Structural defects in transition metal dichalcogenide (TMDC) monolayers (ML) play a significant role in determining their (opto)electronic properties, triggering numerous efforts to control defect densities during material growth or by post-growth treatments. Various types of TMDC have been successfully deposited by MOCVD (metal-organic chemical vapor deposition), which is a wafer-scale deposition technique with excellent uniformity and controllability. However, so far there are no findings on the extent to which the incorporation of defects can be controlled by growth parameters during MOCVD processes of TMDC. In this work, we investigate the effect of growth temperature and precursor ratio during MOCVD of tungsten diselenide (WSe2) on the growth of ML domains and their impact on the density of defects. The aim is to find parameter windows that enable the deposition of WSe2 ML with high crystal quality, i.e. a low density of defects. Our findings confirm that the growth temperature has a large influence on the crystal quality of TMDC, significantly stronger than found for the W to Se precursor ratio. Raising the growth temperatures in the range of 688 °C to 791 °C leads to an increase of the number of defects, dominating photoluminescence (PL) at low temperatures (5.6 K). In contrast, an increase of the molar precursor ratio (DiPSe/WCO) from 1000 up to 100 000 leads to less defect-related PL at low temperatures.
To understand the interfacial bond formation between polycarbonate (PC) and magnetron‐sputtered metal nitride thin films, PC | X interfaces (X = AlN, TiN, (Ti,Al)N) are comparatively investigated by ab initio simulations as well as X‐ray photoelectron spectroscopy. The simulations predict significant differences at the interface as N and Ti form bonds with all functional groups of the polymer, while Al reacts selectively only with the carbonate group of pristine PC. In good agreement with simulations, experimental data reveal that the PC | AlN and the PC | (Ti,Al)N interfaces are mainly defined by interfacial C─N bonds, whereas for PC | TiN, the interface formation is also characterized by numerous C─Ti and (C─O)─Ti bonds. Bond strength calculations combined with the measured interfacial bond density indicate the strongest interface for PC | (Ti,Al)N followed by PC | AlN, whereas the weakest is predicted for PC | TiN due to its lower density of strong interfacial C─N bonds. This study shows that the employed computational strategy enables prediction of the interfacial bond formation between PC and metal nitrides and that it is reasonable to assume that the research strategy proposed herein can be readily adapted to other organic | inorganic interfaces.
20 February 2024 in The Journal of Physical Chemistry C