Basic XPS Information Section

 The Basic XPS Information Section provides fundamental XPS spectra, BE values, FWHM values, BE tables, overlays of key spectra, histograms and a table of XPS parameters.
The Advanced XPS Information Section is a collection of additional spectra, overlays of spectra, peak-fit advice, data collection guidance, material info,
common contaminants, degradation during analysis, auto-oxidation, gas capture study, valence band spectra, Auger spectra, and more.
Published literature references, and website links are summarized at the end of the advanced section.
→  Periodic Table – HomePage                           XPS Database of Polymers                  → Six (6) BE Tables


Iron (Fe)

Ferum

Siderite – FeCO3 Iron – Feo Ferrobrookite – Fe2TiO5

 

  Page Index
  • Expert Knowledge & Explanations


Iron (Feo) Metal

Peak-fits, BEs, FWHMs, and Peak Labels

  .
Iron (Feo) Metal
Fe (2p3/2) Spectrum – raw spectrum
Ultra-high energy resolution		 Iron (Feo) Metal
Peak-fit of Fe (2p3/2) Spectrum (with asymm)
Ultra-high energy resolution
   
→  Periodic Table – HomePage  
Iron (Feo) Metal
Fe (2p) Spectrum – extended spectrum
 Iron (Feo) Metal
Peak-fit of Fe (2p) Spectrum

 

Survey Spectrum of Iron (Feo) Metal
with Peaks Integrated, Assigned and Labelled

 

→  Periodic Table 

XPS Signals for Iron, (Feo) Metal

Spin-Orbit Term,  BE (eV) Value, and Scofield σ for Aluminum Kα X-rays (1486 eV, 8.33 Ang)

Overlaps Spin-Orbit Term BE (eV) Value Scofield σ from 1486 eV X-rays IMFP (TPP-2M) in Å
  Fe (2s) 845 4.57  
  Fe (2p1/2) 720 5.60 13.6
Cu (Auger) & Ni (Auger) overlap Fe (2p3/2) 706.88 10.82 13.6
Ba (4d) overlaps Fe (3s) 92 0.745 21.1
Li (1s) & Mg (2p) overlap Fe (3p) 53 1.669 21.5

σ:  abbreviation for the term Scofield Photoionization Cross-Section which are used with IMFP and TF to generate RSFs and atom% quantitation

Plasmon Peaks

Energy Loss Peaks

Auger Peaks

Intrinsic Plasmon Peak:  ~xx eV above peak max
Expected Bandgap for Fe2O3: 2.3 eV
*Scofield Cross-Section (σ) for C (1s) = 1.0

 

 

Valence Band Spectrum from Feo Metal
 Fresh exposed bulk produced by extensive Ar+ ion etching

 

 

Plasmon Peaks from Iron, Feo Metal
 Fresh exposed bulk produced by extensive Ar+ ion etching

Fe (2p) – Extended Range Spectrum Fe (2p) – Extended Range Spectrum – Vertically Zoomed
 

 

Fe (LMM) Auger Peaks from Iron, Feo Metal
 Fresh exposed bulk produced by extensive Ar+ ion etching
Feo Metal Native Fe Oxide

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 

 

Artefacts Caused by Argon Ion Etching

Iron Carbide(s)

can form when ion etched Reactive Metal Surfaces capture
Residual UHV Gases (CO, H2O, CH4 etc)

Argon Trapped in Feo metal

can form when Argon Ions are used
to removed surface contamination

 

Side-by-Side Comparison of
Feo Native Oxide & Iron Oxide (α-Fe2O3)
Hematite, natural crystal, exposed bulk
Peak-fits, BEs, FWHMs, and Peak Labels
   
Feo Native Oxide α-Fe2O3  – Hematite – natural crystal – exposed bulk
Fe (2p) from Fe Native Oxide
Flood Gun OFF, As-Measured, C (1s) at 285.0 eV 		 Fe (2p) from α-Fe2O3 – crystal
Flood Gun OFF

 
→  Periodic Table 
  . 
Fe Native Oxide α-Fe2O3 – Hematite
C (1s) from Fe Native Oxide
As-Measured, C (1s) at 285.0 eV (Flood Gun OFF)

C (1s) from α-Fe2O3 – crystal
Flood Gun OFF

  . 
Fe Native Oxide α-Fe2O3 – Hematite
O (1s) from Fe Native Oxide
As-Measured, C (1s) at 285.0 eV (Flood Gun OFF)

O (1s) from α-Fe2O3 – crystal
Flood Gun OFF

 
.
Fe Native Oxide α-Fe2O3 – Hematite
Fe (KLL) Auger Peaks from Fe Native Oxide
As-Measured, C (1s) at 285.0 eV (Flood Gun OFF)

Fe (KLL) Auger Peaks from α-Fe2O3 – crystal
Flood Gun OFF

 

 

Survey Spectrum of Iron (Fe) Native Oxide
with Peaks Integrated, Assigned and Labelled

→  Periodic Table 

 

Survey Spectrum of Iron Oxide (α-Fe2O3)
(Hematite, exposed bulk)
with Peaks Integrated, Assigned and Labelled

 


→  Periodic Table  

 

Overlays of Fe (2p) Spectra for
Fe Native Oxide and α-Fe2O3 (Hematite)

Caution: BEs from Grounded Native Oxides can be Misleading if Flood Gun is ON

 Overlay of Fe metal and Fe Native Oxide – Fe (2p)
Native Oxide C (1s) = 285.0
(Flood gun OFF)
  Overlay of Fe metal and α-Fe2O3 – Fe (2p)
Flood Gun is OFF
Chemical Shift: 3.33

→  Periodic Table  Copyright ©:  The XPS Library 

 

Overlay of Fe (2p3/2)
Feo Metal, Fe Native Oxide, & α-Fe2O3

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 

 

Valence Band Spectra
Feo, α-Fe2O3 

Feo
Ion etched clean		 α-Fe2O3 – exposed bulk of Hematite
Flood gun is OFF

Overlay of Valence Band Spectra for
Iron, Feo metal and α-Fe2O3 (Hematite)

 

Multiplet Splitting in the “3s” Orbital

Overlay of Fe (3s) Spectra for:
Feo metal and α-Fe2O3 (Hematite)

Fe (3s) from Feo metal Fe (3s) from Fe2O3

 

Overlay of Fe (3s) Spectra for
Feo metal and α-Fe2O3 – Shifted BE to Overlap Peak Max
(3s) peak splits due to Multiplet Splitting
Fe (3s) from Fe and Fe2O3 – overlaid to show Multiplet Splitting effect Fe (3s) from Fe and Fe2O3 – aligned to reveal shape differences

