Structural and compositional mapping of a phase-separated Langmuir-Blodgett monolayer by X-ray photoelectron emission microscopy

The structure and composition of phase-separated Langmuir-Blodgett monolayer films comprised of mixtures of arachidic acid (C19H39COOH) and perfluorotetradecanoic acid (C13F27COOH) were characterized using a combination of X-ray photoelectron emission microscopy (X-PEEM), secondary electron emission microscopy (SEEM) and atomic force microscopy (AFM). X-PEEM provides high lateral spatial resolution and is directly sensitive to the elemental and chemical (functional group) composition of these ultrathin films through the chemical sensitivity of NEXAFS spectroscopy; AFM provides high-resolution imaging, both in terms of lateral and vertical (height) film topography. SEEM provides additional structural and electronic information through work function and electron scattering effects. The combination is used for chemical mapping of the phase-separated domains in the monolayer film. Our results directly confirm previous AFM measurements that suggested that the discontinuous domains are enriched in arachidic acid, whereas the surrounding continuous domain is a mixture of both arachidic acid and perfluorotetradecanoic acid.