ESCA - Electron Spectroscopy for Chemical Analysis
Technique Description
In Electron Spectroscopy for Chemical Analysis (ESCA), the incident radiation
is a monochromatic X-ray beam. Core electrons are emitted by the sample
as described by the well known photoelectric effect. The emitted electrons
have a kinetic energy equal to the X-ray energy less the binding energy
of the electron and the work function of the instrument. The detected kinetic energies of the electrons are converted to binding energies, thereby enabling element identification. Energy spectra are reported as binding energy vs. intensity. With the use of sensitivity factors, peak intensities can provide quantitative elemental surface compositions. ESCA analysis involves only the top 20-50Å of the sample, making it an extremely surface sensitive technique.
ESCA spectra can also provide information about an element's chemical environment or oxidation state. The chemical environment of an atom affects the strength with which electrons are bound to it. Atoms associated with different chemical environments produce peaks with slightly different binding energies which is referred to as chemical shift. Distinct chemical states which are close in energy can be deconvoluted using peak fitting programs to give percent composition of each state.
Elemental composition with a sampling depth between 20-100
ÅDetection of elements present within a fraction of a monolayerSuperior spatial resolution with the analysis spot diameter
at 300µm Chemical state informationDepth profileCan analyze both conductors and insulators
AES has better spatial resolution for analysis than ESCAESCA can give chemical state information whereas Auger
yields only elemental informationEDX, like ESCA, can analyze insulating materials, but the
sampling depth for EDX is far greater at 1-2 µmSolid samples with dimensions between 0.1 and 4.0 cm2 with low vapor pressures. Conducting and insulating samples can be analyzed by using charge neutralization when necessary. Samples must be clean and free from any high vapor pressure material. It is
Generally samples are analyzed "as received" and then again after removal of 20 Å of material by light sputtering. This is done to ensure that the surface is free of organic or other incidental contaminants.The surface elemental composition of this "20Å surface" can usually be obtained in an hour or less. Depth profile times will vary depending on sample composition and will vary from one to four hours.
Elements H and He are undetectableAccuracy of quantitative analysis limited to 3-4 % Detection limit, depending on element, ~0.2% atomic percentBack to SCIC home page.