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

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Argon (Ar⁺)

 

	Argon in a Discharge Tube

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Page Index
Pure Element Spectra with Peak-fits IMFP and Cross-sections for Pure Element	Overlays and Valence Band Spectra Six (6) Tables of Chemical State BEs  Advanced XPS Information Section	Peak-fits and Overlays of Ar+ Chemical Compounds Quantitation and Atom %s	Auger Peaks and Spectra XPS Facts, Guidance, Information

• Expert Knowledge Examples & Explanations

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Argon (Ar^o)

Argon implanted in Al^o, B^o, Be^o, C^o, Cr^o, Mn^o, Sc^o, Si^o, Ti^o and V^o

Peak-fits, BEs, FWHMs, and Peak Labels

 

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Argon (Aro) Ar (2p) Spectrum – Peak-fitted Ar+ ion implanted into Aluminum metal	Argon (Aro) Survey Spectrum of Ar+ Ion Etched Aluminum Ar+ ion implanted into Aluminum metal
Argon (Aro) Ar (2p) Spectrum – Peak-fitted Ar+ ion implanted into Boron Not charge referenced	Argon (Aro) Ar (2p) Spectrum of Ar+ Ion Etched Boron Ar+ ion implanted into Boron
Argon (Aro) Ar (2p) Spectrum – raw spectrum Ar+ ion implanted into Beryllium metal	Argon (Aro) Ar (2p) Spectrum of Ar+ Ion Etched Beryllium Ar+ ion implanted into Beryllium metal
Argon (Aro) Ar (2p) Spectrum – raw spectrum Ar+ ion implanted into Carbon, HOPG	Argon (Aro) Ar (2p) Spectrum of Ar+ Ion Etched HOPG Ar+ ion implanted into Carbon, HOPG
Argon (Aro) Ar (2s) Spectrum of Ar+ Ion Etched HOPG Ar+ ion implanted into Carbon, HOPG	Argon (Aro) Ar (3p) and (3s) Spectrum of Ar+ Ion Etched HOPG Ar+ ion implanted into Carbon, HOPG
Argon (Aro) Ar (2p) Spectrum – raw spectrum Ar+ ion implanted into Chromium metal	Argon (Aro) Ar (2p) Spectrum of Ar+ Ion Etched Chromium Ar+ ion implanted into Chromium metal
Argon (Aro) Ar (2p) Spectrum – raw spectrum Ar+ ion implanted into Manganese metal	Argon (Aro) Ar (2p) Spectrum of Ar+ Ion Etched Manganese Ar+ ion implanted into Manganese metal
Argon (Aro) Ar (2p) Spectrum – raw spectrum Ar+ ion implanted into Scandium metal	Argon (Aro) Ar (2p) Spectrum of Ar+ Ion Etched Scandium Ar+ ion implanted into Scandium metal
Argon (Aro) Ar (2p) Spectrum – raw spectrum Ar+ ion implanted into Silicon	Argon (Aro) Ar (2p) Spectrum of Ar+ Ion Etched Silicon Ar+ ion implanted into Silicon
Argon (Aro) Ar (2p) Spectrum – raw spectrum Ar+ ion implanted into Titanium metal	Argon (Aro) Ar (2p) Spectrum of Ar+ Ion Etched Titanium Ar+ ion implanted into Titanium metal
Survey Spectrum of Implanted Argon (Aro) in HOPG with Peaks Integrated, Assigned and Labelled
→  Periodic Table  XPS Signals for Argon, (Aro) 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 Ar (2s) 20 1.97 28.2 Ar (2p) 242 3.04 29.6 Ar (3s) 22 0.227 27.6 Ar (3p) 9 0.2418 σ:  abbreviation for the term Scofield Photoionization Cross-Section Energy Loss Peak ~24 eV above peak max *Scofield Cross-Section (σ) for C (1s) = 1.0     Loss Peak from Implanted Aro  produced by extensive Ar+ ion etching Extended Range Spectrum Extended Range Spectrum – Loss Labelled Features Observed xx xx xx →  Periodic Table

Copyright ©:  The XPS Library 

Overlays of Ar (2p) Spectra for:
Ar implanted into various metals

 

Overlay of Ar (2p) spectrum – Ar implanted into C, Si, and Ti	Overlay of Ar (2p) spectrum – Ar implanted into Cr, Al, and Sc
	Copyright ©:  The XPS Library

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Features Observed

• xx
• xx
• xx

→  Periodic Table 

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Valence Band Spectra
Ar (3s) and (3p) in HOPG

Features Observed

• xx
• xx
• xx

→  Periodic Table

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Six (6) Chemical State Tables of Ar (2p3) BEs

 

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

 

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Notes of Caution when using Published BEs and BE Tables:

• 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 

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Table #1

Ar (2p_3/2) Chemical State BEs from:  “The XPS Library Spectra-base”

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

Element	Atomic #	Compound (implanted into metal)	As-Measured by TXL or NIST Average BE	Largest BE	Hydrocarbon C (1s) BE	Source
Ar	18	Ar / Be	241.8 eV			The XPS Library
Ar	18	Ar / C (HOPG)	241.8 eV			The XPS Library
Ar	18	Ar / Si	241.9 eV			The XPS Library
Ar	18	Ar / Al	242.2 eV			The XPS Library
Ar	18	Ar / Mn	242.3 eV			The XPS Library
Ar	18	Ar / Cr	242.7 eV			The XPS Library
Ar	18	Ar / Sc	243.8 eV			The XPS Library
Ar	18	Ar / V	242.8 eV			The XPS Library
Ar	18	Ar / Ti	242.9 eV			The XPS Library

