Chemical and Structural Characterization of Electrochemically Reduced Diazonium Salt Grafted Nanofilms via Photoinduced Force Microscopy

Aryl diazonium salts covalently bind to substrates upon electrochemical reduction. In this study, we advance our understanding into the structure, interface, and core composition of electrochemically reduced and deposited nanofilms on glassy carbon from 4-bromobenzene and 4-nitrobenzene diazonium salts in organic solvents. Using high-resolution atomic force microscopy with mid-infrared vibrational spectroscopy, we achieve chemical imaging at a sub-10 nm spatial resolution, well beyond the diffraction limit of infrared light. Our interdisciplinary approach combining grazing and low incidence angle X-ray microdiffraction, electrochemistry, microscopy, and spectroscopy delivers nanofilm molecular structures, layer thicknesses, metrology, and direct localized chemical identification through infrared surface vibrations at the substrate/film interfaces and at the center of the films to produce both quantitative and qualitative information. This work demonstrates the power of photoinduced force microscopy for chemically analyzing molecules on modified surfaces, paving the way for surfaces, interfaces, electronic or optoelectronic nanoengineering, and protective coatings.