Investigation of Surface Properties of Perovskite Semiconductors using Reflection Electron Energy Loss Spectroscopy (REELS)

The analysis of fundamental semiconductor properties, such as energy level positions and bandgaps, are important to enhance our understanding of these materials and to further improve their performance in applications. In this context, spectroscopic tools such as ultraviolet photoelectron spectroscopy (UPS), inverse photoelectron spectroscopy (IPES) and UV-vis measurements can be employed. In this project, we explore the use of reflection electron energy loss spectroscopy (REELS) for the first time as a novel technique to investigate the surface bandgap of perovskite-based semiconductor materials.<br/>This measurement technique records the energy loss due to inelastic electron scattering processes through the excitation of electronic transitions. Notably, it is a very surface sensitive method with decent energy resolution (ΔE ≈ 120 meV, similar to UPS) which makes it an intriguing technique to gain insights on the surface bandgaps as well as the joint density of states (DOS) over a wide energy range. <br/>In this work, we try to understand the observed energy loss spectra in order to establish guidelines to investigate surface properties of perovskite semiconductors. For that reason, information gathered using REELS are compared to UV-vis measurements. Furthermore, by utilizing various incident electron kinetic energies we are able to vary the probing depth. Having this additional control makes it possible to gain additional information on interface properties, which is important to understand the performances of devices.<br/>Our band gap measurements by REELS agree well with the optical bandgaps, therefore our results show that REELS technique can be used as an effective tool to explore such properties at the surfaces of perovskites as well as other semiconductor materials.