Paper EL+AS+EM+SS+TF-WeA8
Spectroscopic Ellipsometry of Thin Films for Archival Optical Data Storage and for Microfabricated Thin Layer Chromatography Plates

Wednesday, October 30, 2013, 4:20 pm, Room 101 A

Our group is focused on the synthesis and characterization of new materials and over the years this interest has led us into different research areas. Of late we have focused on developing and understanding the materials for archival optical data storage and for separations science (chromatography). In particular, we have recently helped spin out a company from the university that is selling a DVD that has been shown to last for more than 1000 years – see www.mdisc.com. Another company has licensed our technology to microfabricate thin layer chromatography (TLC) plates – see www.diamond-analytics.com.

In this talk we discuss the important role that spectroscopic ellipsometry (200 – 1000 nm) has played in the development and understanding of the materials in these devices. For many of these measurements we use interference enhancement to break the correlation between film optical constants and thicknesses. Some of our measurements have been fairly routine. For example, the thicknesses and optical properties of the ca. 35 nm alumina barrier layers in our microfabrication of TLC plates are easily modeled using a Cauchy dispersion relationship. In other cases the analyses have been challenging, e.g., the thin, ca. 6 nm, Fe films used to make TLC plates appear to be completely oxidized, but thicker Fe films show increasing metallic (Drude) character. An understanding of the optical properties of our bismuth-tellurium-selenium (BTS) write layers on Mylar tape for optical data storage has also been nontrivial. These films show high levels of roughness by AFM, significant void fractions by RBS, and moderately high levels of oxidation by XPS and SIMS, which mandated the use of a roughness layer and optimization of the depolarization factor in the effective medium approximation that described the film. AFM and SEM were also used to characterize these materials, and our final SE analysis of this material might not have been reasonable without the extra information these techniques provided. Both the BTS write layer and Fe films for TLC have been monitored over an extended period of time by SE. The resulting plots of psi and delta vs. several wavelengths reveal the long-term stabilities of these materials. At present we are also attempting to determine the optical constants of the carbon nanotube forests used as templates in TLC plate microfabrication. We believe that the resulting optical constants of these materials, which should show a considerable degree of anisotropy, will be of interest to the community.