Boron

Boron • Metalloid

Primary XPS region: B1s
Overlapping regions: Si2s plasmon, P2s, Zr3d
Binding energies of common chemical states:

Chemical state	Binding energy
B elemental	187.2 eV
ZrB₂	187.8 eV
B sub-oxide^[1]	188.6 eV
Li₂B₄O₇	192.5 eV

Charge referenced to adventitious C1s peak at 284.8eV.

Experimental information

B1s peak has very low sensitivity.
- Use a large number (50) of scans when acquiring B1s spectrum if boron is present in low concentrations.

Interpretation of XPS spectra

When boron is implanted in silicon, the strong Si2s plasmon loss feature strongly overlaps the B1s region.
- Restricts detection of low concentrations of boron implanted in silicon.
- Detection limit for boron in silicon is 7×1020 atoms cm^-3.
  - Actual detection limit depends on implantation depth (more readily visible at surface).

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In the example shown above, the Si2s plasmon has been empirically fitted (this does not represent a theoretically rigorous treatment of the plasmon shape).
It is difficult to confidently assign B1s peak for low concentrations when no secondary peak is observed.
- For high enough concentrations of boron, the B KLL Auger peak will be observed.

X-Ray Induced B KLL spectrum of elemental boron

General comments

Elemental boron samples are usually oxidized at the surface.
- May observe sub-oxide rather than B₂O₃.

References

[1] Ong et al., J. Appl. Phys., Vol. 95, No. 7, 1 April 2004.

About this element

Symbol: B
Date of discovery: 1808
Name origin: Arabic buraq
Appearance: brownish
Discoverer: Sir Davy, et al.
Obtained from: kernite

Melting point: 2349 K
Boiling point: 4200 K
Density[kg/m³]: 2460
Molar volume: 4.39 × 10^-6 m³/mol
Protons/electrons: 5
Neutrons: 6
Shell structure: 2,3
Electron configuration: [He]2s22p1
Oxidation state: 3
Crystal structure: rhombohedral

Although compounds of boron have been known for thousands of years, the element itself was not isolated until Sir Humphry Davy, Gay-Lussac, and L.J. Thenard isolated it to about 50% purity in 1808. Jöns Jacob Berzelius later identified boron as an element in 1824 and American chemist, W. Weintraub, produced pure boron for the first time in 1909. Boron is not found in its elemental form in nature, but is found in compounds. Compounds of boron have many applications: they are used in making insulating fiberglass, sodium perborate bleach, pyrotechnic flares, and making high-strength, lightweight materials primarily important for advanced aerospace structures.

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