Roll-to-roll anodization and etching of aluminum foils for high-throughput surface nanotexturing.

A high-throughput process for nanotexturing of hard and soft surfaces based on the roll-to-roll anodization and etching of low-cost aluminum foils is presented. The process enables the precise control of surface topography, feature size, and shape over large areas thereby presenting a highly versatile platform for fabricating substrates with user-defined, functional performance. Specifically, the optical and surface wetting properties of the foil substrates were systematically characterized and tuned through the modulation of the surface texture. In addition, textured aluminum foils with pore and bowl surface features were used as zeptoliter reaction vessels for the well-controlled synthesis of inorganic, organic, and plasmonic nanomaterials, demonstrating yet another powerful potential use of the presented approach.

Shape-controlled synthesis of single-crystalline nanopillar arrays by template-assisted vapor-liquid-solid process.

Highly regular, single-crystalline nanopillar arrays with tunable shapes and geometry are synthesized by the template-assisted vapor-liquid-solid growth mechanism. In this approach, the grown nanopillars faithfully reproduce the shape of the pores because during the growth the liquid catalyst seeds fill the space available, thereby conforming to the pore geometry. The process is highly generic for various material systems, and as an example, CdS and Ge nanopillar arrays with square, rectangular, and circular cross sections are demonstrated. In the future, this technique can be used to engineer the intrinsic properties of NPLs as a function of three independently controlled dimensional parameters--length, width and height.

Ordered arrays of dual-diameter nanopillars for maximized optical absorption.

Optical properties of highly ordered Ge nanopillar arrays are tuned through shape and geometry control to achieve the optimal absorption efficiency. Increasing the Ge materials filling ratio is shown to increase the reflectance while simultaneously decreasing the transmittance, with the absorbance showing a strong diameter dependency. To enhance the broad band optical absorption efficiency, a novel dual-diameter nanopillar structure is presented, with a small diameter tip for minimal reflectance and a large diameter base for maximal effective absorption coefficient. The enabled single-crystalline absorber material with a thickness of only 2 µm exhibits an impressive absorbance of ∼99% over wavelengths, λ = 300-900 nm. These results enable a viable and convenient route toward shape-controlled nanopillar-based high-performance photonic devices.