Fabrication of Large-Area Self-Organizing Gold Nanostructures with Sub-10 nm Gaps on a Porous Al₂O₃ Template for Application as a SERS-Substrate

Abstract

A new technique for fabrication of large-area self-organizing variably ordered gold nanostructures with sub-10 nm gaps on templates of hexagonally ordered porous anodic aluminum oxide is demonstrated. The size as well as the interparticle distance of the fabricated gold nanostructures are adjusted by application of various electrolytes used in anodization of the aluminum template and the thickness of gold sputter-coated on the pore layer. The fabricated substrates are characterized by SEM and optical extinction measurements in reflection. The applicability as SERS substrates is investigated by adsorption of rhodamine 6G on the nanostructures. These substrates are found to exhibit high and uniform enhancement of the Raman signal across the entire surface. The nanostructures can be utilized as low-cost SERS-active substrates that within a short time can be fabricated reproducibly in large amounts.

Experimental study on polarized surface enhanced resonance Raman scattering of rhodamine 6G adsorbed on porous Al2O3 substrates

“…The relative high value of the local field in the isotropic site necessary to account for the experimental observations must, therefore, be caused by an effect not accounted for so far in the present article or in the various field simulations found in Ref. 34. This conclusion is supported by a closer analysis of the SEM micrographs of the hexagonal structure used in the present study, 35 which shows that a random distribution of nanometer sized Au-particles protrude in the isotropic sites. The estimated average size of these nanoparticles is of the order of magnitude 10 nm.…”

Morphology Dependence on Surface-Enhanced Raman Scattering Using Gold Nanorod Arrays Consisting of Agglomerated Nanoparticles

“…In Fig. 2a, b, it can be seen that oxide cells are self-organized to form a hexagonally close-packed structures [20]. Each nanopore is closed by a thin barrier oxide layer with an approximately hemispherical morphology at the bottom.…”

Two-photon luminescence microscopy of tunable gold nanostructures randomly distributed on templates of anodized aluminum

“…Individual pores, that were not broken during the bending of the sample, can be tracked almost all the way to the end of the pores at the barrier oxide layer. In the case of the porous layer fabricated by HA in oxalic acid at 120 V, the cross sectional SEM micrographs (not shown) look very similar except for the smaller interpore distance of ~270 nm and a thicker oxide layer of ~30 µm instead of 15 µm 11 . Increased magnification of the sample in the marked rectangle at the bottom of the pores (inset Fig.…”

“…The details of preprocessing of Al sheets by electropolishing, annealing, ultrasonic cleaning, build up of protective oxide layers as well as the applied anodization conditions and equipment for basic MA and HA with oxalic-or phosphoric acid as electrolyte have previously been described 11,12 . In brief, this anodization (step 1, Fig.…”

“…We have previously employed two-photon luminescence scanning optical microscopy (TPL-SOM) in the systematic investigation of FE effects achieved with periodic metal nanoparticles 8 , and fractal shaped metal nanostructures 10 . Recently, we demonstrated how to use templates grown under mild anodization (MA) and hard anodization (HA) conditions for large-area self-organizing gold nanostructures 11,12 . We here investigate the enormous electromagnetic fields in the vicinity of randomly distributed gold nanoparticles on templates of porous anodized Al and correlate the magnitude of the FE with reflection measurements and the density of gold particles.…”