Thickness-dependent mechanical properties of nanotubular ZnO

Abstract

ZnO has been focused on hydrogen sensing material because of its thermal stability and high mechanical strength and mobility. But it has the weakness that it is very brittle. And nowadays, flexible electronics technologies are being driven by trend such as low complexity and high reliability. A high strength-to-weight ratio makes interconnected tubular networks creative design strategy for reducing the linear decrease in strength and stiffness of low-density materials with increasing porosity. So we synthesized ultralow-density nanotubular structured ZnO with high surface area to volume ratio for flexible hydrogen gas sensor application using the sacrificial template, nanoporous gold. We measured its mechanical properties by tensile test and hydrogen gas sensing sensitivity. Dog-bone shaped nanoporous gold with pore size 1 ㎛, gauge length 2 mm was prepared by free corrosion dealloying from gold-silver mother alloy. For nanotubular structured ZnO, 50, 100, 150 nm-thick ZnO layer was deposited on nanoporous gold by atomic layered deposition (ALD). After nanoporous gold was selectively etched by gold etchant TFA, nanotubular structured ZnO which have shell thickness of 50, 100, 150 nm were obtained. We synthesized ZnO thin film with 50, 100, 150 nm-thick to compare mechanical properties. We also measured hydrogen gas sensing sensitivity, defined as a ratio of change in conductance upon exposure to H2 gas to that in vacuum, of the ZnO thin film and nanotubular ZnO. We discuss hydrogen sensor efficiency of the nanotubular ZnO based on its high volume-to-surface area.