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Crespillo M. L. Caballero-Calero O. Joco V. Rivera A. Herrero P. Olivares J. Agulló-López F. 《Applied Physics A: Materials Science & Processing》2011,104(4):1143-1152
The thermal annealing of amorphous tracks of nanometer-size diameter generated in lithium niobate (LiNbO3) 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 (<1012 cm−2) to produce isolated tracks. However, the possible effect of track overlapping has been investigated by varying the fluence
between 3×1011 cm−2 and 1012 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 amorphous-crystalline
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 ∼1014 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 crystalline-amorphous 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. 相似文献
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The c(5√2 × √2)R45°-Pb/Cu(1 0 0) surface phase is investigated by means of angle resolved ultraviolet photoemission and low energy electron diffraction in the temperature range between 300 and 550 K. We identify and characterize a temperature-induced surface phase transition at 440 K from the room temperature c(5√2 × √2) R45° phase to a (√2 × √2)R45° structure with split superstructure spots. The phase transition is fully reversible and takes place before the two-dimensional melting of the structure at 520 K. The electronic structure of the split (√2 × √2)R45° phase is characterized by a metallic free-electron like surface band. This surface band is backfolded with c(5√2 × √2)R45° periodicity phase at room temperature, giving rise to a surface band gap at the Fermi energy. We propose that a gain in electronic energy explains in part the stability of the c(5√2 × √2)R45° phase. 相似文献
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