Electron microscopy
Argon (Ar)
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The electronic configuration of Ar is 1s2 2s2 2p6 3s2 3p6. Because the third energy level has eight electrons (full), it is called a Nobel Gas.

As listed in Table 3217, substances with large bonding energies usually have high melting temperatures.

Table 3217. Bonding energies and melting temperatures of van der Waals bonding-type substances.

Bonding type

Bonding energy
Melting point (°C)
kJ/mol kcal/mol eV/Atom, Ion, or Molecule
van der Waals
Typical value 0.1-10      
Ar 7.7 1.8 0.08 -189
Cl2 31 7.4 0.32 -101

Argon contents are often detected in EM (TEM or SEM) samples in the two cases:
         i) The EM samples are milled or finally cleaned using argon ion beam sputtering. This argon contamination is extremely severe especially when high angle milling is used.
         ii) The analyzed films are produced using PVD (physical vapor deposition) technique with argon bombardment. The atomic radius of Ar+ is 0.154 nm, and thus generally argon is believed to be incorporated at grain boundaries.

In electron microscopes, both EELS and EDS techniques can normally be used to detect argon contents in materials.