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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Gold (Au)
Aurum

Krennerite – Au3AgTe8	Gold – Auo	Calverite – AuTe2

 

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 Au Chemical Compounds Flood Gun Effects on Native Oxide Spectra Study of UHV Gas Capture after Cleaning	Auger Peaks and Spectra Contamination XPS Facts, Guidance, Information Chemical State Spectra from Literature

• Expert Examples & Explanations

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Gold (Au^o) Metal
Peak-fits, BEs, FWHMs, and Peak Labels

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Gold (Auo) Metal Au (4f) Spectrum – raw spectrum ion etched clean	Gold (Auo) Metal Peak-fit of Au (4f) Spectrum w/o asymm
→  Periodic Table – HomePage
Gold (Auo) Metal Au (4f) Spectrum – extended range	Gold (Auo) Metal Peak-fit of Au (4f) Spectrum (w asymm)
Survey Spectrum of Gold (Auo) with Peaks Integrated, Assigned and Labelled
→  Periodic Table  XPS Signals for Gold (Auo) Metal Spin-Orbit Term,  BE (eV) Value, and Scofield σ for Aluminum Kα X-rays (1486 eV, 8.33 Ang) Overlaps Spin-Orbit Term BE (eV) Value Scofield σ from 1486 eV X-rays IMFP (TPP-2M) in Å   Au (4s) 751 1.92 9.8 Mn (2p) overlaps Au (4p1/2) 642 2.14 11.8   Au (4p3/2) 546 5.89 11.8   Au (4d3/2) 353 8.06 13.7 Ca (2p) overlaps Au (4d5/2) 335 11.74 13.7   Au (4f5/2) 87.63 7.54 15.8   Au (4f7/2) 83.96 9.58 15.8 Si (2p) overlaps Au (5s) 109 0.479 15.6 Al (2p) & Cu (3p) overlap Au (5p1/2) 73.5 0.463 16.0 Li (1s) overlaps Au (5p3/2) 57.5 1.10 16.0   Au (5d)  3.5 1.808 xx.x σ:  abbreviation for the term Scofield Photoionization Cross-Section which is used with IMFP and TF to generate RSFs and atom% quantitation Plasmon Peaks Auger Peaks Energy Loss    Intrinsic Plasmon Peak:  ~xx eV above peak max Expected Bandgap for Au2O3: 0.8 – 0.9 eV Work Function for Au:  xx eV *Scofield Cross-Section (σ) for C (1s) = 1.0 →  Periodic Table    Valence Band Spectrum from Auo Metal  Fresh exposed bulk produced by extensive Ar+ ion etching     Plasmon Peaks from Auo Metal  Fresh exposed bulk produced by extensive Ar+ ion etching Au (4f) – Extended Range Spectrum Au (4f) – Extended Range Spectrum – Vertically Zoomed →  Periodic Table    Au (MNN) Auger Peaks from Auo Metal  Fresh exposed bulk produced by extensive Ar+ ion etching Auo Metal – main Auger peak Auo Metal – full Auger range     Features Observed xx xx xx →  Periodic Table
Artefacts Caused by Argon Ion Etching
C (1s) from Gold Carbide(s) can form when ion etched Reactive Metal Surfaces capture Residual UHV Gases (CO, H2O, CH4 etc)	Argon Trapped in Auo can form when Argon Ions are used to removed surface contamination
na	na
Side-by-Side Comparison of Auo metal (native oxide) & Gold Oxide, Au2O3 (Au 86%) Peak-fits, BEs, FWHMs, and Peak Labels
Auo metal (native oxide ?)	Au2O3
Au (4f) from Au metal Flood Gun OFF As-Measured, C (1s) at 285.4 eV	Au (4f) from Au2O3 – pellet Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
→  Periodic Table
Au metal (native oxide?)	Au2O3
C (1s) from Au metal Flood Gun OFF As-Measured, C (1s) at 285.4 eV	C (1s) from Au2O3– pellet Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
→  Periodic Table
Au metal (native oxide?)	Au2O3
O (1s) from Au metal Flood Gun OFF As-Measured, C (1s) at 285.4 eV	O (1s) from Au2O3 – pellet Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
→  Periodic Table
Au metal (native oxide?)	Au2O3
Au Valence Band Au metal Flood Gun OFF As-Measured, C (1s) at 285.4 eV	Au Valence Band Au2O3 Flood Gun ON Charge Referenced to C (1s) at 285.0 eV

