Laser-Induced Breakdown Spectroscopy for Microanalysis · PDF fileU of A - R. Fedosejevs 070303 p.1 Laser-Induced Breakdown Spectroscopy for Microanalysis Robert Fedosejevs, Y. Godwal,

U of A - R. Fedosejevs 070303 p.1

Laser-Induced Breakdown Spectroscopy for Microanalysis

Robert Fedosejevs, Y. Godwal, M.T. Taschuk, S. L. Lui, Y.Y. Tsui

Department of Electrical and Computer EngineeringUniversity of Alberta, Edmonton, Alberta

Presented at the

3rd INTERNATIONAL CONFERENCE ON THE FRONTIERS OF PLASMA PHYSICS AND TECHNOLOGY

Bangkok, March 5, 2007

Research Funded by:

MPBT/NSERC/UofA Senior Industrial Research Chair

Natural Sciences and Engineering Research Council of Canada


Outline

• Introduction to LIBS• Scaling of LIBS to µJ Energies• µLIBS Applications

• 2D Surface Microanalysis• Fingerprint Detection & Imaging• Two Pulse Technique to Improve Limit Of Detection• Measurement of Elemental Contaminants in Water• µLIBS in Microfluidic Systems for Lab on a Chip Analysis

• Conclusions


Overview of LIBS Process

Plasma PlumeExpands

FocussingLens

Target Material397398399400401402

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Wavelength (nm)

Spectrometer

21Laser StrikesTarget Material

3Spectra isobtained.

CharacteristicRadiation


Overview of LIBS Plasma Expansion

Target Material Target Material Target Material

Shockwave launchedAtomic emission dominatesContinuum decreases

Plasma expands rapidlyContinuum radiation dominates

Laser initiates breakdownPlasma formsPortion of sample taken into plasma

20 ns

wavelength (nm)

Laser pulse


Typical µLIBS Experimental Set-up

CCD

PD

Sample

Laser Pulse:10 ns, E = 1 - 500 µJI = 0.5 – 250 GW/cm2

50 ps, E = 0.1 - 100 µJI = 0.01 – 10 TW/cm2

100 fs, E = 0.1 - 100 µJI = 0.005 – 5 PW/cm2

~ 5 µm focal spot

OMA

Laser Pulse

Spectrometer/OMAAlignment Camera

Plasma

R = 99%

Dichroic Mirror

300 400 500

1000

10000

Coun

ts

Wavelength (nm)

MicroscopeObjective PM

Filter

Rieger et al., Appl. Spect. 56, 689 (2002)


1 e + 3

1 e + 4

1 e + 5

3 0 0 3 5 0 4 0 0 4 5 0 5 0 0-1 0 0 0

-8 0 0

-6 0 0

-4 0 0

-2 0 0

0

Inte

nsity

W a ve le n g th (n m )

Delay (ns)

Al+

Mn+

Mn

Al+

AlO-bands

Si

Fe

Mn

AlAl

Time Evolution of an Aluminum Alloy PlasmaAl 3003, 10 µm slit248 nm, 10 ns, TG = 300 ns Eav = 200 µJ

U of A - R. Fedosejevs 070303 p.7Wavelength (nm)

397 398 399 400 401 4020.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.6

Wavelength (nm)

397 398 399 400 401 4020.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.6

SPS 17-4 PHChromiumNominalComposition: 0.6%

ChromiumNominalComposition: 16.5%

Cr I Triplet397.6 nm, 398.3 nm, 399.1 nm

SPS steel,0.6% Chromium

17-4 PH steel,16.5% Chromium

Overview of LIBS :Typical Spectra

Observing elements at less than a single percent concentration is straightforward

Choose spectral window according to the material being observed to maximize information gathered


• Laser-Induced Breakdown Spectroscopy:• offers rapid analysis• requires no sample preparation• sensitive to all elements• scalable in sample size• requires no contact with the

sample• work in hostile environments

Advantages of LIBS

Laser beam being directed through the lead glass shield window to measure radioactive materials


LIBS Inspection of Gas Cooled ReactorUsing a fiber optically coupled LIBS system for finding low ductility joints in superheated steam tubes by anomalously high copper content Applied

Photonics


• Lower laser pulse energies ≤ 100 µJ:• Smaller spot sizes reduces damage to sample• Allows micron scale resolution• Higher repetition rate laser systems can be used• Possibility of portable LIBS systems• LODs achieved are comparable to mJ LIBS

