Transmission Electron Microscopy of Ion Erosion Thinned Hard Tissues

Abstract

Material is removed from surfaces undergoing bombardment with nonreactive noble gas ions. Thus, this process can be used to thin down thin samples of hard materials in order that they may be examined in the transmissioh electron microscope (TEM) (6, 7, 1). However, the rate of removal of material depends upon several factors which may vary over very small areas; these factors include the angle of incidence of the ion beam with respect to the surface and with respect to the crystallographic orientation of the surface features. Regions having different compositions, for example, in the case of the hard tissues, differences in the proportion of calcium phosphate to organic matrix, also lead to differences in the rate of removal of superficial layers. An ion bombarded surface will therefore be etched to produce surface relief (or variations in the thickness of a section) if there are local variations in composition or orientation. Boyde and Stewart (3, 4), Stewart and Boyde (15) and Boyde, Switsur and Stewart (5) thus reported etching of enamel prisms due to variations in crystallographic orientation across prisms, a lack of etching in the uniformly orientated outer surface zone of the enamel and etching due to compositional variations in dentine, where the more highly mineralized peritubular dentine was removed at a lower rate than the intertubular dentine.