Vectorial scanning force microscopy using a nanowire sensor

TL;DR

This paper demonstrates a vectorial scanning force microscopy technique using a nanowire sensor that maps force derivatives and electric fields with high sensitivity, leveraging the nanowire's split flexural modes for detailed surface imaging.

Contribution

It introduces a novel method utilizing a single nanowire's orthogonal flexural modes to perform vectorial force microscopy and electric field imaging.

Findings

Successfully mapped tip-sample force derivatives in the plane.

Differentiated forces from charge and polarizability.

Achieved high sensitivity in weak force detection.

Abstract

Self-assembled nanowire (NW) crystals can be grown into nearly defect-free nanomechanical resonators with exceptional properties, including small motional mass, high resonant frequency, and low dissipation. Furthermore, by virtue of slight asymmetries in geometry, a NW's flexural modes are split into doublets oscillating along orthogonal axes. These characteristics make bottom-up grown NWs extremely sensitive vectorial force sensors. Here, taking advantage of its adaptability as a scanning probe, we use a single NW to image a sample surface. By monitoring the frequency shift and direction of oscillation of both modes as we scan above the surface, we construct a map of all spatial tip-sample force derivatives in the plane. Finally, we use the NW to image electric force fields distinguishing between forces arising from the NW charge and polarizability. This universally applicable technique enables a form of atomic force microscopy particularly suited to mapping the size and direction of weak tip-sample forces.