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UHV scanning probe microscopy
Bismuth is a semimetal with extraordinary electronic properties: even at room temperature the electronic mean free path can be many hundreds of nanometres, while the effective masses can be extremely low and the Fermi wavelength extremely long. In combination, these properties make Bi an ideal candidate for observation of interesting quantum effects, and indeed bulk and thin film bismuth have been extensively studied for the last 50 years1,2. Recently there has been renewed interest (see Refs 3,4,5,6 and Refs therein) in the electronic properties of ultra-thin Bi films (UTBFs i.e. <20 atomic layers) and Bi rods / nanowires3 because they might provide ideal components in spintronic, thermoelectric and molecular electronic devices.
We are currently investigating the atomic and electronics structures of the n-UTBFs using UHV-STM with atomic resolution.
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“Nanostars” grown by diffusion and aggregation of Bi2. |
Nanorods and self-assembled circuits resulting from annealing of self-assembled nanostars (see Fig. 1). |
Expected atomic structure for Bi layers on HOPG. |
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Our Omicron UHV-STM with SPM Probe preparation chamber has both STM and AFM capability, variable temperatures (50K-500K), a variety of in built sample cleaning facilities, as well as STS capability to investigate electronic states. It also has a Knudsen cell to allow in-situ preparation of thin film samples such as UTBFs.
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Left: SEM image of Bi nanorods on graphite.
Centre: STM image at moderate resolution showing layer structure around the edge of the rods
Right: High resolution STM image showing atomic arrangement.
References
1 R. Keyes et al, Phys. Rev. B. 104, 1804 (1956).2 See the review: P. Hofmann, Progress In Surface Science 81, 191 (2006).
3 See e.g. S. Cronin et al, Microscopy and Microanalysis 8: 58 (2002).
4 S. Murakumi, Phys. Rev. Lett. 97, 236805 (2006).
5 S. Koroteev et al, Phys. Rev. B. 77, 045428 (2008).
6 T. W. Cornelius et al, Phys. Rev. B 77, 125425 (2008)