ETD

• charge modulation
• chronocoulometry
• electric double layer
• field-effect
• graphene
• lithography
• solid polymer electrolyte

Solid polymer electrolytes (SPEs) are a class of materials obtained by mixing a solid polymeric matrix with a dissolved salt. In recent years, SPEs have found applications in various fields, such as ionic gates to tune charge carriers. Although ionic gating is typically used for global modulation of charge density, the realisation of a patternable SPE would allow for strong and local charge modulation, opening new perspectives for ionic device architectures.

In this thesis project, a bromium-based SPE was employed to study the formation of the electric double layer (EDL), before and after lithography, with the aim of modulating the charge carrier density on graphene. The SPE is composed of a polymethyl methacrylate (PMMA) matrix and dicationic imidazolium bromide, C3(MIM)2Br2, as the salt dissolved inside. The project included the fabrication of several devices from scratch, employing an EBL system.

The lithographed SPE successfully showed the formation of the EDL layer with different geometries. The graphene devices showed a modulation of their charge carrier density that increased with higher temperatures and higher concentrations of the salt in the PMMA matrix. This modulation persisted until, at 100 K, one of the SPE ions stopped moving.
These results make this electrolyte the first patternable SPE that acts as a positive resist to EBL. Both this and the low freezing temperature are novelties, making this SPE an innovation in the current state of the art.