Dangling Bond-Induced Surface Depletion in CdS Leaf

Abstract

Understanding the surface electronic properties of nanostructured CdS is important for the development of next-generation sensors and optoelectronic and photocatalytic devices, as efficiency is solely dependent on surface activity. In this study, we have shown dangling bond-induced surface depletion in the CdS leaf structure. The angle-resolved X-ray photoelectron spectroscopy (ARXPS) data of the Cd 3d peak measured at different take-off angles ranging from 0 to 55 degrees indicate that the spectra contain surface peaks centered at 407.9 and 414.6 eV with the bulk peaks centered at 405.5 and 412.2 eV. Furthermore, the separated Cd 3d XPS peaks of the surface and the bulk are merged by the stray electrons of the electron flood gun operated at a bias voltage of 9 eV and an emission current of 1 mA, indicating that the electron deficiency of the depletion layer can be modulated by external electrons. It is observed that the valence band maxima (VBM) of the surface and the bulk are located at 3.14 and 1 eV below the Fermi energy level, respectively. However, such ARXPS features are not observed in the case of spherical-structured CdS. The analysis of these results suggests that the depletion layer of the leaf structure is formed at the surface due to the high density of dangling bonds. The dangling bonds responsible for surface depletion are further confirmed from the density of states (DOS) calculation using density functional theory (DFT) with Coulomb interaction (U).