Defect mediated growth (DMG) and surfactant mediated growth (SMG) are novel electrochemical deposition methods of producing extremely high-quality epitaxial single-crystal metallic materials. DMG involves reversibly co-depositing with the metal that is to become the epitaxial overlayer a mediator metal. This mediator (e.g., Pb) is repeatedly deposited as a submonolayer on the film surface and then completely stripped by the cycling of the electrochemical potential as the film is grown. Each cycle creates new nuclei on the surface of the growing film, adding to the surface clusters that developed on previous cycles. A high density of two-dimensional clusters can be maintained by appropriately choosing the deposition flux and cycling frequency, resulting in a monolayer of the film material being completed when the two-dimensional clusters eventually coalesce. In this manner, two-dimensional rather than three-dimensional film growth is obtained. SMG uses up to a monolayer of the mediator metal acting as a surfactant that is continuously maintained at the surface during deposition, resulting in two-dimensional growth. Using these approaches, atomically flat single-crystal films (free of the mediator metal) can be electrodeposited at ambient temperature, and the film quality is similar to that obtained by molecular beam epitaxial growth for systems that often display three-dimensional growth during ambient temperature deposition. Specific systems to be studied include Cu on Au, Ni on Cu, and Cu, Ag, Ni, and Co on Si. New features of this work will be the in situ monitoring of the thin film stress generation in real time during DMG and SMG and correlating the stress behavior with the morphological evolution. This of interest both scientifically and technologically, as the stress behavior is associated with microstructural features of growth, and it is important to characterize the stress if DMG and SMG-produced systems are to be used in technological applications (e.g., Cu on Si for interconnects). Real-time monitoring of the stress will also be used to optimize growth conditions and to monitor film quality during deposition.
NON-TECHNICAL SUMMARY: The ability to produce high-quality single-crystal materials for thin film applications (e.g., microelectronics) is critical for maintaining and advancing many important technologies. Defect and surface mediated electrochemical growth are recently developed methods of producing such materials in an inexpensive manner and are processes that can be incorporated into existing and next-generation technologies. The research will investigate synthesizing material systems of both scientific and industrial importance and includes real-time stress monitoring for quality characterization and control. This will be the first time stress measurements will be employed during these synthesis methods and will greatly enhance the potential of converting them into technologically viable processes. This work will be conducted in collaboration with researchers at Arizona State University (ASU) and at IBM Thomas J. Watson Research Center. Outreach activities associated with this project include engaging middle-school students in science-technology-engineering-mathematics (STEM) education through field trips, mentoring, and hands-on modules. The students will be from the Baltimore City Public Schools who are both underrepresented and underserved in STEM education.