A nonlithographic second-order self-assembly process for synthesizing uniform and ordered arrays of nanorods and nanodots is presented and applied to the fabrication of ZnO nanorod arrays. Nucleation sites were defined by patterning Au nanodot catalysts with a self-organized array of nanopores formed in anodized aluminum oxide (AAO). The self-assembled vertically aligned ZnO nanorods grown on GaN exhibit hexagonal facets, and have a uniform diameter of 60 nm and a mean length of 400 nm. The growth technique is simple, robust, and offers a direct control over array and single nanorod configurations. The growth temperature is significantly lower than normal, and yet, the resultant defect level is much lower than normal.

A nonlithographic technique that utilizes highly ordered anodized aluminum oxide porous membrane as template is presented as a general fabrication means for the formation of an array of vastly different two-dimensional lateral superlattices structures. Hexagonal close-packed nanopore arrays were fabricated on Si, GaAs, and GaN substrates via reactive ion etching. Quantum dot arrays of various metals and semiconductors were formed through evaporation and subsequent etching. The two-dimensional lateral superlattice structures fabricated using this method are of a high level of ordering, uniformity, and packing density. The diameter and periodicity of the nanostructures are determined by the features of the original alumina membrane, which can be adjusted by varying the anodization conditions.

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Nb films containing extended arrays of holes with 45-nm diameter and 100-nm spacing have been fabricated using anodized aluminum oxide (AAO) as substrate. Pronounced matching effects in the magnetization and Little-Parks oscillations of the superconducting critical temperature have been observed in fields up to 9 kOe. Flux pinning in the patterned samples is enhanced by two orders of magnitude as compared to unpatterned reference samples in applied fields exceeding 5 kOe. Matching effects are a dominant contribution to vortex pinning at temperatures as low as 4.2 K due to the extremely small spacing of the holes.

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A three-dimensional array of ∼55 nm diameter InGaAsN : Sb quantum dots (QDs) was nonlithographically fabricated starting with a MBE-grown InGaAsN : Sb/GaAs multiple quantum well wafer. The nonlithographic fabrication process relies on the use of a highly ordered nanopore alumina membrane for lateral patterning followed by a reactive ion etching. The dot size uniformity, spatial ordering and three-dimensional packing density are among the best reported so far. Nondestructive Raman scattering was employed to assess the material quality of the samples. While photoluminescence study points towards a moderately increased role of nonradiative transitions in the fabricated QD arrays, the dots show a relatively high emission intensity at room temperature, suggesting improved operation of long wavelength optical devices. Likely mechanisms contributing to the PL increase and the observed ∼50 meV red shift in the emission peak position are discussed. This study might be of great importance for engineering well controllable, ultra-high density, three-dimensionally arranged QD arrays for active optical devices.

Highly ordered carbon nanotube arrays were fabricated by pyrolysis of acetylene using anodic-aluminum-oxide templates. To avoid the natural tendency of the nanotubes sticking together and forming haystack-like bundles when exposing the nanotubes from the growth template, a new postgrowth treatment process using a mixture of 6 wt% phosphoric acid and 1.8 wt% chronium oxide as the etchant, and 0.1 wt% Gum Arabic or 5 wt% polymethacrylic acid as the dispersant, was developed yielding for the first time well aligned and spatially free-standing carbon nanotube arrays. The dispersants can be adsorbed on both the surface of carbon nanotubes and that of the alumina film resulting in the elimination of aggregation of exposed carbon nanotubes, a more uniform dissolution of alumina, and a lower, thereby, more controllable etching rate. The as-prepared carbon nanotube arrays, which are vertically aligned and well separated could be used for many applications such as mechanical oscillators, field emission, and sensors, and the exposed nanotubes offer a good platform for study on collective behavior of electrical and magnetic nano arrays.Index Terms-Anodic aluminum oxide, carbon nanotube array, chemical wet-etching, dispersant.

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