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

在本研究中，我们研制了横向分辨率< 1 nm的扫描超声探针显微镜，并研究了其中涉及的物理过程。样品表面能-为了定量测量样品表面和亚表面的局部复弹性，对探针与样品的界面和悬臂梁的动力学进行了分析在悬臂梁底座或扫描仪上安装换能器，制成扫描超声探针显微镜，能够对悬臂梁或样品施加超声振动。在悬臂梁共振频率以下和以上的不同频率和不同超声振幅下，对Si和GaAs单晶进行了力曲线测量。用迈克尔逊干涉仪对振动振幅进行了标定。得到的力曲线具有以下共同特征：1）在无振动情况下，在接近阶段观察到小的“跳入”，而在缩回阶段观察到大的“跳出”。2)在增大振动幅度的过程中，“跳出”位置迅速接近“跳进”位置。3）在一定振幅以上，在接近和收缩阶段都观察到了一个新的“排斥跳跃”，并通过考虑悬臂梁的运动，用有限差分法对这一结果进行了数值分析。在分析中，我们给出了针尖和样品的弹性，阻尼，粘附力，并假设针尖-样品相互作用的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.