Characterization of sculptured thin films

Physical vapor deposition can be used to synthesize sculptured thin films with high surface areas. Highly directional vapor deposition onto a tilted, rotating substrate has been shown to produce nanostructured materials with controlled columnar features, including zig-zag, cusp, chevron, and helical geometries. Nanoporous coatings such as these are desirable for optical sensing applications due to their accessible high surface area, but few techniques are available to quantify the surface area of thin films. Electron beam and thermal evaporation techniques are used to synthesize highly porous thin films from silicon dioxide and a germanium antimony selenide chalcogenide glass in order to explore their potential for optical applications in both the visible and infrared spectral ranges. Characterization has been performed using nitrogen adsorption isotherms obtained with a quartz crystal microbalance. It is shown that surface area can be increased up to 375 times that of a flat film by deposition at oblique angles. A nitrogen adsorption technique is introduced as a means to examine the porosity of sculptured thin films at a nanoscale.