UNIVERSAL MODEL FOR THE SURFACE-ENERGY OF SOLIDS

The surface energy σ is considered as the work done in reversibly cleaving a bulk solid. Let F(z) be the force per unit area required to increase the spacing between the end planes from a to a+z. For small z, F(z)=Az, where we show how A can be determined from the bulk phonon spectrum, and for large z, F(z)=Cz3, where C can be determined from the bulk frequency-dependent dielectric constant. We assume that, apart from scale, the function F(z) has a universal shape f*(z). It then follows that σ=α*(AC)12 where α* is a universal constant. Preliminary comparison with experiment gives good results with α*=0.476. © 1979 The American Physical Society.