CANADA: The onward march of new two-dimensional materials continues: researchers from China and the US have reported the first successful fabrication of an atom thick layer of tin – stanene. The finding is significant because two-dimensional tin has been predicted to exhibit a range of unusual electronic phenomena, such as topological insulation, where electrons can travel freely along the edges of the material without encountering obstacles such as other electrons or atoms, resulting in no dissipation of energy through heat.
Until now, the production of stanene has proved elusive. ‘Bulk tin with a diamond structure is not a layered material,’ explains one of the team’s leaders, Jin-feng Jia, of Shanghai Jiao Tong University in China. ‘Free-standing stanene may not be stable; in order to get stanene firstly one must have a suitable substrate, secondly one has to determine that the film has the necessary honeycomb-like bilayer atomic structure, and thirdly one has to determine that the film has the right electronic band structure. All the experiments have to be done in situ in an ultrahigh vacuum system.’
A key to the success of the new work was to identify a suitable substrate upon which to condense highly purified tin atoms by molecular beam epitaxy under tightly controlled conditions. The researchers found that bismuth telluride (Bi2Ti3) fitted the bill as a substrate. ‘Stanene has a hexagonal lattice, so the surface of the substrate must also have a hexagonal lattice,’ says Jia. ‘The lattice mismatch between the substrate and the stanene should be small and it should be energetically favourable to stanene to grow in a quasi-two-dimensional growth mode on the substrate.’
The researchers grew a layer of tin atoms on the substrate and confirmed its predicted structure – resembling buckled honeycomb – through scanning tunnelling microscope imaging. Key electronic characteristics were measured using angle-resolved photoemission spectroscopy. ‘With the help of first principle calculations our experimentally determined atomic and electronic structures agree with the theoretical predictions,’ Jia says.
Having created what they are convinced is stanene, the team says that the next task will be to carry out electronic transport measurements to explore the potentially unusual quantum properties that have been predicted for the material.
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