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

---

 

Silicon (Si)

 

Man-made Silicon Carbide – SiC	Man-made Boule of Silicon – Sio	Quartz – SiO2

 

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 Si 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 Knowledge Explanations
  • PDMS, siloxane
  • n-Si, p-Si, and un-doped
  • SiOx, Silicate, SiO₂
  • Ion etching effects

---

Silicon (Si^o) Metalloid 
Peak-fits, BEs, FWHMs, and Peak Labels

Silicon (Sio) Metalloid (single crystal) Si (2p) Spectrum using PE = 10 eV – raw spectrum Ultra-high energy resolution, freshly cleaved in lab air	Silicon (Sio) Metalloid (single crystal) Peak-fit of Si (2p) Spectrum using PE = 10 eV (w/o asymm) using 2p3/2 to 2p1/2 spin-orbit splitting for peak-fit,  ΔBE=0.602, peak area ratio = 2.0
	.
Silicon (Sio) Metalloid (single crystal) Si (2p) Spectrum using PE=50 eV – raw spectrum Normal high energy resolution setting, wafer freshly cleaved in lab air	Silicon (Sio) Metalloid (single crystal) Peak-fit of Si (2p) Spectrum (w/o asymm) using 2p3/2 to 2p1/2 spin-orbit splitting for peak-fit,  ΔBE=0.602, peak area ratio = 2.0
	.
Silicon (Sio) Metalloid (single crystal) Si (2p) and Si (2s) Spectrum with Plasmons raw	Silicon (Sio) Metalloid (single crystal) Si (2p) and Si (2s) Spectrum with Plasmons labelled
	.
Silicon (Sio) Metalloid (single crystal) Si (2s) Spectrum – raw	Silicon (Sio) Metalloid (single crystal) Si (2s) Spectrum – peak-fit
	.
Silicon (Sio) Metalloid (single crystal) Valence Band Spectrum – not ion etched	SiO2 (amorphous silica) Valence Band Spectrum – not ion etched
	.
Silicon (Sio) Metalloid (single crystal) Adventitious C (1s) Spectrum – not ion etched	Silicon (Sio) Metalloid (single crystal) Freshly-Formed UHV Carbon after Ion Etching (inside cryopump system)
Survey Spectrum of Silicon (Sio) Metalloid with Peaks Integrated, Assigned and Labelled
Survey Spectrum of Silicon Dioxide (SiO2) with Peaks Integrated, Assigned and Labelled
→  Periodic Table    XPS Signals for Pure Silicon, (Sio) metalloid 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 Si (2s) 151 0.955 30.0 Hg (4f) overlaps Si (2p1/2) 100.0 0.276 30.9 Si (2p3/2) 99.4 0.541 30.9 Si (3s) 8 0.0808 32.5 Si (3p) 4 0.014 σ:  abbreviation for the term Scofield Photoionization Cross-Section which are used with IMFP and TF to generate atom% and quantitation Plasmon Peaks SiO2 Energy Loss Peaks Intrinsic Plasmon Peak:  ~17 eV above peak max Expected Bandgap for Si: 1.12 eV Expected Bandgap for SiO2: 7.8 eV  *Scofield Cross-Section (σ) for C (1s) = 1.0     Comparison of Plasmon Peaks from Pure Sio to Energy Loss Peaks from SiO2 no ion etching – freshly cleaved – fractured Si (2p) to Si (2s) range with plasmon peaks for Sio   (ΔBE = ~18 eV) Si (2p) to Si (2s) range with energy loss peaks for SiO2 (ΔBE = ~22 eV) . Overlay of Si Plasmon Peaks with SiO2 Energy Loss Peaks Vertically Expanded Overlay of Si Plasmon Peaks with SiO2 Energy Loss Peaks . Si (KLL) Auger Peaks from Pure Sio  Fresh exposed bulk produced by extensive Ar+ ion etching Features Observed xx xx xx →  Periodic Table    Artefacts Caused by Argon Ion Etching C (1s) from Carbides formed by Etching Argon Trapped in Silicon
Side-by-Side Comparison of Sio, Si Native Oxide & Pure Silicon Dioxide (SiO2, amorphous Silica) Peak-fits, BEs, FWHMs, and Peak Labels
Si Native Oxide	Pure SiO2 (amorphous, Silica)
Si (2p) from FRESH Si Native Oxide Flood Gun OFF As-Measured, C (1s) at 285.4 eV	Si (2p) from SiO2 (Silica)- fresh exposed bulk Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
	.
C (1s) from FRESH Native Si Oxide on Silicon As-Measured, C (1s) at 285.4 eV (Flood Gun OFF)	C (1s) from SiO2 (silica)- fresh exposed bulk Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
.
O (1s) from FRESH Native Si Oxide on Silicon As-Measured, C (1s) at 285.4 eV (Flood Gun OFF)	O (1s) from SiO2 (silica) – fresh exposed bulk Flood Gun ON Charge Referenced to C (1s) at 285.0 eV
.
Valence Band Spectrum of Native Si Oxide – fresh bulk exposed on Silicon As-Measured, C (1s) at 285.4 eV (Flood Gun OFF)	Valence Band Spectrum of SiO2 (amorphous silica) – fresh fracture Flood Gun ON Charge Referenced to C (1s) at 285.0 eV

