Length-dependent melting behavior of Sn nanowires
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Fan Gao, Jirui Wang, and Zhiyong Gu Department of Chemical Engineering, University of Massachusetts Lowell, Lowell, MA 01854
Eric A. Stach Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973
Guangwen Zhoua) Department of Mechanical Engineering & Multidisciplinary Program in Materials Science and Engineering, State University of New York at Binghamton, NY 13902 (Received 6 December 2016; accepted 19 January 2017)
Using in situ transmission electron microscopy, we report the observation of the melting behavior of one-dimensional nanostructures of Sn with different length/width aspect ratios. The melting of small aspect-ratio nanowires (nanorods) results in the expansion of liquid Sn along both axial and radial directions with the tendency to form an isometric or spherical particle, thereby minimizing the total surface area. For nanowires with the length/width aspect ratio of ;10.5, perturbation along the liquid stream causes an unstable necking phenomenon and the whole wire tends to shrink into a spherical particle. In contrast, Rayleigh instability sets in for the melting of the nanowires with the length/width aspect ratio as large as ;21, which gives rise to necking and fragmentation of the wire into particles. The amorphous native surface oxide (SnOx) layer serves as a confinement tube and plays an important role in the melting induced morphological evolution of Sn nanowires. A thin SnOx layer is flexible with the ability to shrink or expand upon the flow of molten Sn. The increased rigidity for a thick SnOx surface layer kinetically suppresses bulging and necking formation in molten Sn nanowires.
I. INTRODUCTION
Nanomaterials are intrinsically characterized by a large ratio of surface-to-bulk atoms. This modifies many basic materials properties. The most notable difference in the example from the conventional bulk properties is probably the depression of the melting temperature relative to the bulk counterparts. Because melting is one of the most important phase transformations, extensive experimental and theoretical investigations along with computer simulations have been performed to understand the effect of the size shrinkage on the modifications of the thermodynamic properties.1–3 Most of the theoretical models of nanocrystal melting assume a spherical shape and yield a linear relation of the melting point with the reciprocal of the particle size.4–6 However, the shape of nanocrystals can also affect the melting behavior because the surface-to-volume ratio is shape dependent. The understanding of the melting
Contributing Editor: Edson Roberto Leite a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.45
behaviors of nanomaterials with some unique and practically important geometries is much less compared to the spherical shape. One-dimensional nanostructures are building blocks for nanoscale integration.7,8 Particularly, employing nanowires as the interconnection or joints for nanoscale electronics necessitates understanding of the
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