Far-infrared spectroscopy of Au-implanted lithium niobate (LiNbO3)

The optical phonons and the behavior of dielectric functions of ion-implanted LiNbO3 were studied using far-infrared spectroscopy. First, single crystal LiNbO3 specimens were implanted with −75 keV Au ions at two different levels of ion fluence (1×1016 and 1×1017 cm−2), and then annealed at 800 °C for 1 h. Then, before and after annealing, the optical spectra were measured in two frequency ranges: (1) reflectance far-infrared spectra in the range from 40 to 700 cm−1 and (2) transmission ultraviolet, visible and near-infrared spectra in the range from 250 to 2000 nm. The far-infrared spectra were analyzed by fitting with a harmonic oscillation model of the dielectric function to determine the three oscillation parameters of each optical phonon-mode, namely, mode frequency, oscillator strength and damping constant. The behavior of these oscillation parameters and the dielectric function revealed that the ion implantation caused a phase transition, probably amorphization, in the implanted layer, and that the post-annealing enabled the implanted layers to completely “recover” their dielectric function to that of the unimplanted crystalline LiNbO3 substrate, despite the presence of embedded Au clusters in the layer as seen in the visible spectra. This “recovery” result indicates that the metal-embedded LiNbO3 layer should show a dielectric response to an electric field in high frequency equivalent to the response by an unimplanted structure.