C58 on Au(111)

N. BAJALES; S. SCHMAUS; T. MIYAMACHI; W. WULFHEKEL; M.STENDEL; A. BAGRETS; C. SEILER; F. EVERS; S. ULAS; P. WEIS; ARTUR BÖTTCHER; MANFRED M. KAPPES

Encuentro; Clustertreffen; 2011

Universitaet Wuerzburg

C58 represents the new class of carbon cages, the so called non-IPR fullerenes (IPR, isolated pentagon rule). According to DFT calculations the most stable C58 isomer exhibits two adjacent pentagons in its cage structure, which clearly violate the isolated pentagon rule and act as localized reaction centres. The C58 cages have been deposited on the reconstructed Au(111) surface by means of low-energy cluster beam deposition technique, LECBD [1] extended by quadruple-based mass selection. The properties of thin C58 films have been studied by means of STM (4K) supported by ultraviolet photoionization spectroscopy, UPS, and thermal desorption spectroscopy, TDS. Within the very initial deposition stage the individual C58 cages occupy the elbows of the herringbone reconstruction preferentially. In the topography mode the isolated cage exhibits internal asymmetric structures which extend over an area of ~1.2 nm in diameter. At very low coverages dimers, [C58]2, and trimers, [C58]3, have been identified as well. The isolated cages act as nucleation centres what manifests itself by growth of 3D islands instead to complete the 2D monolayer. C58-TDS analysis shows that the individual cages do not escape from the surface due to heating the sample up to 1000 K, i.e. their estimated binding energy overcomes ~3 eV. Only at coverages >0.5 MLE (5x1013 cage/cm2) detectable emission of C58 cages peaked at ~820 K has been observed. This desorption band reveals the thermal decomposition of the quasi-covalent intercage bonds, C58-C58. The initial adsorption stage is accompanied by gradual destruction of the characteristic surface state (peak in the DOS structure ~380 meV below the Fermi level). This state can not be reactivated by heating the sample up to 1000°C because of the strongly bound C58 leftover. Local density of HOMO and LUMO states has been measured by means of STS for multilayered C58 films. A HOMO-LUMO gap of 1.2 eV has been derived in perfect agreement with previous UPS-measurements of the alkali-metal doped thick C58 films [2]. References [1] A. Böttcher, P. Weis, A. Bihlmeier, and M.M. Kappes, PCCP 6, 5213 (2004). [2] D. Löffler, S. Ulas, S.-S. Jester, P. Weis, A. Böttcher, M.M. Kappes, PCCP 12, 10671 (2010).