Growth and characterization of MAX-phase thin films

We report that magnetron sputtering can be applied to synthesize MAX-phase films of several systems including Ti-Si-C, Ti-Ge-C, Ti-Al-C, and Ti-Al-N. In particular, epitaxial films of the known phases Ti3SiC2, Ti3Ge2, Ti2GeC, Ti3AlC3, Ti2AlC, and Ti2AlN as well as the newly discovered thin film phases Ti4SiC3, Ti4GeC3 and intergrown structures can be deposited at 900-1000 degrees C on Al2O3(0001) and MgO(111) pre-seeded with TiC or Ti(AI)N. From XTEM and AFM we suggest a growth and nucleation model where MAX-phase nucleation is initiated at surface steps or facets on the seed layer and followed by lateral growth. Differences between the growth behavior of the systems with respect to phase distribution and phase stabilities are discussed. Characterization of mechanical properties for Tin+1Si-C-n films with nanoindentation show decreased hardness from about 25 to 15 GPa upon penetration of the basal planes with characteristic large plastic deformation with pile up dependent on the choice of MAX material. This is explained by cohesive delamination of the basal planes and kink band formation, in agreement with the observations made for bulk material. Measurements of the electrical resistivity for Ti-Si-C and Ti-Al-N films with four-point probe technique show values of 30 and 39 mu Omega cm, respectively, comparable to bulk materials. (c) 2004 Elsevier B.V. All rights reserved.