STM imagery and density functional calculations of C${}_{60}$ fullerene adsorption on the 6H-SiC(0001)-3$\ifmmode\times\else\texttimes\fi{}$3 surface

STM imagery and density functional calculations of C $_{60}$ fullerene adsorption on the 6H-SiC(0001)-3 $\times$ 3 surface

T. Ovramenko, F. Spillebout, F. C. Bocquet, A. J. Mayne, G. Dujardin, Ph. Sonnet, L. Stauffer, Y. Ksari, and J.-M. Themlin

Phys. Rev. B 87, 155421 – Published 17 April 2013

Abstract

Scanning tunneling microscopy (STM) studies of the fullerene C $_{60}$ molecule adsorbed on the silicon carbide SiC(0001)- $3 \times 3$ surface, combined with density functional theory (DFT) calculations, show that chemisorption of individual C $_{60}$ molecules occurs through the formation of one bond to one silicon adatom only in contrast to multiple bond formation on other semiconducting surfaces. We observe three stable adsorption sites with respect to the Si adatoms of the surface unit cell. Comprehensive DFT calculations give different adsorption energies for the three most abundant sites showing that van der Waals forces between the C $_{60}$ molecule and the neighboring surface atoms need to be considered. The C $_{60}$ molecules are observed to form small clusters even at low coverage indicating the presence of a mobile molecular precursor state and nonnegligible intermolecular interactions.

Received 15 May 2012

DOI:https://doi.org/10.1103/PhysRevB.87.155421

Authors & Affiliations

T. Ovramenko¹, F. Spillebout², F. C. Bocquet³, A. J. Mayne^1,*, G. Dujardin¹, Ph. Sonnet², L. Stauffer², Y. Ksari³, and J.-M. Themlin³

¹Institut des Sciences Moléculaires d'Orsay, CNRS, UMR 8214, Université Paris Sud 11, 91405 Orsay, France
²Institut de Science des Matériaux de Mulhouse, CNRS UMR 7361, Université de Haute Alsace, 68093 Mulhouse, France
³Aix-Marseille Université, CNRS, IM2NP-UMR 7334, 13397 Marseille, France

^*Email address: andrew.mayne@u-psud.fr

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Vol. 87, Iss. 15 — 15 April 2013

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Figure 1
STM images and adsorption positions of C $_{60}$ on the SiC(0001)- $3 \times 3$ surface. (a), (b) Low-coverage 20.5 × 20.5 nm STM images of the C $_{60}$ deposited on SiC(0001) [tunneling conditions: $U$ $=$ −4 V, $I$ $=$ 0.5 nA (a); $U$ $=$ $+$ 2.5 V, $I$ $=$ 0.3 nA (b)]. (c)–(e) Magnified views of three individual C $_{60}$ molecules; the contours of Si adatom positions are marked by the small continuous circles (images size $2.5 \times 2.5$ nm); (c) C $_{60}$ adsorbed on top (1), (d) C $_{60}$ adsorbed between two Si adatoms (2), and (e) C $_{60}$ adsorbed between three Si adatoms (3). Height scales are shown for (a), (c) and (b), (d), (e).Reuse & Permissions
Figure 2
A series of six STM images illustrating the method used to determine the position of the C $_{60}$ molecule with respect to the underlying Si adatoms. (a) Choose the C $_{60}$ to be analyzed, (b) select a small area of the clean SiC surface adjacent to the molecule in question, (c) the selected small area is made partially transparent and placed over the C $_{60}$ molecule so that the adatoms overlap perfectly. (d) The small rectangle is made opaque to hide the molecule, (e) circles are then placed on the seven or so adatoms that are “under” the molecule so that the center of each circle is concentric with the center of each adatom; position error ±0.5 Å. (f) Remove the small area so that the molecule is again visible leaving the circles in place indicating the adatom positions. STM image size $8.5 \times 8.5$ nm, $U$ $=$ $+$ 2.5 V, $I$ $=$ 0.3 nA.Reuse & Permissions
Figure 3
Statistical analysis of the positions of 50 isolated C $_{60}$ molecules. (a) Schematic diagram showing the measured positions of the C $_{60}$ molecules (blue spots) with respect to the Si adatom + trimer pyramids (red & orange tripods) of the SiC(0001)- $3 \times 3$ surface. The estimated position error of ±1 Å is twice the diameter of each blue spot. The dotted brown circle has a radius of 2.8 Å. (b) The radial distribution of the molecular positions from the center Si adatom. (c) Angular distribution over 360° is folded into a 60° segment in 5° bins, for the positions outside the 2.8 Å circle.Reuse & Permissions
Figure 4
Calculated ball and stick structure of the C $_{60}$ molecule on the SiC surface. Top and side views of a single C $_{60}$ molecule positioned (a) on top (1), (b) between two (2), and (c) between three (3). In the schematic diagrams, only the Si pyramid atoms of the SiC(0001) reconstruction are shown underneath the C $_{60}$ molecule. (d)–(f) Isodensity maps of the C $_{60}$ molecule on the SiC surface for the energy range of −3.5 to −3.0 eV (isodensity $=$ 0.028 $e^{-}$ /Å $^{3}$ ) showing the density of states associated with the Si-C bond (black circles) for (d) the on-top (1), (e) between two (2), and (f) between three (3) sites.Reuse & Permissions
Figure 5
(a) DFT calculations of the density of states for the entire C $_{60}$ molecule in the gas phase (blue) and adsorbed (orange) between −3 and $+$ 3 eV. (b) Isodensity map of the C $_{60}$ molecule on the SiC surface [in configuration (3)] within the energy window from −0.35 to 0 eV (isodensity $=$ 0.028 $e^{-}$ /Å $^{3}$ ). This corresponds to the peak at $E_{F}$ marked in (a). (c) Same isodensity map as in (b) as viewed from the side; the arrow in (b) indicates the direction of vision. (d) Isodensity map of the clean SiC surface in the same energy range as (b) and (c) (isodensity $=$ 0.028 $e^{-}$ /Å $^{3}$ ).Reuse & Permissions
Figure 6
STM images of the C $_{60}$ molecules showing clustering at low coverage. (a) $30 \times 30$ nm STM topography showing individual C $_{60}$ molecules and clusters [tunneling conditions: −3 V, 0.3 nA; height scale is given for (a) only as (b) is identical]. (b) The same image as in (a) overlaid by a square grid. Two different grid sizes were used; the first contains 64 squares of $3.75 \times 3.75$ nm, while second one contains 256 squares, each $1.88 \times 1.88$ nm.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

STM imagery and density functional calculations of C $_{60}$ fullerene adsorption on the 6H-SiC(0001)-3 $\times$ 3 surface

T. Ovramenko, F. Spillebout, F. C. Bocquet, A. J. Mayne, G. Dujardin, Ph. Sonnet, L. Stauffer, Y. Ksari, and J.-M. Themlin

Phys. Rev. B 87, 155421 – Published 17 April 2013

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Physical Review B

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STM imagery and density functional calculations of C60 fullerene adsorption on the 6H-SiC(0001)-3×3 surface

T. Ovramenko, F. Spillebout, F. C. Bocquet, A. J. Mayne, G. Dujardin, Ph. Sonnet, L. Stauffer, Y. Ksari, and J.-M. Themlin

Phys. Rev. B 87, 155421 – Published 17 April 2013

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STM imagery and density functional calculations of C $_{60}$ fullerene adsorption on the 6H-SiC(0001)-3 $\times$ 3 surface