Adhesion Force Measurements Using an Atomic Force Microscope Upgraded with a Linear Position Sensitive Detector

Abstract

The atomic force microscope (AFM), in addition to providing images on an atomic scale, can be used to measure the forces between surfaces and the AFM probe. The potential uses of mapping the adhesive forces on the surface include a spatial determination of surface energy and a direct identification of surface proteins through specific protein-ligand binding interactions. The capabilities of the AFM to measure adhesive forces can be extended by replacing the four-quadrant photodiode detection sensor with an external linear position sensitive detector and by utilizing a dedicated user-programmable signal generator and acquisiton system. Such an upgrade enables the microscope to measure in the larger dynamic range of adhesion forces, improves the sensitivity and linearity of the measurement, and eliminates the problems inherent to the multiple repetitious contacts between the AFM probe and the specimen surface.

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…For larger deflections the difference in the two signals is not proportional to the cantilever deflection anymore because of the distinct shape of the reflected laser beam. To increase the dynamic range the split photodiode has been replaced by a linear position sensitive device or an array detector [79,192,193].…”

Ultrafine cohesive powders: From interparticle contacts to continuum behaviour

“…Some groups have chosen to build custom made devices optimised for this technique (Butt 1994;Pierce 1994;Craig 1996;Braithwaite 1997;Toikka 2001), because standard AFMs have some technical limitations that make them inadequate for colloidal probe experiments. The tip apex of an AFM tip typically has a radius of 5 -50 nm, whereas the radii of colloidal probes are in the range of 1 -50 µm, resulting in much higher adhesion forces.…”

Novel Method of Measuring Cantilever Deflection during an AFM Force Measurement

“…The z-piezo driving signal generated from a computer-controlled function generator 6 was used to create a single movement of the probe toward and away from the specimen surface without "engaging" the two together prior to the measurement. The optical lever signal and the z-piezo driving signal were used to create the cantilever deflection vs piezo displacement plot.…”

“…[1][2][3][4][5][6] Typically, the ligandmodified AFM probe is brought in contact with a specimen surface containing immobilized receptors. Superposition of some ligands and complementary receptors results in the formation of ligand-receptor bonds whose strength is tested by withdrawing the probe away from the surface, creating a tension on the bonds.…”