Each prominent energy peak on the spectrum corresponds to a specific element. An electron energy analyzer produces an energy spectrum of intensity (number of photo-ejected electrons versus time) versus binding energy (the energy the electrons had before they left the atom). Once these photo-ejected electrons are in the vacuum, they are collected by an electron analyzer that measures their kinetic energy. In a typical XPS spectrum some of the photo-ejected electrons inelastically scatter through the sample enroute to the surface, while others undergo prompt emission and suffer no energy loss in escaping the surface and into the surrounding vacuum. The second is that the specific energy of an elemental core level transition occurs at a specific binding energy that can uniquely identify (and in favorable cases quantify) the element. The first is that even photo-ejected electrons from core levels have slight shifts depending on the outer valence configuration of the material examined. Two key features are derived from XPS data. In a typical XPS experiment, sufficient energy is input to break the photoelectron away from the nuclear attraction force of an element. Irradiating a sample with x-rays of sufficient energy results in electrons in specific bound states to be excited. However, at UHV pressures it takes hours before a sample significantly degrades, thus enabling accurate surface interrogation using XPS. Even under optimal instrumental conditions this is too little time in which to conduct an experiment. For example, at a pressure of 10-6 mbar, background gas constituents (O 2, H 2O, etc.) can react with the surface of a sample in several seconds. The ambient atmosphere that a sample is exposed to can change its properties. Atmospheric pressure is aboutġ bar, which means that the number of atoms of gas in a UHV chamber is one-trillionth that of air per unit of volume. XPS is conducted in ultrahigh vacuum (UHV) conditions, around 10-9 millibar (mbar). Photoemission principle: When an x-ray (red arrow) bombards a sample (left), some electrons (yellow spheres) become excited enough to escape the atom (right). It can detect all of the elements except hydrogen and helium. XPS reveals which chemical elements are present at the surface and the nature of the chemical bond that exists between these elements. Kai Siegbahn, who won the Nobel Prize in physics in 1981 for his research, developed XPS in the 1960s. X-ray photoelectron spectroscopy (XPS) is a surface characterization technique that can analyze a sample to a depth of 2 to 5 nanometers (nm). The Actinide Research Quarterly: 2nd Quarter 2004 contents

Xps peak analysis