A Mixed‐Solvent Strategy for Efficient Exfoliation of Inorganic Graphene Analogues

Zhou, Kai‐Ge; Mao, Nannan; Wang, Hang‐Xing; Peng, Yong; Zhang, Hao‐Li

doi:10.1002/ange.201105364

Cited by 222 publications

(216 citation statements)

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“…Alternatively, TMDCs can be exfoliated by ultrasonication in appropriate liquids, including organic solvents, aqueous surfactant solutions, or solutions of polymers in solvents 43,44,58,59 . Typically, ultrasonication results in the mechanical exfoliation of layered crystals to give flakes that are a few hundred nanometres in size.…”

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

et al. 2012

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699M any two-dimensional (2D) materials exist in bulk form as stacks of strongly bonded layers with weak interlayer attraction, allowing exfoliation into individual, atomically thin layers 1 . The form receiving the most attention today is graphene, the monolayer counterpart of graphite. The electronic band structure of graphene has a linear dispersion near the K point, and charge carriers can be described as massless Dirac fermions, providing scientists with an abundance of new physics 2,3 . Graphene is a unique example of an extremely thin electrical and thermal conductor 4 , with high carrier mobility 5 , and surprising molecular barrier properties 6,7 .Many other 2D materials are known, such as the TMDCs 8,9 , transition metal oxides including titania-and perovskite-based oxides 10,11 , and graphene analogues such as boron nitride (BN) 12,13 . In particular, TMDCs show a wide range of electronic, optical, mechanical, chemical and thermal properties that have been studied by researchers for decades 9,14,15 . There is at present a resurgence of scientific and engineering interest in TMDCs in their atomically thin 2D forms because of recent advances in sample preparation, optical detection, transfer and manipulation of 2D materials, and physical understanding of 2D materials learned from graphene.The 2D exfoliated versions of TMDCs offer properties that are complementary to yet distinct from those in graphene. Graphene displays an exceptionally high carrier mobility exceeding 10 6 cm 2 V -1 s -1 at 2 K (ref. 16) and exceeding 10 5 cm 2 V -1 s -1 at room temperature for devices encapsulated in BN dielectric layers 5 ; because pristine graphene lacks a bandgap, however, fieldeffect transistors (FETs) made from graphene cannot be effectively switched off and have low on/off switching ratios. Bandgaps can be engineered in graphene using nanostructuring [17][18][19] , chemical functionalization 20 and applying a high electric field to bilayer graphene 21 , but these methods add complexity and diminish mobility. In contrast, several 2D TMDCs possess sizable bandgaps around 1-2 eV (refs 9,14), promising interesting new FET and optoelectronic devices.TMDCs are a class of materials with the formula MX 2 , where M is a transition metal element from group IV (Ti, Zr, Hf and so on), group V (for instance V, Nb or Ta) or group VI (Mo, W and so on), and X is a chalcogen (S, Se or Te). These materials form layered structures of the form X-M-X, with the chalcogen atoms in two hexagonal planes separated by a plane of metal atoms, as shown in Fig. 1a. Adjacent layers are weakly held together to form the bulk crystal in a variety of polytypes, which vary in stacking orders and metal atom coordination, as shown in Fig. 1e. The overall symmetry of TMDCs is hexagonal or rhombohedral, and the metal atoms have octahedral or trigonal prismatic coordination. The electronic properties of TMDCs range from metallic to semiconducting, as summarized in Table 1. There are also TMDCs that exhibit exotic behaviours such as charge density waves ...

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

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“…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 layered crystal into single and multilayer nanosheets which are then stabilised by interaction with the solvent or a surfactant.…”

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

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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 ...

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“…S10). Note that most of the above solvents possessed low-boiling points, which could offer several obvious advantages, such as easy removal, low cost, lower toxicity and better biocompatibility 18 . In addition, to deeply understand the exfoliation process, we also achieved ZnSe-pa sheets with a desired number of layers through controlling the sonication time of (Zn 2 Se 2 )(pa) in ethanol (Supplementary Figs S11-S13).…”

Section: Characterizations Of Freestanding Znse Single Layersmentioning

confidence: 99%

Fabrication of flexible and freestanding zinc chalcogenide single layers

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Inorganic graphene analogues (IGAs) are a conceptually new class of materials with attractive applications in next-generation flexible and transparent nanodevices. However, their species are only limited to layered compounds, and the difficulty in extension to nonlayered compounds hampers their widespread applicability. Here we report the fabrication of large-area freestanding single layers of non-layered Znse with four-atomic thickness, using a strategy involving a lamellar hybrid intermediate. Their surface distortion, revealed by means of synchrotron radiation X-ray absorption fine structure spectroscopy, is shown to give rise to a unique electronic structure and an excellent structural stability, thus determining an enhanced solar water splitting efficiency and photostability. The Znse single layers exhibit a photocurrent density of 2.14 mA cm − 2 at 0.72 V versus Ag/AgCl under 300 W Xe lamp irradiation, 195 times higher than that of bulk counterpart. This work opens the door for extending atomically thick IGAs to non-layered compounds and holds promise for a wealth of innovative applications.

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A Mixed‐Solvent Strategy for Efficient Exfoliation of Inorganic Graphene Analogues

Cited by 222 publications

References 35 publications

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

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

Fabrication of flexible and freestanding zinc chalcogenide single layers

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