Preparation and Characterization of Nanostructured Multilayered Films.

Abstract Our interest in the field of multilayered films was inspired by their potential usefulness in optical and sensing applications, and by a fundamental interest in the manipulation of matter at the nanometer scale. The work presented in this dissertation represents a new method for the formation of multilayered films exhibiting an unprecedented degree of structural order among films adsorbed from solution onto flat substrates. This method involves the alternate adsorption of a cationic polyelectrolyte and single sheets of an anionic silicate mineral via Coulombic interactions. Elucidating the characteristics of the growth and structure of these films was a central focus of our research. Ellipsometry and ultraviolet-visible spectrophotometry demonstrated that the films exhibited regular growth, and the films' lateral uniformity allowed them to serve as antireflective coatings. X-ray diffractometry indicated that the ordered material in the films comprised an ABAB arrangement of the polymer and silicate. In previous methods for the preparation of multilayered films by self-assembly of monomeric precursors, defects occurring during any preparative step can propagate as the film grows in thickness, resulting in a decrease in structural order. In contrast, our films displayed a high degree of structural order despite the fact that defects (i.e., sheet edges) occur in every layer. We demonstrated that the "two-dimensional" nature of the silicate allowed sheets adsorbing in any given cycle to patch over defects that had formed during preceding cycles. This characteristic allowed substrates that were resistant to the adsorption of either component individually to be covered by a film over the course of several adsorption cycles.Thin films such as ours offer promise for use in sensors due to their large area/mass ratio and the ease with which they can be incorporated into microelectronic devices. Our composite multilayered films responded in a dramatic and reversible way to changes in relative humidity, and we used ellipsometry and micro-gravimetry to characterize this response. The kinetics of water sorption were remarkably fast: the majority of the water sorbed upon turnover between environments of low and high humidity was gained or lost within three seconds.