Atomic force microscopy for next generation metrology of surfaces

The aim of this project is to understand how tip bending affects image quality in atomic force microscopy (AFM) and develop new approaches to correct the errors caused. AFM uses a sharp tip attached to a flexible cantilever to trace out the surface of a sample and form an image. The sharp tip allows very small (down to sub-nanometre, less than a billionth of a metre) features on the surface to be sensed, and attaching the tip to a flexible cantilever allows the signal to be detected using a conventional laser. AFM is an established critical tool for nano-surface-metrology. Modern AFM tips have high aspect ratio (i.e. thin and sharp), and we have recently shown that this means the tip itself tends to bend when imaging surfaces. Unfortunately, using the conventional approach to AFM, if the tip bends, we no longer know which part of the surface we are imaging, and the picture we obtain is distorted. For industrial metrology purposes, and for scientific research, this creates an important source of error, up to tens of nanometres, which has largely been overlooked. Using an approach we recently developed the student will build a full understanding of the bending induced error in both conventional samples and when imaging silicon chips (with Infinitesima). The student will then explore how to fully characterise tip bending during imaging so that the true surface topography can be revealed.