www.inp-greifswald.de

On Recent Progress in Diagnostics of Molecular Plasmas using Mid

Infrared Diode Lasers

Jürgen Röpcke

Utilasation des Diodes Laser

WS2005

March 17th, 2005

Col de Porte France

Vor_Grenoble1_publ.ppt

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2Outline

Introduction and Motivation

TDLAS in Molecular Plasmas Containing Hydrogen

IRMA: Transportable Infrared TDLAS System

Plasmas Containing Boron in Research and Industry

QCLAS for Plasma and Trace Gas Monitoring and Control in Industry

“Q-MACS”- A New Compact QCL System for Plasma and Gas Analysis

Summary

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3Orientation

Orientation in Europe's

Plasma and Diagnostics Community

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4Orientation

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5Greifswald – Old Town at the Baltic Sea

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6INP Greifswald

1999: new building

3700 sqm floor space

110 working places

26 laboratories, clean room, chemical laboratory

15 complete devices for plasma research

mobile measuring and diagnostics equipment

laboratories for applications

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7TDLAS

Tunable Diode Laser Absorption Spectroscopy

for Plasma Diagnostics and Trace Gas Measurements

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8IR Spectroscopy

Why absorption spectroscopyin the mid infrared region,

3 – 20 µm

and NOT in the visible 0.3 – 0.8 µm

or near infrared region ?0.8 – 3 µm

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9IR Absorption Spectroscopy

Species Ratio of Absorption Coefficients αMIR/ αNIR

H2O 5CH4 18NH3 132HBr 2820CO 18400CO2 52500

Many others (e.g. H2S, N2O, NO, HCN) – only absorptions in MIR !

It is the sensitivity !

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10

IR Absorption Spectroscopy with Tunable Diode Lasers (TDLAS)

Detection of Stable and Transient Molecular SpeciesGround State Concentrations

High Sensitivity and Selectivity (∆ν ~ 10-4 cm-1, (I0-I)/I0 ~ 10-4...10-5)

Time Resolution (s ... ms ... µs … ns)

Cooling necessary: Laser Diodes 20-100 K, Detectors 80 K !!Low power: < 1 mW

Alternative:Quantum Cascade Lasers: QCLAS☺ Room Temperature Operation☺ Short Pulses (ns), Power > 10 mW

Plasma Diagnostics by IR Absorption Spectroscopy

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11TDLAS

distance

inte

nsityI0 I

plasma

ν

exponentialdecay

I (ν) = I0 (ν) exp (-k(ν) l n)

Infrared Tunable Diode Laser Absorption Spectroscopy (TDLAS)stable and transient molecular species

ground state information - species concentration

high selectivity and sensitivity (∆ν ~ 10-4 cm-1, (I0-I)/I0 ~ 10-4...10-5)

spatial and temporal resolution (s ... ms ... µs)

Lambert-Beer absorption law

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12TDLAS

+

-

p region

n regionp-n junction

metal contact

metal contact

insulator

resonator front facet

active zone

© U. Haeder

Infrared Diode Laser

U Schießl et al. Booklet of Laser Components 1998

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13Plasma Chemistry and Reaction KineticsPlanar Microwave Plasma Reactor

with optical multi pass set-up (White cell)

Principle of a White cellca. 30 passes possible

improved sensitivity fordetection of transient species

HgCdTedetector

HgCdTedetector

HgCdTedetector

TDL system

monochromator

microwave window

microwave appliancemodule (2.45 GHz)

Discharge vessel with long path cell

planar microwave plasma reactor

plasma regionobjectivemirror box

field mirror box

beam splitter

etalon

reference gas cell

He closed cyclerefigerator

F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98

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14Plasma Chemistry and Reaction KineticsPlanar Microwave Plasma Reactor

A Ohl 1998 J. Phys. IV France 8 Pr7-82, U Haeder INP-Greifswald 2000

basic research of non-stationary excitation - relaxationphenomena and of plasma chemistry

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15Plasma Chemistry and Reaction Kinetics

plasma region below the microwave window

A Ohl 1998 J. Phys. IV France 8 Pr7-82, U Haeder INP-Greifswald 2000

Sideview of a Double Microwave Plasma Source

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16Plasma Chemistry and Reaction Kinetics

606.0 606.1 606.2 606.30.0

0.2

0.4

0.6

0.8

1.0

wavenumber [cm-1]

inte

nsity

[a.u

.]

