![What is LIBS?
Method of identifying the elemental
composition of a sample by
examining the spectrum of light
created by striking a sample with a
highly-focused laser pulse. The
spark that is created contains
blackbody, atomic, and molecular
emissions.
• Blackbody (Thermal radiation)
–> Broad-band emission (UV-VIS-IR)
• Atomic Emissions
–> Narrow line emission (UV-VIS & IR)
• Molecular Emissions
–> Broad-band emission (mainly IR)
Schematics of LIBS setup
[1]](https://image.slidesharecdn.com/c6a0863a-2547-469e-8e43-026374b0a211-150528195909-lva1-app6892/85/Keith_Capstone_Defense-3-320.jpg)
![Research Applications
LIBS is an especially valuable technique
for material identification but at the
present, only information about the UV-
Visible region has been collected.
Current applications of LIBS include:
• De-Mining- Detection and
identification of landmines and other
hazardous objects.
• Robotic LIBS- Using rovers to identify
materials on deep-space landings.
• Stand-off Detection of Explosive
materials
• Underwater LIBS- Specifically its use
in identifying archeological materials.
Advantages of LIBS
LIBS is used in many different ways
simply because of the versatility of the
technique, but it also boasts additional
advantages such as:
• Minimal Sample Preparation
• Spectra may be obtained from long
distances
• Ability to analyze solids, liquids, &
gases
• Minimal amount of material is
required for analysis
• Simple and rapid collection of data
and analysis
[3]
[4]
[2]](https://image.slidesharecdn.com/c6a0863a-2547-469e-8e43-026374b0a211-150528195909-lva1-app6892/85/Keith_Capstone_Defense-4-320.jpg)
Keith_Capstone_Defense
- 1. Visible & Infrared Laser Induced Breakdown Spectroscopy of Potassium based Energetic Materials Deposited on Substrates Keith Tukes Hampton University Department of Physics Research Advisors: Uwe Hommerich EiEi Brown Eric Kumi-Barimah
- 2. Outline • Introduction – Basic Idea of Laser Induced Breakdown Spectroscopy – Structure and Spectroscopy of Atoms – Structure and Spectroscopy of Molecules • Research Objective • Experimental Details – Sample Preparation: bulk pellets, films on substrates – Un-gated visible LIBS using a Miniature Spectrometer System – Infrared LIBS setup • Results and Discussion – Pictures of prepared samples – Visible LIBS spectra in air and element identification – MIR LIBS spectra of bulk and thin film samples – LWIR LIBS spectra of bulk and thin film samples – Identification of IR atomic and molecular LIBS emissions • Conclusions
- 3. What is LIBS? Method of identifying the elemental composition of a sample by examining the spectrum of light created by striking a sample with a highly-focused laser pulse. The spark that is created contains blackbody, atomic, and molecular emissions. • Blackbody (Thermal radiation) –> Broad-band emission (UV-VIS-IR) • Atomic Emissions –> Narrow line emission (UV-VIS & IR) • Molecular Emissions –> Broad-band emission (mainly IR) Schematics of LIBS setup [1]
- 4. Research Applications LIBS is an especially valuable technique for material identification but at the present, only information about the UV- Visible region has been collected. Current applications of LIBS include: • De-Mining- Detection and identification of landmines and other hazardous objects. • Robotic LIBS- Using rovers to identify materials on deep-space landings. • Stand-off Detection of Explosive materials • Underwater LIBS- Specifically its use in identifying archeological materials. Advantages of LIBS LIBS is used in many different ways simply because of the versatility of the technique, but it also boasts additional advantages such as: • Minimal Sample Preparation • Spectra may be obtained from long distances • Ability to analyze solids, liquids, & gases • Minimal amount of material is required for analysis • Simple and rapid collection of data and analysis [3] [4] [2]
