A high density array of free standing alumina nanotubes aligned vertically on solid substrates in a large area

Abstract

We report an innovative fabrication of a high density array of free standing alumina nanotubes (ANTs) aligned vertically on substrates. A nanoporous polyimide (PI) template was first prepared by dry etching with the aid of an anodized aluminum oxide (AAO) membrane mask followed by atomic layer deposition (ALD) of alumina. ANTs with various diameters, lengths, and wall thicknesses were obtained by controlling the pore size, the thickness of the nanoporous PI template, and the deposition thickness of alumina through ALD, respectively. Optical properties of an ANT array were also tuned by changing the wall thickness of ANTs, and an ANT array on a glass showed excellent antireflectance with less than 0.1% reflectance at a visible wavelength. The nanoporous polymer template fabricated in this study could also be used to obtain a high density array of various inorganic nanotubes with uniform wall thickness and length in a large area. It also enables on-demand patterning of the nanotube array.