Dual Plasma Co-Deposition of Mixed-Phase Thin Films James Kakalios , University of Minnesota-Twin Cities, DMR 0705675

1. Dual Plasma Co-Deposition of Mixed-Phase Thin FilmsJames Kakalios, University of Minnesota-Twin Cities, DMR 0705675 Mixed-phase thin films consisting of nanocrystalline inclusions in an amorphous matrix combine the large area advantages of amorphous semiconductors with the superior opto-electronic characteristics of crystals. The mixed-phase films are grown in a novel dual chamber co-deposition system, where one type of nanocrystallite is synthesized, and then entrained by an inert carrier gas into a second PECVD chamber, where the surrounding amorphous matrix is deposited. Using this co-deposition system we have fabricated hydrogenated amorphous silicon (a-Si:H) thin films in which germanium nanocrystallites are embedded. As the nc-Ge concentration is increased, conduction shifts from n-type to p-type, as reflected in measurements of the thermopower. We have previously demonstrated that a-Si:H with silicon nc inclusions has n-type conduction. This opens up the possibility of fabricating a-Si:H based p-n junctions that do not employ chemical impurities, with all of their attendant deleterious influences on the materials properties, but utilize nanocrystalline inclusions to dope the film n-type and p-type. Raman spectra of nc-Ge/a-Si:H films. The TO mode for a-Si is at 480 cm-1 while the TO mode for c-Ge occurs at 290 cm-1. The Germanium concentration is verified using Rutherford Backscattering and varies from 0 to over 24% in the films shown here. Plot of the Seebeck coefficient from thermopower measurements against 1/kT for a series of nc-Ge/a-Si:H films as a function of Ge conc. For Ge concentrations below 10% the thermopower is n-type, while for concentrations above 15% conduction is via holes.

2. Public Outreach and NanophysicsJames Kakalios, University of Minnesota-Twin Cities, DMR 0705675 Kakalios is actively engaged in public outreach, as a member of the A.P.S. Committee on Informing the Public and the recently elected Past-Chair of the new Forum on Outreach and Engaging the Public. He gives many public lectures on physics and materials science, drawing on material in his popular science books THE PHYSICS OF SUPERHEROES (2005, 2nd ed. 2009) and THE AMAZING STORY OF QUANTUM MECHANICS (2010). Kakalios served as one of the volunteer science consultants for the SONY 2012 film The Amazing Spider-Man, through a program established by the National Academy of Science. A video about the science behind an equation Kakalios provided for the film has been viewed over 35,000 times on youtube.com. Kortshagen organized and was involved in a multitude of events that engage the public in research of the Mechanical Engineering Department, including a research lab open house, public lectures around mechanical engineering topics, and a full day of activities for high school students around nanoparticle research.