To understand the origin of substantially expanded plating diameter at failure, surface mechanical properties were evaluated using a nanoindenter under vacuum inside an SEM (Figure ). A cube corner tip was intentionally employed to accelerate the onset of surface cracks with loading force kept to a maximum of 50 mN (Figure Finally, we consider various surface toughening mechanism. Ag-Li ion exchange introduces compressive stress in the nanosized ion-exchange zone due to ionic radius misfit. The concept of surface compressive stress has been experimentally demonstrated for toughening glasses .