扫描电子声显微镜的信号激发和像的空间分辨率

Signal generation and spatial resolution in scanning electron acoustic microscopy

求解热传导方程及Navier-Stokes方程,得到强度以频率f调制的电子束在一圆盘状试样内所激发的三维应力场。再由压电方程得出与试样直接相耦合的压电换能器的输出信号。并由此理论结果讨论了信号激发机理及像的空间分辨率。它表明,一个交变热源同时激发出热波和声波;在界面上发生的热波-声波的模式转换,与热波和热源两者有关,并取决于两者在界面上的幅值及界面上的梯度大小,同时表明,在扫描电子声显微镜和热波显微镜这类近场成象系统中,像的空间分辨率将与源和散射体之间的距离有关,预计扫描电子声显微镜中最佳的横向分辨率约为聚焦电子束直径的量级。

The thermal conduction and Navier-Stokes equations are used to obtain the stress field generated by an electron beam incident on a disk sample. The piezoelectric equation is then used to obtain the output signal of the transducer coupled to the sample. The results lead to a consideration of a signal generation mechanism and the spatial resolution in scanning electron acoustic microscopy (SEAM). It is shown that both thermal and acoustic waves are generated by time-variable heat source simultaneously and the thermal-to-acoustic mode conversion is dependent on the magnitudes of the thermal wave and the driving source and their gradients at boundary surfaces. It is argued that in the near-field the spatial resolution is dependent on the distance beteween the driving source and scatterer and, at best, the lateral resolution is of the order of the diameter of the focal electron beam. Comparisons with experimental findings in SEAM are presented.