AVS 62nd International Symposium & Exhibition
    2D Materials Focus Topic Thursday Sessions
       Session 2D+EM+MG+NS+SE+SM+SS+TF-ThM

Invited Paper 2D+EM+MG+NS+SE+SM+SS+TF-ThM12
A Two-Dimensional Oxide Quasicrystal

Thursday, October 22, 2015, 11:40 am, Room 212C

Session: Emergent 2D Materials
Presenter: Stefan Förster, Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Germany
Authors: S. Förster, Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Germany
J.I. Flege, Institute of Physics, Univerisity of Bremen, Germany
K. Meinel, Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Germany
R. Hammer, Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Germany
M. Trautmann, Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Germany
J. Falta, Institute of Solid State Physics, University of Bremen, Germany
T. Greber, Physik-Institut, University of Zürich, Switzerland
W. Widdra, Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Germany
Correspondent: Click to Email
With the recent discovery of the first oxide quasicrystal (QC) aperiodicity is entering the field of two-dimensional materials [1]. Aperiodicity means that the system exhibits long-range order as expressed by sharp diffraction spots but since the ordering follows an aperiodic function the system is lacking translational symmetry. We report here on the complex growth process of the oxide QC involving a high-temperature wetting process and periodic approximant structures.

The QC is derived from BaTiO3 thin films on a hexagonal Pt(111) substrate and exhibits a sharp twelve-fold diffraction pattern [1]. Based on scanning tunneling microscopy the aperiodic atomic structure had been resolved [1]. It is formed by surface atoms arranged in forms of squares, triangles, and rhombi with a next-neighbour distance of 0.69 nm. In addition to this dodecagonal atomic arrangement, building blocks of squares, triangles, and rhombi are also found on (2+√3) and (2+√3)² larger scales indicating the characteristic self-similarity of an ordered QC [1]. The high-resolution STM measurements allow furthermore to identify atomic flips in the structure indicating lattice excitations in the quasicrystal called phasons. Using low-energy electron microscopy (LEEM) the preparation and the growth of the QC films on top of the hexagonal Pt(111) is monitored in all details from room temperature up to about 1200 K. LEEM shows that upon high-temperature annealing large 3DBaTiO3 islands are formed with bare Pt(111)-(1x1) in between. At temperatures above 1020 K a wetting layer spreads on the free Pt area. This wetting process can be reversed by annealing in an oxygen atmosphere. In-situ LEEM measurements show that under these conditions the QC decays into small BaTiO3 islands. The observed interface-driven formation of a 2D QC from a perovskite oxide in contact with a hexagonal substrate is expected to be a general phenomenon.

1. S. Förster, K. Meinel, R. Hammer, M. Trautmann, and W. Widdra, Nature 502, (2013) 215.