Si incorporation in Ti1-xSixN films grown on TiN(001) and (001)-faceted TiN(111) columns

Thin films consisting of TiN nanocrystallites encapsulated in a fully percolated SiNy tissue phase are archetypes for hard and superhard nanocomposites. Here, we investigate metastable SiNy solid solubility in TiN and probe the effects of surface segregation during growth of TiSiN films onto substrates that are either flat TiN(001)/MgO(001) epitaxial buffer layers or TiN(001) facets of length 1-5 nm terminating epitaxial TiN(111) nanocolumns, separated by voids, deposited on epitaxial TiN(111)/MgO(111) buffer layers. Using reactive magnetron sputter deposition, the TiSiN layers were grown at 550 C and the TiN buffer layers at 900 C. On TiN(001), the films are NaCl-structure single-phase metastable Ti1-xSixN(001) with N/(Ti+Si) = 1 and 0  x  0.19. These alloys remain single-crystalline to critical thicknesses hc ranging from 100±30 nm with x = 0.13 to 40±10 nm with x = 0.19. At thicknesses h > hc, the epitaxial growth front breaks down locally to form V-shaped polycrystalline columns with an underdense feather-like nanostructure. In contrast, the voided epitaxial TiN(111) columnar surfaces, as well as the TiN(001) facets, act as sinks for SiNy. For Ti1-xSixN layers with global average composition values x = 0.16, the local x value in the middle of Ti1-xSixN columns increases from 0.08 for columns with radius r ≃ 2 nm to x = 0.14 with r ≃ 4 nm. The average out-of-plane lattice parameter of epitaxial nanocolumns encapsulated in SiNy decreases monotonically with increasing Si fraction x, indicating the formation of metastable (Ti,Si)N solid solutions under growth conditions similar to those of superhard nanocomposites for which the faceted surfaces of nanograins also provide sinks for SiNy.