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Plasma-particle Interactions in a Laser-induced Plasma The Path Toward Quantitative Analysis David W. Hahn Michael Asgill, Prasoon Diwakar University of Florida SPIE Laser Damage Sept. 26, 2012 Laser-Based Diagnostics Laboratory

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SLIDE 1

Laser-Based Diagnostics Laboratory

David W. Hahn Michael Asgill, Prasoon Diwakar University of Florida SPIE Laser Damage

  • Sept. 26, 2012

Plasma-particle Interactions in a Laser-induced Plasma –

The Path Toward Quantitative Analysis

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SLIDE 2

Laser-induced Plasma Spectroscopy

2

  • Multi-photon and cascade

ionization creates plasma

  • Ne ~ 1018 cm-3
  • T ~ 30,000 K
  • Plasma forms the sample

volume, dissociating molecules & fine particles

  • Well suited as a rapid,

real-time analytical scheme

500 1000 1500 2000 2500 3000 320 340 360 380 400 420 440 460 Wavelength (nm) Relative Intensity (a.u.)

Laser-induced plasma

Nd:YAG (1064-nm) (10-ns) Czerny-Turner ICCD array

Atomic emission spectroscopy

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SLIDE 3

Plasma-particle interactions drive analyte signal

380 385 390 395 400 405

Intensity (a.u.) Wavelength (nm)

  • Plasma-analyte interactions
  • Our evolution of understanding
  • Means to overcome matrix effects

3

Plasma Analyte

Discrete mass Atoms & ions

  • Vaporization & Dissociation
  • Heat & Mass Transfer
  • Matrix Effects?

Overview of Talk

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SLIDE 4

“Quantitative spectrographic analysis has proved to be impossible.”

  • H. Kayser, Handbuch (1910)

“I do not want to arouse exaggerated hopes. The spectrographic analysis has its limitations as have all analytical methods….but the method can compete with other quantitative methods….in the range of low concentrations.”

  • K. Kellerman, Metals and Alloys (1929)

V in steel (1929) Historic perspective: A continuous evolution

Courtesy of Ben W. Smith University of Florida

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SLIDE 5

LIBS has demonstrated promising sensitivity

5

  • B. atrophaeous

(davg ~ 1 mm)

10 mm

Single-shot, Single-spore spectrum

  • f aerosolized B. atrophaeous

385 390 395 400 405 410

Intensity (a.u.) Wavelength (nm) Ca Ca

LOD ~1.5 fg Ca

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SLIDE 6

LIBS has demonstrated promising precision

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Carbon in Steel

  • L. Barrette and S. Turmel, Spectrochimica Acta B, 56, 715-723 (2001)
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SLIDE 7

Nonetheless, calibration remains an issue

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Precision & Accuracy?

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SLIDE 8

An integrated approach to quantitative LIBS

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SLIDE 9

What are the puzzles for quantitative LIBS?

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1 10 100

1 10 100

Silicon Emission P/B (a.u.) Diameter Cubed (mm

3)

Single SiO2 particles

~2.1 mm

Diameter Cubed (mm3)

Upper Size Limit

Carranza & Hahn, Anal. Chem. (2002) Silicon Emission (a.u.)

  • ~5 mm for glucose
  • particles. E. Vors &

Salmon, Anal. Bioanal.

  • Chem. (2006)
  • ~7 mm for copper
  • particles. Gallou et al.,
  • Aero. Sci. Tech. (2011)

Other Studies

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SLIDE 10

Upper size limit: The marble theory

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  • Consider the physics:

Data suggests a rate limitation rather than an energy limitation

Marble Molecule

Incomplete Sampling Complete Sampling

~5 mm

Physical Limit

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SLIDE 11

Upper size limits vs. residence time

11 Nd:YAG

Spectrometer

iCCD

Mixing- drying chamber Flow controller (Air) Exhaust Flow controller (Argon) Delay generator

