3-25. Direct and rapid fabrication of single-crystalline metal nanowires from the solid surface via thermomigration

De-Gang Xie, Zhi-Wei Shan*
Xi’an Jiaotong University

Abstract: The phenomenon of mass transport driven by temperature gradient is defined as thermomigration, which is pronounced in gases and liquids, while almost negligible in solids. However, recent studies have shown that in nanoscale objects, due to the decrease of the characteristic transport distance down to the nanoscale, thermomigration could become a powerful mechanism to induce rapid morphological changes. By in situ transmission electron microscopy, we demonstrate that the contact between a cold nano-tip and a hot solid substrate (>300 °C) can build up an extremely high temperature gradient which can drive large mass flux. When drawing back the cold nano-tip, the transported atoms will continuously deposit onto the cold tip and form a nanowire. Such mass transport mechanism can be exploited for producing single-crystalline aluminum, copper, silver and tin nanowires. This experimental work shows that through rapid short range surface diffusion, solids can rival liquids in rapid morphological changes. We further discovered that, a thin neck-shaped ligament containing a grain boundary (GB) usually forms between the hot and the cold ends during uniform growth, sustaining an extremely high temperature gradient. This GB-containing ligament is quite robust and can adapt to varying drawing directions and velocities, imparting good controllability to the nanowire growth. This method is expected to be applicable to construction of 3D nanostructures on the solid surface or nanodevice repair.
Keywords: thermomigration; single-crystalline metal nanowires; in situ transmission electron microscopy

    利用热迁移从固体表面直接快速构建单晶金属纳米线

解德刚，单智伟*
西安交通大学 

摘要:温度梯度驱动物质扩散的现象称为热迁移，该现象在气体和液体中十分显著，在固体中 却只能缓慢进行。然而最近的研究表明，在微纳尺度结构中，由于物质传输距离的缩短，热迁 移有可能在很短时间内改变固体的形状。本工作采用原位透射电子显微实验技术，利用一个冷 的钨针尖与热的金属基体接触，从而构建出高温度梯度引发热迁移，并移动针尖引导热迁移物 质重新沉积，生成单晶铝、铜、银和锡纳米线。该实验证实了在纳米尺度，固体可以通过短程 快速的表面扩散，获得像液体一样发生迅速形貌变化的能力。我们还进一步发现，纳米线的均匀生长需要有一个含有晶界的颈状韧带在热端和冷端之间形成，从而维持一个极高的温度梯度。 该韧带对针尖的提拉动作变化具有很强的适应能力，随提拉的方向和速率改变自身的大小和形 状，这一特点使得固体提拉法对纳米线相貌及尺寸具有一定的可控性。该方法有望拓展应用在 固体表面构建 3D 纳米结构，纳米器件修复等领域。

关键词:热迁移;单晶金属纳米线;原位透射电子显微镜