Photoelectron Spectroscopy (PES) is a technique used to study the electronic structure of materials. It involves shining ultraviolet or X-ray light onto a sample, which causes electrons to be ejected from the material. By measuring the energy and number of these emitted electrons, researchers can gain insights into the arrangement and energy levels of electrons within atoms and molecules. This method is valuable in various fields, including chemistry, physics, and materials science. PES can help identify chemical states, analyze surface compositions, and investigate the properties of nanomaterials and semiconductors. It is a powerful tool for understanding the fundamental behavior of matter at the atomic level.