Effects of alumina priming on the electrical properties of ZnO nanostructures derived from vapor-phase infiltration into self-assembled block copolymer thin films

Abstract

Alumina priming is frequently employed to facilitate the vapor-phase infiltration (VPI) of weakly reactive organometallic precursors into polymer templates such as self-assembled block copolymer (BCP) thin films. By first infiltrating trimethylaluminum (TMA)—a strong Lewis acid that can readily infiltrate and bind to Lewis-basic groups inside polymers—when exposed to water vapor, it produces molecular alumina terminated with a hydroxyl group. This priming step activates the polymer matrix for the following infiltration of weakly reactive organometallic precursors of a target inorganic material. Nevertheless, given the insulating nature of bulk alumina, alumina priming may negatively impact the electrical properties of the final inorganic nanostructures derived from VPI. In this study, we investigate the effects of alumina-priming on the electrical and structural properties of zinc oxide nanowires derived from VPI of diethylzinc and water into self-assembled lamellar poly(styrene-block-methyl methacrylate) (PS-b-PMMA) BCP thin films. We demonstrate facile tuning of characteristic dimension, chemical composition, and electrical conductivity of the synthesized aluminum-doped ZnO (AZO) nanowires by adjusting the TMA exposure time during a single-cycle alumina priming. Increasing the TMA exposure duration not only promotes the ZnO infiltration fidelity but also minimizes ZnO electrical resistivity at 14.3 kΩ cm at a TMA exposure duration of 100 s with a corresponding Al concentration of 6.02%. The results provide a guideline for controlling the composition, dimensions, and electrical properties of alumina-primed metal oxide nanostructures based on VPI in polymer templates.