Recrystallization of amorphous nanotracks and uniform layers generated by swift-ion-beam irradiation in lithium niobate

Abstract

The thermal annealing of amorphous tracks of nanometer-size diameter generated in lithium niobate (LiNbOs) by Bromine ions at 45 MeV, i.e., in the electronic stopping regime, has been investigated by RBS/C spectrometry in the temperature range from 250°C to 350°C. Relatively low fluences have been used (<10 12 cm -2 ) to produce isolated tracks. However, the possible effect of track overlapping has been investigated by varying the fluence between 3 x 10 11 cm -2 and 10 12 cm -2 . The annealing process follows a two-step kinetics. In a first stage (I) the track radius decreases linearly with the annealing time. It obeys an Arrhenius-type dependence on annealing temperature with activation energy around 1.5 eV. The second stage (II) operates after the track radius has decreased down to around 2.5 nm and shows a much lower radial velocity. The data for stage I appear consistent with a solid-phase epitaxial process that yields a constant recrystallization rate at the amorphouscrystalline boundary. HRTEM has been used to monitor the existence and the size of the annealed isolated tracks in the second stage. On the other hand, the thermal annealing of homogeneous (buried) amorphous layers has been investigated within the same temperature range, on samples irradiated with Fluorine at 20 MeV and fluences of ~10 14 cm -2 . Optical techniques are very suitable for this case and have been used to monitor the recrystallization of the layers. The annealing process induces a displacement of the crystallineamorphous boundary that is also linear with annealing time, and the recrystallization rates are consistent with those measured for tracks. The comparison of these data with those previously obtained for the heavily damaged (amorphous) layers produced by elastic nuclear collisions is summarily discussed.

Analysis and optimization of propagation losses in LiNbO3 optical waveguides produced by swift heavy-ion irradiation

“…In order to compare our experimental data with these theoretical predictions, it is necessary to estimate the barrier thickness of our guides after each annealing step. Note that annealing treatments reduce the amorphous barrier thickness h by epitaxial recrystallization [21], whereas they increase in the same amount the waveguide thickness d. Then, for our estimates, we substract from the initial barrier thickness h (see Table 1) the amount 2Ad, assuming that both barrier boundaries recrystallize at the same speed. In fact, the estimated barrier evolution is roughly consistent with the thermally activated crystallization velocity reported in [21].…”

Current status and future developments of the ion beam facility at the centre of micro-analysis of materials in Madrid

“…This route has been fruitfully used at CMAM in many relevant photonic materials: lithium niobate [53][54][55] and other materials such as KGd(WO 4 ) 2 [56,57], KY(WO 4 ) 2 [58,59], LiTaO 3 [60] and SiO 2 [61]. Along with these studies, the CMAM researchers have also a wide experience in the production of nanotracks generated by SHI impacts [62][63][64]. The applications of this ion-track technology go from fission-fragment dosimetry, to molecular sieves, and to a variety of electronic and magnetic devices.…”

Determination of track radii and relation to the electronic energy density deposited in swift heavy ion irradiated LiNbO3

“…In order to better evaluate the dependence of track dimension on the electronic energy deposition, the track radius determined in this study and track radii obtained from RBS/c measurements by other researchers for various conditions of SHI irradiations in LiNbO3 [14,29,43,19] are depicted in Fig. 8 versus the corresponding electronic energy loss.…”

“…Often, track radii determined by different methods for one and the same material under comparable irradiation conditions differ greatly (see e.g. [19]).…”

“…8: Track radii measured by RBS/c for various irradiation conditions (a) as a function of the energy loss Se, and (b) as a function of the energy density w ~ Se/β 4k , with k empirically determined to be 0.25. The dashed lines in (a), and shaded region in (b) are to guide the eye.The experimental data are taken from Refs [14,19,29,43]…”