This project impacts profoundly infrared camera and smart sensors based upon bolometer imaging arrays that can be monolithically integrated with silicon integrated circuits and operated at or above room temperature. By improving the reliability and sensitivity of uncooled bolometer arrays, it is hoped that every soldier in the field will have another tool with which to ?own the night? and maintain technological and operational superiority. Professor Narayan plans to work closely with ORNL and Kopin Corporation to transition the basic knowledge into practical devices. This work involves training of graduate and undergraduate students at NCSU, and collaborations with NC A&T University to attract minority students into the graduate program at NCSU. The outreach will also involve an annual ASM International-sponsored Summer School for rising high school seniors.
This research deals with the very interesting phenomenon ? an ultrafast phase transition from monoclinic to the tetragonal structure of vanadium oxide (VO2). The principal investigator (PI) will study the role of epitaxy in determining the properties of VO2, a material that exhibits a sharp semiconductor-to-metal transition in bulk form. The transition is associated with energy release (associated, at least in part, with the deformation associated with the transition) that destroys the bulk material. The supposition is that the thin film and its substrate will be able to accommodate the transition without failure due to heat dissipation in the substrate. Of course, the substrate will also impose mechanical boundary conditions that will influence the temperature and "sharpness" of the transition. Furthermore, the detailed microstructure of the epitaxial, textured or amorphous film will influence the nature of the transition. The PI will address the synthesis and processing of vanadium oxide thin films with increasing grain size through to high-quality single-crystal on sapphire and silicon substrates. High-quality single crystal films with controlled strain will be grown by domain matching epitaxy paradigm on substrates with a large lattice misfit, where critical thickness is less than a monolayer and the films are relaxed from the beginning. These epitaxial films should exhibit a sharp transition, large amplitude, and very small hysteresis, similar to bulk single crystals of vanadium oxide. To obtain efficient and reliable infrared camera and smart sensors, the PI will strive to control and optimize the sharpness and amplitude of the transition, and the hysteresis upon heating and cooling.
: Federal Award ID: 0803663: Report Submission Period: 07/01/2013 to 06/30/2014 Outcome: This project focuses on fabrication and properties of vanadium oxide, a material of immense technological importance for infrared sensors, and its epitaxial integration on sapphire and silicon substrates to enhance its functionality for next-generation infrared sensor based devices. With our invention of domain matching epitaxy, complex tetragonal and monoclinic structures of vanadium oxide can be grown as single crystals on sapphire and silicon substrates. By controlling defects in these single crystal films, we can tune the properties of these structures for a variety of smart magnetic and infrared sensors, needed for a variety of military and homeland defense. The program has graduated four Ph.D. students, who are successfully employed in US companies. Undergraduate students, who worked during summer, include, Fangkai Yang and Cao Motao. Under this program, we published over sixteen papers in archival journals and equal number in refereed conference proceedings, in addition to the following honors and awards of the PI: 2014 O. Max Gardner Award (HIGHEST UNC Honor), 2014 TMS RF Mehl Gold Medal and Institute of Metals Lecture Award (Pinnacle TMS Honor), 2012 Holladay Medal (Highest NCSU Faculty Honor). This research is based upon our recent success in growing high-quality single-crystal films via domain matching epitaxy, and in developing a model to address structure-property correlations in a systematic way. We have grown textured VO2 films with increasing grain size all the way to high-quality single-crystal on (0001) and (11-20) sapphire substrates by using pulsed laser deposition. High-quality single crystal VO2 films can be grown via domain matching epitaxy, involving matching of integral multiples of lattice planes between the film of monoclinic structure and the sapphire substrate. To integrate with silicon (111) and (100), we plan to grow these films by Laser-MBE and PLD with and without the buffer layers, such as MgO, YSZ and TiN. These epitaxial films should exhibit a sharp transition, large amplitude, and very small hysteresis, similar to bulk single-crystal of VO2, but unlike bulk single crystals, these films often exhibit reduced transition temperature. The sharpness and amplitude of the transition, and the hysteresis upon heating and cooling are found to be a strong function of crystal structure, thin film strain, chemistry and microstructure (grain size, characteristics of grain boundaries, and defect content). Broader Impact: This research has impacted profoundly on smart sensors and IR camera integrated with silicon microelectronics, and creates a fundamental knowledge base on the critical role of microstructure and chemistry on the characteristics of ultrafast phase transition. We have addressed training of graduate and undergraduate students at NCSU and ORNL jointly, and collaborations with NC A&T and Shaw University to attract minority students into the graduate program at NCSU. The outreach involved ASM-International sponsored Summer School for rising High-School seniors, which PI initiated at NCSU five years ago, and now it has become an annual event. These students are exposed to recent developments in new materials, analysis tools, materials properties and modeling. The PI has an excellent record of research collaboration and supervision of graduate and undergraduate students with NC A&T, Joint School of Nanoscience and Nanotechnology (JSNN), and Shaw University (both minority institutions).The PI teaches a series of courses through distance education at work, where students from NC A&T and Shaw can take courses and learn latest developments in novel materials, processing, characterization and modeling (see attached interinstitutional agreement). Summary: This progress report focuses on the integration of single-crystal films of VO2 on Si(100) with NiO, MgO and TiN buffer layers. These buffer layers are grown by using the paradigm of domain matching epitaxy in a single-chamber in-situ processing by utilizing multiple target holders. This project is linked directly to the development of infrared night-vision camera and smart sensors based upon bolometer imaging arrays that can be monolithically integrated with silicon integrated circuits and operated at or above room temperature. By improving the reliability and sensitivity of uncooled bolometer arrays, it is hoped that every soldier in the field will have another tool with which to "own the night" and maintain technological and operational superiority. The PI has worked closely with ORNL and Kopin Corp to transition the basic knowledge into practical devices. The proposal also addressed training of graduate and undergraduate students at NCSU, and collaborations with NC A&T University to attract minority students into the graduate program at NCSU. The outreach also involved ASM-International sponsored Summer School for rising High-School seniors, which PI initiated two years ago, and now it has become an annual event at NCSU.
