Selective phase growth and precise-layer control in MoTe2

James P Fraser,Adam F Mckenzie,Jessica C Mcglynn,Vishal Panchal,Juan Carlos Moreno-López,Thomas Pichler,David A J Moran,Stacey Laing,Duncan Graham,Olga Kazakova,Jingyi Zhang,Liudvika Masaityte,Alexey Y Ganin,Donald A Maclaren

doi:10.1038/s43246-020-00048-4

Abstract

Minor structural changes in transition metal dichalcogenides can have dramatic effects on their electronic properties. This makes the quest for key parameters that enable a selective choice between the competing metallic and semiconducting phases in the 2D MoTe2 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 MoTe2 films grown by chemical vapour deposition (CVD). When Mo metal is used as a seed layer, semiconducting 2H-MoTe2 is the only product. Conversely, MoO3 leads to the preferential growth of metallic 1T′-MoTe2. The control over phase growth allows for simultaneous deposition of both 2H-MoTe2 and 1T′-MoTe2 phases on a single substrate during one CVD reaction. Furthermore, Rhodamine 6G dye can be detected using few-layered 1T′-MoTe2 films down to 5 nM concentration, demonstrating surface enhanced Raman spectroscopy (SERS) with sensitivity several orders of magnitude higher than for bulk 1T′-MoTe2.

Highlights

Minor structural changes in transition metal dichalcogenides can have dramatic effects on their electronic properties
At deposition temperatures in excess of 600 °C both the semiconducting 2H-MoTe2 and the semi-metallic 1T′-MoTe2 polymorphs are in direct competition with each other at the substrate interface[22,28]
This implies that the simultaneous growth of both 1T′-MoTe2 and 2H-MoTe2 would be impossible to achieve on the same substrate in a single step when the same seed layer is used

Summary

Introduction

Minor structural changes in transition metal dichalcogenides can have dramatic effects on their electronic properties. Few-layered 1T′-MoTe2 may become a promising sensing platform enabled through its ability to suppress fluorescence signals which often prevents reliable detection of Raman scattering from negligible traces of molecules[18] In this context, polymorphism in MoTe2 presents an interesting opportunity to exploit the role of crystal structure on the electronic properties without the need for compositional change:. Through optimisation of reaction conditions it is possible to induce growth of a specific polymorph: for example, high ramping and cooling rates tend to produce 1T′-MoTe2 while slower cooling rates and lower reaction temperatures generally lead to 2H-MoTe2 This implies that the simultaneous growth of both 1T′-MoTe2 and 2H-MoTe2 would be impossible to achieve on the same substrate in a single step when the same seed layer is used. Multiple-step procedures are unpractical from a future industrial applications point of view and finding a protocol for the preferential growth of both MoTe2 polymorphs on the same substrate and through a single step procedure is important

Methods

Results

Conclusion