Cluster Superlattice Membranes

• Applicant: Professor Dr. Thomas Werner Michely
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Experimental Condensed Matter Physics ; Solid State and Surface Chemistry, Material Synthesis
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 452340798

• Final Report Year: 2024

Final Report Abstract

Topic of the proposal was to further develop and investigate a new type of cluster material, namely cluster superlattice membranes (CSLMs). Such a membrane consists of a hexagonal lattice of small clusters with a lattice parameter around 3 nm, templated by the moiré of graphene and an underlying metal substrate. The lattice of clusters is of atomic precision, but of larger scale, and thus a superlattice. The cluster superlattice is sandwiched between graphene and amorphous carbon as matrix material of nm-thickness, such that the entire membrane forms a mechanically stable, nm-thick sheet which can have mm lateral extension. 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 a few to a few 100 atoms. In the world of cluster materials, the unique property of CSLMs is the crystalline order of small clusters with a small, but not atomic, superlattice constant. Within the project new CSLMs were developed which replace graphene by hexagonal boron nitride as templating layer, resulting in superior order of the superlattice, or amorphous carbon by non-conducting boron as matrix material, thereby broadening the potential range of application. It was shown that a closed CSLM is impermeable and provides perfect protection of the embedded clusters even under ambient conditions, which is for instance useful when investigating the magnetic interactions of a lattice of small magnets. To make the clusters accessible for the interaction with the environment, the membrane must be opened by removal of the 2D layer. This required the development of a double transfer method to bring the CSLMs upside-down onto a new substrate and a gentle etching method, removing only the atomically thin templating layer (e. g. graphene), but keeping the clusters stable within the matrix. In situ investigations of CSLMs in the transmission electron microscopy established a stunning thermal stability of the cluster superlattice in the membrane up to a least 850 K, while at even higher temperature the dynamics of cluster ripening via cluster coalescence could be followed. With the results of the project all methods are now available to use CSLMs in order to investigate tunneling transport, magnetic interactions or catalytic properties of a cluster superlattice.

Publications

• Carbon Embedding of Pt Cluster Superlattices Templated by Hexagonal Boron Nitride on Ir(111). The Journal of Physical Chemistry C, 125(42), 23435-23444.
  Hartl, Tobias; Will, Moritz; Bampoulis, Pantelis; Herrmann, Daniel; Valerius, Philipp; Herbig, Charlotte; Boix de la Cruz, Virginia; Lacovig, Paolo; Vonk, Vedran; Chung, Simon; Stierle, Andreas; Lizzit, Silvano; Knudsen, Jan & Michely, Thomas
  
• Growth, Stability, and Electronic Decoupling of Pt Clusters on h-BN/Ir(111). The Journal of Physical Chemistry C, 125(7), 3880-3889.
  Will, Moritz; Hartl, Tobias; Boix de la Cruz, Virginia; Lacovig, Paolo; Lizzit, Silvano; Knudsen, Jan; Michely, Thomas & Bampoulis, Pantelis
  
• Silicon Cluster Arrays on the Monolayer of Hexagonal Boron Nitride on Ir(111). The Journal of Physical Chemistry C, 126(15), 6809-6814.
  Hartl, Tobias; Herrmann, Daniel; Will, Moritz; Falke, Yannic; Grüneis, Alexander; Michely, Thomas & Bampoulis, Pantelis
  
• “Cluster superlattice membranes”, PhD thesis (University of Cologne, 2023)
  Hartl, Tobias