Low temperature solid-state wetting and formation of nanowelds in silver nanowires
Low temperature solid-state wetting and formation of nanowelds in silver nanowires
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DOI：
10.1088/1361-6528/aa7eb8
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发表时间：
2017-08
期刊：
影响因子：
3.5
通讯作者：
V. Radmilović;M. Göbelt;C. Ophus;S. Christiansen;E. Spiecker;V. Radmilović
中科院分区：
文献类型：
--
作者：
V. Radmilović;M. Göbelt;C. Ophus;S. Christiansen;E. Spiecker;V. Radmilović
本文重点研究了银纳米线（AgNWs）之间热诱导纳米场形成的微观机制，这是提高透明电极纳米线网络电导率的关键过程。利用聚焦离子束切片和透射电子显微镜对焊接NW的原子结构进行了研究，包括润湿接触角的测量和缺陷结构的原子精度表征，为研究焊接机理提供了基础信息。通过在高分辨率扫描电镜图像中直接评估原子柱位移得到的晶格应变表明，AgNW五边形结构的五个孪晶段之间的晶格应变不均匀。研究发现，AgNWs的五边形横截面形貌通过控制初始润湿和银原子在NWs之间的扩散，对纳米焊点的形成起主导作用。由于完全的固态润湿，在~ 4.8°的角度，焊接过程开始于（100）表面表面上初始Ag层的同外延形核，被认为具有无限大的曲率半径。然而，由于吉布斯-汤姆森效应，这一过程的强大驱动力要求NW接触通过第二个NW提供小曲率半径的五角形截面的角落发生。在初始层形成后，焊接区继续生长并外延延伸到相邻的孪晶段。
This article focuses on the microscopic mechanism of thermally induced nanoweld formation between silver nanowires (AgNWs) which is a key process for improving electrical conductivity in NW networks employed for transparent electrodes. Focused ion beam sectioning and transmission electron microscopy were applied in order to elucidate the atomic structure of a welded NW including measurement of the wetting contact angle and characterization of defect structure with atomic accuracy, which provides fundamental information on the welding mechanism. Crystal lattice strain, obtained by direct evaluation of atomic column displacements in high resolution scanning transmission electron microscopy images, was shown to be non-uniform among the five twin segments of the AgNW pentagonal structure. It was found that the pentagonal cross-sectional morphology of AgNWs has a dominant effect on the formation of nanowelds by controlling initial wetting as well as diffusion of Ag atoms between the NWs. Due to complete solid-state wetting, at an angle of ∼4.8°, the welding process starts with homoepitaxial nucleation of an initial Ag layer on (100) surface facets, considered to have an infinitely large radius of curvature. However, the strong driving force for this process due to the Gibbs–Thomson effect, requires the NW contact to occur through the corner of the pentagonal cross-section of the second NW providing a small radius of curvature. After the initial layer is formed, the welded zone continues to grow and extends out epitaxially to the neighboring twin segments.