Surface Coordination Chemistry of YBa2Cu3O7-δ

Abstract

The surface coordination chemistry of the cuprate superconductor, YBa2Cu3O7-δ has been extensively surveyed using cyclic voltammetry in conjunction with a series of redox-active ferrocenyl containing adsorbate molecules. Evidence supporting the adsorption of molecules with primary alkylamine, secondary alkylamine, tertiary alkylamine, arylamine, thiol, disulfide, and selenol functionalities is reported. Cyclic voltammetry, atomic force microscopy, scanning electron microscopy, X-ray powder diffraction and resistivity vs temperature measurements were utilized to evaluate the influence of the modification conditions on the bulk and surface properties of the high-Tc superconductor. The spontaneous adsorption of redox-active alkylamines, arylamines, and thiols onto the surfaces of cuprate materials has been shown to produce stable and robust monolayer films with no apparent damage to the bulk properties of the underlying superconductors. Of the molecules studied thus far, primary alkylamines have been determined to be the optimum adsorbates based upon surface coverage values and monolayer durability. Tertiary alkylamines form monolayers on YBa2Cu3O7-δ with an electrochemical persistence comparable to primary alkylamine monolayers, suggesting that hydrogen binding with the surface is not necessary for adsorption. We propose that amines act as Lewis bases and bind to Lewis acidic Cu surface site(s) in YBa2Cu3O7-δ to form stable coordination bond(s).