Thermoelectric nanostructures

In 1993, Hicks and Dresselhaus published theoretical calculations of the electrical conductivity (σ), the Seebeck coefficient (S), and the thermal conductivity (κ), that predicted an enhanced thermoelectrical figure of merit ZT = S2T/κ for 2D quantum-well structures and quantum wires, establishing a new direction in the search of more efficient thermoelectric materials. Promising low-dimensional materials being investigated for thermoelectric applications include bismuth and bismuth compounds. In particular, bulk bismuth telluride based compounds are widely used for room temperature thermoelectric applications, and bismuth antimony exhibits high efficiency at liquid nitrogen temperature.

The synthesis of bismuth compound nanowires with controlled size and crystallinity, and the systematic study of the thermoelectric properties of individual nanowires will contribute thus to understand the influence of mesoscopic and quantum-size effects on the thermoelectric characteristics of nanostructured materials.

We are presently synthesising Bi, Bi2Te3 and Bi1-xSbx (0< x <1) nanowires with diameter between 20 and 300 nm and well-controlled morphological properties. The nanowires are fabricated by electrochemical deposition in etched ion-track templates. Nanowire morphology and crystallinity are investigated by scanning electron microsocopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Transport properties (σ, κ and S) of single nanowires as a function of their crystallinity, diameter, chemical composition, and temperature are being measured by means of specifically designed microchips in collaboration with the group of Prof. F. Voelklein at the University of Applied Sciences Rhein-Main.

Recent Publications

  • Tuning the Geometrical and Crystallographic Characteristics of Bi2Te3 Nanowires by Electrodeposition in Ion-Track Membranes, O. Picht, S. Müller, I. Alber, M. Rauber, J. Lensch-Falk, D.L. Medlin, R. Neumann, M.E. Toimil-Molares, J. Phys. Chem. C 116 (2012) 5367.
  • Electrochemical Synthesis of Bi1-xSbx Nanowires with Simultaneous Control on Size Composition and Surface Roughness, S. Müller, C. Schötz, O. Picht, W. Sigle, P. Kopold, M. Rauber, I. Alber, R. Neumann, M.E. Toimil-Molares, Crystal Growth and Design 12 (2012) 615.
  • Finite- and Quantum-Size Effects of Bismuth Nanowires, T.W. Cornelius and M.E. Toimil-Molares, INTECH Nanowires Book edited by: Paola Prete, ISBN: 978-953-7619-79-4, February 2010.
  • Microchip for the Measurement of Seebeck Coefficients of Single Nanowires, F. Völklein, M. Schmitt, T.W. Cornelius, O. Picht, S. Müller, R. Neumann, Journal of Electronic Materials Special Issue Paper (2009) DOI: 10.1007/s11664-009-0714-6.
  • Oscillations of electrical conductivity in single bismuth nanowires, T.W. Cornelius, M.E. Toimil-Molares, S. Karim, R. Neumann, Physical Review B 77 (2008) 125425.
  • Finite-size effects in the electrical transport properties of single bismuth nanowires, T.W. Cornelius,M.E. Toimil-Molares, R. Neumann, S. Karim, J. of Appl. Phys. 100 (2006) 114307.

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