Our instrument, formerly named "Corrosion I", utilizes several different techniques for analyzing surfaces. They are Auger electron spectroscopy (AES), temperature-programmed desorption spectroscopy (TPD), high-resolution electron energy loss spectroscopy (HREELS), and low energy electron diffraction (LEED).
Auger spectroscopy measures the energy of electrons from the Auger effect of excited electrons in the surface region. There are two different ways that an atom with an excited core electron (a core electron hole) can return to its ground state. The first is that an energetically higher electron “jumps” to the hole left by the excited core electron, thereby releasing characteristic x-ray radiation. The second is the Auger effect, by which the hole left by the excited core electron is filled by an outer electron. The energy from this is transferred by a radiationless process to another electron that will then be ejected from the surface with a characteristic kinetic energy. The result is a spectrum of the intensity of electrons as a function of the kinetic energy of the Auger electron with the placement of the peaks giving a qualitative view of what elements are present on the surface.
Temperature-programmed desorption is the process in which an adsorbed species is heated to a specified temperature, resulting in certain reactions and the desorption of their products from the surface. A mass spectrometer then measures the concentration of each of the products. Analysis of desorption temperatures and of the corresponding desorbed products can yield information about the chemical kinetics of the reactions that are being observed.
High-resolution electron energy loss spectroscopy or HREELS studies the vibrations of surface species by the electron energy loss (EEL) of an electron beam after it is scattered by the surface. There are three different scattering mechanisms that can occur with EEL: dipole, impact, and resonance scattering – though HREELS is mostly concerned with dipole scattering. Dipole scattering occurs when a moving electron and its associated electronic field interact with the surface species analogous to interactions in infrared (IR) spectroscopy. Only vibrations that can induce a dipole moment change normal to the surface become excited. The result is a spectrum of intensity versus energy loss that gives information about the binding to the surface of adsorbates.
Low energy electron diffraction (LEED) directs a beam of electrons of well-defined low energy onto a sample that must be a single crystal surface. The dual wave/particle nature of the electrons will cause the beam to generate a backscattered electron diffraction pattern. Analysis of the spot positions of the diffraction pattern can give information about the size, symmetry, and rotational alignment of absorbates relative to the surface. In addition, the intensity of the spots on the diffraction patterns recorded as a function of the incident electron beam energy may produce information on atomic positions of the atoms in the crystal or ordered sample.
Our instrument is currently equipped with the following.
Equipment:
PowerTen high current power supply
Watlow temperature controller
MKS 300 amu residual gas analyzer
McAllister high resolution electron energy loss spectrometer
Physical Electronics Industries, Inc. 10-155 Auger electron spectrometer
Physical Electronics Industries, Inc. 15-120 low energy electron diffraction optics