An atomic force microscope tip designed to measure time-varying nanomechanical forces

Abstract

Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, interacts and retracts from the sample surface, is the most common AFM imaging method. The tip experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample, yet conventional AFM tips are limited in their ability to resolve these time-varying forces. We have created a specially designed cantilever tip that allows these interaction forces to be measured with good (sub-microsecond) temporal resolution and material properties to be determined and mapped in detail with nanoscale spatial resolution. Mechanical measurements based on these force waveforms are provided at a rate of 4 kHz. The forces and contact areas encountered in these measurements are orders of magnitude smaller than conventional indentation and AFM-based indentation techniques that typically provide data rates around 1 Hz. We use this tool to quantify and map nanomechanical changes in a binary polymer blend in the vicinity of its glass transition.

A nanomechanical interface to rapid single-molecule interactions

“…Calculations of tip-sample force waveforms from the torsional vibration signals are carried out in Labview (National Instruments). We followed the same procedures reported previously 17 to invert the transfer function of the torsional mode and eliminate cross talk from large vertical deflection signals; however, every oscillation cycle is analysed individually. This approach is based on a framework used by Stark et al 34 for the analysis of higher harmonic vibrations.…”

“…The new design is using the torsional harmonic cantilever concept that was developed for high-resolution nanomechanical analysis of samples 17,18 . These T-shaped cantilevers generate high-speed force-distance curves during the tapping-mode AFM imaging process.…”

The use of the PeakForceTMquantitative nanomechanical mapping AFM-based method for high-resolution Young's modulus measurement of polymers

“…The manufacturer claims that the technique can measure Young's moduli of materials ranging from soft gels (~1 MPa) to rigid polymers (>20 GPa), exceeding other AFM based techniques (e.g. HarmoniX [9]) for nanoscale material characterisation.…”

Measuring Electric Field Induced Subpicometer Displacement of Step Edge Ions

“…The site-independent interactions are invariant in the lateral directions so that they do not show up in the torsional signal [37]. Furthermore, the higher mechanical quality factor, compared to that of the flexural mode, can improve the force sensitivity itself [38]. Such extreme sensitivity to site-dependent interaction [39] allows us to measure the potential variations near the step edge of a prototype insulating ionic crystal LiF and investigate its changes with respect to an applied bias voltage.…”