Solid supported 2D assembly of silver nanocubes was fabricated by Langmuir-Blodgett technique and employed to investigate its surface enhanced Raman scattering (SERS) and surface enhance fluorescence (SEF) activities by detecting Rh6G in solution of varied concentrations, that is, 10？12？M, 10？9？M, 10？6？M, and 10？3？M. SERS was detected from a nanomolar concentration of Rh6G whereas SEF was detected from a picomolar concentration. Further, the substrate was subjected to thermal annealing to fabricate plasmonic thin film. The formation of thin film was followed by monitoring its surface plasmon resonance spectra and atomic force microscopic images. It was observed that the characteristic spectral peaks of silver nanocubes merged into a broad spectral band as the annealing time was increased and the intensity of the band decreased with the formation of thin film. The obtained result implies that thermal annealing could be a simple approach to create nanoscale gaps in SERS substrate and to engineer continuous thin film from the assembly of discrete nanoparticles. 1. Introduction Plasmonic metal nanoparticles such as silver, gold, and copper are gaining interest due to their unique optical properties that find applications in numerous fields of technology [1–4]. Noble metal nanoparticles support surface plasmons, coherent oscillation of conduction band electrons, which can be excited by electromagnetic radiation to give rise to an intense electric field. Such phenomenon is called surface plasmon resonance (SPR) [5, 6]. At resonance condition, absorption of light by nanoparticles occurs which appears as absorption peaks in their absorption spectrum. The position of the peak is highly sensitive to the refractive index of the external medium in which nanoparticles are placed. The sensitivity of nanoparticle’s absorption peaks is the basis of SPR based molecular sensing [7–9]. In this context, two classes of surface plasmon resonance (SPR) are applied in sensing devices, for example, surface plasmon polariton (SPPs) and localized surface plasmon resonance (LSPRs). LSPR involves excitation of surface plasmons localized on the surface of discrete nanopartcle. SPPs involve excitation of surface plasmons that propagate along the nanoscale surface of a thin film of plasmonic materials [10, 11]. LSPR is employed to sense molecular events occurring in the vicinity of nanoparticle’s surface as the evanescent electric field exists within a few nanometers (~20？nm) of the surface [11–13]. However, SPPs are employed to sense molecular events in the bulk medium as the
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