Growth and characterization of fullerene nanocrystals on NaCl/Au(111)

Abstract

The growth of fullerene nanocrystals, composed of only C(60), only C(70), or a mixture of both fullerenes, has been investigated by scanning tunneling microscopy (STM). The nanocrystals, formed on a NaCl ultrathin layer partially covering a Au(111) surface, have characteristic truncated-triangular or hexagonal shapes, with lateral size up to 100 nm and a typical height of two to four molecular layers. This growth mode differs considerably from the ones observed on metallic surfaces. STM images with biasdependent submolecular resolution reveal the spatial distribution of the electronic density originating from the molecular orbitals. A comparison of the experimental results with first-principles density functional theory calculations allows us to unambiguously determine the orientation and the nature of individual fullerene molecules in the surface layer of the nanocrystals. Growth and characterization of fullerene nanocrystals on NaCl/Au(111) The growth of fullerene nanocrystals, composed of only C60, only C70, or of a mixture of both fullerenes, has been investigated by Scanning Tunneling Microscopy (STM). The nanocrystals, formed on a NaCl ultrathin layer partially covering a Au(111) surface, have characteristic truncatedtriangular or hexagonal shapes, with lateral size up to 100 nm and a typical height of two to four molecular layers. This growth mode differs considerably from the ones observed on metallic surfaces. STM images with bias-dependent submolecular resolution reveal the spatial distribution of the electronic density originating from the molecular orbitals. A comparison of the experimental results with first principle Density Functional Theory (DFT) calculations allows us to unambiguously determine the orientation and the nature of individual fullerene molecules in the surface layer of the nanocrystals.

Luminescence experiments on supported molecules with the scanning tunneling microscope

“…The observed site-dependent rigid shift of the entire luminescence spectra of C 60 and C 70 nanocrystals [40] gives a direct experimental evidence of the local character of the technique in the presence of an ensemble of molecules, since it is likely to be related, respectively, to the intermolecular orientational correlation in a pair of C 60 molecules over which the excitation is delocalized [196,182,197] and to the sensitivity of the lowest excited electronic states of the C 70 molecule to the environment in which it is trapped [192,186]. The weak interactions with the surrounding molecules may vary with the probed sites due to orientational disorder and to the presence of lattice defects [195].…”

“…19(a)-(c), has also been investigated. The sample was prepared by simultaneous sublimation of high purity powders of each type of fullerene, and the selected molecules in the surface layer were identified as C 60 and C 70 by comparing the STM-imaged orbitals [198,39,195] with DFT calculations [195]. The interesting observation is that the obtained two spectra, see Fig.…”

“…With this procedure, nanocrystals formed by a central part of C 70 and a rim of C 60 can be obtained, see Fig. 20 [195]. In the STM-LE measurements, the sole molecular signature of the considered area is identified down to a distance of about 1.5-2 nm from the boundary between both molecular species, as shown in Fig.…”

Characterization of PTCDA nanocrystals on Ge(001):H-(2×1) surfaces

“…For the purpose of the presented study it is convenient to focus on methods based on formation of an ultrathin buffer layer to assure the decoupling. For example, in case of metal surfaces such a scenario is realized by means of few monolayers of insulator, like NaCl [5][6][7][8][9][10][11][12][13], for semiconductor surfaces it might be either few monolayers of insulator, like KBr on InSb [14,15], or a single layer of atomic hydrogen, e.g. Si:H and Ge:H surfaces [16][17][18][19][20].…”

“…Si:H and Ge:H surfaces [16][17][18][19][20]. The buffer layer dramatically enhances mobility of adsorbed molecular species and eventually may ease their selfassembly and formation of molecular nanocrystals [9][10][11]20,21].…”