Semimetal to semiconductor transition in Bi/TiO2 core/shell nanowires


We demonstrate the full thermoelectric and structural characterization of individual bismuth-based (Bi-based) core/shell nanowires. The influence of strain on the temperature dependence of the electrical conductivity, the absolute Seebeck coefficient and the thermal conductivity of bismuth/titanium dioxide (Bi/TiO2) nanowires with different diameters is investigated and compared to bismuth (Bi) and bismuth/tellurium (Bi/Te) nanowires and bismuth bulk. Scattering at surfaces, crystal defects and interfaces between the core and the shell reduces the electrical conductivity to less than 5% and the thermal conductivity to less than 25% to 50% of the bulk value at room temperature. On behalf of a compressive strain, Bi/TiO2 core/shell nanowires show a decreasing electrical conductivity with decreasing temperature opposed to that of Bi and Bi/Te nanowires. We find that the compressive strain induced by the TiO2 shell can lead to a band opening of bismuth increasing the absolute Seebeck coefficient by 10% to 30% compared to bulk at room temperature. In the semiconducting state, the activation energy is determined to |41.3 ± 0.2| meV. We show that if the strain exceeds the elastic limit the semimetallic state is recovered due to the lattice relaxation.

Activation energy, Crystal defects, Electric conductivity of solids, Nanowires, Oxide minerals, Seebeck coefficient, Temperature distribution, Thermal conductivity, Titanium dioxide, Compressive strain, Core/shell nanowires, Elastic limit, Electrical conductivity, Lattice relaxation, Semiconductor transition, Structural characterization, Temperature dependence, Bismuth compounds
Kockert, M., Mitdank, R., Moon, H., Kim, J., Mogilatenko, A., Moosavi, S. H., et al. (2021). Semimetal to semiconductor transition in Bi/TiO2 core/shell nanowires. 3(1).
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