Optical properties of Cu-implanted LiNbO3

Cu ion implantation in LiNbO3 was done at widely different energies. Optical absorption spectra were measured in the visible range. Samples were heated to 500 °C in air for different times. Depth profiles and the electronic state of Cu for the samples at low ion energies were measured by x-ray photoelectron spectroscopy. Identification of the elements and measurement of the concentration of droplets on the surface were done by inductive coupled plasma spectroscopy. A large, sharp absorption peak is observed at 596 nm for the as-implanted sample at 3 MeV and a large, broad peak at 610 nm for the sample at 25 keV. These absorption peaks are explained in terms of Cu colloids formed in LiNbO3, but the electronic state of Cu in the implanted layer is not that of pure copper. Cu atoms segregate from the implanted layer to the surface, where they form small droplets. The droplet precipitation occurs even at room temperature and is accelerated at high temperature.