Self-intercalation forms covalently bonded 2D transition-metal chalcogenide layers
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Self-intercalation forms covalently bonded 2D transitionmetal chalcogenide layers
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research team led by Kian Ping Loh and Stephen J. Pennycook of the National University of Singapore, as well as Xin Luo of Sun Yat-sen University, report a new class of metal chalcogenides in their article published in Nature (doi:10.1038/s41586-0202241-9). These materials are transitionmetal dichalcogenide bilayers sandwiching metal atoms covalently. The layered structure of metal dichalcogenides enables the synthesis of novel materials. Typically, two-dimensional (2D) metal dichalcogenides are composed of nanosheets stacked together, in analogy to graphene. Adjacent layers are held together via weak van der Waals forces. The interlayer spaces can host guest species, including atoms and ions. Previous work focused primarily on introducing foreign ions or atoms within a single metal-chalcogenide layer, “but somehow, previous researchers missed considering the situation when the same metal atoms sit in between two layers,” says Xiaoxu Zhao, the lead author. The researchers decided to step into this unexplored area. The research team modified the synthesis protocols involving molecular beam epitaxy (MBE) for synthesizing metal dichalcogenides. MBE is a gas-phase technique for growing highly uniform and crystalline thin films. The key to the synthesis of a new family of metal chalcogenides is to enhance the concentration of gaseous metal precursors intentionally. During the thin-film deposition, the additional metal atoms reside in the interstitial space between the as-formed metal dichalcogenide monolayers and formed covalent bonds with neighboring layers. For example,
amorphous growth is a strict criterion for homogeneous deposition. The research team is excited about examining the regimes of glassy electrochemical growth to enable anodes made of other metals. Given its correlation to small current
densities, (i.e., growth rate per unit area), one interesting possibility is to examine three-dimensional structures whose higher area-to-volume ratio can facilitate desired glassy growth for the same total current. Aashutosh Mistry
a increasing the Ta:S TaS2 Self-intercalated Ta7S12 flux ratio from 1:10 (which formed conventional metal diIncrease Ta flux chalcogenide, TaS2) Ta:S flux ratio ≈ 1:10 Ta:S flux ratio ≈ 1:6 to 1:6 resulted in Ta - i n t e r c a l a t e d Ta S Ta S tantalum disulfide, Ta7S12. Changing c b the flux ratio was found to tune the stoichiometry to obtain other compounds, for example, Ta9S16 and Ta10S16. Additionally, this strategy is also applicable to chemical vapor deposition, another common Ta S Intercalated Ta synthesis technique of metal Self-intercalation in TaS2 crystals. (a) Scheme of the synthesis method, dichalcogenides. (b) atomic-resolution scanning electron microscopy–annular dark-field image, and (c) atomic model of Ta7S12. The bright dots in (b) and red circles in In some cases, (c) highlight the location of intercalated Ta atoms. Credit: Nature. the newly synthesized metal chalcogenides possess magn
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