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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Gallium (Ga)

 

Gallium melts in your hand – Gao	Gallium – Gao	Bauxite – Gao metal is trapped inside Bauxite

 

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 Ga Chemical Compounds Flood Gun Effects on Native Oxide Spectra	Auger Peaks and Spectra Contamination XPS Facts, Guidance, Information Chemical State Spectra from Literature

• Expert Knowledge & Explanations

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Gallium (Ga^o) Metal

Peak-fits, BEs, FWHMs, and Peak Labels

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Gallium (Gao) Metal Ga (2p3/2) Spectrum – raw spectrum ion etched clean	Gallium (Gao) Metal Peak-fit of Ga (2p3/2) Spectrum (w/o asymm)
→  Periodic Table – HomePage
Gallium (Gao) Metal Ga (2p) Spectrum – extended range	Gallium (Gao) Metal Peak-fit of Ga (2p3/2) Spectrum (w asymm)
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Gallium (Gao) Metal Ga (3d) Spectrum	Gallium (Gao) Metal Peak-fit of Ga (3d) Spectrum (no asymm)
Survey Spectrum of Gallium (Gao) Metal with Peaks Integrated, Assigned and Labelled
→  Periodic Table  XPS Signals for Gallium, (Gao) 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 Mg (1s) overlaps Ga (2s) 1301       Ga (2p1/2) 1144 11.09 10.7   Ga (2p3/2) 1116.5 21.40 11.3 S (2p) overlaps Ga (3s) 159 1.13 28.7   Ga (3p1/2) 108 1.10 29.7 Si (2p) overlaps Ga (3p3/2) 104 2.11 29.7 In (4d) overlaps Ga (3d) 18.62 1.085 31.1 σ:  abbreviation for the term Scofield Photoionization Cross-Section which are used with IMFP and TF to generate RSFs and atom% quantitation Plasmon Peaks Ga plasmon 1172.5 eV Ga plasmon 1158 eV Auger Peaks  Intrinsic Plasmon Peak:  ~14 eV above peak max Expected Bandgap for Ga2O3: 4.8 eV Work Function for Ga2O3:  ~4.2 eV  (Appl Surfac Sci, 465, p973 (2019)) *Scofield Cross-Section (σ) for C (1s) = 1.0 →  Periodic Table    Ga (3p) Spectra from Gallium (Gao) Metal Fresh exposed bulk produced by extensive Ar+ ion etching Ga (3p) – raw Ga (3p) – peak-fit (no asymm)         Valence Band Spectrum from Gao Metal  Fresh exposed bulk produced by extensive Ar+ ion etching     Plasmon Peaks from Gallium, Gao Metal  Fresh exposed bulk produced by extensive Ar+ ion etching Ga (2p) – Extended Range Spectrum Ga (2p) – Extended Range Spectrum – Vertically Zoomed →  Periodic Table    Ga (LMM) Auger Peaks from Ga Metal  Fresh exposed bulk produced by extensive Ar+ ion etching Ga Metal – wide range Ga Metal – Expanded   Features Observed xx xx xx →  Periodic Table
Artefacts Caused by Argon Ion Etching
Gallium Carbide(s) can form when ion etched Reactive Metal Surfaces capture Residual UHV Gases (CO, H2O, CH4 etc)	Argon Trapped in Ga can form when Argon Ions are used to removed surface contamination
Side-by-Side Comparison of Ga Native Oxide & Gallium Oxide (Ga2O3) Peak-fits, BEs, FWHMs, and Peak Labels
Ga Native Oxide	Ga2O3
Ga (3d) from Ga Native Oxide Flood Gun OFF As-Measured, C (1s) at 286.3 eV	Ga (3d) from Ga2O3 – pressed pellet Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
→  Periodic Table
	.
Ga Native Oxide	Ga2O3
C (1s) from Ga Native Oxide on Gallium As-Measured, C (1s) at 286.3 eV (Flood Gun OFF) C (1s) shifts by 1.8 eV for Native Ga Oxide but Ga BE does not!	C (1s) from Ga2O3 – pressed pellet Flood Gun ON Charge Referenced to C (1s) at 285.0 eV Ga Auger Peaks Overlap C (1s)
→  Periodic Table
	.
Ga Native Oxide	Ga2O3
O (1s) from Ga Native Oxide on Gallium As-Measured, C (1s) at 286.3 eV (Flood Gun OFF)	O (1s) from Ga2O3 – pressed pellet Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
→  Periodic Table
Ga Native Oxide	Ga2O3
Ga (KLL) Auger Peaks from Ga Native Oxide As-Measured, C (1s) at 286.3 eV Flood Gun OFF	Ga (KLL) Auger Peaks from Ga2O3 –  pressed pellet Flood Gun ON Charge Referenced to C (1s) at 285.0 eV

