Photoemission spectroscopy


Photoemission spectroscopy

Photoemission Spectroscopy (PES), also known as photoelectron spectroscopy, refers to energy measurement of electrons emitted from solids, gases or liquids by the photoelectric effect, in order to determine the binding energies of electrons in a substance. The term refers to various techniques, depending on whether the ionization energy is provided by an X-ray photon, an EUV photon, or an ultraviolet photon.

X-ray photoelectron spectroscopy (XPS) was developed by Kai Siegbahn starting in 1957 [Nordling C., Sokolowski E., and Siegbahn K., Phys. Rev. 105, 1676 (1957)] [Sokolowski E., Nordling C. and Siegbahn K., Ark. Fysik. 12, 301 (1957)] and is used to study the energy levels of atomic core electrons, primarily in solids. Siegbahn referred to the technique as Electron Spectroscopy for Chemical Analysis (ESCA), since the core levels have small chemical shifts depending on the chemical environment of the atom which is ionized, allowing chemical structure to be determined. Siegbahn was awarded the Nobel prize in 1981 for this work.

In the ultraviolet region, the method is usually referred to as photoelectron spectroscopy for the study of gases, and photoemission spectroscopy for solid surfaces.

Ultra-violet photoelectron spectroscopy (UPS) is used to study valence energy levels and chemical bonding; especially the bonding character of molecular orbitals. The method was developed originally for gas-phase molecules in 1962 by David W. Turner [Turner D.W. and Al-Joboury M.L., J. Chem. Phys. 37, 3007 (1962)] , and other early workers included David C.Frost, J.H.D. Eland and K. Kimura. Later, Richard Smalley modified the technique and used a UV laser to excite the sample, in order to measure the binding energy of electrons in gaseous molecular clusters.

Extreme ultraviolet photoelectron spectroscopy (EUPS) lies in between XPS and UPS. It is typically used to assess the valence band structure [http://www.physik.uni-kl.de/aeschlimann/pdf/paper_00000012.pdf (source)] . Compared to XPS it gives better energy resolution, and compared to UPS the ejected electrons are faster, resulting in a better spectrum signal.

Physical principle

The physics behind the PES technique is an application of Einstein's photoelectric effect. The sample is exposed to a beam of UV or XUV light inducing photoelectric ionization. The energies of the emitted photoelectrons are characteristic of their original electronic states, and depend also on vibrational state and rotational level. For solids, photoelectrons can escape only from a depth on the order of nanometers, so that it is the surface layer which is analyzed.

Typical PES (UPS) instruments use helium gas sources of UV light, with photon energy up to 52 eV(corresponding to wavelength 23.7 nm). The photoelectrons that actually escaped into the vacuum are collected, energy resolved, slightly retarded and counted, which results in a spectrum of electron intensity as a function of the measured kinetic energy. Because binding energy values are more readily applied and understood, the kinetic energy values, which are source dependent, are converted into binding energy values, which are source independent. This is achieved by applying Einstein's relation E_k=h u-E_B. The h u term of this equation is due to the energy (frequency) of the UV light that bombards the sample.

The binding energies of the measured electrons are characteristic of the chemical structure and molecular bonding of the material. By adding a source monochromator and increasing the energy resolution of the electron analyzer, peaks appear with full width at half maximum (FWHM) <5-8 meV.

References

See also

* Angle resolved photoemission spectroscopy
* Inverse photoemission spectroscopy
* Ultra high vacuum


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • photoemission spectroscopy — fotoemisinė spektroskopija statusas T sritis radioelektronika atitikmenys: angl. photoemission spectroscopy vok. Photoemissionsspektroskopie, f rus. фотоэмиссионная спектроскопия, f pranc. spectroscopie à photo émission, f …   Radioelektronikos terminų žodynas

  • Inverse photoemission spectroscopy — (IPES) is a surface science technique used to study the unoccupied electronic structure of surfaces, thin films and adsorbates. A well collimated beam of electrons of a well defined energy (< 20 eV) is directed at the sample. These electrons… …   Wikipedia

  • ultraviolet photoemission spectroscopy — ultravioletinė fotoemisinė spektroskopija statusas T sritis radioelektronika atitikmenys: angl. ultraviolet photoemission spectroscopy vok. Photoemission Ultraviolettspektroskopie, f rus. ультрафиолетовая фотоэмиссионная спектроскопия, f pranc.… …   Radioelektronikos terminų žodynas

  • Photoemission electron microscopy — (PEEM, also called photoelectron microscopy, PEM) is a widely used type of emission microscopy. PEEM utilizes local variations in electron emission to generate image contrast. The excitation is usually produced by UV light, synchrotron radiation… …   Wikipedia

  • Spectroscopy — Analysis of white light by dispersing it with a prism is example of spectroscopy. Spectroscopy ( …   Wikipedia

  • Photoemission-Ultraviolettspektroskopie — ultravioletinė fotoemisinė spektroskopija statusas T sritis radioelektronika atitikmenys: angl. ultraviolet photoemission spectroscopy vok. Photoemission Ultraviolettspektroskopie, f rus. ультрафиолетовая фотоэмиссионная спектроскопия, f pranc.… …   Radioelektronikos terminų žodynas

  • Absorption spectroscopy — An overview of electromagnetic radiation absorption. This example discusses the general principle using visible light as a specific example. A white beam source – emitting light of multiple wavelengths – is focused on a sample (the complementary… …   Wikipedia

  • X-ray photoelectron spectroscopy — [ right|thumb|350px|Basic components of a monochromatic XPS system.] X ray photoelectron spectroscopy (XPS) is a quantitative spectroscopic technique that measures the elemental composition, empirical formula, chemical state and electronic state… …   Wikipedia

  • Auger electron spectroscopy — (AES; Auger pronounced|oːʒeː in French) is a common analytical technique used specifically in the study of surfaces and, more generally, in the area of materials science. Underlying the spectroscopic technique is the Auger effect, as it has come… …   Wikipedia

  • Ultraviolet photoelectron spectroscopy — (UPS) refers to the measurement of kinetic energy spectra of photoelectrons emitted by ultraviolet photons, to determine molecular energy levels in the valence region.If Einstein’s photoelectric law is applied to a free molecule, the kinetic… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.