Nanostructures - Small and Beautiful

Spatial confinement effects induce fascinating new phenomena in nanostructured media, which are based on structure- and interface-controlled modifications of the bulk material properties. A thorough understanding of the resulting properties and an assessment of the application potential ideally relies on a combination of experimental and modelling techniques, which cover the whole range of nanostructure creation, characterization and applicative integration into larger functional elements. Thus, we apply self-organized patterning by ion-beam-induced surface modifications and top-down electron ltihographic techniques to generate nano-scale functional elements and combine it with nanometrology methods on specific structural, mechanical, optical and transport phenomena and with scale-adapted as well as multi-scale modeling.

Transport properties on the small scale, for instance, have traditionally been addressed by a classical master equation approach for the motion of the different charge carrier species, which is based on rate theory. The rather large quantity of parameters, which enter such an approach, can more or less easily be adjusted to the dimensional characteristics, local potential changes at interfaces, and the electronic settings of the system as well as to temperature effects. On the other hand, a microscopically more detailed and mostly parameter-free picture is obtained from a quantum-mechanical treatment on the basis of the density-functional theory. An extension by a Green's function formalism allows the determination and analysis of electronic transport through contacted nanostructures. We have combined both approaches to study electron transport in several material systems with different degrees of structural and electronic complexity. Examples will be given to demonstrate the applicability of the different approaches for dissipative and hopping transport through a regular array of nanostructures [1], for a mechanically triggered metal-insulator transition in nanowires [2], and for the enhanced conductivity at multiferroic domain walls [3].

[1] Kunze, T.; et al.; Phys. Rev. B 81, 115401 (2010).
[2] Popov, I.; et al.; Nano Lett. 8, 4093-4097 (2008).
[3] Seidel, J.; et al.; Nature Materials 8, 229-234 (2009).