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Survey Spectrum of Gallium (Ga) Native Oxide
with Peaks Integrated, Assigned and Labelled

→  Periodic Table 

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Survey Spectrum of Gallium Oxide (Ga₂O₃)
with Peaks Integrated, Assigned and Labelled

 

 

→  Periodic Table  

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Overlays of Ga (2p_3/2) Spectra for:
Ga^o metal, Ga Native Oxide and Ga₂O₃ 

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

Overlay of Gao metal and Ga Native Oxide – Ga (2p3/2) Native Oxide C (1s) = 286.3 eV  (Flood gun OFF) Chemical Shift: 2.9	Overlay of Gao metal and Ga2O3 – Ga (2p3/2) Pure Oxide C (1s) = 285.0 eV Chemical Shift: 2.6
→  Periodic Table	Copyright ©:  The XPS Library

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Overlay of Ga (2p_3/2)
Ga^o Metal, Ga Native Oxide, & Ga₂O₃  

 

Overlay of Ga (2p_3/2)
Ga^o Metal & Ga₂O₃ showing Plasmons and Loss Peaks:   

Features Observed

• xx
• xx
• xx

→  Periodic Table 

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Valence Band Spectra
Ga^o, Ga₂O₃ 

Gao Ion etched clean	Ga2O3 – pressed pellet Flood gun is ON,  Charge referenced so C (1s) = 285.0 eV
Overlay of Valence Band Spectra for Gao metal and Ga2O3

Features Observed

• xx
• xx
• xx

→  Periodic Table 

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Gallium Man-made Crystals and Chemical Compounds
Lanthanum-gallium-silicate	Gallium Arsenide – GaAs	Gallium Nitride – GaN	Gallium Sulfide – GaS

→  Periodic Table 

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Six (6) Chemical State Tables of Ga (3d) & (2p_3/2) 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 (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

Ga (3d) 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
Ga	31	GaInAs	17.5 eV	18.2 eV	285.0 eV	The XPS Library
Ga	31	GaSe	17.6 eV		285.0 eV	The XPS Library
Ga	31	Ga – element	18.6 eV		285.0 eV	The XPS Library
Ga	31	GaAs (N*16)	18.6 eV	19.7 eV	284.8 eV	Avg BE – NIST
Ga	31	GaSb	18.6 eV	19.1 eV	285.0 eV	The XPS Library
Ga	31	GaSb (N*4)	18.9 eV	19.0 eV	284.8 eV	Avg BE – NIST
Ga	31	GaAs	19.1 eV	19.7 eV	285.0 eV	The XPS Library
Ga	31	GaP (N*5)	19.2 ev	19.9 eV	284.8 eV	Avg BE – NIST
Ga	31	GaN (N*2)	19.5 eV	19.7 eV	284.8 eV	Avg BE – NIST
Ga	31	GaAlAs	19.6 eV		285.0 eV	The XPS Library
Ga	31	Ga2Se3 (N*2)	19.7 eV	19.9 eV	284.8 eV	Avg BE – NIST
Ga	31	GaP	19.7 eV	20.0 eV	285.0 eV	The XPS Library
Ga	31	GaN	20.0 eV		285.0 eV	The XPS Library
Ga	31	Ga2O3 (N*5)	20.2 eV	20.7 eV	284.8 eV	Avg BE – NIST
Ga	31	Ga-2O3	21.3 eV		285.0 eV	The XPS Library
Ga	31	Ga-(OH)3			285.0 eV	The XPS Library
Ga	31	Ga-2O			285.0 eV	The XPS Library
Ga	31	Ga-Cl3			285.0 eV	The XPS Library
Ga	31	Ga-CO3			285.0 eV	The XPS Library
Ga	31	Ga-F3			285.0 eV	The XPS Library
Ga	31	Ga-S			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

