On the thermodynamic definition of surface stress

Surface energy and surface stress have been thoroughly discussed in the literature. However, the widely accepted definition of surface stress as the strain derivative of the total free surface energy divided by the surface area (Shuttleworth, Hening, etc.) is inconsistent with the correct definition of a stress tensor (given in continuum elasticity theory) as the strain derivative of the specific free energy. We analyse this anomaly in detail in order to prevent the erroneous use of the surface stress definition.