16.502 16.500 16.498 16.496 16.494

CH3OH CH3

wavelength [µm]

F Hempel, L Mechold and J Röpcke 2001 XXV. ICPIG, Nagoya, Conf. Proc. 4 223

Example of Sensitive Detection of Methyl Radicalmeasured with optical multi pass cell

H2-Ar-N2-CH3OHp= 1.5 mbar

P= 1.5 kWpulsed diode laser

nCH3 ~ 1012 cm-3 (~ 20 % abs.)

detection of transient species

in a wider dynamic range possible

time resolved analysis for kinetic

studies

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17Plasma Chemistry and Reaction KineticsMolecular Concentrations as a Function of Various H2/N2 Ratios

in H2-N2-Ar-CH3OH Plasmas

microwave plasma, p=1.5 mbar, P=1.5 kW, flowing conditions

0 100 200 300 4001E11

1E12

1E13

1E14

1E15

1E16

CH3OH NH

3 HCN CH3

CH3OH addedCH

3OH added

N2 [sccm]

conc

entra

tion

[mol

ecul

es c

m-3] 400 300 200 100 0

H2 [sccm]

0 100 200 300 400

CH4 C2H2 C2H4 C2H6 CH2O

N2 [sccm]

400 300 200 100 0

1E11

1E12

1E13

1E14

1E15

1E16

H2 [sccm]

F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98

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18Plasma Chemistry and Reaction Kinetics

Calculated Rate Coefficients for Electron Impact Dissociation

Kdis as a function of

reduced field strength E0/N

in H2-N2-Ar-CH4 plasmas

determined from

Boltzmann equation

for model: E0/N= 180 Td

was used100 150 200

1E-16

1E-15

1E-14

1E-13

1E-12

1E-11

1E-10

H2 N2 CH CH2 CH3 CH4

E0/N [Td]

k dis [c

m3 s-1

]

100 150 200

C2H C2H2 C2H3 C2H4 C2H5 C2H6

E0/N [Td]

F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98

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19Plasma Chemistry and Reaction KineticsComparison of Experimental and Modelling Results

in H2-N2-Ar-CH4 Plasmas

prediction of further radicals: [NH] = 6 x 1012 cm-3,[NH2] = 3 x 1011 cm-3, [CH] = 8 x 1010 cm-3, [CH2] = 1 x 1012 cm-3,[C2H] = 7 x 106 cm-3, [C2H3] = 3 x 109 cm-3, and [C2H5] = 5 x 1010 cm-3

NH3 HCN CH3 CH4 C2H2 C2H4 C2H6

1E11

1E12

1E13

1E14

1E15co

ncen

tratio

n [m

olec

ules

cm

-3]

white – measured by TDLAS

grey – calculated

F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98

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20Plasma Chemistry and Reaction KineticsMain Reaction Paths in H2-N2-Ar-CH4 Plasmas

F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98

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21TDLAS Applications

Properties of Radicals

CN, CH3

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22TDLAS for Molecular SpectroscopyPlanar Microwave Plasma Reactor

with optical multi pass set-up (White cell)

Principle of a White cellca. 30 passes possible

improved sensitivity fordetection of transient species

HgCdTedetector

HgCdTedetector

HgCdTedetector

TDL system

monochromator

microwave window

microwave appliancemodule (2.45 GHz)

Discharge vessel with long path cell

planar microwave plasma reactor

plasma regionobjectivemirror box

field mirror box

beam splitter

etalon

reference gas cell

He closed cyclerefigerator

F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98

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23

Detection of Four Isotopic Forms of the CN Radicalin Microwave Discharges

12C15N P(20) line with doublet

splitting at 1931.80 cm-1

1931.75 1931.80 1931.85 1920.20 1920.25

TDLAS for Basic Research

13C15N P(13) line with doublet

splitting at 1920.20 cm-1

2f modulation technique forground state detection (81 lines)

