Highly ordered molecular membranes have been playing important roles in both basic studies and applications. Among the molecules that form such molecular membranes are synthetic amphiphiles. We have observed the N 1s spectral change by aggregation of azobenzene-containing ammonium amphiphiles C12AzoCMN+Br- (M = 2, 10) in water by utilizing the freezing method. By comparing the calculated intensity ratio of azo-group nitrogen to ammonium nitrogen with that experimentally observed, the N 1s spectral change has been successfully correlated with various aggregate's model structures of the amphiphiles, such as the lamella, tube, and globule. With the assumption that the N 1s photoelectron (about 850 eV in kinetic energy) mean free path is about 30 Å, the bilayer lamella model has proved to be most probable for both M = 2 and M = 10 compounds. This paper has successfully demonstrated that XPS (X-ray photoelectron spectroscopy) has the potential for use in analyzing molecular orientation in addition to conventional elemental and functional group analyses.
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