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NIST X-ray Photoelectron Spectroscopy Database (SRD 20), Version 5.0

Data Field Definitions:

# Terminology Definition
1. Elemental symbol The normal chemical symbol for the element which is being observed by photoelectron or Auger-electron spectroscopy.
2. Formula The chemical formula of the compound, written in either the International Union of Pure and Applied Chemistry (IUPAC) or the Chemical Abstracts Service (CAS) notation.
3. XPS Formula The chemical formula with an asterisk (*) to indicate the specific atom which is being observed. The asterisk is present only when two or more atoms of the same element are present in different bonding situations.
4. Name The name of a compound written according to either IUPAC or CAS rules. In some instances, geometrical information is included.
5. CAS Registry Number The identification number assigned by CAS. In some cases, isomers are included separately in this database.
6. Classes A scheme that classifies compounds according to broad and specific categories such as inorganic (cations and anions), organic (broad types, compounds, functional groups, and heteroatoms), ligands and ligand centers, and other classes.
7. Measurement Information a. General information
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.
b. Method of energy-scale calibration
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 47/2 = 84.00 eV, Ag 3d5/2 = 368.27 eV, and Cu 2p3/2 = 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 4f7/2=83.96 eV, Ag 3d5/2=368.21 eV, and Cu 2p3/2=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)].
c. Charge reference
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 4f7/2 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.
8. Energy Scale Evaluation The binding-energy data have been standardized to an energy scale that assumes, with Fermi level referencing, the following binding energies: Au 4f7/2 = 84.0 eV, Ag 3d5/2 = 368.27 eV, Cu 2p3/2 = 932.67 eV, and C 1s (for hydrocarbon or hydrocarbon groups) = 284.8 eV (see also Methods of energy-scale calibration and Charge reference).   Literature data will not ordinarily be included unless correspondence with at least one point on this energy scale can be determined, and any needed corrections made as indicated below.

The descriptors for this field are as follows:

Calibration study:    The measurements have been performed with greater care than most measurements.   The instrumental energy scale has been independently calibrated, and the uncertainty of the energy measurements is less than in most XPS measurements.

Reliable:    The position of the reported line is within 300 eV of a reference point on the energy scale, such as the Au 4f7/2, Ag 3d5/2 or Cu 2p3/2 lines for a conducting specimen or C 1s line for a nonconducting specimen when charge referencing with the carbon line is employed.

Correction #1:    A correction has been made to the reported energy following a one-point correction of the energy scale.   This correction has been made by a comparison of a reference value (84.00 eV for the Au 4f7/2 line, 368.27 eV for the Ag 3d5/2 line, 932.67 eV for the Cu 2p3/2 line, or 284.8 eV for the C 1s line) with a measurement of one of these lines in the paper.

Correction #2:    A correction has been made to the reported energy value following a two-point correction of the energy scale.   This correction has been made by a comparison of two reference values (84.00 eV for the Au 4f7/2 line, 368.27 eV for the Ag 3d5/2 line, or 932.67 eV for the Cu 2p3/2 line) with measurements of two of these lines in the paper.

Correction #3:    A correction has been made to the reported energy value following a three-point correction of the energy scale.   This correction has been made by a comparison of three reference values (84.00 eV for the Au 4f7/2 line, 368.27 eV for the Ag 3d5/2 line, and 932.67 eV for the Cu 2p3/2 line) with measurements of two of these lines in the paper.

Reliable and correction #1 (designation "Rel 1"):    Combination of reliable and correction #1.

Reliable and correction #2 (designation "Rel 2"):    Combination of reliable and correction #2.

Reliable and correction #3 (designation "Rel 3"):    Combination of reliable and correction #3.

For some XPS measurements, a complex lineshape may be observed due to the presence of a multiplet final state (e.g., the 4d line for the rare earths).   In such cases, it is not possible to determine a meaningful binding energy, and the designation "ambiguous multiplet" is placed in the Data Quality field.
9. Specimen Information General information is first provided on the specimen material (e.g., its physical state and/or its method of preparation). More specific information (e.g., concerning the specimen morphology or its processing history) is given in the comments. The methods that may have been used to determine specimen composition and specimen crystallinity are given. The specimen temperature during the XPS analysis is included if the information was available.
10. Citation The author name(s) are shown first and then the journal citation.
11. Data Type Seven types of XPS information are included in the database. Further explanations of each data type are given under Line Designation.
  • 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)
12. Line Designation The spectroscopic notation for the spectral line, doublet separation, or energy difference being reported.
  1. Photoelectron lines
    1s for 1s, 2p for 2p, 4d for 4d, etc.
    2p3/2 for 2p3/2 and 4f7/2 for 4f7/2, 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
    2p3/2,sat for Cr, Ni
    3p,sat for Ni
    3d3/2.sat for Pd
    3d5/2,sat for Pd
    4f5/2,sat for U
    4f7/2,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-3d5/2,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-2p3/2, CS-L355G for CS-L3M45M45(1G), and CS-AP-2p3,L3M45M45G for CS-AP-2p3/2,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.
13. Quality of Data When candidate data entries were reviewed, it appeared likely that the reported energies were obtained by a reliable data-analysis procedure.
14. Energies Numerical values (in eV) of the binding energy for a photoelectron line, the kinetic energy of an Auger line, a doublet separation (for photoelectron lines), separation of an Auger line from the strongest Auger line for that element, Auger parameter, chemical shift, or surface or interface core-level shift.
15. Energy Uncertainty The uncertainty of the energy given on the preceding line (as given in the paper).
16. Background Subtraction Method The function that may have been used for background subtraction (in the curve-fitting process used for peak location).
17. Peak Location Method The curve-fitting function used for peak location.
18. Full Width at Half-Maximum Intensity The value of the full width at half-maximum intensity found for a particular peak and curve-fitting function.

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