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 Bi_1-xSb_x (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

• Effects of Size Reduction on the Electrical Transport Properties of 3D Bi Nanowire Networks, M.F.P. Wagner, A.S. Paulus, J. Brötz, W. Sigle, C. Trautmann, K.-O. Voss, F. Völklein, M.E. Toimil-Molares, Adv. Electr. Mat. 7 (2021) 2001069.
• Magnetotransport measurements on Bi₂Te₃ nanowires electrodeposited in etched ion-track membranes, J. Krieg, R. Giraud, H. Funke, J. Dufouleur, Walter Escoffier, C. Trautmann, M.E. Toimil-Molares, J. of Physical Chemistry of Solids (2019) 128C, 360-366.
• Influence of surface states and size effects on the Seebeck coefficient and electrical resistance of Bi_1-xSb_x nanowire arrays, M. Cassinelli, S. Müller, K.-O. Voss, C. Trautmann, F. Völklein, J. Gooth, K. Nielsch, M.E. Toimil-Molares, Nanoscale 9 (2017) 3169-3179.
• Exploring the electronic structure and chemical homogeneity of individual Bi₂Te₃ nanowires by nano-angle-resolved photoemission spectroscopy, J. Krieg, C. Chen, J. Avila, Z. Zhang, W. Sigle, H. Zhang, C. Trautmann, M.C. Asensio,M.E. Toimil-Molares, Nano Letters 16 (2016) 4001-4007.
• Fabrication and thermoelectrical characterization of three‐dimensional nanowire networks,  M.F. Wagner, F. Völklein, M. Reith, C. Trautmann, M.E. Toimil‐Molares, Physica Status Solidi (a) 213 (2016) 610.
• Structural and compositional characterization of Bi_1−xSb_x nanowire arrays grown by pulsed deposition to improve growth uniformity, M. Cassinelli, S. Müller, Z. Aabdin, N. Peranio, O. Eibl, C. Trautmann, M.E. Toimil-Molares, Nucl. Instr. and Meth. in Phys. Res. B 365 (2015) 668.
• 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 Bi_1-xSb_x 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.

GSI Contact: m.e.toimilmolares(at)gsi.de