Direct integration of metal oxide nanowires into an effective gas sensing device

A simple and large-area scalable methodology has been set up for direct integration of metal oxide nanowire bundles into a functional device for gas sensing. It is based on sequential application of two consolidated techniques, namely high temperature vapour transport and condensation for fabrication of metal oxide nanowires, and wet etching of a sacrificial layer. The alumina substrate patterned with a silicon dioxide sacrificial layer does not influence the growth of nanowires and remains unaltered under the high temperature process. The sacrificial layer is finally removed under hydrofluoric acid, the metal oxide nanowires do not suffer modifications and a clean substrate surface can be obtained for deposition of stable metal contacts. The methodology was proven effective for application in a gas sensor device. Electrical measurements indicate that a slightly rectifying Schottky junction is present at low temperatures (up to T = 150 °C) between nanowires and platinum electrodes, which vanishes as the temperature increases and under high voltage (bias voltage above ∼ 3 V). The results foresee the possibility of growth and integration of nanowire bundles directly into devices, overcoming the need for expensive and time-consuming nanomanipulation techniques.