plasma diagnosticsliterature on diagnostics (general): ! h r griem, plasma spectroscopy (mcgraw-hill...

Richard Engeln

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 ? -

“ 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

O2 plasma expansion

substrate

O2 plasma impinging on a substrate

taken from: A. Lebéhot et al. in ‘Atomic and Molecular Beams’, ed. R. Campargue

Introduction

N2 plasma with O2 injected in the background

O(3P)atm + NOads → NO2{2B1} → NO2{2A1} + hν

Molecule Formation in Plasma Introduction

H2r,v detection via QMS detection of H-

H2 + e --> H- + H

over-population

Molecule Formation in Plasma Introduction

Dark (dense) clouds

!  10-30 K / 104-108 part./cm3

!  Universal molecule factory

Diffuse (translucent) clouds !  40-100 K / 100 part./cm3

!  Unknown absorption features


(from: H. Linnartz, CRD meeting (2004))

Introduction

"  What particles are arriving at the surface ?

"  In which state are the particles arriving ?

"  New molecules are generated: - electronically and/or ro-vibrationally excited ? - substrate material and temperature dependence ?

"  Is there flux dependence on the generation

process ?

Questions when studying molecule formation in plasma ? (when in contact with a surface)

Shuttle glow

Excited NO2

Introduction

"  What particles are arriving at the surface ?

"  In which state are the particles arriving ?

"  New molecules are generated: - electronically and/or ro-vibrationally excited ? - substrate material and temperature dependence ?

"  Is there flux dependence on the generation

process ?

Questions when studying molecule formation in plasma ? (when in contact with a surface)

Shuttle glow

Excited NO2

Introduction

What is needed to answer these questions ?

"  (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

Gas-phase optical diagnostics for the detection of stable molecules and atomic/molecular radicals

Introduction

Plasma Diagnostics (optical)

Optical diagnostic Parameters Examples

Doppler LIF w, T, n Ar-metastable

Two-photon LIF w, T, n H atom

VUV LIF n(v,J), T H2r,v

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:

Ø number of fluorescence photons Nf (λik) originating from V:

Ø signal Sf:

n I na li L l=σ

N n V q I n VAA Rf a f li L l

ik

i= = ⋅

+σ

S N T q Gf f ph ph= ⋅ ⋅ ⋅ ⋅Ω / ( )4π λ

lf nS ∝

V laser

IL

l

i

k

j

σli.IL

Ail

Aik

R

Ø  sensitive

Ø  extra info from time behaviour

Ø  experimentally straightforward

Ø  possibility of 2D-imaging

Ø  not quantitative

Ø  depending on gas composition

(quenching)

LIF on ground-state atoms: ü  ground-state atoms have large energy spacings e.g. H: E(n=2) - E(n=1) = 10.2 eV ü  species selectivity requires high energetic photons (H: λ <121.6 nm)

experimentally demanding techniques for VUV-generation


Advantages Disadvantages

How to detect the hydrogen atom

with LIF ?

How to detect the hydrogen atom

in the groundstate with LIF ?

Ø  no demanding VUV-generation

Ø  non-resonant fluorescence detection

possible

Ø  self-absorption can be avoided

Ø  low 2-photon cross sections require

high laser intensities

Ø  2-photon cross sections often not

known

l

i

k

j

Ail

Aik

R

σli(2).IL2

n=1

3

2

4

486

486

486

656

656

195

193

2 x

205

nm

2 x

243

nm

122

H excitation schemes

2 x

243

nm

2 photon LIF

Advantages Disadvantages

Quantities deduced from LIF

Ø  integrated intensity: n

Ø  Doppler width: T

Ø  Doppler shift ν - ν0: v

MkT

cD ⋅=

Δ 2ln81νν

97490 97492 97494 97496 97498 97500 975020

100

200

300

400

500

Area ~ n

νlif

δν ~ T

νth

Δν ~ v

Fluo

resc

ence

sig

nal (

a.u.

