Shikder Md Ruhul Amin, Ramasubramanian Ajaykrishna, Maksud Mahjabin, Yurkiv Vitaliy, Yoo Jinkyoung, Harris Charles T, Vasudevamurthy Gokul, Mashayek Farzad, Subramanian Arunkumar
Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL 60607, USA.
Nanoscale. 2019 May 9;11(18):8959-8966. doi: 10.1039/c9nr02073j.
This paper reports on plastic recovery and self-healing behavior in longitudinally-twinned and [112] orientated SiGe nanowire (NW) beams when they are subjected to large bending strains. The NW alloys are comprised of lamellar nanotwin platelet(s) sandwiched between two semi-cylindrical twins. The loading curves, which are acquired from atomic force microscope (AFM) based three-point bending tests, reveal the onset of plastic deformation at a characteristic stress threshold, followed by further straining of the NWs. This ductility is attributed to dislocation activity within the semi-cylindrical crystal portions of the NW, which are hypothesized to undergo a combination of elastic and plastic straining. On the other hand, the lamellar nanoplatelets undergo purely elastic stretching. During the unloading process, the release of internal elastic stresses enables dislocation backflow and escape at the surface. As a result, the dislocations are predominantly annihilated and the NW samples evidenced self-healing via plastic recovery even at ultra-large strains, which are estimated using finite-element models at 16.3% in one of the tested devices. Finite element analysis also establishes the independence of the observed nanomechanical behavior on the relative orientation of the load with respect to the nanoplatelet. This first observation of reversible plasticity in the SiGe material system, which is aided by a concurrent evolution of segmented elastic and plastic deformation within its grains during the loading process, presents an important new pathway for mechanical stabilization of technologically important group-IV semiconductor nanomaterials.
本文报道了纵向孪晶和[112]取向的硅锗纳米线（NW）梁在承受大弯曲应变时的塑性恢复和自愈合行为。NW合金由夹在两个半圆柱形孪晶之间的层状纳米孪晶薄片组成。通过基于原子力显微镜（AFM）的三点弯曲试验获得的加载曲线显示，在特征应力阈值处开始塑性变形，随后NW进一步应变。这种延展性归因于NW半圆柱形晶体部分内的位错活动，据推测这些部分经历了弹性和塑性应变的组合。另一方面，层状纳米薄片仅经历弹性拉伸。在卸载过程中，内部弹性应力的释放使位错能够在表面回流和逸出。结果，位错主要被湮灭，并且即使在超大应变下，NW样品也通过塑性恢复表现出自愈合，在其中一个测试器件中，使用有限元模型估计超大应变为16.3%。有限元分析还确定了观察到的纳米力学行为与载荷相对于纳米薄片的相对取向无关。在SiGe材料系统中首次观察到可逆塑性，这在加载过程中得益于其晶粒内分段弹性和塑性变形的同时演变，为技术上重要的IV族半导体纳米材料的机械稳定提供了一条重要的新途径。