 

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 

 

Iron Minerals, Gemstones, and Chemical Compounds

 
Magnetite – Fe3O4 Martite – Fe2O3 Chalcopyrite – CuFeS2 Tualameenite – Pt2CuFe

→  Periodic Table 

 

 

Six (6) Chemical State Tables of Fe (2p) BEs

 

  • The XPS Library Spectra-Base
  • PHI Handbook
  • Thermo-Scientific Website
  • XPSfitting Website
  • Techdb Website
  • NIST Website

→  Periodic Table 

 

Notes of Caution when using Published BEs and BE Tables from Insulators and Conductors:

  • Accuracy of Published BEs
    • The accuracy depends on the calibration BEs used to calibrate the energy scale of the instrument.  Cu (2p3) BE can vary from 932.2 to 932.8 eV for old publications 
    • Different authors use different BEs for the C (1s) BE of the hydrocarbons found in adventitious carbon that appears on all materials and samples.  From 284.2 to 285.3 eV
    • The accuracy depends on when the authors last checked or adjusted their energy scale to produce the expected calibration BEs
  • Worldwide Differences in Energy Scale Calibrations
    • For various reasons authors still use older energy scale calibrations 
    • Some authors still adjust their energy scale so Cu (2p3/2) appears at 932.2 eV or 932.8 eV because this is what the maker taught them
    • This range causes BEs in the higher BE end to be larger than expected 
    • This variation increases significantly above 600 eV BE
  • Charge Compensation
    • Samples that behave as true insulators normally require the use of a charge neutralizer (electron flood gun with or without Ar+ ions) so that the measured chemical state spectra can be produced without peak-shape distortions or sloping tails on the low BE side of the peak envelop. 
    • Floating all samples (conductive, semi-conductive, and non-conductive) and always using the electron flood gun is considered to produce more reliable BEs and is recommended.
  • Charge Referencing Methods for Insulators
    • Charge referencing is a common method, but it can produce results that are less reliable.
    • When an electron flood gun is used, the BE scale will usually shift to lower BE values by 0.01 to 5.0 eV depending on your voltage setting. Normally, to correct for this flood gun induced shift, the BE of the hydrocarbon C (1s) peak maximum from adventitious carbon is used to correct for the charge induced shift.
    • The hydrocarbon peak is normally the largest peak at the lowest BE. 
    • Depending on your preference or training, the C (1s) BE assigned to this hydrocarbon peak varies from 284.8 to 285.0 eV.  Other BEs can be as low as 284.2 eV or as high as 285.3 eV
    • Native oxides that still show the pure metal can suffer differential charging that causes the C (1s) and the O (1s) and the Metal Oxide BE to be larger
    • When using the electron flood gun, the instrument operator should adjust the voltage and the XY position of the electron flood gun to produce peaks from a strong XPS signal (eg O (1s) or C (1s) having the most narrow FWHM and the lowest experimentally measured BE. 

→  Periodic Table 

Table #1

Fe (2p3/2) Chemical State BEs from:  “The XPS Library Spectra-Base”

C (1s) BE = 285.0 eV for TXL BEs
and C (1s) BE = 284.8 eV for NIST BEs

Element Atomic # Compound As-Measured by TXL or NIST Average BE Largest BE Hydrocarbon C (1s) BE  Source
Fe 26 Fe – element 706.6 eV   285.0 eV The XPS Library
Fe 26 FeB2 (N*2) 706.9 eV 707.3 eV 284.8 eV Avg BE – NIST
Fe 26 Fe-B (N*2) 707.1 eV 707.4 eV 284.8 eV Avg BE – NIST
Fe 26 Fe-P (N*4) 707.1 eV 707.2 eV 284.8 eV Avg BE – NIST
Fe 26 Fe4-N 707.2 eV 707.3 eV 285.0 eV The XPS Library
Fe 26 Fe-S2 707.2 eV   285.0 eV The XPS Library
Fe 26 Fe3C (N*1) 708.1 eV   284.8 eV Avg BE – NIST
Fe 26 Fe-O (N*5) 709.4 eV 710.3 eV 284.8 eV Avg BE – NIST
Fe 26 α-Fe-2O3 709.8 eV   285.0 eV The XPS Library
Fe 26 LiFePO4 710.2 eV   285.0 eV The XPS Library
Fe 26 Fe-2O3 710.3 eV   285.0 eV The XPS Library
Fe 26 FeOOH (N*4) 711.2 eV 711.8 eV 284.8 eV Avg BE – NIST
Fe 26 Fe-Cl3 (N*1) 711.3 eV   284.8 eV Avg BE – NIST
Fe 26 Fe-F2 (N*2) 711.3 eV 711.4 eV 284.8 eV Avg BE – NIST
Fe 26 α-Fe-OOH 711.3 eV   285.0 eV The XPS Library
Fe 26 NaFeO2 (N*2) 711.5 eV 711.8 eV 284.8 eV Avg BE – NIST
Fe 26 Fe-F3 (N*2) 713.9 eV 714.8 eV 284.8 eV Avg BE – NIST
Fe 26 Fe-(OH)3     285.0 eV The XPS Library
Fe 26 FeCO3     285.0 eV The XPS Library
Fe 26 γ-Fe-2O3     285.0 eV The XPS Library

 

Charge Referencing Notes

  • (N*number) identifies the number of NIST BEs that were averaged to produce the BE in the middle column.
  • The XPS Library uses Binding Energy Scale Calibration with Cu (2p3/2) BE = 932.62 eV and Au (4f7/2) BE = 83.98 eV.  BE (eV) Uncertainty Range:  +/- 0.2 eV
  • Charge Referencing of insulators is defined such that the Adventitious Hydrocarbon C (1s) BE (eV) = 285.0 eV.  NIST uses C (1s) BE = 284.8 eV 
  • Note:   Ion etching removes adventitious carbon, implants Ar (+), changes conductivity of surface, and degrades chemistry of various chemical states.
  • Note:  Ion Etching changes BE of C (1s) hydrocarbon peak.
  • TXL – abbreviation for: “The XPS Library” (https://xpslibrary.com).  NIST:  National Institute for Science and Technology (in USA)

→  Periodic Table 

Table #2

Fe (2p3/2) Chemical State BEs from:  “PHI Handbook”

