To address the issue, researchers at Sensor Lab and Brescia University, both in Italy, have developed a simple, cheap and large-area scalable methodology for integrating metal oxide nanowire bundles into functional devices. The method relies on the sequential application of two techniques, namely high-temperature vapour transport and condensation (to fabricate metal oxide nanowires), and wet etching of a silicon dioxide sacrificial layer.

After removal of the sacrificial layer, a clean substrate surface is obtained for the deposition of stable metal contacts. The hydrofluoric acid solution used to remove the SiO2 layer does not affect the structure and morphology of the nanowires in the case of SnO2 and In2O3.

Demonstrator device

The methodology was proven to be effective for a gas sensor application. Electrical measurements indicate that a slightly rectifying Schottky junction is present at low temperature (up to T=150 °C) between nanowires and platinum electrodes, which vanishes as the temperature increases or when the voltage bias is raised above 3 V.

One of the main advantages of the approach is that only standard techniques and equipment are needed to obtain the desired result: sputtering apparatus for deposition of the sacrificial layer and the electric contacts; a low-pressure tubular furnace for nanowire growth; wet etching for removal of the sacrificial layer.

The study paves the way for the growth and integration of nanowire bundles directly into devices, overcoming the need for expensive and time-consuming nanomanipulation techniques.

Full details can be found in the journal Nanotechnology.