RESUMEN
Van der Waals heterostructures open up vast possibilities for applications in optoelectronics, especially since it was recognized that the optical properties of transition-metal dichalcogenides (TMDC) can be enhanced by adjacent hBN layers. However, although many micrometer-sized structures have been fabricated, the bottleneck for applications remains the lack of large-area structures with electrically tunable photoluminescence emission. In this study, we demonstrate the electrical charge carrier tuning for large-area epitaxial MoSe2 grown directly on epitaxial hBN. The structure is produced in a multistep procedure involving Metalorganic Vapor Phase Epitaxy (MOVPE) growth of large-area hBN, a wet transfer of hBN onto a SiO2/Si substrate, and the subsequent Molecular Beam Epitaxy (MBE) growth of monolayer MoSe2. The electrically induced change of the carrier concentration is deduced from the evolution of well-resolved charged and neutral exciton intensities. Our findings show that it is feasible to grow large-area, electrically addressable, high-optical-quality van der Waals heterostructures.
RESUMEN
1H-pyrrolo[3,2-h]qinoline (PQ) and 2-(2'-pyridyl)pyrrole (PP) are important systems in the study of proton-transfer reactions. These molecules possess hydrogen bond donor (pyrrole) and acceptor (pyridine) groups, which leads to the formation of cyclic dimers in their crystals. Herein, we present a joint experimental (Raman scattering) and computational (DFT modelling) study on the high-pressure behaviour of PQ and PP molecular crystals. Our results indicate that compression up to 10 GPa (100 kbar) leads to considerable strengthening of the intermolecular hydrogen bond within the cyclic dimers. However, the intramolecular N-HâââN interaction is either weakly affected by pressure, as witnessed in PQ, or weakened due to compression-induced distortions of the molecule, as was found for PP. Therefore, we propose that the compression of these systems should facilitate double proton transfer within the cyclic dimers of PQ and PP, while intramolecular transfer should either remain unaffected (for PQ) or weakened (for PP).