Surface electron-energy-loss fine-structure investigation on the local structure of copper clusters on graphite

The lattice parameters of copper clusters deposited on graphite substrates were determined by surface extended energy-loss fine-structure measurements. The Fourier analysis of the fine structures beyond the M₂,3 copper edge shows a sizable lattice-parameter contraction when the cluster mean diameter d{} decreases. This contraction amounts to 4.7% for the particles with d{}=9 A{}. The contraction is linearly dependent on 1/d{}, which is why it was interpreted in terms of the liquid-drop model. Moreover, the observed strong enhancement of the Debye-Waller factor allowed us to estimate the decrease in melting point for small clusters. The sizable changes in the nearest-neighbor distance of our clusters are closely related to the change in the near-L₂,3-edge features. Our results are in good agreement with recent density-of-state calculations for compressed Cu crystals.