Charge transfer and screening in individualC60molecules on metal substrates: A scanning tunneling spectroscopy and theoretical study

Abstract

We have used scanning tunneling microscopy and spectroscopy to study the electronic structure of individual C 60 molecules adsorbed onto the Au(111) and Ag(100) surfaces. C 60 molecules on Au (111) show an increase in the HOMO-LUMO gap of 0.6 eV compared to C 60 on Ag(100). Splitting of the C 60 LUMO manifold is suppressed for C 60 on Au(111), in contrast to the strong splitting observed for C 60 on Ag(100). Our data implies a 0.6 eV increase in intramolecular Coulomb energy for C 60 on Au(111) as compared to C 60 on Ag(100). Topographs and energy-resolved spectral maps, however, show nearly identical features and indicate a similar influence of the two substrates on molecular-orbital geometry. C 60 -substrate bonding and charge transfer is further investigated by calculating C 60 charge redistribution using ab initio pseudopotential densityfunctional theory methods. These calculations indicate that a negligible amount of charge is transferred from Au(111) to adsorbed C 60 , while about 0.2 electron is transferred to C 60 resting on Ag (100), although the precise amount depends on the definition used. This charge transfer likely changes the electronic screening properties of C 60 , providing an explanation for observed spectroscopic differences on these two substrates.

Graphene nanogap for gate-tunable quantum-coherent single-molecule electronics

“…It has been shown by scanning Kelvin probe microscopy 47 that the application of a back-gate voltage results in a change of the graphene work function between 4.5 eV (electron doped) and 4.8 eV (hole doped). Scanning tunneling experiments and DFT calculations of C 60 on gold and silver surfaces show 48 that the charge transfer to C 60 from gold is vanishingly small, while it is of order 0.2e from silver. The work function of silver is 4.6 eV, while that of gold is 5.3 eV.…”

“…49 Previously atoms and molecules on metal surfaces 48 or large-area graphene 50 have been studied by scanning tunneling microscopy (STM) and spectroscopy (STS), and valuable details about, e.g., orbitals and charge transfer have been obtained. Scanning techniques have been utilized to reveal local information about Coulomb interactions in graphene nanostructures.…”

Scanning Tunneling Spectroscopy of Individual PbSe Quantum Dots and Molecular Aggregates Stabilized in an Inert Nanocrystal Matrix

“…The combination of STM and STS has already proved very useful in probing the geometry and electronic structure of individual atoms and molecules and molecular aggregates at the atomic scale. [6][7][8][9][10][11][12] Furthermore, these techniques have been successfully used for the investigation of individual InAs, CdSe, and PbSe QDs, [13][14][15][16][17] as well as their twodimensional arrays. 18,19 In order to study a single, isolated QD or small aggregates of QDs with STM, they have to be immobilized on a conducting substrate.…”

Single-molecule transistors: Electron transfer in the solid state

“…Assuming that the electronic density of states of the tip is relatively featureless, this technique, known as scanning tunneling spectroscopy (STS), allows the measurement of the local density of states induced by the molecule. This novel spectroscopy has been revelatory, allowing the solid state observation of the alignment and broadening of occupied molecular orbitals [1], vibronic effects [2], inelastic electron tunneling via molecular vibrations [3] and spin flips [4], and electronic correlations such as Kondo physics [5].…”