222 Nuclear Instruments and Methods in Physics Research B32 (1988) 222-224 North-Holland, Amsterdam zyxwvutsrq ELECTRON-BEAM PRODUCTION OF COLOUR CENTRES ON ALKALI HALIDE CRYSTALS AND FILMS Raul A. NUNES, Hypolito J. KALINOWSKI *, Sidnei PACIORNIK, Astor M. DE SOUZA and Luiz C. SCAVARDA DO CARMO * Deportment of Physics and Department of Material Sciences and Metallurgy, Pontificza Unrversidade Catolica do Rio de Janeiro, Cx. P. 38071 - Rio de Janeiro, RJ, Brazil In this article we analyze the production of localized colour centres on the surface of alkali halide crystals and films produced by electron beam radiations in the lo-30 keV range. It was found that the colour centre production is restricted to electron penetration (3-10 pm depending on the material and electron energy) with a very intense local optical density (above lo4 cm-‘). As the refractive index variation calculated using the Kramers-KrBnig relations from the observed absorption bands should be enough for light confinement (1O-3-1O-2), electron beam generated colour centres should allow the production of light wave guides for several applications. Optical absorption bands can be created in ionic crystals anywhere from the ultraviolet to the infrared, preserving transparent regions of the spectrum. With an appropriate computer aided design (CAD) program and a microcomputer interface to the adapted micropositioning mechanical devices and shutter, it was possible to control an electron microprobe sample holder in order to draw precise patterns and have various controlled exposure times. 1. Introduction Alkali halides, due to their simplicity in structure, chemical stability, cleaving properties and ease of pro- duction, are presently among the best known materials in nature. They have been subject to extensive studies by several experimental techniques becoming model cases for theoretical studies that helped to understand the properties of more complex materials (e.g. the ionic-molecular cyanides and hydroxides). The study of lattice defect properties in alkali halides encompassed both the area of small concentration inter- stitial or substitutional dopants and the area of radia- tion induced localized defects (colour centres). Due to the large transparency window (from about 0.05 eV up to about 6 eV), optical analysis allowed to build a vast picture of defect generated local absorption bands rang- ing from the infrared to the ultraviolet. The knowledge of the colour properties and the dynamics of its com- plex photochemical transformations may even make possible the tailoring of the absorption bands to one’s needs, controlling their position in the spectrum and the relative intensities of the absorption peaks of different centres formed in the same material. On the other hand, the developments in the area of ionic-molecular thin film characterization [l] generate a new interest in the production of superficial defects in films deposited on different substrates. * Also telecommunications Engineering Department, Uni- versrdade Federal Fluminense, 24500 - Niteroi, RJ, Brazil. 0168-583X/88/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division) Among the several techniques to produce radiation induced defects, the electron beam sources are very practical and have been extensively used. The penetration depth (d) of the electrons can be easily controlled by the accelerating voltage (E,), and depends on the density of the material. It follows an expression like [2] d = 0.064E; “/p, where d is measured in pm, E,, in kV and p in g/ cm3. The e-beam generated colour centres are restricted to the electron penetration depth. Thus, the use of accel- erating voltages in the lo-30 kV range with several alkali halides allows colour centre production with depths in the l-10 pm range. ---- OIGITN c. A. 0. rJMPulER c. A. Y. GEAN mlmn - A “‘E&m ElECTRrNlCS Fig. 1. Schematic of the electron microprobe automation sys- tem for geometrical patterns imprinting.