 

Survey Spectrum of Silicon (Si) Native Oxide
with Peaks Integrated, Assigned and Labelled

 

 

Survey Spectrum of Pure Silicon Dioxide, SiO₂
(amorphous silica)
with Peaks Integrated, Assigned and Labelled

Copyright ©:  The XPS Library 

---

---

Overlays of Si (2p) Spectra for
Si^o metalloid, Native Si Oxide and Pure SiO₂ Optical Lens

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

Overlay of Sio metalloid and Native Si Oxide – Si (2p) Study of Ion Etch Effect Native Oxide C (1s) = 285.4 eV  (Flood gun OFF) Chemical Shift: 1.5	Overlay of Sio metalloid and Pure SiO2 (silica)  – Si (2p) Pure Oxide C (1s) = 285.0 eV, not ion etched Chemical Shift:  4.4
	Copyright ©:  The XPS Library

 

Overlay of Si (2p)
Si^o metalloid, Native Si Oxide, & Pure SiO₂ (silica)  

 

Features Observed

• xx
• xx
• xx

→  Periodic Table 

---

---

 

Silicon Minerals, Gemstones, and Chemical Compounds
Natural Silicon – Sio	Sodium Silicate – Na2SiO3 – Waterglass	Potassium Silicate – K2SiO4	Magnesium Silicate – Mg2SiO4 – Talc

 

---

---

 

Six (6) Chemical State Tables of Si (2p) BEs

 

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

 

---

---

 

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
  • 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 (2p_3/2) appears at 932.2 eV or 932.8 eV because this is what the maker taught them
    • This range causes BEs in the higher BE end to be larger than expected
    • This variation increases significantly above 600 eV BE
  • Charge Compensation
    • Samples that behave as true insulators normally require the use of a charge neutralizer (electron flood gun with or without Ar+ ions) so that the measured chemical state spectra can be produced without peak-shape distortions or sloping tails on the low BE side of the peak envelop.
    • Floating all samples (conductive, semi-conductive, and non-conductive) and always using the electron flood gun is considered to produce more reliable BEs and is recommended.
  • Charge Referencing Methods for Insulators
    • Charge referencing is a common method, but it can produce results that are less reliable.
    • When an electron flood gun is used, the BE scale will usually shift to lower BE values by 0.01 to 5.0 eV depending on your voltage setting. Normally, to correct for this flood gun induced shift, the BE of the hydrocarbon C (1s) peak maximum from adventitious carbon is used to correct for the charge induced shift.
    • The hydrocarbon peak is normally the largest peak at the lowest BE.
    • Depending on your preference or training, the C (1s) BE assigned to this hydrocarbon peak varies from 284.8 to 285.0 eV.  Other BEs can be as low as 284.2 eV or as high as 285.3 eV
    • Native oxides that still show the pure metal can suffer differential charging that causes the C (1s) and the O (1s) and the Metal Oxide BE to be larger
    • When using the electron flood gun, the instrument operator should adjust the voltage and the XY position of the electron flood gun to produce peaks from a strong XPS signal (eg O (1s) or C (1s) having the most narrow FWHM and the lowest experimentally measured BE.

