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The atomic composition, structural, morphological, and optical properties of N-rich copper nitride thin films have been investigated prior to and after annealing them in vacuum at temperatures up to 300 °C. Films were characterized by means of ion-beam analysis (IBMA), X-ray diffraction (XRD), atomic force microscopy (AFM), and spectroscopic ellipsometry techniques (SE). The data reveal that even when the total (integrated over the whole thickness) atomic composition of the films remains constant, nitrogen starts to migrate from the bulk to the film surface, without out-diffusing, at temperatures as low as 100 °C. This migration leads to two chemical phases with different atomic concentration of nitrogen, lattice parameters, and crystallographic orientation but with the same crystal structure. XRD experimental and Rietveld refined data seem to confirm that nitrogen excess accommodates in interstitial locations within the anti-ReO3 crystal lattice forming a solid solution. The influence of nitrogen migration on the optical (electronic) properties of the films will be discussed. [ABSTRACT FROM AUTHOR]

Relevant damage features associated with femtosecond pulse laser and swift-ion irradiations on LiNbO3 crystals are comparatively discussed. Experiments described in this paper include irradiations with repetitive femtosecond-laser pulses (800 nm, 130 fs) and irradiation with O, F, Si, and Cl ions at energies in the range of 0.2–1 MeV/amu where electronic stopping power is dominant. Data are semiquantitatively discussed by using a two-step phenomenological scheme. The first step corresponds to massive electronic excitation either by photons (primarily three-photon absorption) or ions (via ion-electron collisions) leading to a dense electron-hole plasma. The second step involves the relaxation of the stored excitation energy causing bond breaking and defect generation. It is described at a phenomenological level within a unified thermal spike scheme previously developed to account for damage by swift ions. A key common feature for the two irradiation sources is a well-defined intrinsic threshold in the deposited energy density Uth required to initiate observable damage in a pristine crystal: Uth≈1.3×104-2×104 J/cm3 for amorphization in the case of ions and Uth≈7×104 J/cm3 for ablation in the case of laser pulses. The morphology of the heavily damaged regions (ion-induced tracks and laser-induced craters) generated above threshold and its evolution with the deposited energy are also comparatively discussed. The data show that damage in both types of experiments is cumulative and increases on successive irradiations. As a consequence, a certain incubation energy density has to be delivered either by the ions or laser photons in order to start observable damage under subthreshold conditions. The parallelism between the effects of laser pulses and ion impacts is well appreciated when they are described in terms of the ratio between the deposited energy density and the corresponding threshold value. [ABSTRACT FROM AUTHOR]

The damage kinetics induced by irradiation with a diversity of swift ions (O at 5 MeV; F at 5.1 MeV; Si at 5, 7.5, and 41 MeV; and Cl at 11 and 46 MeV) has been investigated in the range of 1012–1015 at./cm2. It covers from the initial stage where single damage tracks are isolated and well separated, up to the stage where a full amorphous layer is produced. The damage is characterized by the areal fraction of disorder derived from the Rutherford backscattering/channeling spectra. The data approximately fit an abrupt Avrami-type dependence with fluence. The fluence value at which 50% of the sample surface becomes disordered shows a clear increasing trend with the electronic stopping power of the ion. The trend is consistent with Monte Carlo simulations based on a recent model for defect creation. Moreover, the quantitative agreement for the defect generation rate appears also reasonable. [ABSTRACT FROM AUTHOR]

