ABSTRACT
The atomic volume can be calculated without the use of crystallography. The
atomic density N of atoms per cubic centimeter is given by
(1.3)
= ρN N A
where NA is Avogadro’s number, ρ is the mass density in grams per cubic centimeter, and A is the atomic mass number. Taking Al as an example, where ρ is 2.7 g/cm3 and A is 27, the atomic density is N = (6.02 × 1023 × 2.70)/27 = 6.02 × 1022 atoms/cm3. The semiconductors Ge and Si have atomic densities of about 4.4 × 1022 and 5.0 ×1022 atoms/cm3, respectively. Metals such as Co, Ni, and Cu have densities of about 9 × 1022 atoms/cm3. The volume Ωv occupied by an atom is given by
(1.4) =
N 1
with a typical value of 20 × 10-24 cm3. The average areal density of a monolayer, Ns atoms/cm2, also can be esti-
mated without the use of crystallography by taking the atomic density N to the 2/3 power:
Equation (1.5) gives the average areal density of one monolayer for a material
with an atomic density N. Based on this equation, the average areal density Ns for Al is approximately 1.54 × 1015 atoms/cm2.