Ga (2p_3/2) & (3d) Chemical State BEs from:  “PHI Handbook”

C (1s) BE = 284.8 eV

→  Periodic Table 

Copyright ©:  Ulvac-PHI

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Table #3

Ga (2p_3/2) and (3d) Chemical State BEs from:  “Thermo-Scientific” Website

C (1s) BE = 284.8 eV

Chemical state	Binding energy (eV), Ga (2p3)	Binding energy (eV) Ga (3d)
Ga elemental	1116.7	18.7
GaAs	1116.9	19.1
Ga2O3	1118.0	20.5
GaAs native oxide	1117.8	20.3
Ga native oxide	1118.7	20.9

→  Periodic Table 

Copyright ©:  Thermo Scientific 

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Table #4

Ga (2p_3/2) & (3d) 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

J.L. Bourque, M.C. Biesinger, K.M. Baines, Dalton Transactions, 45 (2016) 7678-7696.

→  Periodic Table 

Copyright (c) M. Beisinger

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Table #5

Ga (2p_3/2) & (3d) Chemical State BEs:  “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 Ga 3d Ga 18.6 ±0.3 18.3 ～ 18.8 Ga 3d Ga2O3 18.7 ±0.3 18.4 ～ 18.9 Ga 3d GaAs 19.0 ±0.2 18.8 ～ 19.2 Ga 3d AlGaAs 19.0 ±0.3 18.7 ～ 19.3 Ga 3d GaP 19.3 ±0.6 18.7 ～ 19.9 Ga 2p3/2 Ga 1116.5 ±0.2 1116.3 ～ 1116.7 Ga 2p3/2 GaP 1116.8 ±0.3 1116.5 ～ 1117.0 Ga 2p3/2 Ga2O3 1117.4 ±0.5 1116.9 ～ 1117.8

→  Periodic Table 

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Histograms of NIST BEs for Ga (3d) BEs

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

Histogram indicates:  18.6 eV for Ga metal based on 8 literature BEs	Histogram indicates:  20.4 eV for Ga2O3 based on 6 literature BEs
Histogram indicates:  19.2 eV for GaAs based on 18 literature BEs

Table #6

NIST Database of Ga (3d) & (2p3) 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 Gallium Materials

 

 

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Expert Knowledge Explanations

→  Periodic Table 

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Gallium Chemical Compounds

 

Peak-fits and Overlays of Chemical State Spectra

Pure Gallium (Gao):  Ga (3d) Cu (2p3/2) BE = 932.6 eV	Ga2O3: Ga (3d) C (1s) BE = 285.0 eV	GaF3:  Ga (3d) C (1s) BE = 285.0 eV

Features Observed

• xx
• xx
• xx

→  Periodic Table 

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Overlay of Ga (3d) Spectra shown Above

C (1s) BE = 285.0 eV

 

Chemical Shift between Ga and Ga2O3:  2.6 eV
 Chemical Shift between Ga and GaF3:   3.8 eV

 

→  Periodic Table 

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Gallium Oxide (Ga₂O₃)
3 mm pressed pellet

Survey Spectrum from Ga2O3 Flood gun is ON, C (1s) BE = 285.0 eV	Ga (3d) Chemical State Spectrum from Ga2O3 Flood gun is ON, C (1s) BE = 285.0 eV
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O (1s) Chemical State Spectrum from Ga2O3 Flood gun is ON, C (1s) BE = 285.0 eV	C (1s) Chemical State Spectrum from Ga2O3 Flood gun is ON, C (1s) BE = 285.0 eV
	.
Ga (3s) Chemical State Spectrum from Ga2O3 Flood gun is ON, C (1s) BE = 285.0 eV	Ga (3p) Chemical State Spectrum from Ga2O3 Flood gun is ON, C (1s) BE = 285.0 eV
	.
Valence Band Spectrum from Ga2O3 Flood gun is ON, C (1s) BE = 285.0 eV	Auger Signals from Ga2O3 Flood gun is ON, C (1s) BE = 285.0 eV

