David J. Pena

Surface plasmon resonance of colloidal Au-modified gold films

Abstract The effect of colloidal Au nanoparticle immobilization on surface plasmon resonance (SPR) reflectivity is reported. Immobilization of 25 nm diameter colloidal Au on to an evaporated Au film results in a large shift in plasmon angle, a broadened plasmon resonance and an increase in minimum reflectance. This results in increased SPR sensitivity, demonstrated in several ways, including a sandwich immunoassay for human IgG, enlargement of a 1.4 nm diameter Au cluster, and detection of displacement of surface-bound biotinylated colloidal Au by free biocytin in solution. Similarly large changes in reflectivity are realized upon binding of colloidal Au to electrolessly deposited Au films prepared entirely by wet-chemical methods. These results represent potentially significant advances in the generality and sensitivity of SPR.

Fabrication of two-dimensional photonic crystals using interference lithography and electrodeposition of CdSe

This letter describes a simple synthetic approach to fabricate two-dimensional midinfrared CdSe photonic crystals (PC) by electrodeposition of CdSe in a polymer template defined using interference lithography. Characterization of the transmission spectra of CdSe PCs with a hexagonal array of 1.3 μm diameter and 2.7 μm pitch air voids showed a well-defined drop in transmission at 4.23 μm. The drop in transmission increased with incident angle, reaching a maximum of approximately 2.6 dB at 40° relative to the surface normal. This two-step synthetic approach can be used to incorporate photonic crystals onto arbitrary substrates for integration into future advanced optical circuits.

Electrochemical Synthesis of Multi-Material Nanowires as Building Blocks for Functional Nanostructures

Nanostructures are electrochemically deposited into alumina or polycarbonate templates resulting in monodisperse, anisotropic particles with a range of tunable sizes. These particles have been synthesized with diameters of 20-250 nm and with lengths of 1-10 µm. Currently, structures have been made with stripes of Au, Ag, CdSe, Co, Cu, Ni, Pd, and Pt. These materials offer a variety of different properties. In particular, many of the metals in this group are excellent conductors, meaning these particles can actually be used as nanowires. Co and Ni are ferromagnetic and may be used for separation or assembly. CdSe is a semiconductor, possibly allowing for the synthesis of electronic devices such as transistors. Furthermore, many of these materials have different surface chemistries, making the orthogonal functionalization and assembly of these nanowires more accessible. This research focuses on increasing the number of materials available, especially semiconductors, incorporating these potentially useful materials into multilayered nanowires and evaluating their electrical properties, either individually or in small bundles. In addition, the surface chemistry of the various materials in the nanowires is being compared to aid in orthogonal self-assembly of functional nanostructures such as memory devices. The work presented will demonstrate the effects of rod composition on electrical properties. In particular, the effects of changing the work function of the materials on either side of a semiconductor to form Schottky junctions or ohmic contacts will be shown.