| AVS 58th Annual International Symposium and Exhibition | |
| In Situ Spectroscopy and Microscopy Focus Topic | Monday Sessions |
| Session IS+AS+SS-MoA |
| Session: | In Situ Characterization of Solids: Film Growth, Defects, and Interfaces |
| Presenter: | Bene Poelsema, University of Twente, The Netherlands |
| Authors: | T.R.J. Bollmann, University of Twente, The Netherlands R. van Gastel, University of Twente, The Netherlands H. Zandvliet, University of Twente, The Netherlands B. Poelsema, University of Twente, The Netherlands |
| Correspondent: | Click to Email |
We have investigated the initial growth of Bi/Ni(111) using Low Energy Electron Microscopy (LEEM) and Selected Area Low Energy Electron Diffraction (μLEED). Bismuth represents an interesting material since 1) it has a tendency for allotropism, 2) it forms several ordered alloys with Ni and 3) with Bi being a neighbor of Pb in the periodic system, one may find evidence for quantum size effects in ultrathin Bi layers. Indeed we obtain ample evidence for Bi/Ni(111) as being a very rich system, even at a fixed substrate temperature of 474 K.
We find first that the deposition of Bi leads to the formation of a surface alloy with a (√3x√3)-R30° structure at a Bi-coverage of 1/3. Continued Bi deposition leads to the formation of an incommensurate wetting layer with a continuously decreasing lattice parameter, finally ending in a (7x7) structure. From the variation of the step position at the buried interface, nicely accessible with LEEM, we conclude that the dealloying of the √3 phase is incomplete and that the (7x7) wetting layer in fact involves two layers with a small, but finite Bi content in the second layer. Upon further Bi deposition elongated, 3-4 layers high nanowires emerge, with a p(5x2) structure and a width of about 80 nm, oriented along <110> and <100>-azimuths. Further deposition of Bi-leads to different (sometimes coexisting) structures: (3x3)-patches with a thickness of three atomic layers and patches with a matrix structure (m11=3, m12=-1, m21=1, m22=2) and a thickness of five atomic layers. This accurate height assignment is uniquely enabled by the analysis of LEEM-IV data.
The results are fully consistent with quantum size effect driven thin film morphology: the different film structures and their thicknesses nicely fit with integer numbers of nodes in their specific Fermi wave function, even for the seven layers thick (7x7) structure obtained at a lower temperature of 422 K. Tensor LEED calculations of the interlayer spacing of the different structures concur with this assignment.
The influence of the structure and morphology on electronic properties of various materials is well known. The interaction between electronic and crystal structure should be reciprocal. The Bi/Ni(111) system provides a nice and we think first illustration: electronic properties, in particular quantum size effects, actually drive the structure of the thin bismuth films.