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O: Fachverband Oberflächenphysik

O 82: Nanostructures at Surfaces: Graphene and Other Aspects

O 82.6: Vortrag

Mittwoch, 22. März 2017, 17:15–17:30, REC/PHY C213

Graphene on Ir(110), a twofold-symmetric substrate for van der Waals epitaxy applied to growth of organometallic nanowires — •Felix Huttmann, Stefan Kraus, and Thomas Michely — II. Physikalisches Institut, Universität zu Köln, Germany

Standard substrates for van der Waals heteroepitaxy, such as graphene on hcp or fcc metal surfaces or H-terminated Si, all possess threefold or sixfold rotational symmetry, and if an adsorbed film does not have such symmetry, this leads to the formation of rotational domains, in conflict with the common goal to achieve an effectively single-crystalline film. We have encountered this problem in the growth of carpets of organometallic nanowires of europium cyclooctatetraene (EuCot) on the graphene/Ir(111) surface, where the lack of a global orientation of the nanowires forbids the study of orientation-dependent properties using spatially averaging techniques. Here, we investigate the growth of graphene on Ir(110), a surface with only twofold rotational symmetry. While clean Ir(110) exhibits facetting, exposure to ethylene at elevated temperatures leads to re-flattening of the surface. Two well-ordered overlayer phases are formed depending on the growth temperature of either 1250 K or 1380 K. The high-temperature phase is atomically flat over terrace sizes on the order of 100 nm and permits to grow the EuCot nanowires oriented along the [001] direction of the substrate. A single global orientation of almost all nanowires is thus achieved as intended. On the scale of a few hundred nanometers, a structure of ridges and valleys with step edge bundles in between limits the smoothness of the graphene/Ir(110) surface and provides room for improvement.