Force-induced molecular dissociation at surfaces via a local probe

化学键的解离是所有化学反应的基本过程。扫描隧穿显微镜（STM）已被用于通过隧穿电子诱导分子内单个共价键的断裂。然而，从来没有人尝试过不通过穿隧电子而仅仅通过局部探针施加力来破坏分子内的化学键。该项目的主要目的是探索是否有可能通过使用STM和原子力显微镜（AFM）在单个吸附分子中诱导这样的过程，除了原子分辨成像之外，还可以研究分子和探针之间的短程化学力作为分子-探针分离的功能。力光谱学和地形成像的结合将能够以非常高的分辨率描述探针-分子相互作用过程中的力和势能，以及施加力前后分子的结构。由于之前已经证明有机分子中的碳-卤素（C-X）键可以通过其他方法（例如热活化-促进表面合成过程）选择性地切割，我们将重点研究破坏这种碳-卤素共价键。在这个项目中，含有活性C-X片段的分子物种将被沉积在超高真空（UHV）条件下的表面上，金属探针将接近C-X键，并测量分子和探针之间的力。实验将(1)确定吸附在衬底上的单个分子内的C-X键是否可以通过在低温（120K）下施加力而断裂，(2)测量探针-分子相互作用期间存在的力，从而提供势能景观的信息。被吸附在表面上的分子内的C-X键的断裂通常是由被吸附的分子与金属底物（通常是Cu， Ag或Au）之间的相互作用驱动的；即催化活性的环境。因此，额外的实验将(3)通过改变探针顶端的金属原子（Cu、Ag或Au）或改变分子内的卤素种类（Br或I）来研究所测力对体系化学性质的依赖。此外，在传统的合成过程中，热能经常引发反应，我们将(4)研究底物温度对力诱导键解离过程的影响。这种通过原子间作用力诱导和研究分子键解离的新方法以前从未被探索过，并且有可能在原子尺度上深入了解化学环境和温度在这一解离过程中的作用。

The dissociation of chemical bonds is a fundamental process in all chemical reactions. Scanning tunnelling microscopy (STM) has been used to induce the breaking of single covalent bonds within a molecule via tunnelling electrons. However, it has never been attempted to break a chemical bond within a molecule not via tunnelling electrons but only by applying a force with a local probe. The main objective of this project is to explore whether it is possible to induce such a process within an individual adsorbed molecule by using STM and atomic force microscopy (AFM), which in addition to atomically resolved imaging allows the study of short-range chemical forces between the molecule and the probe as a function of molecule-probe separation. A combination of force-spectroscopy and topographical imaging will allow characterisation of the forces and potential energies during the probe-molecule interaction and the structure of the molecule before and after the applied force with very high resolution.As it has previously been demonstrated that carbon-halogen (C-X) bonds in organic molecules may be cleaved selectively by other methods (e.g. thermal activation - facilitating on-surface synthesis processes), we will focus on breaking such a carbon-halogen covalent bond. Within this project a molecular species containing a reactive C-X moiety will be deposited on a surface held under ultra-high vacuum (UHV) conditions, a metallic probe will be approached towards the C-X bond, and the forces between the molecule and the probe measured. The experiments will (1) ascertain whether a C-X bond within an individual molecule adsorbed on a substrate can be broken by applying a force at low temperatures (120K) and, (2) measure the forces present during the probe-molecule interaction and thus provide information on the potential energy landscape. The breaking of a C-X bond within a molecule that is adsorbed on a surface is typically driven by the interaction between the adsorbed molecule and a metallic substrate (often Cu, Ag, or Au); i.e. a catalytically active environment. Additional experiments will therefore (3) study the dependence of the measured force on the chemical properties of the system by changing the metal atoms at the probe apex (Cu, Ag, or Au) or by changing the halogen species within the molecule (Br or I). Furthermore, as in conventional synthetic processes where thermal energy often initiates the reaction, we will (4) study the effect of the substrate temperature on the force-induced bond dissociation process.This novel approach to inducing and studying molecular bond dissociation by interatomic forces has not previously been explored, and potentially offers an atomic-scale insight into the role of the chemical environment and temperature within this dissociation process.