Delay: 15 to 70 ms Analyte: Silica spheres 2.47 or 4.09 mm

Nd:YAG ~275 mJ @ 1064 nm

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SLIDE 12

Quantify Si emission

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Si I 288.16 nm

284 285 286 287 288 289 290 291 292

Emission Intensity (a.u.) Wavelength (nm)

35/5 gate 70/20 gate Si

4.09 mm 2.47 mm

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SLIDE 13

Quantify Si emission

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(ms)

Residence time does not extend upper size limit

Expect: Ratio of 4.5 for complete vaporization

Now explore rate limits

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SLIDE 14

Consider the physical processes: Limiting Rates

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A) Rate-limited processes: Dissociation & diffusion are slow relative to analytical time-scales B) Infinite rates: Dissociation & diffusion are very fast relative to time- scales for analysis

Plasma Imaging study

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SLIDE 15

Imaging study of single particles

Nd:YAG (1064 nm) Spectro- meter iCCD Pierced Mirror Fiber Optic Sample Chamber: 6-way cross iCCD 1064 mirror with UV-grade substrate 396.2-nm line filter (3-nm fwhm) Aerosol Stream (~2-mm glass particles)

Ca II emission 396.85 nm (0-25,192 cm-1)

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SLIDE 16

2 ms 4 ms 8 ms 15 ms

Evidence of finite rates: Atomic calcium cloud

Plasma Residence Time

100 200 300 400 500 600 5 10 15 20 25 30 35

Total Detected Calcium Mass (fg) Delay Time (ms)

Total detected calcium D ~ 0.04 m2/s ~ 15-20 ms for dissociation

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SLIDE 17

Localized plasma processes and effects

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Calcium emission from a single particle @ 2 ms Plasma-analyte interactions are initially limited to region ~ 1/1000 of total plasma volume Mass Transfer to Plasma Heat Transfer to Particle Finite Rates lead to localized plasma perturbations & matrix effects

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SLIDE 18

Analysis of matrix effects: Experimental details

18 Nd:YAG

Spectrometer

iCCD

Mixing- drying chamber Flow controller (Air) Exhaust Flow controller (Argon) Delay generator

Delay: 100 ns to 100 ms Analyte: Al,Lu,Mn & Al,Lu,Mn + Na

Nd:YAG ~275 mJ @ 1064 nm

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SLIDE 19

Spectral data: Corrected for relative response

19 19

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SLIDE 20

Experimental details: Aerosol generation

20 200 nm 200 nm

Mn/Al/Lu Mn/Al/Lu + Na @ 8x mass

  • ~50-500 nm particles following desolvation
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SLIDE 21

What are the puzzles for quantitative LIBS?

21

Matrix Effects

25 ms

Analyte enhancement & continuum reduction with sodium addition

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SLIDE 22

Are finite process rates related to matrix effects?

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Plasma Residence Time (ms)

Strong matrix effects early in plasma evolution Matrix effects diminish with time

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SLIDE 23

Are finite process rates related to matrix effects?

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~20-30 ms

Break in T decay slope…. Suggests completion of vaporization and equilibration

Plasma Residence Time (ms)

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SLIDE 24

Understanding plasma / analyte dynamics

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Early times Later times

Analyte T & Ne

  • Localized effects
  • Mass/matrix effects

Bulk plasma T & Ne Equilibration between plasma & analyte

?

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SLIDE 25

The path forward for quantitative analysis

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Must allow sufficient plasma residence time for dissociation, diffusion

  • f heat & mass, and equilibration of analyte species with bulk plasma

Local perturbations: Matrix effects Diffuse analyte: Bulk analytical plasma provides more ideal response Residence time

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SLIDE 26

What about direct analysis of solids?

