[en] A topographic investigation of periodically poled lithium niobate (PPLN) crystals was performed by recording a map of the crystal surface after a selective etching process using a standard profilometer. A procedure to correct for the systematic error introduced by the finite size of the tip is discussed in detail so that the width of ferroelectric domains can be mapped with an estimated tolerance of about 3% along the whole length of the sample. The method is applied to a PPLN structure obtained by the Czochralski off-center technique

[en] Iron-doped X-cut lithium niobate crystals were prepared by means of thermal diffusion from thin film varying in a systematic way the process parameters such as temperature and diffusion duration. Secondary Ion Mass Spectrometry was exploited to characterize the iron in-depth profiles. The evolution of the composition of the Fe thin film in the range between 600 C and 800 C was studied, and the diffusion coefficient at different temperatures in the range between 900 C and 1050 C and the activation energy of the diffusion process were estimated. (orig.)

[en] In this work we investigate the iron incorporation in thermally diffused Fe doped LN, by combining two experimental techniques, i.e. micro-Raman spectroscopy and proton induced X rays emission. Our results point out that in substituting for Li, Fe ions induces a decrease of Nb_Li antisite defects and rearrangement of the Nb sublattice.

[en] The photorefractive effect induced by 775-nm laser light on doped lithium niobate crystals is investigated by the direct observation in the far field of the transmitted-beam distortion as a function of time. Measurements performed at various Zr-doping concentrations and different light intensities show that the 775-nm light beam induces a steady-state photorefractive effect comparable to that of 532-nm light, but the observed build-up time of the photovoltaic field is longer by three-orders of magnitude. The 775-nm photorefractivity of lithium niobate crystals doped with 3 mol. % ZrO₂ or with 5.5 mol. % MgO is found to be negligible

[en] Iron ions were implanted with a total fluence of 6 x 10¹⁷ ions/m² into lithium niobate crystals by way of a sequential implantation at different energies of 95, 100 and 105 MeV respectively through an energy retarder Fe foil to get a uniform Fe doping of about few microns from the surface. The implanted crystals were then annealed in air in the range 200-400 ^oC for different durations to promote the crystalline quality that was damaged by implantation. In order to understand the basic phenomena underlying the implantation process, compositional in-depth profiles obtained by the secondary ion mass spectrometry were correlated to the structural properties of the implanted region measured by the high resolution X-ray diffraction depending on the process parameters. The optimised preparation conditions are outlined in order to recover the crystalline quality, essential for integrated photorefractive applications.

[en] A study on LiNbO₃ crystal irradiation by pulsed KrF excimer laser beam is presented. The interaction with the 248 nm laser light modifies the material properties so that, when the irradiation is switched off, a time-periodic variation in the material reflectivity, depending on the irradiation conditions, was observed. This phenomenon can be explained in terms of the electro-optic effect induced by the buildup of internal electric fields since the compositional characterization, performed by the secondary ion mass spectrometry, showed no modification in the element concentration and the high resolution x-ray diffraction did not detect any structural deformation within the crystal

[en] The damage effects produced in the near-surface region of x-cut LiNbO₃ by low dose, high energy implantation of carbon, nitrogen, oxygen, and fluorine ions are investigated as a function of the dose and substrate temperature during the implant process. The damage profiles were obtained by the Rutherford backscattering RBS-channeling technique, whereas the compositional profiles were performed by secondary ion mass spectrometry. The experimental results showed that the mechanisms governing the damage formation at the surface are strongly connected to the interaction of defects produced when the electronic energy loss exceeds a given threshold close to 220 eV/A. In particular, we observed a damage pileup compatible with a growth of three-dimensional defect clusters

[en] We present a phenomenological model and finite element simulations to describe the depth variation of mass density and strain of ion-implanted single-crystal diamond. Several experiments are employed to validate the approach: firstly, samples implanted with 180 keV B ions at relatively low fluences are characterized using high-resolution x-ray diffraction; secondly, the mass density variation of a sample implanted with 500 keV He ions, well above its amorphization threshold, is characterized with electron energy loss spectroscopy. At high damage densities, the experimental depth profiles of strain and density display a saturation effect with increasing damage and a shift of the damage density peak towards greater depth values with respect to those predicted by TRIM simulations, which are well accounted for in the model presented here. The model is then further validated by comparing transmission electron microscopy-measured and simulated thickness values of a buried amorphous carbon layer formed at different depths by implantation of 500 keV He ions through a variable-thickness mask to simulate the simultaneous implantation of ions at different energies. (paper)

[en] By exploiting a Mach–Zehnder interferometer, the r₃₃ electro-optic coefficient of erbium-bulk-doped lithium niobate crystals grown by the Czochralski technique was measured depending on the erbium content. The r₃₃ coefficient decreases with the erbium concentration. Such a trend has been connected with both the reduction of the lattice parameter, measured by high resolution x-ray diffraction, and the increase of lattice defects

[en] We experimentally investigate the formation of self-confined beams in lithium niobate crystals which are doped in the bulk with erbium. Samples have been grown by the Czochralski method with erbium nominal concentrations varying in the range 0.0–0.7 mol% in the melt. The speeds of beam confinement depend on the applied bias and on the beam intensity, as expected, but on the doping level as well. The erbium incorporation influences both the electro-optic coefficient and the photovoltaic field. A very general dependence of the confined beam waist on the refractive index change was experimentally derived, valid now for every lithium niobate crystal, independent on its growing procedure or doping