VARIABLE INDEX OF REFRACTION ULTRATHIN FILMS FORMED FROM SELF-ASSEMBLED ZIRCONIUM PHOSPHONATE MULTILAYERS - CHARACTERIZATION BY SURFACE-PLASMON RESONANCE MEASUREMENTS AND POLARIZATION MODULATION FT-IR SPECTROSCOPY/

Ultrathin (submicrometer) organic films of specified index of refracti on are constructed by the sequential deposition of self-assembled zirc onium phosphonate (ZP) molecular monolayers that contain two different bisphosphonate ions, 1,10-decanediylbis(phosphonate) (BP) and 4,4'azo bis[(p-phenylene)methylene]bis(phosphate) (AZO). By varying the ratio of DBP to AZO monolayers in the ZP multilayer film, the index of refra ction can be controlled. A combination of surface plasmon resonance (S PR) measurements and polarization/modulation Fourier transform infrare d reflection-absorption spectroscopy (PM/FT-IRRAS) is used to examine the structure of the ZP multilayers on vapor-deposited gold substrates , and ellipsometric measurements are utilized to determine the index o f refraction of the ZP multilayers on transparent substrates. ZP films consisting of 100% DBP and 100% AZO molecules are found to have indic es of refraction of 1.51 and 1.64, respectively, at an optical wavelen gth of 632.8 mn. In both the 100% DBP and the 100% AZO multilayers, an average monolayer thickness of 16 +/- 0.5 A is determined from the SP R measurements. The spectroscopic and ellipsometric data indicate that the index of refraction of mixed ZP multilayer films (i.e., films wit h both DBP and AZO self-assembled monolayers) can be varied systematic ally between 1.51 and 1.64, but that the average thickness of the self -assembled monolayers is greater in the mixed films than in either of the 100% DBP or 100% AZO multilayers.