Bi-modal AFM measures 3D force fields


Rebecca Pool

Friday, May 19, 2017 - 19:00
Image: Bi-modal atomic force microscopy provides 3D force vector maps with subatomic resolution.
Researchers from Osaka University, Japan, have developed a new atomic force microscopy technique - bi-modal AFM - that can measure the three-dimensional force fields of atoms.
A precisely controlled tip of the AFM cantilever is moved over a material surface at two different frequencies to provide information about the material surface in both vertical and parallel directions.
Crucially, bimodal AFM obtains information about material surfaces in the X, Y, and Z directions on the subatomic scale.
The researchers measured the total force between an AFM tip and material surface in 3D using a germanium surface as a substrate. 
"A clean Ge(001) surface has alternately aligned anisotropic dimers, which are rotated by 90° across the step, meaning they show a two-domain structure," highlights Professor Yoshitaka Naitoh from Nanophysics.
"We probed the force fields from each domain in the vertical direction by oscillating the AFM tip at the flexural resonance frequency and in the parallel direction by oscillating it at the torsional frequency," he adds.
The cantilever is simultaneously oscillated laterally and vertically to determine the vector mapping over the buckled dimers on the Ge(001) surface 
The team first expressed the force components as vectors, providing the vector distribution above the surface at the subatomic scale.
Computer simulations supported the experimental results and shed light on the nature of chemical tip termination and morphology.
As Naitoh points out, "Our measurements will aid understanding of the structure and chemical reactions of functionalized surfaces."
The developed bimodal AFM approach will allow researchers to investigate the physical properties of materials in greater detail on the nanoscale, which should facilitate development of devices, nanotechnology, and friction/lubrication systems.
Research is published in Nature Physics.
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