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                   XPS Database of Polymers              → Six (6) BE Tables

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Sodium (Na)

Natrium

Villiaumite – NaF	Sodium Metal – Nao (in oil)	Halite – NaCl

 

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 Na Compounds	Auger Peaks and Spectra Contamination XPS Facts, Guidance, Information Chemical State Spectra from Literature

• Expert Knowledge Explanations

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Sodium (Na^o) Metal

Peak-fits, BEs, FWHMs, BE Tables, and Peak Labels

 

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Sodium Metal (Nao) Na (1s) Spectrum – raw Ion etched clean Flood Gun OFF – conductive metal	Sodium Metal (Nao) Na (1s) Spectrum – Peak-fit Ion etched clean Flood Gun OFF – conductive metal
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Sodium Metal (Nao) Na (Auger) Peaks – raw Ion etched clean Flood Gun OFF – conductive metal	Sodium Metal (Nao) Na (2p-2s) Spectrum – raw Ion etched clean Flood Gun OFF – conductive metal
Survey Spectrum of Sodium (Nao) Metal with Peaks Integrated, Assigned and Labelled
→  Periodic Table   XPS Signals for Sodium, (Nao) Metal Spin-Orbit Term,  BE (eV) Value, and Scofield σ for Sodium 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 I (3s) overlaps Na (1s) 1071 8.52 21.2 Ir (4f), Mo (4s) & Ni (3p) overlap Na (2s) 63 0.422 56.5 Ge (3d), Sb (4d), W (4f) & K (3s) Na (2p) 32 0.1941 57.5 σ:  abbreviation for the term Scofield Photoionization Cross-Section which are used with IMFP and TF to produce RSFs and atom% quantitation Plasmon Peaks Energy Loss Peaks Auger Peaks Energy Loss Peak for Compounds:  ~23 eV above each peak max Intrinsic Bulk Plasmon Peaks:  ~6 eV steps Expected Bandgap for NaCl: ~9 eV  at 77 K *Scofield Cross-Section (σ) for C (1s) = 1.0 →  Periodic Table
Plasmon Peaks from Nao Metal Fresh exposed bulk produced by extensive Ar+ ion etching Na (1s) – Plasmon Peaks Na (1s) – Expanded and Labelled   Na (KLL) Auger Peaks from Nao Metal Fresh exposed bulk produced by extensive Ar+ ion etching   Sodium (Na) Auger Peaks   Side-by-Side Comparison of Nao, NaF, NaCl, NaBr, NaI Peak-fits, BEs, FWHMs, and Peak Labels     . Pure Metal, Nao Na (1s) from Sodium metal – raw Ion Etched Sodium Fluoride, NaF Peak-fit of Na (1s) from NaF, natural crystal freshly cleaved in lab air Charge Referenced to 285.0 eV    . Sodium Fluoride, NaF Peak-fit of Na (1s) from NaF, natural crystal freshly cleaved in lab air Charge Referenced to 285.0 eV Sodium Chloride, NaCl, single crystal Peak-fit of Na (1s) from NaCl, xtal freshly cleaved in lab air Charge Referenced to 285.0 eV   .  Sodium Bromide, NaBr, crystallites Peak-fit of Na (1s) from NaBr, xtal freshly crushed in lab air Charge Referenced to 285.0 eV Sodium Iodide, NaI, crystallites Peak-fit of Na (1s) from NaI xtal freshly crushed in lab air Charge Referenced to 285.0 eV
Overlay of Na (1s) Peak from Sodium Nao Metal, NaI, and NaF
Overlay of Na (1s) Peak from NaF, NaCl, NaBr, and NaI

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Survey Spectrum of Sodium Fluoride (NaF)
with Peaks Integrated, Assigned and Labelled

 

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

 

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Survey Spectrum of Sodium Bromide (NaBr)
with Peaks Integrated, Assigned and Labelled

 

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Survey Spectrum of Sodium Iodide (NaI)
with Peaks Integrated, Assigned and Labelled

 

 

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Overlay of C (1s) Spectra
from NaHCO₃ and Na₂CO₃

