Broad band light-emitting nanostructured substrates by ion beam irradiation of lithium fluoride crystals V. Mussi a, * , R.M. Montereali b , E. Nichelatti c , C. Boragno a , F. Buatier de Mongeot a , U. Valbusa a a Physics Department, University of Genova, Via Dodecaneso, 33 16146 Genova, Italy b ENEA, Advanced Physical Technologies, C.R. Frascati, V.E. Fermi 45, 00044 Frascati, Italy c ENEA, Advanced Physical Technologies, C.R. Casaccia, V. Anguillarese 301, 00060 Rome, Italy Available online 20 December 2006 Abstract We present experimental results on simultaneous surface nanostructuring and optical activation of lithium fluoride crystals by 800 eV off-normal Ar + sputtering. Our data demonstrate that the formation of periodic nanostructures is accompanied by the efficient produc- tion of stable electronic defects, optically active in the green and red parts of the visible spectra, thus providing the possibility to conceive and fabricate advanced insulating substrates. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Ion irradiation; Surface nanostructuring; Lithium fluoride; Color centers In 1988 Bradley and Harper [1] introduced a model to ex- plain the production of nanometric structures during ion sputtering of different materials as the result of the compe- tition between ion erosion and surface diffusion processes. In 1999 Fackso et al. [2] demonstrated the possibility of using normal incidence ion sputtering on semiconductor surfaces to produce regular patterns of nanoscale dots with peculiar photoluminescence properties, thus with important possible applications in the fields of quantum devices and optoelectronics. In such a context, lithium fluoride (LiF) definitely appears as a promising material. This is because, when irradiated with low-energy electrons or ions, it acquires a distinctive color due to the stable formation of electronic defects, known as color centers (CCs), with well-defined absorption and emission bands in the visible spectral region [3]. Although also other kinds of ionizing radiation can be exploited to produce CCs, the use of low penetrating particles is particularly appealing because it allows to pre- pare thin surface layers with high concentration of active centers [4,5], opening the way to numerous applications, such as optical waveguides [6], microcavities [7] and laser sources [8]. Here, we show preliminary results that demonstrate the possibility to exploit ion sputtering of LiF crystals to fab- ricate optically active nanostructured substrates [9]. An 800 eV Ar + ion beam produced by a defocused microwave ECR plasma source was used to irradiate a pol- ished LiF crystal at an off-normal incidence angle h = 35°, a temperature of about 80 °C (as measured by means of a thermocouple in direct contact with the back-side of the LiF sample) and two different ion doses, obtained by vary- ing the irradiation time. During argon ions irradiation (5 N purity) the background pressure in the sputtering chamber rose from the initial value of about 10 7 –10 8 mbar to about 10 3 mbar. The measured ion flux on the sample sur- face was about 160 lA/cm 2 and, to prevent the charging of the sample, a Th-coated W filament was positioned at the end of the source, thus ensuring the efficient charge neutral- ization of the substrate. 0039-6028/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2006.12.043 * Corresponding author. Fax: +39 010 311066. E-mail address: mussi@fisica.unige.it (V. Mussi). www.elsevier.com/locate/susc Surface Science 601 (2007) 2746–2749