B4 - Physics of planar carbon tunnel junctions

Principal investigator: Prof. Dr. Heiko Weber, FAU Erlangen, [webpage]

Charge tunneling is most often studied with metals, in particular STMs. At high bias, besides currents, also light emission is observed. Although being most fundamental, there is no consensus how these effects are related: light emission is either associated with current fluctuations or with thermal effects.[1] Graphene and, in particular, PCL junctions with their structural perfection allow studying this effect in transparent and unobscured conditions. One-dimensional graphene nanoribbons (1D GNRs) on SiC[2] with epitaxially defined edges can be prepared on the same substrate. Graphene electrodes are also nicely suited for providing ultraflat electrodes to study electrical transport in molecular materials.

© Heiko Weber
Charge injection and light emission in planar carbon tunnel junctions
Figure: Charge injection and light emission in planar carbon tunnel junctions.

The finding of ultrahigh electronic temperature has many interesting aspects that we will tackle. We will search for thermionic electron emission and answer the question whether emitted electrons contribute to light emission. This point-like (thermal but cold) light source is interesting per se and we will identify further scientific applications.

Thesis topic: Multi-observable investigation of electron tunnelling

We will apply a variety of techniques, including transport, electron emission spectra, confocal microscopy and optical spectroscopy (NIR, MIR, THz range) to understand the interplay of electromagnetic environment and light emission in detail. Electronic noise[3] will be studied in depth, disentangling shot-, structural, and Johnson-Nyquist noise, along with correlations with the optical signal.

[1] C. Ott, S. Götzinger, H. B. Weber, “Thermal origin of light emission in nonresonant and resonant nanojunctions”, Phys. Rev. Research 2020, 2, 042019.
[2] J. Baringhaus, M. Ruan, F. Edler, A. Tejeda, M. Sicot, A. Taleb-Ibrahimi, A.-P. Li, Z. Jiang, E. H. Conrad, C. Berger, C. Tegenkamp, W. A. de Heer, Nature 2014, 506, 349.
[3] C. Schinabeck, R. Hartle, H. B. Weber, M. Thoss, “Current noise in single-molecule junctions induced by electronic-vibrational coupling”, Phys. Rev. B 2014, 90, 075409.