A Guide to the Theory and Applications of LIBS

Laser Induced Breakdown Spectroscopy (LIBS) is a type of atomic emission spectroscopy that uses a laser to vaporize or ablate a microscopic layer of a sample’s surface.

The resultant plasma caused by this laser ablation process emits light as it cools. This is then followed by collecting the light and then analyzing it with a spectrometer for qualitative and quantitative material analysis.

This virtually nondestructive spectral analysis method has valuable applications in several physical science fields. There are a number of advantages in LIBS when compared to other available analytic methods as well, and Avantes is considered to be the trusted partner for the development of customized LIBS systems.

What is LIBS?

LIBS is a process for material analysis that uses a very short-duration pulsed laser (usually a Nd:YAG 1064nm Laser) to excite particles at the surface of the sample. Such excitation by the laser leads to a breakdown of chemical bonds and produces vapor, high temperature microplasma and aerosol particulate.

Plasma is the ionized gas produced in laser ablation and it is capable of reaching temperatures as high as 15000 degrees Kelvin, but cools quickly. During the cooling phase, plasma generates light that, when examined, reveals spectral peaks much like a chemical fingerprint. All elements on the periodic table emit light in the 200-900 nm spectral range and will have their own unique spectral signature. This spectral signature refers to the theoretical foundation that enables Scientists to use LIBS measurements for material quantification and qualification.

The light generated by the plasma can be collected with fiber optics and then delivered to a spectrometer for spectral characterization. The spectrometer then transfers spectra data to the computer control system for data analysis and processing.

Comparing the sample against spectra references might be relatively simple when reference spectra are available. More commonly, LIBS spectra must be examined using a wide range of multivariate analysis processes to provide for quantitative and qualitative measurements. Then again, it is essential to test and verify theoretical models that rely on basic assumptions against real world applications as any application will have its own unique calibration curve.

Methods have been developed for calibration free approaches when reference calibration data is not available or the composition of the sample is unknown. These methods involve multiple rapid sampling and often apply mathematical models that simulate probabilistic optimums.

A variation of the single pulse LIBS approach has also been developed. The use of a second pulse has become common for some applications, specifically with liquid measurements. In the double pulse method, the first laser pulse develops a minute plasma filled bubble while the second pulse further excites the plasma to generate a more intense light for measurement.

The Advantages of LIBS Measurements

LIBS is considered to be a highly useful research and analysis tool. LIBS analysis is extremely versatile as it can be used on any material, whether liquid, solid or gas, and will detect any and all chemical elements in a sample with a single pulse. LIBS is particularly sensitive in the detection of light elements like Beryllium, Helium, Lithium, Oxygen and Nitrogen that cannot be easily detected by other analytical methods.

Unlike many other investigative tools, LIBS spectroscopy needs little to no sample preparation. This lack of sample preparation supports field applications and real-time, in-situ LIBS measurements.

Additionally, since the sample size per pulse (µg to ng) is so small it could be assumed to be almost non-destructive on a sample’s surface. And yet, it has adequate sensitivity to measure at resolution down to a single grain (below 10 µm) and powerful enough to bore a microscopic crater in a solid sample in order to target a small mineral inclusion or individual particle.

LIBS Applications in the Physical Sciences

Researchers Lebedev and Shestakov at the Institute of Laser Instruments and Technologies, Ustinov, St. Petersburg, Russia, developed a series of experiments demonstrating the use of LIBS spectroscopy identification of solids. The Researchers document the use of a Q-switched diode pumped Nd3+-YAG laser emitting 20-100 mJ with a repetition rate of generation reaching 30 Hz and a pulse duration of 10 ns.

Lebedev’s system pairs the excitation laser with the AvaSpec-ULS2048-USB2 spectrometer by Avantes . The AvaSpec-ULS2048 includes an ultra-low straylight, symmetrical Czerny-Turner spectrometer with a linear 2048 pixel array CCD detector. This spectrometer is mostly selected for LIBS measurements, particularly in an arrayed or multi-channel configuration.

