Characterisation on Spontaneous Redox-state Transition Property of Phosphomolybdic Acid Molecule Functionalised on Carbon Nanotube

摘要

Polyoxometalate (POM) is molecule that displays various properties such as multi-redox, luminescence, catalysis, and magnetism Due to these remarkable properties, development of super-capacitor, flash-type memory cell, solar cell, light-emitting device, and water oxidation system using POM has been made possible. Furthermore, certain types of POM have been reported to have anti-tumor and anti-HIV effect. Among various POM, we set our target on phosphomolybdic acid (hereinafter PM012) that has shown to display 24-electron multi-redox property. Due to this exceptionally high electron storing ability, PM0_(12) has been implemented as high-capacity cathode material in molecular cluster battery. Our research group has also previously reported the generation of unique random telegraph signal (RTS) due to the redox state fluctuation of a single PM012 molecule adsorbed to the sidewall of carbon nanotube (CNT). Despite these interesting discoveries, the charge transfer process through PM0_(12) molecule has not been examined comprehensively. Motivated by the discovery of 24-electron multi-redox property in PM0_(12), we created a system that is made up of CNT/PM0_(12) device in order to study the charge transfer process through PM012. AC. dielectrophoresis technique was applied to position few CNTs across 1μm-gapped electrodes. This device was then soaked in PM0_(12) solution to allow the formation of "PM012 junction" between CNT and electrode, as illustrated in Fig.1.When DC bias of few tens of millivolt was applied to this CNT/PM0_(12) device, we observed output current response with spontaneous transition between "OFF state" at nearly 0 A and "ON state" at certain maximum current range, accompanied by occasional appearance of intermediate states, as depicted in Fig. 2. This spontaneous switching in conductance is speculated to originate from the spontaneous redox-state transition of a single PM0_(12) junction, suggesting that the multi-redox property governs the charge transfer process through PM0_(12). This newly discovered relationship deserves further analysis for the fundamental understanding and characterisation on the multi-redox property of PM0_(12).