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Energy Loss Peaks for Gallium Oxide, Ga₂O₃

Energy Loss Peaks for Ga2O3 – Ga (3d), Ga (3p) and Ga (3s)

 

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Multiplet Splitting Features for
Gallium Compounds

Ga metal – NO Splitting for Ga (3s)	Ga2O3 Compound – NO Multiplet Splitting for Ga (3s)

Features Observed

• xx
• xx
• xx

→  Periodic Table 

 

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Gallium Chemical Compounds

 

Gallium Fluoride, GaF₃

Survey Spectrum	Ga (3d) Spectrum
	.
F (1s) Spectrum	C (1s) Spectrum
	.
Ga (2p3/2) Spectrum	Valence Band Spectrum
	.
Ga (Auger) Spectrum

→  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 Gallium

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 Gallium

 

Native Oxide of Gallium Sheet – Sample GROUNDED

 

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Native Oxide of Gallium Sheet – Sample Grounded

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

Ga (3d)	O (1s)	C (1s)
→  Periodic Table

Copyright ©:  The XPS Library

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Chemical State Spectra from Slow Depth Profile of:
Ga Native Oxide by AES

Native Ga Oxide on Ga ribbon was slowly ion etched using High Energy Resolution conditions to measure Chemical States by Auger

Ga (LMM)	O (KLL)

 

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Gallium Alloys

XxCu	XxCu
→  Periodic Table
XxCu	XxCu

 

Copyright ©:  The XPS Library 

 

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XPS Facts, Guidance & Information

→  Periodic Table 

		Element		Gallium (Ga)
		Primary XPS peak used for Peak-fitting:		Ga (2p)  or Ga (3d)
		Spin-Orbit (S-O) splitting for Primary Peak:		Spin-Orbit splitting for “p” orbital, ΔBE = 26.9 eV
		Binding Energy (BE) of Primary XPS Signal:		1117 eV  for Ga (2p3/2) 18 eV for Ga (3d)
		Scofield Cross-Section (σ) Value:		Ga (2p3/2) =21.40      Ga (2p1/2) =11.09 Ga (3d) =1.085     Ga (3p) =3.21
		Conductivity:		Ga resistivity =   Native Oxide suffers Differential Charing
		Range of Ga (2p) Chemical State BEs:		xx – xx eV range   (Ga to GaF2)
		Signals from other elements that overlap Ga (2p) 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 Ga (3d)

• Ga (3d) FWHM (eV) of Pure Ga metal :  ~0.6 eV using 50 eV Pass Energy after ion etching:
• Ga (3d) FWHM (eV) of Ga₂O₃ xtal:  ~1.3 eV using 50 eV Pass Energy  (before ion etching)
• Binding Energy (BE) of Primary Signal used for Measuring Chemical State Spectra:  18 eV for Ga (3d) with +/- 0.2 uncertainty
• List of XPS Peaks that can Overlap Peak-fit results for Ga (3d):  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) = ~0.95 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.

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 Gallium

• Gallium develops a thick native oxide due to the reactive nature of clean Gallium .
• The native oxide of Ga O_x is 5-9 nm thick.
• Gallium thin films often have a low level of iron (Fe) in the bulk as a contaminant or to strengthen the thin film
• Gallium 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 Ga (2p) peak as well as Ga (3d).
• 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 Gallium (Ga)

• Conductivity:  Gallium 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:  Ga (3d) at 18 eV and Ga (2p3) at 1116 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:  10 – 30 eV
• Recommended Extended BE Range for Measuring Chemical State Spectrum:  0 to 110 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

• 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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