Application of AC magnetic field compensation to a scanning electron microscope

The influence of an AC magnetic field on the image of a scanning electron microscope is derived by simple theory. The magnitude of the perturbation using several field intensities is evaluated from measurements carried out on a JSM-50A scanning electron microscope under different imaging conditions using the emissive mode of operation. The performance of a JSM-50A scanning microscope equipped with an automatically compensating device, recently developed for transmission microscopes, is tested under several AC field intensities. It is demonstrated that the influence of an AC magnetic field of power frequency on the image quality is eliminated to a high degree and no difference in image quality exists between micrographs of the same object taken in a low field of about 0.1 A m -1 and in fields as high as 1 A m -1 .