Publishing XPS Experimental Details in Journals

by B. Vincent Crist

“XPS Analysis Details” that must be included in each Publication that uses XPS

The following is an example of an XPS analysis description that will be included in the experimental section of your publication. Your description may have to be modified from this somewhat if non-standard conditions were used.


X-ray Photoelectron Spectroscopy Analyses:
XPS analyses were carried out by using a [insert name of your instrument and model name or model #] instrument using a monochromatic Al Kalpha X-ray source (xx mA, xx kV).  The instrument BE energy scale (work function) was calibrated to give a binding energy (BE) at 83.96 eV for the Au 4f7/2 signal for freshly ion etched metallic gold (Au). The spectrometer dispersion (energy range) was adjusted to give a BE at 932.62 eV for the Cu 2p3/2 line of freshly ion etched metallic copper (Cu). High energy resolution spectra from these Cu 2p3/2 and Au 4f7/2 signals were measured at the start of the data collection and also at the end of data collection to confirm the reproducibility of the energy scale.  Their measured BEs are XXX.XX and XX.XX eV, respectively.  The charge compensation (neutralizer) system was used on all non-conductive specimen samples. The surface of each non-conductive sample was irradiated with a flood of electrons accelerated to XX eV to produce a nearly neutral surface charge. The XY position of the flood gun was optimized for each sample just before analyzing that sample. Survey scan analyses  (0-1100 eV range) were carried out by using an X-ray beam size of XXX x XXX microns, and a pass energy of XXX eV. High energy resolution chemical state analyses (20-50 eV wide range) were carried out by using an X-ray beam size of XXX x XXX microns and a pass energy of XX eV. Data from all insulating materials have been charge corrected (referenced) using the main signal of the carbon 1s spectrum (hydrocarbon, C-C, moiety) assigned to occur at 285.0 eV. The C (1s) spectrum was collected using high energy resolution settings. XPS can detect all elements except hydrogen and helium, probes the surface of the sample to a depth of 5-10 nanometers depending on the atomic number of the elements measured. XPS has a routine detection limits that ranges from 0.1 to 0.5 atomic percent depending on the element and its main signal.

Below is a list of various XPS experimental details that may be useful or need to be reported in various scientific publications.

1) Instrument Name: (for example) Thermo K-Alpha, Thermo NEXSA, Kratos Axis Ultra, Kratos Axis Supra, Surface Science Laboratories S-Probe, PHI Quantum 2000, PHI Quantera, Ulvac-PHI Quantes, Ulvac-PHI VersaProbe III, VG ESCALAB 250
2) X-ray Source: (for example)  monochromatic Al Kalpha 1487 eV, achromatic Mg Kalpha, beta 1253 eV, He(I), He(II), synchrotron, with an X-ray angle of incidence: 35 deg (45 deg)
3) X-ray Power:  (for example)  XX mA and XX kV, 210 W (= 15mA x 14 kV)
4) Spectrometer Energy Calibration Details:  (Version #1 example) When peak maximum BEs from high energy resolution spectra of Cu 2p3/2 and Au 4f7/2 were found to deviate outside the accepted error range, the instrument energy scale (work function) was adjusted (calibrated) to give the desired Calibration binding energies (BEs) at 83.96 eV for the Au 4f7/2 line for freshly ion etched metallic gold and the spectrometer dispersion was adjusted to give a BE of 932.62 eV for the Cu 2p3/2 line of freshly ion etched metallic copper. (Version #2 example) On the same day that each sample was analyzed by XPS, the BEs for Cu (2p3/2) and Au (4f7/2) were measured. When the BEs deviated by >0.2 eV from the true BE values, the spectrometer energy scale was adjusted to produce the true BEs for Cu and Au with an error <0.2 eV.
5) Spot (Beam) Size, or Area of Analysis:  (for example)  300 micron spot, 300×700 micron beam size (area of analysis) with an X-ray angle of incidence: 35 deg (45 deg)
6) Charge Neutralizer (electron flood gun) Use: (for example)  The instrument’s on-board charge compensation system was used on all non-conducting samples.  A low voltage beam of electrons from an electron flood gun was operated at ‘X.X’ eV and ‘XX‘ mA settings. The gun included a beam of low voltage Ar ions. The XY positions were adjusted to give the most intense signal with the most narrow FWHM. (HDPE or PP can be used to check these)
7) Effectiveness of Neutralizer: (for example) XY beam position was adjusted until the charge neutralization was deemed to have been fully achieved by monitoring the FWHM and BE of the O 1s signal or C (1s) signal for the hydrocarbon signal of adventitious carbon.  The XY positions of the flood gun were adjusted to give the most intense signal with the most narrow FWHM.
8) Charge Correction (Reference) Procedures(for example) Spectra have been charge corrected (referenced) to force the main (hydrocarbon) signal of the carbon 1s spectrum (adventitious carbon) to appear at 285.0 eV (or 284.6 eV) for all non-conductive specimen samples.  The voltage difference (delta eV) used to charge correct the carbon (1s) was used to charge correct (reference) all other signals from that same sample. A thick gold dot can also be used.  (Note: Very thin deposited films of Gold are not reliable.)
9) Instrument Base Pressure: (for example) 8 x 10-10 Torr (with no samples inside).
10) Instrument Operating Pressure: 5 x 10-8 Torr (with sample inside) or 2 x 10-7 torr when Argon is used with a flood gun or an ion gun.
11) Scan Details, Pass Energy, Number of Sweeps, Step Size, Scan Window: (for example) The C 1s spectra were taken with a minimum of 10 scans with a scan window of 278-295 eV using a 0.05 eV step and 20 eV pass energy.
12) Electron Collection Lens: (for example) Electron take-off angle is 0 degrees with respect to the collection lens (produces max sampling depth). The electron collection angle is 60 degrees.  (Note:  very old XPS used a 6-7 degree electron collection angle.)
13) Spectrometer Resolution Details: (for example) Ag 3d5/2 line FWHM at 10 eV pass energy was 0.48 eV (after ion cleaning).  Ag 3d5/2 line FWHM at 50 eV pass energy was 0.65 eV. Ultimate source resolution for monochromatic Al K(alpha) X-rays is ~0.16-0.21 eV which is broadened by the electron energy analyzer.  The instrumental resolution was determined to be 0.35 eV at 10 eV pass energy using the Fermi edge of the valence band for metallic silver. Ultimate FWHM energy resolution with charge compensation system turned on is <0.68 eV for the FWHM of clean. scraped PET.
14) Software Used for Curve-Fitting: (for example) SDP v8.0, CasaXPS v2.3.35, XPSPeak, Vision 2 Processing Software
15) Peak-shape Fitting Details: (for example)  80% Gaussian/20% Lorentzian, Asymmetric line-shape, XX% Voigt, GHM and LHM, Convolved Voigt
16) Background Used for Curve-Fitting: (for example)  Linear, Iterated Shirley, Sherwood-Proctor, Castle-Vegh, Tougaard
17) Other Curve-Fitting Details as used: (for example)  FWHM, constraints, doublet separations, peak-area ratios controlled, peak BE differences controlled