26

  • LIBS combines the target

sampling with the analytical measurement

  • Different plasma evolution for

different materials

  • Necessitates matrix-matched

standards

Consider LA-ICP-OES

  • Uncouples the

laser sampling event from the analytical plasma

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SLIDE 27

Laser-Ablation LIBS (LA-LIBS)

27

  • Separate the laser-ablation process and

analytical plasma to uncouple these effects

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SLIDE 28

LA-LIBS: Transport efficiency considerations

28

Positive Pressure Reduced Pressure Analytical Plasma Laser Ablation

Single-shot crater

Ablation Cell LIBS Cell

  • Minimize ablation cell volume
  • Transport directly to LIBS

plasma via carrier gas flow

  • Vacuum vs. positive pressure?
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SLIDE 29

LA-LIBS: Transport efficiency considerations

29

  • Clear maximum in analyte signal
  • 50% improvement with suction
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SLIDE 30

LA-LIBS: Experimental Sample Matrix

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Glass 2 Copper- Nickel Cobalt- Chrome Sample Fe (%) Mn (%) SM-10 Al-alloy 1.96 0.30 1276-a Cu-Ni alloy 0.56 1.01 1242 Co-Cr alloy 1.80 1.58 1297 Fe-Cr alloy 69.4 7.11 1761 High Fe 95.3 0.68 Glass 1* Si-K-Ca 0.64 1.12 Glass 2* Si-K-Ca 0.27 0.66

*Courtesy of Anna Matiaske & Ulrich Panne – BAM (Berlin, Germany)

Wide range

  • f sample

matrices

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SLIDE 31

LA-LIBS: Sample spectra

31 Mn Mn

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SLIDE 32

LA-LIBS: Mn/Fe calibration curve

32

NIST 1242 Co-Cr Cr line interference with Mn line

  • Al alloy
  • Cu-Ni
  • Fe-Cr
  • High Fe
  • Glass
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SLIDE 33

LA-LIBS: Absolute calibration?

33

Long-standing interest in LIBS for analysis of soils

*In collaboration with Prof. Alejandro Molina and Jhon Pareja University of Colombia - Medellin

  • Use LA-LIBS for analysis
  • f soils
  • Dope with fertilizer to

different concentrations

  • f N, P and K
  • Use a single-laser

configuration for total concentration analysis

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SLIDE 34

LA-LIBS: Experimental set-up

34

Laser beam Lens Mirror Fiber optic Ablation spark Lens Lens

Pierced Mirror

Beam splitter Carrier gas inlet Shaft Laser ablation cell Analytical LIBS plasma Soil sample

Split the laser to produce both beams Analytical Plasma Laser Ablation

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SLIDE 35

LA-LIBS: Spectral data for soils

35

K K

LA-LIBS Direct LIBS

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SLIDE 36

LA-LIBS: Calibration results

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LA-LIBS Direct LIBS

R2=0.8843 R2=0.6954

Superior correlation & near-zero intercept

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SLIDE 37

Summary remarks

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  • Particle dissociation, atomic diffusion, & heat transfer have

similar, finite time-scales that result in localized plasma

  • perturbations. Temporal considerations are important to

minimize matrix effects for quantitative analysis.

  • LA-LIBS approach can improve LIBS by

uncoupling the laser-ablation process from the analytical plasma processes. Moves us closer to the use of non-matrix matched standards.

  • Understanding of the fundamental processes

will improve LIBS as an analytical method, with implications to the larger analytical community (e.g. ICP-AES & LA-ICP-MS). L I B S

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SLIDE 38

The future of LIBS: Applications

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SLIDE 39

The future of LIBS: Advanced spectral analysis

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SLIDE 40

Acknowledgements

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Graduate students: Michael Asgill Prasoon Diwakar Bret Windom Kris Loper Vince Hohreiter Jorge Carranza Collaborators:

  • Prof. Nico Omenetto
  • Prof. Kay Niemax
  • Prof. Ulich Panne
  • Prof. Alejandro Molina

Funding:

  • NSF (CHE 0822469)
  • NSF (CBET 0317410)
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SLIDE 41

Thank you

41

2009 North American Symposium on LIBS Mississippi River, New Orleans

Laser-Based Diagnostics Laboratory

Florida Museum of Natural History