C (1s) BE = 284.8 eV

→  Periodic Table 

Copyright ©:  Ulvac-PHI

Table #3

Fe (2p3/2) Chemical State BEs from:  “Thermo-Scientific” Website

C (1s) BE = 284.8 eV

Chemical state Binding energy (eV), Fe (2p3)
Fe metal 706.7
FeO 709.6
Fe2O3 710.8
FeCl2 710.4

→  Periodic Table 

Copyright ©:  Thermo Scientific 

Table #4

Fe (2p3/2) Chemical State BEs from:  “XPSfitting” Website

Chemical State BE Table derived by Averaging BEs in the NIST XPS database of BEs
C (1s) BE = 284.8 eV

         Compound                           BE (eV)   FWHM (eV)

→  Periodic Table 

Copyright ©:  Mark Beisinger

Table #5

Fe (2p3/2) Chemical State BEs from:  “Techdb.podzone.net” Website

 

XPS Spectra – Chemical Shift | Binding Energy
C (1s) BE = 284.6 eV

XPS(X線光電子分光法)スペクトル 化学状態 化学シフト ケミカルシフト

Element Level Compound B.E.(eV) min   max
Fe 2p3/2 FeS2  (markasite, pyr) 706.8 ±0.3 706.5 ～ 707.0
Fe 2p3/2 Fe 707.0 ±0.3 706.7 ～ 707.2
Fe 2p3/2 K4Fe(CN)6 707.9 ±0.8 707.1 ～ 708.6
Fe 2p3/2 FeO 709.4 ±0.3 709.1 ～ 709.6
Fe 2p3/2 K3Fe(CN)6 709.6 ±0.3 709.3 ～ 709.8
Fe 2p3/2 FeCl2 710.7 ±0.3 710.4 ～ 710.9
Fe 2p3/2 Fe2O3 710.9 ±0.1 710.8 ～ 710.9
Fe 2p3/2 FeCl3 711.3 ±0.3 711.0 ～ 711.5
Fe 2p3/2 FeOOH 711.6 ±0.3 711.3 ～ 711.9
Fe 2p3/2 FeS 712.0 ±0.4 711.6 ～ 712.3
Fe 2p3/2 FeSO4 712.1 ±0.2 711.9 ～ 712.3

 

→  Periodic Table 

 


Histograms of NIST BEs for Fe (2p3/2) BEs

Important Note:  NIST Database defines Adventitious Hydrocarbon C (1s) BE = 284.8 eV for all insulators.

Histogram indicates:  707.3 eV for Feo based on 27 literature BEs Histogram indicates:  709.8 eV for FeO based on 7 literature BEs

 

Histogram indicates:  711.3 eV for FeO(OH) based on 4 literature BEs

Histogram indicates:  709.9 eV for Fe3O4 based on 8 literature BEs

Table #6


NIST Database of Fe (2p3/2) Binding Energies

NIST Standard Reference Database 20, Version 4.1

Data compiled and evaluated
by
Alexander V. Naumkin, Anna Kraut-Vass, Stephen W. Gaarenstroom, and Cedric J. Powell
©2012 copyright by the U.S. Secretary of Commerce on behalf of the United States of America. All rights reserved.

Important Note:  NIST Database defines Adventitious Hydrocarbon C (1s) BE = 284.8 eV for all insulators.

 

