Temperature-controlled Vapor Deposition of Highly Conductive P-type Reduced Molybdenum Oxides by Hydrogen Reduction.

Reduced molybdenum oxide, generally MoO3-x, is a family of conductive metal oxides. During the reduction from MoO3 to various MoO3-x phases, the dielectric material becomes increasingly metallic all the way to MoO2. The interesting property through oxygen control has recently intrigued research of the MoO3-x family in multiple research areas including electrical and electrochemical application. One of the research difficulties in reduced molybdenum oxide is the lack of effective tools to control the oxygen level. Herein, we report a facile synthesis method by temperature-controlled synthesis of triangular MoO2 and square Mo4O11. The triangular and square flakes show a metallic behavior in our DC measurement with a conductivity as high as ~940 S/cm and ~28 S/cm respectively. Further Mott-Schottky analysis of samples regrown on carbon fiber paper (CFP) reveals the hole mobility as high as 105 - 108 cm2 V-1 s-1. The decrease in oxygen level from Mo4O11 to MoO2 affects the density of states mapped in Mo 4d orbitals, leading to a higher conductivity for triangular MoO2. The excessive hole carriers and p-type behavior in Mott-Schottky measurement at high frequencies could be attributed to potential oxygen acceptors and molybdenum vacancies resulted from low reduction power of hydrogen.