The formation of buried heavily damaged and amorphous layers by a variety of swift-ion irradiations (F at 22 MeV, O at 20 MeV, and Mg at 28 MeV) on congruent LiNbO3 has been investigated. These irradiations assure that the electronic stopping power Se(z) is dominant over the nuclear stopping Sn(z) and reaches a maximum value inside the crystal. The structural profile of the irradiated layers has been characterized in detail by a variety of spectroscopic techniques including dark-mode propagation, micro-Raman scattering, second-harmonic generation, and Rutherford backscattering spectroscopy/channeling. The growth of the damage on increasing irradiation fluence presents two differentiated stages with an abrupt structural transition between them. The heavily damaged layer reached as a final stage is optically isotropic (refractive index n=2.10, independent of bombarding ion) and has an amorphous structure. Moreover, it has sharp profiles and its thickness progressively increases with irradiation fluence. The dynamics under irradiation of the amorphous-crystalline boundaries has been associated with a reduction of the effective amorphization threshold due to the defects created by prior irradiation (cumulative damage). The kinetics of the two boundaries of the buried layer is quite different, suggesting that other mechanisms aside from the electronic stopping power should play a role on ion-beam damage. [ABSTRACT FROM AUTHOR]

A thermal-spike model has been applied to characterize the damage structure of the latent tracks generated by high-energy ion irradiations on LiNbO3 through electron excitation mechanisms. It applies to ions having electronic stopping powers both below and above the threshold value for lattice amorphization. The model allows to estimate the defect concentrations in the heavily damaged (preamorphized) regions that have not reached the threshold for amorphization. They include the halo and tail surrounding the core of a latent track. The existence of the preamorphized regions accounts for a synergy between successive irradiations and predicts a dependence of the amorphization threshold on previous irradiation fluence. The predicted dependence is in accordance with irradiation experiments using N (4.53 MeV), O (5.00 MeV), F (5.13 MeV), and Si (5 and 7.5 MeV). For electronic stopping powers above the threshold value the model describes the generation of homogeneous amorphous layers and predicts the propagation of the amorphization front with fluence. A theoretical expression, describing this propagation, has been obtained that is in reasonable agreement with silicon irradiation experiments at 5 and 7.5 MeV. The accordance is improved by including in a simple phenomenological way the velocity effect on the threshold. At the highest fluences (or depths) a significant discrepancy appears that may be attributed to the contribution of the nuclear collision damage. [ABSTRACT FROM AUTHOR]

The relaxation of poled guest–host polyphosphazene (PPZ) films containing the 4-[(4′-nitrophenyl)azo]phenoxy (NPAP) azo-dye chromophore (T[sub g]=144 °C) has been investigated by measuring the time decay of the nonlinear optical susceptibility tensor in the 80–120 °C temperature range. The kinetic data have been analyzed on the basis of the Legendre polynomial decomposition of the orientational distribution function. In the measuring time range, two components (fast and slow) of the decay have been found together with a constant component that disappears at temperatures close to T[sub g]. This component accounts for the nonreorientable fraction of the molecules at each temperature. The temperature dependence of the two lifetimes has been determined and fitted to an Adam–Gibbs law. At a high temperature, (120 °C) the ratio of lifetimes closely follows the predictions of the orientational diffusion equation. This allows one to determine the two nonlinear components β[sub zzz]=-88.10[sup -30] esu and β[sub zxx]=71.10[sup -30] esu of the quadratic hyperpolarizability tensor in our rodlike (C[sub ∞v] symmetry) molecules, showing the non-negligible contribution of the nondiagonal components. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Elastic recoil detection with a time of flight discrimination method using [sup 127]I ions has been applied to the simultaneous determination of the H and Li depth profiles as well as of the stoichiometry of the mixed phases formed by thermal annealing in proton-exchanged LiNbO[sub 3] waveguides. For both, as-exchanged and annealed waveguides, a one-to-one local correlation between the H and Li profiles has been obtained so that [H]+[Li]=constant. Moreover, the stoichiometry of the H[sub x]Li[sub 1-x]NbO[sub 3] compound, where x is the exchange rate, has been correlated with x-ray diffraction (rocking curves) data in order to identify the generated phases after the exchange and annealing processes. In as-exchanged guides, the value x≃0.85 is mainly associated with a broad β[sub 2]-phase peak. In annealed guides, a well-defined β[sub 2]-peak is associated with x≃0.5, a broad κ[sub 2]-peak is associated with x≃0.40, a broad κ[sub 1]-peak to x≃0.19 and 0.21, and a α-shoulder to x≃0.09 and 0.12. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]