Engineered nanoporous and nanostructured films

Abstract

Nanoporous and nanostructured films and surfaces have been exploited by nature to spectacular effect. Plant leaves use nanostructured surfaces to shed water(1, 2) as shown in Fig. 1 and the Namib desert beetle uses a similar surface to collect water from dew(3,) (4,). Butterflies have fashioned nanostructured surfaces to attract mates, deter predators, and provide camouflage(5,) (6) (Fig. 2). Geckos(7,) (8), flies, and other insects(9) use nanostructured surfaces to adhere to walls (Fig. 3), and all cell membranes can be thought of as sophisticated nanoporous films(10). The development of nanoporous nanostructured thin films is relatively recent and has been driven by the need for low dielectric constant materials in the semiconductor industry(11-15), the need for low refractive index materials in the photonics industry(16-20), the need for nearly blackbody absorptivity in the solar cell industry(21), the need for nanoporous membranes in the gas separations industry(22), the need for superhydrophobic or superoleophobic materials to control wetting and spreading(23,) (24), and the general need for thin film catalytic and separations processes in the fuel cell(25,) (26), and biotechnology(27,) (28) fields. Since the range of applications is so vast and the materials and methods used to fabricate these materials is so broad, this article will focus primarily on nanoporous and nanostructured dielectric films for potential use in the microelectronics and photonics industries.