Desorption of Fullerene Dimers upon Heating Non-IPR Fullerene Films on HOPG

Abstract

Low energy ion beam deposition of mass-selected fullerene ions was used to generate thin films of non-IPR fullerenes, C2n (2n = 48–58 and 52–68) on graphite under UHV. These were probed by mass-resolved thermal desorption spectroscopy. We observe the emission of dimers in addition to dominant monomer desorption for 2n = 58–68, while for 2n = 48–56 no dimer desorption was detected. Dimer signals were typically at <1% level compared to the monomers. The desorption temperature ranges of these dimer species were higher and much narrower than for the corresponding monomers. Building also on theoretical considerations, we came to the conclusion that coalescence reactions between the fullerenes must take place below 1000 K and that fullerenes with more than three pairs of adjacent pentagons cross-link too strongly to allow the desorption of dimers.

High‐Purity Er3N@C80 Films: Morphology, Spectroscopic Characterization, and Thermal Stability

“…In order to avoid issues due to the transmission of the analyzer (see supplement of ref. [37]), we measured the intensity of Er 3 N@C 2þ 80 , which is expected to be similar to the single charged species [9] at our settings. The desorption takes place around a maximum of 667 K, which is 110 K higher than for C 60 (see also Ulbricht et al and Weippert et al [37,41] ) and 70 K higher than for C 70 .…”

“…[69] We observed nearly the same AFM topography of the surface created by heating thin C 58 films deposited by LECBD on HOPG. [37] The C 58 aggregates covalently pinned by step edges (surviving the HT treatment) were identified as oligomers consisting of fused or/and multifold covalently interlinked C 58 cages. Yet, we have to acknowledge the possibility that these aggregates are not fused but rather debris that resulted from the cages cracking in a similar manner as N@C 60 does [7] at elevated temperatures.…”

“…HOPG was chosen as a substrate as it is conducting and rather inert and is a tried and tested substrate for fullerene film growth with this particular method. [35][36][37]39] The nominal coverage was determined by integrating the ion current; it has previously been determined [35] that in this setup 20 nAmin of fullerenes corresponds to 1 monolayer (ML) equivalent.…”

“…These cages may form bonds both via vdW interaction and via polymerization that may occur both directly at the adjacent pentagon site and in its vicinity. [37] Figure 2B shows one example illustrating the initial growth stage of C 58 islands on HOPG. All imperfections in the basal plane are more reactive than the sp 2 -hybridized network of the graphene layer and consequently act as pining sites where the nucleation of small 2D-C 58 islands onsets.…”

“…[34] In the last two decades we routinely applied the low-energy cluster beam deposition technique (LECBD) to grow monodispersed IPR (C 60 , C 70 ) and non-IPR (C 58 À C 48 and C 68 À C 62 ) fullerene films. [35][36][37] The study of the film growth and thermal stability has proven to be a valuable way to explore the interaction and possible reactions between the cages with respect to their structure. In the unique case of the non-IPR fullerenes the morphology of the films is primarily governed by the ability of the gently landed cages to form covalent intercage C─C bonds bridging the nearest non-IPR sites.…”