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Quantification of adsorption on three-dimensional spatially coherent thin films at the solid-liquid interface
Sculptured thin films comprising highly spatially coherent three-dimensional nanostructures exhibit strongly anisotropic properties. The anisotropic response of the nanostructures is modulated by the uptake of adsorbate due to screening of anisotropic polarization charges. This phenomenon, termed here surface-enhanced anisotropy modulation, is a new detection principle that allows for quantification of adsorbate by generalized ellipsometry. Additionally, the nanostructures have a higher surface area than respective flat surfaces and allow for additional attachment. Applications for surface-enhanced anisotropy are numerous and include contraband detection, diagnostics, in-line monitoring of surface modification, and evaluation of the conformational state of organic materials embedded within porous nanostructure thin films. Ellipsometry and quartz crystal microbalance with dissipation are characterization techniques that have been used to benchmark the attachment of adsorbate onto isotropic flat and rough surfaces. The data analysis approaches of these techniques must consider the anisotropic properties and significant surface roughness of nanostructure thin films. An anisotropic Bruggeman effective medium approximation is applied for optical modeling, and a frequency overtone analysis is developed to consider the mechanical effects of liquid on oscillating nanostructures. In this work, data analysis approaches for generalized ellipsometry and quartz crystal microbalance with dissipation are introduced and developed for anisotropic surfaces at the solid-liquid interface. Water and its deuterated analogue are exposed over a slanted columnar thin film to determine the quantity of liquid that rigidly couples with nanostructures during quartz crystal microbalance measurement. The surface-enhanced anisotropy detection principle is demonstrated by monitoring the adsorption of fibronectin protein onto Ti slanted nanocolumns. The formation of a nanohybrid functional material is described, whereby decanethiol chemisorbs onto and functionalizes Ti slanted nanocolumns coated with Pt by atomic layer deposition.
Chemical engineering|Electrical engineering
Rodenhausen, Keith B., "Quantification of adsorption on three-dimensional spatially coherent thin films at the solid-liquid interface" (2013). ETD collection for University of Nebraska - Lincoln. AAI3604729.