Information is first given on the conditions of the XPS experiment, including whether an X-ray monochromator was used, the excitation energy (indicated by the anode material if an X-ray tube was used or a photon energy from a synchrotron-radiation source), and the overall energy resolution.

Information is then provided on how the binding-energy scale was calibrated. In most measurements, strong lines of certain metals were used to calibrate the binding-energy scale. Gold, silver, and copper are most frequently used as calibrants, and the following binding energies have been used as reference data: Au 4_7/2 = 84.00 eV, Ag 3d_5/2 = 368.27 eV, and Cu 2p_3/2 = 932.67 eV [M. P. Seah, Surf. Interface Anal. 14, 488 (1989)]. If these lines were used for calibration, the symbols Au, Ag, or Cu indicate the respective lines. If an author used other values for these reference energies, the reported binding energies were adjusted to correspond to the reference energies listed here. The carbon 1s line (for hydrocarbon or hydrocarbon groups) has also been used to calibrate the binding-energy scale for XPS measurements with non-conducting specimens; a binding energy of 284.8 eV has been assumed for this purpose. All energies are referred to the Fermi level. Ordinarily, values are shown to tenths of an eV, with some quoted to hundredths of an eV.

M. P. Seah, I.S. Gilmore, and G. Beamson [Surf. Interface Anal. 26, 642 (1998)] have reported slightly revised binding energies for the calibrant lines of gold, silver and copper (Au 4f_7/2=83.96 eV, Ag 3d_5/2=368.21 eV, and Cu 2p_3/2=932.62 eV for monochromatic Al K X-rays and values differing by up to 0.01 eV for unmonochromated Al K and Mg K X-rays).   Since the difference between the newer measurements and those used for the calibration of the instruments for most of the measurements in the database are less than or equal to 0.06 eV and the precision of most reported energies is generally no better than 0.1 eV, it was decided not to adjust the energies in the database for the change in calibration reference data.

Some other techniques have been used to calibrate the binding-energy scale:

Fermi level (FL):   the instrument was calibrated by determining the zero of the binding-energy scale from a measurement of the Fermi edge of a metal (usually with a high density of states near this edge).

Onset (ON):    the instrument was calibrated by determining the zero of the kinetic-energy scale from the onset of electron emission.

Digital voltmeter (DVM):    voltages used to determine the energy scale were calibrated directly with the aid of an accurate digital voltmeter.

The International Organization for Standardization (ISO) has developed and published ISO 15472:2010, Surface chemical analysis - X-Ray photoelectron spectrometers - Calibration of energy scales; a brief description of this standard has been published [M. P. Seah, Surf. Interface Anal. 31, 721 (2001)]. This standard specifies a method for calibrating the binding-energy scales of XPS instruments equipped with unmonochromated Al and Mg X-ray sources and with monochromated Al X-ray sources. ASTM has developed a standard based on ISO 15472, E 2108-16, Standard Practice for Calibration of the Electron Binding-Energy Scales of an X-Ray Photoelectron Spectrometer. A brief description of the latter standard has been published [C. J. Powell, J. Vac. Sci. Tech. A 19, 2689 (2001)].

Data for insulators are not included unless a technique for charge referencing was used that was believed to be valid. However, recent work has shown that there is no single or simple way to extract binding energies on insulating materials [D. R. Baer, K. Artyushkova, H. Cohen, C. D. Easton, M. Engelhard, T. R. Gergenbach, G. Greczynski, P. Mack, D. J. Morgan, and A. Roberts, J. Vac. Sci. Technol. A 38, 031204 (2020); G. Greczynski and L.Hultman, Prog. Materials Science 107, 100591 (2020)].

Some common methods of charge referencing are:
Conductor (Cond):    the material is sufficiently conducting, either because of its nature or because it is sufficiently thin, and the reported energies do not require charge correction.

Gold (Au):    gold vapor deposition method with the Au 4f_7/2 binding energy assumed to be 84.0 eV.

Adventitious carbon (AC):    use of the C 1s line of adventitious hydrocarbon on the specimen surface which is assumed to have a binding energy of 284.8 eV.

Internal hydrogen (IC):    use of an internal hydrocarbon group of the specimen compound, with the same assumed binding energy (284.8 eV).

Co-condensed hydrocarbon (CC):    a hydrocarbon was co-condensed with the vapor-deposited specimen and used as the charge reference with an assumed binding energy of 284.8 eV.

Argon (Ar):    implanted Ar with the Ar 2p line used as the charge reference.   An energy value follows the symbol Ar.   An average Ar 2p binding energy of 241.82 eV for Ar implanted in graphite has been recommended [C. J. Powell, Appl. Surf. Science 89, 141 (1995)]. The Ar 2p binding energy, however, will vary depending on the material in which the ions were implanted [P. H. Citrin and D. R. Hamann, Phys. Rev. B 10, 4948 (1974)].

Valence band minimum (VBMin):    The valence band minimum was used as a reference.

Element (Elem):    use of a pure element.

• binding energy (for a photoelectron line)
• Auger kinetic energy (for an Auger-electron line)
• doublet separations in photoelectron lines
• separation from the strongest Auger line
• Auger parameter
• chemical shift (for a photoelectron line, an Auger-electron line, or an Auger parameter)
• surface or interface core-level shift (for a photoelectron line)

1. Photoelectron lines

   1s for 1s, 2p for 2p, 4d for 4d, etc.
   2p3/2 for 2p_3/2 and 4f7/2 for 4f_7/2, etc.