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Survey Spectrum of Au metal  (native oxide?)
with Peaks Integrated, Assigned and Labelled

 

→  Periodic Table 

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Survey Spectrum of Gold Oxide (Au₂O₃)
with Peaks Integrated, Assigned and Labelled

→  Periodic Table  

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Overlays of Au (4f) Spectra for:
Au^o metal, Native Oxide (?) and Au₂O₃

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

Overlay of Auo  (native oxide?) and Au2O3 – Au (4f) Native Oxide C (1s) = 285.4 eV  (Flood gun OFF)	Overlay of Auo metal and Au2O3 – Au (4f) Native Oxide C (1s) = 285.0 eV  (Flood gun ON)
→  Periodic Table	Copyright ©:  The XPS Library

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Overlay of Au (4f)
Au^o metal & Au (native oxide) 

 

Features Observed

• xx
• xx
• xx

→  Periodic Table 

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Valence Band Spectra
Au^o, Au₂O₃ 

Auo Ion etched clean	Au2O3 – pellet Flood gun is ON,  Charge referenced so C (1s) = 285.0 eV
Overlay of Valence Band Spectra for Auo metal and Au2O3
Overlay of Valence Band Spectra for Auo metal and Au (native oxide?)

Features Observed

• xx
• xx
• xx

→  Periodic Table 

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Gold Minerals, Gemstones, and Chemical Compounds
Gold Oxide – Au2O3	Gold Hydroxide – Au(OH)3	Gold Bromide – AuBr3	Gold Single Crystal – Au <111> on Sapphire

→  Periodic Table 

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Six (6) Chemical State Tables of Au (4f_7/2) 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 (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 between 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

Au (4f_7/2) 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
Au	79	Au (N*26)	83.7 eV	84.2 eV	284.8 eV	Avg BE – NIST
Au	79	Au – element	83.9 eV		285.0 eV	The XPS Library
Au	79	AuSi (N*3)	83.9 eV	84.5 eV	284.8 eV	Avg BE – NIST
Au	79	Au-Te2 (N*1)	84 eV		284.8 eV	Avg BE – NIST
Au	79	Au-Cu (75:25)	84.11 eV		285.0 eV	The XPS Library
Au	79	Au-Cu (50:50)	84.25 eV		285.0 eV	The XPS Library
Au	79	Au-Cu (25:75)	84.42 eV		285.0 eV	The XPS Library
Au	79	Au-I (N*1)	84.5 eV		284.8 eV	Avg BE – NIST
Au	79	Au-Cl (N*1)	84.6 eV		284.8 eV	Avg BE – NIST
Au	79	Au-In (N*2)	84.6 eV	84.9 eV	284.8 eV	Avg BE – NIST
Au	79	AuInOx (N*3)	84.8 eV	85.8 eV	284.8 eV	Avg BE – NIST
Au	79	Au-2O3	85.1 eV		285.0 eV	The XPS Library
Au	79	Au-Ga (N*2)	85.3 eV	85.6 eV	284.8 eV	Avg BE – NIST
Au	79	Au2O3 (N*1)	85.9 eV		284.8 eV	Avg BE – NIST
Au	79	Au-(OH)3			285.0 eV	The XPS Library

Charge Referencing Notes

• (N*number) identifies the number of NIST BEs that were averaged to produce the BE in the middle column.
• The XPS Library uses Binding Energy Scale Calibration with Cu (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

Au (4f_7/2) Chemical State BEs from:  “PHI Handbook”

