ANALYSIS OF THE SCANNING ELECTRON-MICROSCOPE MIRROR-IMAGE BASED ON THE DIELECTRIC SURFACE MICROSTRUCTURE

This paper addresses hitherto unexplained phenomena associated with th e electrostatic mirror technique, such as (i) the influence of the, su rface microstructural parameters of a polycrystalline dielectric (e.g. alumina) on mirror images, and (ii) the distortion of mirror images. The formation of a mirror image on an as-machined alumina surface was found to be nearly impossible, but on a polished specimen, possessing low surface damages, mirror images were easily formed. A smooth and lo w-damage surface seems to be a prerequisite for the formation of a mir ror image. The size of mirror images, observed at different locations on a polished alumina surface, was found to vary significantly, indica ting that an inhomogeneous surface charging occurs in polycrystalline dielectrics. It was shown that the variation in the grain and grain bo undary volumes constituting the charged region is responsible for the variation in the size of the mirror image. The distortion of the mirro r images was studied using single crystal quartz specimens. The asymme try of the equipotential boundary-caused by (i) the tilt of the crysta l axis (theta not-equal 0-degrees) with respect to the probing electro n beam, or by (ii) the asymmetrical electron interaction volume, i.e., deviation from the standard pear shape-was demonstrated to be respons ible for the distortion of the mirror images.