General Materials
ID #1018
X-Ray Photoelectron Spectroscopy,Photoelectron Spectroscopy
General Uses
· Elemental analysis of surfaces of all elements except hydrogen
· Chemical state identification of surface species
· In-depth composition profiles of elemental distribution in thin films
· Composition analysis of samples when destructive effects of electron beam techniques must be avoided
Examples of Applications
· Determination of oxidation states of metal atoms in metal oxide surface films
· Identification of surface carbon as graphitic or carbide
Samples
· Form: Solids (metals, glasses, semiconductors, low vapor pressure ceramics)
· Size: ≤6.25 cm3 (≤0.4 in.3)
· Preparation: Must be free of fingerprints, oils, or other surface contamination
Limitations
· Data collection is slow compared with other surface analysis techniques, but analysis time can be
decreased substantially when high resolution or chemical state identification is not needed
· Poor lateral resolution
· Surface sensitivity comparable to other surface analysis techniques
· Charging effects may be a problem with insulating samples. Some instruments are equipped with
charge-compensation devices
· The accuracy of quantitative analysis is limited
Estimated Analysis Time
· Requires an overnight vacuum pumpdown before analysis
· Qualitative analysis can be performed in 5 to 10 min
· Quantitative analysis requires 1 h to several hours, depending on information desired
Capabilities of Related Techniques
· Auger electron spectroscopy: Compositional analysis of surfaces. Faster, with better lateral resolution
than XPS. Has depth-profiling capabilities. Electron beam can be very damaging; bonding and other
chemical state information are not easily interpreted
· Low-energy ion-scattering spectroscopy: Sensitive to the top atom layer of the surface and has profiling
capabilities. Quantitative analysis requires use of standards; no chemical state information; poor mass
resolution for high-Z elements
· Secondary ion mass spectroscopy: The most sensitive of all surface analysis techniques. Can detect
hydrogen, and depth profiling is possible. Has pronounced matrix effects that can cause orders of magnitude variations in elemental sensitivity and make quantitative analysis difficult.
X-ray photoelectron spectroscopy (XPS) has two associated phenomena whose physical basis has been known for years.
The photoelectric effect (Ref 1) was described in 1905, and the radiationless transition (Ref 2) was discovered in 1923
during an investigation of radioactive decay. However, these phenomena attracted only limited attention for many years
following their discovery.
Interest in these effects was revived soon after World War II. High-resolution spectrometers, which had been developed
to measure the energy of β-rays, were applied to study electrons ejected by x-rays. An x-ray photoelectron spectrometer
was constructed, and use of the technique was proposed for chemical analysis of surfaces (Ref 3).
Developments that led to current XPS date from 1954, when a discrete XPS line was obtained. This was followed by the
systematic measurement of the atomic binding energies of many elements with improved accuracy. The chemical
environment was observed to affect core-level binding energies, originating the term electron spectroscopy for chemical
analysis (ESCA) (Ref 4).
Commercial x-ray photoelectron spectrometers appeared in 1969. Reliable ultra-high vacuum (UHV) systems were
developed and combined with x-ray photoelectron spectrometers in commercial instruments during the early 1970s.
Today, XPS has advanced from the atomic physics laboratory to routine use for chemical analysis of surfaces.
· Elemental analysis of surfaces of all elements except hydrogen
· Chemical state identification of surface species
· In-depth composition profiles of elemental distribution in thin films
· Composition analysis of samples when destructive effects of electron beam techniques must be avoided
Examples of Applications
· Determination of oxidation states of metal atoms in metal oxide surface films
· Identification of surface carbon as graphitic or carbide
Samples
· Form: Solids (metals, glasses, semiconductors, low vapor pressure ceramics)
· Size: ≤6.25 cm3 (≤0.4 in.3)
· Preparation: Must be free of fingerprints, oils, or other surface contamination
Limitations
· Data collection is slow compared with other surface analysis techniques, but analysis time can be
decreased substantially when high resolution or chemical state identification is not needed
· Poor lateral resolution
· Surface sensitivity comparable to other surface analysis techniques
· Charging effects may be a problem with insulating samples. Some instruments are equipped with
charge-compensation devices
· The accuracy of quantitative analysis is limited
Estimated Analysis Time
· Requires an overnight vacuum pumpdown before analysis
· Qualitative analysis can be performed in 5 to 10 min
· Quantitative analysis requires 1 h to several hours, depending on information desired
Capabilities of Related Techniques
· Auger electron spectroscopy: Compositional analysis of surfaces. Faster, with better lateral resolution
than XPS. Has depth-profiling capabilities. Electron beam can be very damaging; bonding and other
chemical state information are not easily interpreted
· Low-energy ion-scattering spectroscopy: Sensitive to the top atom layer of the surface and has profiling
capabilities. Quantitative analysis requires use of standards; no chemical state information; poor mass
resolution for high-Z elements
· Secondary ion mass spectroscopy: The most sensitive of all surface analysis techniques. Can detect
hydrogen, and depth profiling is possible. Has pronounced matrix effects that can cause orders of magnitude variations in elemental sensitivity and make quantitative analysis difficult.
X-ray photoelectron spectroscopy (XPS) has two associated phenomena whose physical basis has been known for years.
The photoelectric effect (Ref 1) was described in 1905, and the radiationless transition (Ref 2) was discovered in 1923
during an investigation of radioactive decay. However, these phenomena attracted only limited attention for many years
following their discovery.
Interest in these effects was revived soon after World War II. High-resolution spectrometers, which had been developed
to measure the energy of β-rays, were applied to study electrons ejected by x-rays. An x-ray photoelectron spectrometer
was constructed, and use of the technique was proposed for chemical analysis of surfaces (Ref 3).
Developments that led to current XPS date from 1954, when a discrete XPS line was obtained. This was followed by the
systematic measurement of the atomic binding energies of many elements with improved accuracy. The chemical
environment was observed to affect core-level binding energies, originating the term electron spectroscopy for chemical
analysis (ESCA) (Ref 4).
Commercial x-ray photoelectron spectrometers appeared in 1969. Reliable ultra-high vacuum (UHV) systems were
developed and combined with x-ray photoelectron spectrometers in commercial instruments during the early 1970s.
Today, XPS has advanced from the atomic physics laboratory to routine use for chemical analysis of surfaces.
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Last update: 2008-03-25 20:50
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