→  Periodic Table 

---

Table #1

Si (2p) 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
Si	14	Mg2Si	98.5 eV		285.0 eV	The XPS Library
Si	14	NiSi (N*6)	98.8 eV	99.7 eV	284.8 eV	Avg BE – NIST
Si	14	MoSi2	99.0 eV		285.0 eV	The XPS Library
Si	14	Si3H2 (N*4)	99.0 eV		284.8 eV	Avg BE – NIST
Si	14	Si (p)	99.2 eV		285.0 eV	The XPS Library
Si	14	Si – element	99.5 eV		285.0 eV	The XPS Library
Si	14	Si (n)	99.8 eV		285.0 eV	The XPS Library
Si	14	SiC (N*5)	100.4 eV	100.7 eV	284.8 eV	Avg BE – NIST
Si	14	SiC	100.5 eV		285.0 eV	The XPS Library
Si	14	Si2O	100.8 eV		285.0 eV	The XPS Library
Si	14	Si3N4 (N*12)	101.5 eV	102.1 eV	284.8 eV	Avg BE – NIST
Si	14	Si-O	101.5 eV		285.0 eV	The XPS Library
Si	14	Si3N4	101.7 eV		285.0 eV	The XPS Library
Si	14	SiCN	101.8 eV		285.0 eV	The XPS Library
Si	14	B4Si  (N*1)	101.9 eV		284.8 eV	Avg BE – NIST
Si	14	Pyrope	102.1 eV		285.0 eV	The XPS Library
Si	14	HfSiOx	102.3 eV		285.0 eV	The XPS Library
Si	14	Si2O3	102.3 eV		285.0 eV	The XPS Library
Si	14	Mica	102.4 eV		285.0 eV	The XPS Library
Si	14	M-SiO3 (N*2)	102.4 eV	103.3 eV	284.8 eV	Avg BE – NIST
Si	14	Si-PDMS	102.4 eV	102.6 eV	285.0 eV	The XPS Library
Si	14	Al2SiO5	102.8 eV		285.0 eV	The XPS Library
Si	14	Aluminosilicates	102.8 eV		285.0 eV	The XPS Library
Si	14	SiON	102.8 eV	103.0 eV	285.0 eV	The XPS Library
Si	14	LiAlSi2O6	103.0 eV		285.0 eV	The XPS Library
Si	14	SiO2	103.1 eV		285.0 eV	The XPS Library
Si	14	SiO2 thermal	103.2 eV		285.0 eV	The XPS Library
Si	14	SiO2 fused	103.4 eV		285.0 eV	The XPS Library
Si	14	Si-(OH)4  Opal	103.7 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 (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

Si (2p) Chemical State BEs from:  “PHI Handbook”

C (1s) BE = 284.8 eV

→  Periodic Table 

Copyright ©:  Ulvac-PHI

---

Table #3

Si (2p) Chemical State BEs from:  “Thermo-Scientific” Website

C (1s) BE = 284.8 eV

Chemical state	Binding energy Si (2p) / eV
Si element	99.4
Si3N4	101.7
ZrSiO4	102
Organic Si	~102
Aluminosilicate	102.7
SiO2	103.5

→  Periodic Table 

Copyright ©:  Thermo Scientific 

---

Table #4

Si (2p) 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

Si (2p) 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 Si 2p Silicon 99.2 ±0.4 98.8 ～ 99.5 Si 2p Silicides 99.7 ±0.3 99.4 ～ 99.9 Si 2p Carbides 100.4 ±0.5 99.9 ～ 100.9 Si 2p Nitrides 101.9 ±0.4 101.5 ～ 102.2 Si 2p Silicones (Silanes) 102.4 ±0.5 101.9 ～ 102.9 Si 2p Silicates 102.5 ±0.5 102.0 ～ 103.0 Si 2p Silica 103.6 ±0.4 103.2 ～ 103.9

→  Periodic Table 

---

---

 

Histograms of NIST BEs for Si (2p) BEs

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

Histogram indicates:  99.4 eV for Sio based on 37 literature BEs Doping type is Unknown n-Si can be 0.6 eV smaller than p-Si	Histogram indicates:  103.5 eV for SiO2 based on 54 literature BEs
Histogram indicates:  101.9 eV for Si3N4 based on 15 literature BEs	Histogram indicates:  99.2 eV for SiHx based on 16 literature BEs
Histogram indicates:  102.5 eV for -((CH3)2SiO)n– based on 7 literature BEs PDMS = Silicone Oil = Poly-dimethylsiloxane	Histogram indicates:  100.6 eV for SiC based on 11 literature BEs

