In situ Control of Atomic-Scale Si Layer with Huge Strain in the Nanoheterostructure NiSi/Si/NiSi through Point Contact Reaction

Nanoheterostructures of NiSi/Si/NiSi in which the length of the Si region can be controlled down to 2 nm have been produced using in situ
point contact reaction between Si and Ni nanowires in an ultrahigh vacuum transmission electron microscope. The Si region was found to be
highly strained (more than 12%). The strain increases with the decreasing Si layer thickness and can be controlled by varying the heating
temperature. It was observed that the Si nanowire is transformed into a bamboo-type grain of single-crystal NiSi from both ends following the
path with low-activation energy. We propose the reaction is assisted by interstitial diffusion of Ni atoms within the Si nanowire and is limited
by the rate of dissolution of Ni into Si at the point contact interface. The rate of incorporation of Ni atoms to support the growth of NiSi has
been measured to be 7 × 10-4 s per Ni atom. The nanoscale epitaxial growth rate of single-crystal NiSi has been measured using high-resolution lattice-imaging videos. On the basis of the rate, we can control the consumption of Si and, in turn, the dimensions of the
nanoheterostructure down to less than 2 nm, thereby far exceeding the limit of conventional patterning process. The controlled huge strain
in the controlled atomic scale Si region, potential gate of Si nanowire-based transistors, is expected to significantly impact the performance
of electronic devices.

通过在超高真空透射电子显微镜中，利用硅纳米线与镍纳米线之间的原位点接触反应，已成功制备出长度可调控至2纳米的NiSi/Si/NiSi纳米异质结构。研究发现，硅区域呈现出极高的应变状态（超过12%），且随着硅层厚度的减小，应变程度也随之增加，通过调节加热温度可进行控制。观察发现，硅纳米线从两端开始，沿着具有低活化能的路径，转变为单晶NiSi的竹节状晶粒。我们提出，该反应由硅纳米线内部的镍原子间隙扩散所辅助，并且受限于镍在点接触界面溶解入硅的速率。已测量到镍原子融入以支持NiSi生长的速率为每镍原子7 × 10^-4秒。通过高分辨率晶格成像视频，已测量出单晶NiSi的纳米级外延生长速率。基于这一速率，我们可以控制硅的消耗，进而调控纳米异质结构的尺寸至小于2纳米，从而远远超出传统图案化工艺的极限。在可控的原子尺度硅区域内，巨大的应变有望成为基于硅纳米线晶体管的潜在栅极，预计将对电子器件的性能产生显著影响。