Sodium Carbonate, Na2CO3 Peak-fit of C (1s) from Na2CO3, powder pressed onto stage Charge Referenced to 285.0 eV	Sodium Hydrogen Carbonate, NaHCO3 Peak-fit of C (1s) from NaHCO3, crystallites freshly crushed Charge Referenced to 285.0 eV
Overlay of C (1s) Spectra from NaHCO3 and Na2CO3
Overlay of Na (1s) Spectra from NaHCO3 and Na2CO3
Sodium Carbonate (Na2CO3) Peak-fit of Na (1s) from Na2CO3, powder pressed onto stage Charge Referenced to 285.0 eV	Sodium Hydrogen Carbonate (NaHCO3) Peak-fit of Na (1s) from NaHCO3, crystallites freshly crushed Charge Referenced to 285.0 eV
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Overlay of Na (1s) Spectra from NaHCO3 and Na2CO3

Features Observed

• xx
• xx
• xx

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Sodium, Na (Auger) Peaks
from NaHCO₃ and Na₂CO₃
often overlap O (1s) BE Spectra

 

Na (Auger) Peaks overlap O (1s) of Na2CO3	Na (Auger) Peaks overlap O (1s) of NaHCO3
Overlap of O (1s) spectra from NaHCO3 and Na2CO3 showing Na (Auger) overlaps

→  Periodic Table 

Valence Band Spectra
NaF, NaCl, NaBr, NaI

 

Sodium Fluoride, NaF Valence Band	Sodium Chloride, NaCl Valence Band
	.
Sodium Bromide, NaBr Valence Band	Sodium Iodide, NaI Valence Band

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Overlay of Valence Band Spectra
from NaF, NaCl, NaBr and NaI

Copyright ©:  The XPS Library 

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Sodium Minerals, Gemstones, and Chemical Compounds
Dawsonite – NaAlCO3(OH)2	Nahcolite – NaHCO3	Glauberite – Na2Ca(SO4)2	Natrolite – Na2Al2Si3O10 • 2H2O

→  Periodic Table 

 

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Six (6) Chemical State Tables of Na (1s) BEs

 

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

→  Periodic Table 

 

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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 (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
• There are uncertainties and error ranges in nearly all BEs 
  • Flood guns
• 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

Na (1s) 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 NIST BE	Hydrocarbon C (1s) BE	Source
Na	11	Na – element  (N*4)	1070.8 eV	1071.8 eV	284.8 eV	Avg BE – NIST
Na	11	Na2WO4	1070.9 eV		284.8 eV	Avg BE – NIST
Na	11	Na2O (NaHCO3)	1071.1 eV	1071.5 eV	285.0 eV	The XPS Library
Na	11	Na-F (N*3)	1071.2 eV	1072.7 eV	285.0 eV	The XPS Library
Na	11	NaHCO3	1071.3 eV		285.0 eV	The XPS Library
Na	11	Na2CO3	1071.5 eV		285.0 eV	The XPS Library
Na	11	Na – element	1071.6 eV			PHI Handbook
Na	11	Na2W2O7	1071.7 eV		285.0 eV	The XPS Library
Na	11	Na2Si3O7	1071.9 eV		285.0 eV	The XPS Library
Na	11	Na2SO4	1072.1eV		285.0 eV	The XPS Library
Na	11	Na-Br	1072.1 eV		285.0 eV	The XPS Library
Na	11	Na-Cl	1072.3 eV		285.0 eV	The XPS Library
Na	11	Na2O (N*1)	1072.5 eV		284.8 eV	Avg BE – NIST
Na	11	Na-Br (N*1)	1072.5 eV		284.8 eV	Avg BE – NIST
Na	11	Na3AlF6	1072.5 eV		285.0 eV	The XPS Library
Na	11	Na-F	1072.6 eV		285.0 eV	The XPS Library
Na	11	Na-I	1073.1 eV		285.0 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 (1s_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 (SO) 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

Na (1s) Chemical State BEs from:  “PHI Handbook”

C (1s) BE = 284.8 eV

Copyright ©:  Ulvac-PHI

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Table #3

Na (1s) Chemical State BEs from:  “Thermo-Scientific” Website

C (1s) BE = 284.8 eV

Chemical state	Binding energy, Na 1s (eV)
Sodium compounds	1071–1071.5

Copyright ©:  Thermo Scientific website

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Table #4

Na (1s) 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

Copyright ©:  Mark Beisinger

 

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Table #5

Na (1s) Chemical State BEs from:  “Techdb.podzone.net” Website

 

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

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Advanced XPS Information Section

for XPS Research Studies on Sodium (Na) Containing Materials

 

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XPS Spectra

 

from Common Sodium Compounds

                           

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Sodium Oxide, Na₂O
Lump, Bulk Exposed, Auto-oxidized to NaHCO₃

Survey Spectrum from Exposed Bulk of Na2O (NaHCO3?)	Na (1s) Chemical State Spectrum from Exposed Bulk of Na2O (NaHCO3?)
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C (1s) Chemical State Spectrum from Exposed Bulk Na2O (NaHCO3?)	O (1s) Chemical State Spectrum from Exposed Bulk of Na2O (NaHCO3?)
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Valence Band Spectrum from Na2O 80% (NaHCO3 ?)

