ELECTRIC-FIELDS AND INTERFERENCE EFFECTS INSIDE NONCENTROSYMMETRIC MULTILAYER FILMS AT ELECTRODE SURFACES FROM ELECTROCHEMICALLY MODULATED SURFACE-PLASMON RESONANCE EXPERIMENTS

The electric field profile inside a self-assembled noncentrosymmetric zirconium phosphonate (ZP) multilayer film at a gold electrode is dete rmined by the in situ optical technique of electrochemically modulated surface plasmon resonance (EM-SPR). In these experiments, changes in the index of refraction (Delta n) of a ZP film during potential modula tion are measured via the EM-SPR differential reflectivity curves. Mod ulated SPR experiments on the ZP films incorporated into air-gap capac itors are used to relate Delta n to changes in the electric field stre ngth (Delta E) inside the film. The noncentrosymmetric ZP films utiliz e the nonlinear optical chromophores exyl)sulfonyl]phenyl]azo]phenyl]p entoxy]phosphonic acid (HAPA) and thyl)amino]phenyl]azo](5-phosphonope ntyl)]pyridium bromide (PY-AZO). For a 6.7 nn ZP HAPA film, a change i n electrode potential (Delta phi(m)) of 50 mV corresponds to a change in electric field strength (Delta E) of 1.4 x 10(4) V/cm. EM-SPR exper iments on mixed ZP multilayers of HAPA and the centrosymmetric molecul e 1,10-decanediylbis(phosphonate) are used to measure the spatial vari ations of the electric fields within the ultrathin films. Evidence for ion and solvent penetration into the ZP films is observed in the elec trochemical environment. Additional studies of interference effects in mixed multilayers of HAPA and PY-AZO are used to verify the retention of directional order during the ZP multilayer deposition process.