Element Spectral Line Formula Energy (eV) Reference
Fe 2p3/2 Fe 706.50  Click
Fe 2p3/2 Fe 706.50  Click
Fe 2p3/2 Fe70Ni30 706.55  Click
Fe 2p3/2 [Fe(C10H14)3](ClO4)2 706.60  Click
Fe 2p3/2 FeS2 706.60  Click
Fe 2p3/2 Fe 706.70  Click
Fe 2p3/2 Fe 706.70  Click
Fe 2p3/2 FeS2 706.70  Click
Fe 2p3/2 Fe(2/3/4)N 706.70  Click
Fe 2p3/2 Fe 706.74  Click
Fe 2p3/2 Na4[Fe(CN)5(NO2)] 706.80  Click
Fe 2p3/2 Fe 706.80  Click
Fe 2p3/2 Fe 706.80  Click
Fe 2p3/2 Fe 706.80  Click
Fe 2p3/2 Fe 706.80  Click
Fe 2p3/2 FeS2 706.80  Click
Fe 2p3/2 Fe/Cu 706.80  Click
Fe 2p3/2 Fe 706.81  Click
Fe 2p3/2 Fe 706.82  Click
Fe 2p3/2 Fe 706.88  Click
Fe 2p3/2 Fe2B 706.90  Click
Fe 2p3/2 Fe 706.90  Click
Fe 2p3/2 Fe/Cu 706.90  Click
Fe 2p3/2 Fe/Cu 706.90  Click
Fe 2p3/2 B20Fe80 706.90  Click
Fe 2p3/2 B20Fe80 706.90  Click
Fe 2p3/2 B20Fe80 706.90  Click
Fe 2p3/2 Al46Fe54 706.90  Click
Fe 2p3/2 Fe/Ta 706.90  Click
Fe 2p3/2 Fe 706.95  Click
Fe 2p3/2 Fe 707.00  Click
Fe 2p3/2 Fe 707.00  Click
Fe 2p3/2 Fe 707.00  Click
Fe 2p3/2 Fe 707.00  Click
Fe 2p3/2 Fe85Cr15 707.00  Click
Fe 2p3/2 Fe/Cu 707.00  Click
Fe 2p3/2 Fe/Cu 707.00  Click
Fe 2p3/2 Fe/Cu 707.00  Click
Fe 2p3/2 Cr24Fe76/O2 707.00  Click
Fe 2p3/2 O2/Cr24Fe65Mo11 707.00  Click
Fe 2p3/2 O2/Fe 707.00  Click
Fe 2p3/2 FeB 707.10  Click
Fe 2p3/2 K4[Fe(CN)6] 707.10  Click
Fe 2p3/2 Fe 707.10  Click
Fe 2p3/2 Fe 707.10  Click
Fe 2p3/2 Fe 707.10  Click
Fe 2p3/2 Fe 707.10  Click
Fe 2p3/2 FeP 707.10  Click
Fe 2p3/2 Fe2P 707.10  Click
Fe 2p3/2 Fe3P 707.10  Click
Fe 2p3/2 Fe76Cr24 707.10  Click
Fe 2p3/2 UFe2 707.10  Click
Fe 2p3/2 B20Fe80 707.10  Click
Fe 2p3/2 B6Cr14Fe32Ni36P12Ox 707.10  Click
Fe 2p3/2 FeP 707.20  Click
Fe 2p3/2 O2/Fe/Cu 707.20  Click
Fe 2p3/2 O2/Fe/Cu 707.20  Click
Fe 2p3/2 O2/Fe/Cu 707.20  Click
Fe 2p3/2 O2/Fe/Cu 707.20  Click
Fe 2p3/2 O2/Fe/Cu 707.20  Click
Fe 2p3/2 Fe/Ni 707.20  Click
Fe 2p3/2 Cr21Fe8Ni71 707.20  Click
Fe 2p3/2 FeS2 707.25  Click
Fe 2p3/2 Fe2B 707.30  Click
Fe 2p3/2 Fe 707.30  Click
Fe 2p3/2 Fe 707.30  Click
Fe 2p3/2 [Fe(C5H5)2] 707.30  Click
Fe 2p3/2 FeS2 707.30  Click
Fe 2p3/2 Na3[Fe(CN)5(N2O)] 707.40  Click
Fe 2p3/2 FeB 707.40  Click
Fe 2p3/2 Fe 707.40  Click
Fe 2p3/2 Fe 707.50  Click
Fe 2p3/2 Fe3Si 707.50  Click
Fe 2p3/2 Na3[Fe(CN)5(NH3)] 707.60  Click
Fe 2p3/2 AlFe3 707.60  Click
Fe 2p3/2 O2/Fe/Ni 707.60  Click
Fe 2p3/2 Na3[Fe(CN)5(N2H4)] 707.70  Click
Fe 2p3/2 [Fe(C5H5)2] 707.70  Click
Fe 2p3/2 [Fe(C5H5)2] 707.70  Click
Fe 2p3/2 FeP2 707.70  Click
Fe 2p3/2 [Fe(C5H5)2] 707.80  Click
Fe 2p3/2 Fe(CO)5/Pt 707.80  Click
Fe 2p3/2 [Fe(NCS)2(C6H4(As(CH3)2)2)] 707.90  Click
Fe 2p3/2 [Fe(NCS)2(C6H4(As(CH3)2)2)2] 707.90  Click
Fe 2p3/2 [FeCl(NO2)(C6H4(As(CH3)2)2)] 707.90  Click
Fe 2p3/2 [FeCl2(C6H4(As(CH3)2)2)2] 707.90  Click
Fe 2p3/2 Fe 707.90  Click
Fe 2p3/2 O2/Fe24Zr76 707.90  Click
Fe 2p3/2 [FeCl(NO2)(C6H4(As(CH3)2)2)]B(C6H5)4 708.00  Click
Fe 2p3/2 [FeI(C6H4(As(CH3)2)2)]I 708.00  Click
Fe 2p3/2 Fe3C 708.10  Click
Fe 2p3/2 Fe3O4 708.10  Click
Fe 2p3/2 CuFeS2 708.10  Click
Fe 2p3/2 Fe3O4 708.20  Click
Fe 2p3/2 O2/Fe/Ni 708.20  Click
Fe 2p3/2 [Fe(NO)((C2H5)2NC(S)SH)2] 708.30  Click
Fe 2p3/2 CuFeS2 708.30  Click
Fe 2p3/2 [Fe(C5H4COOH)2] 708.40  Click
Fe 2p3/2 [Fe(NO)I(C6H4(As(CH3)2)2)]I 708.50  Click
Fe 2p3/2 K4[Fe(CN)6] 708.50  Click
Fe 2p3/2 [Fe((C2H5)2NC(S)SH)2] 708.60  Click
Fe 2p3/2 [Fe2(CO)6(CH3S)2] 708.60  Click
Fe 2p3/2 FeS2 708.60  Click
Fe 2p3/2 [Fe(CO)3(P(C6H5)3)2] 708.70  Click
Fe 2p3/2 [FeI2(C6H4(As(CH3)2)2)2]PF6 708.70  Click
Fe 2p3/2 Fe 708.70  Click
Fe 2p3/2 KFeS2 708.70  Click
Fe 2p3/2 CuFeS2 708.70  Click
Fe 2p3/2 [Fe(CO)3SCH3] 708.80  Click
Fe 2p3/2 Fe(CO)5/Pt 708.80  Click
Fe 2p3/2 K[Fe4S3(NO)7].2H2O 708.90  Click
Fe 2p3/2 [FeCl(NO)(C6H4(As(CH3)2)2)]B(C6H5)4 709.00  Click
Fe 2p3/2 [FeCl((C2H5)2NC(S)SH)2] 709.00  Click
Fe 2p3/2 [Fe2(CO)6((C6H5)2PP(C6H5)2)] 709.00  Click
Fe 2p3/2 Fe3O4 709.00  Click
Fe 2p3/2 [Fe2(CO)6(HPC6H5)2] 709.10  Click
Fe 2p3/2 [Fe3(CO)9(PC6H5)2] 709.10  Click
Fe 2p3/2 [Fe(NO)(NCC(S)C(S)CN)(CH2CH2)(P(C6H5)2)2] 709.10  Click
Fe 2p3/2 [Fe(C6H4(CN)2)4] 709.10  Click
Fe 2p3/2 Na2[Fe(CN)5(NO)].2H2O 709.10  Click
Fe 2p3/2 [Fe(NO)2C2H5S] 709.20  Click
Fe 2p3/2 O2/Fe/Cu 709.20  Click
Fe 2p3/2 Fe/NiO/Ni 709.20  Click
Fe 2p3/2 Fe3O4 709.20  Click