 

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Cryolite, Na₃AlF₆
natural crystal
freshly exposed bulk

Survey Spectrum from Na3AlF6	Na (1s) Chemical State Spectrum from Na3AlF6
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Al (2p) Chemical State Spectrum from Na3AlF6	C (1s) Chemical State Spectrum from Na3AlF6
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F (1s) Chemical State Spectrum from Na3AlF6	Na (1s) Chemical State Spectrum from Na3AlF6

le 

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Valence Band Spectra Comparison and Overlay
NaHCO₃,  Na₂CO₃

NaHCO3 – exposed bulk Bands Aligned	Na2CO3 – powder Bands Aligned
	.
Valence Band Spectra Overlay of NaHCO3 and Na2CO3

Features Observed

• xx
• xx
• xx

→  Periodic Table 

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Chemical State Na (KLL) Auger Spectra by XPS

Overlay of NaF, NaCl, NaBr, NaI and Na Metal – by XPS	Overlay of NaF, NaCl, NaBr and NaI – by XPS

Features Observed

• xx
• xx
• xx

→  Periodic Table 

Copyright ©:  The XPS Library  

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XPS Facts, Guidance & Information

→  Periodic Table 

		Element		Sodium (Na)
		Primary XPS peak used for Peak-fitting :		Na (1s)
		Spin-Orbit (S-O) splitting for Primary Peak:		NO Spin-Orbit splitting for “s” orbitals
		Binding Energy (BE) of Primary XPS  Signal:		1071.6 eV
		Scofield Cross-Section (σ) Value:		Na (1s):  8.52
		Conductivity:		Metal form is very conductive Sodium Resistivity = xx
		Range of Na (1s) Chemical State BEs:		1071-1073 eV range   (Nao to NaF)
		Signals from other elements that overlap Na (1s) Primary Peak:		xx
		Bulk Plasmons:		~ 6 eV above peak BE max
		Shake-up Peaks:		xx
		Multiplet Splitting Peaks:		not possible
		General Information about Sodium Compounds:		xx
		Cautions – Chemical Poison Warning		Flammable

Copyright ©:  The XPS Library

 

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Information Useful for Peak-fitting Na (1s)

• FWHM (eV) of Pure Sodium metal:  0.82 eV using 50 eV Pass Energy after ion etching and very fast data collection cycles
• FWHM (eV) of Sodium Halides:  1.6 – 2.2 eV using 50 eV Pass Energy  (before ion etching)
• Binding Energy (BE) of Primary Signal used for Measuring Chemical State Spectra:  1071.6 eV for Na (1s) with +/- 0.2 uncertainty
• List of XPS Peaks that can Overlap Peak-fit results for Na (1s):  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 Metal Oxide:  Pure element FWHM << Metal 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 metal or a conductive compound.
• Typical Peak-Shape:  80% G: 20% L,   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 can be constrained but it is difficult due to the 0.4 eV separation.
• Constraints on Peak-fitting: It is difficult to use the 1s3/2 : 1s1/2 area ratio to constrain peaks in chemical state spectra because the peaks are only 0.4 eV apart

Notes:

• Other Oxidation States such as Na₂O or NaOH can appear as small peaks when peak-fitting
• Pure element signals normally have asymmetric tails that should be included in the peak-fit.
• Peak-fits of C (SO) 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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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.

 

→  Periodic Table 

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Contaminants Specific to Sodium Metal

• Sodium metal develops a native oxide that is usually 6-7 nm thick.  .
• With heat the native oxide becomes thicker and the BE of the oxide shifts to higher BE
• Sodium does not readily form a 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 (SO) peak max BE.
• Low levels of carbonate is common on many metals that readily oxidize in the air.
• High levels of carbonate appear on reactive metal 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 (SO) 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 metals.  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
• 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 Na (1s)

• Primary Peak (XPS Signal) used to measure Chemical State Spectra:  Na (1s) at 1072 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:  1060 – 1080 eV
• Recommended Extended BE Range for Measuring Chemical State Spectrum:  1050 – 1150 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 can appear after ion etching various reactive metals.  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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