Scanning Probe-Based Chemical Conversion of Organic Monolayers

Abstract

Atomic force microscopy (AFM) has been applied to localized surface chemical conversion of organosilane self-assembled monolayers (SAMs). Current was injected from a conductive AFM probe into a SAM in order to induce electrochemical reactions of the SAM in the presence of adsorbed water. Two examples were demonstrated. First was oxidation of an alkylsilane SAM. Modification processes were dependent on the operation mode of AFM, that is, contact, intermittent-contact and noncontact modes. In the contact mode, the alkylsilane SAM was decomposed and removed from the substrate Si accompanied with anodization of Si, while in the intermittent-contact mode, methyl groups terminating the SAM were converted to carboxyl groups without causing any changes on the main part of the SAM and the substrate Si. In addition, no modification was induced when the noncontact mode was used. The next example was oxidation and reduction of an amino-terminated SAM in a reversible manner. Oxidation of amino groups on the SAM to nitoroso groups and their reduction back to amino groups were successfully conducted by the current-injecting AFM in the contact mode while applying positive and negative sample biases, respectively. This process could be repeated several times.