[1] Inst Venezolano Invest Cient, Ctr Quim, Caracas 1020A, Venezuela
[2] Natl Inst Stand & Technol, Phys & Chem Properties Div, Gaithersburg, MD 20899 USA
[3] Kraft Foods R&D, Nanotechnol Lab, Glenview, IL 60025 USA
[4] Harvard Univ, Dept Phys, Cambridge, MA 02138 USA
[5] Harvard Univ, DEAS, Cambridge, MA 02138 USA
[6] Los Alamos Natl Lab, Div Chem, Los Alamos, NM 87545 USA