Direct observation of the homogeneous nucleation of manganese in the vapor phase and determination of surface free energy and sticking coefficient

We examined the homogeneous condensation of thermally evaporated manganese vapor in an atmosphere of argon gas and determined the temperature and concentration during homogeneous nucleation in the vapor phase by using a Mach-Zehnder type interferometer. Condensation occurred at 660-785 K below the equilibrium temperature and the degree of supersaturation was as high as ∼5 × 10 ⁴. Using the condensation temperature and size of the condensed particles, which were measured by transmission electron microscopy, we determined the surface free energy and sticking coefficient of Mn at 1106 ± 50 K to be 1.55 ± 0.10 J/m ² and 0.39-0.20 _+0.39, respectively, by classical nucleation theory (CNT) and 1.57 ± 0.35 J/m ² and 0.42-0.21 _+0.42, respectively, by a semiphenomenological theory (SP). The nucleation theories predict that the critical nucleus contains only three and six atoms for CNT and SP, respectively, which are fewer than the number of atoms in a unit cell of Mn. This suggests that the polymorphic form of manganese is decided during particle growth rather than during nucleation from the vapor phase.