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

---

 

Tantalum (Ta)

 

Tantalcarbide – TaC	Tantalum – Tao	Tantalite – MnTa2O6

 

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	Overlays and Valence Band Spectra Six (6) Tables of Chemical State BEs  Histograms of NIST BEs Advanced XPS Information Section	Peak-fits and Overlays of Ta Chemical Compounds Quantitation and Atom %s 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

---

Tantalum (Ta^o) Metal

Peak-fits, BEs, FWHMs, and Peak Labels

---

	.
Tantalum (Ta) Metal Ta (4f) Spectrum – raw spectrum ion etched clean	Tantalum (Ta) Metal Peak-fit of Ta (4f) Spectrum w/o asymm
→  Periodic Table – HomePage
Tantalum (Ta) Metal Ta (4f) Spectrum – extended range	Tantalum (Ta) Metal Peak-fit of Ta (4f) Spectrum (w asymm)
.
Tantalum (Ta) Metal Ta (4d) Spectrum	Tantalum (Ta) Metal  Ta (5p) Spectrum
Survey Spectrum of Tantalum (Tao) Metal with Peaks Integrated, Assigned and Labelled
→  Periodic Table  XPS Signals for Tantalum, Tao 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 Ta (4s) 563 1.79 16.4 Ta (4p1/2) 462 2.06 18.4 N (1s) overlaps Ta (4p3/2) 400 5.02 18.4 Ta (4d3/2) 238 6.40 20.6 Ta (4d5/2) 226 9.24 20.6 F (2s) overlaps Ta (4f5/2) 23.65 3.80 23.0 O (2s) overlaps Ta (4f7/2) 21.74 4.82 23.0 Ta (5s) 68 0.363 22.5 Ta (5p1/2) 43 0.346 22.9 Ta (5p3/2) 33 0.754 22.9 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 Ta2O5: ~4 eV Work Function for Ta:  xx eV *Scofield Cross-Section (σ) for C (1s) = 1.0 →  Periodic Table    Valence Band Spectrum from Tao Metal  Fresh exposed bulk produced by extensive Ar+ ion etching Plasmon Peaks from Tao Metal  Fresh exposed bulk produced by extensive Ar+ ion etching Ta (4f) – Extended Range Spectrum Ta (4f) – Extended Range Spectrum – Vertically Zoomed →  Periodic Table    Ta (MMN) Auger Peaks from Tao Metal  Fresh exposed bulk produced by extensive Ar+ ion etching Tao Metal – main Auger peak Ta Metal – full Auger range   Features Observed xx xx xx →  Periodic Table
Artefacts Caused by Argon Ion Etching
C (1s) from Tantalum Carbide(s) can form when ion etched Reactive Metal Surfaces capture Residual UHV Gases (CO, H2O, CH4 etc)	Argon Trapped in Tao can form when Argon Ions are used to removed surface contamination
	na overlap with Ta 4d
Side-by-Side Comparison of Ta Native Oxide & Tantalum Pentoxide (Ta2O5) Peak-fits, BEs, FWHMs, and Peak Labels
Ta Native Oxide	Ta2O5
Ta (4f) from Ta Native Oxide Flood Gun OFF As-Measured, C (1s) at 285.1 eV	Ta (4f) from Ta2O5 – pressed pellet Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
→  Periodic Table
	.
Ta Native Oxide	Ta2O5
C (1s) from Ta Native Oxide As-Measured, C (1s) at 285.1 eV Flood Gun OFF	C (1s) from Ta2O5 – pressed pellet Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
→  Periodic Table
	.
Ta Native Oxide	Ta2O5
O (1s) from Ta Native Oxide As-Measured, C (1s) at 285.1 eV (Flood Gun OFF)	O (1s) from Ta2O5 – pressed pellet Flood Gun ON, Charge Referenced to C (1s) at 285.0 eV
→  Periodic Table

 

 

Survey Spectrum of Tantalum Pentoxide, Ta₂O₅
with Peaks Integrated, Assigned and Labelled

→  Periodic Table  

---

Overlays of Ta (4f) Spectra for
Ta Native Oxide and Ta₂O₅

Caution: BEs from Grounded Native Oxides can be Misleading

Overlay of Tao metal and Ta Native Oxide – Ta (4f) Native Oxide C (1s) = 285.1  (Flood gun OFF)	Overlay of Tao metal and Ta2O5 – Ta (4f) Pure Oxide C (1s) = 285.0 eV Chemical Shift: 4.4 eV
→  Periodic Table	Copyright ©:  The XPS Library

---

 

Overlay of Ta (4f) 
Ta^o Metal, Ta Native Oxide, & Ta₂O₅ 

Features Observed

• xx
• xx
• xx

→  Periodic Table 

---

 

