Aryl diazonium salts are well-known
for electrochemically
grafting
conductive surfaces. The substrate surface chemistry, the solvent
used, and the salt’s variable functional group tamper with
the grafted layer density, packing, and morphology. Standard surface
microscopy methods are unable to determine the chemical structure
of a modified surface at the nanoscale, which prevents associating
nanometric features to chemical identities. Photoinduced force microscopy
(PiFM) is a vibrational nanospectroscopy technique capable of simultaneously
measuring topography by atomic force microscopy and surface chemistry
by infrared spectroscopy with an ∼5 nm spatial resolution.
Compared to other localized infrared surface vibrational techniques,
PiFM has a higher signal-to-noise ratio, enabling monolayer sensitivity
and making it useful for the investigation of thin layers, like reduced
aryl diazonium salts. We used PiFM to study grafted samples morphologically
and spectroscopically, providing insights into chemical structure.
Lastly, a micrometer area was functionalized using scanning electrochemical
cell microscopy (SECCM) and then chemically mapped with the PiFM.