Investigation of tip current and normal force measured simultaneously during local oxidation of titanium using dual-mode scanning probe microscopy

In this reported work, scanning probe microscopy is used to perform localised oxidation of Ti as a bottom-up nanofabrication method. The effects of normal force setpoint and oxidation voltage on oxide nanofeatures during atomic force microscopy (AFM) mode and scanning tunnelling microscopy (STM) mode oxidation are investigated. The normal force between the probe and sample and electrochemical current in the anodic oxidation process are measured using a custom control system, and the effects of these variables on the size and resistivity of oxidised nanopatterns are investigated. It is shown that a direct relation exists between oxidation voltage and written oxide resistivity as well as written feature width in the STM mode oxidation. In AFM mode oxidation, the normal force setpoint is shown to have a positive correlation with feature size, but an inverse relation with oxide resistivity. By leveraging the presented system´s ability to operate in both AFM and STM mode, the dynamics and feature fabrication dependencies are shown to be a continuum of writing voltage and normal force. This reported work suggests that STM and AFM mode oxidation can be thought of as similar processes but working at different operating points in terms of normal force and tip-surface spacing.