Publication date: 28th August 2024
Wet chemical synthetic routes for transition metal dichalcogenides (TMDCs) of the composition MX2 (M = Mo, W; X = S, Se), which have been studied extensively in the past, yield colloidal inks of ultrathin (mono- and bilayer) laterally smaller nanoplatelets (NPLs) and laterally larger nanosheets (NSs) with interesting photophysics.[1-5] In contrast, the telluride analogues remain elusive, with only MoTe2 nanocrystals being synthetically accessible in the semimetallic 1T' phase,[6] despite the fact that their direct band gap in the NIR region (0.95 eV[7]) make semiconducting MoTe2 monolayers a promising candidate for fibre-optic applications in the O-band.
One major challenge in synthesizing semiconducting MoTe2 is the small difference of only 35 meV between the semiconducting (stable) 2H phase and the semimetallic 1T' phase,[8] making it difficult to target one phase over the other during the reaction. Meanwhile the transformation between the 1T' and 2H phase is unfavored at typically accessible reaction temperatures in colloidal systems (~ 300 °C).[6,8]
In addition, reactive tellurium sources are scarce and often require more sophisticated tailoring of the precursor chemistry in comparison to sulfur and selenium. Here we adapt a synthesis using TeO2 and thiol precursor chemistry[9] to yield MoTe2 and WTe2 NPLs primarily consisting of the 2H phase, which we substantiate using insights from spectroscopic and microscopic analyses.
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