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Crystal phase effects in group IV nanowire polytypes and their homojunctions

Mercoledì 12 luglio ore 11:00, aula Seminari, S3 Cnr Nano, Dipartimento FIM, Modena

Relatore: Michele Amato (Centre de Nanosciences et de Nanotechnologies (C2N), Université Paris-Sud, Orsay (France))
Abstract: Crystal structure and interface engineering are acquiring an increasing importance in nanoscience because of their enormous potential to conceive new properties and functionalities [1]. As for nanowires (NWs), the emergence of new stable polytypes of common semiconductors promises to have a crucial impact in materials design [2].
Recent experimental investigations have confirmed the possibility to synthesize and exploit polytypism in group IV nanowires. Indeed, while the crystal structure of Si and Ge nanowires (NWs) at standard conditions usually takes a well-defined cubic-diamond phase (as for their bulk counterparts), in the last few years several experimental observations of NWs exhibiting other phases — i.e. the hexagonal-diamond one — have been reported [3-4]. Other studies have instead succeeded in growing Si and Ge NWs containing both the cubic-diamond and the hexagonal-diamond phases opening the way to the fabrication of well-ordered group IV polytype homojunctions [5].
Driven by this promising evidence, here I will discuss recent first-principles calculations of the electronic and optical properties of hexagonal-diamond and cubic-diamond Si and Ge NWs as well as their homojunctions [6-7]. I will outline how a change in the crystal phase can strongly modify the electronic structure and optical response of the NW inducing novel and fascinating properties. Furthermore, I will show that, in the case of homojunctions, playing on crystal phase, size and length of the junction is an efficient tool to modulate band offsets and electron-hole separations.

References
[1] D. Jacobsson, F. Panciera, J. Tersoff, M. C. Reuter, S. Lehmann, S. Hofmann, K. Dick, F. Ross, Nature 531, 317-322 (2016)
[2] R. E. Algra, M. A. Verheijen, M. T. Borgström, L.-F. Feiner, G. Immink, W. J. P. van Enckevort, E. Vlieg, E., E. Bakkers, Nature 456, 369-372 (2008)
[3] S. Assali, L. Gagliano, D. S. Oliveira, M. A. Verheijen, S. R. Plissard, L. F. Feiner, E. Bakkers, Nano Lett. 15, 8062-8069 (2015)
[4] J. Tang, J.-L. Maurice, F. Fossard, I. Florea, W. Chen, E. V. Johnson, M. Foldyna, L. and P. Roca i Cabarrocas, Nanoscale, 9, 8113-8118 (2017)
[5] L. Vincent, G. Patriarche, G. Hallais, C. Renard, C. Gardès, D. Troadec, D. Bouchier, Nano Lett. 14, 4828-4836 (2014)
[6] M. Amato, T. Kaewmaraya, A. Zobelli, M. Palummo, R. Rurali, Nano Lett. 16, 5694-5700 (2016).
[7] T. Kaewmaraya, L. Vincent, M. Amato, J. Phys. Chem. C 121, 5820-5828 (2017).

Ospiti: Stefano Ossicini.

[Ultimo aggiornamento: 05/07/2017 18:16:01]