Tuning the exchange reaction between a self-assembled monolayer and potential substituents by electron irradiation

Self-assembled monolayers (SAMs) can undergo an exchange-reaction with the molecules capable of building a SAM on the same substrate upon the immersion into the respective solution. However, for most systems, the exchange reaction is very slow at normal conditions and occurs to a limited extent. Using the primary SAMs on nonsubstituted alkanethiols (ATs) and several omega-substituted ATs as the potential substituents, we show that the rate and extent of the exchange reaction can be significantly enhanced and precisely tuned by electron irradiation with a small dose. We assume that the irradiation results in the appearance of subtle structural and chemical defects in the target SAM, which promote the molecular exchange. The effect of irradiation and exchange reaction were monitored in detail by contact angle goniometry, infrared reflection absorption spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and X-ray photoelectron spectroscopy. The developed approach, irradiation-promoted exchange reaction, can be considered as a platform for the preparation of mixed SAMs and, in combination with e-beam lithography, for the fabrication of chemical patterns, including gradient ones.