Table #6

NIST Database of Si (2p) 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 

---

 

 

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 Silicon Materials

 

---

 

Expert Knowledge Examples & Explanations

 

---

 

Silicon Chemical Compounds

 

Peak-fits and Overlays of Chemical State Spectra

Pure Silicon:  Si (2p) Cu (2p3/2) BE = 932.6 eV	Silicone Oil (PDMS):  Si (2p) C (1s) BE = 285.0 eV	SiO2:  Si (2p) C (1s) BE = 285.0 eV

Features Observed

• xx
• xx
• xx

→  Periodic Table 

---

 

Overlay of Si (2p) Spectra shown Above

C (1s) BE = 285.0 eV

 

→  Periodic Table 

---

 

FRESH Silicon (Si) Native Oxide on Silicon
Naturally Formed at 25 C^o 1 atm after freshly cleaving in lab air (age ~30 min)

Survey Spectrum from FRESH Native Oxide on Sio Flood gun is OFF, C (1s) BE = 285.4 eV	Si (2p) Chemical State Spectrum from FRESH Native Oxide on Sio Flood gun is OFF, C (1s) BE = 285.4 eV
	.
O (1s) Chemical State Spectrum from FRESH Native Oxide on Sio Flood gun is OFF, C (1s) BE = 285.4 eV	C (1s) Chemical State Spectrum from FRESH Native Oxide on Sio Flood gun is OFF, C (1s) BE = 285.4 eV

Features Observed

• xx
• xx
• xx

→  Periodic Table 

 

---

 

Silicon Dioxide (SiO₂), silica – fresh fractured bulk
Silica (amorphous) optical lens – fractured to expose bulk

Survey Spectrum from SiO2 Silica optical lens Flood gun is ON, C (1s) BE = 285.0 eV Freshly cleaved to expose bulk	Si (2p) Chemical State Spectrum SiO2 Silica optical lens Flood gun is ON, C (1s) BE = 285.0 eV Freshly cleaved to expose bulk
	.
O (1s) Chemical State Spectrum from SiO2 Silica optical lens Flood gun is ON, C (1s) BE = 285.0 eV Freshly cleaved to expose bulk	C (1s) Chemical State Spectrum from SiO2 Silica optical lens Flood gun is ON, C (1s) BE = 285.0 eV Freshly cleaved to expose bulk
	.
Si (2p) Chemical State Spectrum from SiO2 Silica optical lens Flood gun is ON, C (1s) BE = 285.0 eV Freshly cleaved to expose bulk	Si (2s) Chemical State Spectrum from SiO2 Silica optical lens Flood gun is ON, C (1s) BE = 285.0 eV Freshly cleaved to expose bulk
	.
Valence Band Spectrum from SiO2 Silica optical lens Flood gun is ON, C (1s) BE = 285.0 eV Freshly cleaved to expose bulk	Si (2p) and Si (2s) spectrum from SiO2 Silica optical lens Flood gun is ON, C (1s) BE = 285.0 eV Freshly cleaved to expose bulk
Comparison of Si (2s) and Si (2p) Peak-shapes from SiO2 (silica)

Features Observed

• xx
• xx
• xx

→  Periodic Table 

 

---

 

Silicon Chemical Compounds

Surveys and Peak-fits

 

PDMS (silicone oil)    -(CH3)2Si-O)n–
Survey Spectrum
Si (2p)	O (1s)	C (1s) at 285.0 eV
→  Periodic Table
Water Glass Solution – Na2Si3O7
Survey Spectrum
Si (2p)	O (1s)	C (1s)
→  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.

→  Periodic Table 

 

---

 

 

Flood Gun Effect on Native Oxide of Silicon

 

Native Oxide of Silicon Ribbon – Sample GROUNDED
versus
Native Oxide of Silicon Ribbon – Sample FLOATING

 

---

 

Native Oxide of Silicon Disk – Sample Grounded Electron Flood Gun:  0 Voltage (FG OFF), Min Voltage versus Max Voltage
Si (2p)	O (1s)	C (1s)
Differential Shift of SiOx Peak is due to Differential Charging	Differential Shift of O (1s) Peak is due to Differential Charging	Differential Shift of Adventitious Carbon is a Slightly Larger
Features Observed xx xx xx →  Periodic Table    Native Oxide of Silicon Disk – Sample Floating Electron Flood Gun:  0 Voltage (FG OFF), Min Voltage versus Max Voltage
Si (2p)	O (1s)	C (1s)
All Peaks Shift Linearly NO Differential Charging	All Peaks Shift Linearly NO Differential Charging	All Peaks Shift Linearly NO Differential Charging
Features Observed xx xx xx

