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H2.7.1

Fabrication of Ordered Metallic Nanocluster Arrays Using a Focused Ion Beam Matthew D. McMahon, Anthony B. Hmelo, Rene Lopez, Wesley T. Ryle, Allen T. Newton, Richard F. Haglund, Jr., Leonard C. Feldman, Robert A. Weller1, and Robert H. Magruder III1,2 Dept of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, U.S.A. 1 Dept of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN 37235, U.S.A. 2 Dept of Chemistry and Physics, Belmont University, Nashville, TN 37212-3757, U.S.A. ABSTRACT We have fabricated ordered arrays of gold nanocrystals on FIB-processed silicon substrates using electroless deposition. We have also fabricated ordered arrays of silver nanocrystals on silicon with diameters 40-60 nm separated by 180 nm center-to-center, using pulsed-laser deposition (PLD) to deposit silver on the substrate. The metal nanocrystal arrays are characterized using SEM as well as AFM and energy dispersive xray (EDX) analysis. AFM confirms particle sizes measured in SEM, and EDX analysis demonstrates that Ag preferentially clusters at sites that have been damaged by the ion beam. These results suggest that the FIB-PLD combination can be used to create ordered arrays of Ag nanocrystals with diameters of 10 nm or less. INTRODUCTION Ordered arrays of metal nanoclusters have potential applications as elements of nonlinear or near-field optical circuits, as sensitizers for fluorescence emitters and photodetectors, and as anchor points for arrays of biological molecules. Metal nanocrystals are strongly confined electronic systems with a band structure drastically altered by the small size of the system and the reduced population of conduction-band electrons. Their optical response is extremely sensitive to the size, size distribution and spatial arrangement of individual nanocrystals. This effort is focused on the fabrication of ordered metallic nanocrystal arrays for optical investigations. Our approach is to promote the formation of metal nanocrystals on a spatially arranged lattice of holes that has been prepared by focused ion beam (FIB) processing. Periodic arrays of metal nanocrystals embedded in a dielectric have several interesting properties. The property we wish to exploit is the third-order nonlinear optical response of these arrays, which gives rise to such effects as intensity-dependent index of refraction. Ordered arrays using this property could be used in photonic circuits, particularly in interferometry schemes and all-optical switching. The purpose of the experiments described in this paper is to create ordered arrays of metal nanocrystals for such optical experiments.

H2.7.2

EXPERIMENTAL We use a FIB to create arrays of sites at which metal nanocrystals will nucleate and grow following the deposition of a heteroepitaxial metal layer. The principles of material removal via sputter erosion using the FIB are well known. [1, 2] Facilities at the Vanderbilt Nanofabrication Laboratory include the FEI FIB 200, which features a 30kV liquid Ga+ ion source. In the