A Universal Platform for Selective Phase Growth and Precise-Layer Control in MoTe2

Abstract

Minor structural changes in transition metal dichalcogenides can have dramatic effects on their electronic properties. This makes the quest for key parameters that can enable a selective choice between the competing metallic and semiconducting phases in the 2D MoTe<sub>2</sub> system compelling. Herein, we report the optimal conditions at which the choice of the initial seed layer dictates the type of crystal structure of atomically-thin MoTe<sub>2</sub> films grown by chemical vapour deposition (CVD). When Mo metal is used as a seed layer, phase-pure semiconducting 2H-MoTe<sub>2</sub> is the only product. Conversely, MoO<sub>3</sub> leads to the preferential growth of phase-pure metallic 1Tꞌ-MoTe<sub>2</sub>. The control over phase growth allows for simultaneous deposition of both 2H-MoTe<sub>2</sub> and 1Tꞌ-MoTe<sub>2</sub> phases on a single substrate during one CVD reaction. Furthermore, Rhodamine 6G dye can be detected using few-layered 1Tꞌ-MoTe<sub>2</sub> films down to 5 nM concentration which is several orders of magnitude higher than the value observed for bulk 1Tꞌ-MoTe<sub>2</sub>.

The covalent functionalization of few-layered MoTe2 thin films with iodonium salts

“…The precursor films were then converted into 2H-and 1T'-MoTe2 by CVD with the nature of the precursor layer dictating the phase of MoTe2 as described in previously published work. [22] The substrate with precursor layer was placed in the hot zone of a horizontal Lenton tube furnace with the FeTe2 source (30 mg) positioned 7 cm upstream. The dwell temperature of the source and substrate were set at 630 and 650 °C, respectively.…”

“…Thin films of the monoclinic 1T'and hexagonal 2H-MoTe2 were prepared in a CVD reactor at 650 o C using FeTe2 precursor as the source of tellurium similar to previous work. [22] According to Raman spectroscopy the resulting products were either single-phased 1T'-MoTe2 or 2H-MoTe2 (Supplementary Fig. S1, Supplementary Table S1A) depending on the seeding layer used.…”

“…Since both metallic and semiconducting polymorphs of MoTe2 can be prepared as atomically-thin and continuous films [21][22][23] there are exciting opportunities for investigating the role of crystal structure of MoTe2 on the reactivity with small molecules. The difference in reactivity between MoS2 and MoTe2 suggests that alternative reagents could be explored for surface functionalization as well.…”