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

 

Uranium (U)

 

Uraninite – UO2 Uranium Metal – Uo Curite – Pb3(H2O)2[(UO2)4O4(OH)3]2

 

  Page Index
  • Expert Knowledge & Explanations


Uranium (Uo) Metal

Peak-fits, BEs, FWHMs, and Peak Labels

.
Uranium (Uo) Metal
U (4f) Spectrum – raw spectrum
ion etched clean		 Uranium (Uo) Metal
Peak-fit of U (4f) Spectrum (w/o asymm)
Spin-orbit Splitting:  10.8 eV
→  Periodic Table – HomePage  
Uranium (Uo) Metal
U (4f) Spectrum – extended range 
 Uranium (Uo) Metal
Peak-fit of U (4f) Spectrum (w asymm)
   
 

Survey Spectrum of Uranium (Uo) Metal
with Peaks Integrated, Assigned and Labelled

 
→  Periodic Table 

XPS Signals for Uranium, (Uo) 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
U (4p3/2) 1044 7.71
U (4d3/2) 779 11.25
U (4d5/2) 736 17.05
N (1s) overlaps U (4f5/2) 388.01 21.5
U (4f7/2) 377.14 27.36
Ar (2s) overlaps U (5s) 322 0.732
U (5p1/2) 261 0.674
Cl (2p) overlaps U (5p3/2) 194 2.22
Si (2p) overlaps U (5d3/2) 103 2.36
U (5d5/2) 94 3.46

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

Plasmon Peaks

Energy Loss Peaks

Auger Peaks

 

Energy Loss    Intrinsic Plasmon Peak:  ~xx eV above peak max
Expected Bandgap for UOx: 3.5 – 4.5 eV  (https://materialsproject.org/)
Work Function for U:  xx eV
*Scofield Cross-Section (σ) for C (1s) = 1.0

→  Periodic Table 

 

Valence Band Spectrum from Uranium, Uo Metal
 Fresh exposed bulk produced by extensive Ar+ ion etching.  Note: Ion Etched Uranium rapidly reacts w gases in UHV

 

Expanded View of Fermi Edge

 

 

 

 

Plasmon Peaks from Uranium, Uo Metal
 Fresh exposed bulk produced by extensive Ar+ ion etching

U (4f) – Extended Range Spectrum U (4f) – Extended Range Spectrum – Vertically Zoomed
→  Periodic Table 
 

U (MNN) Auger Peaks from Uo Metal
 Fresh exposed bulk produced by extensive Ar+ ion etching
Uo Metal – main Auger peak Uo Metal – full Auger range

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 
 

Artefacts Caused by Argon Ion Etching

C (1s) from Metal Carbide(s)

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

Argon Trapped in Uo

can form when Argon Ions are used
to removed surface contamination
 

Side-by-Side Comparison of
U Native Oxide & Uraninite (UO2, black grains)
Peak-fits, BEs, FWHMs, and Peak Labels
(Uraninite is reported to be mainly UO2)
NOTE:  Based on Comparing with Literature spectra, the as-received surface of our Uraninite sample has a significant amount of UO3 and U3O8

 
U Native Oxide Uraninite (black grains)
U (4f) from Uranium Native Oxide, as received – raw spectrum
Flood Gun OFF
As-Measured, C (1s) at 284.3 eV 		 U (4f) from Uraninite – black grains – as received, raw spectrum
Flood Gun OFF
Charge Referenced to C (1s) at 284.3 eV
.

U (4f) from Uranium native oxide
as received from supplier
Flood Gun OFF
Charge Referenced to C (1s) at 284.3 eV

U (4f) from Uraninite – (black grains)
as received from supplier
Flood Gun OFF
Charge Referenced to C (1s) at 284.3 eV
→  Periodic Table 
   
U Native Oxide Uraninite (black grains)
C (1s) from Uranium Native Oxide, as received
Flood Gun OFF
As-Measured, C (1s) at 284.3 eV

C (1s) from Uraninite – black grains
Flood Gun OFF
Charge Referenced to C (1s) at 284.3 eV
 
→  Periodic Table 
  . 
U Native Oxide Uraninite (black grains, UO2)
O (1s) from Uranium Native Oxide, as received
As-Measured, C (1s) at 284.3 eV
Flood Gun OFF

