Scanning Electron-Acoustic Microscopy: Do You Know Its Capabilities?

Abstract

Characterization of materials usually requires microscopy techniques. Some of the most useful are based on a scanning microscope and involve scanning the sample surface with a focused beam (e.g., photons, electrons, ions, etc.). For example, photoacoustic microscopy uses a laser beam, acoustic microscopy uses an ultrasound beam, and scanning electron microscopy uses an electron beam. The interaction between the material and the beam produces a signal that can be used to generate a two-dimensional image.In scanning photoacoustic microscopy (SPAM), an intensity-modulated light beam is used to produce oscillations in the surface temperature of the sample. These oscillations induce changes in the pressure of a fluid in the photoacoustic cell as a consequence of the periodic heat conduction from the surface to the cell fluid. Subsequently many material-characterization methods have employed the same philosophy as SPAM, using a modulated beam as an excitation probe. The breadth of such techniques is due to the large number of possible excitation sources and signal detectors that have been proposed to probe the specimen response. In particular, scanning electron-acoustic microscopy (SEAM), also referred to as thermal wave microscopy, is a technique based on the utilization of a scanning electron microscope developed in 1980 and applied in recent years to material characterization. It can be considered an additional mode of scanning electron microscopy (SEM), which uses the generation of acoustic waves in the sample. Most reviews have concentrated on the application of SEAM to metals and semiconductors. However many other possibilities exist.