   Information is given in the database for a limited number of photoelectron satellite lines. These lines are indicated by x,sat where x represents the main photoelectron line (e.g., 1s, 2p, etc.) Data are available for the following satellite lines and the indicated elements:

   1s,sat for C, N, O
   2p,sat for Si, S
   2p_3/2,sat for Cr, Ni
   3p,sat for Ni
   3d_3/2.sat for Pd
   3d_5/2,sat for Pd
   4f_5/2,sat for U
   4f_7/2,sat for Ir, U

2. Auger-electron lines
   Normally, the Auger-electron line notation designation involves (1) the shell in which the primary vacancy is created, (2) the shell participating in the Auger transition, and (3) the shell from which the Auger electron is ejected. Subshell information is included as subscripts. Unresolved structure is indicated by double subscripts. The spectroscopic designation for the atomic final state may be included in parentheses.
   
   In the NIST XPS Database, subscripts are written on line. Examples are:

   KL₂₃L₂₃(¹D is written as KL23L23(1D)
   L₃M₄₅M₄₅(¹G) is written as L3M45M45(1G)
   M₄N₄₅N₄₅ is written as M4N45N45
   M₅N₆₇N₆₇ is written as M5N67N67
   N₆O₄₅O₄₅ is written as N6O45O45

   Transitions involving the valence shell are indicated by a V.
   
   
3. Doublet separations for photoelectron lines
   These are indicated by DS followed by the line notation from (a) above, e.g., DS-2p, DS-3p, DS-4p, DS-4d, etc.
4. Separation from the strongest Auger-electron line
   This category is used for all Auger-electron line energies other than KVV, KL₂₃L₂₃(¹D), LVV, L₃M₄₅M₄₅(¹G), M₄N₄₅N₄₅, M₅N₆₇N₆₇, and N₆O₄₅O₄₅.   The kinetic energy of the minor line cited is subtracted from the standard line in its series, and the energy value has a leading plus or minus sign.
   
   The line designation begins with SA and is followed by the designation for the Auger line, e.g.,SA-KL23L23(1S) for SA-KL₂₃L₂₃(¹S), SA-L3M23M45(3P) for SA-L₃M₂₃M₄₅(³P), etc.
5. Auger parameter
   As used here in the modified form, the Auger parameter is the kinetic energy of the sharpest Auger line minus the kinetic energy of the most intense photoelectron line plus the photon energy used.   In this database, the Auger Parameter is derived simply from the sum of the kinetic energy of the Auger electron and the binding energy of the photoelectron.
   
   The line designation begins with AP, and is followed by the line designations for the photoelectron line and the Auger line.   Examples are AP-3d5/2,M4N45N45 for AP-3d_5/2,M₄N₄₅N₄₅, AP-1s,KL23L23(1D) for AP-1s,KL₂₃L₂₃(¹D), etc.
   
   In some cases, if the Auger-electron line and the photoelectron line were reported in a paper, but not the Auger parameter, the Auger parameter was calculated by the data evaluator and the notation "AP derived" is given in the charge reference field.   When the charge references are of doubtful validity, the binding energy and the Auger energy are omitted but the Auger parameter (calculated or reported) is retained.
6. Chemical shift
   The chemical shift is the difference between the energy of a photoelectron line, Auger-electron line, or Auger parameter for an element in a specific compound and the corresponding energy for the element in its pure state.   The chemical shift is frequently reported in publications, particularly when peaks for both species are present in the same spectrum.   Also included in this category are data from separate spectra where the author did not supply the absolute line energies or when the supplied line energies are believed to be inaccurate.   If a chemical shift is not reported with data for a compound in a paper, the database will supply a "calculated" chemical shift using reference data for elements; in such cases, the chemical shift is followed by "c".  The reference elemental data have been derived from an analyses of Handbook data [C. J. Powell, J. Electron Spectrosc. Relat. Phenom. 185, 1 (2012)].  Calculated chemical shifts are included as guides but their uncertainties will generally be greater than measured chemical shifts because the calculated shifts are based on a reported measurement for a compound with an instrument that may not have been adequately calibrated.
   
   Chemical shifts are included for strong photoelectron lines, the common Auger-electron lines, and Auger parameters.   A leading plus or minus sign on the chemical shift energy is required.   The designation begins with CS, followed by the symbol for a photoelectron line, an Auger line, or an Auger parameter, e.g., CS-2p3 for CS-2p_3/2, CS-L355G for CS-L₃M₄₅M₄₅(¹G), and CS-AP-2p3,L3M45M45G for CS-AP-2p_3/2,L₃M₄₅M₄₅(¹G).
   
   
7. Surface/Interface core-level shift
   The surface or interface core-level shift is the difference in binding energy for a designated photoelectron line between an atom near a surface or interface and a corresponding atom in the bulk of the specimen.   The line designation begins with SS for a surface shift and with INT for an interface shift, and this is followed by the symbol for the photoelectron line, e.g. SS-2p or INT-2p.   In some experiments, the surface core-level shifts have been determined for the first layer of atoms adjacent to a surface, for the second layer of atoms adjacent to a surface, and for the third layer of atoms adjacent to a surface; these shifts are designated SS1, SS2, and SS3, respectively.