Special CMP Seminar: Collective Motion, Surface Alloying, and Unusual Growth Behavior of Metals on Germanium

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Date/Time:Friday, 25 Oct 2019 from 11:00 am to 11:50 am
Location:A401 Zaffarano
Channel:Condensed Matter Physics
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Dr. Shirley Chiang, Department of Physics, UC Davis

We have used low energy electron microscopy (LEEM) and scanning tunneling microscopy (STM) to measure real space images of Ag/Ge(110), Au/Ge(110), and Ir/Ge(111). As Ag was deposited onto Ge(110) above 400C, LEEM movies showed the formation of long, one-dimensional (1D) islands. Unusual collective behavior of the growth and collapse of islands suggests that the wetting layer provides the material for the islands to grow at very high rates that cannot be due to stochastic diffusion. In contrast, 0.5ML Au dosed onto Ge(110) at 800C forms Au/Ge liquid alloy droplets that move at higher temperature, absorbing smaller islands upon collision. The motion is explained by a temperature gradient across the sample causing a Ge concentration gradient across the islands, inducing movement in the direction of increasing temperature. For Ir on Ge(111), STM images show a new form of growth consisting of Ir pathways forming on substrate domain boundaries that connect larger Ir islands. Density functional theory (DFT) was used to examine the basic bonding features of Au and Ir adsorbed on Ge (110), with Ir showing a larger effect of polarization than Au in the presence of neighboring Ge atoms as a result of the differences in d-state filling. Work funded by NSF DMR and NSF PHY