O (1s) from Uraninite – black grains
Flood Gun OFF
Charge Referenced to C (1s) at 284.3 eV
→  Periodic Table

 

 

Survey Spectrum of Uranium (U) Native Oxide
with Peaks Integrated, Assigned and Labelled

 

→  Periodic Table 

 

 

Survey Spectrum of Uraninite (UO2)
with Peaks Integrated, Assigned and Labelled
Surface is mainly UO2, but has some UO3 and U3O8

→  Periodic Table  

Overlay of U (4f) Spectra for
Uranium, Uo, Metal, Uranium (U) Native Oxide, and Uraninite

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

 Overlay of Uo metal and U Native Oxide – U (4f)
Native Oxide C (1s) = 284.3 eV (Flood gun OFF)

  Overlay of Uo metal and Uraninite – U (4f)
C (1s) = 284.3 eV (Flood gun OFF)
 
→  Periodic Table  Copyright ©:  The XPS Library 

 

Overlay of U (4f7/2)
Uo Metal, Uranium Native Oxide, & Uraninite

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 

 

Valence Band Spectra
Uo metal, Uraninite 

Uo Metal
 Black grains, Uraninite
Flood gun is OFF,  C (1s) = 284.3 eV

Overlay of Valence Band Spectra for
Uranium, Uo Metal and Uraninite (UO2)

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 

 

​

Uranium Minerals, Gemstones, and Chemical Compounds

 
Brammerite  – UTi2O6 Umohoite – (UO2)MoO4 · 2H2O Studtite – [(UO2)(O2)(H2O)2] · H2O Schoepite – (UO2)8O2(OH)12 · 12H2O

→  Periodic Table 

 

Six (6) Chemical State Tables of U (4f7/2) 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 (2p3/2) 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

U (4f7/2) 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
U 92 U – element  (N*12) 376.4 eV 377.6 eV 284.8 eV Avg BE – NIST
U 92 U – element 376.9 eV 377.6 eV 285.0 eV The XPS Library
U 92 UI3 (N*1) 379.0 eV 284.8 eV Avg BE – NIST
U 92 U-O2 379.5 eV  (first peak) 285.0 eV The XPS Library
U 92 U-O2 (N*9) 379.8 eV 380.6 eV 284.8 eV Avg BE – NIST
U 92 U3O8 (N*4) 380.7 eV 381.1 eV 284.8 eV Avg BE – NIST
U 92 U-O3 285.0 eV The XPS Library
U 92 U-O3 (N*8) 380.9 eV 381.9 eV 284.8 eV Avg BE – NIST
U 92 UF4 (N*7) 382.2 eV 382.7 eV 284.8 eV Avg BE – NIST
U

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

U (4f7/2) Chemical State BEs from:  “PHI Handbook”

C (1s) BE = 284.8 eV

→  Periodic Table 

Copyright ©:  Ulvac-PHI

Table #3

U (4f7/2) Chemical State BEs from:  “Thermo-Scientific” Website

C (1s) BE = 284.8 eV

 

No BE Table for Uranium

→  Periodic Table 

Copyright ©:  Thermo Scientific 

Table #4

U (4f7/2) 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

 

No BE Table for Uranium

→  Periodic Table 

Copyright ©:  Mark Beisinger

Table #5

U (4f7/2) 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
U 4f7/2 U 377.1 ±0.2 376.9 ～ 377.3
U 4f7/2 U-Selenides 379.7 ±0.6 379.1 ～ 380.2
U 4f7/2 U-(acac)4 379.7 ±0.3 379.4 ～ 380.0
U 4f7/2 U-Sulfides 379.8 ±0.5 379.3 ～ 380.2
U 4f7/2 U-Halides 380.6 ±2.3 378.3 ～ 382.8
U 4f7/2 Ca-UO4 380.8 ±0.3 380.5 ～ 381.0
U 4f7/2 U-Tellurides 380.8 ±0.4 380.4 ～ 381.2
U 4f7/2 U-Oxides 380.9 ±0.9 380.0 ～ 381.7
U 4f7/2 U-Oxy Halides 381.5 ±1.5 380.0 ～ 382.9
U 4f7/2 U(SO4)2 381.6 ±0.3 381.3 ～ 381.9
U 4f7/2 K2UF6 382.5 ±0.3 382.2 ～ 382.7

