A survey of STM-based methods to measure micro-indentations

Scanning tunnelling microscope (STM) was used to image microindentations made on a gage block using a Vickers indenter. The morphology of the indentations shows that the boundary is not sharply defined and therefore accurate STM-based microhardness measurements need image analysis methods for measuring either the indentation area or a parameter well correlated with the geometry of the indentation. Two methods have been investigated. The first method estimate the level of the undisturbed surface of the tested material before the indentation is made, and the indentation area is subsequently calculated as the intersection between the average of the block surface and the indentation itself. The second method uses a filling algorithm to calculate the ratio between volume and surface of the indentation and the border is obtained from the maximum of this ratio. A factorial analysis was used on a set of experimental data to evaluate the contributions (individual and combined) of several STM imaging parameters to the measurement uncertainty.