DEGRADATION OF C60 NANOCRYSTALS ON SI(111)-(7×7) SURFACES UPON LOW-ENERGY ELECTRON IMPACT

ISSN： 1058-725X

Source： Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, Vol.386, Iss.1, 2002-01, pp. : 129-133

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Abstract

Electron irradiation of thin (4-6 monolayers) nanocrystals of C₆₀ fullerenes formed on Si(111)-(7×7) substrates were performed with intense flux of field-emission (FE) electrons (10⁵-10⁸ electrons nm^-2 s^-1) extracted at 10-100 V from probe tips of a scanning tunneling microscope (STM). At extraction voltage of 10-30 V, stimulated migration of C₆₀ caused long-lasting changes of morphology of nanocrystals on a time scale of minutes after irradiation. With increase of extraction voltage beyond 40 V, fragmentation of C₆₀ became dominant leading to creation of large carbon structures with apparent height of 0.4-1.5 nm as a result of coalescence of fragments. The contributions of different phenomena including polymerization and evaporation to nanocrystal degradation vary with electron energy and dose.