Silicon • Metalloid

Primary XPS region: Si2p
Overlapping regions: Al2p plasmon, La4d
Binding energies of common chemical states:

Chemical stateBinding energy Si2p / eV
Si element99.4
Organic Si~102

Silicates and nitride referenced to C1s at 284.8eV

Experimental Information

  • In the presence of high lanthanum concentrations, acquire Si2s as well as (or instead of) Si2p peak.

Interpretation of XPS Spectra

  • Si2p peak has closely spaced spin-orbit components (Δ=0.63eV)
    • Normally only needs to be considered for elemental Si.
      • Splitting may be ignored for Si2p peaks from silicon compounds.
  • Observed as either two distinct, symmetric components (at low pass energy) or as single, asymmetric peak (at higher pass energy).
  • Observed spectral resolution of spin-orbit components is affected by the crystallinity/amorphous character of the elemental silicon.
    • More crystalline, better resolution of spin-orbit components.
    • More amorphous (caused by Ar+ sputtering, for example), worse resolution of spin-orbit components.

General comments

  • Silicon is the basis of semiconductor manufacture and silicon wafers are the most common substrate.
  • Silicon will usually have a native oxide of a few angstroms thickness although the exact thickness will depend upon the nature of the final surface cleaning.
    • The relative intensities of the oxide and elemental peaks will also change with oxide thickness.
    • This effect allows XPS to measure the thickness of Si oxide films.
  • H-passivated or H-terminated silicon has a treatment which replaces surface Si-Si dangling bonds with Si-H bonds. These prevent the formation of a surface oxide layer.
  • Organic silicon compounds are widely used as lubricants and release agents especially in the preparation of polymer materials.
    • Traces of silicon may therefore be observed on polymer surfaces.
    • Can also be present on other materials which may have been in contact with other surfaces e.g., polythene bags.
    • Spectrum below is from typical “as received” industrial PET film and shows Si contamination (siloxane).

About This Element

Symbol: Si
Date of Discovery: 1787
Name Origin: Latin silex
Appearance: dark gray, bluish tinge
Discoverer: Antoine Lavoisier
Obtained From: silicon dioxide or silicate

Melting Point: 1414 K
Boiling Point: 2900 K Density[kg/m3]: 2.33
Molar Volume: 12.06 × 10-6 m3/mol Protons/Electrons: 14
Neutrons: 14
Shell Structure: 2,8,4
Electron Configuration: [Ne]3s23p2
Oxidation State: 4
Crystal Structure: Cubic

Present in the sun and stars, silicon is the second most abundant element, making up over a quarter of the earth’s crust. Silicon is important in both animal and plant life. However, it can cause the serious lung disease silicosis if siliceous dust is inhaled. This dust, the most common form of silicon, is silvery gray with a bluish tinge. As an important ingredient in several materials such as glass, aluminum, and steel, silicon can be used to make bricks or concrete, computer chips, and silicone implants used in a variety of medical applications.