Growth and crystallographic structure of TiTe$_2$ on Au(111): From sub-monolayer structures to single- and multi-layer films

TL;DR

This study explores the growth, structure, and lattice properties of TiTe₂ films on Au(111), revealing initial molecular arrangements, monolayer formation, and lattice expansion in multilayer films through combined experimental and theoretical methods.

Contribution

It provides detailed insights into the growth mechanisms, structural configurations, and lattice parameters of TiTe₂ on Au(111), including the transition from sub-monolayer to multilayer films and their crystallographic characteristics.

Findings

Submonolayer TiTe₂ forms a stable $(5×\sqrt{3})_{rect}$ superstructure with Ti substituting Au atoms.

A homogeneous 1T-TiTe₂ monolayer forms after annealing, with a moiré pattern close to $(4×4)$.

Thicker TiTe₂ films exhibit increased lattice parameters, up to 1.5% larger than bulk.

Abstract

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 $R \le 0.13$.