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Atomic Layer Deposition of Cerium Oxide for Solid Oxide F uel C ells

Atomic Layer Deposition of Cerium Oxide for Solid Oxide F uel C ells . Rachel Essex , Rose- Hulman Institute of Technology Jorge Ivan Rossero Agudelo , Christos G. Takoudis , Gregory Jursich University of Illinois at Chicago.

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Atomic Layer Deposition of Cerium Oxide for Solid Oxide F uel C ells

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  1. Atomic Layer Deposition of Cerium Oxide for Solid Oxide Fuel Cells Rachel Essex, Rose-Hulman Institute of Technology Jorge Ivan RosseroAgudelo, Christos G. Takoudis, Gregory Jursich University of Illinois at Chicago

  2. Benefits of Solid Oxide Fuel Cells as Alternate Power Source • No NOx, SOx, or hydrocarbon emissions • Reduced CO2 emissions • Fuel flexibility • Higher power density than batteries • High efficiency R.M., Ormerod: Chemical Society Reviews, 2003, 32, 17-28.

  3. O2 (air) How a Solid Oxide Fuel Cell Works Cathode O-2 e- Electrolyte Anode CO2 and H2O H2 and CO • Solid oxide fuel cells components: • Cathode • Solid inorganic oxide electrolyte • Anode Fuel (hydrocarbon and steam or oxygen) R.M., Ormerod: Chemical Society Reviews, 2003, 32, 17-28.

  4. The biggest setback for solid oxide fuel cell use is the high operating temperature • Operating temperature: 800-1000 ºC • Long heat up and cool down periods • Limited materials M. Cassir and E. Gourba: Annales de Chimie Science des Matériaux, 2001, 26, 49-58.

  5. Decreasing Operating Temperatures • New materials with lower ion resistivity • Decreasing thickness can increase ion permeability • Thickness can be decreased using thin films M. Cassir and E. Gourba: Annales de Chimie Science des Matériaux, 2001, 26, 49-58.

  6. Deposition of thin films • Physical vapor deposition -thin film deposition method by the condensation of a vaporized form a desired material onto surface • Purely physical process • High temperature vacuum evaporation or plasma sputter bombardment

  7. Deposition of thin film (con’t) • Chemical vapor deposition -chemical process used to produce high-purity, high-performance solid materials • Metal organic chemical vapor deposition (MOCVD) • Atomic Layer Deposition (ALD)

  8. Atomic Layer Deposition • Each exposure to precursor saturates the surface with a monolayer • Purge of inert gas in-between precursor exposures • Each cycle creates one monolayer S.M. George: Chem. Rev., 2010, 110, 111-131

  9. substrate substrate Atomic Layer Deposition is a cyclic process consisting of four steps Step One: Substrate is exposed to precursor Step Two: Reactor is purged of first precursor

  10. substrate substrate Step Three: Substrate is exposed to coreactant Step Four: Reactor is purged of coreactant and byproducts Process is repeated until the film is at the desired thickness

  11. Cerium oxide was created using atomic layer deposition • Precursor: tris(i-propylcyclopentadienyl)cerium • Coreactant/Oxidizer: water • Purge and Carrier Gas: Nitrogen • Uses in solid oxide fuel cells: anode and electrolyte • Cerium oxide has lower ion resistivity at lower temperatures than yttrium stabilized zirconium

  12. Goals of This Project • Find optimum ALD conditions including: • Precursor Temperature • Oxidizer Pulse Length • ALD window • Saturation Curve • Linear Growth

  13. ALD Operating Conditions TReactor 160 ºC 150 ºC 170mTorr 140 ºC Plug: short time pulse of precursor 130 ºC Q. Tao, Ph.D. Thesis, University of Illinois at Chicago, 2011

  14. Precursor Temperature of 140 ºC

  15. 50 msWater Pulse

  16. ALD Window Conditions: 170 mTorr, 130 °C Precursor Temperature, 140 °C Valve Temperature, 150 °C Leg Temperature, 160 °C Manifold Temperature, 50 Cycles, 55 msWater Pulse, 6 plugs, Silicon Wafer are cleaned with standard RCA-1 treating, Silicon Oxide Layer is reduced using HF 2% giving a oxide layer of 8-10 Å

  17. Saturation Curve Conditions: 170 mTorr, 130 °C Precursor Temperature, 140 °C Valve Temperature, 150 °C Leg Temperature, 160 °C Manifold Temperature, 250 ºC Reactor Temperature, 50 Cycles, 55 msWater Pulse, Silicon Wafer standard RCA-1 treating, Silicon Oxide Layer is reduced using HF 2% giving a oxide layer of 8-10 Å

  18. Linear Growth Conditions: 170 mTorr, 130 °C Precursor Temperature, 140 °C Valve Temperature, 150 °C Leg Temperature, 160 °C Manifold Temperature, 250 ºC reactor temperature, 5 plugs, 55 msWater Pulse, Silicon Wafer are cleaned with standard RCA-1 treating, Silicon Oxide Layer is reduced using HF 2% giving a oxide layer of 8-10 Å

  19. Conclusions • Optimum ALD conditions of cerium oxide were found. • Precursor Temperature: 130 ºC • Oxidizer Pulse Length: 55 ms • ALD window: 210-280 ºC- previous work indicated the no ALD window existed when tris(i-propylcyclopentadienyl)cerium was used • Saturation: 4 plugs of precursor pulse and higher • Linear growth: deposition follows a linear trend with 1.2 Å/cycle M. Kouda, K. Ozawa, K. Kakushima, P. Ahmet, H. Iwai, Y. Urabe, and T. Yasuda: Japanese Journal of Applied Physics, 2011, 50, 6-1-6-4.

  20. Future Work • Dope CeO2 films with yttrium and test as electrolyte in solid oxide fuel cells • Dope CeO2 films with nickel and test as anode in solid oxide fuel cells

  21. Acknowledgements • National Science Foundation, EEC Grant # 1062943 • National Science Foundation, CBET Grant # 1067424 • Air Liquide (provided the precursor)

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