Force-induced molecular dissociation at surfaces via a local probe
Final Report Abstract
The objective of this project is to explore whether it is possible to break a chemical bond within an individual molecule adsorbed on a metal surface by applying a force with a local probe. Scanning probe microscopy (SPM) experiments allow a ‘visual’ identification of the individual chemical components within a molecule lying on a surface, and allow a probe coated with a catalytically active material (in this case gold atoms) to be approached above a site-specific location with atomic precision. To ensure that the molecules remain stationary during the measurements the experiments are carried out at 125K (approximately -150°C). Images of the molecule acquired before and after the interaction with the probe allow any change in structure (including the breaking of chemical bonds) to be visualised. The frequency-modulated atomic force microscopy (FM-AFM) technique allows the force between the probe and the molecule to be measured. By probing different sites on a molecule the chemical-force between different ‘reactive’ and ‘non-reactive’ regions may be compared. The work undertaken during this project has provided an insight into the question as to whether a covalent bond can be broken within a molecule on a surface at 125K using only an applied force. For a Au functionalised probe it is apparent that force induced bond breaking is not possible at 125K. The forces between the probe and the molecule have been measured, and the project has demonstrated that this technique allows the measurement of the force between a catalytically active probe and a molecule. This represents an important advance in the state-of-the-art for such measurements as these results demonstrate that it is possible to chemically distinguish between different parts of a molecule using FM-AFM and that such measurements provide details about the interaction force. These experiments have been highly successful in terms of implementing a complicated technique usually performed at 5K (-268°C), where chemical reactions are unlikely to occur, at much higher temperatures where chemical reactions may potentially be investigated. Further experiments in this area will focus on the functionalisation of the probe with more reactive catalytic species in order to investigate different interaction chemistries and potentially observe a force induced bond breaking.
Publications
- Physisorption Controls the Conformation and Density of States of an Adsorbed Porphyrin. J. Phys. Chem. C, 2015, 119 (50), pp 27982–27994
S.P. Jarvis, S. Taylor, J.D. Baran, D. Thompson, A. Saywell, B. Mangham, N.R. Champness, J.A. Larsson & P. Moriarty
(See online at https://doi.org/10.1021/acs.jpcc.5b08350)
