Germanium nanowire synthesis using a localized heat source and a comparison to synthesis in a uniform temperature enviro
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In this work, we compare the synthesis of germanium nanowires (GeNWs) using a highly localized heat source with GeNWs synthesized in a uniform temperature environment. With the exception of thermal environment, identical synthesis parameters were maintained in all experiments. The localized heat source, a suspended silicon microscale heater, enabled site-specific synthesis and thus the direct integration of GeNWs which is presented for the first time. The effect of heat source implementation and local temperature gradients on the resulting nanowires is assessed in terms of resulting nanowire geometry, growth rate, and quality. Overall, we note a reduction in growth rate and elevated kinking levels in locally synthesized nanowires when compared to nanowires synthesized in uniform temperature processes. The taper which typically characterizes GeNWs, however, is significantly reduced. Finally, we explore branching behavior which hints of instabilities in the synthesis process as nanowires grow away from the heat source.
I. INTRODUCTION
One-dimensional (1D) nanostructures have attracted considerable interest as potential building blocks and functional components in next generation nanoscale sensing, nanoelectromechanical systems (NEMS), circuits, and interconnect applications.1 One-dimensional nanostructures can be quickly and reliably produced using bottom-up synthesis techniques. The reliable, reproducible, and robust integration of nanowires into systems and devices, however, remains a challenge. Postsynthesis steps have been developed for the purpose of manipulating and transferring 1D nanostructures into place.1 These postsynthesis techniques tend to be complex often requiring numerous processing steps. These steps can be avoided by developing direct integration techniques where the nanostructures grow into place and form desired contacts in situ. The localized nanostructure synthesis approach, for example, could contribute to simplified 1D nanostructure-based device integration while providing a highly processcompatible solution. In this approach, bottom-up synthesis reactions are carried out on chip using a spatially confined heat source, which restricts the high-temperature exposure of the chip while permitting localized nanostructure growth and thus enabling site-specific nanostructure integration among various device components.2,3 In this work, we consider localized heating realized upon the resistive heating of microscale line heaters. The range of material systems successfully realized using the localized heating approach a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.181 J. Mater. Res., Vol. 26, No. 17, Sep 14, 2011
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has been largely limited to carbon nanotubes2,4–13 although the use of silicon nanowires has been demonstrated as well.2,13–17 Here, we demonstrate for the first time the localized synthesis of germanium nanowires (GeNWs) on suspended microelectromechanical systems (MEMS) microbridges which
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