Growth, structure and electrical properties of tungsten oxide nanorods

Tungsten trioxide has shown good sensing properties towards various gases. Recently thin nanostructured WO3 films have been tested. Due to their large surface area to volume ratio they exhibit good sensitivity depending on the grain size. However in conventional WO3 thin films the average grain size exceeds the thickness of the surface space charge layer, so the electrical conduction is mainly controlled by the carriers transport across the grain boundaries. An alternative way seems to be in a monocrystalline material with nanometric dimensions. Our objective is to fabricate nanosized tungsten oxide rods and to test their sensing properties under gas adsorption. In this work, we focus on the growth, the structure and the electrical properties of tungsten nanorods. The tungsten oxide nanorods were grown by vapour transport from a WO3 layer onto a substrate (Mica). The nanorods growth was controlled by the temperature gradient between the WO3 layer and the substrate. Their morphology was investigated by AFM and their structure by TED and TEM. We have investigated the conductivity of the WO3 nanorods with a technique derived from Atomic Force Microscopy operating in contact mode with a conductive tip (Resiscope).