)

Frequency (cm-1)


Applications: Ø  deposition of a-C:N Ø  plasma etching (photo-resist)

Applications: Ø  fast deposition of a-Si:H Ø  H-source Ø  surface passivation

1s

3s,d

2p Hα

205 nm

205 nm 656 nm

3p

3s

207 nm

207 nm 745 nm

2p

monitoring H monitoring N

2 photon LIF on atoms

(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

Lambert-Beer : Absorption:

If is small:

]exp[)()(0

lIIνκνν −=

ννσκ ),( Jvn=

lνκ l

II

νκ=

Δ

0

Light Source

)(0νI

)(νIl

Sample

IR laser absorption

spectroscopy

IR absorption

IR laser absorption

spectroscopy

IR absorption

1306.0 1306.2 1306.40.7

0.8

0.9

1.0

Tran

smis

sion

Wavenumber [cm-1]

1306.0 1306.2 1306.40.7

0.8

0.9

1.0

CH4

N2O H2O

Trace gas detection

Fourier Transform absorption spectroscopy

189500 190000 190500 191000

-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015

0.020

inte

nsity

(a.u

.)

mirror position (cm-1)

interferogram

FTIR absorption

vessel

arc

window

interferometer

detectors

sample compartiment

glowbar

13120 13125 13130 13135 13140 13145 13150 13155 13160 13165 13170

0.030

0.032

0.034

0.036

vesselfinalabsorption / graph 3

inte

nsity

(a.

u.)

frequency (cm-1)

background sample

O2 FTIR measurement in a vessel

FTIR absorption

vessel

arc

window

interferometer

detectors

sample compartiment

glowbar

O2 FTIR measurement in a vessel

13120 13130 13140 13150 13160 13170-0.005

0.000

0.005

0.010

0.015

0.020

0.025

0.030

13120 13130 13140 13150 13160 13170-0.005

0.000

0.005

0.010

0.015

0.020

0.025

0.030

abso

rptio

n

frequency (cm-1)

FTIR absorption

ü  Multiplex advantage

ü  Very large wavelength range

FT IR absorption IR laser absorption

ü  Very high wavelength resolution

ü  High sensitivity

ü  Low wavelength resolution

ü  Sensitivity

ü  Very small wavelength range

absorption

+

-

Homo-nuclear diatomic species not detectable in IR

Sensitivity

(pulsed lasers)

è 

Example: è Alternative schemes:

Fourier Transform spectroscopy (multiplex, but low sensitivity) Cavity Ring Down spectroscopy (high sensitivity)

310−≥lνκ

3

0

10−≥Δ

II

m 1.0=l218 m 10−=σ

-316 m 10),( ≥Jvn

-318

,m 10),(∑ ≥=

Jvtot

JvnN

absorption

ü  absorption per unit of pathlength (cavity loss):

ü  non-intrusive and remote ü  high sensitivity due to effective multipassing ü  absorption per unit of ü  direct absorption –> line of sight measurement

Sensitive direct absorption technique (A. O’Keefe and D.A.G. Deacon, Rev. Sci. Instrum. 59 (1988) 2544)

dLnRc /)1(/1 σ+−=τ

CRD absorption

Basic scheme of the pulsed CRD spectrometer

1τ =c1-R nσL+d d

Cavity loss

=τc

d(1-R+nσL)

Ring-down time

CRD absorption

Performing a pulsed CRD experiment

Ring-down transient CRD spectrum

frequency (cm-1)

Rin

g-do

wn

time

(ns)

Inte

nsity

(a.

u.)

13100 13101 13102 0

1000

500

1500

time (ns) 0 1000 2000 3000 4000

CRD absorption

Performing a pulsed CRD experiment

CRD absorption spectrum

frequency (cm-1)

Cav

ity lo

ss

(10-

5 1/

cm)

13100 13101 13102 0

4

2

5

3

1

1τ =c1-R nσL+d d

If cavity length is 45 cm, determine R. 1.  R = 99 % 2.  R = 99.9 % 3.  R = 99.99 % 4.  Not enough information

Cavity loss (1/cm)

1τ =c1-R nσL+d d

baseline

absorption spectrum

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

CRD absorption

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

cascadedarc plasma source

expanding plasma

substrate holder

PMTfilter

R

laser pulse(tunabledye-laser)

protection flow (Ar)

R

precursorinjection

oscilloscope

Ar

CRD for the detection of SiH during a:Si-H deposition

CRD absorption during deposition

CRD spectrum of SiH measured during a:Si-H deposition


nσL/d

CRD spectrum of SiH measured during a:Si-H deposition

(1-R)/d


412,5 413,0 413,5 414,0 414,5

0

50

100

150

Experimental

Simulated (LIFBase)

R2(14.5)

Q1(14.5)

Q1(11.5)

Q2

Q1

Tvibr = 3000KTrot(v=0) = 1800K

Abs

orpt

ion

(x10

-6)