- 5. Blackbody Radiation • Blackbody Radiation – Thermal Radiation – Any object based on its temperature emits blackbody radiation – Appears as broad-band spectra with low resolution – The peak amount of radiation occurs at different wavelengths depending on temperature – Planck’s Equation gives the spectral radiance distribution as a function of the temperature T – Blackbody emission is overlapping LIBS atomic emissions (-> gated spectroscopy needed) 1 1 * 2 )( /5 2 kThc e hc I T=300K T~5000K
- 6. Atomic Transitions • Bohr’s Model: The atom looks like the solar system. • There exist discrete atomic energy levels and states (orbits) • Atomic Emission – Occurs due to electrons being excited into higher energy states (absorption) – Following excitation, electrons return to the ground state by emitting photons (Emission) Figure 2: Bohr’s Atomic Model 2S+1 LJ Spectroscopic notation 2 2 ( 13.6 )n Z E eV n Z=1 for hydrogen
- 7. Molecular Transitions • Molecular Emission – Slowest emissions – Broad bands (Infrared region) • Molecular Transitions: – Create the smallest changes in the total energy of a molecule – Total energy: • Nuclear energy levels are quantized • Vibrational Energy • Rotational Energy Etot = Eele +Enuc
- 8. • Schrodinger’s Equation is used to identify the energy of electron in atoms – Quantum numbers can be derived from Schrodinger’s Equation • Quantum Numbers describe the characteristics of electrons and their orbitals • Principal Quantum Number (n) – Describes the amount of energy the electron will have. • Spectroscopic Notation – Notation that uses quantum numbers to describe an electron • L: Total orbital angular momentum • S: Total Spin • J: Total Angular Momentum 2S+1 LJ Quantum Numbers and the Quantum Mechanical Model 2 2 ( 13.6 )n Z E eV n hydrogen
- 9. Research Objectives • Prepare bulk pellets and thin-films of potassium based compounds used as energetic materials (e.g. KClO3, KClO4). Use an air-spray technique to deposit films on substrate including aluminum, cement, asphalt, and glass. • Determine amount of deposited material necessary to obtain sufficient emission signatures in LIBS. • Use visible LIBS to identify atomic emissions from potassium based compounds as bulk materials and then as thin films. Use the NIST database to identify background emissions from substrate materials. • Extend visible LIBS to the infrared region and use the NIST database to identify atomic and molecular emission wavelengths from bulk and thin-film materials. Identify background emissions from substrates. Use IR emission signatures to assist material identification.
- 10. Sample Preparation • Bulk Pellets – Compressed pellets of the energetic material (i.e. KClO3) Uncoated Substrates •Substrate Films –Substrates coated with energetic materials Sample Press (7 metric tons) Bulk Pellet (KClO3) Energetic Material (KClO3) Weighed 5.2 g for each sample Aqueous Solution (2 g KClO3) Spray Gun Connected to Nitrogen gas tank (25 psi) Coated Substrates Aluminum Substrate Cement Substrate Asphalt Substrate
- 11. ND:YAG Laser Boxcar Averager Oscilloscope Computer Sample Stage Infrared Spectrometer C F Infrared Detector Visible LIBS Spectrometer Visible LIBS mount and detector CF • Pulsed Nd:YAG laser beam is directed and focused onto sample surface • Sample is struck by laser which results in ablation of material from surface • Emitted light is collected using collimating lenses and focused onto fiber or spectrometer • Visible LIBS: • CaF2 Lenses, Optical fiber, miniature CCD array-spectrometer system, Ungated • Infrared LIBS: • ZnSe lenses, grating spectrometer, IR detector (InSb) • Boxcar and Oscilloscope are use for gated LIBS detection Experimental Details: UV-VIS & IR LIBS
