20nm以下金属、金属合金的结构、力学行为及性能调制

To meet the demand of developing higher-level-performance MEMS and NEMS, the dimensions of the structure units in many devices are continuously reduced to improve their integrities in recent years. This dimension-reduction makes the metal components, frames, units and interconnects of the nanodevices generally approach the size around 20nm. However, nanometals with sizes smaller than 20nm usually exhibit quite different physical (mechanical, electrical, thermal etc.) properties, comparing to their bulk counterparts, due to size effects and surface effects. Hence, whether nanometals having such sizes can still fix the requirements of NEMS design is still unknown. Several research groups, including ours, have started some investigations of the mechanical behaviors of nanometals with sizes smaller than 20nm. The results show that the mechanical behaviors of nanometals are crucially determined by their dimensions and free surfaces. Ag nanocrystals having sizes around 10nm even behave as liquid nanodroplets during deformation. However, the essential mechanisms and determinants of such unique properties in nanometals are still unknown. In this proposal, through the aberration-corrected HRTEM and in situ STM-TEM/AFM-TEM platforms, we plan to systemically investigate the mechanical behaviors of nanometals with size less than 20nm. We mainly focus on the issues, (1)the relationship between mechanical behavior and nanometal dimension, their physical mechanisms, (2) how free surfaces affect the mechanical behaviors in nanometals, (3) how temperature affects the mechanical behavior in nanometals, (4) the mechanical behaviors of nanoalloys and how to modulate the mechanical property of nanometals. Through these investigations, we hope to establish a deep understanding of the mechanical behavior of nanometals, which can further provide important information for future NEMS design.

随着MEMS的发展和NEMS的突破，器件中许多结构单元、互连线宽的尺寸已开始走向20nm以下。在该尺度下，金属结构常呈现出不同于其宏观状态下的新异物性，其力、电、热学行为以及结构稳定性是否依然满足器件要求是当前材料学、电子学发展中所面临到的关键问题。国内外对金属纳米线的相关研究指出，纳米金属的塑性行为严重受其表面、尺寸的影响；本课题组研究发现，10nm大小的Ag纳米晶已不再遵从传统塑性理论，而呈现出“液态”赝弹性。然而，对20nm以下金属结构力学行为的探索才刚刚起步，其物理机制、决定因素等关键问题都有待于进一步认知。本项目拟通过球差矫正的高分辨电子显微技术并结合原位力电操控、测试平台，系统化研究20nm以下金属、金属合金的力学行为，揭示其奇异力学行为的机制，并探索实现其力学性能调制的方法。本项目的开展既有利于完善纳米金属力学行为的相关理论，也可为NEMS器件的设计、制造奠定材料方面的基础。

纳机电系统（NEMS）和IC已进走入了7nm以下的特征尺寸，许多电子器件中的结构单元、互连线宽的尺寸也在迎合新工艺相应地逐步减小。在器件中，一些金属结构/互联的特征尺寸已走向20nm以下，在该尺度下，金属材料常常呈现出不同于其宏观状态下的新异物性，其力学、电学、热学行为以及结构稳定性是否依然满足未来器件设计要求是当前材料学、电子学发展中所面临到的重要问题之一。针对该问题，本项目提出以纳米金属为主要研究对象，通过原位电子显微技术研究20nm以下金属、合金、异质结构的力学、热学行为机制及影响因素，探索纳米金属新异物性与尺寸、表/界面之间的本质关联，探索纳米金属新异物性的调控和功能化应用。.通过项目研究，我们（1）揭示了纳米金属、金属合金赝弹性的产生根源与机制，揭示了在20nm以下尺度，表面扩散对纳米金属、合金力学行为的关键性影响；（2）研究了表面扩散型变形机制和位错主导型变形机制受温度的影响规律，揭示了这两种变形机制之间随颗粒尺寸、温度变化下的竞争关系；（3）测定了纳米金属的浸润特性，揭示了纳米金属浸润特性随尺寸的变化规律；（4）实验测定了纳米金属Ag的表面能并验证了其表面热稳定性，澄清了关于表面能、表面稳定性长期以来存在的争议；（5）揭示了AuAg、CuAg合金在高温下的结构稳定性和相萃取/偏析机制，揭示了表面效应对其异质界面类型的影响机制；（6）制备了AuAg异质纳米结构、Ag颗粒组装结构，基于其特性制备了功能衬底并应用于SERS传感探测；（7）发明了一种可以限域调控单颗半导体纳米颗粒结构的方法；（8）发明了一种可以原位制备纳米合金颗粒的技术方法，可以获得表面极其清洁的纳米合金颗粒，可为认知气相纳米颗粒的成核、生长、扩散融合等动力学过程提供直观的物理图像。