that surfaces become saturated with N atoms and NO radicals.
3. In Ar-NO plasmas, up to 90% conversion of NO
into N2 and O2 IR absorp on spectroscopy VUV-LIF spectroscopy on Absorp on spectroscopy on r,v N2H/O 22 plasma molecules in plasma Why study hydrogen plasma expansions? (produced from a cascaded arc)
1. Use of H2 gas in processing plasma application - etching and cleaning - passivation during deposition
2. Astrophysical interest
- ‘hot’ H2, formed at grains through surface association, and acts as precursor in astro-chemistry
3. Fundamental study of H2/HD/D2 Lyman transitions - extension of database
4. The cascaded arc might be used as H- ion source, because r,v of high fluxes of H2 at low Te (around 1 eV)
/ Plasma & Materials Processing 9/7/12 PAGE 1 Plasma source and expansion
I = 40 – 60 A P = 5 – 10 kW
Φarc = 3 slm
5 parc = 0.2x10 Pa
pbg = 100 Pa
/ Plasma & Materials Processing 9/7/12 PAGE 2 Plasma expansion
T = 6000 K T = 1000 K T = 2000 K T = 400 K
/ Plasma & Materials Processing 9/7/12 PAGE 3 PLEXIS setup
/ Plasma & Materials Processing PAGE 4 PLEXIS setup
Laser table Vacuum chamber • Movable plasma Nd:YAG cylindrical (2m x 0.3m) source and substrate (450 mJ/shot @ 355 nm) 9 Pa / 3000 sccm H2 dye laser • Axial magnetic field (50 mJ/shot @ 460 nm) Bmax = 0.2 T ( 8 mJ/shot @ 230 nm)
/ Plasma & Materials Processing 9/7/12 PAGE 5 Ar/H2 plasma expansion
9/7/12 PAGE 6 Two photon Absorption LIF (TALIF) on atomic hydrogen
ion Ø Produce 205 nm via THG of a Nd:YAG 13.6 pumped dye laser 3s2S 3p2P 3d2D Ø From spectral scans data on: n,T,v,f(v) 12.1 Hα 656.5 nm
10.2 2s2S 2p2P
121.56 nm Lyman α 205.14 nm energy (eV) energy
0 2 cascaded arc 1s S 205 nm 3.5 slm H2 I=40A, V=150V 205 nm
slitmaskslit mask fliterfilter gated PMT gates PMT
9/7/12 PAGE 7 H atom density in H2 plasma expansion (TALIF)
21 10 ) -3
20 10 Density (m
20 Pa 100 Pa
19 10 1 10 100 Axial position (mm)
Mazouffre et al. Phys. Rev. E 64, 016411 (2001) 9/7/12 PAGE 8 r,v VUV-LIF detection of H2
H2 energy scheme Excitation and detection
Ø X à B transition in H2 (~11 eV) Ø Detection of fluorescence in the VUV range Ø Excitation with 120 – 165 nm photons, produced via SARS
1 10 depleted pump
0
10 AS1 AS2 10-1 AS3 -2 10 AS4 AS5
-3 AS6 AS7 Energy Energy (mJ) 10 AS8
10-4 AS9
120 140 160 180 200 220 wavelength (nm)
9/7/12 PAGE 9 SARS technique
Four-wave mixing process
M. Spaan, A. Goehlich, V. Schultz-von der Gathen, H. F. Döbele, Applied Optics 33 (1994) 3865 T. Mosbach, H. M. Katsch, H. F. Döbele, Rev. Sci. Instrum. 85 (2000) 3420 P. Vankan, S.B.S. Heil, S. Mazouffre, R. Engeln and D.C. Schram, H. F. Döbele, Rev. Sci. Instrum. 75 (2004) 996
/ Plasma & Materials Processing 9/7/12 PAGE 10 r,v VUV-LIF detection of H2
H2 energy scheme Excitation and detection
Ø X à B transition in H2 (~11 eV) Ø Detection of fluorescence in the VUV range Ø Excitation with 120 – 165 nm photons, produced via SARS
1 10 depleted pump
0
10 AS1 AS2 10-1 AS3 -2 10 AS4 AS5
-3 AS6 AS7 Energy Energy (mJ) 10 AS8
10-4 AS9
120 140 160 180 200 220 wavelength (nm)
9/7/12 PAGE 11 r,v VUV-LIF detection of H2
H2 energy scheme VUV-LIF detection scheme
9/7/12 PAGE 12 VUV-LIF setup
to pump Nd:YAG THG plasma S
M Dye (C440) M W PMT BBO
220 nm LN M 2 W
BS
M L W M H2 M 440 nm
to pump
PMT VUV PMT mono NO cell
9/7/12 PAGE 13 VUV-LIF setup
to pump Nd:YAG THG plasma S
M Dye (C440) M W PMT BBO
