Growth of two-dimensional materials and Investigation of their structural and electronic properties.

My research activities focused on the growth and characterisation of two-dimensional materials. Initially Physical Vapour Deposition (PVD) growth of single layer (SL) MoS2 on Au(111) was performed by dosing Mo in H2S atmosphere at room temperature followed by annealing (Temperature Programmed Growth (TPG)) and we studied the evolution of intermediate species during the transformation by measuring fast-XPS. Thereafter by careful tuning the growth parameters, we developed a new procedure that leads to the direct growth of high quality SL MoS2 by dosing Mo in H2S atmosphere at high temperature (High Temperature Growth (HTG). Besides the improved quality of the layer the HTG growth method results in just one single orientation of the layer, leading to complete out-of plane spin polarisation in Spin-resolved ARPES measurements, whereas TPG produced a mixture (70:30) of two opposite orientations. We studied the growth of SL WS2 on Au(111) by following the HTG method. In-situ fast XPS allowed to find the proper growth parameters leading to singly oriented WS2 high quality layer. The absence of partially sulfided peaks in the W 4f and S 2p core levels and sharp LEED spots indicated the high quality of the grown layer that was also reflected in the ARPES measurements that presented sharper bands than previously reported values and allowed the observation of moirè-induced mini gaps and the quantification of branch-dependent electron-phonon coupling strength. MoS2 growth on Ag(111) was also performed by HTG method and resulted in the formation of two 180° rotated domains in equal proportion, as seen with LEED and XPD. LEED pattern indicated a very high structural order of the layer supported by the STM measurements. The Mo 3d core level presented a larger asymmetry than that measured for MoS2/Au(111) which is likely due to a semiconductor to metal transition of the MoS2 layer due to the strong interaction with the Ag(111) substrate. HTG growth of SL MoS2 on Ag(110) was performed to explore the effect of the different substrate geometry on the properties of MoS2. The resulting layer was of very high quality, as determined with XPS, LEED, STM and ARPES measurements. The LEED and XPD patterns showed the presence of equal proportions of two mirror domains. A structural model for the relative arrangement of the hexagonal MoS2 lattice with respect to the rectangular lattice of the substrate was obtained based on LEED and STM measurements. In order to study the reported growth of Silicene on Ir(111), the adsorption of Si on Ir(111) was studied for Si coverages up to more than one monolayer and characterized by high-resolution XPS and LEED. Experiments and DFT calculations showed dominant Si adsorption at the hollow sites together with segregation into the surface and even bilayer formation at high coverage, thereby implying the instability of Si/Ir(111) interface towards Si-Ir alloys, rather than formation of silicene layer.