Fe 2p3/2 Fe(CO)5/Pt 709.20  Click
Fe 2p3/2 Cs[Fe(B9C2H11)2] 709.30  Click
Fe 2p3/2 FeO 709.30  Click
Fe 2p3/2 [Fe(C6H4(As(CH3)2)2)](ClO4)3 709.40  Click
Fe 2p3/2 Fe 709.40  Click
Fe 2p3/2 FeO 709.40  Click
Fe 2p3/2 O2/Fe/Cu 709.40  Click
Fe 2p3/2 Cr24Fe76/O2 709.40  Click
Fe 2p3/2 O2/Cr24Fe65Mo11 709.40  Click
Fe 2p3/2 O2/Fe/Ni 709.40  Click
Fe 2p3/2 [Fe(CO)2(NO)2] 709.50  Click
Fe 2p3/2 [Fe2O((C4H2N2CC6H5)4)2] 709.50  Click
Fe 2p3/2 B6Cr14Fe32Ni36P12Ox 709.50  Click
Fe 2p3/2 Fe(CO)5/Ni 709.50  Click
Fe 2p3/2 K3[Fe(CN)6] 709.60  Click
Fe 2p3/2 [Fe(CO)5] 709.60  Click
Fe 2p3/2 FeO 709.60  Click
Fe 2p3/2 FeO 709.60  Click
Fe 2p3/2 O2/Fe/Cu 709.60  Click
Fe 2p3/2 Na2[Fe(CN)3(NO)] 709.70  Click
Fe 2p3/2 Fe(CO)5/Ni 709.70  Click
Fe 2p3/2 [FeCl(CO)(C6H4(As(CH3)2)2)]B(C6H5)4 709.80  Click
Fe 2p3/2 [FeI3(C5H5)2] 709.90  Click
Fe 2p3/2 Fe2O3 709.90  Click
Fe 2p3/2 FeO 709.90  Click
Fe 2p3/2 Fe/Al2O3 709.90  Click
Fe 2p3/2 Fe/SiO2 709.90  Click
Fe 2p3/2 [Fe(NO)(C6H4(As(CH3)2)2)](ClO4)2 710.00  Click
Fe 2p3/2 Al2FeO4 710.00  Click
Fe 2p3/2 FeBr3 710.10  Click
Fe 2p3/2 [Fe(C4H2NCC6H5)4]Cl3 710.10  Click
Fe 2p3/2 Fe3O4 710.20  Click
Fe 2p3/2 FeBr2 710.30  Click
Fe 2p3/2 FeO 710.30  Click
Fe 2p3/2 FeS 710.30  Click
Fe 2p3/2 (Mg/Fe)2SiO4 710.40  Click
Fe 2p3/2 (Mg/Fe)2SiO4 710.40  Click
Fe 2p3/2 [Fe(C5H4Si(CH3)3)2].BF4 710.40  Click
Fe 2p3/2 Fe2O3 710.40  Click
Fe 2p3/2 Fe3O4 710.40  Click
Fe 2p3/2 O2/UFe2 710.40  Click
Fe 2p3/2 CoFe2O4 710.50  Click
Fe 2p3/2 NiFe2O4 710.50  Click
Fe 2p3/2 O2/Fe/Cu 710.50  Click
Fe 2p3/2 FeCr2O4 710.50  Click
Fe 2p3/2 (C6H4S4)2FeCl3 710.50  Click
Fe 2p3/2 (C6H4S4)3FeBr3 710.50  Click
Fe 2p3/2 [FeCl2(C6H4(As(CH3)2)2)] 710.60  Click
Fe 2p3/2 FeCl2 710.60  Click
Fe 2p3/2 FeCr2O4 710.60  Click
Fe 2p3/2 Ni/O2/Fe/Cu 710.60  Click
Fe 2p3/2 O2/Fe/Cu 710.60  Click
Fe 2p3/2 O2/Fe/Cu 710.61  Click
Fe 2p3/2 Fe 710.70  Click
Fe 2p3/2 FeO 710.70  Click
Fe 2p3/2 [Fe3Al(SiO4)3] 710.70  Click
Fe 2p3/2 Cr24Fe76/O2 710.70  Click
Fe 2p3/2 Fe2O3 710.70  Click
Fe 2p3/2 Fe2O3 710.70  Click
Fe 2p3/2 O2/Cr24Fe65Mo11 710.70  Click
Fe 2p3/2 B6Cr14Fe32Ni36P12Ox 710.70  Click
Fe 2p3/2 Fe3O4 710.70  Click
Fe 2p3/2 (Mg/Fe)2SiO4 710.80  Click
Fe 2p3/2 (Mg/Fe)SiO3 710.80  Click
Fe 2p3/2 [Fe(CH3C(O)C(C6H5)C(O)CH3)3] 710.80  Click
Fe 2p3/2 Fe2O3 710.80  Click
Fe 2p3/2 Fe2O3 710.80  Click
Fe 2p3/2 CoFe2O4 710.80  Click
Fe 2p3/2 Fe3O4 710.80  Click
Fe 2p3/2 Fe/Al2O3 710.80  Click
Fe 2p3/2 Fe2O3 710.80  Click
Fe 2p3/2 Fe3O4 710.80  Click
Fe 2p3/2 O2/UFe2 710.80  Click
Fe 2p3/2 Fe2O3 710.80  Click
Fe 2p3/2 O2/Fe 710.80  Click
Fe 2p3/2 Fe2O3 710.90  Click
Fe 2p3/2 Fe2O3 710.90  Click
Fe 2p3/2 O2/Fe/Ni 710.90  Click
Fe 2p3/2 [Fe(C6H4C(O)CH2C(O)C6H5)3] 711.00  Click
Fe 2p3/2 Fe(OH)O 711.00  Click
Fe 2p3/2 Fe2O3 711.00  Click
Fe 2p3/2 Fe2O3 711.00  Click
Fe 2p3/2 Fe/SiO2 711.00  Click
Fe 2p3/2 O2/Fe 711.00  Click
Fe 2p3/2 FeSO4.7H2O 711.05  Click
Fe 2p3/2 Fe2O3 711.10  Click
Fe 2p3/2 O2/Fe/Ni 711.10  Click
Fe 2p3/2 FeCl2 711.10  Click
Fe 2p3/2 Fe2O3 711.20  Click
Fe 2p3/2 Fe(OH)O 711.25  Click
Fe 2p3/2 FeCl3 711.30  Click
Fe 2p3/2 FeF2 711.30  Click
Fe 2p3/2 Fe(OH)O 711.30  Click
Fe 2p3/2 KFeO2 711.30  Click
Fe 2p3/2 Fe2O3 711.30  Click
Fe 2p3/2 Fe2O3 711.30  Click
Fe 2p3/2 FeF2 711.40  Click
Fe 2p3/2 [Fe((C6H5)C(O)CH2C(O)CH2)3] 711.40  Click
Fe 2p3/2 Fe2O3 711.40  Click
Fe 2p3/2 Fe3O4 711.40  Click
Fe 2p3/2 Fe2O3 711.40  Click
Fe 2p3/2 NaFeO2 711.50  Click
Fe 2p3/2 Fe2O3 711.50  Click
Fe 2p3/2 FeOOH 711.50  Click
Fe 2p3/2 Fe2O3 711.60  Click
Fe 2p3/2 [Fe(NO)(C6H5C(O)CHC(S)C6H5)2] 711.80  Click
Fe 2p3/2 Fe(OH)O 711.80  Click
Fe 2p3/2 LiFeO2 711.80  Click
Fe 2p3/2 NaFeO2 711.80  Click
Fe 2p3/2 FeCl3 711.80  Click
Fe 2p3/2 FeS 712.10  Click
Fe 2p3/2 [Ca3Fe2(SiO4)3] 712.30  Click
Fe 2p3/2 [Fe(CH3C(O)CClC(O)CH3)3] 712.40  Click
Fe 2p3/2 [Fe(CH3C(O)CHC(O)CH3)3] 712.60  Click
Fe 2p3/2 [Fe(CH3C(O)CBrC(O)CH3)3] 712.60  Click
Fe 2p3/2 FePO4 712.80  Click
Fe 2p3/2 K2FeO4 713.00  Click
Fe 2p3/2 Fe2(SO4)3 713.30  Click
Fe 2p3/2 FeSO4 713.60  Click
Fe 2p3/2 FeS 713.60  Click
Fe 2p3/2 O2/Fe/Cu 713.70  Click
Fe 2p3/2 FeF3 713.90  Click
Fe 2p3/2 FeF3 714.20  Click
Fe 2p3/2 Fe2(SO4)3(NH4)2SO4.24H2O 714.20  Click
Fe 2p3/2 K3FeF6 714.40  Click
Fe 2p3/2 FeF3 714.80  Click

