Current measurements in the intermittent-contact mode of atomic force microscopy using the Fourier method: a feasibility analysis

Abstract

Atomic force microscopy (AFM) is an important tool for measuring a variety of nanoscale surface properties, such as topography, viscoelasticity, electrical potential and conductivity. Some of these properties are measured using contact methods (static contact or intermittent contact), while others are measured using noncontact methods. Some properties can be measured using different approaches. Conductivity, in particular, is mapped using the contact-mode method. However, this modality can be destructive to delicate samples, since it involves continuously dragging the cantilever tip on the surface during the raster scan, while a constant tip–sample force is applied. In this paper we discuss a possible approach to develop an intermittent-contact conductive AFM mode based on Fourier analysis, whereby the measured current response consists of higher harmonics of the cantilever oscillation frequency. Such an approach may enable the characterization of soft samples with less damage than contact-mode imaging. To explore its feasibility, we derive the analytical form of the tip–sample current that would be obtained for attractive (noncontact) and repulsive (intermittent-contact) dynamic AFM characterization, and compare it with results obtained from numerical simulations. Although significant instrumentation challenges are anticipated, the modelling results are promising and suggest that Fourier-based higher-harmonics current measurement may enable the development of a reliable intermittent-contact conductive AFM method.

Soft sample deformation, damage and induced electromechanical property changes in contact- and tapping-mode atomic force microscopy

“…The figure also provides the SEM micrograph of the tip, which showed no attachment of polymeric matter (compare to figure 2). This information could be beneficial in the development of intermittent-contact multi-property techniques, such as the previously proposed intermittent-contact conductive AFM method, whereby electrical properties could be measured simultaneously with low-damage tapping-mode imaging [83]. Reference [83] provides an extensive discussion of the potential applications and benefits, as well as required theoretical and experimental developments associated with such type of characterization.…”