Preparation, Characterization, and Properties of Mixed Organic and Polymeric Self-Assembled Multilayers

Multilayer thin films consisting of layer-pairs of oppositely charged macrocycles (nickel phthalocyanine tetrasulfonate, NiPc) and macromolecules (poly(diallydimethylammonium) chloride, PDDA) were fabricated using self-assembly techniques. The film structures were characterized with X-ray reflectometry, from which the roughness (∼2−7 Å) of the film growth surface, the average electron density of each layer-pair, the mean thickness of the layer-pairs (∼10.5 Å), and the overall thickness of the multilayer samples were deduced. Measurements of film thicknesses were applied as constraints to an analysis of spectroscopic ellipsometry measurements of the films. Imposition of these constraints increased the confidence of the optical constant refinements deduced from ellipsometry. We find, for multilayers of PDDA and NiPc, a refractive index of n ≈ 1.6−1.8 in the nonabsorption region of the visible and near-infrared (IR) spectrum and an extinction coefficient in close agreement with the measured electron optical absorption at 630 and 665 nm. Atomic force microscopy was also used to observe surface morphology and determine grain size distribution and roughness for selected films. An increase in surface roughness (∼5−15 Å) was observed as the number of layer-pairs in the film increased from 3 to 27.