engleski

Characterization of nanoscale defects in 2D layered materials

Nanoscale defects substantially influence electronic, optical and magnetic properties of twodimensional transition metal dichalcogenides (2D TMDs) since surface-to-volume ratio becomes considerably great in contrast with that of their bulk counterparts. A detailed examination of domain size and morphology may provide insight into physical and mechanical properties of 2D TMDs family members. The objective of this thesis is to investigate the following morphological features: regularity of grain boundaries, domain topography and growth / nucleation centres of different geometries observed in some domains in relation to synthesis conditions and to the atomic ratio of chalcogen to transition metal in the grown samples. A pair of two-dimensional (2D) structural analogues to graphene: MoS2, WS2 as well as their heterostructure namely 2D WS2/MoS2 were synthesized on 285 and 300 nm SiO2/Si substrates by chemical vapour deposition (CVD). Three techniques were further employed to characterise the samples: X-ray photoelectron spectroscopy (XPS) to identify the chemical nature, bonding state and concentration of each chemical element, Scanning electron microscope (SEM) to obtain an overview of substrate coverage, average grain size and predominant morphology of grains, and Atomic force microscopy (AFM) to investigate domain topography and thickness as well as grain boundaries of choice in one or more locations on the same grain. Both single crystal triangular domains and polycrystalline ones which contain tilt and/or mirror twin grain boundaries were characterised via SEM and AFM.

2D materials ; graphene ; TMDs ; polymorph ; molybdenum disulphide ; tungsten disulphide ; heterostructure ; nucleation ; CVD ; XPS ; SEM ; AFM ; defects ; sulphur vacancies ; grain boundaries ; morphology ; serration ; surface topography ; single crystals ; polycrystalline grains/domains

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