Wavelength (nm)

SiH detection: A 2 Δ à X 2Π, 405 – 430 nm

line width

temperature

absorption

cross-section

density

+

CRD absorption on SiH

TALIF spectroscopy on

H atoms

gas

stationaryshock wave

supersonic flowM > 1

subsonic flowM < 1

Mach diskM = 1

Cascaded arcPlasma expansion

cathode (×3)anode

(nozzle)cathodes (3)

gas inlet

Ar/H2 plasma expansion

Cascaded arc

anode (nozzle)

1 10 1001020

1021

1022

20 Pa 100 Pa

H2 d

ensi

ty (m

-3)

axial position (mm)

Rayleigh scattering on H/H2 plasma expansion

1/z2

Ø  produce 205 nm via THG of a Nd:YAG

pumped dye laser

Ø  from spectral scans data on: n,T,v,f(v)

1s2S

3s2S

2p2P

205.14 nm

Hα 656.5 nm

3d2D3p2P

2s2S

0

10.2

12.1

13.6ion

ener

gy (e

V)

121.56 nmLyman α

slitmaskflitergates PMT

205 nm205 nm

cascaded arc3.5 slm HI=40A, V=150V

2

TALIF detection of H atoms

1 10 1001019

1020

1021 100 Pa 20 Pa

Den

sity

(m-3)

z (mm)

H atom density along the jet axis (TALIF)

1 10 100

1019

1020

1021

nozzle length 6 mm 14 mm

H d

ensi

ty (m

-3)

axial position (mm)

Effect of nozzle-length on H density

-6 -4 -2 0 2 4 6

0

1

2

3

4

5

nozzle

arc

long

nozzle

arc

shortshort nozzlelong nozzle (x5)

H fl

ux d

ensi

ty (1

025 m

-2s-1

)

radial position (mm)

Effect of nozzle-length on H flux

-15 -10 -5 0 5 10 15

0.0

0.2

0.4

0.6

0.8

1.0

nozzle

arc

8

nozzle

arc

8large diam. nozzleshort nozzle

H fl

ux d

ensi

ty (1

025 m

-2s-1

)

radial position (mm)

Effect of nozzle-width on H flux

2H Hrv2

HH

H22H Hrv

2

J

nozzle

Conclusions

1.  Large influence of nozzle geometry on

H flux

2.  Loss of H atoms due to surface

association (volume association far

too slow)

H flux: ΦH > 1021 s-1

Dissociation degree = 0.4

P. Vankan et al., Appl. Phys. Lett. 86 (2004) 101501

S. Mazouffre et al., Phys Rev. E 64 (2001) 066405

loss of H atoms = production of

H2rv at the surface

Doppler-‐LIF spectroscopy on

Ar atoms

+

+

SiH3 reflection ~85% SiH3 reaction ~15%:5-fold bonded Si SiH3 surface diffusion:strong bond formation with danling bond

dangling bond creation byEley-Rideal H-abstractiondangling bond creation by ion

dangling bond surface diffusion

Plasma chemistry

Plasma creation

Material processing

Expanding Thermal Plasma (ETP)

Ar plasma expansion

Doppler LIF

Ar density as function of distance from the exit of the source

1 10 1001020

1021

1022

Ar

den

sity

(m-3)

Axial position (mm)

42 Pa 100 Pa

Rayleigh scattering

Doppler LIF experimental setup

Doppler LIF

BSBS

chopper

Lock inamplifier

diode laser

Argonlamp

FabryPerot

diodes

PMT

filter

reference

trigger

z-axis

1 2 3 4 5 6 7 8 9 10 11

0.0

0.5

1.0

Argon lamp

Fabry Perot

LIF signal

inten

sity (

a.u.

)

piezo voltage (a.u.)

Doppler LIF

Typical result of a Doppler LIF measurement

-1 0 1 2 3 4 5 60.00.51.01.5 z=174 mm

velocity (km/s)

inte

nsi

ty (

a.u

.)

