Dual Friction Force/Fluorescence Microscopy

Abstract

Friction force microscopy (FFM) is a mode of atomic force microscopy (AFM) that quantifies both normal and horizontal forces against substrates. Recent improvement in its accuracy at nanonewton ranges and the possibility of combining AFM with fluorescence microscopy enabled the simultaneous characterization by FFM and fluorescence microscopy. This Tutorial describes the operation principle of the dual friction force/fluorescence microscopy setup and highlights its emerging applications in mechanochromic materials.

Mechanical Properties of Polydiacetylene Multilayers Studied by AFM Force Spectroscopy

“…Gold-coated silicon nitride triangular probes with a spring constant of approximately k = 26 N/m (AC160TSA-R3, Oxford Instruments, UK) were used for all the measurements. The actual vertical spring constant, K v , was calibrated through the thermal noise method. , The deflection sensitivity was roughly estimated from the force curve on the substrate (control experiment). Nevertheless, each force curve on PDA films was further corrected in such a way that the curve on the solid substrate (region iii in Figure e) becomes vertical as glass is incompressive.…”

“…A limitation in their experiments was that the measured shear forces were qualitative, as the standard AFM quantifies only vertical forces. To overcome this issue, recently, we have introduced friction force microscopy, a mode of AFM that quantifies both vertical and lateral (shear) forces, , to provide quantitative evidence for the anisotropic mechanochromism. , Based on the same technique, we have also found that Young’s modulus of PDA films is strongly correlated with their force sensitivities at the nanoscale, where softer PDAs are more force sensitive . These local force applications by AFM tips are believed to induce a crystal-to-amorphous transition in the PDA structure by breaking the inter- and intramolecular interactions, such as hydrogen bonds between PDA headgroups and the hydrophobic interactions between the alkyl chains, as the morphology after AFM scanning was typically rougher.…”