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REU in Physics at Howard University

REU in Physics at Howard University. Raman Spectroscopy, COMSOL Multiphysics and Molecular Dynamics Simulation Studies of Tungsten Oxide (WO3) as a Potential Metal-Oxide Gas Sensor. Larkin Sayre. Metal-Oxide Gas Sensors (MOGS). The basic principle

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REU in Physics at Howard University

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  1. REU in Physics at Howard University Raman Spectroscopy, COMSOL Multiphysics and Molecular Dynamics Simulation Studies of Tungsten Oxide (WO3) as a Potential Metal-Oxide Gas Sensor Larkin Sayre

  2. Metal-Oxide Gas Sensors (MOGS) • The basic principle • The conductivities of metal oxides change when they undergo reversible reactions with the gases we are trying to detect • This conductivity change can be measured and used to identify the gases present • 4 components of MOGS:gas sensing material, substrate, electrodes, heater. • Applications: • Environmental – gases associated with climate change • Safety – sensing harmful gases - NOx

  3. Overview of the projectMain goal: Look at behavior of WO3 and its interaction with NOx 3 main aspects of my project: • Raman Spectroscopy – the molecular structure of WO3 • COMSOL modelling – the macro side • LAMMPS simulations – the nano side

  4. What is Raman Spectroscopy? The basic principle: A laser is directed towards the molecule and the scattered light is detected and interpreted. Key points: • Rayleigh Scattering • Raman Scattering • Equipment • Thermo-Scientific DXR SmartRaman Spectrometer • Interpretation of the spectra produced

  5. Silicon substrate Using the Equipment - Procedure Top view WO3 deposit Laser The sensors must first be calibrated The sample is placed in a plastic holder Short test iterations to ensure laser is hitting the sample

  6. Sample of polystyrene used Analyzing the Spectrum Examples of peak assignments: • Peaks at 1002, 1602, 1583 and 620 cm-1 correspond to benzene ring vibrations • 1002 – “ring breathing mode” • 2800-3100 – C-H stretching vibrations Units are “wavenumber” – 1/wavelength

  7. Effect of heating on the Raman Spectrum of WO3 Raman spectra increasing temperature from 30 Celcius to 190 Celcius. Raman spectra decreasing temperature from 190 Celcius to 30 Celcius

  8. Using COMSOL Multiphysics to model Metal Oxide on Silicon Substrate

  9. Results • My model outputs plots for: • Temperature • Electric Potential • Isothermal Contours

  10. LAMMPS Citation: S. Plimpton, Fast Parallel Algorithms for Short-Range Molecular Dynamics, J Comp Phys, 117, 1-19 (1995), http://lammps.sandia.gov/ LAMMPS and Molecular Dynamics Simulation • Large-scale Atomic/Molecular Massively Parallel Simulator • LAMMPS is a program that carries out molecular dynamics simulations • It predicts how the system of atoms will behave using classical mechanics approximations(Newton’s Equations of Motion) • How does molecular dynamics relate to research using Raman Spectroscopy? • Simulating the vibrational modes of the molecules • Using trajectories to model Raman spectrum

  11. Visualizing the results VMD – Visual Molecular Dynamics

  12. ConclusionWhere do I go from here? • Continue to improve my LAMMPS and COMSOL models • COMSOL workshop in Greenbelt July 8th • Carry out exposures of WO3to NO and investigate effect on Raman Spectrum • Continue to Investigate behavior of WO3

  13. Acknowledgements Raul Garcia and Daniel Casimir Professor Misra NSF for REU funding

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