220 nm LN M 2 W
BS
M L W M H2 M 440 nm
to pump
PMT VUV PMT mono NO cell Measured H2 Lyman spectrum
10
8
6
4 Fluorescence (a.u.) 2
0 43650 43700 43750 43800 43850 43900 SH frequency (cm-1)
76890 AS8 frequency (cm-1) 77140
81045 AS9 frequency (cm-1) 81295
/ Plasma & Materials Processing 9/7/12 PAGE 15 VUV-LIF setup
to pump Nd:YAG THG plasma S
M Dye (C440) M W PMT BBO
220 nm LN M 2 W
BS
M L W M H2 M 440 nm
to pump
PMT VUV PMT mono NO cell
/ Plasma & Materials Processing 9/7/12 PAGE 16 VUV-LIF setup
to pump Nd:YAG TALIF spectrum of NO P =THG 2 mbar plasma S
M
Dye(a.u.) Fluorescence (C440) M W 44000 44020 44040 44060 44080 44100 44120 44140 44160 44180 44200 PMT
BBO
220 nm LN M 2 W Fluorescence (a.u.) Fluorescence 44200 44220 44240 44260 44280 44300 44320 44340 44360 44380 WavenumberBS (cm-1)
M L W M H2 M 440 nm
to pump
PMT VUV PMT mono NO cell
/ Plasma & Materials Processing 9/7/12 PAGE 17 VUV-LIF spectroscopy
TALIF spectrum of NO P = 2 mbar to pump Nd:YAG THG plasma S -1 dye laser frequency (cm )(a.u.) Fluorescence 22048 M22049 22050 22051 22052440002205344020 44040 44060 44080 44100 44120 44140 44160 44180 44200 Dye (C440) M W PMT NO via TALIF BBO
220 nm LN M 2 W Fluorescence (a.u.) Fluorescence 44200 BS44220 44240 44260 44280 44300 44320 44340 44360 44380 -1 H (v= 4,J= 7) Wavenumber (cm ) 2 via VUV-LIFM L W M H2 M 440 nm
to pump
73182 73184 73186 73188 73190 PMT VUV AS7 frequency (cm-1) PMT mono NO cell
/ Plasma & Materials Processing 9/7/12 PAGE 18 Measured H2 Lyman spectrum
H (rv) 2 v=3,J=5
v=3,J=12 v=4,J=2 v=2,J=9
state-selective
v=4,J=7 spatially resolved Intensity non-intrusive
FP
dynamic range > 4 orders NO detection limit ~ 1013 m-3
44040 44060 44080 44100 frequency (cm-1)
P. Vankan et al., Rev. Sci. Instrum. 75 (2004) 996
/ Plasma & Materials Processing 9/7/12 PAGE 19 Measured H2 Lyman spectrum
2.0 (3,5)
1.5 (4,7)
1.0
(3,9) (v,J)=(3,7) (3,6) 2 fluoresence (a.u.) fluoresence
0.5 H (3,8) (4,11) / (9,1) / (4,11) (2,17) (3,14) Advantages multiplexing: (2,10) (6,7) ü spectrum more dense 0.0 ü efficient measurement
44020 44060 44100 44140 44180 SH frequency (cm-1)
77260 AS8 frequency 77440
81415 AS9 frequency 81595
/ Plasma & Materials Processing 9/7/12 PAGE 20 Measured H2/HD/D2 Lyman spectra
100 Pa
1500 sccm H2 / 1500 sccm D2 45 A, z = 8 mm
O. Gabriel et al. Chemical Physics Letters 451 (2008) 204
/ Plasma & Materials Processing 9/7/12 PAGE 21 Measured and calculated Lyman Measured and calculated H /HD/D Lyman spectrum spectra 2 2
Spectroscopic data for H2 Spectroscopic data for HD Spectroscopic data for D2
H. Abgrall et al. Astron. H. Abgrall, E. Roueff, Astron. H. Abgrall et al. J. Phys. B: Astrophys. Suppl. Ser. 101 Astrophys. 445 (2006) 361 At., Mol. Opt. Phys. 32 (1993) 273 (1999) 3813
All H2 Lyman transitions HD Lyman transitions J < 11 D2 Lyman transitions J < 12
/ Plasma & Materials Processing 9/7/12 PAGE 22 Measured and calculated Lyman Measured and calculated H /HD/D Lyman spectrum spectra 2 2
New calculated Lyman transitions including higher rotational states (J > 10), incollaboration with Abgrall and Roueff
O. Gabriel et al. J. Mol. Spectrosc 253 (2009) 64
/ Plasma & Materials Processing 9/7/12 PAGE 23 Non-Boltzmann distribution for H2
“Hockey stick” 700 K for low J
3800 K for high J
/ Plasma & Materials Processing 9/7/12 PAGE 24 Non-Boltzmann distributions in H2/D2 jet
