Studies of swift heavy ion induced colour centres in LIF thin films deposited on silica substrates

Abstract

Swift heavy ion induced colour centres in polycrystalline LiF thin films deposited on silica substrate were studied. LiF thin films of 200 nm thickness, deposited by the electron beam evaporation method, and silica substrates were irradiated with 120 MeV Au9+ ions in the fluence range 5 × 1010–1 × 1013 ions cm−2. Optical absorption, photoluminescence (PL) and glancing angle x-ray diffraction (GAXRD) techniques were used for the characterization of the irradiated films. Optical absorption spectroscopy was performed on irradiated LiF films by using irradiated silica substrates as reference sample. The resulting spectra show three bands at 260 nm, 380 nm and 445 nm corresponding to F, F3 and F2 colour centres, respectively. Absorbance of colour centres increases with fluence and seems to saturate at higher fluences. PL spectra, performed by an excitation source of 442 nm, show two broad bands of F2 and colour centres. The intensity of both the centres increases upto 3 × 1011 ions cm−2 followed by some decrease. The GAXRD results show that the average grain size decreases systematically from 35 nm for the pristine film to 20 nm for the sample irradiated at a fluence of 1 × 1013 ions cm−2.

Photoluminescence properties of SHI induced F2 and F3+ color centers in nano-granular LiF thin films

“…Baldacchini et al [12,13] compared CCs formation by extreme ultraviolet radiation, soft X-rays and by electrons in LiF crystals and thick film ($6 mm thickness) and they showed that the main spectroscopic features of the defects in polycrystalline films were same as those observed in crystals, but the formation efficiency of CCs was higher in film, where surface to volume ratio and the film compactness played a major role because of the presence of high density of grain boundaries. At the same time, in our previous reports [16,18], we observed that the grain size in nanometric films also played an important role in defect creation process and influenced the CCs concentration. The SHI irradiation of nano-granular LiF thin films leads to the formation of CCs as well as grain fragmentation simultaneously.…”

“…PL properties of CCs in LiF crystals [6][7][8][9][10][11][12][13] and films [5,[12][13][14][15][16][17] has been extensively investigated, however, only a few reports are available on PL properties of swift heavy ions (SHI)-induced CCs in nanometer sized LiF thin films [16][17][18]. In case of thin film, the PL intensity strongly depends on growth and irradiation parameters.…”

“…LiF thin films of 200 nm thickness were deposited at RT 300 K on amorphous substrates (glass and silica) of 10 Â 10 mm dimensions by electron beam evaporation method under a vacuum of $10 À6 Torr [16,18]. All the substrates were thoroughly cleaned before the deposition.…”

Formation of nano-hillocks by impact of swift heavy ions on thin films of TiO2

“…It is reported that SHI beam induces radiative defects in insulators and semiconductors and PL-intensity is sensitive to damages created by SHI beam [17]. Photoluminescence studies of unirradiated and irradiated TiO 2 thin films are carried out using spectrofluorimeter SPEX-Fluorolog.…”

“…Increase in luminescence intensity observed after irradiation may be due to SHI-induced defects in TiO 2 which act as radiative recombination centers [17]. Oxygen vacancies have been considered as the most common defects and usually act as radiative centers in luminescence processes [21].…”