Elastic deformations of tip and sample during atomic force microscope measurements

Two established models, based on continuum mechanics, are discussed to describe the elastic deformation of the tip and the sample in the atomic force microscope. We present arguments why the elastic deformation of a surface is more rigorously described by Sneddon mechanics rather than by the habitually used Hertzian mechanics. The results presented here show that elastic deformations are an important issue for measurements with the atomic force microscope. We demonstrate how elastic deformations impose limits to the capability of the atomic force microscope to image at true atomic resolution and how elastic deformations can be used to measure local elastic properties of a sample. Against the commonly accepted assumption of a ''rigid'' tip, we show that the elastic deformation of the tip can become a significant factor, when imaging hard samples. With few exceptions, the atomic force microscope has not been operated at true atomic resolution so far and more complex contrast mechanisms, with multiple atom interaction, must be considered. (C) 1996 American Vacuum Society.