Improved estimation of contact compliance via atomic force microscopy using a calibrated cantilever as a reference sample

A method to improve accuracy of surface compliance determination by atomic force microscopy is presented, based on using calibrated cantilevers as the reference samples. During each work session, a 1-D compliance map of a reference cantilever is calculated from force–indentation curves along its axis, by the standard ‘indentation mode’. An independent measurement of local compliance on the reference cantilever is obtained by 2-D imaging in constant deflection and using analytical equations based on its known geometry and material properties, called ‘imaging mode’. A re-mapping of the apparent (‘indentation mode’) to the true (‘imaging mode’) compliance is thus obtained, which is applied on ‘indentation mode’ measurements of an unknown sample. This method demonstrates correction in the right direction for a polystyrene plate and a Teflon foil reference samples. The method is then applied on an unknown sample of flat agarose gel patterned with spots of polylysine protein.

► Standard indentation mode provides good qualitative mapping of compliance in AFM.
► Quantitative results are not reliable due to experimental deviation from model.
► Measuring a reference structure of known elasticity (cantilever) is recommended.
► The reference cantilever should match the range of expected sample compliance.
► The proposed method, though more tedious, gives reliable quantitative compliance.