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 


Sulfur (S)
 

Acanthite – Ag2S Sulfur – S8  (natural crystals)
 Marcarsite – FeS2

 

  Page Index
  • Peak-fits and Overlays of  Cl Chemical Compounds
  • Expert Knowledge Explanations


Sulfur (S8)

Freshly Exposed Bulk of Natural Sulfur Crystal
Peak-fits, BEs, FWHMs, and Peak Labels


Natural Sulfur, S8
S (2p) Spectrum – raw
as received crystal surface,
charge referenced so C (1s) = 285.0 eV
Natural Sulfur, S8
S (2p) Spectrum – peak-fit
as received crystal surface,
charge referenced so C (1s) = 285.0 eV

Natural Sulfur, S8
S (2s) spectrum – raw
as received crystal surface
charge referenced so C (1s) = 285.0 eV
Natural Sulfur, S8
S (2s) spectrum – peak-fit
as received crystal surface
charge referenced so C (1s) = 285.0 eV
→  Periodic Table – HomePage  
Natural Sulfur, S8
Sulfur Valence Band spectrum
as received crystal surface
charge referenced so C (1s) = 285.0 eV
 Natural Sulfur, S8
C (1s) spectrum
as received crystal surface
charge referenced so C (1s) = 285.0 eV
 

Survey Spectrum of Sulfur, (S8), Natural Crystal
with Peaks Integrated, Assigned and Labelled
→  Periodic Table 

XPS Signals for Sulfur, S

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
Mo (3d) & Ta (4d5) overlap S (2s) 229 1.43 28.7
S (2p) 165.44 0.567 29.9
S (2p) 164.26 1.11 29.9
S (3s) 19 0.1465 32.5
S (3p) 4 0.0774

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

Expected Bandgaps from https://materialsproject.org
Expected Bandgap for S8:  ~2.5 eV
Expected Bandgap for Ag2S:  1-1.3 eV
Expected Bandgap for CdS:  0.3 – 1.1 eV
Expected Bandgap for FeS2:  0.5 – 1.0 eV
Expected Bandgap for HgS:  ~1.7 eV
Expected Bandgap for PbS:  1-2 eV
Expected Bandgap for ZnS:  ~2 eV

*Scofield Cross-Section (σ) for C (1s) = 1.0

 

 

Energy Loss Peaks from S (2p) in Natural Sulfur, S8
freshly cleaved natural crystal

S (2p & 2s) – Extended Range Spectrum S (2p & 2s) – Extended Range Spectrum – Vertically Zoomed 

Features Observed

  • xx
  • xx
  • xx

→  Periodic Table 
 

Side-by-Side Comparison of

S (2p) Spectra from Metal Sulfides (S2-)
and Metal Sulfates (SO42-)
Ag, Cd, Fe, Hg, Pb, Zn

Peak-fits, BEs, FWHMs, and Overlays
 .
Silver (1+) Sulfide, Ag2S
S (2p) spectrum
Flood Gun OFF
C (1s) appears at 284.9 eV		 Silver (1+) Sulfate, Ag2SO4
S (2p) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Overlay of S (2p) Spectra 
from Ag2S and Ag2SO4
Chemical Shift:  7.2 eV
→  Periodic Table   
Cadmium (2+) Sulfide, CdS
S (2p) spectrum
Flood Gun OFF
C (1s) appears at 284.6 eV		 Cadmium (2+) Sulfate, CdSO4
S (2p) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Overlay of S (2p) Spectra 
from CdS and CdSO4
Chemical Shift:  7.3 eV
 .
Iron (2+) Sulfide, FeS2
S (2p) spectrum
Flood Gun OFF
C (1s) appears at 284.6 eV		 Iron (2+) Sulfate, FeSO4
S (2p) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Overlay of S (2p) Spectra 
from FeS2 and FeSO4
Chemical Shift:  6.9 eV
→  Periodic Table   .
Mercury (2+) Sulfide, HgS
S (2p) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Mercury (1+) Sulfate, Hg2SO4
S (2p) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Overlay of S (2p) Spectra 
from HgS and Hg2SO4
Chemical Shift:  7.1 eV
 .
Lead (2+) Sulfide, PbS
S (2p) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Lead (2+) Sulfate, PbSO4
S (2p) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Overlay of S (2p) Spectra 
from PbS and PbSO4
Chemical Shift:  7.4 eV
→  Periodic Table   
Zinc (2+) Sulfide, ZnS
S (2p) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Zinc (2+) Sulfate, ZnSO4
S (2p) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Overlay of S (2p) Spectra 
from ZnS and ZnSO4
Chemical Shift:  6.9 eV

