A research team led by Prof. Dr. Peter Woias, microsystems engineer and member of the cluster of excellence livMatS at the University of Freiburg, and the physicist Prof. Dr. Saskia F. Fischer from the Humboldt University of Berlin has been awarded the Helmholtz Prize 2020 in the "Applications" category. With this award, the Helmholtz Fund honours the team's work on the metrological characterization of nanomaterials, in particular the thermoelectric properties of individual nanowires. The researchers have succeeded for the first time in developing a standardisable procedure for such measurements. In the science of exact measurement, called metrology, the Helmholtz Prize is considered one of the most important international awards. It is endowed with 20,000 euros each in the categories "Fundamentals" and "Applications".
Materials with structural dimensions in the nanometer range often have different properties than macroscopic materials that are identical in terms of composition. This is because at the nano level, it is not only the type of material, i.e. its atomic composition, that plays an important role. The structural dimensions of the material, its crystallinity and the nature of its surfaces are also decisive for the later characteristics. This makes it possible to tailor the properties of nanomaterials by means of shaping. This makes it all the more important to measure relevant material parameters accurately and reliably on very small nanostructures – which poses a major challenge for metrology.
In its work, the research team presents standardizable precision measurements of the thermoelectric properties of nanowires. The measurement techniques developed can be extended from their model system, namely wires made of silver with diameters in the range of 100 nanometers and a crystalline structure, to other nanowires, other nanostructures and other parameters.
For this purpose, the research team around Woias has developed a novel measurement platform for nanowires. On this silicon microsystem, individual nanowires can be mounted and electrically and thermally examined. Fischer's research group has used this platform to characterize silver nanowires with regard to their thermoelectric properties – and this in a range from room temperature to ultra-cold temperatures.
The interdisciplinary research team from Freiburg and Berlin has thus shown that high-precision measurements for the complete thermoelectric characterisation, i.e. for the measurement of electrical conductivity, thermal conductivity and the Seebeck coefficient, are also possible for metallic nanomaterials in a standardised way over a broad temperature range. The team has published its results in "Scientific Reports".
The work of the researchers took place within the priority program SPP 1386 of the German Research Foundation.
M. Kockert, D. Kojda, R. Mitdank, A. Mogilatenko, Z. Wang, J. Ruhhammer, M. Kroener, P. Woias, S. F. Fischer: Nanometrology: Absolute Seebeck coefficient of individual silver nanowires. Scientific Reports 9, 20265 (2019).