Regensburg 2016 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 45: Graphene: Adsorption, Intercalation and Doping

O 45.8: Poster

Dienstag, 8. März 2016, 18:15–20:30, Poster E

Square ice sandwiched in graphene: a theoretical NMR study — •Achraf Jaadouni, Eva Rauls, Wolf Gero Schmidt, and Uwe Gerstmann — Uni Paderborn, Theoretische Physik, Pohlweg 55, 33100 Paderborn

Bulk water can exist in many forms, liquid, vapour and at least 16 crystalline phases, including the famous hexagonal ice [1]. Theory suggests, that many further phases can occur, if water is adsorbed on surfaces or confined on nanoscopic pores. A determination of the microscopic structure, however, provides a major challenge for experiment. Recently, locked between two graphene sheets, a new high-density phase has been observed by transmission electron microscopy (TEM) [2]. The so-called 'square ice' provides a symmetry qualitatively different from both hexagonal ice as well as graphene.

Modelling bilayer and trilayer lattices within density functional theory (DFT), we show that the phase transition from hexagonal to square ice is accompanied by a characteristic change of the NMR chemical shifts for the included protons. Hence, the detection via NMR spectroscopy appears as a promising alternative to electron imaging, in particular in case of nanostructures with a high amount of disorder, e.g. hydrophobic nanocapillaries.

[1] G. Malenkov, J. Phys. Condens. Matter 21, 283101 (2009).

[2] G. Algara-Siller et al., Nature 519, 443 (2015).