Investigation of the electrode/electrolyte interface using ultra fast electrochemical ellipsometry

Abstract

Electrochemical ellipsometry is employed to determine the real and imaginary parts of the refractive index and the thickness of thin films as functions of the potential applied to the electrode upon which the film is grown. The relatively recent advent of an analyser with no moving parts, the Stokesmeter, has removed previous time restraints and allows microsecond resolution. The Newcastle system is extremely novel, using a Stokesmeter, and thus being capable of 325 gs resolution, and also being electrochemically interfaced. The ellipsometric studies have concentrated on the growth and behaviour of a series of electroactive polymers derived from salicylaldehydes (Salens). [Ni(SaltMe)] and [Ni(SaIdMe)] were found to yield stable homogeneous films upon polymerisation, however while the behaviour during film growth was similar, marked differences were observed during potential cycling, poly[Ni(SaIdMe)] showing a marked decrease in thickness near the anodic limit not observed for poly[Ni(Saltme)], indicating that even minor changes to ligand structure well away from the site of polymerisation may have significant effects on the resulting film. The behaviour of poly[Ni(OMeSaltMe)] during polymerisation is more complicated; initially a homogeneous film is produced, however about half way through the growth process the film becomes inhomogeneous, and remains so during subsequent potential cycling. This behaviour was also observed for poly[Pd(OMeSalen)], indicating electron donating groups around the phenyl rings of the ligand have a profound effect on the nature of the polymer films, possibly far more so than the identity of the central metal.