 

 

Side-by-Side Comparison of

Metal – HSO4(1-)   to   Metal – SO4(2-)


from Metal   bi-Sulfate   and   Sulfates

NaHSO4, Na2SO4
Peak-fits, BEs, FWHMs, and Overlays

→  Periodic Table   
NaHSO4 
S (2p) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Na2SO4
S (2p) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Overlay of S (2p) Spectra 
from NaHSO4 and Na2SO4
 .
NaHSO4 
O (1s) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Na2SO4
O (1s) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Overlay of O (1s) Spectra 
from NaHSO4 and Na2SO4
→  Periodic Table   
NaHSO4 
Na (1s) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Na2SO4
Na (1s) spectrum
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV		 Overlay of Na (1s) Spectra 
from NaHSO4 and Na2SO4

 


Survey Spectra from Sodium bi-Sulfate (NaHSO4)
with Peaks Integrated, Assigned and Labelled

 

 

Survey Spectra from Sodium Sulfate (Na2SO4)
with Peaks Integrated, Assigned and Labelled

→  Periodic Table 

 

 

Sulfur (S) in an Organic Polymer

Peak-fits, BEs, FWHMs, and Peak Labels

Poly-Phenylene Sulfide (PPS)
cast from solution in THF
analyzed bottom side of film that touched glass

 

Poly-phenylene sulfide, PPS
S (2p) Spectrum – raw
film formed from solution in THF
charge referenced so C (1s) = 285.0 eV		 Poly-phenylene sulfide, PPS
S (2p) Spectrum – peak-fit
film formed from solution in THF
charge referenced so C (1s) = 285.0 eV
 
→  Periodic Table 
Poly-phenylene sulfide, PPS
C (1s) Spectrum – raw 
film formed from solution in THF
charge referenced so C (1s) = 285.0 eV		 Poly-phenylene sulfide, PPS
C (1s) Spectrum – peak-fit
film formed from solution in THF
charge referenced so C (1s) = 285.0 eV

.
Poly-phenylene sulfide, PPS
Valence Band Spectrum 
Freshly formed film from solution
charge referenced so C (1s) = 285.0 eV		 Poly-phenylene sulfide, PPS
S(2p) Spectrum – Expanded
film formed from solution in THF
charge referenced so C (1s) = 285.0 eV
→  Periodic Table 

 

 

Survey Spectrum of Poly-Phenylene Sulfide (PPS)
with Peaks Integrated, Labelled and Assigned

 

Copyright ©:  The XPS Library 

→  Periodic Table 

 

Metal Sulfate Minerals, Crystals, and Chemical Compounds

 
Adanite – Pb2(TeO3)(SO4) Anhydrite – CaSO4 Alum – KAl(SO4)-12H2O Anglesite – PbSO4

 

 

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

 

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

 

 

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

S (2p) 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
S 16 Ag2S (N*2) 160.7 eV 160.8 eV 284.8 eV Avg BE – NIST
S 16 Na2S (N*2) 160.6 eV 161.8 eV 284.8 eV Avg BE – NIST
S 16 PbS 161.1 eV 285.0 eV The XPS Library
S 16 CuS 161.5 eV 285.0 eV The XPS Library
S 16 TaS2 161.5 eV 285.0 eV The XPS Library
S 16 CdS 161.6 eV 285.0 eV The XPS Library
S 16 MoS2 161.8 eV 163 eV 285.0 eV The XPS Library
S 16 HgS 162.0 eV 285.0 eV The XPS Library
S 16 WS2 162.1 eV 285.0 eV The XPS Library
S 16 WS2 (N*4) 162.1 eV 163.1 eV 284.8 eV Avg BE – NIST
S 16 Na2S2O3 162.4 eV 285.0 eV The XPS Library
S 16 As2S3 162.5 eV 285.0 eV The XPS Library
S 16 FeS2 162.5 eV 285.0 eV The XPS Library
S 16 ZnS 162.5 eV 285.0 eV The XPS Library
S 16 PPS, phenylene sulfide 163.7 eV polymer film 285.0 eV The XPS Library
S 16 S – element  (S8) 164.2 eV 285.0 eV The XPS Library
S 16 Na2SO3 (N*6) 166.5 eV 167.2 eV 284.8 eV Avg BE – NIST
S 16 Ag2-SO4 168.2 eV 285.0 eV The XPS Library
S 16 M-SO4 (N*12) 168.5 eV 170.1 eV 284.8 eV Avg BE – NIST
S 16 Na2S2O3 168.5 eV 285.0 eV The XPS Library
S 16 Na2SO4 168.9 eV 285.0 eV The XPS Library
S 16 H2SO4 (N*1) 169.6 eV 284.8 eV Avg BE – NIST
S 16 SF6 (N*2) 173.4 eV 174.4 eV 284.8 eV Avg BE – NIST

