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Unformatted text preview: 1 Nucleation Nucleation Concept of Surface Energy Concept of Surface Energy Differential Energy dE cost for creating a surface are dA dA dG = b F dx ) b ( dA Fdx dA W dE 2 2 = = = = = dA VdP SdT dG dA PdV TdS dE + + = + = 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/m 2 ) is the same as the surface tension Physical understanding of the origin of surface energy Physical 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. ! depends 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 100 111 fcc fcc < 2 Physical understanding of the origin of surface energy Physical understanding of the origin of surface energy ! Charge neutrality @ the surface leads to lower...
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This note was uploaded on 12/29/2011 for the course CHE 142 taught by Professor Ceweb during the Fall '09 term at UCSB.
- Fall '09