What is surface energy?

[Titans86]

I checked Wiki and ran a forum search, yet I am in need of an explanation of "Surface Energy" that works for me.

I'm clueless on the concept...

(btw, just joined physics forums today, seems like a really cool community here...)

 

[handsomecat]

I checked Wiki and ran a forum search, yet I am in need of an explanation of "Surface Energy" that works for me.

I'm clueless on the concept...

(btw, just joined physics forums today, seems like a really cool community here...)

Surface energy is the additional energy per unit surface area for a system of atoms with a surface.

Imagine that you have a perfect FCC crystal of 3 × 3 × 3 unit cells with periodic boundary conditions in all 3 directions. This means that it is effectively an infinite perfect crystal. Let's call this system A.

Then you have the same 3 × 3 × 3 unit cells but with periodic boundary conditions in 2 directions. Effectively, this is a thin film with a perfect crystal, and you have two surfaces. Let's call this system B.

Clearly system B will have higher energy because of the surface.

Surface Energy = (Energy of B - Energy of A)/(Total Surface Area).

You can have surface with different crystal orientations, eg (100) or (111) and the surface energy will be different.

 

[saray1360]

total surface area of the unit cell ?! or ...