 

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 (2p_3/2) BE = 932.62 eV and Au (4f_7/2) 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 

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Table #2

Ar (2p_3/2) Chemical State BEs from:  “PHI Handbook”

C (1s) BE = 284.8 eV

→  Periodic Table 

Copyright ©:  Ulvac-PHI

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Table #3

Ar (2p_3/2) Chemical State BEs from:  “Thermo-Scientific” Website

C (1s) BE = 284.8 eV

Chemical state	Binding energy Ar+ (2p3)
Implanted Ar	~243 eV

→  Periodic Table 

Copyright ©:  Thermo Scientific 

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Table #4

Ar (2p_3/2) 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

→  Periodic Table 

Copyright ©:  Mark Ar+isinger

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Table #5

Ar (2p_3/2) 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 Ar 2p3/2 Ar in Pt 240.3 ±0.2 240.1 ～ 240.5 Ar 2p3/2 Ar in Au 240.5 ±0.2 240.3 ～ 240.7 Ar 2p3/2 Ar in Cu 241.0 ±0.3 240.7 ～ 241.3 Ar 2p3/2 Ar in Ag 241.1 ±0.3 240.8 ～ 241.4 Ar 2p3/2 Ar in graphite 241.8 ±0.5 241.3 ～ 242.3 Ar 2p3/2 Ar in Si 241.8 ±0.2 241.6 ～ 242.0

→  Periodic Table 

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 Table #6

NIST Database of Ar (2p_3/2) 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.

→  Periodic Table 

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Statistical Analysis of Binding Energies in NIST XPS Database of BEs

 

 

→  Periodic Table 

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Advanced XPS Information Section

 

Expert Knowledge, Spectra, Features, Guidance and Cautions  

for XPS Research Studies

on Argon Materials

 

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Expert Knowledge Explanations

 

Overlay reveals shift	Shake-up Example	Auger signal overlaps X

 

→  Periodic Table 

 

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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.

 

• KE^^0.66 IMFP:  ~xx ang (x nm) for xxx  at KE=xxx eV, BE=xxx eV
• TPP-2M IMFP:  ~29.6 ang (2.96 nm) for Ar+ (2p) at KE=1244 eV, BE=242 eV
• Caution:  Need to include Energy Loss peaks to produce more accurate atom% quantitation.
• Peak Background Integration:
• Transmission Function effect on Quantitation:
• IMFP effect on Quantitation:
• Energy loss peaks affect on Quantitation:
• RSF vs Cross-section terminology:

→  Periodic Table 

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AES

Ar (KLL) Signal:

Features Observed

• xx
• xx
• xx

→  Periodic Table 

Copyright ©:  The XPS Library 

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XPS Facts, Guidance & Information

→  Periodic Table 

		Element		Argon (Ar+)
		Primary XPS peak used for Peak-fitting :		Ar+ (2p3)
		Spin-Orbit (S-O) splitting for Primary Peak:		Spin-Orbit splitting for “p” orbital, ΔBE = 2.2 eV
		Binding Energy (BE) of Primary XPS Signal:		242 eV
		Scofield Cross-Section (σ) Value:		Ar+ (2p3) = 3.04
		Conductivity:
		Range of Ar+ (2p3) BEs as implanted gas:		241 – 243 eV range
		Signals from other elements that overlap Ar+ (2p3) Primary Peak:		Mg Auger
		Loss Peak:		~24 eV above peak max
		Shake-up Peaks:		??
		Multiplet Splitting Peaks:		not possible
		General Information about XXX Compounds:		xx
		Cautions – Chemical Poison Warning		xx

Copyright ©:  The XPS Library 

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Information Useful for Peak-fitting Ar (2p3)

 

• FWHM (eV) of Pure Ar+ :  ~0.86 eV using 50 eV Pass Energy after ion etching:
• Binding Energy (BE) of Primary Signal used for Measuring Chemical State Spectra:  242 eV for Ar+ (2p) with +/- 0.3 uncertainty
• List of XPS Peaks that can Overlap Peak-fit results for Ar+ (2p3):  Mg Auger

→  Periodic Table 

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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 (3d_5/2) FWHM (eV) = ~0.95 eV for PE 50 on Thermo K-Alpha
  • Ag (3d_5/2) FWHM (eV) = ~1.00 eV for PE 80 on Kratos Nova
  • Ag (3d_5/2) 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 

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Contamination

 

Contaminants Specific to Argon

 

• Argon develops a thick native oxide due to the reactive nature of clean Argon .
• The native oxide of Ar+O_x is 6-7 nm thick.
• Argon thin films often have a low level of iron (Fe) in the bulk as a contaminant or to strengthen the thin film
• Argon 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 

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Data Collection Guidance

 

• Chemical state differentiation can be difficult
• Collect principal Ar+ (2p3) peak as well as Ar+ (1s).
• 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 

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Data Collection Settings for Argon (Ar+)

 

• Conductivity:  Argon 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:  Ar+ (1s) at 49.6 eV
• Recommended Pass Energy for Measuring Chemical State Spectrum:  40-50 eV    (Produces Ag (3d_5/2) 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:  40 – 60 eV
• Recommended Extended BE Range for Measuring Chemical State Spectrum:  40 – 100 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 

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Effects of Argon Ion Etching

• Carbides appear after ion etching Ar+ 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 

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