First principles study of the adsorption of C60 on Si(1 1 1)

Abstract

Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in:Surface science 482 (2001) The adsorption of C60 on Si(111) has been studied by means of first-principles density functional calculations. A 2x2 adatom surface reconstruction was used to simulate the terraces of the 7x7 reconstruction. The structure of several possible adsorption configurations was optimized using the ab initio atomic forces, finding good candidates for two different adsorption states observed experimentally. While the C60 molecule remains closely spherical, the silicon substrate appears quite soft, especially the adatoms, which move substantially to form extra C-Si bonds, at the expense of breaking Si-Si bonds. The structural relaxation has a much larger effect on the adsorption energies, which strongly depend on the adsorption configuration, than on the charge transfer.

C60adsorption on theSi(111)-p(7×Rurali1, Cuadrado2, Cerdá3 2010Phys. Rev. B17072View full textAdd to dashboardCite

“…The relaxations were indeed found to be very large and essential to the stability of the adsorbed C 60 , while several metastable phases could be identified depending on the initial molecule's orientation and adsorption site in the totalenergy minimizations. 12,19 Surprisingly, the Tersoff-Hamann ͑TH͒ images at negative biases for these new optimized geometries hardly fitted the experimental images, in contrast with the simulations of Hou et al despite their guessed geometry is less reliable.…”

“…All energies are in eV and distances are in Å. with the L configuration that was found to be the most stable among those considered in Ref. 19. At this respect, it should be recalled that the CH could not be considered by Sánchez-Portal et al 19 because they did not model the full Si͑111͒-p͑7 ϫ 7͒ surface and were restricted to a ͑2 ϫ 2͒ adatom reconstruction.…”

“…19. At this respect, it should be recalled that the CH could not be considered by Sánchez-Portal et al 19 because they did not model the full Si͑111͒-p͑7 ϫ 7͒ surface and were restricted to a ͑2 ϫ 2͒ adatom reconstruction. The adsorption process and the adsorbed configurations when the C 60 is found close to the R and M positions shows qualitative differences with respect to the C positions.…”

Computing the Properties of Materials from First Principles with SIESTA

“…Two adsorption configurations are deduced from STM images: a large molecule with apparent height of~0.6 nm that appears more round and fuzzy, and a small molecule with a height of~0.5 nm which produces a clear internal structure and a large variety of shapes (orientations on the substrate) [176]. In order to identify the most favorable adsorption sites and structures and compare with the STM information, Sanchez-Portal et al [179] have made an extensive study of the structure of C 60 on the Si(111) surface using SIESTA. A 22 adatom surface was used as a model to simulate the terraces of the 77 reconstruction.…”

“…Estimated binding energies, charge transfers to the fullerene, and height of the molecule center of mass over the substrate are also indicated. Reproduced with permission from [179] bands are mainly derived from Si 3sp lobes pointing towards the Au atoms on the surface; thus they are silicon bands. The idea that the observed features are related with band structure effects, and not with spin-charge separation, seems to be confirmed by more recent photoemission studies [182].…”