Creation of nanosize defects in LiF crystals under 5- and10−MeVAu ion irradiation at room temperature

Abstract

Investigation of radiation defects induced by the irradiation of LiF crystals with 5-or 10-MeV Au ions ͑fluences of 10 11-2ϫ 10 14 ions/ cm 2 ; flux varies by 2 orders of magnitude͒ at room temperature has been performed using the methods of optical absorption and high-temperature ͑400-750 K͒ thermoactivation spectroscopy. The creation efficiency of color centers ͑F , F 2 , F 3 ,. . .͒ and colloids drastically depends on both the fluence and ion flux ͑beam current͒. Besides impurity ͑magnesium͒ colloids with the absorption band peaked at 4.4-4.6 eV, the broad absorption band at 2.3-3.3 eV related to intrinsic Li colloids is reliably distinguished. The creation efficiency of Li colloids by 5-MeV Au ions is lower than that by 10-MeV ions, which form ␦ electrons with higher energies sufficient for the creation of cation excitons ͑ϳ62 eV͒. The cation exciton decays, in turn, with the formation of a group of spatially close F centers. At a high ion flux, the next bombarding ions hit the same crystal region with a small time delay ͑10-100 s͒ and also form, after similar intermediate processes, the groups of F centers that participate in the formation of stable agglomerates of several F 3 or even more complex centers, which serve as stable ͑up to 620 K͒ seeds for nanosize Li colloids. The peculiarities of the formation, enlargement, and annealing of intrinsic colloids in LiF crystals are considered, invoking a formal analog with the processes in photographic materials based on silver halides.

Оптические спектры гамма-облученных кристаллов LiF с анизотропными наночастицами лития

“…Спектры снимали через 30 min после каж-дого этапа облучения, чтобы увидеть нестабильные цен-тры и динамику релаксации пространственного заряда комптон-электронов, создаваемого в ионном кристалле LiF гамма-квантами с энергиями 1.17 и 1.32 MeV. Иден-тификацию полос или линий от точечных, агрегатных и коллоидных центров проводили в соответствии с вышеприведенными литературными данными [1][2][3][4][5][6][7][8][9][10][11][12].…”

“…Далее нами исследована электропроводность в интервале температур 190−400 K в кристаллах LiF до и после облучения при 300 K в интервале доз 7.8 · 10 5 −10 8 R при 406 R/s [6]. Только после облучения обнаружена характерная скачкообразная проводимость по локализованным состояниям с пиком около 300 K, когда образуются агрегаты 2 и более электронных F-центров и наноколлоиды Li [1,[4][5][6][7][8][9]. Нами было пока-зано, что образование 2 агрегатов F-центров приводит к расщеплению полосы 250 nm, а образование 4 агрегатов F-центров приводит к расщеплению полосы 445 nm и появлению слабых широких полос 320, 380 nm и неста-бильных полос 500−650 nm.…”

Thin‐film layers and multilayer nano‐structures with controllable properties

“…The OA spectra of non-irradiated LiF nanostructures and initial crystals with small content of Mg 2+ , O colloids [22][23][24] (Fig. 4a).…”

“…(The non-irradiated and γ-irradiated substrates remain non-absorbing in the above spectral range.) According to the literature [22][23][24], besides impurities, Mg colloids with the absorption band peaked at 4.4-4.6 eV, the low-wavelength absorption band at 3.6-4.1 eV related to formation of more large Mg colloids or intrinsic Li colloids, are reliably distinguished in non-irradiated LiF nanostructures and initital LiF crystals γ-irradiated with various doses and bleached by annealing after irradiation [13,25] (Fig. 4a, insert).…”

Material characterization and modification using helium lon microscopy : various examples

“…Both the ion fluence and current density were previously demonstrated to influence F-center production efficiency in experiments irradiating LiF with heavy swift ions [138,139]. As long as the current density is low and the period between two arriving ions is relatively long, each cascade event can be considered individually.…”