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 recently there has been renewed interest in the electronic properties of Bi nanostructures because they might provide ideal components in spintronic, thermoelectric and molecular electronic devices. They also have potentially exciting topological properties.

We have studied the atomic and electronic structures of Bi using UHV-STM with atomic resolution, and have demonstrated novel quantum size effects. We continue to investigate the rich variety of structures and electronic effects in related materials.

Omicron UHV-SPM

Our Omicron UHV-SPM system 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 nanostructures.

Nanostars

“Nanostars” grown by diffusion and aggregation of Bi on HOPG have been shown to have “wedding cake structures”: each tier on the cake is exactly 2 atomic layers since the Bi atoms form paired layers similar to the black phosphorous structure. The layers with different thicknesses have radically different bandstructures and therefore very different Fermi wavelengths. The measured widths of the structures with different heights are found to be controlled by the Fermi wavelength: electronic effects called “Quantum Size Effects” stabilise widths that match the Fermi wavelength.

atomic resolution STM

An atomic resolution STM image. Only every second atom in the unit cell is visible.

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