X-Ray Photoemission Spectroscopy (XPS, formerly known as ESCA - Electron Spectroscopy for Chemical Analysis) was developed at Uppsala University, Sweden in the 60's by a group headed by Kai Siegbahn, who in 1981 won the Nobel Prize for Physics for his work in developing the technique. Uppsala University (Swedish Uppsala universitet) is a public university in Uppsala, Sweden. ... Kai Manne Börje Siegbahn (born April 20, 1918) is a Swedish physicist. ... 1981 (MCMLXXXI) is a common year starting on Thursday of the Gregorian calendar. ... List of Nobel Prize laureates in Physics from 1901 to the present day. ...

Physical principle

The physics behind the XPS technique is really an application of Einstein's result on the photoelectric effect. The material to be analyzed is exposed to either a monochromatic or non-monochromatic (achromatic) beam of X-rays, inducing photoelectric ionization of sample atoms. In XPS, these photoelectrons are collected and their kinetic energy is determined resulting in a recorded spectrum of electron intensity as a function of the measured energy. Using Einstein's relation E_k = hν − E_B it is now possible to calculate the binding energy for a certain intensity peak since the incoming X-rays have a known frequency. This binding energy is material dependent, and moreover, it is also affected by the precise chemical structure and bonding of the material. By comparing the spectrum with tables of known elements and bindings, the chemical contents on the surface is determined. Albert Einstein photographed by Oren J. Turner in 1947. ... The photoelectric effect is the emission of electrons from matter upon the absorption of electromagnetic radiation, such as visible light or ultraviolet radiation. ... Something which is monochromatic has a single color. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...

Due to the short range in the material (because of absorption) for photoelectrons excited in this process, XPS tends to be highly surface sensitive. The information depth is typically of the order of 3 nanometres. The lateral resolution is on the other hand negatively affected by the difficulty in focusing X-ray beams effectively. The XPS technique is therefore not commonly applied for surface imaging, as opposed to e.g. SEM or Auger spectroscopy. Absorption has a number of meanings: In physics, absorption is a process in which particles of some sort encounter another material and are taken up by or even disappear in it. ... Possible meanings: Scanning electron microscope Search Engine Marketing Security Event Manager Society for Experimental Mechanics Steam Engine Makers Strategic Enterprise Management Standard Error of Measurement Structural Equation Modeling Swedish Evangelical Mission SmartStream Encryptor/Modulator This page concerning a three-letter acronym or abbreviation is a disambiguation page — a navigational aid... Auger electron spectroscopy is an analytical technique in surface chemistry and materials science. ...

Instrument details

Commercial XPS instruments include an x-ray source, e.g. Aluminium K_α radiation is common. The beam is monochromatized using Bragg reflection on a crystal and is then directed towards the sample. This whole part of the instrument is kept in an UHV Ultra high vacuum environment to avoid sample and instrument contamination due to adsorption of molecules. Most instruments are also equipped with a sputtering gun to remove unwanted molecules from the surface prior to measurement, and for extracting depth profiles. Ultra high vacuum is that regime of vacuum characterised by pressures lower than about 10-9 torr (0. ... In chemistry, adsorption of a substance or adsorbate is its concentration on a particular surface of adsorbent. ... Sputtering is a physical process whereby atoms in a solid target material are ejected into the gas phase due to bombardment of the material by energetic ions. ...

The photoelectrons are collected most often using a electrostatic lens system, although some magnetic lens designs are available. An electrostatic energy analyzer, most often consisting of concentric hemispheres, is used to determine the kinetic energy of the collected photo-electrons.

See also

• X-ray photoelectron spectroscopy
• Ultra high vacuum
• Derivatization