1Nucleation Nucleation –Concept of Surface EnergyConcept of Surface EnergyDifferential Energy dE cost for creating a surface are dAdAdGγ=bFdx)b(dAFdxdAWdE22=====γγγγδdAVdPSdTdGdAPdVTdSdEγγ++−=+−=Force per unit length of the circumference (N/m) is the surface tension and in case of the liquids surface energy per unit area (J/m2) is the same as the surface tensionPhysical understanding of the origin of surface energyPhysical understanding of the origin of surface energy!Why is there a surface energy associated with solid surfaces?!What is the physical explanation/interpretation?!No bonds from the top. Compared to bulk the bonding may not be satisfied.!Surface energy tries to minimize itself by diffusion. If surface diffusion is fast the nuclei will expose the lowest energy surfaces.!γdepends on ⇒Chemical composition⇒Atomic scale roughness⇒Atomic scale reconstruction⇒Crystallographic orientation!Example: (111) plane of an FCC structure is the closest pack plane. The # of bonds in the plane is maximized and the number out of the plane are minimized. Consequently 100111fccfccγγ<
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