→  Periodic Table 

 
 

Histograms of NIST BEs for U (4f7/2) BEs

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

 

Histogram indicates:  377.4 eV for Uo based on 13 literature BEs Histogram indicates:  380.1 eV for UO2 based on 11 literature BEs

Table #6


NIST Database of U (4f7/2) 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
U 4f7/2 U 376.50  Click
U 4f7/2 AlNiU 376.70  Click
U 4f7/2 U 376.90  Click
U 4f7/2 U 377.00  Click
U 4f7/2 U 377.10  Click
U 4f7/2 U 377.10  Click
U 4f7/2 U 377.20  Click
U 4f7/2 D2O/U 377.30  Click
U 4f7/2 U 377.40  Click
U 4f7/2 U 377.40  Click
U 4f7/2 U 377.40  Click
U 4f7/2 U 377.40  Click
U 4f7/2 O2/U 377.50  Click
U 4f7/2 D2O/U 377.50  Click
U 4f7/2 U 377.60  Click
U 4f7/2 U 377.60  Click
U 4f7/2 O2/U 377.60  Click
U 4f7/2 D2O/U 377.70  Click
U 4f7/2 D2O/U 377.70  Click
U 4f7/2 UFe2 377.80  Click
U 4f7/2 UCl3 378.30  Click
U 4f7/2 UBr3 378.40  Click
U 4f7/2 UI3 379.00  Click
U 4f7/2 USe3 379.10  Click
U 4f7/2 UO2 379.20  Click
U 4f7/2 US3 379.40  Click
U 4f7/2 AlNiUOx 379.60  Click
U 4f7/2 [U(CH3C(O)CHC(O)CH3)4] 379.70  Click
U 4f7/2 UO2 379.80  Click
U 4f7/2 UO2 379.80  Click
U 4f7/2 UBr4 379.90  Click
U 4f7/2 U4O9 379.90  Click
U 4f7/2 O2/U 379.90  Click
U 4f7/2 UO2 380.00  Click
U 4f7/2 UClO 380.00  Click
U 4f7/2 UF3 380.10  Click
U 4f7/2 UO2 380.10  Click
U 4f7/2 UBrO 380.10  Click
U 4f7/2 US 380.10  Click
U 4f7/2 D2O/O2/U 380.10  Click
U 4f7/2 D2O/O2/U 380.10  Click
U 4f7/2 UO2 380.15  Click
U 4f7/2 UCl4 380.20  Click
U 4f7/2 UO2 380.20  Click
U 4f7/2 UO2 380.20  Click
U 4f7/2 U 380.20  Click
U 4f7/2 UNb4O12 380.20  Click
U 4f7/2 UNb3O10 380.20  Click
U 4f7/2 O2/UFe2 380.20  Click
U 4f7/2 O2/UFe2 380.20  Click
U 4f7/2 O2/AlNiU 380.20  Click
U 4f7/2 UO2 380.30  Click
U 4f7/2 UO2 380.30  Click
U 4f7/2 UCl2O 380.30  Click
U 4f7/2 USe 380.30  Click
U 4f7/2 UBr2O 380.40  Click
U 4f7/2 UNb3O10.17 380.40  Click
U 4f7/2 O2/UFe2 380.40  Click
U 4f7/2 UO2Br 380.50  Click
U 4f7/2 U2Te3 380.50  Click
U 4f7/2 UBr4 380.50  Click
U 4f7/2 D2O/O2/U 380.50  Click
U 4f7/2 UO2 380.60  Click
U 4f7/2 USbO5 380.60  Click
U 4f7/2 D2O/U 380.60  Click
U 4f7/2 UO2+x 380.60  Click
U 4f7/2 UO2 380.70  Click
U 4f7/2 CaUO4 380.70  Click
U 4f7/2 U3O8 380.70  Click
U 4f7/2 UNb2O7 380.70  Click
U 4f7/2 O2/U 380.70  Click
U 4f7/2 O2/U 380.70  Click
U 4f7/2 U3O8 380.80  Click
U 4f7/2 D2O/U 380.80  Click
U 4f7/2 Cs2U2O7 380.80  Click
U 4f7/2 Cs2UO4 380.80  Click
U 4f7/2 U(UO2)(PO4)2 380.80  Click
U 4f7/2 UO3 380.90  Click
U 4f7/2 UO3 380.90  Click
U 4f7/2 D2O/U 380.90  Click
U 4f7/2 [UO2(C2H3O2)2].2H2O 381.00  Click
U 4f7/2 UO2MoO4 381.00  Click
U 4f7/2 U3O8 381.00  Click
U 4f7/2 U3O7 381.00  Click
U 4f7/2 U0.5Th0.5(UO2)(PO4)2 381.00  Click
U 4f7/2 USb3O10 381.10  Click
U 4f7/2 UBr2O2 381.10  Click
U 4f7/2 UO3 381.10  Click
U 4f7/2 U3O8 381.10  Click
U 4f7/2 Th(UO2)(PO4)2 381.10  Click
U 4f7/2 U0.2Th0.8(UO2)(PO4)2 381.10  Click
U 4f7/2 UCl4 381.30  Click
U 4f7/2 UCl4 381.30  Click
U 4f7/2 UO3 381.30  Click
U 4f7/2 U3O8 381.30  Click
U 4f7/2 UTe3 381.30  Click
U 4f7/2 Li2UO4 381.40  Click
U 4f7/2 UNb3O10.34 381.40  Click
U 4f7/2 UO2Cl2 381.60  Click
U 4f7/2 UO3 381.60  Click
U 4f7/2 U(SO4)2 381.60  Click
U 4f7/2 UO3 381.70  Click
U 4f7/2 UO3 381.75  Click
U 4f7/2 UO3 381.80  Click
U 4f7/2 UO3 381.80  Click
U 4f7/2 UCl5 381.90  Click
U 4f7/2 UO3 381.90  Click
U 4f7/2 UO3 381.90  Click
U 4f7/2 UO3 381.90  Click
U 4f7/2 UO2(NO3)2.6H2O 382.00  Click
U 4f7/2 U(UO2)(PO4)2 382.00  Click
U 4f7/2 UF4 382.20  Click
U 4f7/2 UF4 382.20  Click
U 4f7/2 UF4 382.30  Click
U 4f7/2 UF4 382.30  Click
U 4f7/2 U0.2Th0.8(UO2)(PO4)2 382.30  Click
U 4f7/2 K2UF6 382.40  Click
U 4f7/2 U0.5Th0.5(UO2)(PO4)2 382.50  Click
U 4f7/2 UF4 382.60  Click
U 4f7/2 UF4 382.60  Click
U 4f7/2 UF5 382.60  Click
U 4f7/2 Th(UO2)(PO4)2 382.60  Click
U 4f7/2 UF4 382.70  Click
U 4f7/2 UO2F2 382.70  Click
U 4f7/2 UO2F2 383.00  Click
U 4f7/2 UF5 383.40  Click
U 4f7/2 UF6 384.90  Click

