Synthesis and characterization of ruthenium dioxide nanostructures

We report the synthesis of ruthenium dioxide (RuO₂) nanostructures by thermal evaporation of RuO₂ powder. RuO₂ nanostructures of different shapes were synthesized at various concentration, flow rate, and pressure of oxygen. At a constant pressure of 3 torr of flowing oxygen, polygonal prism-like RuO₂ nanorods with flat tips were grown at an O₂ flow rate of 100 sccm; club-shaped nanorods with obelisk tip were formed at 300 and 600 sccm, and hollow rods with square tip were formed at 1800 sccm. A mixture of O₂ and Ar at a total flow rate of 600 sccm led to the formation of short club-shaped nanorods indicating the suppression effect of Ar on the growth of nanorods. The pressure also had a significant effect on the formation of RuO₂ nanostructures, at a fixed flow rate of 600 sccm of O₂, a pressure of 3 torr resulted in the growth of club-shaped RuO₂ nanorods, while high pressures of 380 and 760 torr resulted in the formation of both linear club-shaped and pine tree-like hierarchical RuO₂ nanorods. X-ray diffraction and transmission electron microscopy analysis indicated the formation of tetragonal phase of RuO₂ with high crystallinity. A density functional calculation on RuO₂, RuO₃, and RuO₄ was performed to help to explain the experimental results.