On-surface chemistry using local high electric fields
On-surface chemistry is a promising topic in nanoscience and is widely applied for the generation of nanostructures and to the chemical modification of adsorbed molecules in order to tune their properties. In this work we developed an approach based on the application of a high electric field between the tip of a scanning tunnelling microscope(STM) and a metallic substrate across well-organized layers of organic molecules to induce chemical reactions. Using an electric field to control chemical reactions is a concept that has been discussed in the early works of Shaik et al. In fact, electro-chemistry is based on the modification of the chemical potential by applying a voltage between the two electrodes of an electro-chemical cell in order to initiate redox reactions. This implies, however, a charge transport using an electrolyte and this scheme is not applicable to ultra-high vacuum. In this work we address the following question: can a dehydrogenation reaction in vacuum be triggered by an electric field gradient in the absence of electron tunneling and thus in the zero-current limit? This mechanism has been successfully demonstrated for some rare cases. Here we extended this idea from the chemical modification of a single molecule to an extended molecular layer. As a prototype molecule, we use dihydrotetraazapentacene (DHTAP) molecule, which was previously reported to form layers on Au(111). By locally applying a high electric field synthesized TAP and MHTAP molecules derived from DHTAP by the double or single dehydrogenation, respectively, in a self-assembled layer. We have also shown that it is possible to dehydrogenate either individual molecules by voltage pulses or a group of molecules by scanning a larger area at high voltages. Our observations suggest that it could be possible to prepare large-scale TAP layers via the non-local application of a high electric fields.
 T. Leoni, T. Lelaidier, A. Thomas, A. Ranguis, O. Siri, C. Attaccalite and C. Becker, Nanoscale Adv., 2021, 3, 5565
 S. Shaik, S. de Visser and D. Kumar, J. Am. Chem. Soc., 2004, 126, 11746
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