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Epitaxial transition-metal dichalcogenide monolayers for spin-valleytronics

Final Report Summary - SPINVALLEY (Epitaxial transition-metal dichalcogenide monolayers for spin-valleytronics)

Final summary of work progress and achievements with respect to the planned tasks;

With respect to WP1 – VdWE and in-situ characterization of TMD monolayers, and WP2 – Surface modification of TMD monolayers resulting from WP1 during the outgoing phase at NUS (M1-M24), the fellow has achieved the following results:
• Successful development a UHV-MBE system for the VdWE growth of high-quality 2D-TMDs studied in this project.
• Investigation of the modifications of the 2D-TMD surfaces by oxygen and water molecules.
In response to WP3 – Electrical manipulation and readout of coupled spin-valley phenomena during the return phase at UT (M25-M32), the fellow has obtained the following results:
• Manipulation of the electronic and magnetic properties of 2D-vanadium TMDs by electronic orbital hybridization with 3d ferromagnets.
• Modification of the 2D vanadium TMD surfaces by molecular magnets, such as cobalt phthalocyanine (CoPc) molecules.

Final summary of training activities/transfer of knowledge activities;
During the course of this project, the fellow has benefited from the following training activities/transfer of knowledge activities:
• Regular seminars organized by the host group as well as by the Graphene Research Centre (now Centre for Advanced 2D Materials) in NUS for knowledge transfer.
• Coaching of several research students, including two exchange students from the Fontys University of Applied Sciences in the Netherlands, and from the Indian Institute of Science Education and Research at Pune, respectively. The fellow has also supervised two PhD research students, Mr. Zhang Lei and Ms. Rebekah Chua, in the outgoing host group.
Highlight of significant results;
The fellow has obtained the following significant results within the scope of the SpinValley project, which are expected to lead to a total of 4 top-tier peer-reviewed publications:
For the outgoing phase (M1-M24)
• In-situ growth and characterization of vanadium-based TMD monolayers (i.e. VSe2 and VTe2) on graphite and graphene/SiC(0001) by molecular-beam epitaxy for the first time.
• Successfully developed capping/decapping processes of the vanadium-based TMDs using an amorphous Se cap for ex-situ sample transfer.
• Surface modification of the vanadium-based TMDs by oxygen and water molecules, and in-situ characterization of the corresponding electronic structures by core-level electron spectroscopy and surface-based microscopy.
For the return phase (M25-M32)
• In-situ investigation of electronic orbital hybridization effects at 3d ferromagnet (FM)/2D-TMD interfaces using synchrotron-based core-electron spectroscopies (XPS, XAS and XMCD). Hybridization-induced magnetic moment in the vanadium atoms has been observed for the first time at the Co/2D-VSe2 interface. Such magnetic moment can persist up to room temperature and is found to couple antiferromagentically with that of the Co layer.
• Surface adsorption of CoPc molecules on 2D-VSe2 has been studied by STM and STS. The in-situ measurements indicate considerable charge transfer between the transition metal ions of the molecular magnets and the 2D-TMD. This first study will be complemented with additional electron spectroscopic measurements to be performed in May at the NSRRC.