Microstructure of nanoscratched semiconductors

The crystal defect structure of InP following scratches with an atomic force microscope (AFM) tip has been studied by transmission electron microscopy. The (100) surface of InP single crystals were scratched along <100> and <110> directions with an AFM diamond tip under applied normal forces ranging from 7 to 120 μN. For a given applied force, deeper plastic flow has been observed in the <110> case than in the <100> case. Under increasing applied forces, plastic flow was first observed at 15 μN for <110>, and at 30 μN for <100>. The crystal deformation during a scratch event has been observed to consist of three stages: (a) surface conformation to the shape of the AFM tip during the early stages of the process, and it is associated with slip at the nanoscale with the formation of an inverted triangular region with high dislocation density; followed by (b), a sudden displacement (pop-in) that signals the beginning of downward slip at the bulk scale; and (c), for sufficiently large forces, recovery of the bulk elastic strain by upward slip (pop-up). The <110> scratch direction is aligned along the {111} slip planes, and yields at lower applied forces than in the <100> case. Dislocations introduced by scratching are mostly screw type, as determined by series of g.b analysis.