Properties of W/a-C nanometric multilayers produced by RF-pulsed magnetron sputtering

Single-layer W and a-C thin films and multilayer W/a-C coatings were deposited by either continuous or pulsed RF magnetron sputtering. The films were deposited on silicon substrates using two opposite RF magnetron sputtering heads that allowed single or alternate deposition of W and a-C. Multilayer films consisted of 15 bilayer structures with bilayer period in the nanometric (8-16 nm) range, whereas single-layer films were between 140 and 380 nm thick. Transmission electron microscopy showed the regular structure of the W/a-C multilayers with well-defined interfaces. X-Ray diffraction measurements revealed the presence of alpha and beta phases of tungsten and provided the bilayer period of the multilayer structures by means of the modified Bragg law, High reflectivity of X-rays was found in the multilayer samples at low incident angles. Multilayer coatings had less stress than single-layer W or a-C films. Nanoindentation measurements indicated an enhancement of hardness and elastic modulus, up to 18 and 191 GPa, respectively, in the multilayer W/a-C coatings as the bilayer thickness decreased to 8 nm. Furthermore, adherence to the substrate was improved compared to a-C single films. All coatings showed low friction coefficients (0.03-0.07). (C) 2002 Elsevier Science B.V. All rights reserved.