C (1s) BE = 284.8 eV

→  Periodic Table 

Copyright ©:  Ulvac-PHI

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Table #3

Au (4f_7/2) Chemical State BEs from:  “Thermo-Scientific” Website

C (1s) BE = 284.8 eV

Chemical state	Binding energy (eV), Au (4f7/2)
Au metal	84.0 eV

→  Periodic Table 

Copyright ©:  Thermo Scientific 

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Table #4

Au (4f_7/2) 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

Au (4f_7/2) 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 Au 4f7/2 Au 84.0 ±0.2 83.8 ～ 84.2 Au 4f7/2 (-AuCH2PEt2CH2-)2 84.1 ±0.3 83.8 ～ 84.3 Au 4f7/2 AuSn 84.5 ±0.3 84.2 ～ 84.8 Au 4f7/2 YbAu2 84.6 ±0.3 84.3 ～ 84.8 Au 4f7/2 (-AuSPEt2S-)2 84.9 ±0.3 84.6 ～ 85.1 Au 4f7/2 AuSn4 85.1 ±0.3 84.8 ～ 85.3 Au 4f7/2 ClAu(Ph3As) 85.2 ±0.3 84.9 ～ 85.4 Au 4f7/2 ClAu(Ph3P)2 85.5 ±0.3 85.2 ～ 85.7 Au 4f7/2 (Ph3P)AuNo3 85.5 ±0.3 85.2 ～ 85.7 Au 4f7/2 ClAuPh3P 85.5 ±0.2 85.3 ～ 85.7 Au 4f7/2 Cl3AuPh3P 87.3 ±0.3 87.0 ～ 87.5

→  Periodic Table 

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Histograms of NIST BEs for Au (4f_7/2) BEs

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

 

Histogram indicates:  83.98 eV for Auo based on 27 literature BEs

Table #6

NIST Database of Au (4f_7/2) 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.

 

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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 Gold Materials

 

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Expert Knowledge Examples & Explanations

→  Periodic Table 

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Gold Chemical Compounds

Peak-fits and Overlays of Chemical State Spectra

Pure Gold:  Au (4f) Cu (2p3/2) BE = 932.6 eV	Au2O3:  Au (4f) C (1s) BE = 285.0 eV

Features Observed

• xx
• xx
• xx

→  Periodic Table 

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Overlay of Au (4f) Spectra shown Above

C (1s) BE = 285.0 eV

 

Chemical Shift between Au and Au₂O₃:  3.0 eV

 

→  Periodic Table 

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Gold Oxide (Au₂O₃)
pressed pellet

Survey Spectrum from Au2O3 Flood gun is ON, C (1s) BE = 285.0 eV	Au (4f) Chemical State Spectrum from Au2O3 Flood gun is ON, C (1s) BE = 285.0 eV
	.
O (1s) Chemical State Spectrum from Au2O3 Flood gun is ON, C (1s) BE = 285.0 eV	C (1s) Chemical State Spectrum from Au2O3 Flood gun is ON, C (1s) BE = 285.0 eV
	.
Valence Band Spectrum from Au2O3 Flood gun is ON, C (1s) BE = 285.0 eV	Auger Signals from Au2O3 Flood gun is ON, C (1s) BE = 285.0 eV
	na

Shake-up Features for Au₂O₃

na

 

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Multiplet Splitting Features for Gold Compounds

Au metal – NO Splitting for Au (4s)	Au2O3 – Splitting Peaks for Au (4s)
NA	NA

 

Features Observed

• xx
• xx
• xx

→  Periodic Table 

 

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Gold Alloys

 

Au:Cu Alloys
full plots are displayed later

Au (4f) from Au:Cu Alloy Series (shown at end)	Cu (2p3/2) from Au:Cu Allow Series (shown at end)

→  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.

