Rotational Excitation Spectroscopy with the STM through Molecular Resonances

Abstract

We investigate the rotational properties of molecular hydrogen and its isotopes physisorbed on the surfaces of graphene and hexagonal boron nitride ($h$-BN), grown on Ni(111), Ru(0001), and Rh(111), using rotational excitation spectroscopy (RES) with the scanning tunneling microscope. The rotational thresholds are in good agreement with $\Delta J=2$ transitions of freely spinning para-H${}_2$ and ortho-D${}_2$ molecules. The line shape variations in RES for H${}_2$ among the different surfaces can be traced back and naturally explained by a resonance mediated tunneling mechanism. RES data for H${}_2$/$h$-BN/Rh(111) suggests a local intrinsic gating on this surface due to lateral variations in the surface potential. An RES inspection of H${}_2$, HD, and D${}_2$ mixtures finally points to a multi molecule excitation, since either of the three $J=0\to 2$ rotational transitions are simultaneously present, irrespective of where the spectra were recorded in the mixed monolayer.

References in corpus (3)

• Unit cell of graphene on Ru(0001): a 25 x 25 supercell with 1250 carbon atoms
• Vibrationally Induced Two-Level Systems in Single-Molecule Junctions
• Huge negative differential conductance in Au-H2 molecular nanojunctions

Cited by in corpus (2)

• Creating and Probing Electron Whispering Gallery Modes in Graphene
• Probing Magnetic Excitations and Correlations in Single and Coupled Spin Systems with Scanning Tunneling Spectroscopy