 

 

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 Uranium Materials

 

 

 

Expert Knowledge Explanations

 

→  Periodic Table 

 

Uranium Chemical Compounds

 

Peak-fits and Overlays of Chemical State Spectra

Pure Uranium:  U (4f)
Cu (2p3/2) BE = 932.6 eV		 UO2:  U (4f7/2)
C (1s) BE measured at 284.3 eV		 Ux: U (4f7/2)
C (1s) BE = xxx eV

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 

 

Overlay of U (4f) Spectra shown Above

C (1s) BE = 285.0 eV

 

 

 

→  Periodic Table 

 

Auto-Oxidation Experiment on Uranium, Uo
Clean Uranium, Uo, Exposed to Lab Air for 7 days time, then analyzed

Atom% results indicate the product is UO3
Based on literature U (4f) BEs the auto-oxidized product is UO2

  .
U (4f) Chemical State Spectrum from auto-oxidized UOx  – Raw
Flood gun is OFF, C (1s) BE = 285.0 eV		 U (4f) Chemical State Spectrum from auto-oxidized UOx – Peak-fit
Flood gun is OFF, C (1s) BE = 285.0 eV
  . 
O (1s) Chemical State Spectrum from auto-oxidized UOx
Flood gun is OFF, C (1s) BE = 285.0 eV		 C (1s) Chemical State Spectrum from auto-oxidized UOx
Flood gun is OFF, C (1s) BE = 285.0 eV
  . 
Valence Band Spectrum from auto-oxidized UOx
Flood gun is OFF, C (1s) BE = 285.0 eV		 Expanded Plasmon range Spectrum from auto-oxidized UOx
 

