Abstract:
Since the initial discovery that Pb/Si(111) uniform height islands can be grown in an easy and reproducible way [1], several additional aspects of the growth have been adressed. Differences in the electronic structure of stable vs unstable islands have been measured with STS and confirm that the origin of the unusual growth mode is Quantum Size Effects (QSE) i.e the dependence of the energy of the confined electrons on island height. These structures are metastable so kinetics play an important role for their formation. We have measured [2] the key controlling barrier Delta E = 0.32eV at the island edges which determines the incorporation of atoms from the surrounding region to the island top. Oxygen adsorption (after the islands are grown at lower temperature) increases the edge barrier and therefore suppresses Pb atom diffusion to the island top which extends island stability to higher temperature [3]. Furthermore for better correlation of the measured energy spectra ( with either STS or angle resolved photo-emission) to the island dimensions, we have shown the thickness of the layer between the island and the substrate to be 1ML and settle controversial literature results. A different type of self-organization in the Pb/Si(111)system is the formation of numerous 2-dimensional equilibrium phases in the coverage range 6/5ML< θ <4/3ML driven by the long range stress mediated interactions [4]. This is one of the best realizations of the well-known statistical mechanics prediction, the "Devil's Staircase" phase diagram.
1. K. Budde et. al Phys. Rev.B61 Rap. Com, 10602 (2000)
2. A. Menzel. et al Phys. Rev. B 67 165314 (2003)
3. S. Stepanovsky et al. Surface Science 515 187 (2002)
4. M.Hupalo , et al Phys Rev Lett. 90 216106 (2003)

Work supported by Ames Laboratory-DOE in collaboration with M.Hupalo, K.Budde, E. Abram, V. Yeh, S. Kremmer ,L.Berbil- Bautista, M.Kammler, A Menzel , E. Conrad, C. Z. Wang, K.M.Ho, J. Schmalian.