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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Chlorine (Cl)

 

Chloroargyrite – AgCl	Chlorine – Cl2  (gas), a solid at -150 C	Fiedlerite – Pb3FCl4(OH) · H2O

 

Page Index
Pure Element Spectra with Peak-fits IMFP and Cross-sections for Pure Element Native Oxide Spectra with Peak-fits Pure Oxide Spectra with Peak-fits	Valence Band Spectra Six (6) Tables of Chemical State BEs  Histograms of NIST BEs Advanced XPS Information Section	Peak-fits and Overlays of  Cl Chemical Compounds	Contamination XPS Facts, Guidance, Information Chemical State Spectra from Literature

• Expert Knowledge & Explanations

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Cl^(-) in Lithium Chloride (LiCl)
(freshly exposed bulk of bead)
Peak-fits, BEs, FWHMs, and Peak Labels

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Lithium Chloride, LiCl Cl (2p) Spectrum – raw  as received crystal surface, charge referenced so C (1s) = 285.0 eV	Lithium Chloride, LiCl Cl (2p) Spectrum – peak-fit as received crystal surface, charge referenced so C (1s) = 285.0 eV
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Lithium Chloride, LiCl Cl (2s) spectrum – raw as received crystal surface charge referenced so C (1s) = 285.0 eV	Lithium Chloride, LiCl Cl (2s) spectrum – peak-fit as received crystal surface charge referenced so C (1s) = 285.0 eV
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Lithium Chloride, LiCl Valence Band spectrum as received crystal surface charge referenced so C (1s) = 285.0 eV	Lithium Chloride, LiCl C (1s) spectrum as received crystal surface charge referenced so C (1s) = 285.0 eV
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Lithium Chloride, LiCl Li (1s) spectrum as received crystal surface charge referenced so C (1s) = 285.0 eV
Survey Spectrum of Lithium Chloride (LiCl) with Peaks Integrated, Assigned and Labelled
→  Periodic Table  XPS Signals for Chlorine, Cl 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   Cl (2s) 269.98 1.69 27.9   Cl (2p3/2) 200.66 0.775 29.2 Se (Auger) overlaps Cl (2p3/2) 199.01 1.51 29.2   Cl (3s) 16.49 0.1852 32.5   Cl (3p3/2) 5.3 0.1433   σ:  abbreviation for the term Scofield Photoionization Cross-Section which is used with IMFP and TF to produce RSFs and atom% quantitation Energy Loss Peak:  ~  eV above peak max Expected Bandgap for LiCl:  6.0 – 6.4 eV  (https://materialsproject.org/) Expected Bandgap for NaCl:  4.5 – 5.0 eV *Scofield Cross-Section (σ) for C (1s) = 1.0     Energy Loss Peaks from Cl (2p) in KCl freshly cleaved crystal Cl (2p) – Extended Range Spectrum Cl (2p) – Extended Range Spectrum – Vertically Zoomed Features Observed xx xx xx →  Periodic Table
Side-by-Side Comparison of Cl (2p) Spectra in:   LiCl, NaCl, KCl, NH4Cl Peak-fits, BEs, FWHMs, and Peak Labels
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LiCl Cl (2p) spectrum Flood Gun ON Charge Referenced to C (1s) at 285.0 eV	NaCl Cl (2p) spectrum Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
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KCl Cl (2p) spectrum Flood Gun ON Charge Referenced to C (1s) at 285.0 eV	NH4Cl Cl (2p) spectrum Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
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CuCl2 Cl (2p) spectrum Flood Gun ON Charge Referenced to C (1s) at 285.0 eV	Overlay of Cl (2p) from LiCl, NaCl, KCl, and NH4Cl C (1s) BE = 285.0 eV

 

Survey Spectrum of Sodium Chloride, NaCl
with Peaks Integrated, Assigned and Labelled

 

