XPS - X-rays Photoelectron Spectroscopy

25 of 25 videos summarized

This playlist provides detail explanation about the MOST asked questions regarding XPS analysis. I have tried my best to answer maximum questions. The following topics related XPS are covered. Working Principle of XPS: X-rays Photoelectron Spectroscopy (XPS) is a very important and key surface analysis technique. In XPS, an x-ray photon of known energy is shine on the sample, and photoelectron emitted from the core level of the atom. The Kinetic Energy (KE) of the photoelectrons detect by the XPS detector and then Binding Energy(BE) for the core- electrons are calculated by the famous equation, BE = hv - KE - ϕspec. The BE then reveals information for the elements exist at the surface or near surface. For instance, what type of elements exist, what the atom or element bonded with, the oxidation state or chemical state of the elements, the electron removed or added to the atoms etc.... Why Studying Surface is important? Response: All materials contains surfaces, which interact with other materials. For instance, the key properties such as surface wettability, corrosion, adhesion, charge transfer, and CATALYSIS are all determined by surfaces…. Survey Spectra in XPS Why we perform Survey Spectra? To know if we are analyzing the correct sample or NOT? Did somebody hand over us the wrong sample, or they have made the wrong coating! To know the contamination level etc. Simply, when the surface composition is unknown! Binding Energy (BE) in XPS analysis Binding energy (BE) generally refers how tightly the electron is attached to the nucleus. In XPS, it is a crucial concept used to understand elemental composition & their chemical environment How to measure Binding Energy? What are the common x-rays sources in XPS analysis? In XPS, two common x-rays sources are Mg Kα line (1253.6 eV) and Al Kα line (1486.6 eV). Most elements show major photoelectron or Auger peaks below 1100 eV. Why Core Electrons in XPS analysis? These core electrons are tightly bound to the nucleus having high BE and mostly influenced by the nucleus. In XPS, the common x-rays sources are Al Kα~1486.6 eV and Mg Kα ~1253.6 eV. When these high energy x-rays interact with the sample, the energy matching with the core-electron BE and the probability (cross section) of core electron emission is higher. Generally, the core level electrons are less affected as compared to the valance level electrons. The BE of these core-electrons are the characteristic of particular element. What is the Beer Lambert law of XPS? KE vs. BE in XPS Why KE and BE are inversely related in XPS analysis? Survey Spectra vs. High Resolution Spectra in XPS Types of Peaks in XPS spectra How Does XPS Technology Work? XPS data interpretation XPS surface analysis! X-ray Photoelectron Spectroscopy (XPS) is a surface technique in which x-rays bombard the surface of a material and the KE of the emitted electrons is measured. Why is XPS Surface Sensitive Technique? Multiplet Splitting / Doublet in XPS analysis If orbital angular momentum (l) = 0, single XPS peak, If *l* greater than zero, a doublet XPS peak The doublet simply occurs when there is unfilled shells containing unpaired electrons. For instance transition metals with unfilled p and d orbitals show doublet. Similarly, rare earths elements with unfilled f orbital also show doublet (multiplet splitting). hv = BE + KE + φspec Where hv is the x-rays photon energy (known value, Al ~1486.6 eV and Mg line ~ 1253.6) BE - Binding Energy of the electron or the atomic orbital from which the electron originates (unknown variable) KE - Kinetic Energy of the photoelectrons (measure in the XPS spectrometer) Øspec - Spectrometer work function (a constant value in few eV ~ 4.6 eV).