Unraveling Chemical Interactions between Titanium and Graphene for Electrical Contact Applications

The chemical interaction between Ti and graphene is of significant interest for engineering low-resistance electrical contacts. To study the interface chemistry, sequential depositions of Ti are performed on both as-received and ultrahigh-vacuum (UHV)-annealed chemical-vapor-deposition-grown graphene samples. In situ X-ray photoelectron spectroscopy (XPS) reveals no experimental evidence for the reaction of Ti with graphene at room temperature or after heating to 500 °C. The presence of the TiC chemical state is instead attributed to reactions between Ti and background gases in the UHV chamber as well as adventitious C on the surface of the graphene sample. We find that surface contamination can be substantially reduced by annealing in UHV. The deposition of Ti on graphene results in n-type doping, which manifests in core-level shifts and broadening of the graphene C 1s peak. Annealing the sample following the deposition of Ti reverses the n-type doping. The Raman spectroscopy results are in agreement with XPS analysis, which together provide insight into the possible mechanisms driving the changes in graphene doping