Observation and manipulation of subsurface atomic layers

在微电子机械系统(MEMS)和纳米技术中，亚表面原子层的观测和操纵是确定材料和器件可靠性的关键技术。在这个研究项目中，我们开发并应用了超声原子力显微镜(UAFM)来建立对亚表面原子层的观察和操纵。在UAFM中，可以观察到位于10 nm或更深的亚表面缺陷，横向分辨率为5 nm。层状晶体中伴随着刃位错的亚表面间隙被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MoS_2，观察到亚表面边缘位错。我们发现共振频率明显低于无缺陷模型的共振频率。在接触半径大于5 nm的100 nN以上的载荷作用下，谐振频率接近无缺陷模型，但在较低载荷下的共振频率较低。通过对不同载荷下HOPG位错行为的观察，发现载荷增加285nN时，位错横向移动40 nm，载荷减小，位错恢复到原来的位置。为了解释这一结果，我们提出了位错横向运动的模型。这一大横向运动的发现证实了地下原子层的操纵。建立了由硬化或软化弹簧表示的接触的非线性振动分析，模拟了亚表面原子层之间的亚表面间隙的开闭行为。通过比较观察和计算的共振频率和共振谱形状对缺陷区和无缺陷区的显著依赖关系，验证了这些方法。

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.