Valence Band Spectra
Ta^o, Ta₂O₅ 

Tao Ion etched clean	Ta2O5 – pressed pellet Flood gun is ON,  Charge referenced so C (1s) = 285.0 eV
Overlay of Valence Band Spectra for Tao metal and Ta2O5

Features Observed

• xx
• xx
• xx

→  Periodic Table 

---

---

 

Tantalum Minerals, Gemstones, and Chemical Compounds
Aluminotantite – AlTaO4	Wodginite – MnSnTa2O8	Lithiotantite – LiTa3O8	Liandratite – UTa2O8

→  Periodic Table 

---

---

 

Six (6) Chemical State Tables of Ta (4f_7/2) BEs

 

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

→  Periodic Table 

---

---

 

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 (2p3/2) 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 (2p3/2) 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 

---

Table #1

Ta (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
Ta	73	Ta  – element	21.8 eV		285.0 eV	The XPS Library
Ta	73	TaSi2 (N*1)	22.3 eV		284.8 eV	Avg BE – NIST
Ta	73	Ta-N	22.8 eV	23.2 eV	285.0 eV	The XPS Library
Ta	73	Ta-N0.28 (N*1)	22.8 eV		284.8 eV	Avg BE – NIST
Ta	73	CoTaZr	23.2 eV		285.0 eV	The XPS Library
Ta	73	Ta-C	23.2 eV	23.9 eV	285.0 eV	The XPS Library
Ta	73	TaS2	23.5 eV		285.0 eV	The XPS Library
Ta	73	KTaO3 (N*1)	25.9 eV		284.8 eV	Avg BE – NIST
Ta	73	Ta-2O5	26.5 eV	27.1 eV	285.0 eV	The XPS Library
Ta	73	Ta2O5 (N*4)	26.5 eV	26.9 eV	284.8 eV	Avg BE – NIST
Ta	73	Ta-Br5 (N*1)	26.9 eV		284.8 eV	Avg BE – NIST
Ta	73	Ta-Cl5 (N*1)	27.3 eV		284.8 eV	Avg BE – NIST
Ta	73	Ta-F5 (N*1)	27.8 eV		284.8 eV	Avg BE – NIST
Ta	73	Ta-F3	28.3 eV		285.0 eV	The XPS Library
Ta	73	Ta-F5	29.3 eV		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 

---

Table #2

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

C (1s) BE = 284.8 eV

→  Periodic Table 

Copyright ©:  Ulvac-PHI

---

Table #3

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

C (1s) BE = 284.8 eV

Chemical state	Binding energy (eV), Ta (4f7/2)
Ta metal	21.8
TaN	23.0
Ta2O5	26.2

→  Periodic Table 

Copyright ©:  Thermo Scientific 

---

Table #4

Ta (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

---

Table #5

Ta (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 Ta 4f7/2 Ta 21.8 ±0.3 21.5 ～ 22.0 Ta 4f7/2 Cl6(Ta6Cl12)(Et4N)2 26.2 ±0.2 26.0 ～ 26.4 Ta 4f7/2 Br6(Ta6Cl12)(Bu4N)2 26.3 ±0.3 26.0 ～ 26.5 Ta 4f7/2 TaS 26.6 ±0.3 26.3 ～ 26.8 Ta 4f7/2 TaS2 26.7 ±0.3 26.4 ～ 26.9 Ta 4f7/2 Ta2O5 26.7 ±0.3 26.4 ～ 26.9 Ta 4f7/2 Halides 27.4 ±0.5 26.9 ～ 27.9

→  Periodic Table 

---

---

 

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

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

 

Histogram indicates:  21.7 eV for Ta metal based on 9 literature BEs	Histogram indicates:  26.7 eV for Ta2O5 based on 4 literature BEs

Table #6

NIST Database of Ta (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.

 

