Surface Cleaning and Adsorbate Layer Formation:  Dual Role of Alkylamines in the Formation of Self-Assembled Monolayers on Cuprate Superconductors

The development of monolayer adsorption chemistry for superconductor surfaces is particularly important for a number of practical and fundamental reasons. As high-T{sub c} superconductors begin to approach the marketplace in areas of communications, power industries, medical applications, and scientific instrumentation, the development of new soft chemistry approaches for the surface modification of these technologically relevant electronic materials becomes increasingly important. Monolayer adsorption chemistry has been developed extensively for electronic materials such as metals, semiconductors, and insulators. These methodologies have been expanded recently to include a variety of high-temperature superconductors (HTSCs). The authors describe a series of new X-ray photoelectron spectroscopy (XPS), four-point conductivity, critical current, atomic absorption spectroscopy (AAS), grazing angle infrared spectroscopy, and GE--MS experiments, which lead the suggestion that an entirely different mechanism is involved in the formation of HTSC-localized monolayers. According to the new model, the amine reagents serve two chemically distinct roles. In the initial phase, the degraded superconductor exteriors is etched away with the help of the amine compounds. The etching process proceeds to the point where fresh YBa{sub 2}Cu{sub 3}O{sub 7} is exposed, and only at this point do the amines adsorb and remain at the YBa{sub 2}Cu{sub 3}O{sub 7} surface. As the adsorption process continues, there is an accumulation of an organized monolayer at the surface, which prevents further etching of the YBa{sub 2}Cu{sub 3}O{sub 7} material.