Interfacial Events in Graphene-Based Technologies for Neural Interfaces

Active implantable neural interfaces have experienced great advances in the last years, partially thanks to the use of novel materials. Graphene is one of these new materials contributing to the recent progress thanks to its outstanding mechanical, electrical and electrochemical properties. Neural interfaces based on graphene have the potential to make these implants softer and more conformable, adapting better to the tissue morphology; furthermore, it is possible to prepare smaller devices while maintaining high performance, which can lead to improved spatial selectivity and specificity. Yet, this flourishing technology presents important challenges related to two-dimensional nature of graphene, in particular the impact of interfacial phenomena on its properties.<br/>Among the existing interfacial phenomena impacting on the graphene properties, and thus on the device performance and stability, in this work we explore two main phenomena: electrolyte intercalation between graphene and the substrate and residue deposition over graphene during fabrication.<br/>To address water intercalation, we combine electrical and morphological (KPFM and Raman) characterization. We study the influence of different factors on the amount of water under graphene, including device size and aspect ratio, the passivation layer design or the cleanness of graphene surface. Furthermore, we will present a novel methodology to investigate the amount of residual charge on graphene; this approach is based on the response of graphene electronic properties to the electrolyte pH and ionic strength, which is monitored by immersion Raman spectroscopy.<br/>Our results reveal the existence of trapped water between graphene and the substrate and of non-controlled residual charges on graphene after fabricated. Finally, graphene protection strategies are presented revealing promising improved capabilities of graphene-based device performance.