“…This type of delamination can present as a circular pattern appearing to have originated from a blister that forms when the compressive stress forces the film to buckle away from the underlying substrate. , The blister formation is seen as a driving force on the crack interface, resulting in additional advancement of the film delamination. Studies of buckling-driven debonding have demonstrated that both circular and sinusoidal (“telephone cord”) patterns can be understood as originating from an increase in compressive stress caused by water molecules diffusing through the film to the film−substrate interface. ,, The critical stress required for buckling to occur, σ c , can be calculated using eq normalσ normalc = normalπ 2 E 12 false( 1 − normalυ 2 false) true( h b true) 2 Where E = the elastic modulus of the film, v = Poisson’s ratio, h = film thickness, and b = the half blister width. Although we have not directly measured E and v for our films, Peponas et al have done so for a-C:N x films that are similar in composition to those deposited here. ,, Thus, if we assume their values for our films, E = 22.5 GPa and v = 0.3, we can calculate an approximate value for σ c .…”