Probing Exfoliated Graphene Layers and Their Lithiation with Microfocused X-rays

Abstract

X-ray diffraction is measured on individual bilayer and multilayer graphene single-crystals and combined with electrochemically induced lithium intercalation. In-plane Bragg peaks are observed by grazing incidence diffraction. Focusing the incident beam down to an area of about 10 μm × 10 μm, individual flakes are probed by specular X-ray reflectivity. By deploying a recursive Parratt algorithm to model the experimental data, we gain access to characteristic crystallographic parameters of the samples. Notably, it is possible to directly extract the bi/multilayer graphene c-axis lattice parameter. The latter is found to increase upon lithiation, which we control using an on-chip peripheral electrochemical cell layout. These experiments demonstrate the feasibility of in situ X-ray diffraction on individual, micron-sized single crystallites of few- and bilayer two-dimensional materials.

Emerging field of few-layered intercalated 2D materials

“…For the further development of this key technology a thorough understanding of the processes at the atomic level is highly desired. Studying the intercalation at the 2D level allows to follow the electrochemical intercalation process by various techniques in situ such as XRD, 161 Hall measurements 22,93 and also to follow the process by optical microscopy 89,162 and even transmission electron microscopy at atomic resolution. 15,93,163 TEM imaging not only allows to optically follow the intercalation and deintercalation of the ions into the few-layered 2DM, but also identies areas of varying crystallinity and grain sizes (Fig.…”

Electrochemical Intercalation in Atomically Thin van der Waals Materials for Structural Phase Transition and Device Applications

“…Reproduced with permission. [ 50 ] Copyright 2019, American Chemical Society. f) AFM topography of MoS 2 electrode at different potentials.…”

“…Given that the structural evolution of host materials can be achieved by the ion intercalation, it is advantageous for X‐ray absorption/reflection to probe the intercalation of foreign species. [ 50,51 ] As shown in Figure 3d,e, combining microfocused X‐ray reflection (XRR) with an electrochemical cell for intercalation, Zielinski et al. demonstrated the structural evolution of lithiated bilayer and multilayer graphene.…”

“…demonstrated the structural evolution of lithiated bilayer and multilayer graphene. [ 50 ] By applying a gate voltage, Li ions from the gel‐like electrolyte intercalate into the few‐layer graphene covered by the electrolyte, and then diffuse into the uncovered area of the flake driven by concentration gradients of Li ions within the flake. By focusing the incident X‐ray beam onto the uncovered part of the flake filled with Li ions, the structural evolution induced by ions intercalation has been in situ probed by X‐ray reflectivity.…”

“…Hexagonal boron nitride ( h ‐BN) is a layered insulator with excellent chemical inertness, which can be used to eliminate parasitic surface side reactions during electrochemical intercalation process. As mentioned before, Kim's group reported an electrochemical strategy to controllably intercalate lithium ions into BN/graphene/BN and BN/bigraphene/BN heterostructures, [ 49–56 ] and the intercalation stages and carrier density of graphene are in situ monitored by Hall measurements and Raman/PL spectra. The electron density in graphene/h‐BN heterointerface and graphene/graphene homointerface are determined to be about 7 × 10 13 cm −2 and 4.8 × 10 14 cm −2 , respectively, suggesting that more Li ions reside in the graphene/graphene homointerface than that in the h‐BN/graphene interface.…”