Topographical and Chemical Imaging of a Phase Separated Polymer Using a Combined Atomic Force Microscopy/Infrared Spectroscopy/Mass Spectrometry Platform

In this paper, the use of a hybrid atomic force microscopy/infrared spectroscopy/mass spectrometry imaging platform was demonstrated for the acquisition and correlation of nanoscale sample surface topography and chemical images based on infrared spectroscopy and mass spectrometry. The infrared chemical imaging component of the system utilized photothermal expansion of the sample at the tip of the atomic force microscopy probe recorded at infrared wave numbers specific to the different surface constituents. The mass spectrometry-based chemical imaging component of the system utilized nanothermal analysis probes for thermolytic surface sampling followed by atmospheric pressure chemical ionization of the gas phase species produced with subsequent mass analysis. The basic instrumental setup, operation, and image correlation procedures are discussed, and the multimodal imaging capability and utility are demonstrated using a phase separated poly(2-vinylpyridine)/poly(methyl methacrylate) polymer thin film. The topography and both the infrared and mass spectral chemical images showed that the valley regions of the thin film surface were comprised primarily of poly(2-vinylpyridine) and hill or plateau regions were primarily poly(methyl methacrylate). The spatial resolution of the mass spectral chemical images was estimated to be 1.6 μm based on the ability to distinguish surface features in those images that were also observed in the topography and infrared images of the same surface.