Charge Referencing

  • (N*number) identifies the number of NIST BEs that were averaged to produce the BE in the middle column.
  • Binding Energy Scale calibration expects 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

S (2p) Chemical State BEs from:  “PHI Handbook”

C (1s) BE = 284.8 eV

→  Periodic Table 

Copyright ©:  Ulvac-PHI

Table #3

S (2p) Chemical State BEs from:  “Thermo-Scientific” Website

C (1s) BE = 284.8 eV

Chemical state Binding energy S (2p) / eV
Metal sulfide ~161.5 eV
Thiol bound to gold, Au-S 162.5 eV
Thiol, R-SH ~164 eV
Na2(SO3)2 166.5 eV
Metal sulfate ~169 eV

→  Periodic Table 

Copyright ©:  Thermo Scientific 

Table #4

S (2p) 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

 

→  Periodic Table 

Copyright ©:  Mark Beisinger

Table #5

S (2p) 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
S 2p3/2 Sulfide 162.0 ±1.9 160.1 ～ 163.9
S 2p3/2 Mercaptan 162.7 ±0.6 162.1 ～ 163.2
S 2p3/2 Cysteine 163.6 ±0.5 163.1 ～ 164.1
S 2p3/2 S 163.8 ±0.3 163.5 ～ 164.0
S 2p3/2 Thiophene 164.0 ±0.3 163.7 ～ 164.2
S 2p3/2 Sulfite 166.5 ±1.0 165.5 ～ 167.5
S 2p3/2 SO2 167.7 ±0.8 166.9 ～ 168.4
S 2p3/2 Sulfone 168.1 ±1.8 166.3 ～ 169.8
S 2p3/2 Sulfate 169.8 ±1.4 168.4 ～ 171.1
S 2p3/2 SF6 175.9 ±1.5 174.4 ～ 177.3

→  Periodic Table 

 
 

Histograms of NIST BEs for S (2p) BEs

 

Histogram indicates:  163.9 eV for S (2p) in pure S based on 9 literature BEs Histogram indicates:  161.7 eV for S (2p) in CdS based on 9 literature BEs

Table #6


NIST Database of S (2p) 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.

→  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 Sulfur Containing Materials

 

 

 

Expert Knowledge Explanations

 


Sulfur Minerals – Chemical Compounds

Molybdenite, MoS2 Tungstenite, WS2 Tantalite, TaS2
 


Molybdenum Sulfide, MoS2
Molybdenite, freshly delaminated
  . 
Survey Spectrum from Molybdenite, MoS2
Flood gun is OFF, C (1s) BE = 284.2 eV
freshly delaminated 		 S (2p) Chemical State Spectrum from Molybdenite, MoS2
Flood gun is OFF, C (1s) BE = 284.2 eV
freshly delaminated
  . 
C (1s) Chemical State Spectrum from Molybdenite, MoS2
Flood gun is OFF, C (1s) BE = 284.2 eV
freshly delaminated		 Mo (3d) Chemical State Spectrum from Molybdenite, MoS2
Flood gun is OFF, C (1s) BE = 284.2 eV
freshly delaminated
  . 
Valence Band Spectrum from Molybdenite, MoS2
Flood gun is OFF, C (1s) BE = 284.2 eV
freshly delaminated		  S (2p) Loss Peaks Spectrum from Molybdenite, MoS2
Flood gun is OFF, C (1s) BE = 284.2 eV
freshly delaminated
 