M. Hübner, M. Castillo, P. B. Davies, and J. Röpcke 2005 Spectrochim. Acta A 61 57.F. Hempel, J. Röpcke, A. Pipa and P. B. Davies 2003 Mol. Phys. 101 589

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24

12C14N and 13C14N (dotted) lines

1900 1950 2000 2050 21000

5

10

15

20

inte

nsity

[a.u

.]

wavenumber [cm-1]1900 1950 2000 2050 2100

0

5

10

15

inte

nsity

[a.u

.]

wavenumber [cm-1]

M. Hübner, M. Castillo, P. B. Davies, and J. Röpcke 2004 Spectrochim. Acta A Mol. Spectrosc. A 61 57.F. Hempel, J. Röpcke, A. Pipa and P. B. Davies 2003 Mol. Phys. 101 589

TDLAS for Basic Research

Stick Diagrams of CN Absorption Lines from the Fundamental Band

determination of molecular parameters and constants:- band origins, Bv, Dv, re - values

12C15N and 13C15N (dotted) lines

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25TDLAS for Basic Research at Radicals

The CH3 Radical

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26

5 µmWhy CHWhy CH33 ??

- Important growth species growth species for diamond anddiamond-like carbon films

- Key role in the complex chemical scheme ofcarbon-containing species discharges

- Important in interstellar chemistry

Why ν2 Band?

- The strongest band of CH3 - IR at 16.5 µm

- Successfully used for [CH3] by IR-TDLAS

- ν2 band pattern detected on the upperatmosphere of Neptune

TDLAS for Basic Research at Radicals

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27

microwavegenerator

optical unit

IRMA system

control unit

discharge vessel with mutiple pass optics

planar microwave plasma reactor

microwave appliancemodule ( 2.45 Ghz )

IR detectormicrowave window

objective mirror box

functiongenerator

Experimental set-up: Pulsed microwave plasma with optical multiple pass IR-TDLAS arrangement

Characteristics:

- f = 2.45 GHz;- fpulse = 50 mHz;- P = 1.5 kW;- p = 1 mbar;- precursor:

[(CH3)3CO]2diluted in Ar 20 sccm

IRMA +TDL Wintel Software

- integral of absorption

coefficient

- ms – time resolution

TDLAS for Basic Research at Radicals

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28

Decay method for CH3 Concentration- during the plasma off phase – decaymeasurements of the ∫ k(ν)dν

- the main loss channel of CH3:

CH3 + CH3 + M K1 C2H6 + M

- time dependency of the concentration:

0 5 10 15 20 250.0

0.2

0.4

0.6

0.8

1.0N(t)/N0=K2/[(K2+2N0K1)exp(K2t)-2K1N0]

N(t)/N0=1/(1+2N0K1t)

N(t)/N0=exp(-K2t)

N(t)

/N0

time [ms]

0 5 10 15 20 250

6

12

18 N0/N(t)=1+2K1N0t

N0/N

(t)

time [ms]

The recombination into C2H6 - the mainloss channel.

NKNKdtdN

22

12 −−=

The concentration is obtained from theslope of:

N0/N(t)=1+2K1N0t

K1 - the recombination rate constant

K2 - other loss channels

Based on the new data of K1 the total [CH3] was determined.

TDLAS for Basic Research at Radicals

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29

Temperature dependence of the line strength

200 400 600 800 1000 1200 1400 16001E-22

1E-21

1E-20

1E-19

1E-18

S [c

m m

olec

ule-1

]

temperature [K]

Q(3,3) Q(6,6) Q(12,12)

Region IIIRegion IIRegion I

- for practical purpose - line strength values are more convenient

- three temperature regions where Q(3,3), Q(6,6) or Q(12,12) is recommended

- changes about two orders of magnitude of line strengths in 1000 K temperature range

Region I:

- astrophysics

Region II:

- moderate temperature

plasmas

Region III:

- diamond processplasmas

TDLAS for Basic Research at Radicals

G. D. Stancu, P. B. Davies, and J. Röpcke 2005 J. Chem. Phys. 122 014306.

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30

Transition dipole moment of the ν2 fundamental band

The present value 0.22±0.02 D leads to two times higher concentrations!

