Formation of GaSb core-shell nanofibers by a thermally induced phase decomposition process
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Yanwen Zhang Pacific Northwest National Laboratory, Richland, Washington 99352 (Received 28 January 2009; accepted 22 April 2009)
Dense networks of amorphous GaSb nanofibers were fabricated by ion irradiation of bulk GaSb, and following formation, they were thermally annealed at a low temperature. Contrary to expectations, annealing of the GaSb fibers at just 50% of their melting temperature resulted in complete chemical decomposition of the nanofibers into coreshell structures consisting of crystalline Sb cores surrounded by amorphous shells. In this study, we investigate the transition of the single-phase nanofibers to their core-shell configuration, and we analyze the unique, temperature-dependent phase decomposition process. Thermodynamic considerations are discussed, and a model is presented to explain the thermally induced decomposition of the GaSb semiconductor fibers into coreshell structures, based upon the singular interaction of several size-dependent material properties.
I. INTRODUCTION
GaSb is a narrow band gap semiconductor that has been studied extensively for use in a variety of optoelectronic devices, including laser diodes, photodetectors, and high-frequency electronic devices.1 GaSb can be used to create ordered nanodot arrays,2 and recently GaSb has been reported as a promising material for use in thermophotovoltaic systems and tandem concentrator solar cells.3,4 Ion irradiation-induced swelling in GaSb was first reported in the early 1990s,5,6 when studies showed that relatively low amounts of ion damage could create extremely porous GaSb void networks, similar to those reported in Ge and InSb.7–10 Several studies over the past decade have focused on the mechanism of formation of these porous, nanofiber networks,11–13 as well as the ability to pattern their surfaces and fabricate templates using the material.14,15 Because of quantum confinement and surface passivation effects at the nanoscale, nanoporous semiconductors have been targeted as ideal materials for many optoelectronic and photovoltaic devices.16 Porous Si has been the focal point of much of the recent research, but nanoscale porous GaSb, which exhibits a shift in its optical spectra similar to that in nanoporous Si, could also be useful for device fabrication.17 However, research indicates that quantum confinement effects that a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0287
2286
http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 7, Jul 2009 Downloaded: 04 Apr 2015
produce changes in the luminescence properties of a material are often dependent upon the crystallinity of the material,18 and research has shown that the ion irradiation process used to fabricate GaSb nanofibers turns the material amorphous.13–15 In this study, we investigate the effects of thermal annealing on the crystallinity and composition of ion irradiation-induced GaSb nanofibers, and we comment on the unique chemical decomposition that is observed. II. EXPERIMENTAL DETAILS
Some 1-cm2 samples were s
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