 

→  Periodic Table 

 

 

Statistical Analysis of Binding Energies in NIST XPS Database of BEs

 

 

→  Periodic Table 

 

Advanced XPS Information Section

Expert Knowledge, Spectra, Features, Guidance and Cautions
for XPS Research Studies on Iron Materials

 

 

 

Expert Knowledge Explanations

→  Periodic Table 

 

Iron Chemical Compounds

 

Peak-fits and Overlays of Chemical State Spectra

Pure Iron (Feo):  Fe (2p3/2)
Cu (2p3/2) BE = 932.6 eV		 Fe2O3:  Fe (2p)
C (1s) BE = 285.0 eV		 FeF3:  Fe (2p)
C (1s) BE = 285.0 eV

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 

 

Overlay of Fe (2p) Spectra shown Above

C (1s) BE = 285.0 eV

 

 

Chemical Shift between Fe vs Fe2O3: 3.33 eV
 Chemical Shift between Fe vs FeF3:  5.04 eV

 

→  Periodic Table 

 

Iron Oxide (Fe2O3)
exposed bulk of single crystal Hematite

 

Survey Spectrum from Fe2O3
Flood gun is Off, C (1s) BE = 285.0 eV
 Fe (2p) Chemical State Spectrum from Fe2O3
Flood gun is Off, C (1s) BE = 285.0 eV
   .
O (1s) Chemical State Spectrum from Fe2O3
Flood gun is Off, C (1s) BE = 285.0 eV
 C (1s) Chemical State Spectrum from Fe2O3
Flood gun is Off, C (1s) BE = 285.0 eV
  . 
Fe Auger Chemical State Spectrum from Fe2O3 Fe (3s) Chemical State Spectrum from Fe2O3
Flood gun is Off, C (1s) BE = 285.0 eV
Freshly cleaved to expose bulk
   .
Valence Band Spectrum from Fe2O3
Flood gun is ON, C (1s) BE = 285.0 eV
Freshly cleaved to expose bulk		 Auger Signals from Fe2O3
Flood gun is ON, C (1s) BE = 285.0 eV
Freshly cleaved to expose bulk

Shake-up Features for
Fe2O3

 

 

 

Multiplet Splitting Features for
Fe (3s) in Iron Compounds

Fe metal – NO Splitting for Fe (3s) Fe2O3 Compound – Multiplet Splitting Peaks for Fe (3s)
.
Fe metal – NO Splitting for Fe (3s) FeF3 Compound – Multiplet Splitting Peaks for Fe (3s)

 

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 

 

 


Iron Chemical Compounds

 

FeF3
from Aldrich, pressed onto stage

   
   
   
   
   
   
   
   
   
   

 . Survey Spectrum from FeF3
Flood gun is ON, C (1s) BE = 285.0 eV
Powder pressed onto stage
Fe (2p) Chemical State Spectrum from FeF3
Flood gun is ON, C (1s) BE = 285.0 eV
Powder pressed onto stage

 . F (1s) Chemical State Spectrum from FeF3
Flood gun is ON, C (1s) BE = 285.0 eV
Powder pressed onto stage
C (1s) Chemical State Spectrum from FeF3
Flood gun is ON, C (1s) BE = 285.0 eV
Powder pressed onto stage

 . Fe (3p) Chemical State Spectrum from FeF3
Flood gun is ON, C (1s) BE = 285.0 eV
Powder pressed onto stage
Fe (3s) Chemical State Spectrum from FeF3
Flood gun is ON, C (1s) BE = 285.0 eV
Powder pressed onto stage

 . Valence Band Spectrum from FeF3
Flood gun is ON, C (1s) BE = 285.0 eV
Powder pressed onto stage
Auger Signals from FeF3
Flood gun is ON, C (1s) BE = 285.0 eV
Powder pressed onto stage

→  Periodic Table 

 

Quantitation Details and Information

Quantitation by XPS is often incorrectly done, in many laboratories, by integrating only the main peak, ignoring the Electron Loss peak, and the satellites that appear as much as 30 eV above the main peak.  By ignoring the electron loss peak and the satellites, the accuracy of the atom% quantitation is in error.

When using theoretically calculated Scofield cross-section values, the data must be corrected for the transmission function effect, use the calculated TPP-2M IMFP values, the pass energy effect on the transmission function, and the peak area used for calculation must include the electron loss peak area, shake-up peak area, multiplet-splitting peak area, and satellites that occur within 30 eV of the main peak.

 

Quantitation from Pure, Homogeneous Binary Compound
composed of Iron – Fe2O3

This section is focused on measuring and reporting the atom % quantitation that results by using:

  • Scofield cross-sections,
  • Spectra corrected to be free from Transmission Function effects
  • A Pass Energy that does not saturate the detector system in the low KE range (BE = 1000-1400 eV)
  • A focused beam of X-ray smaller than the field of view of the lens
  • An angle between the lens and the source that is ~55 deg that negates the effects of beta-asymmetry
  • TPP-2M inelastic mean free path values, and
  • Either a linear background or an iterated Shirley (Sherwood-Proctor) background to define peak areas

The results show here are examples of a method being developed that is expected to improve the “accuracy” or “reliability” of the atom % values produced by XPS.

