AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM7
Growth and Stability of Bi Films on Si(111) Studied by LEEM

Tuesday, November 4, 2003, 10:20 am, Room 328

Session: Nucleation and Growth
Presenter: R.M. Tromp, IBM T.J. Watson Research Center
Authors: G.E. Thayer, IBM T.J. Watson Research Center
J.T. Sadowski, Tohoku University, Japan
R.M. Tromp, IBM T.J. Watson Research Center
Correspondent: Click to Email
The structural and electronic properties of ultra-thin metal films on semiconductor surfaces have attracted much recent interest primarily due to the dominating dependence of novel device performance on metal contacts. Since contacts are interfaces, contact issues are real problems where surface science can provide insightful solutions. Understanding the factors governing heteroepitaxial growth, such as surface free energies and stress relaxation effects are important, and in situ electron microscopy can play a unique role in investigating the processes involved. Using low-energy electron microscopy (LEEM) we observed real-time growth of Bi on Si(111). With the surprisingly large lattice mismatch of 17% between bismuth and silicon, one might expect growth of Bi/Si(111) to be almost certainly dominated by strain, and therefore three dimensional. Up to about five monolayers, the Bi film grows with small grain (012) oriented islands on top of a uniform wetting layer. Above five monolayers, the crystal orientation dramatically flips from (012) to (111), from a four-fold symmetry to a three-fold symmetry, into a flat single crystal film (grains are approximately 100µm@super 2@ in size). The transition occurs very quickly with grains transitioning at a rate of 1µm@super2@s@super -1@. After the transition into a (111) oriented epitaxial film, the growth continues in a two-dimensional layer-by-layer mode of bi-layers. The thermodynamic stability of Bi/Si(111) films was also investigated by annealing the films to temperatures of up to 150°C (melting temperature of Bi is 220°C), where dewetting becomes important, even prior to melting.