→ New Subfield of µLIBS

• Applications• 3D surface Microanalysis with µm lateral and sub-µm depth

resolution• On line pollution monitoring of industrial effluents• Monitoring of drinking water standards• Microfluidic point of care medical diagnostic systems

Scaling of LIBS to µJ Energies


Definition of Limit of Detection

• Noise is evaluated from the pixel to pixel variation on either side of the signal

• LOD (limit of detection) is the point where signal within the full linewidth of the emission line is 3σabove the average noise scaled to the integration width

Signal

Noise


Single Shot Surface Probe Capability


Correlation of elements within precipitates - identification

Single Shot µLIBS Aluminum Precipitates

Aluminum 2024 Alloy

Cravetchi et al., Spectrochimica Acta. 59, (2004)


• Accumulation of 100 0.5 µJ pulses yields useful spectra

• High rep-rate fiber or microchip lasers have potential for LIBS

• Remaining Issues:

• Scaling to sub micron resolution with different materials

• Integration of high rep-rate laser source with ICCD

Al2024, 100 shot average, 0.5 µJ, 266 nm, 130 fs600 l/mm, 100 µm slit, Gate Delay 2.5 ns, Gate Width 100 ns, Pixel Time 16 µs, Gain 275 counts/photoelectron, 9 counts/photon @ 270 nm, 27 counts/photon @ 440 nm

Surface Mapping at sub-µJ Energies with Femtosecond Pulses

0.5 µJ Spectra


Surface Mapping at sub-µJ Energies

Grey – background matrix, Black – Al2CuMg, White - Al6(Cu,Fe,Mn)

Can build up a map of aluminum alloy surfaces with many single shots2D map of aluminum alloy possible with sub microjoule energiesHowever, a limited number of photons are available at these energies

Al 2024 Alloy, 0.85 µJ, 266 nm, 120fs


Experimental Setup for µLIBS measurement of fingerprints

LIBS Fingerprint Detection and Imaging


Nshots = 1, Elaser= 80 µJ, 400 nm 130 fs pulseTdelay = 5 ns, Tgate = 1 µs, Slit = 100 µm, Readout Time = 16 µs1200 lines/mm grating

2D mapping technique can be applied to latent fingerprints

80 µJ, 130 fs fs pulses at 400 nm

Fingerprint Detection Characteristic Spectra

Sample spectra from a fingerprint ridge and gap between fingerprint ridges on silicon wafer

Na 589.2 nm

Si 288.2 nm (2nd order)



Fingerprint Detection - Line Scan

• Si signal suppressed at locations with a fingerprint ridge

• Femtosecond probe pulses only sensitive to surface layer

Na signal

Si signal



2D LIBS scan of a 1 mm by 5 mm area of a latent fingerprint from right thumb

Ridge detail is clearly visible in the Na image (upper) and Siimage (lower)

Fingerprint Detection – 2D Scans

Na signal

Si signal

M. Taschuk et al., Applied Spectroscopy 60, pp.1322 –1327 (2006)


Sodium signals:Original

After 2 cleaning wipes with alcohol soaked lens tissue

After 4 cleaning wipes with alcohol soaked lens tissue

Durability of Na Signature



• Thus far used 80 µJ 400nm femtosecond pulses• Sample is mostly destroyed using a 50 µm sampling grid

• Try with 5 µJ 266nm femtosecond pulses• stronger UV absorption allows lower pulse energy threshold• Much smaller 10 µm craters• Large surface area preserved for future analysis if necessary• Better suited to lower energy, higher repetition rate laser

Shift to UV Excitation and Lower Energies


Fingerprint Detection 5 µJ 120 fs 266nm Probe Pulses

Reflective laser focusing and achromatic plasma imaging system

to collect broadband spectrum

SchwarzchildObjective


Large amount of the surface area remains undamaged by the craters

Craters from Scanning with 5 µJ 266 nm Pulses


Nshots = 100 shot average, 266 nm, 130 fs pulsesTdelay = 1 - 5 ns, Tgate = 1 µs, Slit = 100 µm, Readout Time = 16 µs600 lines/mm grating

