Facile Formation of Ordered Vertical Arrays by Droplet Evaporation of Au Nanorod Organic Solutions

Droplet evaporation is a simple method to induce organization of Au nanorods into ordered superstructures. In general, the self-assembly process occurs by evaporation of aqueous suspensions under strictly controlled experimental conditions. Here we present formation of large area ordered vertical arrays by droplet evaporation of Au nanorod organic suspensions. The uncontrolled (free air) evaporation of such suspensions yielded to formation of ordered nanorod domains covering the entire area of a 5 mm diameter droplet. Detailed investigation of the process revealed that nanorods organized into highly ordered vertical domains at the interface between solvent and air on a fast time scale (minutes). The self-assembly process mainly depended on the initial concentration of nanorod solution and required minimal control of other experimental parameters. Nanorod arrays displayed distinct optical properties which were analyzed by optical imaging and spectroscopy and compared to results obtained from theoretical calculations. The potential use of synthesized arrays as surface-enhanced Raman scattering probes was demonstrated with the model molecule 4-aminobenzenthiol

Surface-Enhanced Raman Scattering of 4‑Aminobenzenethiol on Au Nanorod Ordered Arrays

A droplet evaporation/stamping method was employed to fabricate closely packed arrays of Au nanorods aligned parallel or perpendicular to a support. The potential as SERS substrates was investigated using model molecule 4-aminobenzenethiol (4-ABT), for which enhanced signals where obtained compared to the signals of the bulk molecule. Enhancement factors of the order of 10⁴ and 10⁵ were calculated for parallel and perpendicular arrays, respectively. Quantitative Raman detection of 4-ABT was obtained with detection limits in the nM concentration range. Fabricated arrays displayed good stability and uniformity, showing their potential as sensing platforms for plasmon-induced optical molecular detection

Hot-Electron Injection in Au Nanorod–ZnO Nanowire Hybrid Device for Near-Infrared Photodetection

In this Letter, we present a new class of near-infrared photodetectors comprising Au nanorods–ZnO nanowire hybrid systems. Fabricated hybrid FET devices showed a large photoresponse under radiation wavelengths between 650 and 850 nm, accompanied by an “ultrafast” transient with a time scale of 250 ms, more than 1 order of magnitude faster than the ZnO response under radiation above band gap. The generated photocurrent is ascribed to plasmonic-mediated generation of hot electrons at the metal–semiconductor Schottky barrier. In the presented architecture, Au-nanorod-localized surface plasmons were used as active elements for generating and injecting hot electrons into the wide band gap ZnO nanowire, functioning as a passive component for charge collection. A detailed investigation of the hot electron generation and injection processes is discussed to explain the improved and extended performance of the hybrid device. The quantum efficiency measured at 650 nm was calculated to be approximately 3%, more than 30 times larger than values reported for equivalent metal/semiconductor planar photodetectors. The presented work is extremely promising for further development of novel miniaturized, tunable photodetectors and for highly efficient plasmonic energy conversion devices