QUANTUM EFFECTS IN ULTRATHIN METAL OVERLAYER EPITAXY

Zhenyu Zhang

Solid State Division, Oak Ridge National Laboratory, Oak Ridge TN 37831, USA

This talk presents the main results from recent studies of metal overlayer growth on semiconductor substrates [1]. It will be shown that a variety of novel phenomena can exist in such systems, resulting from several competing interactions. The confined motion of the conduction electrons within the metal overlayer can mediate a surprisingly long-range repulsive force between the metal-semiconductor interface and the growth front, acting to stabilize the overlayer. Electron transfer from the overlayer to the substrate leads to an attractive force between the two interfaces, acting to destabilize the overlayer. Interface-induced Friedel oscillations in electron density can further impose an oscillatory modulation onto the two previous interactions. These three competing factors, all of electronic nature can make a flat metal overlayer critically, marginally, or magically stable, or totally unstable against roughening. We further show that, for many systems, these electronic effects can easily win over the effect of stress. First-principles studies of a new representative systems support the main features of the present "electronic growth" concept [2]. We also present experimental support of the concept [3].

*Work done with the collaborators listed below. Supported by US Department of Energy and US National Science Foundation.

[1] Z. Y. Zhang, Q. Niu, and C.-K. Shih, Phys. Rev. Lett. 80, 5381 (1988). Z. G. Suo and Z. Y. Zhang, Phys. Rev. B 58, 5116 (1998).

[2] J. H. Cho, Q. Niu, and Z. Y. Zhang, Phys. Rev. Lett. 80, 3582 (1998).

[3] L. Gavioli, K. R. Kimberlin, M. C. Tringides, J. F. Wendelken, and Z. Y. Zhang, Phys. Rev. Lett. 82, 129 (1999).