Solvent Exfoliation of Transition Metal Dichalcogenides: Dispersibility of Exfoliated Nanosheets Varies Only Weakly between Compounds

Abstract

Abstract:We have studied the dispersion and exfoliation of four inorganic layered compounds, WS 2 , We found that the dispersed concentration of each material falls exponentially with  as predicted by solution thermodynamics. This work shows that solution thermodynamics and specifically solubility parameter analysis can be used as a framework to understand the dispersion of 2-dimensional materials. Finally, we note that in good solvents such as 2 cyclohexylpyrrolidone, the dispersions are temporally stable with >90% of material remaining dispersed after 100 hours. ToC figOver the last decade, 2-dimensional nanomaterials have become one of the most studied subfields of nanoscience. These developments have been spearheaded by research into graphene, a material that is unique due to its combination of thermal, electronic, optical and mechanical properties. 1-5 However, over the last few years, it has become clear that a range of other inorganic layered compounds can be mechanically exfoliated in small quantities to give 2-dimensional nanosheets with interesting properties. 6-10 For example, exfoliated hexagonal boron nitride has been used as a dielectric support in graphene-based transistors 11 while MoS 2 has been fabricated into sensors 10, 12 , transistors 13-15 and integrated circuits. 16 The availability of a wide range of 2-dimensional materials is important as it allows access to a broad palette of physical and chemical properties. A good example is provided by the family of transition metal dichalcogenides (TMDs). These materials have the chemical composition MX 2 where M is a transition metal (commonly, but not limited to Ti, Nb, Ta, Mo, W) and X is a chalcogen (i.e. S, Se, Te). As in graphite, these atoms are covalently bonded into nanosheets which stack into 3-dimensional crystals by van der Waals interactions. These materials are of particular interest because, depending on the combination of metal and chalcogen, the material can be semiconducting or metallic. 17 In addition, the bandgap can vary from a few hundred meV to a few eV, 17 suggesting these materials have potential as versatile electronic device materials.Furthermore, these materials have interesting electrochemical properties which make them suitable for applications such as battery electrodes. 18,19 As with graphene, many applications will require relatively large quantities of material suggesting that a solution processing route is required. 20 A number of possibilities exist. For example, it has been known for many years that materials such as MoS 2 can be exfoliated by 3 lithium intercalation. 21 However, such a route tends to result in structural deformations in some TMDs leading to considerably altered electronic properties. 22 Alternatively, TMDs can be synthesised in the liquid phase. 7,8 Probably the simplest route to liquid exfoliation of layered compounds is sonication assisted exfoliation in solvents [23][24][25][26][27][28][29] or aqueous surfactant solutions. 19,[30][31][32] Here, sonication results in the exfoliation of the ...

Large-Scale Production of Size-Controlled MoS2 Nanosheets by Shear Exfoliation

“…This results in the production of nanosheets which are stabilised against aggregation via the interaction with the liquid. 12,15,17,18 This method has been used to successfully produce dispersions of nanosheets of a range of materials, including graphene, 8,19 BN,6,20 and various transition metal dichalcogenides 6,10,21,22 such as MoS2 and WSe2. Using sonication-assisted exfoliation, dispersions of volumes typically in the range of hundreds of millilitres can be produced.…”

Edge and confinement effects allow in situ measurement of size and thickness of liquid-exfoliated nanosheets

“…More recently, a much simpler method, liquid phase exfoliation (LPE), has been reported [16][17][18][19][20][21][22][23][24][25][26][27] . This method involves the sonication 18 or shearing 27 of layered crystals in certain solvents or solutions of surfactants or polymers.…”

“…The resultant dispersions can be easily processed into films, coatings or composites: systems which are ideal for applications in a range of areas from batteries 28,29 to photodetectors 30 to reinforced materials. 21,25,31 This method is general and has been used to give exfoliated dispersions of graphene 16,17,20 , BN, 18,23,25 TMDs such as MoS 2 and WS 2 18,19,24,26,29,32 , transition metal oxides such as MnO 2 (ref. 29) and MoO 3 (ref.…”

A two-step process for growth of highly oriented Sb2Te3 using sputtering

“…[12][13][14][15] The most widely used techniques to fabricate 2D chalcogenides are exfoliation from a bulk single crystal, chemical vapor deposition (CVD), and molecular beam epitaxy (MBE). [16][17][18][19][20][21] However, the area of films that can be fabricated by exfoliation is limited and sample sizes are not uniform. Although CVD and MBE techniques are well suited for industry, to the best of the authors' knowledge, there have been no reports on the deposition of the GeSbTe phase change material by these processes in industry for non-volatile memory applications, but sputtering has been widely used to grow chalcogenide phase change materials.…”