Insights and Implications of Intricate Surface Charge Transfer and sp3-Defects in Graphene/Metal Oxide Interfaces

Adherence of metal oxides to graphene is of fundamental significance to graphene nanoelectronic and spintronic interfaces. Titanium oxide and aluminum oxide are two widely used tunnel barriers in such devices, which offer optimum interface resistance and distinct interface conditions that govern transport parameters and device performance. Here, we reveal a fundamental difference in how these metal oxides interface with graphene through electrical transport measurements and Raman and photoelectron spectroscopies, combined with ab initio electronic structure calculations of such interfaces. While both oxide layers cause surface charge transfer induced by p-type doping in graphene, in sharp contrast to TiOx, the AlOx/graphene interface shows the presence of appreciable sp3 defects. Electronic structure calculations disclose that significant p-type doping occurs due to a combination of sp(3) bonds formed between C and O atoms at the interface and possible slightly off-stoichiometric defects of the aluminum oxide layer. Furthermore, the sp(3) hybridization at the AlOx/graphene interface leads to distinct magnetic moments of unsaturated bonds, which not only explicates the widely observed low spin-lifetimes in AlOx barrier graphene spintronic devices but also suggests possibilities for new hybrid resistive switching and spin valves.

Automated summary

The adherence of metal oxides to graphene is crucial for graphene nanoelectronics and spintronics interfaces. This study reveals a fundamental difference in how titanium oxide and aluminum oxide interface with graphene. Titanium oxide induces minimal p-type doping, while the aluminum oxide interface exhibits significant sp3 defects. The sp3 hybridization at the aluminum oxide/graphene interface leads to distinct magnetic moments and suggests possibilities for new hybrid resistive switching and spin valves.