Temperature-Controlled Vapor Deposition of Highly Conductive p-Type Reduced Molybdenum Oxides by Hydrogen Reduction.

Reduced molybdenum oxide, generally MoO3- x, becomes increasingly metallic as the oxygen level decreases during the reduction of MoO3 to MoO2. Its interesting properties have recently intrigued research on MoO3- x in electrical and electrochemical areas. Lacking effective tools to control the oxygen level is one of the research difficulties for MoO3- x. Herein, we report facile temperature-controlled synthesis of triangular MoO2 and square Mo4O11. The triangular and square flakes showed metallic behavior with conductivity as high as ∼940 and ∼28 S/cm in DC measurement, respectively. The decrease in oxygen level from Mo4O11 to MoO2 affected the density of states mapped in Mo 4d orbitals, leading to higher conductivity for triangular MoO2. Further Mott-Schottky analysis on MoO3- x regrown on carbon fiber paper (CFP) revealed hole mobility of 105-108 cm2 V-1 s-1. The hole carriers at high frequencies are attributed to potential oxygen acceptors, and molybdenum vacancies resulted from limited reduction power of hydrogen.