→  Periodic Table 

 

 

 

Flood Gun Effect on Native Oxide of Iron, Fe

 

Native Oxide of Iron Sheet – Sample GROUNDED
versus
Native Oxide of Iron Sheet – Sample FLOATING

 

 

Native Oxide of Iron Sheet – Sample Grounded

Electron Flood Gun:  0 Voltage (FG OFF), Min Voltage versus Max Voltage

Fe (2p3/2) O (1s)  C (1s)
     
→  Periodic Table     

 

Native Oxide of Iron Sheet – Sample Floating

Electron Flood Gun:  0 Voltage (FG OFF), Min Voltage versus Max Voltage

Fe (2p3/2) O (1s)  C (1s)
     
→  Periodic Table     

→  Peri

 

 

Study of UHV Gas Captured
by Freshly Ion Etched Iron by XPS
 
Reveals Chemical Shifts and Chemical States that Develop from Highly Reactive, Freshly Ion Etched, Iron Metal

Surface was strongly Ar+ ion etched to remove all contaminants, and
then allowed to react overnight with the UHV Gases – CO, H2, H2O, O2 & CH4
that normally reside inside on the walls of the chamber, on the sample stage,
and on the nearby un-etched surface a total of 10-14 hours.  UHV pump was a Cryopump.
Initial spectra are at the front.  Final spectra are at the rear. Flood gun is OFF.
 
 
 
Fe (2p) Signal
  O (1s) Signal C (1s) Signal
     
 
 
Copyright ©:  The XPS Library
 

 

AES Chemical State Spectra from
UHV Gas Captured by Freshly Ion Etched Iron

Iron sheet was ion etched and allowed to react with residual UHV gases overnight – ~14 hr run.

Fe (LMM) Signal:
Fe at start -> FexOy at finish
Fe KE = 698.5 eV,    Fe2O3 KE = 698.5 eV (695 shoulder)		 O (KLL) Signal:
Fe at front -> FexOy at rear 
O KE = 507.9 eV at finish		 C (KLL) Signal:
Fe at front -> Fe2O3 X at rear 
O KE = XXXX eV
     

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 

 

Chemical State Spectra from
Slow Depth Profile of Fe Native Oxide by AES

Native Fe Oxide on Fe ribbon was slowly ion etched using High Energy Resolution conditions to measure Chemical States by Auger

Fe (LMM) O (KLL) C (KLL)
     

 

 

 

Iron Alloys

   
XxCu XxCu
→  Periodic Table   
XxCu XxCu

 

Copyright ©:  The XPS Library 

 

 

 

XPS Facts, Guidance & Information

→  Periodic Table 

    Element   Iron (Fe)
  
    Primary XPS peak used for Peak-fitting:   Fe (2p)  
    Spin-Orbit (S-O) splitting for Primary Peak:   Spin-Orbit splitting for “p” orbital, ΔBE = 13.0 eV
  
    Binding Energy (BE) of Primary XPS Signal:   706.9 eV
  
    Scofield Cross-Section (σ) Value:   Fe (2p3/2) = 10.82,      Fe (2p1/2) = 5.60
  
    Conductivity:   Fe resistivity =  
Native Oxide is conductive		  
    Range of Fe (2p) Chemical State BEs:   706 – 712 eV range   (Fe to FeF3)  
    Signals from other elements that overlap
Fe (2p) Primary Peak:		   xx (xx)  
    Bulk Plasmons:   ~xx eV above peak max for pure  
    Shake-up Peaks:   xx  
    Multiplet Splitting Peaks:   xx  

 

 

 General Information about
XXX Compounds:		   xx  
    Cautions – Chemical Poison Warning  

xx 

  

Copyright ©:  The XPS Library 

→  Periodic Table 

 

Information Useful for Peak-fitting Fe (2p)

  • FWHM (eV) of Fe (2p3/2) from Pure Fe:  ~1.1 eV using 25 eV Pass Energy after ion etching:
  • FWHM (eV) of Fe (2p3/2) from Fe2O3 xtal:  ~1.0 eV using 50 eV Pass Energy  (before ion etching)
  • Binding Energy (BE) of Primary Signal used for Measuring Chemical State Spectra:  707 eV for Fe(2p3/2) with +/- 0.2 uncertainty
  • List of XPS Peaks that can Overlap Peak-fit results for Fe (2p):  xxxx

→  Periodic Table 

 

General Guidelines for Peak-fitting XPS Signals

  • Typical Energy Resolution for Pass Energy (PE) setting used to measure Chemical State Spectra on Various XPS Instruments
    • Ag (3d5/2) FWHM (eV) = ~0.95 eV for PE 50 on Thermo K-Alpha
    • Ag (3d5/2) FWHM (eV) = ~1.00 eV for PE 80 on Kratos Nova
    • Ag (3d5/2) FWHM (eV) = ~0.95 eV for PE 45 on PHI VersaProbe
  • FWHM (eV) of Pure Elements: Ranges from 0.4 to 1.0 eV across the periodic table
  • FWHM of Chemical State Peaks in any Chemical Compound:  Ranges from 1.1 to 1.6 eV  (in rare cases FWHM can be 1.8 to 2.0 eV)
  • FWHM of Pure Element versus FWHM of Oxide:  Pure element FWHM << Oxide FWHM  (e.g. 0.8 vs 1.5 eV, roughly 2x)
  • If FWHM Greater than 1.6 eV:  When a peak FWHM is larger than 1.6 eV, it is best to add another peak to the peak-fit envelop.
  • BE (eV) Difference in Chemical States: The difference in chemical state BEs is typically 1.0-1.3 eV apart.  In rare cases, <0.8 eV.
  • Number of Peaks to Use:  Use minimum. Do not use peaks with FWHM < 1.0 eV unless it is a or a conductive compound.
  • Typical Peak-Shape:  80% G: 20% L,   or Voigt : 1.4 eV Gaussian and 0.5 eV Lorentzian
  • Spin-Orbit Splitting of Two Peaks (due to Coupling):  The ratio of the two (2) peak areas must be constrained.
  • Constraints on Peak-fitting: ??

Notes:

  • Other Oxidation States can appear as small peaks when peak-fitting
  • Pure element signals normally have asymmetric tails that should be included in the peak-fit.
  • Gaseous state materials often display asymmetric tails due to vibrational broadening.
  • Peak-fits of C (1s) in polymers include an asymmetric tail when the energy resolution is very high.
  • Binding energy shifts of some compounds are negative due to unusual electron polarization.

