Ultrathin Anodic Aluminum Oxide Research Articles

Plasmon resonance properties of silver-patterned glass substrates fabricated by anodic alumina oxide templates

Ultra-thin anodic aluminum oxide membranes were prepared and served as deposition masks for fabrication of uniformly sized Ag nanodots with different aspect ratios on glass substrates. The surface plasmon resonance (SPR) properties of the supported Ag nanodots were investigated and compared with the predictions of the generalized Maxwell–Garnett theory. By modeling the nanodots as spheroids without adjusting their real geometrical parameters input to the calculation, the resulting theoretical SPR wavelengths are in good agreement with measured extinction peaks. The discrepancy between the theoretical and experimental plasmon resonance peak maxima is within 10 nm for the nanodots with an aspect ratio of less than 1.5. Although this wavelength discrepancy becomes large as the aspect ratio is increased, it is kept at approximately 35 nm for the nanodots with an aspect ratio of 2.44.

Ultrafast excited state deactivation of doped porous anodic alumina membranes

Free-standing, bi-directionally permeable and ultra-thin anodic aluminum oxide (AAO) membranes establish attractive templates (host) for the synthesis of nano-dots and rods of various materials (guest). This is due to their chemical and structural integrity and high periodicity on length scales of 5–150 nm which are often used to host photoactive nano-materials for various device applications including dye-sensitized solar cells. In the present study, AAO membranes are synthesized by using electrochemical methods and a detailed structural characterization using FEG-SEM, XRD and TGA confirms the porosity and purity of the material. Defect-mediated photoluminescence quenching of the porous AAO membrane in the presence of an electron accepting guest organic molecule (benzoquinone) is studied by means of steady-state and picosecond/femtosecond-resolved luminescence measurements. Using time-resolved luminescence transients, we have also revealed light harvesting of complexes of porous alumina impregnated with inorganic quantum dots (Maple Red) or gold nanowires. Both the Förster resonance energy transfer and the nano-surface energy transfer techniques are employed to examine the observed quenching behavior as a function of the characteristic donor–acceptor distances. The experimental results will find their relevance in light harvesting devices based on AAOs combined with other materials involving a decisive energy/charge transfer dynamics.

Adhesive modification of indium–tin-oxide surface for template attachment for deposition of highly ordered nanostructure arrays

Polyvinyl alcohol (PVA), a very cheap polymer with one hydroxyl group in each repeating unit, was spun coated on the surface of an indium–tin-oxide (ITO) substrate to improve the adhesion between the substrate and a nanoporous anodic aluminum oxide (AAO) template layer for a template-directed fabrication of nanostructures. Compared with dihydroxy-terminated polystyrene (PS-dOH) and a silane coupling agent (KH550), PVA was a superior binder because of its abundant hydroxyl groups for adhesion enhancement and its low cost for applications. As an example, a highly ordered CdSe nanorod array free standing on the ITO substrate was electrochemically deposited by using an ultrathin AAO layer as the template on the PVA modified surface. It was demonstrated that the PVA modified ITO can be reliably used for the template-directed fabrication of nanostructures.

Fabrication and characterization of extended arrays of Ag2S/Ag nanodot resistive switches

Well-ordered Ag2S/Ag nanodot arrays with a density of >60 Gbit/in.2 have been fabricated by sputtering Ag on a silicon substrate using ultrathin porous anodic aluminum oxide membranes as shadow masks, followed by sulfurization treatment at room temperature. The morphology, microstructure, and electrical properties of the as-prepared nanodots were characterized by scanning electron microscopy, x-ray diffractometry, transmission electron microscopy, and conductive atomic force microscopy, respectively. Well-defined resistive switching behavior was observed in these nanodots, and the ON/OFF ratio was found to be higher than 102. The Ag2S/Ag nanodot arrays hold substantial promise for use as ultrahigh density nonvolatile memory devices.

Individual switching of film-based nanoscale epitaxial ferroelectric capacitors

We have investigated the individual switching of nanoscale capacitors by piezoresponse force microscopy. Nanoscale epitaxial ferroelectric capacitors with terabyte per inch square equivalent density were fabricated by the deposition of top electrodes onto a pulsed laser deposited lead zirconate titanate thin film by electron beam evaporation through ultrathin anodic aluminum oxide membrane stencil masks. Using bias pulses, the nanoscale capacitors were uniformly switched and proved to be individually addressable. These film-based nanoscale capacitors might be a feasible alternative for high-density mass storage memory applications with near terabyte per inch square density due to the absence of any cross-talk effects.

Vortex Polarization States in Nanoscale Ferroelectric Arrays

Two-dimensional arrays of ferroelectric lead zirconate titanate (PZT) nanodots were fabricated using pulsed laser deposition through ultrathin anodic aluminum oxide membrane stencil masks. The static distribution of polarization configurations was investigated using in- and out-of-plane piezoresponse force microscopy (PFM). The observed presence of an in-plane polarization component in nominally (001) oriented PZT suggests the existence of a significant deviation from the regular tetragonal structure that allows the formation of complex core-polarization states. Core-polarization states may indicate the presence of quasi-toroidal polarization ordering. The experimental results are compared with a theoretical model to determine the fingerprint of a vortex polarization state in PFM.

Gold Nanoparticles Partially Embedded in Ultrathin Anodic Alumina Films

Gold nanoparticles with diameters ranging from 3.2 to 9.7 nm were prepared on an ultrathin anodic aluminum film by means of molecular beam deposition. Coverages ranging from 17.9% to 48.5% and the subsequent anodic anodization behavior were studied. Further oxide growth does not completely cover the gold nanoparticles but takes place preferentially under the particles with a surprisingly low kinetic hindrance. The gold nanoparticles are electrically isolated from the substrate as demonstrated by the absence of electrocatalytic reactions on the gold surface. A strong surface charge phenomenon is observed, which increases with increasing gold coverage that yields an increase of the capacity up to the minimum potential required for further oxide formation.

Fabrication of in situ ultrathin anodic aluminum oxide layers for nanostructuring on silicon substrate

The authors demonstrate a method for the fabrication of in situ ultrathin porous anodic aluminum oxide layers (aspect ratio<2:1) on Si, which can be directly used as templates for nanodot preparation and for pattern transfer. The regular shape of the aluminum oxide pores is maintained even when the thickness of the aluminum oxide template is reduced to 50nm. By using these in situ ultrathin templates as lift-off masks, the authors successfully prepared a BaxSr1−xTiO3 nanodot array on Si surface. Furthermore, these nanotemplates are employed as lithographic masks to transfer the nanopattern into the silicon substrate.

Preparation of Bowl-like Hexagonal ZnO Nanostructures by a Template-assisted Solvent-thermal Route

Abstract Bowl-like ZnO nanostructures with hexagonal shape have been fabricated by a solvent-thermal synthesis route with the assistance of ultrathin anodic aluminum oxide (AAO) template. Transmission electron microscopy and high-resolution transmission electron microscopy investigations confirm that the bowl-like ZnO structures are single-crystalline. The room temperature photoluminescence investigation shows that the products have a sharp near band-edge emission and another broad green emission band centered at 386 nm and around 525 nm, respectively.