Growth and crystallographic structure of TiTe$_2$ on Au(111): From sub-monolayer structures to single- and multi-layer films
We investigated the initial growth of TiTe$_2$ on Au(111) from sub-monolayer to multi-layer coverage by scanning tunneling microscopy (STM), low-energy electron diffraction intensity analysis (LEED-IV), and density functional theory (DFT). In the submonolayer regime we find a stable and well-ordered $(5\times\sqrt{3})_{\mathrm{rect}}$ superstructure consisting of separated TiTe$_2$ molecules, whereby the Ti atoms substitute Au atoms of the first substrate layer as proven by LEED-IV. By adding further Ti and Te in a 1:2 ratio and proper annealing dealloying sets in and a homogeneous 1T-TiTe$_2$ monolayer film on an unreconstructed substrate is formed. The resulting moir\'e structure is close to a $(4 \times 4)$ superstructure w.r.t. Au(111) and has a slightly expanded in-plane lattice parameter compared to the 1T-TiTe$_2$ bulk value. With further stoichiometric deposition, thicker 1T-TiTe$_2$ films grow. Surprisingly, a five layer thick film exhibits an even larger lattice-parameter (1.5 % larger than the bulk value). All LEED-IV analyses are based on best-fit R-factors of $R \le 0.13$.