Element	Spectral Line	Formula	Energy (eV)	Reference
Ta	4f7/2	Ta	21.60	Click
Ta	4f7/2	Ta	21.60	Click
Ta	4f7/2	Ta	21.60	Click
Ta	4f7/2	Ta	21.61	Click
Ta	4f7/2	Ta	21.62	Click
Ta	4f7/2	Ta	21.64	Click
Ta	4f7/2	Ta	21.70	Click
Ta	4f7/2	Ta	21.70	Click
Ta	4f7/2	Ta	21.80	Click
Ta	4f7/2	Ta	21.90	Click
Ta	4f7/2	Ta	21.90	Click
Ta	4f7/2	Ta	21.90	Click
Ta	4f7/2	Ta	21.90	Click
Ta	4f7/2	Ta	22.00	Click
Ta	4f7/2	TaSi2	22.30	Click
Ta	4f7/2	TaN0.07	22.50	Click
Ta	4f7/2	Ta0.4N0.5	22.80	Click
Ta	4f7/2	TaN0.28	22.85	Click
Ta	4f7/2	Ta2N	22.85	Click
Ta	4f7/2	TaS2	22.90	Click
Ta	4f7/2	TaC0.95	22.90	Click
Ta	4f7/2	Ta2C	23.08	Click
Ta	4f7/2	(PbS)1.13TaS2	23.10	Click
Ta	4f7/2	(PbS)1.14(TaS2)2	23.10	Click
Ta	4f7/2	(SnS)1.16TaS2	23.10	Click
Ta	4f7/2	Ta4C3	23.11	Click
Ta	4f7/2	TaC0.75	23.25	Click
Ta	4f7/2	Ta3C2	23.26	Click
Ta	4f7/2	TaC0.95	23.50	Click
Ta	4f7/2	O2/TaC0.95	23.50	Click
Ta	4f7/2	TaC0.98	23.55	Click
Ta	4f7/2	TaS2	23.60	Click
Ta	4f7/2	Ta3N5	24.20	Click
Ta	4f7/2	NaTaO3	25.70	Click
Ta	4f7/2	NaTaO3	25.70	Click
Ta	4f7/2	[Ta6Cl12(H2O)4]Cl2.4H2O	25.80	Click
Ta	4f7/2	RhTaO4	25.80	Click
Ta	4f7/2	KTaO3	25.90	Click
Ta	4f7/2	Ta2O5	26.00	Click
Ta	4f7/2	Ta2O5	26.00	Click
Ta	4f7/2	[N(C2H5)4]2[Ta6Cl12Cl6]	26.20	Click
Ta	4f7/2	[N(C4H9)4]2[Ta6Cl12Br6]	26.30	Click
Ta	4f7/2	Ta2O5/Si	26.40	Click
Ta	4f7/2	Ta2O5	26.50	Click
Ta	4f7/2	Ta2O5	26.60	Click
Ta	4f7/2	TaS	26.60	Click
Ta	4f7/2	TaS2	26.70	Click
Ta	4f7/2	Ta2O5/Si	26.80	Click
Ta	4f7/2	TaBr5	26.90	Click
Ta	4f7/2	Ta2O5	26.90	Click
Ta	4f7/2	Ta2O5	26.90	Click
Ta	4f7/2	Ta2O5/Si	26.90	Click
Ta	4f7/2	TaSi2	27.00	Click
Ta	4f7/2	TaOx	27.00	Click
Ta	4f7/2	Ta2O5	27.00	Click
Ta	4f7/2	Ta2O5/Ta2N	27.05	Click
Ta	4f7/2	Ta2O5/Ta2N	27.05	Click
Ta	4f7/2	TaCl5	27.30	Click
Ta	4f7/2	TaSi2Ox	27.50	Click
Ta	4f7/2	TaF5	27.80	Click
Ta	4f7/2	K2TaF7	29.40	Click

---

 

 

Statistical Analysis of Binding Energies in NIST XPS Database of BEs

 

 

→  Periodic Table 

---

 

Advanced XPS Information Section

Expert Knowledge, Spectra, Features, Guidance and Cautions
for XPS Research Studies on Tantalum Materials

 

 

---

 

Expert Knowledge Examples & Explanations

→  Periodic Table 

---

 

 

Tantalum Chemical Compounds

 

Peak-fits and Overlays of Chemical State Spectra

Pure Tantalum, Tao:  Ta (4f) Cu (2p3/2) BE = 932.6 eV	Ta2O5:  Ta (4f) C (1s) BE = 285.0 eV	TaF3: Ta (4f) C (1s) BE = 285.0 eV

Features Observed

• xx
• xx
• xx

→  Periodic Table 

---

 

Overlay of Ta (4f) Spectra shown Above

C (1s) BE = 285.0 eV

 

Chemical Shift between Ta and Ta₂O₅:  4.4 eV
 Chemical Shift between Ta and TaF₅:   6.7 eV

 

→  Periodic Table 

---

 

Tantalum Oxide (Ta₂O₅)
pressed powder

Survey Spectrum from Ta2O5 Flood gun is ON, C (1s) BE = 285.0 eV	Ta (4f) Chemical State Spectrum from Ta2O5 Flood gun is ON, C (1s) BE = 285.0 eV
	.
O (1s) Chemical State Spectrum from Ta2O5 Flood gun is ON, C (1s) BE = 285.0 eV	C (1s) Chemical State Spectrum from Ta2O5 Flood gun is ON, C (1s) BE = 285.0 eV
	.
Valence Band Spectrum from Ta2O5 Flood gun is ON, C (1s) BE = 285.0 eV	Auger Signals from Ta2O5 Flood gun is ON, C (1s) BE = 285.0 eV
	na