- 12. Experimental Details: UV-VIS & IR LIBS CaF2 Lenses ZnSe Lenses Sample Stage UV-Vis-NIR Fiber Optic Detector IR Spectrometer Liquid Nitrogen Cooled IR Detector Mounted Sample ND:YAG Laser Data Collecting Interface Boxcar Averager Spectrometer Controller Sample Stage Controller
- 13. Visible-NIR LIBS spectrum of background air Observed obs(nm) Literature * lit (nm) Element 399.5 399.5 N-II 403.9 403.9 Ar-II 444.9 444.9 Ar-II 500.6 500.7 N-II 567.7 567.9 N-II 795.1 795.1 O-I 868.4 868.3 N-I 300 400 500 600 700 800 900 1000 1100 1200 0 10000 20000 30000 40000 50000 60000 70000 Intensity(AU) Wavelength (nm) N-II 399.5 nm Ar-II 403.9 nm Ar-II 444.9 nm N-II 500.6 nm O-I 795.1 nm N-I 868.4 nm laser scatter - Air spark shows a rich UV-VIS LIBS emission spectrum. - Several atomic emissions were identified including those of Nitrogen, Argon and Oxygen. *NIST atomic database AIR
- 14. Visible-NIR LIBS spectrum of bulk KClO3 Pressed pellets: 800 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Intensity WaveLength (nm) Aluminum Sample2 KClO3 (0.0374g) Sample3 KClO3 (0.0474g) Sample1 KClO3 (0.0593) 766.490nm 769.896 nm Dominant Potassium Emission Lines: • Bulk KClO3 sample shows dominant potassium emission lines at 766.490nm and 769.896 nm (consistent with NIST database) • Thin film of KClO3 also reveals potassium emission lines. In addition, strong emission lines at ~395nm from aluminum substrate was observed 300 400 500 600 700 800 900 1000 1100 1200 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Intensity WaveLength (nm) (K) 766.5 nm Air Aluminum KClO3 KClO3 on Aluminum
- 15. MIR (2-4 µm) LIBS spectrum of KClO3: bulk sample and films on substrates Pressed pellets Film on Al-substrate • MIR LIBS shows no emission features from background air. • MIR LIBS shows distinct potassium MIR atomic emission lines from bulk sample and from a thin film of KClO3 on aluminum substrate. NIST database shows K-emissions at: 2.7µm, 3.2µm, 4.03µm Al-substrate 2000 2500 3000 3500 4000 4500 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Intensity Wavelength (nm) Pure KClO3 Air KClO3 on Aluminum Aluminum ~2.7µm ~4.0µm ~3.2µm
- 16. LWIR (4-12 µm) LIBS spectrum of KClO3: bulk sample and films on substrates 4000 6000 8000 10000 12000 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 Intensity(a.u.) Wavelength (nm) Bulk KClO3 KClO3 film on Aluminum Aluminum FTIR spectrum • Bulk pellet of KClO3 shows atomic and molecular LIBS emission features. • The molecular emission at ~10500nm matches IR absorption of chlorate anion (ClO3 -). • Molecular emission of KClO3 films is only weak from film, due to small sample amount. ~6.2µm atomic ~10.5µm molecular
- 17. Conclusions • Bulk pellets and thin-film samples of KClO3 were prepared for UV-VIS and IR LIBS studies. The thin-film samples were deposited on aluminum substrates using an air-spray system. • A combined UV-VIS and IR LIBS experimental setup was carefully aligned for LIBS studies in air. • Background air revealed strong UV-VIS atomic emission signatures from oxygen, nitrogen, and argon. Observed UV-VIS atomic emissions were identified using the NIST database. Background air did not reveal any emission in the MIR region from 2000-4000nm. • KClO3 pellets and thin films exhibited characteristic potassium emission lines in the UV-VIS and IR region useful for sample identification. • Initial LWIR LIBS were performed and showed indications of a molecular LIBS emission at ~11000nm due to the ClO3- ion. • Additional studies using different substrate materials and different sample concentrations need to be carried out in the future.
