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Atomic layer deposition of two-dimensional transition metal dichalcogenide nanolayers

Periodic Reporting for period 4 - ALDof 2DTMDs (Atomic layer deposition of two-dimensional transition metal dichalcogenide nanolayers)

Reporting period: 2020-02-01 to 2020-12-31

Two-dimensional transition metal dichalcogenides (2D-TMDs) are an exciting class of new materials. Their ultrathin body, and special properties make them very promising candidates for a vast new range of (opto-)electronic applications. So far, most experimental work on 2D-TMDs has been performed on exfoliated flakes made by the ‘Scotch tape’ technique. The major next challenge is the large-area synthesis of 2D-TMDs by a technique that ultimately can be used for commercial device fabrication.
Building upon pure 2D-TMDs, even more functionalities can be gained from 2D-TMD alloys and heterostructures. Theoretical work on these derivates reveals exciting new phenomena, but experimentally this field is largely unexplored due to synthesis technique limitations.
The goal of this project is to combine atomic layer deposition (ALD) with plasma chemistry to create a novel surface-controlled, industry-compatible synthesis technique that will make large area 2D-TMDs, 2D-TMD alloys and 2D-TMD heterostructures a reality. This innovative approach will enable systematic layer dependent studies, likely revealing exciting new properties, and provide integration pathways for a multitude of applications.
Plasma Enhanced ALD processes have been developed to to tune the thickness and the morphology of 2DTMDs from horizontally aligned 2D nanolayers to vertically aligned fins. The 2D nanolayers are investigated for electronics, while the fin structures are evaluated for catalysis applications. Mechanism of formation of the morphology was studied by HRTEM and polarized raman spectroscopy. Atomistic simulations revealed that a buffer layer forms in between the 2D nanolayers and the substrate during the first cycles of ALD. This can have a large impact on the electronic behaviour of the 2D nanolayer.
We have shown that tunability and control over the electrical and electronic properties of TMDs can be realized by alloying and doping these materials using ALD by switching between different ALD processes during deposition.
Patterned growth of 2DTMDS have been developed by using a combination of oxide ALD and thermal sulfurization, avoiding patterning and etching of the 2DTMD and selective ALD.
Nanometer-thick 2D TMD heterostructures consisting of TiS2-NbS2 on both planar and 3D structures using atomic layer deposition (ALD) at low temperatures (200−300 °C) have been successfully synthesized. Precise thickness control of the individual TMDC material layers was demonstrated by fabricating multilayer (5-layer) TiS2-Nb2x heterostructures with independently varied layer thicknesses.
We have established new large scale, low temperature ALD processes for the growth of 2D transition metal dichalcogenides and their alloys and heterostructures.
Phase control of two-dimensional TiS2/TiS3 by plasma enhanced atomic layer deposition