In situ chemical oxidation of ultrasmall MoO x nanoparticles in suspensions

Abstract

Nanoparticle suspensions represent a promising route toward low cost, large area solution deposition of functional thin films for applications in energy conversion, flexible electronics, and sensors. However, parameters such size, stoichiometry, and electronic properties must be controlled to achieve best results for the target application. In this report, we demonstrate that such control can be achieved via in situ chemical oxidation of MoO x nanoparticles in suspensions. Starting from a microwave-synthesized suspension of ultrasmall (d 2 nm) MoO x nanoparticles in n-butanol, we added Hat room temperature to chemically oxidize the nanoparticles. We systematically varied Hconcentration and reaction time and found that they significantly affected oxidation state and work function of MoO x nanoparticle films. In particular, we achieved a continuous tuning of MoO x work function from 4.4 to 5.0 eV, corresponding to oxidation of as-synthesized MoO x nanoparticle (20 Mo 6+) to essentially pure MoO This was achieved without significantly modifying nanoparticle size or stability. Such precise control of MoO x stoichiometry and work function is critical for the optimization of MoO x nanoparticles for applications in organic optoelectronics. Moreover, the simplicity of the chemical oxidation procedure should be applicable for the development of other transition oxide nanomaterials with tunable composition and properties. © 2012 Yun-Ju Lee et al.