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| An analytical solution shows that a competition between bond order loss and the associated bond strength gain of the lower coordinated atoms near the edge of a surface dictates the mechanics of the surface and hence a nanosolid. Bond order loss lowers the activation energy for atomic dislocation whereas bond strength gain enhances the energy density, or mechanical strength, in the region near the surface. Therefore, the surface is harder than the bulk interior at temperature far below the melting point (Tm) and the surface becomes softer at temperature closing to the surface Tm that drops because of bond order loss. Matching predictions to measurements reveals that transition happens to the Hall-Petch relationship for a nanosolid when the effect of bond order loss becomes dominant and the critical size of Hall-Petch transition depends intrinsically on the bond nature of the specimen and the ratio of T/Tm, where T is the temperature of operation. |
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| Keywords:nanostructures, surface, mechanics |
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