Semimetal to semiconductor transition in Bi/TiO 2 core/shell nanowires

• Published in: Nanoscale advances Vol. 3; no. 1; pp. 263 - 271
• Main Authors: Kockert, M., Mitdank, R., Moon, H., Kim, J., Mogilatenko, A., Moosavi, S. H., Kroener, M., Woias, P., Lee, W., Fischer, S. F.
• Format: Journal Article
• Language: English
• Published: 07-01-2021
• ISSN: 2516-0230; 2516-0230
• DOI: 10.1039/D0NA00658K

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/TiO
2
) 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/TiO
2
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 TiO
2
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.