0.00.51.0 z=100 mm

0.0

0.5z=59 mm

Doppler LIF Ar velocity distribution functions

10-3 10-2 10-1

100

1000

velo

city

(m/s

)

z (m)10-3 10-2 10-1

1000

z (m)T

(K)

calculated with:

20 Pa

Ar atom velocity Ar atom temperature

γ = 1.4 (theoretically: 5/3 for mono-atomic gas) zref = 0.0025 m T0 = 6000 K

Doppler LIF

IR absorp*on spectroscopy on

N2/O2 plasma

N2/O2 plasma setup (IR diode laser absorption spectroscopy)

pumps

ArN2

Ar, N2

H2, O2

p = 20 Pa

window

retroreflector

gas inlet

diode laser

PMT

IRMA system

QMS

pump

I = 55 A

window window

window

N2 plasma with O2 injected in the background

Introduction

O(3P)atm + NOads → NO2{2B1} → NO2{2A1} + hν


NO formation in an Ar-N2-O2 plasma

0 10 20 30 40 50 60 70 80 90 1000

1

2

3

4

5

6

0.0

1.0

2.0

3.0

100 90 80 70 60 50 40 30 20 10 0

20 Pa

NO

den

sity

(1019

m-3)

Percentage of O2 (%)

105 Pa

NO

den

sity

(1020

m-3)

Percentage of N2 (%)

N + NO → N2 + O N + NOads → N2O

0 10 20 30 40 50 60 70 80 90 100

0

1

2

3

4

5

6

N2O

den

sity

(1018

m-3)

Percentage of O2 (%)

20 pa 105 Pa

100 90 80 70 60 50 40 30 20 10 0

Percentage of N2 (%)

N2O formation in an Ar-N2-O2 plasma

N2O only formed at low O2 flow

150 200 2500.0

0.5

1.0

1.5 O2 off after 3 min

N2 off after 3 min

NO

den

sity

(1019

m-3)

Time (s)

Time behavior of NO formation in Ar-N2-O2 plasma

τres≅1s no O2 flow ⇓

no NO formation

no N2 flow ⇓

NO formation >> τres

N on/in the surface (no O storage)

0 50 100 150 200 250 300 3500

1

2

3 O2 off after 1 min

O2 off after 5 min

N2O

mol

e fra

ctio

n (1

0-4)

Time [s]

Time behavior of N2O formation in an N2-O2 plasma

no O2 flow ⇓

N2O formation >> τres

τres≅1s

NO on/in the surface (depends upon O2 conditioning)

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

Absorp'on spectroscopy IR absorp'on spectroscopy on N2/O2 plasma

VUV-‐LIF spectroscopy on

H 2r,v molecules in plasma

Why study hydrogen plasma expansions? (produced from a cascaded arc)

/ Plasma & Materials Processing PAGE 1 9/7/12

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

of high fluxes of H2r,v at low Te (around 1 eV)

Plasma source and expansion


I = 40 – 60 A

P = 5 – 10 kW

Φarc = 3 slm

I = 40 – 60 A

P = 5 – 10 kW

parc = 0.2x105 Pa

pbg = 100 Pa

Plasma expansion


T = 2000 K T = 1000 K T = 6000 K

T = 400 K

/ Plasma & Materials Processing PAGE 4

PLEXIS setup

PLEXIS setup


Laser table Nd:YAG

(450 mJ/shot @ 355 nm) dye laser

(50 mJ/shot @ 460 nm) ( 8 mJ/shot @ 230 nm)

Vacuum chamber cylindrical (2m x 0.3m) 9 Pa / 3000 sccm H2

•  Movable plasma source and substrate

•  Axial magnetic field Bmax = 0.2 T

Ar/H2 plasma expansion

PAGE 6 9/7/12

Ø  Produce 205 nm via THG of a Nd:YAG pumped dye laser

Ø  From spectral scans data on: n,T,v,f(v)

1s2S

3s2S

2p2P

205.14 nm

Hα 656.5 nm

3d2D3p2P

2s2S

0

10.2

12.1

13.6ion

ener

gy (e

V)

121.56 nmLyman α

slitmaskflitergates PMT

205 nm205 nm

cascaded arc3.5 slm HI=40A, V=150V

2

Two photon Absorption LIF (TALIF) on atomic hydrogen

PAGE 7 9/7/12

slit mask filter

gated PMT

1 10 1001019

1020

1021

20 P a 100 P a

Den

sity (m

-‐3)

A x ia l pos ition (mm)

Mazouffre et al. Phys. Rev. E 64, 016411 (2001)

H atom density in H2 plasma expansion (TALIF)