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Survey Spectrum of Potassium Chloride, KCl
with Peaks Integrated, Assigned and Labelled

 

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Survey Spectrum of Ammonium Chloride, NH₄Cl
with Peaks Integrated, Assigned and Labelled

 

 

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Chlorine (Cl) in an Organic Polymer

Peak-fits, BEs, FWHMs, and Peak Labels

Poly-Vinyl Chloride (PVC) cast from solution in THF analyzed bottom side of film that touched glass

Poly-Vinyl Chloride, (-CH2-CH-Cl-)n Cl (2p) Spectrum – raw film formed from solution in THF charge referenced so C (1s) = 285.0 eV	Poly-Vinyl Chloride, (-CH2-CH-Cl-)n Cl (2p) Spectrum – peak-fit film formed from solution in THF charge referenced so C (1s) = 285.0 eV
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Poly-Vinyl Chloride, (-CH2-CH-Cl-)n C (1s) Spectrum – raw  film formed from solution in THF charge referenced so C (1s) = 285.0 eV	Poly-Vinyl Chloride, (-CH2-CH-Cl-)n C (1s) Spectrum – peak-fit film formed from solution in THF charge referenced so C (1s) = 285.0 eV
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Poly-Vinyl Chloride, (-CH2-CH-Cl-)n Valence Band Spectrum  Freshly formed film from solution charge referenced so C (1s) = 285.0 eV	Poly-Vinyl Chloride, (-CH2-CH-Cl-)n Cl (2s) Spectrum – peak-fit film formed from solution in THF charge referenced so C (1s) = 285.0 eV

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Survey Spectrum of Poly-Vinyl Chloride (PVC)
with Peaks Integrated, Assigned, and Labelled

 

Copyright ©:  The XPS Library 

→  Periodic Table 

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Chloride Minerals, Crystals, and Chemical Compounds
Pyromorphite – Pb5(PO4)3Cl	Salammoniac – NH4Cl	Hephaistosite – TlPb2Cl5	Halite – NaCl

 

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Six (6) Chemical State Tables of Cl (2p_3/2) 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 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 (2p_3/2) 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 (2p_3/2) 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

Cl (2p_3/2) 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
Cl	17	Cl-NH4	198.1 eV		285.0 eV	The XPS Library
Cl	17	Cl-K	198.5 eV		285.0 eV	The XPS Library
Cl	17	Cu-Cl2	198.9 eV		284.8 eV	Avg BE – NIST
Cl	17	Cl-Li	199.0 eV		285.0 eV	The XPS Library
Cl	17	Cl-Na	199.3 eV		285.0 eV	The XPS Library
Cl	17	Pt-Cl2	199.6 eV		285.0 eV	The XPS Library
Cl	17	Cl-C polymer	200.4 eV	200.8 eV	285.0 eV	The XPS Library
Cl	17	KClO3 (N*3)	205.9 eV	206.7 eV	284.8 eV	Avg BE – NIST
Cl	17	KClO4 (N*2)	208.3 eV	208.7 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 (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

Cl (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

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

C (1s) BE = 284.8 eV

Chemical state	Binding energy, Cl (2p3/2) / eV
Organic Cl	200
Metal	198.5-200

→  Periodic Table 

Copyright ©:  Thermo Scientific 

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Table #4

Cl (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 Beisinger

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Table #5

Cl (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 Cl 2p3/2 K2IrCl6 198.4 ±0.4 198.0 ～ 198.8 Cl 2p3/2 Pt(NH3)2Cl2 198.5 ±0.4 198.1 ～ 198.9 Cl 2p3/2 PdCl2 198.6 ±0.4 198.2 ～ 198.9 Cl 2p3/2 Alkali Chloride 198.7 ±0.6 198.1 ～ 199.2 Cl 2p3/2 NiCl2 199.4 ±0.4 199.0 ～ 199.7 Cl 2p3/2 CuCl2 199.7 ±0.4 199.3 ～ 200.0 Cl 2p3/2 p(CH2=CHCl) 200.0 ±0.3 199.7 ～ 200.3 Cl 2p3/2 C6H5Cl 200.5 ±0.5 200.0 ～ 201.0 Cl 2p3/2 KClO3 206.7 ±0.4 206.3 ～ 207.0 Cl 2p3/2 NaClO4 208.5 ±0.3 208.2 ～ 208.8 Cl 2p3/2 Perchlorate 208.7 ±0.5 208.2 ～ 209.2

