Of course, XPS survey scans aren’t exactly self-explanatory. XPS analysis is a widely used surface analysis technique, with applications across numerous industries.Īlso referred to as electron spectroscopy for chemical analysis (ESCA), XPS is suitable for a broad range of materials, and can provide valuable information about the elemental and binding energy of a material’s surfaces and interfaces. If you’ve ever sent a sample in for surface analysis, there’s a good chance that you’re already familiar with x-ray photoelectron spectroscopy (XPS).
Thermal Gravitational Analysis (TGA) Lab Services.Electron Spectroscopy for Chemical Analysis (ESCA).Gas Chromatography Mass Spectrometry (GC/MS).Fourier Transform Infrared Spectroscopy (FTIR).Differential Scanning Calorimetry (DSC) to Measure Heat Flow.In Figure 4, the relative proportions of iron oxidation states are plotted as a function of heating temperature. 4 The changes in peak position and structure indicate that the oxide film undergoes oxidation state changes throughout the heating, and eventually is almost completely reduced to iron metal. An Fe (110) single crystal was oxidized in a vacuum chamber with ~4,000 L of pure oxygen, then heated to 800☌ while collecting XPS spectra. The use of iron oxidation state analysis is illustrated by the example shown in Figures 3 and 4. 3 The fit result indicates that the spectrum contains 28☒% Fe(0), 41±5% Fe(II), and 32☖% Fe(III). Inelastic backgrounds were removed using the Tougaard method. The measured spectrum is well fit by a linear combination of the reference spectra from Figure 1. The main disadvantage is that oxidation state standards can be difficult to prepare, especially for surface analysis were the outermost layers can be more oxidized than the bulk of the material.įigure 2 shows an example linear peak fit of a mixed iron oxidation state sample. This approach avoids having to describe the peak shapes analytically. Peak fitting can be performed on spectra of mixtures of iron oxidation states, but the use of analytic functions for the peaks can be complex and result in highly correlated parameters.Īn alternative approach to fitting complex transition metal XPS spectra is to use spectra from standards as the basis functions for linear peak fitting. The spectra exhibit a variety of structure due to initial and final state effects, including chemical shifts, asymmetric peaks, spin-orbit coupling, multiplet splitting and shake-up satellites. 1 The Fe (III) standard was measured from Fe 2O 3 powder. The Fe (II) standard was produced by heating an iron oxide film under vacuum. The Fe (0) standard was measured from an iron foil cleaned by argon ion sputtering. Chemical shifts can be used to distinguish the oxidation state of transition metals.įigure 1 shows examples of iron XPS spectra from reference compounds. Binding energies are usually reported in units of electron volts (eV).Īt high energy resolution, shifts in photoelectron peak position and structure are observed for atoms in different chemical states. These shifts are produced by ionic and covalent bond differences between atoms. The energy of photoelectron peaks is commonly expressed as binding energy, which is the energy required to remove a photoelectron from an atom.
The spectrum of photoelectron energies contains peaks characteristic of the elements present on the sample. This is the basis of the surface sensitivity of XPS.
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The mean free path of XPS photoelectrons in solids is only a few nanometers, so the photoelectrons that are analyzed originate from the outermost 1-10 nm of the sample. The energy of the photoelectrons is related to the atomic and molecular characteristics of the sample, whereas the number of photoelectrons emitted is related to the concentration of the emitting atom in the sample. The photoelectrons that are emitted are collected and energy analyzed to produce an electron energy spectrum. X-ray photoelectron spectroscopy ( XPS also known as ESCA-electron spectroscopy for chemical analysis) is a surface analysis technique in which a solid surface in a vacuum is irradiated with x-rays to produce photoelectrons by direct transfer of energy from the x-ray photons to core-level electrons in the atoms of the sample.
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