From vapor to adatoms

Atoms in the vapor come into contact with the substrate surface where 

10 eV/K is the Boltzmann constant and Tv is the absolute temperature of the vapor. If the vapor becomes supersaturated, a free energy difference between the vapor and the interior of the crystal exists, providing a chemical potential for driving the advance of the interface toward the vapor. As the interface advances in a self-similar way, a remote layer of vapor of some mass is converted into an interior layer of crystal of the same mass. The interface does not advance or retreat when these energies are identical. 

In film deposition, the situation is often complicated by the fact that the vapor and the substrate are not phases of the same material, and by the fact that the temperature of the substrate is usually lower than that of the vapor. The definition of equilibrium vapor pressure is not so clear in this case. However, in most cases there will be some level of vapor pressure below which deposition of film material onto the growth surface will not occur this serves as an operational definition of Pe for film growth. 

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