Electrochemical Intercalation of Europium into Bilayer Graphene

Abstract

This thesis is dedicated to the electrochemical intercalation of europium (Eu) into bilayer graphene. The theoretical understanding of metals intercalation into layered structures underpins a multitude of applications. Owing to their unique electrochemical and physical properties of rare earth metals (REM), there is a potential for applications of rare earth metals (REM) intercalated into bilayer graphene. However, the electrochemical intercalation of REM remains entirely unexplored. This research primarily focuses on the mechanisms and kinetics of Eu electrochemical intercalation, as well as on the characterisation of new heterostructures. Utilizing a combination of theoretical calculations, electrochemical and electronic transport measurement experiments, I explore the key factors of the intercalation process, field-effect controlled Eu intercalation, Eu layer formation, interaction between co-intercalated Eu and ionic liquid, direct current influence on the co-intercalation process, and the hysteretic behaviour of few-layer graphene and intercalation compounds. I discovered that the REM europium can be electrochemically intercalated into bilayer graphene at elevated temperatures with thermal activation playing a significant role in facilitating the process through interlayer space expansion. A layer of europium forms within the interlayer space. By conducting the electrochemical intercalation in a split-step process: (i) electrochemical reaction, and (ii) intercalation, I determined that Eu is intercalated as ionic species. A field-effect-controlled reversible intercalation of europium was also achieved. The ionic liquid BMP-BTI co-intercalates with europium into bilayer graphene at room temperature, and the interaction between ionic liquid and Eu significantly affects electronic transport properties of the intercalation compound and results in a distinct Eu cluster phase within the bilayer graphene interlayer. The co-intercalation of [AMPYRR]TFSI and Eu was notably accelerated by applying a small direct current along the bilayer graphene channel. The acceleration of the intercalation process is primarily attributed to the local heating of the intercalation cell, which is induced by the direct current. The hysteretic behaviour of the gate voltage dependence on the longitudinal resistivity of monolayer graphene, bilayer graphene, and europium intercalation compound is highly temperature dependent. The hysteretic behaviour of bilayer graphene after 10 h heating and the europium intercalation compound at elevated temperatures shows characteristics similar to ferroelectric hysteresis.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Konstantin Novoselov (Supervisor) & Artem Mishchenko (Supervisor)