Ion Beam-Induced Changes in Optical Properties of MgO
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YING QIAN*, D. ILA*, K. X. HE**, M. CURLEY**, D. B, POKER# AND L. A. BOATNER" * Center for Irradiation of Materials, **Center for Nonlinear Optics, Alabama A&M University, Normal, Alabama 35762-1447 4Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6057 ABSTRACT The implantation of Ag into MgO (100) single crystals, followed by thermal annealing at 1 00°C, leads to dramatic changes in their optical properties. The changes in the optical
properties are due to the presence of small Ag clusters which are formed in the annealed samples. The small Ag clusters are obtained by thermal annealing of the implanted MgO crystals between 600'C and 11 00°C to investigate the changes in cluster sizes and to correlate with changes in their optical properties. Sample characterization is carried out using optical spectrophotometry to confirm the effective presence of Ag clusters and Rutherford Backscattering Spectrometry (RBS) to study the profile of Ag clusters. INTRODUCTION Ion implantation is the most successful and widespread surface modification technique in insulators and ceramic materials. An area which has drawn considerable attention is the use of implantation to cause changes in the optical properties of these materials [1][2]. One way to cause dramatic changes in the optical properties is through the formation of small metallic clusters which absorb light at the surface plasmon resonance frequency [3-5]. With regard to the phase formation in MgO implanted with a high dose (more than 1016 ions/cm 2) of metallic ions, three cases have been distinguished [6] a) the alkaline ions [7] (Li, Na, K, Rb), which form metallic clusters, b) Ag and Au [8], which form metallic precipitates and binary alloys with magnesium, and c) Fe, which forms oxides and spinel ferrites [9]. In the present study, we have found that the implantation of Ag into MgO (100) single crystals, followed by thermal annealing at 11 00IC, results in the formation of Ag clusters. These small metallic clusters are identified by optical absorption and Rutherford Backscattering Spectrometry (RBS). In addition, we have investigated the effects of thermal annealing on small metallic cluster sizes and correlated with changes in optical properties. The positions of the maximum and the full width at half maximum (FWHM) of the optical absorption band are related to the sizes of the small metallic clusters. Toward this objective, MgO single crystals were implanted with 1.5 MeV Ag and then subjected to thermal annealing at 600'C, 800'C, 1000IC and I 100°C, each sample for 30 minutes. EXPERIMENTAL PROCEDURE Sample Preparation Samples of approximately 10 x 10 x 0.5 mm 3 of MgO (100) single crystals were implanted with Ag' ions using a 1.7 MV General lonex Tandem ion accelerator at Oak Ridge National Laboratory. The beam energy was 1.5 MeV and the current density was maintained rather low (- I ýtA cm2 ) in order to restrict thermal effects during implantation. The theoretical 423 Mat. Res. Soc. Symp. Proc. Vol. 396 ©1996 Materials Research Society
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