PAGE 8 9/7/12

VUV-LIF detection of H2r,v

H2 energy scheme

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

AS

8A

S9 A

S7

AS

7

AS

6

AS

5 AS

4 AS

3

AS

2 AS

1

120 140 160 180 200 220

10-4

10-3

10-2

10-1

100

101 depleted pump

Ener

gy (m

J)

wavelength (nm)

Excitation and detection

PAGE 9 9/7/12

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


H2 energy scheme

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

AS

8A

S9 A

S7

AS

7

AS

6

AS

5 AS

4 AS

3

AS

2 AS

1

120 140 160 180 200 220

10-4

10-3

10-2

10-1

100

101 depleted pump

Ener

gy (m

J)

wavelength (nm)

Excitation and detection

PAGE 11 9/7/12

H2 energy scheme VUV-LIF detection scheme


PAGE 12 9/7/12

VUV-LIF setup

PMT

PMT

H2

LN2

VUV mono

L W

BS

MM

plasma

W

S

WM

M

Nd:YAGTHG

Dye (C440)

BBO

M

M

220 nm

to pump

to pump

440 nm

PMT

NO cell

PAGE 13 9/7/12

PMT

PMT

H2

LN2

VUV mono

L W

BS

MM

plasma

W

S

WM

M

Nd:YAGTHG

Dye (C440)

BBO

M

M

220 nm

to pump

to pump

440 nm

PMT

NO cell

VUV-LIF setup

Measured H2 Lyman spectrum


43650 43700 43750 43800 43850 43900

0

2

4

6

8

10

Fluo

resc

ence

(a.u

.)

SH frequency (cm-1)

81295 81045 AS9 frequency (cm-1)

77140 76890 AS8 frequency (cm-1)

VUV-LIF setup


PMT

PMT

H2

LN2

VUV mono

L W

BS

MM

plasma

W

S

WM

M

Nd:YAGTHG

Dye (C440)

BBO

M

M

220 nm

to pump

to pump

440 nm

PMT

NO cell

PMT

PMT

H2

LN2

VUV mono

L W

BS

MM

plasma

W

S

WM

M

Nd:YAGTHG

Dye (C440)

BBO

M

M

220 nm

to pump

to pump

440 nm

PMT

NO cell

44000 44020 44040 44060 44080 44100 44120 44140 44160 44180 44200

44200 44220 44240 44260 44280 44300 44320 44340 44360 44380

TALIF spectrum of NOP = 2 mbar

Fluo

resc

ence

(a.u

.)

Wavenumber (cm-1)

Flu

ores

cenc

e (a

.u.)


VUV-LIF setup


PMT

PMT

H2

LN2

VUV mono

L W

BS

MM

plasma

W

S

WM

M

Nd:YAGTHG

Dye (C440)

BBO

M

M

220 nm

to pump

to pump

440 nm

PMT

NO cell

44000 44020 44040 44060 44080 44100 44120 44140 44160 44180 44200

44200 44220 44240 44260 44280 44300 44320 44340 44360 44380

TALIF spectrum of NOP = 2 mbar

Flu

ore

scence

(a.u

.)Wavenumber (cm-1)

Flu

ore

scence

(a.u

.)

73182 73184 73186 73188 73190

22048 22049 22050 22051 22052 22053

H2(v= 4,J= 7)

via VUV-‐LIF

AS7 frequency (cm-1)

NO via TALIF

dye laser frequency (cm-1)

VUV-LIF spectroscopy

44040 44060 44080 44100

H2(rv)

FP

frequency (cm-1)

NO

Inte

nsity

v=3,

J=12

v=4,

J=7

v=4,

J=2

v=2,

J=9

v=3,

J=5


state-selective

spatially resolved

non-intrusive

dynamic range > 4 orders

detection limit ~ 1013 m-3

P. Vankan et al., Rev. Sci. Instrum. 75 (2004) 996



Advantages multiplexing: ü  spectrum more dense ü  efficient measurement


81595 81415 AS9 frequency

44020 44060 44100 44140 44180

0.0

0.5

1.0

1.5

2.0

(6,7

)

(3,6

)

(3,1

4)

(3,9

)

(2,1

7)

(4,7

)

(4,1

1) /

(9,1

)(3

,5)

(3,8

)(2

,10)

H 2(v,J

)=(3

,7)

fluor

esen

ce (a

.u.)