→  Periodic Table 

 

Contaminants Specific to Iron

  • Iron develops a thick native oxide due to the reactive nature of clean Iron .
  • The native oxide of Fe Ox is 4-8 nm thick.
  • Iron thin films often have a low level of iron (Fe) in the bulk as a contaminant or to strengthen the thin film
  • Iron forms a low level of carbide when the surface is ion etched inside the analysis chamber

 

Commonplace Contaminants

  • Carbon and Oxygen are common contaminants that appear on nearly all surfaces. The amount of Carbon usually depends on handling.
  • Carbon is usually the major contaminant.  The amount of carbon ranges from 5-50 atom%.
  • Carbon contamination is attributed to air-borne organic gases that become trapped by the surface, oils transferred to the surface from packaging containers, static electricity, or handling of the product in the production environment.
  • Carbon contamination is normally a mixture of different chemical states of carbon (hydrocarbon, alcohol or ether, and ester or acid).
  • Hydrocarbon is the dominant form of carbon contamination. It is normally 2-4x larger than the other chemical states of carbon.
  • Carbonate peaks, if they appear, normally appear ~4.5 eV above the hydrocarbon C (1s) peak max BE.
  • Low levels of carbonate is common on many s that readily oxidize in the air.
  • High levels of carbonate appear on reactive oxides and various hydroxides.  This is due to reaction between the oxide and CO2 in the air.
  • Hydroxide contamination peak is due to the reaction with residual water in the lab air or the vacuum.
  • The O (1s) BE of the hydroxide (water) contamination normally appears 0.5 to 1.0 eV above the oxide peak
  • Sodium (Na), Potassium (K), Sulfur (S) and Chlorine (Cl) are common trace to low level contaminants
  • To find low level contaminants it is very useful to vertically expand the 0-600 eV region of the survey spectrum by 5-10X
  • A tiny peak that has 3 or more adjacent data-points above the average noise of the background is considerate to be a real peak
  • Carbides can appear after ion etching various reactive s.  Carbides form due to the residual CO and CH4 in the vacuum.
  • Ion etching can produce low oxidation states of the material being analyzed.  These are newly formed contaminants.
  • Ion etching polymers by using standard Ar+ ion guns will destroy the polymer, converting it into a graphitic type of carbon

→  Periodic Table 

 

Data Collection Guidance

  • Chemical state differentiation can be difficult
  • Collect principal Fe (2p) peak as well as Fe (3p)
  • Long time exposures (high dose) to X-rays can degrade various polymers, catalysts, high oxidation state compounds
  • During XPS analysis, water or solvents can be lost due to high vacuum or irradiation with X-rays or Electron flood gun
  • Auger signals can sometimes be used to discern chemical state shifts when XPS shifts are very small

→  Periodic Table 

 

Data Collection Settings for Iron (Fe)

  • Conductivity:  Iron readily develops a native oxide that is sensitive to Flood Gun – Differential Charging Possible – float sample recommended
  • Primary Peak (XPS Signal) used to measure Chemical State Spectra:  Fe (2p3) at 707 eV
  • Recommended Pass Energy for Measuring Chemical State Spectrum:  40-50 eV    (Produces Ag (3d5/2) FWHM ~0.7 eV)
  • Recommended # of Scans for Measuring Chemical State Spectrum:  4-5 scans normally   (Use 10-25 scans to improve S/N)
  • Dwell Time:  50 msec/point
  • Step Size:  0.1 eV/point   (0.1 eV/step or 0.1 eV/channel)
  • Standard BE Range for Measuring Chemical State Spectrum:  690 – 730 eV
  • Recommended Extended BE Range for Measuring Chemical State Spectrum:  680-830 eV
  • Recommended BE Range for Survey Spectrum:  -10 to 1,100 eV   (above 1,100 eV there are no useful XPS signals, except for Ge and Ga)
  • Typical Time for Survey Spectrum:  3-5 minutes for newer instruments, 5-10 minutes for older instruments
  • Typical Time for a single Chemical State Spectrum with high S/N:  5-10 minutes for newer instruments, 10-15 minutes for older instruments
  •  

→  Periodic Table 

 

Effects of Argon Ion Etching

  • Carbides appear after ion etching Fe and various reactive s.  Carbides form due to the residual CO and CH4 in the vacuum.
  • Ion etching can produce low oxidation states of the material being analyzed.  These are newly formed contaminants.
  • Ion etching polymers by using standard Ar+ ion guns will destroy the polymer, converting it into a graphitic type of carbon

 

→  Periodic Table 

Copyright ©:  The XPS Library 
 
 
Gas Phase XPS or UPS Spectra
 
 
     
     
     
     
     
     
     
     
     
 
 
 
 

 

Chemical State Spectra from Literature
 
from Thermo-Scientific Website

Interpretation of XPS spectra

  • Fe2p region has significantly split spin-orbit components (Δmetal=13.1eV).
  • Fe2p peaks have asymmetric shape for metal.
    • A well resolved Fe2p3/2 spectrum for metal shows multiplet splitting.
    • Second component (shifted by 0.9eV from main peak) can be neglected when fitting typical mixed oxide/metal spectra.

XPS spectrum of iron metal

  • Fe oxide peaks are significantly shifted to higher binding energy than the metal.
    • Fe compounds can be reduced by Ar ion sputtering, even at relatively low ion energies.
  • Iron compounds may be described as high-spin or low-spin (as defined by crystal field theory).
    • Fe(III) compounds are always high-spin, leading to complex multiplet-split Fe2p spectra[1].
    • Fe(II) compounds may be high or low-spin[1].
      • Fe2p spectra of high-spin compounds (e.g., FeO or FeCl2) exhibit complex multiplet splitting and have satellite features.
      • Spectra from low-spin compounds (e.g. FeS2) do not show multiplet splitting or satellite features.
    • It is possible to distinguish Fe oxidation states using satellite features of Fe2p.

XPS spectrum iron(III) oxide

  • The relative binding energies and intensity ratio of the core level XPS peaks versus satellite features will vary according to compound, e.g. FeCl2 has a very strong satellite feature compared to FeO.
  • In the case of air-exposed marcasite (FeS2), no satellite feature is observed since the Fe2+ is in a low-spin configuration.
    • The broad structure to higher binding energy (~710.5eV) of the main Fe2p3/2 peak is NOT satellite structure but is due to Fe3+ states from oxidation of the surface.
    • The higher binding energy, smaller marcasite peak (708.4eV) is possibly due to electron-deficient Fe2+ sites, created by the breaking of Fe-S bonds[2].
XPS spectrum of air-exposed marcasite

 

References

 

  • [1] MC Biesinger et al., Applied Surface Science 257 (2011) 2717-2730
  • [2] Uhlig et al., Applied Surface Science 179 (2001) 222-229
 

End of File