Observation and manipulation of subsurface atomic layers

在微机电系统（MEMS）和纳米技术中，亚表面原子层的观测和操纵是建立材料和器件可靠性的关键技术。在本研究计画中，我们发展并应用超音波原子力显微镜（UAFM）来观察及操控次表面原子层。在UAFM中，可以以5 nm的横向分辨率观察到位于10 nm或更深处的亚表面缺陷。一个亚表面的间隙伴随着层状晶体中的刃位错成像为低接触刚度区。我们将UAFM应用于高取向热解石墨（HOPG）和二硫化钼，并观察到亚表面刃位错。我们发现，共振频率是显着低于无缺陷模型。当载荷大于100 nN，接触半径大于5 nm时，谐振频率接近无缺陷模型的谐振频率，但载荷越小，谐振频率越低。通过对不同载荷下HOPG中位错行为的观察，发现当载荷增加285 nN时，位错横向移动40 nm，当载荷减小时，位错又回到原来的位置。为了解释这一结果，我们提出了一个位错横向运动的模型。大的横向运动的这一发现证实了亚表面原子层的操纵。一个非线性振动分析的接触所代表的一个硬化或软化弹簧的开发模型的打开-关闭行为的亚表面原子层之间的间隙。这些方法进行了验证，通过比较观察到的和计算出的响亮的依赖性的共振频率和形状的共振谱，无论是对缺陷的区域和无缺陷的区域。

Observation and manipulation of subsurface atomic layers is a key technology to establish the reliability of materials and devices in the micro electromechanical systems (MEMS) and in the nanotechnology. In this research project, we developed and applied the ultrasonic atomic force microscopy (UAFM) to establish observation and manipulation of subsurface atomic layers. In UAFM, subsurface defects located at the depth of 10 nm or more can be observed with the lateral resolution of 5 nm. A subsurface gap accompanied by an edge dislocation in layered crystals is imaged as a low-contact-stiffness area. We applied UAFM to highly oriented pyrolytic graphite (HOPG) and MoS2 and observed subsurface edge dislocations. We found that the resonance frequency is significantly lower than that of the defect-free-model. Under the load higher than 100 nN where the contact radius is larger than 5 nm, the resonance frequency approached that of the defect-free-model, but it is lower under the lower load. Through observation of the dislocation behavior in HOPG under different loads, we found that the dislocation moved laterally by 40 nm us the load increased by 285 nN, and ii returned to the original position as the load decreased. To explain this result, we proposed a model for the lateral motion of the dislocation. This finding of the large lateral motion confirms the manipulation of subsurface atomic layers. A nonlinear vibration analysis of the contact represented by a stiffening or softening spring was developed that models the opening-closure behavior of the subsurface gap between subsurface atomic layers. These methods were verified by comparing the observed and calculated loud dependence of the resonance frequency and the shape of resonance spectra, both on a defect area and defect-free area.