Functional interfaces can be considered ‘materials within materials’ that are active at the nanoscale and are responsive to an applied external stimulus. At these interfaces, the material properties are not only distinct from the bulk, but new functionalities or phases can emerge. Notable examples of such functional interfaces include structural phase boundaries and domain walls in ferroelectric oxides. In this chapter, nano-mechanical–electromechanical properties of the morphotropic phase boundaries in bismuth ferrite thin films are reviewed. Specifically, using scanning probe microscopy techniques, factors governing nano-mechanical and electromechanical properties of morphotropic bismuth ferrite are identified and potential applications in oxide nanoelectronics are discussed.