Light-dependent ionic-electronic conduction in an amorphous octahedral molybdenum cluster thin film

Abstract

We developed a new environment-sensing device based on the opto-ionic-electronic phenomena of an octahedral molybdenum metal (Mo₆) cluster. When the Mo₆ cluster is electrochemically deposited on a transparent electrode in an organic solvent containing a trace amount of water, the water permeates the deposited film. During the process, some ligand species that stabilize the frame structure of the Mo₆ cluster are substituted with hydroxyl groups, and the negatively charged frame structure of the Mo₆ cluster unit is stabilized by hydronium counterions. As a result, the transparent film of the Mo₆ cluster fabricated by this method exhibits ionic-electronic mixed conduction of the hydronium ion. The ionic conduction greatly changes depending on the temperature and humidity in the atmosphere, and the electrical conductivity greatly changes depending on the wavelength and intensity of the irradiated light. These unique multisensing properties present new possibilities for environmental sensing applications.

Nanomaterials: Atom clusters for sensing applications

Researchers in Japan and France have developed a novel nanomaterial based on thin films with properties sensitive to the environment. One approach to building these nanomaterials is to use so-called atomic clusters, consisting of metal atoms bound to each other, often with accompanying non-metallic atoms. The properties of a material can be altered to suit a specific application by adding functional substances. Motohide Matsuda from Kumamoto University, Thi Kim Ngan Nguyen from the National Institute for Materials Science, Tsukuba, both from Japan, and colleagues created transparent films of indium tin oxide on which they deposited the hexamolybdenum atomic cluster. They investigated the humidity and temperature dependence of the electrical properties of the films, and how their conductivity altered under different light conditions. The results indicated that the innovative nanomaterial could find applications in atmospheric sensors.