Synthesis of Molybdenum Nanowires with Millimeter-Scale Lengths Using Electrochemical Step Edge Decoration

Molybdenum (Mo 0 ) nanowires with diameters ranging from 13 nm to 1 μm and having lengths of up to 500 μm have been synthesized by a two-step process involving the electrodeposition of molybdenum dioxide (MoO 2 ) on a highly oriented pyrolytic graphite (HOPG) surface followed by reduction of the MoO 2 nanowires at 500 °C to form molybdenum metal. MoO 2 nanowires were electrodeposited reductively from an alkaline MoO 4 2 - solution using a low overpotential of <|200 mV|. Under these conditions, the nucleation of MoO 2 occurred selectively at step edges present on the HOPG surface, and a high linear density (>30 μm - 1 ) of MoO 2 nuclei was formed along each step edge on the graphite surface. With continued growth, MoO 2 nuclei that were 10−15 nm in diameter coalesced with adjacent nuclei along the step edge to form continuous nanowires having approximately this same diameter. Longer deposition times, t dep, produced smooth MoO 2 nanowires with diameters proportional to t dep 1/2 . These nanowires had a uniform diameter and a smooth surface, and the nanowire-to-nanowire variation in diameter was 10−30%. In contrast to nanowires of MoO 2, which were brittle and subject to breakage, molybdenum metal (Mo 0 ) nanowires were resilient and resistant to breakage. Arrays of Mo 0 nanowires could be embedded in a polymer film and lifted off the graphite surface. In humid air (≈55% relative humidity) at room temperature, the resistivity of Mo 0 nanowires increased by 10% h - 1 as an insulating surface oxide of MoO 3 formed.