Letter Cite This: Nano Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/NanoLett
Seeded Nanowire and Microwire Growth from Lithium Alloys Sang Yun Han,† Matthew G. Boebinger,‡ Neha P. Kondekar,‡ Trevor J. Worthy,‡ and Matthew T. McDowell*,†,‡ †
George W. Woodruff School of Mechanical Engineering and ‡School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States S Supporting Information *
ABSTRACT: Although vapor−liquid−solid (VLS) growth of nanowires from alloy seed particles is common in various semiconductor systems, related wire growth in all-metal systems is rare. Here, we report the spontaneous growth of nano- and microwires from metal seed particles during the cooling of Li-rich bulk alloys containing Au, Ag, or In. The as-grown wires feature Au-, Ag-, or In-rich metal tips and LiOH shafts; the results indicate that the wires grow as Li metal and are converted to polycrystalline LiOH during and/or after growth due to exposure to H2O and O2. This new process is a simple way to create nanostructures, and the findings suggest that metal nanowire growth from alloy seeds is possible in a variety of systems. KEYWORDS: Nanowires, phase transformations, lithium, nanomaterials
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metal alloys are used in a variety of applications; for instance, Li-containing Al alloys have been developed and deployed in aerospace systems because of their lower density and higher stiffness than conventional Al alloys.16 Li-rich alloys have also been investigated as high-capacity electrode materials and interfacial protection layers for Li-ion batteries.17−19 In addition to these applications, lithium-alloying reactions have recently been shown to be useful for fabricating nanostructured materials. For instance, Chen et al. created porous nanostructures and hollow core−shell particles by removing Li from Li Sn alloys.20 Lei et al. extracted Li from LiAl and LiMg alloys to create alkoxide nanowires; this method is suitable for large-scale synthesis of oxide nanostructures.21 These examples show that Li alloying/dealloying reactions could enable the fabrication of novel materials, but it is also critical to develop an improved understanding of nanostructure growth mechanisms so these materials can be tailored for applications. Here, we report the growth of LiOH nanowires and microwires directly from Li-rich alloys at relatively low temperature. Multiple metals (Au, Ag, and In) were observed to induce nanowire/microwire growth from a macroscale liquid melt during cooling, and the results indicate these wires convert from Li metal to LiOH during and/or after growth. The observation of Au-, Ag-, or In-rich alloy tips and the high surface diffusion rate of Li suggest a mechanism similar to VLS growth. This work introduces a new and simple method to
anowires have been extensively investigated because of the remarkable optical, electrical, mechanical, and thermal properties1−3 which arise from their one-dimensional geometry, high surface area, tunable length, controllable chemistry, and mechanical flexibility. Because of these properties, nanowires have been used for energy storage and energyharvesting devices,3−5 lightweight structural composites,6 flexible electronic devices,7 and nanoelectronics such as fieldeffect transistors and logic gates.8−10 Many types of nanowires are synthesized via colloidal fabrication routes.2,11 However, seeded growth of nanowires from metal catalysts via the vapor− liquid−solid (VLS) mechanism and its derivatives is potentially more versatile, as these procedures are inherently scalable and allow for the encoding of different compositions, structures, and morphologies along the wire axis.12 Wagner and Ellis first introduced the growth of silicon “whiskers” via the VLS mechanism in 1964.13 In the VLS mechanism, droplets of catalyst material form a liquid alloy with another atomic species supplied via the vapor phase. Upon continued alloying and eventual saturation of the added species, unidirectional singlecrystalline growth of the nanowire material occurs from the catalyst seed droplet.2,13 Whereas the family of VLS-type growth mechanisms has proved to be useful for the growth of semiconductor nanowires (e.g., InAs, InSb, and GaAs),2,14,15 this type of growth for nano/microwires in all-metal systems has not been widely investigated. Growth of metallic nanowires via seed-based processes could open the door to a variety of new one-dimensional nanomaterials. Lithium forms alloys with many other metals at relatively low temperatures (
