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Barium calcium titanate thin film optical detectors grown on a platinum substrate via pulsed laser deposition

Barium calcium titanate thin film optical detectors grown on a platinum substrate via pulsed laser deposition. Ms. Sarah Stahl T C SAM Student Symposium May 17, 2005. Barium. Oxygen. Titanium. Photoferroelectric Oxides. Unique properties caused by the large band gap (3-4 eV) Examples:

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Barium calcium titanate thin film optical detectors grown on a platinum substrate via pulsed laser deposition

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  1. Barium calcium titanate thin film optical detectors grown on a platinum substrate via pulsed laser deposition Ms. Sarah Stahl TCSAM Student Symposium May 17, 2005

  2. Barium Oxygen Titanium Photoferroelectric Oxides • Unique properties caused by the large band gap (3-4 eV) • Examples: • (Pb0.92La0.08)(Zr0.52Ti0.48)O3 or PLZT • (Ba0.95Ca0.05)TiO3 or BCTO • Potential use: microdetectors

  3. Diagrams of the eye and retina Eye diagram taken from The Encyclopedia Brittanica. Retina diagram taken from The First Steps in Seeing by Rodieck.

  4. Our thin film optical detector (TOD) design Top Electrode (Au or remaining retinal cell) Optically active ferroelectric oxide (PLZT, BCTO) Bottom electrode (Pt) TOD DIMENSIONS Diameter: 20-80 microns Thickness: ~1 micron

  5. Picture of Optobionics Corp. design Other Artificial Vision Research Microdetectors are being developed at the University of Southern California, John Hopkins University, the Optobionics Corporation, University of Bonn (Germany), Tubingen University (Germany) • Drawbacks: • Silicon photodiode • Requires encapsulation • Long-term current injection can be cytotoxic • Large size prevents cell nourishment • Device are “tacked” into the eye • Devices require bulky hardware “accessories”

  6. Benefits of our TOD design • TODs contain platinum and a ceramic oxide; both are expected to be stable within the eye • Voltage stimulation by TODs minimizes cytotoxicity • Surgical implantation is facile and non-intrusive • Device design is quite simple • TODs require no bulky hardware or accessories

  7. Optically active ferroelectric oxide layer • Original TOD design: PLZT • BCTO is also being considered as an alternative • Both are photovoltaic in the visible light range • Grown via pulsed laser deposition

  8. Pulsed laser deposition Platinum substrate, heated to 800 ºC Plasma plume Laser Beam BCTO Target *The optimum growth parameters for our system had to be developed since BCTO has never been grown via pulsed laser deposition before at TCSAM.

  9. X-ray diffraction of BCTO/Pt films

  10. Optical response of BCTO/Pt films Most sample responses were in the range of several hundred microvolts; however, a few samples grown at the optimum parameters had a response of a few millivolts.

  11. Transmission Electron Microscopy Response No Response 100 mTorr 150 mTorr 200 mTorr

  12. Optical response after saline solution testing

  13. Further saline solution testing: SEM, before *The surface investigation used BCTO grown on lanthanum aluminum oxide (LAO).

  14. Further saline solution testing:SEM, after

  15. Conclusions and future work • The optimum growth parameters for BCTO on platinum substrates has been determined • The optical response has been correlated to poor adhesion (TEM) • Preliminary saline solution testing shows surface damage • Investigation into the use of a coating is required

  16. Acknowledgements • Dr. Alex Ignatiev • Dr. NaiJuan Wu • Dr. Ali Zomorrodian • Dr. Irene Rusakova (TEM) • Dr. Bill Foster • Collaborators at UT Hermann Eye Center (saline solution)

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