Percolating Superconductivity in Air‐Stable Organic‐Ion Intercalated MoS₂

Abstract

When doped into a certain range of charge carrier concentrations, MoS 2 departs from its pristine semiconducting character to become a strongly correlated material characterized by exotic phenomena such as charge density waves or superconductivity. However, the required doping levels are typically achieved using ionic-liquid gating or air-sensitive alkali-ion intercalation, which are not compatible with standard device fabrication processes. Here, the emergence of superconductivity and a charge density wave phase in air-stable organic cation intercalated MoS 2 crystals are reported. By selecting two different molecular guests, it is shown that these correlated electronic phases depend dramatically on the intercalated cation, demonstrating the potential of organic ion intercalation to finely tune the properties of 2D materials. Moreover, it is found that a fully developed zeroresistance state is not reached in few-nm-thick flakes, indicating the presence of 3D superconductive paths that are severed by the mechanical exfoliation. This behavior is ascribed to an inhomogeneous charge carrier distribution, which is probed at the nanoscale using scanning near-field optical microscopy. The results establish organic-ion intercalated MoS 2 as a platform to study the emergence and modulation of correlated electronic phases.

Engineering Magnetism and Superconductivity in van der Waals Materials via Organic‐Ion Intercalation

“…However, the superconductivity in intercalated flakes remains largely unexplored. A first step in this direction was taken by Pereira et al [39] In this work, the authors studied the superconductivity in organic-ion intercalated MoS 2 . While it is well established that MoS 2 can be made superconductor via ionic-liquid gating [47,63] and through the intercalation of alkali metal ions, [28,64] the intercalation of organic cations in MoS 2 had not been previously [39] Copyright 2022, Wiley-VCH.…”

“…Figure a shows that MoS 2 bulk crystals intercalated with tetraethylammonium (TEA) cations display a superconductive transition. [ 39 ] Additionally, the electronic properties of a flake exfoliated from a TEA‐intercalated bulk crystal were also investigated. In this case, while a resistance drop is measured at low temperature, the zero‐resistance state was not reached (Figure 3b).…”

“…This method provides a fast intercalation process which can be controlled using the electrochemical parameters and can be used for bulk crystals and exfoliated flakes contacted by microscopic electrodes. Electrochemical intercalation has been reported for many layered materials, including graphite, MoS 2 , [ 32,39 ] NbSe 2 , [ 40 ] black phosphorous, [ 31 ] and NiPS 3 [ 41 ] among others. However, the procedure tends to be rather aggressive, so that electrochemically intercalated crystals typically display broad X‐ray diffraction peaks, indicative of structural disorder, and sometimes, the materials are even exfoliated in solution.…”

“…b) These superconductive properties are also present in micrometric flakes, although a zero-resistance state is not reached, due to the reduced number of layers and the inhomogeneous charge distribution introduced by the molecules. a,b) Reproduced with permission [39]. Copyright 2022, Wiley-VCH.…”

Unveiling the capacitive energy storage of linear CTAB or tetrahedral TBAB organic-molecule intercalated MoS2

“…Thus, it is highly desired to engineer the interlayer spacing of 2H-MoS 2 to solve its restacking and optimize the pore structure, enhancing the charge-transport properties and charge-storage capability. Recently, it has been shown that the interlayer spacing of MoS 2 can be extended by the insertion of multiple guest molecules or ions, such as water molecules, 24,32 N , N -dimethyl fumarate (DMF), 33 cetyltrimethylammonium bromide (CTAB), 34 NH 4 + ions, 35 poly(3-hexylthiophene) (P3HT) blended with phenyl-C61-butyric acid methyl ester (PCBM), 36 cetyltrimethylammonium (CTA + ), tetramethylammonium (TEA + ), 37 quaternary ammonium molecules, 38 TBAOH, 39 polyethyleneimine, polyethylene glycol, 40 poly(3,4-ethylenedioxythiophene) (PEDOT), 41 phenylenediamine (PPD) and N , N -dimethyl- p -phenylenediamine (DMPD). 42 In detail, Yang's team developed a simple, mild and efficient polymer-direct-intercalation strategy where polyethyleneimine/polyethylene glycol can directly intercalate into the 2H-MoS 2 interlayers, forming interlayer-expanded 2H-MoS 2 /carbon heteroaerogels after carbonization, beneficial for fast charge transport and enhanced pseudo-capacitance.…”