Applications of X-ray photoelectron spectroscopy (XPS)

X-ray photoelectron spectroscopy (XPS) patterns are expressed as photoelectron intensity in terms of bond energy. These patterns may have three peaks in the background, which are caused by light emission from central electron levels, light emission from valence levels, and object electron emission due to X-ray excitation. The figure below shows the X-ray photoelectron spectroscopy pattern of the silver surface, in which the peaks of the central energy levels are shown as s3, p3 and d3. Capacitance level peaks are shown as d4 and Auger peaks are shown as MNN. Photoelectron peaks of central energy levels are the main peaks used for elemental analysis. Valence peaks are those with low binding energy (0 to 20 eV) and are mostly used for studying the electronic structure of materials. Auger peaks, produced by the X-ray stimulated Auger process, are also useful for chemical analysis .

Figure 1-X-ray photoelectron spectroscopy pattern of silver stimulated with MgKα with a pass energy of 100 electron volts.

X-ray photoelectron spectroscopy and Auger electron spectroscopy are powerful tools for surface chemical analysis. These methods can identify chemical elements in the inner layer several nanometers from the surface. The important point is that the peak positions of the elements in X-ray photoelectron spectroscopy and Auger electron spectroscopy are sensitive to their chemical position (chemical bond with other elements). For example, the carbon peak positions in ₂ CO and saturated hydrocarbons are different from each other. This phenomenon, known as chemical shift in X-ray photoelectron spectroscopy and Auger electron spectroscopy, provides additional information for chemical analysis. X-ray photoelectron spectroscopy and Auger electron spectroscopy can also produce images of the depth of the surface layer of bulk materials and reveal the spatial distributions of different elements on the surface of bulk materials.

Qualitative analysis   

Identifying the peaks of spectra is the main task of qualitative analysis. For example, we can use the data in Figure 9-8 to identify the peaks of Auger electron spectroscopy patterns. The binding energy of the elements in the central energy levels are the main source of identifying the peaks of X-ray photoelectron spectroscopy spectra. Peak identification is very important in X-ray photoelectron spectroscopy. In addition to the spectrum characteristics discussed in the previous section, other factors such as chemical shift and surface charge complicate peak identification.

Courier identification

It is easy to identify the peaks in the Auger electron spectroscopy patterns. The peaks in the Auger electron spectroscopy pattern are identified by comparing the experienced peaks with the index peaks listed in reference books or computer databases. But the identification of peaks in X-ray photoelectron spectroscopy spectra is more complicated, because Auger peaks may also exist. Usually, two different X-ray sources are used to distinguish the Auger peak from the photoelectron peaks. The Auger peak shows the kinetic energy of the Auger electron, which changes with the primary X-ray energy. Therefore, the Auger peak in its apparent binding energy in the X-ray photoelectron spectroscopy model is shifted by changing the X-ray source. For example, by changing the radiation from MgKα (1253.6 eN) to AlKα (1486.6 eN), the Auger peak in the X-ray photoelectron spectroscopy spectrum shifts by 233 eN.

Applications of X-ray photoelectron spectroscopy (XPS)

X-ray photoelectron spectroscopy (XPS) patterns are expressed as photoelectron intensity in terms of bond energy. These patterns may have three peaks in the background, which are caused by light emission from central electron levels, light emission from valence levels, and object electron emission due to X-ray excitation. The figure below shows the X-ray photoelectron spectroscopy pattern of the silver surface, in which the peaks of the central energy levels are shown as s3, p3 and d3. Capacitance level peaks are shown as d4 and Auger peaks are shown as MNN. Photoelectron peaks of central energy levels are the main peaks used for elemental analysis. Valence peaks are those with low binding energy (0 to 20 eV) and are mostly used for studying the electronic structure of materials. Auger peaks, produced by the X-ray stimulated Auger process, are also useful for chemical analysis .

Figure 1-X-ray photoelectron spectroscopy pattern of silver stimulated with MgKα with a pass energy of 100 electron volts.

X-ray photoelectron spectroscopy and Auger electron spectroscopy are powerful tools for surface chemical analysis. These methods can identify chemical elements in the inner layer several nanometers from the surface. The important point is that the peak positions of the elements in X-ray photoelectron spectroscopy and Auger electron spectroscopy are sensitive to their chemical position (chemical bond with other elements). For example, the carbon peak positions in ₂ CO and saturated hydrocarbons are different from each other. This phenomenon, known as chemical shift in X-ray photoelectron spectroscopy and Auger electron spectroscopy, provides additional information for chemical analysis. X-ray photoelectron spectroscopy and Auger electron spectroscopy can also produce images of the depth of the surface layer of bulk materials and reveal the spatial distributions of different elements on the surface of bulk materials.

Qualitative analysis   

Identifying the peaks of spectra is the main task of qualitative analysis. For example, we can use the data in Figure 9-8 to identify the peaks of Auger electron spectroscopy patterns. The binding energy of the elements in the central energy levels are the main source of identifying the peaks of X-ray photoelectron spectroscopy spectra. Peak identification is very important in X-ray photoelectron spectroscopy. In addition to the spectrum characteristics discussed in the previous section, other factors such as chemical shift and surface charge complicate peak identification.

Courier identification

It is easy to identify the peaks in the Auger electron spectroscopy patterns. The peaks in the Auger electron spectroscopy pattern are identified by comparing the experienced peaks with the index peaks listed in reference books or computer databases. But the identification of peaks in X-ray photoelectron spectroscopy spectra is more complicated, because Auger peaks may also exist. Usually, two different X-ray sources are used to distinguish the Auger peak from the photoelectron peaks. The Auger peak shows the kinetic energy of the Auger electron, which changes with the primary X-ray energy. Therefore, the Auger peak in its apparent binding energy in the X-ray photoelectron spectroscopy model is shifted by changing the X-ray source. For example, by changing the radiation from MgKα (1253.6 eN) to AlKα (1486.6 eN), the Auger peak in the X-ray photoelectron spectroscopy spectrum shifts by 233 eN.