 

Quantitation from Pure, Homogeneous Binary Compound
composed of Gold – Au₂O₃

This section is focused on measuring and reporting the atom % quantitation that results by using:

• Scofield cross-sections,
• Spectra corrected to be free from Transmission Function effects
• A Pass Energy that does not saturate the detector system in the low KE range (BE = 1000-1400 eV)
• A focused beam of X-ray smaller than the field of view of the lens
• An angle between the lens and the source that is ~55 deg that negates the effects of beta-asymmetry
• TPP-2M inelastic mean free path values, and
• Either a linear background or an iterated Shirley (Sherwood-Proctor) background to define peak areas

The results show here are examples of a method being developed that is expected to improve the “accuracy” or “reliability” of the atom % values produced by XPS.

→  Periodic Table 

 

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Flood Gun Effect on Native Oxide of Gold

 

Native Oxide of Gold Sheet – Sample GROUNDED

 

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Native Oxide of Gold Sheet – Sample Grounded

Electron Flood Gun:  0 Voltage (FG OFF), Min Voltage versus Max Voltage

Au (4f) Flood Gun Induced Shift: 0.07 eV	O (1s) Flood Gun Induced Shift:  0.12 eV	C (1s) Flood Gun Induced Shift:  0.26 eV
→  Periodic Table

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AES Study of UHV Gas Captured by Freshly Ion Etched Gold

Gold sheet was ion etched and allowed to react with residual UHV gases overnight – ~14 hr run.

Au (MNN) Signal: Au at front -> AuOx at rear  Au KE = XXXX eV,    AuO KE = XXXX eV	O (KLL) Signal: Au at front -> AuOx at rear  O KE = XXXX eV	C (KLL) Signal: Au at front -> AuOx at rear  O KE = XXXX eV
Au (KLL)

Features Observed

• xx
• xx
• xx

→  Periodic Table 

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Gold Alloys

Au:Cu ratios =   75:25,  50:50,  25:75

 

Au:Cu 75:25 Survey Spectrum	Au:Cu 75:25 Au (4f7/2) BE = 84.11 eV	Au:Cu 75:25 Cu (2p3/2) BE = 932.41 eV
		.
Au:Cu 50:50 Survey Spectrum	Au:Cu 50:50 Au (4f7/2) BE = 84.25 eV	Au:Cu 50:50 Cu (2p3/2) BE = 932.55 eV
→  Periodic Table
Au:Cu 25:75 Survey Spectrum	Au:Cu 25:75 Au (4f7/2) BE = 84.42 eV	Au:Cu 25:75 Cu (2p3/2) BE = 932.65 eV

Effect of Bond Polarization  Due to Alloying Gold and Copper Metals
Overlay of Au (4f) from the 3 AuCu Alloys	Overlay of Cu (2p3/2) from the 3 AuCu Alloys
Au (4f7/2) BEs:  84.11, 84.25 and 84.42 eV	Cu (2p3/2):  932.41, 932.55 and 932.65 eV
Difference in Minimum and Maximum BEs for Au (4f7/2):   0.31 eV	Difference in Minimum and Maximum BEs for Cu (2p3/2):  0.24 eV

Copyright ©:  The XPS Library 

 

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XPS Facts, Guidance & Information

→  Periodic Table 

		Element		Gold (Au)
		Primary XPS peak used for Peak-fitting:		Au (4f7/2)
		Spin-Orbit (S-O) splitting for Primary Peak:		Spin-Orbit splitting for “f” orbital,  ΔBE = 3.67 eV
		Binding Energy (BE) of Primary XPS Signal:		83.96 eV
		Scofield Cross-Section (σ) Value:		Au (4f7/2) = 9.58    Au (4f5/2) = 7.54
		Conductivity:		Au resistivity =   Native Oxide suffers Differential Charing
		Range of Au (4f7/2) Chemical State BEs:		84  – 87 eV range   (Auo to AuF3)
		Signals from other elements that overlap Au (4f7/2) Primary Peak:		xx (xx)
		Bulk Plasmons:		~xx eV above peak max for pure
		Shake-up Peaks:		xx
		Multiplet Splitting Peaks:		xx
		General Information about XXX Compounds:		xx
		Cautions – Chemical Poison Warning		xx