SH frequency (cm-1)

77440 77260 AS8 frequency

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

Measured and calculated Lyman spectra


Spectroscopic data for D2 H. Abgrall et al. J. Phys. B: At., Mol. Opt. Phys. 32 (1999) 3813

Spectroscopic data for HD H. Abgrall, E. Roueff, Astron. Astrophys. 445 (2006) 361

Spectroscopic data for H2 H. Abgrall et al. Astron. Astrophys. Suppl. Ser. 101 (1993) 273

All H2 Lyman transitions HD Lyman transitions J < 11 D2 Lyman transitions J < 12

Measured and calculated H2/HD/D2 Lyman spectrum

Measured and calculated Lyman spectra


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

Measured and calculated H2/HD/D2 Lyman spectrum

Non-Boltzmann distribution for H2


700 K for low J 3800 K for high J

“Hockey stick”

Non-Boltzmann distributions in H2/D2 jet


Low J: T = 300 K High J: T = 3000 K

Low J: T = 700 K High J: T = 3800 K

Low J: T = 500 K High J: T = 3400 K

O. Gabriel et al, J. Chem. Phys. 132 (2010) 104305


Results on H- production through DA process

Production rate of H- ions by dissociative attachment

Te = 5000 K

ne = 1017 m-3

J. Horáček et al, Phys. Rev. A, 70 (2004) 052712

O. Gabriel et al, J. Chem. Phys. 132 (2010) 104305

Absorp'on spectroscopy

CRD spectroscopy on

N2/H2 plasma

+

+



dangling bond surface diffusion

NH3 production in N2/H2 plasma

+

+



dangling bond surface diffusion Plasma chemistry leading to e.g. NHx

N2/H2 plasma creation

NH3 formation ?


Ø  absorption per unit of pathlength (cavity loss):

Ø  non-intrusive Ø  high sensitivity due to effective multipassing Ø  direct absorption –> line of sight measurement

(O’Keefe and Deacon, Rev. Sci. Instrum. 59 (1988) 2544)

Det.

R

d

L 5 ns

lightpulse

R

n, σ

time

inte

nsity

τ

withabsorption

emptycavity

1/e

dLnRc /)1(/1 σ+−=τ

Cavity Ring Down: principals and features

Rev. Sci. Instrum. 69, 3763 (1998)

Cavity Enhanced Absorption detection scheme

CEA measurement recorded in a vessel in which N2/H2-plasma expands

6568.3 6568.4 6568.5 6568.6 6568.70.00

0.02

0.04

0.06

0.08

0.10

inte

nsity

(a.u

.)

frequency (cm-1)

Scanning frequency: 30 Hz Frequency range: 15 GHz Averages: 1000 Measurement time: 30 s The absorption coefficient κ(ν) from intensity by:


1( ) νν

κ ν⎛ ⎞ ⎛ ⎞= − ×⎜ ⎟ ⎜ ⎟

⎝ ⎠⎝ ⎠0S ( ) 1-RS( ) d

6568.4 6568.5 6568.6 6568.70

1

2

3

4

abso

rptio

n (in

10-5

cm

-1)

frequency (cm-1)


Part of the absorption spectrum of NH3 as measured in an expanding N2/H2 plasma

σ ≈ 10-22 m2

N ≈ 1019 m-3

Ttr = 600 K

Line width

0.0 0.1 0.2 0.3 0.4 0.50.0

0.5

1.0

1.5

2.0

2.5

3.0

(φH2

+ φN2

)

Pbg= 100 Pa

NH

3 den

sity

(1019

m-3)

φH2

Total N+ flow is consumed

Saturation behavior explained by rate determining steps: N+ + H2 -> NH+ + H NH+ + e -> N + H


Ammonia density produced in expanding N2 plasma in which H2 is injected in the background


Ammonia density as function of background pressure at constant gas flow (N2-arc/H2-background)

0 50 100 150 2000.0

1.0

2.0

3.0

4.0

NH

3 den

sity

(1019

m-3)

Pressure (Pa)

Linear with pressure (dNH3/dt constant)

Wall production (?)

3 particle reaction stable intermediate


NH3 production in two different vessels

0.0 0.2 0.4 0.6 0.8 1.00

2

4

6

8

10

12

14

0.0

0.5

1.0

1.5

2.0

2.5

% N

H3

φH2

/φtotal

% N

H3

Ø  Total gas flow of 2 slm through cascaded arc

Ø  At maximum 12 % of the background gas is NH3

larger surface-to-volume ratio

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.

plasma diagnosticsliterature on diagnostics (general): ! h r griem, plasma spectroscopy (mcgraw-hill...

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