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Cluster superlattice membranes (Clusterübergittermembranen); 
DFG research grant (DFG Einzelantrag)

Cluster superlattice membranes are a new type of two dimensional (2D) material. Such a membrane consists of clusters positioned in a 2D hexagonal array with a lattice constant of 2-4 nm. The lattice of clusters is of atomic precision, but of larger than atomic scale, and thus a superlattice. The cluster superlattice is sandwiched between a single crystal 2D layer of atomic thickness and an embedding matrix of nm thickness, such that the matrix together with the clusters and the 2D layer forms a mechanically stable sheet which can have mm lateral extension as shown in the figure. Its mechanical integrity enables the transfer from a host substrate to another substrate or its use as a freestanding membrane. The clusters are tunable in size from the single atom limit up to about 400 atoms.

It is a central goal of this project to create a diverse range of membranes through development of synthesis methods. This will include the realization of open membranes, such that the clusters can interact with the environment, e.g. for applications in electrocatalysis. Post-growth of clusters and combination of open membranes with new metallic films will broaden their application potential for nanomagnetic investigations. Realizing membranes with oxides as a host material will give access to optical as well as electrical transport properties, and enable heterogeneous catalysis at elevated temperatures. 

Synthesis and development of the membranes for new applications is conducted in ultrahigh vacuum in Cologne together with initial characterization by STM and STS. Together with collaboration partners, methods like transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and surface sensitive X-ray diffraction are used to obtain deeper insight into the membranes’ properties. 

Top row, left: STM topograph of an Ir cluster superlattice grown on graphene on Ir(111); right: sketch of superlattice embedding with carbon. Bottom row, right: electrochemical delamination of the membrane; right: sketch of the free-standing membrane and transmission electron microcope image of the membrane. Inset displays superlattice diffraction spots. [more