Anomalous heat capacity of nanoparticles

The heat capacity of nanosized particles exceeds (from few to tenth percents) the same values of the corresponding bulk materials, and this difference increases with the diminishing of the sizes. In the present Letter we give an explanation of this phenomenon on an example of a nanocrystal with simple cubic lattice and an arbitrary shape. The simplest harmonic interaction potential of the nearest neighbors is used. A qualitative agreement with experimental data is obtained. The decisive role is attributed to the choice of boundary conditions: free boundaries provide the "softening" of vibrational spectrum thus giving larger contribution to the heat capacity. The increase in heat capacity depends on the particle size, shape and sample perfection. (c) 2006 Elsevier B.V. All rights reserved.