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

unknown third body

K1 - new dataJ.Pacansky,W.Koch and M.D. Millertheoretical calculations (1990)

present workmeasurement (2004)

J.Wormhoudt and K.E.McCurdymeasurement (1989)

P.Botshwina,J.Flesch and W.Meyerwavefunctions calculation (1983)

C.Yamada and E. Hirotameasurement (1983)

µ(v=1 0) [D]

C.Yamada,E.Hirota and K.Kawaguchiassumption (1981)

TDLAS for Basic Research at Radicals

G. D. Stancu, P. B. Davies, and J. Röpcke 2005 J. Chem. Phys. 122 014306.

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31Tunable Diode Laser Absorption Spectroscopy

Status:

Detection of Only One Molecule or Radical in Time

Time Resolution: Rather Slow and Difficult

Data Handling: Slow and Difficult

New Approach:

TDLAS System with 4 Diodes (T ≥ 30 K)

Time Resolution ~ 1 ms (Lifetime of Radicals, ...)

Simultaneous Detection of ~ 4 Species

Spatial Resolution Inside Plasma

Exhaust Gas Detection (Multi Path Cell)

System: Compact and Transportable !!

Objective: ☺ TDLAS for Plasma Process Control in Industry !!

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32IRMA System

J Röpcke, L Mechold, M Käning, J Anders, F G Wienhold, D Nelson, M Zahniser2000 Rev. Sci. Instrum. 71 3706

left: optical table

right: data acquisition

with controllers and PCs

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33Properties of Plasmas Containing Boron

J Röpcke, L Mechold, M Osiac, S Saß and A Liebetrau 2000 Zwischenbericht BMBF-Projekt, FKZ: 13N7451

Measurement Campaign in Cooperation with IndustryTDLAS and OES at industrial reactors

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34Properties of Plasmas Containing Boron

B P Lavrov, M Osiac, A V Pipa, J Röpcke 2003 Plasma Sources Sci. Technol. 12 576

64 % H2 + 33 % Ar + 3 % B2H6

p= 1.5 mbar, φtotal= 150 sccm

OES

Fragmentation of Diborane in Microwave Plasmasdepending on power and admixture

0.0 0.5 1.0 1.5 2.0 2.5

0.0

0.5

1.0

BH

BH3

B2H6

abso

rptio

n co

effic

ient

s [a.

u.]

P [kW]

TDLAS

H2 + Ar + B2H6

P= 2.5 kW, p= 2.5 mbar, φtotal= 150 sccm

0 1 2 3 4

0

1

2

3

4

[B] [

1011

ato

ms c

m-3]

B2H6 admixture [%]

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35

Measurement Campaign at Uni Erlangen 05/2004

TDLAS in Hot Filament Reactors

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36QCLAS

Quantum Cascade Laser Absorption Spectroscopy

(QCLAS)

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37Scheme of a DFB-QCL

Alpes Lasers, Neuchatel, Switzerland

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38Photo of a DFB-QCL

Product of Alpes Lasers, Neuchatel, Switzerland

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39Systems with DFB-QCL

Advantages:• Decreased Instrument Size and Weight

• Reduced Transport Logistics

• Unattended Remote Monitoring

• “Turn-Key” Operation

• Improved Safety

Disadvantages:• Increased Laser Line Width

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40Q-MACS-System

QCL-System „Q-MACS“

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41Q-MACS Idea

Problem: In-situ controlling of plasma processes and trace gas analysis in ppb range - on-line not available

Idea: Using of a new class of infrared laser: Quantum Cascade Lasers (QCL) – working without heavy cooling at room temperature

Result: Development of a new compact measuring system for industrial applications of QCLAS : Q-MACS

Q-MACS: Quantum Cascade Laser Measuring and Controlling System

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42Q-MACS-System

Working at room temperature: Q-MACS-Heads

recent development for industrial application of QCLAS

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43View Inside a DFB-QCL

Alp

es L

a ser

s, N

euch

a tel

, Sw

itzer

land

back- contact

top-contact

buried grating

active regions& injectors

InP substrate

high intensity (3-20 µm)short pulsestuneablesmall line width

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44Plasma – and Trace Gas Analysis with Q-MACS