Low J: T = 700 K Low J: T = 500 K High J: T = 3800 K High J: T = 3400 K
Low J: T = 300 K High J: T = 3000 K O. Gabriel et al, J. Chem. Phys. 132 (2010) 104305
/ Plasma & Materials Processing 9/7/12 PAGE 25 Results on H- production through DA process
Te = 5000 K
Production rate of H- ions by dissociative attachment
17 -3 ne = 10 m O. Gabriel et al, J. Chem. Phys. 132 (2010) 104305
J. Horáček et al, Phys. Rev. A, 70 (2004) 052712
/ Plasma & Materials Processing 9/7/12 PAGE 26 Absorp on CRD spectroscopy spectroscopy on N2/H2 plasma NH3 production in N2/H2 plasma
+ dangling bond creation by Eley-Rideal H-abstraction
SiH3 reflection dangling bond ~85% SiH surface diffusion: creation by ion SiH reaction 3 3 strong bond formation + ~15%: with danling bond 5-fold bonded Si dangling bond surface diffusion NH3 production in N2/H2 plasma
N2/H2 plasma creation
+ dangling bond creation by Eley-Rideal H-abstraction
SiH3 reflection dangling bond ~85% SiH surface diffusion: creation by ion SiH reaction 3 3 strong bond formation + ~15%: with danling bond 5-fold bonded Si dangling bond surface diffusion Plasma chemistry
leading to e.g. NHx
NH3 formation ? Cavity Ring Down: principals and features
(O’Keefe and Deacon, Rev. Sci. Instrum. 59 (1988) 2544)
empty R R cavity 5 ns L with intensity Det. absorption light σ pulse n, 1/e d τ time
Ø absorption per unit of pathlength (cavity loss): 1/ cτ = (1− R + nσL) / d Ø non-intrusive Ø high sensitivity due to effective multipassing Ø direct absorption –> line of sight measurement Cavity Enhanced Absorption detection scheme
Rev. Sci. Instrum. 69, 3763 (1998) NH3 production in N2/H2 plasma
CEA measurement recorded in a vessel in which
N2/H2-plasma expands
Scanning frequency: 30 Hz Frequency range: 15 GHz 0.10 Averages: 1000 Measurement time: 30 s 0.08
0.06
The absorption coefficient ( ) κ ν 0.04 from intensity by:
(a.u.) intensity 0.02
⎛⎞S()0 ν ⎛⎞1-R κν()=⎜⎟−×1 ⎜⎟0.00 ⎝⎠S(ν )⎝⎠ d 6568.3 6568.4 6568.5 6568.6 6568.7 frequency (cm-1) NH3 production in N2/H2 plasma
Part of the absorption spectrum of NH3 as measured in an expanding N2/H2 plasma
4 Line width ) -1 3 cm -5
Ttr = 600 K 2
σ ≈ 10-22 m 2 1 absorption (in 10
N ≈ 1019 m-3 0 6568.4 6568.5 6568.6 6568.7 frequency (cm-1)
NH3 production in N2/H2 plasma
Ammonia density produced in expanding N2 plasma in
which H2 is injected in the background
3.0 Saturation behavior ) 2.5 explained by rate -3 determining steps: m 19 2.0 + + N + H2 -> NH + H + 1.5 NH + e -> N + H
1.0 density (10 density 3
+ NH 0.5 P = 100 Pa Total N flow is bg consumed 0.0 0.0 0.1 0.2 0.3 0.4 0.5
φH 2 ( + ) φH φN 2 2 NH3 production in N2/H2 plasma
Ammonia density as function of background pressure at
constant gas flow (N2-arc/H2-background)
Linear with pressure 4.0 )
(dNH3/dt constant) -3 m 19 3.0
3 particle reaction 2.0 stable intermediate density (10 density 3 1.0 NH Wall production (?) 0.0 0 50 100 150 200 Pressure (Pa) NH3 production in N2/H2 plasma
NH3 production in two different vessels
14 2.5 Ø Total gas flow of 2 slm through cascaded arc 12 2.0 Ø At maximum 12 % of 10 the background gas is NH3 1.5
8 3 3
6 1.0 % NH 4 % NH 0.5 larger surface-to- 2 volume ratio 0 0.0 0.0 0.2 0.4 0.6 0.8 1.0 / φH φtotal 2
Appl. Phys. Lett. 2002, 81, 418 Conclusions
Input gas mixture, N2/H2, changes into
N2/H2/NH3 mixture
(12 % of the background gas is NH3).
NH3 is formed at surfaces.