Controlled Electrochemical Intercalation of Graphene/h-BN van der Waals Heterostructures

Abstract

Electrochemical intercalation is a powerful method for tuning the electronic properties of layered solids. In this work, we report an electrochemical strategy to controllably intercalate lithium ions into a series of van der Waals (vdW) heterostructures built by sandwiching graphene between hexagonal boron nitride (h-BN). We demonstrate that encapsulating graphene with h-BN eliminates parasitic surface side reactions while simultaneously creating a new hetero-interface that permits intercalation between the atomically thin layers. To monitor the electrochemical process, we employ the Hall effect to precisely monitor the intercalation reaction. We also simultaneously probe the spectroscopic and electrical transport properties of the resulting intercalation compounds at different stages of intercalation. We achieve the highest carrier density > 5 x 10 13 cm 2 with mobility > 10 3 cm 2 /Vs in the most heavily intercalated samples, where Shubnikov-de Haas quantum oscillations are observed at low temperatures. These results set the stage for further studies that employ intercalation in modifying properties of vdW heterostructures.Graphite intercalation compounds (GICs) exhibit a variety of interesting properties that differ significantly from semimetal graphite [1]. For example, CaC6 and YbC6 display superconductivity [2], while Li0.25Eu1.95C6 and EuC6 exhibit ferro-and antiferromagnetic ordering, respectively [3]. Intercalation compounds also represent technologically significant materials. LiC6 is the prototypical anode material in Li ion batteries. By analogy to these bulk graphite intercalation compounds, the intercalation of few-layer graphene has also been realized [4, 5, 6]. Upon intercalation of Li, the optical properties of few-layer graphene crystals (with thicknesses down to 1 nm) change significantly [4], Ca-intercalated few-layer-graphene is superconducting [5], and FeCl3 intercalated bilayer graphene showed a hint of ferromagnetism [6]. In addition, there have been theoretical predictions that heavy doping and proximity induced spin-orbit coupling from certain intercalants may induce exotic electronic properties in the graphene channel [7].Recently, it was demonstrated that one can stack different van der Waals (vdW) atomic layers to form vdW heterostructures, creating a new generation of few-atomic-layer functional heterostructures with emergent properties [8,9]. In particular, graphene encapsulated by h-BN, a layered insulator, forms a vdW heterostructure where the 2-dimensional (2D) graphene channel is well isolated from the environment [8]. As in intercalation compounds of bulk vdW materials, the intercalation of vdW heterostructures may create a new generation of functional heterostructures with emergent properties. Furthermore, the use of h-BN protecting layers may enable the formation of stable intercalation compounds that differ significantly from the bulk intercalation compound due the presence of two dissimilar surfaces at the heterointerface [10].Compared to traditional intercalati...

Reversible and selective ion intercalation through the top surface of few-layer MoS2

“…Recently, based on the same principle (intercalation/de-intercalation) as in electrochemical applications, guest species such as alkali metal ions (Li + , Na + , and K + ) have been introduced into the large interlayer spacing (~ 0.615 nm) to manipulate and optimize the optical and electrical properties of few-layer MoS 2 12 – 14 . Ion intercalation 12 , 15 – 24 enables extremely high doping level (e.g., 6 × 10 14 cm −2 in few layer graphene after Li intercalation 25 ) compared with electrical gating. Such high doping levels allow new physics to be discovered, such as superconductivity 26 and facilitates applications of few-layer MoS 2 in optoelectronic and nanoelectronic devices.…”

Li Intercalation Effects on Interface Resistances of High‐Speed and Low‐Power WSe2 Field‐Effect Transistors

“…Intercalation is the process of inserting various guest species into various vdW gaps formed at the interlayer interfaces [20,21] and vdWH interfaces. [22,23] In particular, for various future applications using vdW layered materials, Li-ion intercalation has received significant attention as one of the most attractive techniques for tuning electrical and optical characteristics, such as phase transition, [24][25][26][27] superconductivity, [28,29] ferromagnetism, [30] tunable thermal conductivity, [31] or tunable optical transmittance. [32,33] Our study demonstrated that Li ions intercalated to vdW interfaces lower the potential energy and Schottky barriers owing to the low potential energy of Li and the mild electron doping from intercalation, which can reduce the resistance at vdW interfaces and improve current flow for high-speed and lowpower n-type WSe 2 FETs.…”

Customizing H3Sb3P2O14 nanosheet sensors by reversible vapor-phase amine intercalation

“…In contrast to the other approaches, however, electrochemical intercalation requires a more complex experimental set-up. 18,37,38 Therefore, strategies for the straightforward, reversible and gradual fine-tuning of nanosheet properties with soft chemical intercalation methods are in high demand.…”