High Lateral Resolution Imaging by Secondary Ion Mass Spectrometry of Photopatterned Self-Assembled Monolayers Containing Aryl Azide

Imaging secondary ion mass spectrometry (SIMS) is used to map the distribution of molecular and elemental species in a patterned self-assembled monolayer (SAM) with 1 μm lateral resolution. The patterned SAMs are made by exposing polycrystalline Au to a solution of bis(ll-(4-azido(benzoyloxy))-1-undecyl) disulfide, I, which forms a photosensitive SAM (Au-I) on the Au. Subsequent UV irradiation (λ > 260 nm) of Au-I SAMs through a mask and a thin film of a secondary amine results in attachment of the amine to the Au-I SAM only in the irradiated regions. The Au-I SAM is photosensitive by virtue of a pendant aryl azide group which reacts with secondary amines under UV irradiation to form hydrazine or azepine photoadducts. A large molecular fragment ion corresponding to vinyl ferrocene (m/z 212) was mapped with 1 μm lateral resolution on a Au-I SAM that had been irradiated through a mask and a thin film of (2-ferrocenylethyl)(2′,2′,2′-trifluoroethyl)amine. SIMS can also detect intact molecular ions M+ corresponding to the 3H-azepine and hydrazine photoadducts obtained upon irradiation of Au-I SAMs in the presence of diethyl- and dibutylamines. Smaller fragment ions characteristic of the 3H-azepine and hydrazine adducts weee also observed. The mass assignments were verified by a series of isotopic labeling experiments in which the observed ions displayed the expected isotopic shifts.