Mapping of Elasticity With Nano-Meter Resolution Using a Mass-Concentrated Cantilever in Atomic Force Acoustic Microscopy

近场声学显微镜如原子力声学显微镜(AFAM)是一种很有前途的成像和评估局部弹性的技术。在AFAM中，带有传感器尖端的微悬臂梁的共振频率给出了样品与尖端之间接触刚度的度量。对于金属和陶瓷等硬质样品，原子荧光检测法的灵敏度明显较低。村冈提出的质量集中悬臂梁为解决这一问题提供了一个理想的解决方案。本研究改进了质量集中悬臂梁的技术，使其能够稳定工作而不会突然发生功能故障。主要研究结果如下：1.建议采用较小的悬臂梁振幅，以抑制多个寄生共振峰。2.延性涂层，如钛/铂，更适合于尖端，而不是像W_2C那样的脆性涂层。后者非常坚硬，但很容易分层。相比之下，延性涂层延长了针尖的使用寿命。本研究还讨论了MC悬臂梁对弹性的定量评估。3.平端针尖极大地简化了评估。接触面积保持不变，接触刚度与粘附力和接触力无关。使用MC悬臂梁和平端针尖的方法对标准样品、钻石和刻蚀硅片给出了很好的评估，误差小于1%，其表面和层的弹性系数定义良好。4.MC悬臂和平端针尖也显示了非常清晰的图像，反映了硬盘、PZT薄膜、沉积碳膜和钛片中的Co-Cr薄膜的样品弹性。疲劳后的钛板表面也观察到了纳米结构，如位错堆积或滑移带。

Near-field acoustic microscopy such as atomic force acoustic microscopy (AFAM) is a promising technique of imaging and evaluating such local elasticity. In AFAM, the resonant frequency of a micro-cantilever equipped with a sensor tip gives a measure of the contact stiffness between a sample and a tip. For stiff samples like metal and ceramics, AFAM is confronted with significantly low sensitivity. A mass-concentrated (MC) cantilever proposed by Muraoka gives an ideal solution for the problem.This study refined the technique of MC cantilevers so as to work stably without abrupt failures of its functions. The results are summarized as follows :1.Small amplitudes of the cantilever are recommended so that many parasite resonant peaks are depressed.2.Ductile coating such as Ti/Pt prefers for the tip rather than brittle coating like W_2C. The latter is very hard but easily delaminated. In contrast the ductile coating prolong the lifetime of the tip.Quantitative evaluation of elasticity using MC cantilevers also was discussed in this study.3.A flat-ended tip greatly simplifies the evaluation. The contact area is kept constant with the contact stiffness independent of the adhesion force and the contact force. The present method using a MC cantilever and a flat-ended tip gives a good evaluation with less than one percent of error for standard samples, diamond and etched Si wafers, having well-defined elastic coefficients for its surface, layers.4.The MC cantilever and a flat-end tip also demonstrated very sharp images reflecting sample elasticity for Co-Cr thin film in hard disks, PZT thin film, deposited carbon film, and Ti sheet. Fatigued surfaces of Ti sheets also were examined for nano-structures such as dislocation piling or slip bands.