Growth and Property Characterization of Epitaxial MAX-Phase Thin Films from the Tin+1(Si, Ge, Sn)Cn Systems
Epitaxial Mn+1AXn phase (n=1, 2 or 3) thin films from the chemically related Ti-Si-C, Ti-Ge-C, and Ti-Sn-C systems were grown on Al2O3(0001) substrates at temperatures in the region of 700-1000 oC, using d.c. magnetron sputtering from individual sources. In addition to growth of the known phases Ti3SiC2, Ti3GeC2, Ti2GeC, and Ti2SnC the method allows synthesis of the new phases Ti4SiC3, Ti4GeC3, and Ti3SnC2 as well as the intergrown structures Ti5A2C3 and Ti7A2C5 in the Si and Ge systems. Characterization by XRD, TEM and nanoindentation show similarities with respect to phase distribution, mechanical, and electrical properties, particularly pronounced when comparing Si and Ge. The Ti-Sn-C system is, however, the most liable system with respect to surface segregation of the A-element. This causes less favorable growth of MAX phases as seen by a preferential growth of the binary carbide TiC and metallic Sn. Nanoindentation on films from the Ti-Si-C and Ti-Ge-C systems shows large plastic deformation with extensive pile up. The typical thin film hardness is 20 GPa, and the Young’s modulus in the region of 320 GPa. The four-point probe resistivity is low for all systems, but differs depending on materials system and phase, with values of 25 μcm for Ti3SiC2, and 17 μcm for Ti2GeC.
H. Högberg et al., "Growth and Property Characterization of Epitaxial MAX-Phase Thin Films from the Tin+1(Si, Ge, Sn)Cn Systems", Advances in Science and Technology, Vol. 45, pp. 2648-2655, 2006