Variable Thickness Porous Anodic Alumina/Metal Film Bilayers for Optimization of Plasmonic Scattering by Nanoholes on Mirror

Abstract

Continuously variable thickness porous anodic aluminum oxide (PAAO) films were obtained using electrochemical oxidation of bulk aluminum sheet while both electrodes were simultaneously withdrawn from the electrolyte solution. The thickness gradient was controlled by the withdrawal rate (1–10 mm/min range) and thickness variation demonstrated from below 50 nm to above 1 micrometer. The thickness increased linearly with the sample lateral coordinate, whereas the nanopore structure (diameter and interpore distance) remained unchanged. Effects of the initial pore growth and capillary forces are discussed. The presented method can be used for tuning optimal PAAO thickness for optical and other applications as exemplified by finding maximum plasmonic scattering in structured Al–PAAO–Au multilayers. Enhanced scattering from porous gold film separated by a specific-thickness PAAO layer from aluminum mirror surface is demonstrated.

Visible Photoluminescence of Variable-Length Zinc Oxide Nanorods Embedded in Porous Anodic Alumina Template for Biosensor Applications

“…The optical approach had the advantage that layer thickness and consequently ZnO NR length could be measured continuously and rapidly across entire sample without dissection. The hybrid layer thickness varied linearly depending on lateral sample coordinate (Figure 3d) with minor jumps due to crystallographic grain structure of the aluminum substrate [35].…”

“…PAAO templates were produced from high purity (99.999%) bulk aluminum sheet (GoodFellow) using a modified two-step anodization protocol in 0.3 M oxalic acid electrolyte at constant 40 V voltage [20,49] with the key difference that during the second anodization step the sample was gradually withdrawn from the electrolyte solution, which terminated the pore growth at different time moments [35]. At a 4.6 mm/min withdraw rate, continuously variable thickness (from approximately 100 nm to above 500 nm) PAAO membranes were produced on the same sample (typically 9 mm wide and 18 mm long).…”

“…The hexagonal pore arrangement with nearest neighbor center-to-center distance 100 nm and pore diameter 40-50 nm was confirmed using scanning electron microscope (SEM, Hitachi 4800, Tokyo, Japan). Full details on variable thickness PAAO synthesis can be found in [35].…”

“…In this work, we demonstrate a method to produce aligned ZnO NR embedded in PAAO with virtually continuous length variation and fixed diameter. PAAO with controlled thickness gradient [35] was filled with ZnO using ALD [36]. The subcomponents of visible PL from ZnO NR-PAAO composite film on aluminum substrate varied with periodicity depending on NR length (PAAO thickness), indicating that thin-film interference effects must be taken into account when analyzing PL of NR arrays.…”

Surface structure promoted high-yield growth and magnetotransport properties of Bi2Se3 nanoribbons

“…Previously, the AAO membranes have proven to be ideal substrates for the production of nanowire arrays using electrochemical, supercritical fluid and CVD-based techniques 19–23 , as well as for sorting and ordering of nanoparticles on the surface of AAO membranes 24,25 , and enhancement of plasmonic scattering in structured Al-AAO-Au layers 26 . In this work, porous anodized aluminium oxide (AAO) substrates are used for catalyst-free PVD synthesis of Bi 2 Se 3 nanoribbons.…”