SNR scaling for 3 fingerprints using 266 nm pulses

SNR approaching limit for single shot acquisitions at ~ 3 uJ

SNR scaling with Pulse Energy



Na

Si

2D LIBS scan of a 2 mm by 5 mm area of a latent fingerprint

Ridge detail is clearly visible in the Na image (upper) and Siimage (lower)

Energy requirements reduced to levels easily compatible with fiber or microchip lasers

Portable system at kHz acquisition rate may be possible

Fingerprint Imaging 5 µJ 266 nm Pulses


Two Pulse LIBS: Laser Ablation - Laser Induced Fluorescence

• Utilizes two pulse technique• One pulse to ablate the sample and create a plume• Second pulse resonantly excites the atomic species of

interest• Improvement of detection limit to ppb from ppm level• Must optimize the parameters for the two laser pulses

• Pulse energies• Inter-pulse temporal separation• Detector efficiency


Typical LA-LIF Experiment Layout

50 cm lens

2 ω Dye laser wavelength set to 257 nm for Al and 283 for Pb

Waterjet diameter: 1 mm

Probe Pulse

Breakdown Pulse


Single Pulse µLIBS of 500 ppm Pb

• At shorter gate delays plasma exhibits significant continuum background

• As the plasma cools continuum decreases rapidly

• Optimization of LOD requires optimum gate time

Nshots=100, Elaser=260 µJ, 500 ppm Pb in waterGatewidth=100ns, Slit = 300µm, Detector gain = 255


LA-LIF of Pb

Ground J=0 3P0

6p1/26p3/2J=2

J=1 7819.263 3P1

10650.327 3P2

6p1/26p1/2

6p1/27s1/2J=1

J=035287.224 3P1

34959.908 3P0

283.389nm

364.061nm

405.895nm

368.451nm

5.8 x 107 s-1

3.4 x 107 s-1

8.9 x 107 s-1

1.5 x 108 s-1

Excitation wavelength

Fluorescencewavelength


0

0.2

0.4

0.6

350 370 390 410 430

Mill

ions

wavelength (nm)

inte

nsity

(cou

nt)

364nm 368nm

405nm

Nshots=1000, Elaser= 170 µJ, E2pulse= 10 µJ, ∆T=300ns, Slit width = 300 µm, Grating 1200l/mm, [Pb]: 50ppm

LA-LIF spectrum of Pb


Time Resolved LA-LIF Signal for Pb

• Signal only appears with the probe pulse

• Enhancement is short-lived, on nanosecond time scale

0 200 400 600 800 1000 12000

20000

40000

60000

80000

100000

120000

Sig

nal (

coun

ts)

Time (ns)

single pulse LA-LIF signal

Nshots=100, Elaser=260 µJ, E2nd pulse= 45nJ, 500ppm of Pb in water, ∆T= 700ns, Gatedelay=700ns, Slit = 300µm, Detector gain = 255

FluorescenceSignal


380 400 420wavelength (nm)

inte

nsity

(cou

nt)

Selective enhancement of LA-LIF

2534735287Upper level (cm-1)

15010Conc (ppm)

AlPb

Al

Pb

2 pulses

1 pulse

* The two spectra have been offset vertically

Nshots=100, Elaser= 170 µJ, E2pulse= 10 µJ, Gatewidth=100ns, ∆T=300ns, Slit = 300 µm, Detector gain = 255

FluorescenceSignal


Optimization – Pulse Separation

Nshots=1000,Elaser= 170 µJ E2pulse= 8 µJ, Gatewidth=100ns, Slit = 300 µm, Detector gain = 255, [Pb]= 50 ppm in water

Pulse Separation (ns)

0 500 1000 1500 2000 2500 3000 3500

Sig

nal (

coun

t)

0

1e+6

2e+6

3e+6

4e+6

5e+6

6e+6

7e+6

3

4

5

6

7

8

200 400 600 800 1000

4

6

8

1

2


Scaling with Probe Pulse Energy

Nshots=1000, ∆T= 300ns, Slit = 300 µm, Detector gain = 255, [Pb]= 50 ppm in water

0.00E+00

2.00E+00

4.00E+00

6.00E+00

8.00E+00

1.00E+01

0 2 4 6 8 10 12 14Second Pulse Energy (µJ)

Sign

al (c

ount

)

First Pulse Energy


380 400 420Wavelength (nm)

Inte

nsity

(cou

nt)

