Copper dihydrogen complex in ZnO

Local vibrational modes of a copper-dihydrogen complex CuH(2) in ZnO have been identified by using IR absorption spectroscopy. Two O-H modes at 3347 and 3374 cm(-1) are observed after Cu in-diffusion at 1200 degrees C and subsequent hydrogenation at 725 degrees C in sealed ampoules filled with an H(2) gas. Isotope substitution experiments revealed that the defect consists of two equivalent hydrogen atoms. From uniaxial stress measurements, the defect was found to have monoclinic symmetry. Based on these results, the observed local modes are ascribed to a defect consisting of a substitutional Cu atom and two adjacent bond-centered hydrogen atoms, each of which is bound to the oxygen atoms in the basal plane of the defect. The hydrogen motion around the Cu atom was found to be thermally activated with an activation energy of 0.29 +/- 0.04 eV. The apparent thermal stability of CuH(2) depends on the Cu doping profile and the interaction with a hydrogen species that is invisible in IR absorption.