| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS-WeM |
| Session: | Environmental Interfaces, Ambient Surfaces, In-Operando Studies and Adsorption on 2D Materials |
| Presenter: | Vladimir Korolkov, University of Nottingham, UK |
| Authors: | V. Korolkov, University of Nottingham, UK S. Svatek, University of Nottingham, UK L. Yang, University of Nottingham, UK J. Kerfoot, University of Nottingham, UK A. Summerfield, University of Nottingham, UK N. Champness, University of Nottingham, UK T. Taniguchi, The National Institute for Materials Science, Japan K. Watanabe, The National Institute for Materials Science, Japan N. Besley, University of Nottingham, UK P. Beton, University of Nottingham, UK |
| Correspondent: | Click to Email |
Hexagonal boron nitride (h-BN) is a layered material and a wide-gap semiconductor with a band gap of 5.2 e.V. The latter property makes it highly attractive as a support to study optical and electrical properties of monolayered molecular assemblies stabilized by non-covalent interactions. Although h-BN has been known since 1940s it is a relatively new substrate in the area of molecular self-assembly. In part this is due to the widespread use of scanning tunneling microscopy to acquire images of molecules, but this technique is not compatible with h-BN.
The adsorption of a range of molecules on BN and other layered materials has been investigated using using high resolution atomic force microscopy (AFM). We have observed several arrangements of molecules which are stabilized by hydrogen bonding including a bimolecular layer formed by perylene tetracarboxylic di-imide (PTCDI) and melamine which form an open nanporous array in which the planar PTCDI molecules are adsorbed parallel to the substrate. The networks are deposited from solution by immersion of BN substrate and the ordering may be improved by post-annealing in an inert atmosphere. We have also investigated the adsorption of 5,10,15,20-tetrakis(4- carboxylphenyl)porphyrin (TCPP), a dye molecule with a planar porphyrin macrocycle as its core. This molecule forms an open square array, also stabilized by hydrogen bonding through carboxlic acid pendant groups which steer the arrangement so that macrocycle lies parallel to the surface. In this arrangement the molecular layer is strongly fluorescent showing lines which are red-shifted from solution. When molecules are adsorbed on MoS2 they form similar structures but the resulting islands are smaller and less ordered, and, due to the smaller band gap of MoS2, fluorescence is quenched. We also present density functional theory calculations of the conformation of adsorbed molecules and numerical estimates of the hydrogen bonding and adsorption energies. We discuss this approach as a route to the molecular functionalization of two-dimensional materials and the formation of hybrid molecular devices.
The work will present an outstanding examples of single molecule and submolecular resolution achieved in the ambient on standard Atomic Force Microscopes. Most of the presented results will be on level with the published UHV-STM studies.