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

Photoferroelectric Oxides Unique properties caused by the large band gap (3-4 eV) Examples: –(Pb 0.92 La 0.08 )(Zr 0.52 Ti 0.48 )O 3 or PLZT –(Ba 0.95 Ca 0.05 )TiO 3 or BCTO Potential use: microdetectors Barium Oxygen Titanium

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

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

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” Picture of Optobionics Corp. design

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

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

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

X-ray diffraction of BCTO/Pt films

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.

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

Optical response after saline solution testing

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

Further saline solution testing: SEM, after

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

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)