IMAGING OF CRACKS IN SEMICONDUCTORS USING SCANNING TUNNELING MICROSCOPY

Scanning tunneling microscopy (STM) has developed into a useful tool for atomic-scale characterization of material surfaces. It has a great advantage over other high-resolution techniques in that no extensive sample modification, such as thinning or polishing, is required to obtain atomic resolution images. This is especially useful in the field of fracture, as the vast majority of high-resolution images of fracture processes are made in the transmission electron microscope, where thin-film effects may greatly modify crack tip stresses and dislocation structures. This investigation involved imaging of cracks introduced in single crystals of galena (PbS) by rapid indentation at 77 K. Images were obtained both at the arrested crack tip and along the flanks of the crack in the dynamic growth region. Measurements were made of both crack-tip morphology and upsets observed along the flanks of the crack. The latter is discussed in terms of plasticity upsets associated with dislocation emission from rapidly growing cracks. Effects of STM tip geometry and scan conditions on the resulting image of the cleavage crack, as well as work in progress on other material systems, is discussed.