Ellipsometric Study Of YBa2Cu3O7-x

ABSTRACT The high- temperature superconducting material, YBa2Cu3O7_x, and other related materials have acomplex chemical bonding structure that makes the electronic structure difficult to understand. In addition,the oxygen stoichiometry, which is variable, is critical to the conductivity and superconductivity of the material. Using spectroscopic ellipsometry, we have studied the chemical dependence of the opticalproperties and found that these properties can be separated into contributions of the local chemical structures. This includes the identification of a strong absorption feature at 4.1 eV with linear O- Cul + -Ocomplexes that form as a result of oxygen vacancies. Therefore we can use this feature to indicate oxygenloss at the surface. We have found that the formation of interfaces with Al or In causes such oxygen loss,but interfaces with Ag and Au do not. Room temperature vacuum exposure does not cause measurableoxygen loss at the surface.1. INTRODUCTIONThe copper -oxide superconductors are now found in four structural families including those of: