The Role of Glass Structure in the Formation of Implanted Gold Nanoclusters for Enhanced Nonlinear Optical Properties
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ABSTRACT Various silicate glasses (fused silica, soda-lime, Na- and K-borosilicates, lithia-alumina silicate, and Pyrex®) were implanted with 8 x 1015 285 keV Au/cm 2 . Colloid growth was monitored as a function of annealing and N implantation (2 x 1017 35 keV N/cm 2 ). Annealing to 1040 'C for fused silica and to 600 'C for the other glasses resulted in Au aggregation and optical absorption. Radiation damage removal is associated with the fused silica annealing, the aggregation of Au at lower temperatures for the other glasses is expected because of the lower glass transition temperature. Phase-separation in the alkali-borosilicates may be important because of grainboundary diffusion. N implantation did not significantly affect nanocluster growth. INTRODUCTION Ion implantation is potentially a valuable and versatile tool to employ in the fabrication of integrated optoelectronics devices. It has a two-fold value; it produces densification in almost all glasses of interest and this, although small (typically AL/L - Ap/p - 1%) is adequate for waveguiding, and implantation can be used to insert metal ions into the wave guide which in nanocluster form can provide an enhanced 3rd-order nonlinear susceptibility. This latter effect
yields an intensity-dependent refractive index which allows fast optical switching in implantationpatterned devices, e.g., directional couplers. A recent comprehensive review [1] has been given of the reported metal-ion implantation studies into glass substrates, which have been predominantly fused silica and a much smaller number into soda-lime glass. In the present paper, we have chosen to concentrate on the effects of glass type and structure on the aggregation of 8 x 1015 285 keV Au/cm 2 implanted at room temperature. The glasses were fused silica and nine other silicate glasses as described in the Experimental section below. Nanocluster growth was promoted by annealing; nitrogen implantation was also employed in order to assess the effects of electronic energy deposition on aggregation. EXPERIMENTAL The glasses investigated were: fused silica (Corning 7940 and/or Suprasil W I), Pyrex®, sodalime, alkali borosilicates (molar composition: xM 2 0.(1-x)B 2 0303SiO 2 , for M = Na and K, and x = 0.2, 0.4, and 0.6) and a lithia-alumina-silica glass used and described in an earlier study [2]. (The obvious acronyms for the glasses have been used occasionally in what follows, i.e., CFS, SSWI, PYR, SLG, 0.xNa, 0.xK, and LAS). The implants of 8 x 1015 285 keV Au/cm 2 were 397 Mat. Res. Soc. Symp. Proc. Vol. 396 ©1996Materials Research Society
made at room temperature. Half of each Au-implanted sample was also implanted with 2 x 1017 35 keV N/cm 2 . Thermal annealing was done in air for 2 hours at each succesive temperature; 600, 800, 1040 'C for fused silica and 300, 450, and 600 'C for the other glasses. Rutherford backscattering (RBS) depth profiles were determined using 2.2 MeV He. The optical absorption measurements were made with a Perkin-Elmer Lambda 9 UV-VIS-NIR dual beam spectrophotometer. T
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