Fig. 2
Highly delocalized LUMO state of C60 on BP. a STM image of a C60 monolayer island on BP obtained with Vb = 0.80 V and I = 30 pA. The image appears like a 2D herringbone stich pattern knitted fabric. C60 ball-and-stick models are superimposed on the STM image in the inset to relate the molecular structure of C60 with the wave-like contrast. b Position-dependent STS spectra obtained on a typical C60 molecule within the island. The STS data are recorded at locations around a C60 molecule shown in the STM image. The STS dI / dV spectra in the inset are taken over a larger energy range, to record the band gap of C60 molecules. The main unoccupied features due to the LUMO are highlighted in the inset. A low energy shoulder, which has not been observed from previous work, is highlighted by the light-green rectangle. c Position-dependent STS spectra obtained for C60 molecules approaching an edge of a monolayer island. The colored dots correlate the STS spectra with molecule locations; spectra show that the shoulder feature gradually fades when approaching the island edge (blue and green spectra). d Position-dependent STS spectra acquired on the locations across the C60/BP edge. The light-green rectangle highlights the energy region where the spectroscopic shoulder feature is observed. (e) STS spectroscopic image recorded monitoring the shoulder feature in (b) at 0.80 V. The DOS distribution appears delocalized in both the arm-chair and zig-zag directions skirting the indicated C60 molecule centers. The black circles in the enlarged image of the insert indicate the four arms connecting C60 molecules in the arm-chair direction. The blue circles indicate the two arms in the zig-zag direction. The arms of C60 knit the 2D delocalized electronic net of the monolayer. The STM topography images are obtained at 77 K and the dI/dV spectra and the dI/dV mapping at 4.5 K
