Infrared and Computational Studies of Spontaneously Adsorbed Amine Reagents on YBa₂Cu₃O₇:  Structural Characterization of Monolayers atop Anisotropic Superconductor Surfaces

Methods capable of forming highly organized monolayers on top of YBa₂Cu₃O₇ (YBCO), a high-T_c superconductor, have been identified and are described for the first time. Here, grazing reflectance infrared fourier transform spectroscopy (GRIFTS) is employed to evaluate the degree of order for these monolayer structures. Through these investigations, it is found that while octadecylamine forms a well-ordered, crystalline-like monolayer on the surface of c-axis-oriented YBa₂Cu₃O₇ thin films, the same reagent adsorbed onto polycrystalline YBa₂Cu₃O₇ pellets affords disordered, liquid-like monolayers. Computational studies of alkylamine packing, using a molecular mechanics methodology, reveal two plausible structures for the crystalline-like monolayer. A GRIFTS comparison of primary, secondary, and tertiary alkylamine reagents also has been completed, and the substitution pattern dependence of the monolayer order has been assessed experimentally. Moreover, comparisons between amine monolayers on top of YBa₂Cu₃O₇ and alkyl thiol reagents on gold surfaces are made using GRIFTS and thermal desorption experiments. This work documents the initial report of the assembly and characterization of organized monolayers supported on high-T_c superconductor surfaces, the most complex substrate yet reported capable of fostering ordered adsorbate layers.