LA-LIF spectrum of 100 ppb Pb sample: 1000 shot

SNR~5

Nshots=1000, Elaser= 170 µJ E2pulse= 10 µJ, ∆T= 300ns, Slit = 300 µm, Detector gain = 255, Gate width = 300 ns


Pb spectrum of 100 ppb Pb sample: 10000 shots

380 400 420Wavelength (nm)

Inte

nsity

(cou

nt)

SNR~12

Nshots=10000, Elaser= 170 µJ E2pulse= 10 µJ, ∆T= 300ns, Slit = 300 µm, Detector gain = 255, Gate width = 300 s


100 shot LOD for Pb in Water

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0.1 1 10 100 1000Pb Concentration (ppm)

Cou

nts

normalized signal3σ noise floor

200 ppb

20Gate width (ns)

300∆T (ns)

200 ppbLoD (3σ)

102nd Pulse (µJ)

170Ablation pulse (µJ)


1000 shot LOD for Pb in Water

20Gate width (ns)

300∆T (ns)

73 ppbLoD (3σ)

102nd Pulse (µJ)

170Ablation pulse (µJ)

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

0.01 0.1 1 10 100 1000

Pb Concentration (ppm)

coun

t

normalized signal3σ noise floor

73 ppb


Comparison with Previous Pb LOD Reports

All values scaled to 100 shot equivalents

[1] R. Kopp, et. al. Fresenius’ J. Anal. Chem. 355, 16 (1996).

[2] G. Arca, et. al. IGARSS 96, Vol 1, 27-31 May 1996, 520-522.

[3] M. Taschuk, et. al. EMSLIBS 2003, Heraklion, Crete October 1st, 2003

[4] K. M. Lo, et. al. Appl. Spectrocopy, vol. 56, Number 6, 2002

[5] X.Y.Pu, Appl. Spectroscopy 57,5,

[6] Le Bihan et. al. Annal. Bioanal. Chem 2003 Le Bihan et. al.20030.3ppt (20 shots)ETA-LEAF

http://pyrite.chem.northwestern.edu/

1.5ppbICP-AES

http://servant.geol.cf.ac.uk/icppage.htm

0.01-0.1ppbICP-MS

sourceLimit of detectionmethod

Detection limit of Pb using other techniques

µLIBS


282 284 286 288 290

Wavelength nm

0

1

2

3

x10 4

Cou

nts (

Bg

Cor

rect

ed)

Apply LIBS in microfluidic systemDetection of single cell contentsLab-on-a-chip application – micro Total Analytic Systems (µTAS)

Drop-on-demand actuator (thermal or piezoelectric)

microchannel ~50µm

orifice, ~ few µm

1-10µm droplet

µLIBS in Microfluidic Systems

LIBS probe


Rapid thermal heater

Piezoelectric pulser

µs-pulse

Microdroplet Generation


microheater

The orifice, the channel, and the reservoir are all machined by laser-micromachining

microheater

orifice

microchannel

Prototype Thermal Droplet Ejector

Micro-Heater Element


• Development of µLIBS• High resolution and small probe spot size demonstrated• LODs in ppm range demonstrated

• Initial µLIBS Applications: • Surface mapping of alloys for quality control of metal

manufacturing• Micron scale size resolution• Fingerprint detection both by Na and substrate lines

• Overcomes fluorescence masking for some materials• µJ energies with fs uv pulses leaves large surface area

for further investigation or as evidence• Can increase acquisition speed to multi-kHz repetition rates• High resolution 3D scans possible – µm lateral and sub-µm

depth

Conclusions


• LA-LIF• µJ energies sufficient for excitation and resonant probing• Increase sensitivity to ppb levels

• Initial LA-LIF Applications: • Monitoring of water quality• 25 ppb detection of Pb in water with 10000 shots

• High repetition rate lasers (10-100 kHz) would allow 2.5 ppb sensitivity in 10 - 100 second measurement times

• i.e. real time water quality monitoring

• Can be scaled to portable systems using upconverted fiber lasers with fiber Bragg gratings to generate the exact probe wavelengths

• Future applications in lab on a chip for medical diagnostics in the doctors office

Conclusions


The End

Documents

Laser-Induced Breakdown Spectroscopy for Microanalysis · PDF fileU of A - R. Fedosejevs 070303 p.1 Laser-Induced Breakdown Spectroscopy for Microanalysis Robert Fedosejevs, Y. Godwal,