A new metric to assess the tip condition of AFM probes based on three-dimensional data

Atomic Force Microscopy (AFM) is a widely used technique to measure dimensions and material properties on the nanoscale and to realize a range of nanofabrication operations. The effective implementation of AFM-based techniques critically depends on the bluntness of the used tip as this affects directly the achievable resolution. In this paper, a novel metric is proposed to evaluate the tip bluntness of AFM probes. Its main advantage is that it relies on three-dimensional (3D) tip data, which can be obtained in-situ, i.e. without removing the probe from the head of the AFM instrument. Indeed, by using the probe to scan a tip characteriser, it is possible to extract very accurate 3D data on the real shape of the tip apex. Such tip characteriser is a common test structure consisting of an array of silicon sharp pin-like asperities. Based on these data, it is proposed to calculate the ratio of the volume of the tip to the volume of an imaginary cylinder in which the tip is contained. In this way, depending on the measured ratio, the bluntness of the AFM tip can be assessed. The utilisation of this metric is demonstrated on four different non-axisymmetric tips as received from the manufacturer. The obtained results correlate well with the assessment of the condition of these tips evaluated with a different approach, also investigated by the authors.