Nuclear Instruments and Methods in Physics Research B 127/ 128 ( 1997) 524-527 ELSMER zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA NIOMI zyxwvutsrq B Beam Intwaotions wlth Materials (L Atoms MeV silver ion implantation induced changes in optical properties MgO (100) of Y. Qian a, D. Ila a**,R.L. Zimmerman a, D.B. Poker b, L.A. Boatner b, D.K. Hensley b zyxwvutsrqp a Center& Irradiation zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Moreriuls, Department of Physics, Alabama A&M University, P.O. Box 1447, Normal, AL 35762-1447, UsA b Solid State Diuision, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA zyxwvutsrqponmlkjihgfedcbaZY Abstract The implantation of 1.5 MeV Ag ions at 1.2 X IO” ion/cm’ into Mg0(100) single crystals produces optical absorption color centers which can be reduced by heat treatment at temperatures above 1000°C. We observed the formation of both F-centers and V-centers. We observed optical absorption due to the formation of silver nanoclusters at heat treatment temperatures above 550°C and due to F-center aggregates at heat treatment above 800°C. Upon further heat treatment, the color centers diminish while absorption due to the Ag nanoclusters is enhanced. Using Mie’s theory we confirmed that Ag is in the form of nanoclusters and by using Rutherford backscattering spectrometry (RBS) and ion channeling, we confirmed that these Ag metallic clusters have, in fact, orientations similar to that of the host substrate, MgO. The measured optical absorption due to Ag nanocrystals, 430 nm, is in agreement with the theoretical prediction. 1. Introduction Irradiation of MgO has been studied for many years [ 1,2]. It has been shown that heavy ion implantation into MgO generates intrinsic defects such as F+ and V-centers [l]. These defects disappear after heat treatment at temper- atures above 6OO“C,while a new optical absorption band appears located at 360 nm, due to the aggregation of F-centers [3]. Recently, attention has been directed toward the use of ion implantation to cause changes in the linear and nonlinear optical properties [4,5]. Another way to cause dramatic changes in the optical properties is by implanting ions that after heat treatment form small clus- ters which absorb light at the surface plasmon resonance frequency [3,6-81. Three cases of phase formation have been distinguished in MgO implanted with a high dose, above lOr6 ions/cm2, of metallic ions [9]: (a) alkaline ions (Li, Na, K, Rb) [lo], which form metallic clusters; (b) Ag and Au [ll], which form metallic precipitates and binary alloys with magne- sium, and (c) Fe, which forms oxides and spine1 fetrites [121. We have found that the implantation of Ag into MgO (100) single crystals, followed by thermal annealing at above 55O”C, results in the formation of Ag metallic clusters. The formation of Ag metallic clusters is identified l Corresponding author. Fax: + l-205-85 l-5868; email: ila@cim.aamu.edu. by an increase in the optical absorption at 410 nm to 430 nm. The position of the absorption band depends on what element is implanted. The size of the formed nanoclusters depends on the full width at half maximum (FWHM) of the absorption band. 2. Experimental procedures Implantations were made into epi-polished 1 X 1 cm’, 0.5 mm thick MgO (100) single crystals, a commercial product of Commercial Crystal Laboratories, Inc., using 1.5 MeV Ag ions at 1.2 X 10” ion/cm2 and 6 X lOI ion/cm’ at room temperature. The beam current was maintained low, 1 l.tA cm - ‘, to avoid premature formation of clusters due to the ion beam heating of the MgO samples. Heat treatment was performed in air at temperatures between 550°C and 1100°C for 30 min at each heat treatment temperature. The heat treatment at 1100°C was repeated for an additional 390 and 1200 min. After each heat treatment, optical spectrophotometry was performed to obtain the absorption spectrum from which we calcu- lated the size of the nano-metallic-clusters which are re- sponsible for the optical absorption band at a 410 to 430 nm range. RBS and ion channeling were performed using 2.0 MeV alpha particles, at a 170” backscattered angle, on virgin MgO as well as on silver implanted MgO, both before and after heat treatment. The ion channeling was 0168-583X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII SO1 68-583X(96)00984-6