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Free keywords:
atomic force microscope; AFM; surface stress; surface energy of solids; biosensor
Abstract:
A technique for determining surface stress changes at solid–gas and solid–liquid interfaces with an atomic force microscope is presented. Therefore, the bending of a microfabricated cantilever, prepared with different opposite faces, is measured. This bending is directly proportional to a change of Δσ1− Δσ2, where σ1and σ2are the surface stresses of the two faces. To demonstrate the possibilities and limitations of the technique (i) a reduction of the surface stress of silicon nitride upon the covalent binding of gaseous dimethyldichlorosilane was measured; (ii) an increase of the surface stress of silicon nitride in aqueous medium with increasing pH was detected; (iii) the unspecific adsorption of the protein bovine albumin in buffer was monitored. The accuracy of the method is better than 0.005 J m−2. The main limit is residual drift of the cantilever deflection. As a consequence only changes of the surface stress which occurred more rapidly than ≈0.02 J m−2h−1 could be reliably detected.
