The Enemy Within: Hydrogen Poisoning in On-Surface Synthesis

Abhishek Singh^1*, Akash Gupta¹, Hsuan-Ting Lin¹, Ngo Tieu Khanh¹, Le Quang Nhat¹, Hideki Okamoto², Germar Hoffmann¹

¹Physics, National Tsing Hua University, Hsinchu, Taiwan
²Chemistry, Okayama University, Okayama, Japan

* Presenter:Abhishek Singh, email:abhisheksinghji@gmail.com

Introduced in 2019 [1,2], atomic hydrogen dosing is nowadays established for advanced processing in On-Surface Synthesis (OSS). OSS is the synthesis of extended covalent structures from simple precursors directly on a substrate. Unlike molecular hydrogen, atomic hydrogen can deactivate molecular radical sites and remove synthesis byproducts. These effects are demonstrated for OSS reactions activated above room temperature [3]. We show the influence of atomic hydrogen on reactions activated below and near room temperature. We employ Scanning Tunneling Microscopy to investigate the Wurtz-type coupling reaction using 3,10-bis(bromomethyl)-[5]phenacene. On Au(111), atomic hydrogen passivates intermediate products, removes byproducts, and suppresses C-C covalent coupling. On Ag(111), molecular precursors remain intact. Hydrogen exposure induces debromination and modifies the molecular self-assembly; however, C–C covalent coupling between molecules is not fully inhibited. These findings highlight that atomic hydrogen at room temperature can strongly affect surface reactions, making it essential to control its presence to avoid unintended products and to interpret results correctly in OSS.



References

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Keywords: Scanning Tunneling Microscopy (STM), On-Surface Synthesis, Atomic Hydrogen, Wurtz-type coupling reaction