A short region of the spectrum (a few hundred nanometers) with very high resolution is measured by each channel in the array. The AvaSpec-ULS2048 spectrometer is popular for use in many applications in the physical sciences, from metallurgy and geology to environmental and climate science measurements, and Scientists from all over the world depend on Avantes spectrometers for LIBS measurements.

Mineral, Rock, Sediment, and Soil Analysis

Minerals are the fundamental building blocks of most soils and rocks with over 4,000 identified minerals on Earth. It is essential to know about chemical composition in order to understand the formation and characteristics of any soil or rock body. The field capabilities and prep-less sampling of LIBS measurements explains why this spectroscopic technique is generally used across many different areas of the geosciences.

LIBS spectroscopy was used in the characterization of stalagmites for Strontium and Magnesium in the Caves of Nerja near Malaga, Spain. Researchers isolated deposits of strontium (Sr), magnesium (Mg), manganese (Mn), iron (Fe) and calcium (Ca) in speleothems obtained from the caves ¹.

Deep Ocean Analysis

The short laser pulse produced in LIBS measurements, when focused on a liquid will lead to dielectric breakdown, and the instant heating creates explosive expansion resulting in a gas vapor bubble.

The spectral emissions are less intense when using a laser pulse focused into a liquid owing to absorption of the energy by water, and from diffraction and scattering due to microbubbles and particles. The plasma is also quenched in a rapid manner. The second pulse LIBS method is specifically useful when conducting LIBS analysis in liquids.

Researchers working towards developing deep sea LIBS methodology had to overcome difficulties posed by environmental conditions. High-pressure, including spectral emission intensity and energy input requirements, affect several spectroscopic parameters.

However, recent developments have led to the development of LIBS spectroscopy systems rated to 3000 m below sea level and tested to 1000 m ².

Pollution Monitoring

Climate and environmental testing and monitoring are in-demand fields. LIBS systems have been deployed for nonstop, in-line monitoring for industrial pollution in natural waterways where pollution is a problem ³.

Polar Ice Research

LIBS technology is also employed in the study of alpine glacial and polar ice. Glacial ice formed over millennia of Earth’s history, has trapped particles and air from the time the ice was forming. Using LIBS to study the composition of ice core samples contributes to the understanding of the role of atmospheric carbon dioxide (CO₂) on Earth’s climate ⁴.

Space Exploration

LIBS has been extensively used in space exploration for investigating extraterrestrial bodies, such as meteorites, using a calibration-free (CF-LIBS) approach ⁵. LIBS systems can also be expected to take center stage on future missions to Mars. It will be critical in future Mars missions to be able to understand Martian ecology with complete chemical and mineral analysis ⁶.

Industrial Applications for LIBS

It is an established fact that LIBS is a highly regarded research tool, but this measurement technique has significant applications even in industrial environments.

Semiconductor

Metal alloys and metals are used to transfer electrical signals in semiconductor components. Thin film coatings and substrates applied to the wafer are needed for manufacturing these increasingly complex devices.

These films which usually are around a few hundred nanometers thick are deposited onto a silicon wafer before and after treatments, such as thermal cycling to strengthen it. LIBS can be used in semiconductor wafer and coating characterization and quality control.

Gemology

LIBS, as a minimally destructive technique, may be used in the validation and characterization of gemstones. Laser beam shaping permits micro ablations of materials such that the measurement spot size is 50 microns in diameter.

LIBS perfectly meets the requirements of the metallurgical and mining industries. The potential for high speed sampling without sample preparation enables in line analysis of metal alloys and ores during extraction and processing. The Avantes EVO electronics platform enables high speed USB3, or gigabit ethernet communication with a control system is well suited for such applications.

LIBS Developments

LIBS, like several other technologies, has experienced accelerating advancements over the past 10 years, and will continue to discover new applications and uses in the future. Avantes, a key global player in the design and manufacturing of high-quality LIBS spectrometers, is excited to be an ideal partner for years to come.

