Raman Spectroscopy of
Tungsten Trioxide and
COMSOL© Computer
Simulation in Gas Sensor
Technology
C. Craig
Mentor: Dr. P. Misra
REU Team Members: R. Garcia-Sanchez, Dr. D. Casimir, S. Bartley
Summer 2015 REU Program
Howard University Department of Physics and Astronomy
Outline
• Motivation for research
• Background:
• What are semiconducting metal oxide gas sensors?
• How are optical gas sensors used today?
•
•
•
•
What is Raman Spectroscopy?
Research methodology and Results
Comsol© Simulation
Conclusions and Future Research
Why use spectroscopy in gas sensing?
• Semi-conducting metal oxide gas sensors are
•
•
•
•
Small
Portable
Cheap
But inefficient
• Optical gas sensors will
• Improve time-efficiency
• Improve precision of concentration detection
Semiconducting Metal-Oxide Gas Sensors [1]
• Composition:
• Thin film layer of
semiconducting metal
oxide
• Substrate
• Heating track
Fine et al. 2010
Carbon Dioxide Sensor http://www.futurlec.com/Gas_Sensors.shtml
Changes in Resistivity
• Semiconducting
metal-oxide gas
sensors use
changes in
resistivity to detect
the presence of
certain gases
http://www.ipm.fraunhofer.de/content/dam/ipm/en/PDFs/Prod
uct%20sheet/GP/ISS/semiconductor-gas-sensors.pdf
Optimal Operating Temperature
• Optimal gas detecting
temperatures differ
depending on the gas
• ZnO detects
• Chlorobenzene at
~200°C
• Ethanol at ~380°C
Optical Gas Sensors Used Today
Mars Land Rover http://news.rpi.edu/content/2013/09/26/nasamars-rover-curiosity-finds-water-first-sample-planet-surface
What is Raman Spectroscopy?
• Study of the interactions of matter and light (visible and
invisible)
• Raman Spectroscopy uses monochromatic light to identify
molecules based on light scattering from the vibration that
occurs between bonded atoms in lattice structures.
Tungsten Trioxide Monoclinic
Lattice Structure
Bignozzi et al. 2012
• Atoms bond in a lattice structure to form solids.
• Bonds vibrate at different frequencies.
• Vibration-laser beam interaction creates spectral lines.
Fingerprint of WO3
https://www.mdsp.org
/
• The major Raman peaks of Tungsten Trioxide are 808,
719, and 274 cm-1.
• These peaks result from the W-O stretching mode,
the W-O bending mode, and the W-O-W deformation
mode, respectively, in the lattice structure.
Methodology
• A DXR Smart Raman
spectrometer
• 780 nm laser
• OmnicTM Specta Software
• Ventacon H-4-200 Sealed
Hot Cell
• Tungsten Trioxide Sample
Imaging
CCD
Spectrometer Detector
Collection
Lens
Notch Filter
780 nm
Narrowband
Mirror
Objective
Lens
Sample
Temperature Controlled
Environmental Chamber
CW Laser
(780nm)
P. Misra et al. 2015
P. Misra et al. 2015
www.ventacon.com/hotcell/hotcell2.htm
Results
• The peaks exhibited a slight red-shift in
frequency as the temperature increased
from 30 to 200°C.
P. Misra et al. 2015
Red-Shift in
Frequencies
Slopes:
• 808 peak: -0.006, -0.038
• 718 peak: -0.0043, -0.0038
• 275 peak: -0.0179, -0.0172
808 Peak v. Temp
809
Peak 1 v. Temp
up/F 1350
808.5
Peak 1 v. Temp
down/F 1500
808
y = -0.006x + 808.77
807.5
Linear (Peak 1 v.
Temp up/F
1350)
807y = -0.0038x + 807.73
806.5
806
0
274 Peak v. Temp
100
200
300
Linear (Peak 1 v.
Temp down/F
1500)
718 Peak v. Temp
276
720
275.5
275 y = -0.0179x + 275.8
Peak 3 v. Temp
up
274.5
274
Peak 3 v. Temp
down
273.5
273
272.5
Linear (Peak 3 v.
Temp up)
272
y = -0.0172x + 275.03
271.5
Linear (Peak 3 v.
Temp down)
271
719.5
Peak 2 v. Temp
up
719
Peak 2 v. Temp
down
y = -0.0043x + 719.27
718.5
Linear (Peak 2 v.
Temp up)
718
y = -0.0038x + 718.57
717.5
Linear (Peak 2 v.
Temp down)
717
0
100
200
300
0
100
200
300
Discussion of Results
• The decrease in frequency
• Thermal expansion
• Phonon Interactions
• Temperature uncertainty at extremity of hot cell.
• Use of Comsol© Simulation to resolve uncertainty.
Comsol© Simulation of Hot Cell
• Build geometry
• Apply materials and physics
• Run simulations
Simulation Results
Multislice Electric Potential (V)
Surface Temperature (K)
Isosurface Temperature (K)
Future Work and Goals
• Tungsten Trioxide samples will be exposed to SO2 and NO gas
and the resulting Raman spectra will be taken.
• These spectra will be compared to the WO3 spectra previously
gathered.
• Relate intensity to concentration.
• Break into the gas sensor industry with optical sensors
• Miniaturized
• Fingerprint indicates the gas
• Intensity of spectral lines indicates concentration
Acknowledgments
• NSF Funding
• My mentor, Dr. P. Misra
• My REU Team Members: R. Garcia, Dr. D. Casimir, S.
Bartley
Bibliography
[1] http://www.ipm.fraunhofer.de/content/dam/ipm/en/PDFs/Product%20sheet/GP/ISS/semiconductor-gas-sensors.pdf
[2] Raul Garcia. Ph.D. Dissertation
[3] inphotonics.
Carbon Dioxide Sensor http://www.futurlec.com/Gas_Sensors.shtml
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energy storage and gas sensing applications. Poster session presented at: Name of Convention. Number of conference; 2015 June 15; Lake
Forest, CA.
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Liu X, Cheng S, Hong L, Hu S, Zhang D, Ning H. 2012. A survey on gas sensing technology. Sensors.
Fine GF, Cavanagh LM, Afonja A, Binions R. 2010. Metal Oxide Semi-Conductor Gas Sensors in Environmental Monitoring. Sensors (10): Basel,
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Lou, LF. 2003. Introductions to Phonons and Electrons. Singapore: World Scientific Publishing Company.
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•
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(Leboffe and Pierce 2010)