Shake-up Features
for Ta₂O₅

Ta (4f)

 

---

→  Periodic Table 

 

 

Tantalum Chemical Compounds

 

Tantalum Pentafluoride, TaF₅
(Danger: sublimes in vacuum and degrades)

Survey	Ta (4f)
	.
C (1s)	F (1s)
	.
Valence Band

→  Periodic Table 

---

---

 

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 Tantalum – Ta₂O₅

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 

---

 

 

Flood Gun Effect on Native Oxide of Tantalum

 

Native Oxide of Tantalum Sheet – Sample GROUNDED

 

---

 

Native Oxide of Tantalum Sheet – Sample Grounded

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

Ta (4f)	O (1s)	C (1s)
→  Periodic Table

---

 

---

 

AES Study of UHV Gas Captured by Freshly Ion Etched Tantalum

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

Ta (MNN) Signal: Ta at front -> Ta2O5x at rear  Ta KE = 1670.1 eV	O (KLL) Signal: Ta at front -> Ta2O5x at rear  O KE = 507.3 eV	C (KLL) Signal: Ta at front -> Ta2O5x at rear  O KE = 266.3 eV
Auger Chemical State Spectra from Ta2O5 using Charge Control Conditions
Ta (MNN) Signal: Ta2O5 w charge control – Hemi-sphere (HSA) – 10 kV High Energy Resolution Mode for Chemical States	O (KLL) Signal: Ta2O5 w charge control – Hemi-sphere (HSA) – 10 kV High Energy Resolution Mode for Chemical States	C (KLL) Signal: Ta2O5 w charge control – Hemi-sphere (HSA) – 10 kV High Energy Resolution Mode for Chemical States

Features Observed

• xx
• xx
• xx

→  Periodic Table 

---

 

 

Tantalum Alloys

XxCu	XxCu
→  Periodic Table
XxCu	XxCu

 

Copyright ©:  The XPS Library 

 

---

---

 

 

XPS Facts, Guidance & Information

→  Periodic Table 

		Element		Tantalum (Ta)
		Primary XPS peak used for Peak-fitting:		Ta (4f7/2)
		Spin-Orbit (S-O) splitting for Primary Peak:		Spin-Orbit splitting for “f” orbital,  ΔBE = 1.9 eV
		Binding Energy (BE) of Primary XPS Signal:		21.8 eV
		Scofield Cross-Section (σ) Value:		Ta (4f7/2) = 4.82    Ta (4f5/2) = 3.80
		Conductivity:		Ta resistivity =   Native Oxide suffers Differential Charing
		Range of Ta (4f7/2) Chemical State BEs:		21 – 28 eV range   (Ta to TaF5)
		Signals from other elements that overlap Ta (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 

---

---

 

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

• FWHM (eV) of Ta (4f_7/2) for Pure Ta^o :  ~0.6 eV using 25 eV Pass Energy after ion etching
• FWHM (eV) of Ta (4f_7/2) for Ta2O5:  ~1.1 eV using 50 eV Pass Energy  (before ion etching)
• Binding Energy (BE) of Primary Signal used for Measuring Chemical State Spectra:  21.8 eV for Ta (4f_7/2) with +/- 0.2 uncertainty
• List of XPS Peaks that can Overlap Peak-fit results for Ta (4f_7/2):  xxx

→  Periodic Table 

---

 

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.

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 

---

 

Contaminants Specific to Tantalum

• Tantalum develops a thick native oxide due to the reactive nature of clean Tantalum.
• The native oxide of Ta2O5_x is 4-6 nm thick.
• Tantalum thin films can have a low level of iron (Fe) in the bulk as a contaminant or due to sputter coater shields
• Tantalum 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 

---

 

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 Ta (4f_7/2) 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.

→  Periodic Table 

---

 

Data Collection Settings for Tantalum (Ta)

• Conductivity:  Tantalum 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:  Ta (4f_7/2) at 21.8 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:  15 – 35 eV
• Recommended Extended BE Range for Measuring Chemical State Spectrum:  10 – 100 eV
• Recommended BE Range for Survey Spectrum:  -10 to 1,100 eV   (above 1,100 eV there are no useful XPS signals, except for Ge, 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 

→  Periodic Table 

---

 

Effects of Argon Ion Etching

• Carbides appear after ion etching Ta 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

 

→  Periodic Table 

---

 

---

---

End of File