Synthesis and spectroscopic characterization of novel self-assembled zirconium phosphonate multilayer films on gold and silica surfaces

Self-assembled multilayer films based on the zirconium phosphonate (ZP) ligand deposition chemistry are formed on gold and fused silica surfaces. These films which incorporate interesting linear and nonlinear optical (NLO) chromophores are characterized with the surface-sensitive techniques of polarization-modulation Fourier transform infrared reflection-absorption spectroscopy (PM-FTIRRAS) for molecular structure information and surface plasmon resonance (SPR) measurements for the optical determination of the film thickness on gold surfaces. In addition to the spectroscopic measurements on gold substrates, the optical indices of refraction for the ZP multilayer films formed on transparent silica substrates are obtained from ellipsometric measurements.; Noncentrosymmetric ZP films incorporating the nonlinear optical chromophore (5-(4-((4-((6-hydroxyhexyl)sulfonyl) phenyl) azo) phenyl) pentoxy) phosphonic acid (HAPA) exhibited the second-order nonlinear optical processes of second harmonic generation (SHG) and the electro-optic effect. The SHG response from the ZP films increased quadratically with the number of HAPA monolayers. The electro-optic coefficient {dollar}rsb{lcub}33{rcub}{dollar} for a HAPA monolayer was determined to be 11 pm/V at 632.8 nm from modulated surface plasmon resonance experiments made on ZP films incorporated into air-gap capacitors. This value is similar to those measured for NLO poled-polymer films.; This modulated SPR technique is then applied to an electrochemical environment in order to determine the electric field strength within noncentrosymmetric ZP films at gold electrode surfaces. In addition to determining the electric field strength within pure HAPA films, mixed ZP multilayers of HAPA and 1,10-decanediylbis(phosphonate) (DBP) are used to measure the spatial variations of the electric fields within the ultrathin films.