Tailoring low-dimensional structures of bismuth on monolayer epitaxial graphene.

H.-H Chen,B.-Y Cheng,S.-L Chang,S W Chen,M.-F Lin,J C A Huang,S H Su,H.-Y Chen

doi:10.1038/srep11623

H.-H Chen, B.-Y Cheng + Show 6 more

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https://doi.org/10.1038/srep11623

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Abstract

To improve graphene-based multifunctional devices at nanoscale, a stepwise and controllable fabrication procedure must be elucidated. Here, a series of structural transition of bismuth (Bi) adatoms, adsorbed on monolayer epitaxial graphene (MEG), is explored at room temperature. Bi adatoms undergo a structural transition from one-dimensional (1D) linear structures to two-dimensional (2D) triangular islands and such 2D growth mode is affected by the corrugated substrate. Upon Bi deposition, a little charge transfer occurs and a characteristic peak can be observed in the tunneling spectrum, reflecting the distinctive electronic structure of the Bi adatoms. When annealed to ~500 K, 2D triangular Bi islands aggregate into Bi nanoclusters (NCs) of uniform size. A well-controlled fabrication method is thus demonstrated. The approaches adopted herein provide perspectives for fabricating and characterizing periodic networks on MEG and related systems, which are useful in realizing graphene-based electronic, energy, sensor and spintronic devices.

Highlights

Semimetal Bi, being one of the most extensively studied elements, exhibits many extraordinary physical properties, including low carrier density, a long Fermi wavelength, and high carrier mobility[6]
Bi-based low-dimensional structures (LDSs) form narrow band gap semiconductors due to strong quantum confinement effect[8,9] but are more active than thin films when their size is restricted to the nanoscale
We report the scanning tunneling microscopy (STM) and density functional theory (DFT) studies of Bi adatoms on MEG formed on Si- terminated 4H-SiC (0001) substrate

Summary

Results

STM imagings of MEG and Bi adatoms. Fig. 1(a) presents an atomically clean surface of MEG. The spectrum of NCs, as shown, reveal similar characteristic peak located at ~− 0.72 eV (black arrow) to that in the dI/dV profile of the Bi adatom in hexagonal array, but with a lager FWHM, indicating stronger feature of the p-state of Bi atoms in NCs. Based on the above, a well-controlled method for forming Bi-based LDSs can be developed. Within STM experiments and DFT calculations, Bi adatoms show a structural transition from 1D linear chains to 2D triangular islands, from four times to 2 3 times the lattice spacing of Bi nanoribbon, as coverage increased from below 0.01 ML to above 0.03 ML Such 2D growth mode is clearly affected by the corrugated substrate. It demonstrates a reliable process toward multifunctional hybrid architectures for use in graphene-based devices at room temperature

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