Determination of Fluorescence Density Profiles of Langmuir-Blodgett-Deposited Films by Analysis of Variable-Angle Fluorescence Data Curves
By use of the method of Langmuir-Blodgett deposition thin films with three different spatial distributions of fluorophores were constructed. The films were deposited on the flat surface of a sapphire hemicylindrical prism. Each film had a thickness of 55.44 nm. The spatial distribution of each film type was in the form of a rectangular fluorescence density profile: monolayers containing fluorophores were confined to be within a specific range in terms of distance from the prism/film interface. Rectangular profiles can be characterized by the parameters of amplitude, position (center), and width. Light from an argon ion laser (488-nm line), which was incident on the prism/film interface, was used to excite fluorescence in each of the film types. Fluorescence was collected as a function of both incident and observation angles. It was found that variable-angle fluorescence data curves taken from the films could be used to predict an approximate position of each rectangular profile. Based on reduced x2 values predictions of position made from variable incident angle curves were more reliable than those made from variable observation angle curves. The effect of an index matching fluid, placed adjacent to the film, was to cause the position to be underestimated. An analysis of data curves did not result in a reliable estimation of the parameter of width. Results from simulated data indicate that data curves could support fitting of all three parameters (amplitude, position, and width) at quantum noise levels comparable to the noise levels of the actual data. Therefore, the failure of the analysis to predict the width parameter is attributed to a distortion in the data curves rather than the effect of quantum noise from photon collection. Possible improvements in the apparatus which may reduce this distortion are discussed. © 1988, American Chemical Society. All rights reserved.
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