Propriedades vibracionais e eletrônicas de cristais de iodeto de chumbo

Abstract

Lead iodide (PbI2) is a semiconductor that has recently attracted attention due to its unique physical properties, with applications in high sensitivity photodetector and X and 𝛾 ray detectors. PbI2 consists of a layer of lead atoms sandwiched between two layers of iodine atoms that weakly interact by van der Waals forces, making it stand out as a bidimensional material (2D). This work focuses on the study of structural, vibrational and electronic properties of bulk and 2D PbI2 crystals. The bulk samples were synthesized by the solution evaporation method at a constant temperature. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) were performed to confirm the 𝑃3̅𝑚1 (𝐷3𝑑) trigonal symmetry and the chemical composition, respectively. UV-VIS reflectance measurements allowed us to identify two forbidden energy regions at 2.27 eV and 2.56 eV, with the first attributed to defects and the latter corresponding to the bandgap of PbI2. These states were later identified in the photoluminescence spectra of the material, acquired at both low and ambient temperatures. Raman scattering measurements at various excitation energies revealed a resonant effect at 2.33 eV, which can be related to defect states caused by the lead atoms vacancy. We also investigated the vibrational modes dependency with the layer number of PbI2 flakes. Atomic Force Microscopy were carried out to obtain the height and layer number of each flake. We observe a strong dependency of the Raman intensity ratio between the 𝐴1𝑔 and 𝐸𝑔 modes with the number of layers, as well as a blueshift of the photoluminescence emission peak of PbI2.