**3.6 X-ray photoelectron spectroscopy (XPS)**

X-ray photoelectron spectroscopy (XPS) is one of the most widely investigated research methods for further chemical reactions, it is also used to classify nanoscale objects. What is clear from physical thought is the effect of electrical images [67]. XPS is an effective quantitative process for determining elements' electronic structure, primary structure, and oxidation conditions in a matter. It can also test the ligand exchange interactions with local NP operations and key structures/shells and operate under very high vacuum conditions. Nag and colleagues have published a review paper outlining the role of XPS as a fun way to study the internal heterostructures of NPs. For example, it was used to investigate the structure of a crystal structure dependent on the environment of the metal chalcogen NPs of various sizes [67]. It can also distinguish between core/shell and homogeneous alloy structures and identify ligand binding modes such as trioctylphosphine oxide (TOPO) on the surface of metal chalcogenide NPs. For example, if a TOPO bond is preferable to the surface of the metal, then a portion of the excess chalcogenide may be easily oxygenated in the air. In contrast to microscopy techniques, such as TEM, which uses side-by-side alignment to determine elements in a straight line to the test electron column, XPS investigates the formation of an object aligned with an electron line. Concerning the core-shell NPs, shard has published a text that reports the precise way to translate XPS data for those types of particles. It involves a straightforward approach to turning XPS firmness into an overlay layer, ideal for round NPs. As an additional benefit of XPS, the author mentions that it provides in-depth information, such as the size of NPs (at a depth of 10 nm from the top), and does not seriously damage the samples. Two barriers to XPS analysis are sample preparation (i.e., solid dry form is required without contamination) in addition to the information definition.
