An improved strategy for transferring and adhering thin nanoporous alumina membranes onto conducting transparent electrodes for template assisted electrodeposition of high aspect ratio semiconductor nanowires with increased optical absorption

This article presents a new method for transferring and enhancing the adhesion of thin nanoporous alumina (NPA) membranes onto non-atomically flat substrates like fluorine-doped tin oxide (FTO) coated glass. The study reports use of glycerol as an additive to reduce the brittleness of the polystyrene filler that was used to fill the pores of the NPA membrane. Additionally, a new reflux-based method is reported here for the complete removal of the polystryrene filler from the porous channels of alumina. The adhesion between an NPA membrane and an underlying electrode was enhanced by electrodepositing a thin (∼40 nm) intermediate layer of the conducting polymer polyaniline (PANI). The PANI layer acts as an efficient electrostatic adhesive between the NPA and the conducting glass electrode and ensures ultra-strong adhesion of the NPA membrane, which can survive the harsh conditions of CdTe nanowire electrodeposition (60 °C temperature and an acidic electrolyte) without delamination for 30 min. The resulting nanowires clearly templated the structure of NPA and displayed free-standing nanowires over a large area with a diameter of around 60 nm, a length of approximately 2.8 μm (aspect ratio ∼47) and an areal density of 5.9 × 10¹² nanowires cm⁻². Total optical absorption measurement on the free-standing CdTe nanowires exhibited a 45% enhancement over a wavelength range of 350–1400 nm as compared to a CdTe planar thin film of same thickness. (paper)