O Vacancy Left Behind By The Emitted Photoelectron

Figure 1. Schematic representation of x-ray photoelectron emission.

Figure 2. Sampling depth in XPS as represented by a plot of escape depth against kinetic energy of the escaping electron (reference 1).

XPS Quantification

The concentration of a given element in the surface is represented by the intensity of electrons (counts/second) emitted at a given characteristic energy. A typical spectrum of intensity of electrons versus electron binding energy is shown in Figure 3. This spectrum can be expanded with the computer used to acquire the data and the intensity of any peak can be measured. The computer does this by performing a background subtraction around the peak of interest and calculating the area under the peak. If there are partially overlapping peaks, a peak synthesis routine is used to extract the peak of interest. For example, the peaks synthesis routine was used to separate the yttrium 3d5/2 and 3d3/2

BINDING ENERGY (eV)

Figure 3. Typical CoCrAlY XPS spectra after sputtering through initial oxide layer.

• Low magnification

• Low resolution

• Start energy of scan, lOOOeV

• True time averaging

All XPS peaks were referenced to the adventitious carbon Is peak of 284.6eV.

The approximate binding energy of the XPS peaks used in the quantitative analyses are given in Table 1. To assist in identifying the chemical state of the yttrium, XPS spectra were made of pure standards of yttrium oxide (Y2O3) and yttrium aluminum garnet (Y3Al50j2)» The yttrium oxide and the yttrium aluminum garnet had purities of 99.999% and 99.995%, respectively. These oxides are non-conductive and charge-up during the spectra acquisition. To compensate for this, the adventitious carbon peak in peaks. All intensities are then corrected by a multiplication factor which represents the spectrometer efficiency and the probability of emission from a particular electron energy level in a given atom. These correction factors have been determined by the manufacturer of the analyzer. These factors are given in Table 1. The equation^»^ used to calculate the results in atomic percent is

Qx = quantification factor for a given element and electron orbital Ix = peak intensity for a given element.

The details of the analysis parameters used to acquire the XPS data are:

Element

Electron Designation

Approximate Binding Energy Location of the Peak (eV) for Elemental and/or Oxide State

KRATOS Quantification Factor

Cobalt

2p3/2

778 - elemental 780 - oxide

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