Simultaneous detection of vertical and lateral forces by bimodal AFM utilizing quartz tuning fork sensor with a long tip

Abstract

Simultaneous detection of vertical and lateral forces at the nanoscale by atomic force microscopy (AFM) yields important knowledge on nanotribology. Although silicon (Si) cantilevers are capable of detecting both the forces, it has not been achieved by quartz tuning fork sensors including qPlus sensors. In this study, we found that the tip apex of the qPlus sensor with a long tip oscillates vertically at the lowest resonance frequency (ƒ₁) and laterally at the second lowest resonance frequency (ƒ₂) by the finite element method simulation. The lateral oscillation was experimentally confirmed by atomic resolution imaging, where the imaged atoms were apparently connected when increasing the oscillating amplitude at ƒ₂. We also demonstrated the nanometer-scale friction force measurement by using the developed bimodal AFM. The obtained result was in good agreement with the contact-mode lateral force microscopy utilizing a Si cantilever.