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 Engineering University 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
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Laser-Induced Breakdown Spectroscopy for Microanalysis · U of A - R. Fedosejevs 070303 p.2 Outline • Introduction to LIBS • Scaling of LIBS to µJ Energies • µLIBS Applications
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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
U of A - R. Fedosejevs 070303 p.2
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
Observing elements at less than a single percent concentration is straightforward
Choose spectral window according to the material being observed to maximize information gathered
U of A - R. Fedosejevs 070303 p.8
• 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
U of A - R. Fedosejevs 070303 p.9
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
U of A - R. Fedosejevs 070303 p.10
• 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
U of A - R. Fedosejevs 070303 p.11
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
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Single Shot Surface Probe Capability
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Correlation of elements within precipitates - identification
Single Shot µLIBS Aluminum Precipitates
Aluminum 2024 Alloy
Cravetchi et al., Spectrochimica Acta. 59, (2004)
U of A - R. Fedosejevs 070303 p.14
• 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
Surface Mapping at sub-µJ Energies with Femtosecond Pulses
0.5 µJ Spectra
U of A - R. Fedosejevs 070303 p.15
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
U of A - R. Fedosejevs 070303 p.16
Experimental Setup for µLIBS measurement of fingerprints
• 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
[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
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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
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Rapid thermal heater
Piezoelectric pulser
µs-pulse
Microdroplet Generation
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microheater
The orifice, the channel, and the reservoir are all machined by laser-micromachining
microheater
orifice
microchannel
Prototype Thermal Droplet Ejector
Micro-Heater Element
U of A - R. Fedosejevs 070303 p.43
• 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
U of A - R. Fedosejevs 070303 p.44
• 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