Tungsten Sulfide, WS2
Tungstenite, freshly ground powder (solid lubricant)
   .
Survey Spectrum from Tungstenite, WS2
Flood gun is OFF, C (1s) BE = 284.0 eV
freshly ground powder		 S (2p) Chemical State Spectrum from Tungstenite, WS2
Flood gun is OFF, C (1s) BE = 284.0 eV
freshly ground powder
   .
C (1s) Chemical State Spectrum from Tungstenite, WS2
Flood gun is OFF, C (1s) BE = 284.0 eV
freshly ground powder		 W (4f) Chemical State Spectrum from Tungstenite, WS2
Flood gun is OFF, C (1s) BE = 284.0 eV
freshly ground powder
   .
Valence Band Spectrum from Tungstenite, WS2
Flood gun is OFF, C (1s) BE = 284.0 eV
freshly ground powder 		 S (2p) Loss Peaks Spectrum from Tungstenite, WS2
Flood gun is OFF, C (1s) BE = 284.0 eV
freshly ground powder
 

Tantalum Sulfide, TaS2
Tantalite, freshly delaminated
   .
Survey Spectrum from Tantalite, TaS2
Flood gun is OFF, C (1s) BE = 284.2 eV
freshly delaminated		 S (2p) Chemical State Spectrum from Tantalite, TaS2
Flood gun is OFF, C (1s) BE = 284.2 eV
freshly delaminated
Poor fit, not optimized using known peak area ratios or known BE differences
   .
C (1s) Chemical State Spectrum from Tantalite, TaS2
Flood gun is OFF, C (1s) BE = 284.2 eV
freshly delaminated		 Ta (4f) Chemical State Spectrum from Tantalite, TaS2
Flood gun is OFF, C (1s) BE = 284.2 eV
Poor fit, not optimized. 
   .
Valence Band Spectrum from Tantalite, TaS2
Flood gun is OFF, C (1s) BE = 284.2 eV
freshly delaminated		  S (2p) Loss Peaks Spectrum from Tantalite, TaS2
Flood gun is OFF, C (1s) BE = 284.2 eV
freshly delaminated

 

Quantitation

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 Sulfur

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.

Copyright ©:  The XPS Library 

 

 

XPS Facts, Guidance & Information

→  Periodic Table 

    Element Sulfur (S)
  
    Primary XPS peak used for Peak-fitting : S (2p)  
    Spin-Orbit (S-O) splitting for Primary Peak: Spin-Orbit splitting for Sulfur “p” orbital:  1.2 eV
  
    Binding Energy (BE) of Primary XPS Signal: 164 eV
  
    Scofield Cross-Section (σ) Value: S (2p3/2) = 1.11     S (2p1/2) = 0.567
  
    Conductivity:  
    Range of S (2p) Chemical State BEs: 161 – 170 eV range   (S)  
Signals from other elements that overlap
S (2p) Primary Peak:		  
Bulk Plasmons:   ~xxx eV above peak max for pure
Shake-up Peaks: ??
Multiplet Splitting Peaks:   not possible

 

 

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

xx 

Copyright ©:  The XPS Library 

 

Information Useful for Peak-fitting S (2p)

  • FWHM (eV) of S (2p3/2) for pure Sulfur (S8) :  ~0.66 eV using 25 eV Pass Energy after ion etching:
  • FWHM (eV) of S (2p3/2) for SO4  ~1.2 eV using 50 eV Pass Energy  (before ion etching)
  • Binding Energy (BE) of Primary Signal used for Measuring Chemical State Spectra:  162 eV for S (2p) in Metals with +/- 0.2 uncertainty
  • List of XPS Peaks that can Overlap Peak-fit results for S (2p):  xx

→  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 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.

→  Periodic Table 

 

Contaminants Specific to Metal Sulfides

  • METAL Sulfide thin films often have a low level of iron (Fe) in the bulk as a contaminant or to strengthen the thin film
  • METAL Sulfide degrades slightly 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 Sulfur (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 S (2p) peak as well as S (2s)
  • 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 Metal Sulfide (S)

  • Conductivity:  Metal Sulfides do not readily develops a native oxide that is sensitive to Flood Gun.
  • Primary Peak (XPS Signal) used to measure Chemical State Spectra:  S (2p) at xxx 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:   xxx eV
  • Recommended Extended BE Range for Measuring Chemical State Spectrum:  xxx 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 metals and various reactive surfaces.  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

 

NIST XPS Database BEs for S (2p)

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