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1256-N10-02

Synthesis of Complex-oxide Nanorods via Pulsed-Laser Deposition John E. Mathis,1 Gyula Eres,2 Claudia Cantoni,2 Kyunghoon Kim,2 and Hans M. Christen2 1

Physical Sciences Department, Embry-Riddle University, Daytona Beach, FL 32114, U.S.A.

2

Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, U.S.A.

ABSTRACT Nanorods composed of complex oxides have been synthesized using hydrothermal and solgel methods, but pulsed-laser deposition (PLD) provides precise, layer-by-layer control of growth, and is the method of choice for synthesizing complex structures. However, producing complex-oxide nanorods by PLD has proved elusive. Here we report on our efforts to produce nanorods composed of the best-understood complex oxide, strontium titanate (STO). The results suggest it is indeed possible to produce STO nanorods via PLD by using a template of MgO nanorods. INTRODUCTION Complex oxides are known for the richness in their physical properties such as ferroelectricity, magnetism, and superconductivity, with many of their properties resulting from intrinsic cluster self-organization [1]. Complex oxide heterostructures also exhibit unique characteristics such as quasi-two dimensional electron gases being generated at the interface [2]. Shaping these complex oxides into nanostructures is of great fundamental and practical importance. Nanorods and nanowires show promise as components of devices with enhanced capabilities. Indeed, nano-dimensioned diodes and field-effect transistors (FET’s) have been constructed from nanowires [3],[4],[5]. Nanorod superlattices, synthesized as alternating layers of semiconducting materials, have found applications such as gas sensors [6],[7], ultraviolet photodetectors [8], and light-emitting diodes (LED’s) [9],[10]. Although many non-PLD methods have produced complex oxide nanorods, these methods share the drawback of difficulty in maintaining precise control of stoichiometry. By contrast, the method of pulsed laser deposition (PLD) has manifested its value for growing thin films composed of complex materials. Its precise control of stoichiometry and gas phase environment lends itself for producing novel materials and is a useful tool for producing heterostructured thin films. PLD relies on the interaction of a high-powered laser pulse interacting with a target. The pulse rapidly heats the target material, ablating the material into an energetic plume. The atoms and molecules from the plume deposit on a substrate as pulses of supersaturated vapor. Figure 1 shows the laser pulse striking the target and the resulting plume.

Figure 1 Plume generated by an ultraviolet laser beam striking a target (upper left).

With PLD, unlike many other vapor deposition methods, the composition of the deposited material is usually very close to that of the target, except in the case of complex compositions containing highly-volatile elements such as Bi, Pb, etc. Thus, one can tailor the composition in the laboratory before the actual deposition takes place.