Growth of Ti3SiC2 thin films by elemental target magnetron sputtering

Abstract

Epitaxial Ti3SiC2(0001) thin films have been deposited by dc magnetron sputtering from three elemental targets of Ti, C, and Si onto MgO(111) and Al2O3(0001) substrates at temperatures of 800–900°C. This process allows composition control to synthesize Mn+1AXn (MAX) phases (M: early transition metal; A: A-group element; X: C and∕or N; n=1–3) including Ti4SiC3. Depositions on MgO(100) substrates yielding the Ti–Si–C MAX phases with (101¯5), as the preferred orientation. Samples grown at different substrate temperatures, studied by means of transmission electron microscopy and x-ray diffraction investigations, revealed the constraints of Ti3SiC2 nucleation due to kinetic limitations at substrate temperatures below 700°C. Instead, there is a competitive TiCx growth with Si segregation to form twin boundaries or Si substitutional incorporation in TiCx. Physical properties of the as-deposited single-crystal Ti3SiC2 films were determined. A low resistivity of 25μΩcm was measured. The Young’s modulus, ascertained by nanoindentation, yielded a value of 343–370GPa. For the mechanical deformation response of the material, probing with cube corner and Berkovich indenters showed an initial high hardness of almost 30GPa. With increased maximum indentation loads, the hardness was observed to decrease toward bulk values as the characteristic kink formation sets in with dislocation ordering and delamination at basal planes.

The M+1AX phases: Materials science and thin-film processing

“…The idea behind using a TiC seed layer is that the Ti 3 SiC 2 {0001} and TiC{111} planes can form epitaxial and coherent interfaces [259]. This follows from the isomorphism of the TiC (111) [101], shows an example of the use of seed layers for MAX phases. For the case of an intentionally deposited TiC x seed layer [see Fig.…”

“…Low-temperature films differ among M-A-X systems. For example, Al tends to dissolve in TiC forming a metastable solid solution (Ti,Al)C [48], while the solubility of Si in TiC is much lower; thus, the latter system tends to yield nanocrystalline TiC together with amorphous phases (e.g., SiC) [25,101].…”

“…Some of the initial work [45,89,100,101] on epitaxial growth of MAX phase thin films suggested the importance of using a seed layer to promote nucleation of the MAX phase. Typically, a TiC x (111) seed layer was employed for the TiC-based MAX phases.…”

“…When the term is used in thin-film growth, the concept normally refers to homogeneous surface nucleation, i.e., that the probability for nucleation is the same at any point on a given surface. In principle, the nucleation of a MAX phase may be either homogeneous or heterogeneous; for example, buildup of a Si reservoir on the growth surface 51 [101,113] increases the driving force (Si supersaturation) for homogeneous nucleation. However, in practice, in epitaxial growth of MAX phases, nucleation occurs heterogeneously over a surface, i.e., the probability for a nucleation event is higher at preferential nucleation sites such as steps, edges, kinks, and ledges.…”

“…At high temperature, epitaxial growth of a nearly phase-pure MAX phase is typically obtained, provided that the substrate is suitable. A reduction in temperature yields polycrystalline MAX-phase growth, often (depending on composition) with competing phases such 49 as Ti 5 (Si, Ge) 3 C x in the Ti-(Si,Ge)-C system [46,101] or the inverse perovskite Ti 3 AlC in the Ti-Al-C system [48]. Further reduction in temperature yields the binary carbide as the main crystalline phase, either in a nanocomposite structure together with amorphous phases [25] or in solid solution [48].…”