RESUMEN
One-pot chemical vapor deposition (CVD) growth of large-area Janus SeMoS monolayers is reported, with the asymmetric top (Se) and bottom (S) chalcogen atomic planes with respect to the central transition metal (Mo) atoms. The formation of these 2D semiconductor monolayers takes place upon the thermodynamic-equilibrium-driven exchange of the bottom Se atoms of the initially grown MoSe2 single crystals on gold foils with S atoms. The growth process is characterized by complementary experimental techniques including Raman and X-ray photoelectron spectroscopy, transmission electron microscopy, and the growth mechanisms are rationalized by first principle calculations. The remarkably high optical quality of the synthesized Janus monolayers is demonstrated by optical and magneto-optical measurements which reveal the strong exciton-phonon coupling and enable an exciton g-factor of -3.3.
RESUMEN
Colossal permittivity materials exhibit extreme polarization in an applied electric field, providing applications in electronics and energy transmission. Understanding the atomic-scale mechanism behind colossal permittivity remains a challenging task and is key to optimizing materials with this property. The fundamental mechanism of colossal permittivity is reported and, using CaCu3 Ti4 O12 as an example, it is attributed to the formation of an unusual metallic interface between the grain and grain boundary materials (CaCu3 Ti4 O12 and Cux O (x = 1, 2), respectively), not created by oxygen vacancies as is normally the case in oxide materials. This metallic layer around the grain forms confined shells of charge that pool on one side when under an applied field, which results in colossal permittivity. A route towards enhancing colossal permittivity is explained by means of manipulating the interface properties, as well as altering sample geometries. A methodology to artificially engineer colossal permittivity metamaterials is also shown.