Structural Manipulation of Hydrogen-Bonding Networks in Amide-Containing Alkanethiolate Monolayers via Electrochemical Processing

We report the electrochemically driven phase transformation of amide-containing alkanethiol, 3-mercapto-N-nonylpropionamide (1ATC9) self-assembled monolayers (SAMs) into a linear nanostructure. Hydrogen-bonding interactions between buried amide groups cause multistep electrochemical desorption and enable an unusual phase change, affording a less dense, textured structure. Single-component 1ATC9 SAMs prepared in solution at room temperature for 24 h consist of two phases with different apparent heights in scanning tunneling microscope images; these phases are readily manipulated by controlling solution temperature and deposition time. Intermolecular hydrogen-bonding interactions give high thermal stability to the films. The presence of two independent cathodic peaks in 1ATC9 monolayer voltammograms indicates two-step reductive desorption. A monolayer phase transition occurs after the first cathodic peak, transforming a close-packed monolayer into a striped phase that is energetically favored at low surface-thiolate density. Scanning tunneling microscopy, cyclic voltammetry, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy reveal electrochemical nanostructuring, driven by partial reductive desorption and strong interchain hydrogen bonding. The resultant striped, low-coverage phase is inaccessible by other synthetic preparations, except controlled dosing in ultrahigh vacuum.