Face centered cubic indium nano-particles studied by UHV-transmission electron microscopy

Structures of indium nano-particles of 3-20 nm were observed by ultra-high vacuum transmission electron microscopy. Structural fluctuation of such sma ll particles was suppressed by cooling the temperature down to 120 K. Indiu m nano-particles were found to have face centered cubic (fcc) structure bel ow 5 nm in diameter. The larger particles had the body centered tetragonal (bct) structure of the bulk crystal. The particles of fee and bet structure s had different morphology. Wulffs criterion for their morphologies showed equalization of the surface energies of the (111), (100) and (001) facets f or the fee nano-particles. Theoretical estimation of the elastic energy and free energy suggested that structure change to fee can occur at 5 nm, if t he 2% expansion of the a-axis (4% compression of the c-axis) of the bet lat tice results in the 4% increase of the {1 1 1} surface energy. (C) 2001 Els evier Science B.V. All rights reserved.