[Paper Review] Spatial corrugation and bonding of single layer graphene on Rh(111)

Mikhail Fonin, M. Sicot+7 more|arXiv (Cornell University)|Oct 7, 2010

Graphene research and applications3 citations

TL;DR

This study investigates epitaxial single-layer graphene on Rh(111), revealing a unique, highly corrugated moiré superstructure with strong bonding at 'bridge' regions of the supercell. High-resolution STM and valence-band photoemission confirm pronounced orbital hybridization between graphene and Rh(111), leading to distinct depressions in STM images and a 0.44 eV splitting in C 1s core-level spectra, indicating strong, spatially modulated interaction critical for designing graphene-based nanosystems.

ABSTRACT

Topographic scanning tunneling microscopy (STM) images of epitaxial single layer graphene on the Rh(111) surface reveal that extended single crystalline graphene domains are produced without any defects on a large scale. High resolution imaging shows that the moiré structure resulting from the lattice mismatch between the Rh(111) substrate and graphene is highly corrugated, containing regions of an additional spatial modulation in the moiré supercell compared with those previously reported for graphene on Ir(111) or graphene on Ru(0001). These areas, which correspond to the "bridge" regions of the moiré structure appear as depressions in STM images indicating a strong orbital hybridization between the graphene layer and the metallic substrate. Valence-band photoemission confirms the strong hybridization between graphene and Rh(111) which leads to the pronounced corrugation of the graphene layer. Our findings underline the importance of considering substrate effects in epitaxially grown graphene layers for the design of graphene-based nanoscale systems.

Motivation & Objective

• To understand the atomic-scale structure and bonding of epitaxial single-layer graphene on Rh(111), a system intermediate between strongly bonded graphene/Ru(0001) and weakly bonded graphene/Ir(111).
• To investigate the origin of spatial corrugation in the moiré superstructure and its correlation with electronic hybridization.
• To determine how substrate-specific interactions influence the electronic and geometric structure of epitaxial graphene.
• To compare the bonding and electronic response of graphene/Rh(111) with other graphene/metal systems, including graphene/Ni(111) and h-BN/Rh(111).

Proposed method

• Performed in situ scanning tunneling microscopy (STM) in ultra-high vacuum at room temperature using W tips, with constant-current mode and sample-biased voltage.
• Conducted low-energy electron diffraction (LEED) to verify long-range order and moiré periodicity of the graphene overlayer on Rh(111).
• Carried out valence-band and core-level photoemission spectroscopy (PES) at BESSY using a PHOIBOS 100 energy analyzer with 80 meV energy resolution.
• Used thermal decomposition of propene at 900–1100 K to grow continuous, single-crystalline graphene domains on pre-cleaned Rh(111) surfaces.
• Performed surface cleaning via Ar+ sputtering, flash-annealing to ~1500 K, and O2 annealing to ensure a pristine Rh(111) surface.
• Compared experimental results with known systems (e.g., graphene/Ru(0001), graphene/Ir(111), h-BN/Rh(111)) to highlight unique bonding characteristics.

Experimental results

Research questions

• RQ1 How does the atomic structure of the moiré supercell in graphene/Rh(111) differ from that in graphene on Ir(111) or Ru(0001)?
• RQ2 What is the origin of the pronounced spatial corrugation observed in STM images of graphene on Rh(111)?
• RQ3 How does orbital hybridization between graphene and Rh(111) vary across different regions of the moiré supercell?
• RQ4 To what extent does the electronic structure of graphene on Rh(111) reflect strong hybridization, as evidenced by photoemission spectroscopy?
• RQ5 Why does graphene/Rh(111) exhibit distinct contrast variations in STM despite a metallic nature, unlike h-BN/Rh(111)?

Key findings

• High-resolution STM reveals a unique moiré superstructure on Rh(111) with additional corrugated regions not observed in graphene on Ir(111) or Ru(0001).
• The 'bridge' regions of the moiré supercell appear as depressions in STM images, indicating strong orbital hybridization between graphene and Rh(111).
• C 1s core-level PES shows a 0.44 eV energy splitting, with the higher binding energy component attributed to strongly bonded regions (A2, A3, A4), confirming spatially modulated bonding strength.
• Valence-band PES reveals a 2.3 eV shift in π-states relative to graphite, indicating strong hybridization between graphene π-bands and Rh 4d states.
• The absence of π/σ band splitting in graphene/Rh(111), unlike in h-BN/Rh(111), suggests differences in electronic response due to graphene’s metallic character and lower corrugation effects.
• The bonding strength in graphene/Rh(111) is comparable to that in graphene/Ru(0001), but with a more complex local hybridization pattern due to distinct atomic registry in the moiré unit cell.