Sputter-deposited Cu/Cu(O) multilayers exhibiting enhanced strength and tunable modulus

By means of brief pauses in radiofrequency (RF) sputter deposition between individual layers, ultrathin copper oxide layers were formed through adsorption in the Cu/Cu multilayers. Their mechanical properties were compared with the Cu/Cu(O) multilayers whose oxide layers were deliberately deposited between copper layers. The mechanical hardness value of the Cu/Cu(O) multilayers approached that of nanostructured copper thin films. The Young's modulus of the multilayers was tunable, in accordance with the elasticity theories of composites. In addition, the Hall-Petch slope of the RF sputter-deposited Cu monolayers indicated that their theoretical strength approached the shear modulus of copper.