Solution-based Production of 2D-layered Materials
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Solution-based Production of 2D-layered Materials Anupama B. Kaul Department of Electrical and Computer Engineering; Department of Metallurgical, Materials and Biomedical Engineering University of Texas, El Paso; El Paso, TX 79968 Email: [email protected]
ABSTRACT Two dimensional (2D) nanomaterials such as graphene and transition-metal dichalcogenides (TMDCs) have attracted tremendous attention over recent years due to their unique properties and potential for numerous applications. Given the wide range of compositions of 2D-layered materials that have emerged in recent years, it is not surprising that they offer a rich spectrum of properties, ranging from metallic, insulating, superconducting to semiconducting. Here we report on the solution-based production of 2D layered material flakes, in particular graphene and MoS2 where the materials are chemically exfoliated in organic solvents which can then be ink jet printed using a commercially available material printer, for printed electronics applications. INTRODUCTION The hexagonal honeycomb lattice of two-dimensional (2D) graphene represents the thinnest material we know of to date and yet, this membrane-like material is 5X stronger than steel owing to the strong in-plane sigma bonds, and yet it is far lighter than steel. Graphene is all surface and no bulk and exhibits a high mobility > 100,000 cm2/V-s at room temperature and a high thermal conductivity of 5 x 103 W/m-K. Graphene has an ultra-high current carrying capability ~ 1 x 109 A/cm2. Due to its flexibility, strength, high conductivity, transparency and low cost, graphene has been proposed as a replacement for indium tin oxide for solar cells,1 and organic light emitting diodes, as well as in touch screens.2 The large surface area to volume ratio of graphene suggests that it also has promise in ultra-capacitor applications.3 Recently, layered 2D crystals of other materials similar to graphene have been realized which include insulating hexagonal-BN (band gap ~5.5 eV) and transition metal di-chalcogenides (TMDCs) which display properties ranging from metallic NbS2 to semiconducting MoS2. The TMDCs consist of hexagonal layers of metal M atoms sandwiched between two layers of chalcogen atoms X with stoichiometry MX2 (e.g. for MoS2, M = Mo, X = S). As with TMDCs in general, the interatomic binding in MoS2 is strong arising from the covalent in-plane bonding but the subsequent layers interact through the weaker van der Waals interlayer forces. Depending on the combination of the transition metal atom and the chalcogen (S, Se or Te), a wide variety of TMDCs are possible, each offering a unique set of properties.4 The coordination and oxidation state of the metal atoms determines whether the TMDC will be metallic, semi metallic or semiconducting. Superconductivity and charge density wave effects have also been observed in some TMDCs. Besides the TMDCs, the chalcogenides of group III (GaSe, GaTe,
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