 

→  Periodic Table 

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Histograms of NIST BEs for Cl (2p_3/2) BEs

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

Histogram indicates:  196.4 eV for Cl- in NaCl based on 8 literature BEs	Histogram indicates:  195.0 eV for Cl- in KCl based on 7 literature BEs

Table #6

NIST Database of Cl (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.

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

 

→  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 Chlorine-containing Materials

 

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Expert Knowledge Explanations

 

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Chlorine Chemical Compounds

Cupric Chloride, CuCl2 pressed powder

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Survey Spectrum from CuCl2 Flood gun is ON, C (1s) BE = 285.0 eV pressed powder	Cl (2p) Chemical State Spectrum from CuCl2 Flood gun is ON, C (1s) BE = 285.0 eV pressed powder
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C (1s) Chemical State Spectrum from CuCl2 Flood gun is ON, C (1s) BE = 285.0 eV pressed powder	Cu (2p3/2) Chemical State Spectrum from CuCl2 Flood gun is ON, C (1s) BE = 285.0 eV pressed powder
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Valence Band Spectrum from CuCl2 Flood gun is ON, C (1s) BE = 285.0 eV pressed powder	Cu (3s) and Cu (3p) Spectrum from CuCl2 Flood gun is ON, C (1s) BE = 285.0 eV pressed powder

 

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 KCl

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.

 

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XPS Facts, Guidance & Information

→  Periodic Table 

		Element		Chlorine (Cl)
		Primary XPS peak used for Peak-fitting :		Cl (2p)
		Spin-Orbit (S-O) splitting for Primary Peak:		Spin-Orbit splitting for Chlorine “p” orbital:  1.64 eV
		Binding Energy (BE) of Primary XPS Signal:		199 eV
		Scofield Cross-Section (σ) Value:		Cl (2p3/2) = 1.51       Cl (2p1/2) = 0.775
		Conductivity:
		Range of Cl (2p3/2) Chemical State BEs:		xxx eV range   (Cl- to -Clx)
		Signals from other elements that overlap Cl (2p3/2) 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 

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Information Useful for Peak-fitting Cl (2p_3/2)

• FWHM (eV) of Cl (2p_3/2) in Metal Cl- :  ~1.1 eV using 50 eV Pass Energy after ion etching:
• FWHM (eV) of Cl (2p_3/2) in Cl-C polymer  ~1.6 eV using 50 eV Pass Energy  (before ion etching)
• Binding Energy (BE) of Primary Signal used for Measuring Chemical State Spectra:  199 eV for Cl (2p_3/2) in Metals with +/- 0.2 uncertainty
• List of XPS Peaks that can Overlap Peak-fit results for Cl (2p3/2):  xx

→  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 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 

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Contaminants Specific to Metal Chlorides

• METAL Chloride thin films often have a low level of iron (Fe) in the bulk as a contaminant or to strengthen the thin film
• METAL Chloride 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 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 Cl (2p) peak as well as Cl (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 

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Data Collection Settings for Metal Chloride (Cl)

• Conductivity:  Metal Chlorides do not readily develops a native oxide that is sensitive to Flood Gun.
• Primary Peak (XPS Signal) used to measure Chemical State Spectra:  Cl (2p) at 199 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:  190 – 210 eV
• Recommended Extended BE Range for Measuring Chemical State Spectrum:  180 – 280 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 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 

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