Gas Molecules

Q-MACS

Principle: Absorption of the laser beam by gas / plasma molecules

Result: On-line concentration of molecules

Control Unit

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45Q-MACS System

Q-MACS Head with Control Unit

Prototype

compact, exact, easy to usewww.q-macs.de

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46Q-MACS System

Applications: Insight into plasma chemical processes

Trace gas monitoring for environmental studies

High sensitive gas analysis in chemical industry

Advantages: Ground state concentrations of molecules

Monitoring and control of combustion and plasma processes

Temporal resolution of concentration measurements

Software for industrial requirementsFor improvements of process effectiveness, reliability and reproducibility

Disadvantage: Line-off-sight method: Difficult spatial resolution

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47Q-MACS System

Technical Features: Width of single pulses: 10 … 255 ns

Power: 10 – 30 - … mW

Pulse frequency: up to 1 MHz

Working regime: Single pulse

Ramp

Gate

Temperature range: - 30 … + 40 °CAdapted to TDLWintel (Aerodyne Research, USA)Adapted to QCLs from Alpes Lasers, CH

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48Wide Spread Applications

Exhaust Gas Treatment / Environmental Technology

Process Control in Deposition and Etching ReactorsSemiconductor IndustryCar IndustryMedicine TechniqueCombustion Fusion Devices...

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49Q-MACS-System

System Test

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50Q-MACS-SystemExample of a fast measurement

NH3 Spectrum with FitMeasured in a Single Pulse

100 ns

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51Q-MACS-System

Example of a slow measurement

NH3 Absorption Lines at 1614 cm-1 with FitMeasured with Current Ramp

1 ms

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52Q-MACS-System

Test at Aerodyne Research Inc., USA

In a QCLAS System for Air-born Measurements - May 2004

Q-MACS Head

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53Q-MACS-SystemQ-MACS Trace

1 channel system with56 m long path cell

Sensitivity: ppb(e.g. NH3, CH4)

Q-MACS Head

Control Unit

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54Q-MACS-System

Measurements at Industrial Plasma Reactors

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55Plasma Reactors of Eltro GmbH, Baesweiler

Open DC-Reaktorof Average Size

Working in Pulse Mode

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56Q-MACS-System

Measurements at DaimlerChrysler AG

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57Q-MACS-SystemMeasurements at DaimlerChrysler AG

View into the Plasma of the Pulsed Reactor

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58

Time Dependence of Diborane Concentration in DC-Reactor

B2H6 Spectrumwith Fit

[B2H6] = f(t)

t

C4%

0

cm-1

I

ca. 1618 cm-1

First QCLAS Measurements inIndustrial Plasma Reactors !!

Q-MACS-System

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59QCLAS at Industry

Related Problems of QCLAS at Industry

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60Measurement of Complex Spectra - TDLAS

BCl3-Absorption Spectra Measured with TDLAS and IRMA TDLWintel: Aerodyne Research Inc. USA

left: 963.4 – 963.8 cm-1, right: 964.3 – 964.6 cm-1

Software: In Co-operation with Dr. C. Harward, Nottaway, VA, USA

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61BCl3-Concentration - TDLAS

Monitoring of the BCl3-Concentration in a Plasma Reactorrel. Precision: ca. 0.1 %

t

C

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62Chemistry in CH4 Plasma - QCLAS

On-Line Measurement of CH4 Dissociation and C2H2 Productionat 1300 cm-1

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63Software for Industrial Applications

Time Dependence of [BCl3] in Plasma Reactor

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64SummaryApplication of TDLAS to study plasma chemistry and reaction kinetics

TDLAS Status: 16 stable and 10 transient molecules in 12 different

discharge configurations

Multiple on-line concentration measurement possible in ms

QCLs provide cryogen-free trace gas detection with both open and closed path sampling: sensitivity up to ppb level, temporal resolution: >20 ns

QCLAS - potential for compact instrumentation and remote operation

and industrial process monitoring and controlCH4, C2H2, C2H4, NH3, NO2, BCL3, B2H6 measured by QCLAS

QCL-System „Q-MACS“ – recent development for industrial application