DIRECT MECHANICAL MEASUREMENT OF INTERATOMIC POTENTIALS

THE bonding potential between atoms determines all the key properties of matter. It is usually deduced from a nide variety of experimental p arameters such as elastic moduli, binding energy and vibrational nonli nearities. These provide an indirect route to quantities such as viria l coefficients which characterize the variation of potential energy,vi th interatomic spacing(1). Here we report use of a modified atomic for ce microscope(2) to measure mechanically the interatomic forces betwee n a tip and the sample surface as a function of separation. We use a m agnetically controlled feedback mechanism to resist the 'jump to conta ct' that commonly occurs in mechanical force measurements at small sep arations, enabling us to map out reversible curves to separations clos er than the point of inflection in the potential-energy curve. This me thod provides a direct means for continuous measurement of forces betw een atoms as they approach towards contact.