- 18. Acknowledgment • Dr. Hommerich • Dr. Brown • Dr. Kumi-Barimah • Hampton University Physics Department • Army Research Office • National Science Foundation
- 20. Results and Discussion – Visible LIBS spectrum of background air – Visible LIBS spectra of KClO3 (bulk and film on substrate) – Infrared LIBS spectrum of air – Infrared LIBS spectrum of KCLO3 (bulk and film on substrate – Identification of atomic and molecular emissions
- 21. Laser-Induced Breakdown Spectroscopy (LIBS) is a valuable tool for the chemical analysis of materials. In this study we used LIBS to identify atomic and molecular emissions of potassium-based energetic materials in the ultraviolet-visible (UV-VIS) and mid-infrared (MIR) regions. LIBS has become useful because of its ability to rapidly obtain information from a sample in solid, liquid or gaseous form. LIBS has been applied to element identification in planetary exploration, stand-off detection of dangerous chemicals and explosives, and deep-sea geochemical studies. In this research, the samples were prepared using an air-spray technique to deposit thin-films of potassium-based energetic materials onto substrates. During analysis, the substrate emissions were identified and subtracted from sample emissions leaving only the relevant atomic and molecular LIBS features from the energetic materials to be used for sample identification. Abstract
Editor's Notes
- #5: Find at least 3 advantages to LIBS on google, divide slide into adv. & app.
- #7: Start from sample at ground state absorbsion, then emission gives spectra
- #9: Schrodinger eq is used to find the energy levels Put in the equation that gives the difference between two energy levels, can be derived from schrodinger’s eq Equations that derive the other quantum numbers from the principal qn Principal num is used in bohr’s model http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/quantum.html Principal Quantum Number (n) Describes the average distance from the nucleus that an electron may be and the energy of the electron much like Bohr’s model. Can hold integer values starting from 1. Angular Momentum Quantum Number (l) Describes the shape of the orbital (note that the size/volume of the shape is always determined by the Principal Quantum Number (n)). The values of l can be any integer value from 0 to n-1, hence the size of the orbital and the value of the second Quantum number are all limited by the Primary Quantum number. Subshells Orbitals may have the same value of n but different values of l, these are called subshells. Subshells are designated with the values s, p, d, f ,g … to help chemists distinguish between them. As you move through the list of subshells for a specific value of l the shapes shall become more and more complex. Magnetic Quantum Number (ml) Describes the orientation of the orbital in space. Depends on the Angular Momentum Quantum Number and may hold values from –l to l. This means that subshells may have the same energy but be oriented differently within space. This is depicted in the second row of figure 3 where the 2p orbital is shown aligned along the x, y, and z axes. Spin Quantum Number (ms) Describes the direction that the electron spins in a magnetic field (clockwise or counter-clockwise) It can only hold the values +1/2 or -1/2 and in each subshell there can only be two electrons which cannot hold the same value Spin Quantum Number. Figure 3: Shapes of the S and P orbitals. Note the change in size of the S orbitals as the Principal Quantum Number changes and the difference in shape of the 2p orbital. The two 2p orbitals but have different Magnetic quantum numbers due to their different orientations.
- #10: Be more straight forward Be sure to specify how (NIST Database) I identified the atomic and molecular emissions Final we know atomic molecular emiss occur in the infrared region Because of the rotational and vibrational transitions Identify the molecular emission signatures from the substrates using the infrared emission spectra
- #11: Scale (measured 5.2 g of material) Compressed Nitrogen Tank (25 psi)
- #12: ND:YAG (Wavelength, Pulse Length, Reppitition Rate of Laser) Laser Beam is directed towards sample using mirrors Sample is struck by Laser, resulting in a “spark” and ablation of the sample surface Light collected using collimating lens (C), focused using focusing lens (F) Visible LIBS: focused light is collected by mounted detector Light is analyzed and sent to the computer by the spectrometer. Infrared LIBS light is collected by spectrometer sent to the detector data is sent to the boxcar averager Averager averages the signal and sends the signal to the Oscilloscope send data points to the computer The plasma comes from the interaction between the reppetitive laser pulses and the abalated mass Averager (averages and stores) is connected to the computer, oscilloscope is connected to the detector
- #14: We took a spectrum of air and used the nist database to identify known elements in air’s emission peaks Comparing these peaks with the ones we found we were able to validate our measurement and identification of these elements
- #21: *I haven’t been able to identify any molecular emissions. Am I looking for the right things? Or Have there just not been any to see? If so, why? (not enough material/not looking at long enough wavelengths/not enough resolution)