Applying UV-Vis spectroscopy to step-by-step molecular self assembly on surface: Does it bring pertinent information?

UV-Vis spectroscopy is often used to follow the growth of films built by self-assembly, by plotting [Absorbance vs. number of layers]. In most cases, a linear or nearly linear evolution is observed and, based on the Lambert-Beer law, a layer-by-layer self-assembling process is quite often deduced. Data evaluation, based on a simple Lambert-Beer law approach and distinct growth modes (perfect layer-by-layer, pyramidal growth, self-assembled and lateral growth simultaneous pyramidal and lateral growth and islands growth), is proposed in order to investigate the validity of this conclusion. The apparent linearity is obtained with all the proposed growing modes. Moreover, with special values of some parameters, an exponential behaviour is observed in the case of simultaneous pyramidal and lateral growth. Each model was evaluated by direct comparison to experimental data from the literature. (c) 2007 Elsevier B.V. All rights reserved.