| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF+SA+MI-TuM |
| Session: | Thin Films for Synchrotron and Magnetism Applications |
| Presenter: | Alexander Kozen, U.S. Naval Research Laboratory |
| Authors: | A.C. Kozen, U.S. Naval Research Laboratory H. Joress, Cornell University V.D. Wheeler, U.S. Naval Research Laboratory C.R. Eddy, Jr., U.S. Naval Research Laboratory |
| Correspondent: | Click to Email |
VO2 is a thermochromic material, one class of “smart materials” that are receiving considerable interest due to a sharp semiconductor to metal (S-M) phase transition that occurs at a specific, material dependent temperature (Tc = 68˚C for VO2). The S-M transition occurs as a result of a phase transition between a semiconducting monoclinic phase below Tc and a metallic tetragonal phase above Tc. While VO2 has been widely utilized as a microbolometer material for IR detectors, current deposition processes used to fabricate thin film VO2 (PLD, MBE, sputtering) are not adequate to realize complex device architectures. Use of ALD to deposit VO2 thin films allows for uniform, low temperature coating of large area 3D substrates that could open the door to new applications.
Temperature dependent in-situ grazing incidence synchrotron XRD was utilized to probe lattice strain and structural reordering in both as-deposited (amorphous) and annealed (polycrystalline) ALD VO2 thin films during the S-M transition. GIXRD allows us to selectively sample the bulk or the film-substrate interface of thin ALD films with excellent depth resolution, while the high flux provided by the synchrotron (1012 photons/s) enables fast data collection. Initial results show that as-deposited ALD VO2 films are polycrystalline at the VO2-sapphire interface, while the bulk of the as-deposited VO2 is amorphous. Annealing VO2 on sapphire in an oxygen-rich environment forms a fiber-textured polycrystalline VO2 film with a more pronounced S-M transition. We will discuss how substrate selection, ALD growth and processing conditions, and film thickness influence VO2 morphology and/or structure and relate these materials properties to device data.
The authors wish to acknowledge Cornell University's CHESS synchrotron facilities for GIXRD work and The Office of Naval Research for support. Dr. Kozen acknowledges support by the ASEE-NRL postdoctoral fellows program.