Seeing at the Nanoscale 2012

Bristol, July 09-11, 2012

Invited talk by Dr. Jamie Hobbs on "The molecular structure of semi-crystalline polymers imaged with AFM"

Dr. Nic Mullin with a talk on "Quantitative, dynamic lateral force imaging and measurement by Torsional Resonance mode Atomic Force Microscopy".

Ross Carter, Nusrat Sajid, Jake Albon, Rik Bailey, Elisa Leera and Paul Chapman will present their results during the poster session.

 

Quantitative, dynamic lateral force imaging and measurement by Torsional Resonance mode Atomic Force Microscopy

Nic Mullin and Jamie K. Hobbs,
Department of Physics & Astronomy, University of Sheffield, UK.

 
Torsional Resonance (TR) mode Atomic Force Microscopy utilizes torsional cantilever oscillations to allow the measurement of forces in the plane of the sample surface. The dynamic nature of TR mode imaging and favourable properties of torsional cantilever resonances allow high resolution imaging of delicate samples and the simultaneous measurement of forces both parallel and perpendicular to the sample surface. Due to the proximity of the tip to the surface throughout the oscillation cycle, this technique is also of interest for distance regulation in optical and electrical measurements. In the work presented here, the tip-sample interaction in TR mode AFM is studied via the use of both frequency and amplitude modulation. It is demonstrated that, for typical feedback setpoints, TR mode operates under conditions of net-attractive normal force, and that in this regime the tip-sample interaction is mediated by contaminant molecules between the tip and the sample surface. “Layering” of water molecules in the tip-sample contact is observed under ambient conditions and a high sensitivity to lateral discontinuities, such as grain boundaries and step edges, is demonstrated. A simple, analytical solution to the equation of motion of a torsionally oscillating cantilever is presented, which, together with the appropriate contact mechanics allows the extraction of in-plane surface properties from TR mode images and approach curves. Further development of the technique, including optimisation of cantilevers for TR mode, and the combination of TR mode AFM with conventional tapping will also be discussed.