金属纳米线冷焊接机制的原子级模拟研究

The welding techniques of metallic nanowires have been attracting extensive interest with the rapid development of nanoelectronic devices and nanoelectromechanical systems. Recently, cold welding was successfully performed on gold nanowires at remarkably low loads in experiments. However, attributing to the difficulties in observation induced by the nanoscale sample dimention, the deep mechanism has not been well understood: even the exact contact geometry and applied load at the joining interface were unable to be quantified. Therefore, this project intends to investigate the cold welding process of metallic nanowires by molecular dynamics methods. The study aims to obtain a clear picture of the atomic diffusion and the surface relaxation, make a quantitive analysis of the microstructure evolution and the distribution of stress and strain,and explore the influences of diameter, orientation, element types and contact geometry of metallic nanowires on welding process. In addition, this investigation will clarify the effects of twin boundaries on both welding process and quality by comparing the results of single-crystalline and twinned structures, thus reveal the applicability of cold weling in metallic twinned nanowires, which are one of the most potential materials in microcircuits. The purpose of ascertaining these basic problems is to provide theoretical supports for in situ processing of the new generation of nanodevices and nanosystems.

随着纳电子器件与纳机电系统的快速发展，有关金属纳米线焊接技术的研究吸引了广泛的关注。最近，实验证实金纳米线可在较小的机械外载下实现冷焊接。然而，由于尺度效应带来的观测困难，此过程的深层机制仍不清楚，甚至连焊接触点的精确几何情况以及界面处的外载大小，都只能进行估算。因此，本项目拟采用分子动力学方法，对金属纳米线的冷焊接过程展开模拟研究，期望得到冷焊接过程中有关原子扩散、表面弛豫的原子级图像，并对纳米线的微结构演化以及应力应变分布做出定量的分析。然后，在此基础上，获得金属纳米线的直径、晶向、元素种类以及接触几何对焊接过程的影响规律，并进一步针对在微电路中极具应用潜力的孪晶金属纳米线，探索晶界的存在对焊接机制与结果的影响，揭示冷焊接技术对孪晶金属纳米线的可适用性。预期通过对以上基础问题的研究，为新一代纳米器件与纳米系统的原位加工工艺提供理论支持和科学依据。

随着纳电子器件与纳机电系统的快速发展，有关金属纳米线焊接技术的研究吸引了广泛的关注。已有实验证实金纳米线可在较小的机械外载下实现冷焊接。然而，由于尺度效应带来的观测困难，此过程的深层机制仍不清楚，甚至连焊接触点的精确几何情况以及界面处的外载大小，都只能进行估算。本项目采用分子动力学方法，对金属铜纳米线的冷焊接过程展开了模拟研究，得到了冷焊接过程中有关原子扩散、表面弛豫的原子级图像，并对纳米线的微结构演化以及应力-应变响应做出了定量的分析。然后，在此基础上，获得金属纳米线的长径比与元素种类对焊接过程的影响规律，并进一步针对在微电路中极具应用潜力的孪晶金属纳米线，探索了晶界的存在对焊接机制与结果的影响，揭示了冷焊接技术对孪晶金属纳米线的可适用性。对焊接过程的结构演化分析发现，孪晶纳米线的接触区域可恢复完美的晶格结构。这说明，在较小的机械加载下，同样可实现孪晶纳米线的冷焊接。同时，孪晶金属纳米线中由于晶界对位错形核与运动的排斥，会导致更大的应力积聚，从而形成与单晶金属纳米线中完全不同的应力-应变响应。本项目通过对以上基础问题的研究，为新一代纳米器件与纳米系统的原位加工工艺提供了理论支持和科学依据。