X-Ray Diffraction from Periodically Patterned GaAs Nanorods Grown onto GaAs[111]B
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SEMICONDUCTOR nanorods (NRs) grown by vapor-liquid-solid (VLS) epitaxy are of particular interest for the creation of materials with new electronic and optical properties.[1] Exploiting quantum effects, one is able to tune the emission wavelength and to induce onedimensional (1-D) electronic transport. In the VLS mode, NRs are grown onto [111] planes of a zinc-blend or diamond-type semiconductors by solution from a molten eutectic alloy formed by a metallic seed, with the diameter and position of grown NRs crucially depending on the statistical process of the metallic droplet formation. The spatial position and the diameter of the molten seeds (typically, Au) determine the position and size of the grown NRs onto the substrate. Due to the statistical character of both quantities, the NRs are nonuniform and rather randomly located at the substrate. One route to prepare NRs of uniform diameter and defined inter-rod spacing is the use of prepatterned ANTON DAVYDOK and ANDREAS BIERMANNS, Postdoctoral Students, and ULLRICH PIETSCH, Professor and Solid State Group Leader, are with Solid State Physics, Siegen University, 57068 Siegen, Germany. JO¨RG GRENZER, Scientist, is with FZ-Dresden Rossendorf, 013414 Dresden, Germany. HENDRIK PAETZELT, Postdoctoral Student, is with the Leibniz Institute for Surface Modification, Ion Beam Technology Department, 04318 Leipzig, Germany. VOLKER GOTTSCHALCH, Scientist, is with Solid State Chemistry, University of Leipzig, 04103 Leipzig, Germany. This article is based on a presentation given in the symposium entitled ‘‘Neutron and X-Ray Studies for Probing Materials Behavior,’’ which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee. Article published online June 16, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
substrates.[2] This can be performed via selective area– metal organic vapor phase epitaxy (SA-MOVPE), where the NRs are grown from small circular openings defined by electron-beam lithography and wet chemical etching of a thin SiNx layer.[3] Using opening diameters in the range of a few hundred nanometers and inter-rod distances in the range of several microns, uniformly sized NRs were grown.[4] One key problem for the understanding of NR growth in such arrays is the mutual interaction of growing NRs with the SiNx mask, which can result in alloy formation or recrystallization of the initially amorphous SiNx. Structure characterization of individual NRs is typically performed by high-resolution transmission electron microscopy at single NRs.[5] In addition, X-ray diffraction has been used to obtain structural information from a statistical ensemble of nonuniform NRs.[6,7] Nowadays, the achievements in X-ray optics to define an intense coherent X-ray beam with submicron diameter allows for three-dimensional (3-D) characterization of individual nano-objects using coherent diffraction i
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