Copyright ©:  The XPS Library 

→  Periodic Table 

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Information Useful for Peak-fitting Au (4f_7/2)

• FWHM (eV) of Au (4f_7/2) for Pure Au^o :  ~0.7 eV using 25 eV Pass Energy after ion etching
• FWHM (eV) of Au (4f_7/2) for Au₂O₃:  ~1.37 eV using 50 eV Pass Energy  (before ion etching)
• Binding Energy (BE) of Primary Signal used for Measuring Chemical State Spectra:  83.96 eV for Au (4f_7/2) with +/- 0.1 uncertainty
• Typical Peak-Shape:  70% G: 30% L,   or     Voigt : 1.4 eV Gaussian and 0.5 eV Lorentzian
• Asymmetry for Conductive materials:  20-30% with increased Lorentzian %
• List of XPS Peaks that can Overlap Peak-fit results for Au (4f_7/2):  xxxx

→  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) = ~0.90 eV for PE 50 on Thermo K-Alpha
  • Ag (3d_5/2) FWHM (eV) = ~0.95 eV for PE 80 on Kratos Nova
  • Ag (3d_5/2) FWHM (eV) = ~0.95 eV for PE 45 on PHI VersaProbe
  • Ag (3d_5/2) FWHM (eV) = ~0.85 eV for PE 50 on SSI S-Probe
• FWHM (eV) of Pure Elements: Ranges from 0.4 to 1.0 eV across the periodic table
• FWHM of Chemical State Peaks in any Chemical Compound:  Ranges from 1.1 to 1.6 eV  (in rare cases FWHM can be 1.8 to 2.0 eV)
• FWHM of Pure Element versus FWHM of Oxide:  Pure element FWHM << Oxide FWHM  (e.g. 0.8 vs 1.5 eV, roughly 2x)
• If FWHM Greater than 1.6 eV:  When a peak FWHM is larger than 1.6 eV, it is best to add another peak to the peak-fit envelop.
• BE (eV) Difference in Chemical States: The difference in chemical state BEs is typically 1.0-1.3 eV apart.  In rare cases, <0.8 eV.
• Number of Peaks to Use:  Use minimum. Do not use peaks with FWHM < 1.0 eV unless it is a 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 a very few compounds are negative due to unusual electron polarization.

→  Periodic Table 

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Contaminants Specific to Gold

• Gold develops a thick native oxide due to the reactive nature of clean Gold.
• The native oxide of AuO_x is 0-1 nm thick for very old metal surfaces.
• Gold thin films can have a low level of iron (Fe) in the bulk as a contaminant or due to sputter coater shields
• Gold forms a low level of carbide when the surface is argon 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. The BE for C (1s) is a useful guide.  It is not absolute. Chemical shifts from native oxides can be erroneous.
• Collect spectra from the valence band, and the principal Au (4f) peak.  Auger peaks are sometimes used to decide chemical state assignments.
• Long time exposures (high dose) to X-rays can degrade various polymers, catalysts, and 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 are sometimes used to discern chemical states when XPS shifts are very small. Auger shifts can be larger than XPS shifts.

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Data Collection Settings for Gold (Au)

• Conductivity:  Gold 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:  Au (4f_7/2) at 84 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:  75- 95eV
• Recommended Extended BE Range for Measuring Chemical State Spectrum:  70- 170 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, As, and Ga)
• Typical Time for Survey Spectrum:  3-5 minutes for newer instruments, 5-10 minutes for older instruments
• Typical Time for a single Chemical State Spectrum with high S/N:  5-10 minutes for newer instruments, 10-15 minutes for older instruments 

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Effects of Argon Ion Etching

• Carbides appear after ion etching Au and various reactive surfaces.  Carbides form due to the presence of residual CO and CH₄ in the vacuum.
• Ion etching can produce low oxidation states of the material being analyzed.  These are newly formed contaminants.
• Ion etching polymers by using standard Ar+ ion guns will destroy the polymer, converting it into a graphitic type of carbon

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