MIE Special Seminar Presentation: Controlled 3-d metal island growth on graphene and Pb/Si(111). By Professor Michael C. Tringides
~~Abstract: Graphene based electronic and spintronic devices require understanding the growth of metals, either to improve metal contacts or for spin filters. Several metals (Gd, Dy, Eu and Fe) were studied with STM. The grown morphology (island density and domain size distributions) was used to extract the metal diffusion and adsorption barriers. For Gd, Dy, Fe growth is 3-d, with columnar islands grown with high aspect ratios. (The figure shows Fe islands ~20 layers high after only a small 0.6ML deposition). Although partially this is a result of the lower metal adsorption energy on graphene than the metal cohesive energy, it is not clear what are the key kinetic barriers controlling the columnar growth. The growth of Fe on graphene is especially unusual because it does not follow classical nucleation. The nucleated island density is unexpectedly high; it increases continuously with deposited amount and shows no temperature dependence . These surprising results indicate the presence of long range repulsive interactions and can be used to tune the island density with the Fe coverage. Dysprosium was found to grow fcc(111) instead of hcp(0001) islands, expected from its bulk structure. This is seen from the triangular island shapes and the ABCABC (instead of ABABAB) stacking sequence of islands nucleating on successive layers . The Dy islands are also columnar with very high aspect ratios. 3-d islands of “magic” 7-layer high were observed in a different system Pb/Si (111) as a result of Quantum Size Effects (QSE). The islands form unusually fast (over few minutes) at low temperatures T~150 K because of a novel collective type motion of the Pb wetting layer well below room temperature . Comparison with other metal systems where metal 3-d columnar growth has been observed and modeled  can be used to learn more about the key kinetic barriers in the metal/graphene and Pb/Si(111) systems. References 1.S. Binz, M.Hupalo, Xiaojie Liu, C. Z. Wang, Wen-Cai Lu, P. A. Thiel, K. M. Ho, E.H.Conrad and M. C. Tringides Phys. Rev. Let. 109, 026103 (2012) 2. M T Hershberger, M Hupalo, P A Thiel and M C Tringides J. Phys.: Condens. Matter 25 225005 (2013) 3. M. C. Tringides, M. Jalochowski and E. Bauer in Physics Today 60, No. 4, 50 (2007). 4. 4. K. L. Man, M. C. Tringides, M. M. T. Loy, and M. S. Altman Phys. Rev. Lett. ,110(3):036104–5, 2013. 5. X. Niu, S. P. Stagon, H. Huang, J. K. Baldwin, and A. Misra Phys. Rev. Lett. 110, 136102 (2013)
Brief Bio: Prof. Michael C. Tringides graduated from Yale University in 1977 with a joint degree in Math and Physics and he received a PhD in Physics 1984 at the University of Chicago working with Prof. R. Gomer to measure surface diffusion from density fluctuations. He spent two years as a postdoc with Prof. M. Lagally at the University of Wisconsin working on measuring the kinetics of ordering in surface overlayers with High resolution diffraction (SPA-LEED, RHEED) and STM. This was followed by joining the Iowa State University and Ames Laboratory and since 1996 he is a Physics Professor at Iowa State University and Senior Scientist at Ames laboratory. He is currently a team (FWP) leader of the group Surface Structures Far from equilibrium. His research interests included epitaxial growth using STM and SPA-LEED to identify the growth mechanisms responsible for the observed morphologies. He has authored or co-authored 168 publications, he has given 180 invited talks at conferences/institutions and has edited 2 books on surface diffusion from two major international conferences he has organized (Rhodes 1996 and Prague 2000). He is a Fellow of the American Physical Society.
Friday, September 19, 2014 at 4:00pm to 5:00pm
Shillman Hall, 325