Multilayer Structure

X-ray or neutron reflectivity measurements of polyion films show patterns with profound intensity oscillations, as demonstrated in Figure 2. They are so-called Kiessig fringes, due to the interference of radiation beams reflected from interfaces solid support/film and air/film. From the periodicity of these oscillations, one can calculate the film thickness (with the help of the Bragg-like equation and taking into account refraction phenomena that are essential at small angles). Growth steps for a bilayer of 1.1-2.0 nm are typical for alternate linear polyion assembly, and a thickness of one layer often equals to half of this value [6-14]. These values correspond to a polyion cross-section and show that in one cycle of excessive adsorption we have approximately one monolayer coverage of the substrate. The nanoparticle/polyion bilayer thickness is determined by the diameter of the particle. Model fitting of X-ray data gives

X-ray (X=1.54 A) and neutron (X=2.37 A) reflectivity from

PEI+(PSS/PEI)2+{PSS/Mb/PSS-d/Mb}8 multilayer, film thickness is 940 A, four-unit cell thickness is 111 A

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