Resources

• Harmon, Russell; Richard Russo, and Richard Hark (2013). Applications of Laser-induced Breakdown Spectroscopy for Geochemical and Environmental Analysis: A Comprehensive Review. Atomic Spectroscopy Volume 87, p 11-26. Accessed 15 Apr. 2017. https://goo.gl/LbmusP
• Lebedev, Vyacheslav Fedorovich and A.A. Shestakov (2010). Fast LIBS Identification of Solids During the Laser Ablation Process Institute of Laser Instruments and Technologies, Ustinov, St. Petersburg, Russia; Technical University, St. Petersburg, Russia; and Moscow University of Physics and Technology, Moscow, Russia. Accessed 15 Apr. 2017.
• Lebedev, Vyacheslav Fedorovich (2015). Qualitative analysis of lithium in laser crystals Mg2SiO4:Cr using laser-induced breakdown spectroscopy. ITMO University, St. Petersburg, Russia. Accessed 15 Apr. 2017.
• Laser Induced Breakdown Spectroscopy https://en.wikipedia.org/wiki/Laser-induced_breakdown_spectroscopy

Footnotes

1 Vadillo, Jose; I. Vadillo, F. Carrasco, and J.J. Laserna (1997) Spatial distribution profiles of magnesium, and strontium in speleothems using laser-induced breakdown spectroscopy. Fresenius Journal of Analytical Chemistry. Vol 361, p 119-123. Accessed 16 Apr. 2017.

2 Thornton, Blair, et al. (2015) Development of a deep-sea laser-induced breakdown spectrometer for in situ multi-element chemical analysis. Deep Sea Research Part 1: Oceanographic Research Papers. Volume 95, January 2015, p 20-36. Accessed 16 Apr. 2017. https://goo.gl/y2Oqjj

3 Arca, G.; A. Ciucci; V. Palleschi; et al. (1996) Detection of pollutants in liquids by laser induced breakdown spectroscopy technique. Geoscience and Remote Sensing Symposium, 1996. IEEE. Accessed 16.Apr.2017. https://goo.gl/9GcXax

4 Lüthi, D., et al. 2008. EPICA Dome C Ice Core 800,000 Year Carbon Dioxide Data. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # 2008-055. NOAA/NCDC Paleoclimatology Program, Boulder CO, USA. Accessed from the Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy. Accessed 16 Apr. 2017.  This is imperiled research maintained by the Carbon Dioxide Information Analysis Center, part of the World Data Center for Paleoclimatology, National Oceanic and Atmospheric Administration (NOAA) and will cease operations as of 30 Sep. 2017, Preservation beyond that time will depend on data transition by the DOE.

5 Gaudiuso, Rosalba (2010) Laser-induced breakdown spectroscopy for elemental analysis in environmental, cultural heritage and space applications: a review of methods and results. Sensors 2010; vol 10 p. 7434-7468. Accessed 16 Apr. 2017. https://goo.gl/q7qUpz

6 Patel, M.R.; M.C. Towner; et al. (2003) A miniature UV/VIS spectrometer for the surface of Mars. Third European Workshop on Exo-Astrobiology. Madrid, Spain. Accessed 16 Apr. 2017. https://goo.gl/osxALz

7 Galmed, A.H.; A.K. Kassen, et al. (2011) A study of using femtosecond LIBS in analyzing metallic thin film-semiconductor interface. Applied Physics B January 2011, Vol 102 Is 1, p 197-204. Accessed 16 Apr. 2017. https://goo.gl/I3glwi

8 Darwiche, Sarah; M. Benmansour, et al. (2012) Laser-induced breakdown spectroscopy for photovoltaic silicon wafer analysis. Progress in Photovoltaics Research and Applications vol 20 is 4. Accessed 16 Apr. 2017. https://goo.gl/MPV1RQ

This information has been sourced, reviewed and adapted from materials provided by Avantes BV.

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