The thermomechanical behavior of thin metal films on silicon substrates can be dramatically influenced by changes in the chemistry at the interfaces between the films and adjacent barrier and passivation layers. By adjusting interface chemistry, large changes in stress levels and in the shape of stress temperature curves can be seen. Phenomena including strong stress asymmetry (higher flow stresses in tension than in compression), negative yielding (compressive plastic deformation during tensile unloading) and very large anelastic recovery effects can be induced. These behaviors are consistent with variations in the ability of interfaces to constrain deformation in thin films. We suggest that mechanisms such as the spreading of dislocation cores into the interface and other local interface sliding events may account for the observed behaviors. The role of the interface in constraining deformation in films and the effect of reduced adhesion, here defined as resistance to local interface sliding, will be discussed.