Multicolor Chemical Imaging by Sum Frequency Generation Imaging Microscopy of Monolayers on Metal Surfaces

摘要

Sum frequency generation imaging microscopy (SFG-IM) is a unique surface-specific technique that can detect the spatial distributions of differing monolayer species based on chemical contrast. Here SFG images of microcontact-patterned multicomponent self-assembled monolayers derived by the adsorption of alkanethiols on gold were analyzed by factor analysis (FA) utilizing a library consisting of SFG alkanethiol spectra to determine the chemical identity and spatial distribution of the patterned monolayers across the images. By utilizing the spectral library as a target test for factor analysis, we correctly identified the monolayer species, and their spatial distributions were mapped. The chemical identity and spatial distribution of a random-pattern multicomponent alkanethiol sample were determined and mapped. Furthermore, utilizing the alkanethiol library, factor analysis was able to identify an unknown monolayer region, the vibrational spectra of which were not present in the target library. The results demonstrate the capability of FA combined with the spectral library to determine the chemical composition and spatial distribution of organic molecules on the surface of multicomponent complex chemical systems acquired by SFG-IM.