Wettability Engineering for Studying Ion Transport in 2D Layered Materials

Abstract

Layered materials are widely used for their capacity to incorporate and store foreign ionic species. It has become possible to exploit this process at the level of single crystals consisting of individual atomic layers: 2D materials and their van der Waals heterostructures. Due to the small size of available high‐quality specimen, however, it remains challenging to probe ion transport and storage in these systems. To promote future advances in this field, wettability engineering is introduced as a strategy for the on‐chip integration of electrolytes with micrometer‐sized samples of 2D materials. Contact angles are systematically measured for a variety of electrolyte–surface couples to identify a rational device design, and engineer lateral contrasts in surface chemistry to control the rims of drop cast electrolytes with micrometer precision. This allows covering single crystalline flakes of 2D materials only partially, leaving most of the sample surface uncovered and imposing directionality on ion transport. Wettability engineering is used to fabricate few‐layer graphene electrochemical micro two‐compartment cells that display chemical diffusion of lithium on the order of 10−8 cm2 s−1. While the approach is transferrable to other 2D materials and ionic species, it can also benefit device design for the study of nonlocal electrolyte gating effects.

Electrolyte versus Dielectric Gating of Two-Dimensional Materials

“…Dielectric gating was employed for copper metallization of the channel between two sheets of monolayer MoS 2 in an effort to create an atomic-scale memristor with the potential use in neuromorphic circuits . In another study, the differing wettability of graphene, SiO 2 , Au, and other surfaces allowed the fabrication of on-chip microscale electrochemical cells for studying intercalation in few-layer graphene as a means of controlling its physicochemical properties …”

A Review: Ion Transport of Two-Dimensional Materials in Novel Technologies from Macro to Nanoscopic Perspectives

“…When restricted by a 2D planar surface, the diffusion in normal and anomalous diffusion (the sub-diffusive and super-diffusive processes) is a quintessential property. Since our understanding of ion diffusion is a foundation of ion transport, few articles have studied the subject via simulation [134] or experiments [139].…”

“…To lower these barriers, the membrane system needs to acquire additional energy to initiate ion transport. This additional energy can come in the form of pressure, chemical reagent, electrical bias, temperature or and photons [32,33,132,139]. Light can also be used to lower the potential barrier for ion transport on 2D materials and through porous membranes.…”