Use of simple annealing processes to prepare anisotropic iridium and iridium dioxide nanostructures

Abstract

Free-standing one-dimensional (1D) wires, two-dimensional (2D) platelets (triangular and hexagonal in shape) of iridium (Ir) and iridium dioxide (IrO₂) with open-ends and flower-like structures have been prepared successfully in the absence of a catalyst or template by a simple annealing process. This paper describes the first examples of the growth of 1D Ir wires and 2D Ir platelets. The Ir wires and platelets grown at an angle on sapphire were over a few tens of micrometres long. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) observations revealed that Ir wires and IrO₂ rods are grown in the preferential orientation along [110] and [001] directions, respectively. The probable growth models for the formations of the Ir and IrO₂ nanostructures are proposed. Electrical measurements indicated that the highly crystalline Ir wires had a low resistivity and exhibited electronic transport properties similar to bulk Ir. The failure current density was greater than 1 × 10⁸ A cm⁻². This value is comparable to that reported for Pt nanobelts (1 ×10⁷ A cm⁻²) and silver nanobeams (1.8 × 10⁸ A cm⁻²). These unique Ir wires are attractive nanoscale building blocks for potential use as electrodes in nanoelectronic devices.