Survey Spectrum of Clean Uo metal Auto-Oxidized
over 7 days in Lab Air – UOx
Based on atom% results the product is UO3
Based on literature U (4f) BEs the main product is UO2


Shake-up Features:
Comparing Uo metal with Auto-oxidized UOx

Uo metal – clean Auto-oxidized UOx

 

 

Multiplet Splitting Features
Uranium Compounds

Uo metal – NO Splitting for U (4f) UOx – Multiplet Splitting Peaks for auto-oxidized UOx (4f)
na na

 

 

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 

 

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

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 8 hours.  UHV pump was a Cryopump.
Initial spectra are at the front.  Final spectra are at the rear. Flood gun is OFF.
U (4f) Signal O (1s) Signal
.
Valence Band Signal C (1s) Signal

 

 

 

Uranium Chemical Compounds

 

→  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 Uranium – UOx

 

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 

 

Uranium Alloys

   
XxCu XxCu
→  Periodic Table   
XxCu XxCu

 

Copyright ©:  The XPS Library 

 

 


XPS Facts, Guidance & Information

→  Periodic Table 

    Element Uranium (U)
  
    Primary XPS peak used for Peak-fitting: U (4f7/2)  
    Spin-Orbit (S-O) splitting for Primary Peak: Spin-Orbit splitting for “f” Orbital, ΔBE = 10.8 eV
  
    Binding Energy (BE) of Primary XPS Signal: 377 eV
  
    Scofield Cross-Section (σ) Value: U (4f7/2) = 27.36.     U (4f5/2) = 21.50
  
    Conductivity: U resistivity =  
Native Oxide suffers Differential Charing		  
    Range of U (4f7/2) Chemical State BEs: xxx eV range   (Uo to UF4)  
Signals from other elements that overlap
U (4f7/2) Primary Peak:		   K (2s), Ag (3d)
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 

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Information Useful for Peak-fitting U (4f7/2)

 

  • FWHM (eV) of U (4f7/2) for Pure Uo :  ~0.92 eV using 25 eV Pass Energy after ion etching:
  • FWHM (eV) of U (4f7/2) for UO2:  ~1.4 eV using 50 eV Pass Energy  (before ion etching)
  • Binding Energy (BE) of Primary Signal used for Measuring Chemical State Spectra:  377 eV for U (4f7/2) with +/- 0.2 uncertainty
  • List of XPS Peaks that can Overlap Peak-fit results for U (4f7/2):  K (2s), Ag (3d)

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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) = ~0.90 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
    • Ag (3d5/2) FWHM (eV) = ~0.85 eV for PE 50 on SSI S-Probe
  • 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 used on Peak-fitting: typically constrain the peak area ratios based on the Scofield cross-section values
  • Asymmetry for Conductive materials:  20-30% with increased Lorentzian %
  • Peak-fitting “2s” or “3s” Peaks:  Often need to use 50-60% Lorentzian peak-shape

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.

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Contaminants Specific to Uranium

 

  • Uranium develops a thick native oxide due to the reactive nature of clean Uranium .
  • The native oxide of U Ox is 8-9 nm thick.
  • Uranium thin films often have a low level of iron (Fe) in the bulk as a contaminant or to strengthen the thin film
  • Uranium 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

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Data Collection Guidance

 

  • Chemical state differentiation can be difficult
  • Collect principal U (4f) peak and U (4d)
  • 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

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Data Collection Settings for Uranium (U)

 

  • Conductivity:  Metal 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:  U (4f7/2) at 377 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:  374 – 404 eV
  • Recommended Extended BE Range for Measuring Chemical State Spectrum:  370 – 470 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 

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Effects of Argon Ion Etching

 

  • Carbides appear after ion etching Th and various reactive surfaces.  Carbides form due to the presence of 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

 

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Gas Phase XPS or UPS Spectra

 

Chemical Information and Literature Info about Uranium
Common Chemical Reactions of Uranium Metal from Wikipedia

This paper is a review that provides the list of U (4f) BEs from Uranium Compounds shown here.

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