Abstract
In the race towards two-dimensional electronic and optoelectronic devices, semiconducting transition metal dichalcogenides (TMDCs) from group VIB have been intensively studied in recent years due to the indirect to direct band-gap transition from bulk to the monolayer. However, new materials still need to be explored. For example, semiconducting TMDCs from group IVB have been predicted to have larger mobilities than their counterparts from group VIB in the monolayer limit. In this work we report the mechanical exfoliation of ZrX2 (X = S, Se) from bulk down to the monolayer and we study the dimensionality dependence of the Raman spectra in ambient conditions. We observe Raman signal from bulk to few layers and no shift in the peak positions is found when decreasing the dimensionality. While a Raman signal can be observed from bulk to a bilayer for ZrS2, we could only detect signal down to five layers for flakes of ZrSe2. These results show the possibility of obtaining atomically thin layers of ZrX2 by mechanical exfoliation and represent one of the first steps towards the investigation of the properties of these materials, still unexplored in the two-dimensional limit.
Highlights
Layered transition metal dichalcogenides (TMDCs) have recently attracted strong interest in the scientific community due to the new properties that may arise from the two-dimensional (2D) limit and their possible dependence on the number of layers [1]
ZrS2, we could only detect signal down to five layers for flakes of ZrSe2. These results show the possibility of obtaining atomically thin layers of ZrX2 by mechanical exfoliation and represent one of the first steps towards the investigation of the properties of these materials, still unexplored in the two-dimensional limit
We identify them by optical contrast and atomic force microscopy (AFM) and we study the dimensionality fingerprint in the Raman contrast and atomic force microscopy (AFM) and we study the dimensionality fingerprint in the spectrum under conditions
Summary
Layered transition metal dichalcogenides (TMDCs) have recently attracted strong interest in the scientific community due to the new properties that may arise from the two-dimensional (2D) limit and their possible dependence on the number of layers [1]. TMDCs of the group VIB (Mo, W) have acquired a relevant role [4] These materials present remarkable layer-dependent properties in the transition from an indirect band-gap (bulk) to a direct one (monolayer). With these 2D materials and their combination in heterostructures, it is possible to fabricate new electronic and optoelectronic devices such as flexible FETs, high-electron-mobility transistors (HEMTs), p-n junctions, alternative thin-film solar cells, or photodetectors, among others [5]. In addition to despite their strong potential, up to date most of the layered TMDCs still remain the predicted higher mobility, it has been theoretically foretold that ZrX2 monolayer may exhibit almost or completely unexplored. The gray arrows represent the relative movement of the chalcogen atoms while the zirconium one remains at rest
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