Evaluation of local elasticity and inelasticity with nonoscale spatial resolution with scanning ultrasonic force microscope

在这项研究中，我们研制了横向分辨率为&1 nm的扫描超声探头显微镜，并对其所涉及的物理问题进行了研究。为了实现表面和亚表面局部复弹性的定量测量，分别分析了样品-针尖界面的弹性、粘性、表面能对样品和悬臂梁动力学的贡献，对商用原子力显微镜进行了改进，将PZT换能器安装在悬臂梁底座或扫描器上，制成了能够对悬臂梁或样品施加超声振动的扫描超声探针显微镜。在悬臂梁共振频率以下和以上的不同频率下，在不同的超声振幅下，对Si单晶和GaAs单晶进行了力曲线测量。振动幅度用迈克尔逊压力计进行校准。得到的力曲线有以下共同特点：1)在无外加振动的情况下，在接近阶段有小的“跳入”，在收回阶段有很大的“跳出”。2)随着振动幅值的增大，“跳出”位置迅速接近“跳入”位置。3)在一定的振动幅值以上，无论是接近阶段还是收回阶段，都观察到了一种新的“排斥跳跃”，并用有限差分方法对结果进行了数值分析。在分析中，我们给出了针尖和试件的弹性、阻尼力、粘附性，并假定了针尖与试件相互作用的JKR模型。结果定量地解释了1)和2)的特征，证明了分析的有效性。

In this research, we develop the scanning ultrasonic probe microscope with lateral resolution < 1 nm and study the physics involved in it. The contributions of elasticity, viscosity, surface energy at the sample-tip interface to the sample and cantilever dynamics are analyzed distinctively in order to carry out the quantitative measurement on the surface and subsurface local complex elasticity.A commercial AFM is modified by attaching the PZT transducer at the cantilever base or on the scanner to make the scanning ultrasonic probe microscopy which is capable to apply the ultrasonic vibration to the cantilever or the sample. At various frequency below and above the cantilever resonance frequency and at various ultrasonic amplitude, we carry out the force curve measurement on Si and GaAs single crystals. The vibration amplitude is calibrated with Michelson enterferomenter. The obtained force curve has the following common features : 1)In case of no applied vibration, small "jump-in" in the approach phase and large "jump-out" in the retraction phase are observed. 2)Within creasing the vibration amplitude, the "jump-out" position rapidly approaches to the "jump-in" position. 3)At above certain vibration amplitude, a new "repulsive jump' is observed for both approach and retraction phase.These results are analyzed by considering the cantilever motion numerically with the finite difference method. In the analysis, we give the elasticity of the tip and sample, damping, adhesion, and assume the JKR model for the tip-sample interaction. The result explains the features 1)and 2)quantitively and proves the validity of the analysis.