Exploring the laser-induced Phase Changes in two-dimensional MoTe₂ via Electron Microscopy and Spectroscopy Techniques

Session

EMAG - Microscopy of Semiconductors

Authors

Samad Abdus (1), Eoin Moynihan (1, 2), Dr Alan Harvey (1), Prof Ursel Bangert (1)

Affiliations

1. University of Limerick
2. University of Warwick

Keywords

Two dimensional (2D) materials, phase change observation, atomic resolution imaging (HREM), energy dispersive X-ray spectroscopy (EDS),  Electron Energy Loss Spectroscopy (EELS),  in-situ transmission electron microscopy observations 

Abstract text

Two-dimensional (2D) materials, especially 2D transition metal dichalcogenides (TMDCs), have risen enormous and constantly increasing interest regarding their potential for future, novel applications in nano-technology, e.g., for the creation of quantum devices. MoTe₂ is one of these candidates; it is a Van der Waals material from which 2D sheets can be extracted. It has both, semiconducting and semimetal phases. The semimetal phases have potential ferroelectric properties. In a number of recent studies the phase transition of the semiconducting (2H) to the semimetal (1T’) phase, induced via laser irradiation, has been investigated. There is a conflict in the literature regarding the mechanisms of this 2H to 1T’ phase transition, as in many papers large scale characterisation techniques are used, lacking local information, which can be obtained via imaging and spectroscopic mapping on the nanometer down to the atomic scale. In our study high resolution scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), and Electron Energy Loss Spectroscopy (EELS) techniques have been employed to reveal the effects of laser irradiation on MoTe₂ on a highly spatially (atomically) resolved scale. Observations of this work reveal that the laser degrades the MoTe₂, rather than creating a phase transition, leading to large Te losses in the MoTe2 sheet, and to oxidation of the MoTe₂ surface, resulting in the formation and agglomeration of Te-nanocrystals and Mo-oxide particles. The results are compared to those of Raman spectroscopy, akin to previous papers of this topic, showing how the story changes when studies on the atomic scale are carried out by employing highly spatially resolved characterisation techniques.

References