→  Periodic Table 

---

 

---

 

AES Study of UHV Gas Capture by Freshly Ion Etched Silicon 

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

Si (LMM) Signal: Si at front -> SiOx at rear (normal display)	O (KLL) Signal: Si at rear -> SiOx at rear
	.
Si (KLL) Signal: Si at front -> SiOx at rear (normal display)	C (KLL) Signal: Si at front -> SiOx at rear (normal display)
AES Chemical State Spectra from Sio exposed bulk using High Energy Resolution (HSA)
Si (KLL) Signal: Low Energy Resolution Mode (4%)	Si (KLL) Signal: High Energy Resolution Mode (0.5%)
Si (LMM) Signal: Low Energy Resolution Mode (4%)	Si (LMM) Signal: High Energy Resolution Mode (0.5%)

Features Observed

• xx
• xx
• xx

→  Periodic Table

---

 

 

Silicon Alloys

XxCu	XxCu
→  Periodic Table
XxCu	XxCu

 

Copyright ©:  The XPS Library 

 

---

---

 

XPS Facts, Guidance & Information

→  Periodic Table 

		Element		Silicon (Si)
		Primary XPS peak used for Peak-fitting :		Si (2p)
		Spin-Orbit (S-O) splitting for Primary Peak:		Spin-Orbit splitting for “p” orbital, ΔBE = 0.602 eV
		Binding Energy (BE) of Primary XPS Signal:		100.0 eV
		Scofield Cross-Section (σ) Value:		Si (2p) = 0.817
		Conductivity:		Si resistivity = SiO resistivity = Semiconductor
		Range of Si (2p) Chemical State BEs:		99 – 105 eV range   (Sio to SiF2)
		Signals from other elements that overlap Si (2p) Primary Peak:		Hg (4f)
		Bulk Plasmons:		~17 eV above peak max for pure
		Shake-up Peaks:		??
		Multiplet Splitting Peaks:		not possible
		General Information about XXX Compounds:		xx
		Cautions – Chemical Poison Warning		xx

Copyright ©:  The XPS Library 

---

---

 

Information Useful for Peak-fitting Si (2p)

• FWHM (eV) of Si (2p_3/2) from Pure Si^o :  ~0.36 eV for Si (2p_3/2) peak using 10 eV Pass Energy with no ion etching
• FWHM (eV) of Si (2p_3/2) from SiO₂ xtal:  ~1.32 eV for Si (2p_3/2) using 50 eV Pass Energy  (exposed bulk – cleaved in air)
• Binding Energy (BE) of Primary Signal used for Measuring Chemical State Spectra:  99.5 eV for Si (2p_3/2) with +/- 0.1 uncertainty
• List of XPS Peaks that can Overlap Peak-fit results for Si (2p):  Hg (4f)

→  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) = ~0.95 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 

---

 

Contaminants Specific to Silicon

• Silicon develops a thin native oxide due to the reactive nature of clean Silicon .
• The native oxide of SiO_x is 2-3 nm thick.
• Silicon thin films often have a low level of iron (Fe) in the bulk as a contaminant or to strengthen the thin film
• Silicon 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 

---

 

Data Collection Guidance

• Chemical state differentiation can be difficult
• Collect principal Si (2p) peak as well as Si (2s).
• Long time exposures (high dose) to X-rays can degrade various polymers, catalysts, high oxidation state compounds
• During XPS analysis, water or solvents can be lost due to high vacuum or irradiation with X-rays or Electron flood gun
• Auger signals can sometimes be used to discern chemical state shifts when XPS shifts are very small

→  Periodic Table 

---

 

Data Collection Settings for Silicon (Si)

• Conductivity:  Silicon 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:  Si (2p) at 10 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:  90-110 eV
• Recommended Extended BE Range for Measuring Chemical State Spectrum:  90- 160 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 

---

 

Effects of Argon Ion Etching

• Carbides appear after ion etching Si and 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 

---

 

---

---

End of File