Wide-band-gap wrinkled nanoribbon-like structures in a continuous metallic graphene sheet

To generate a moderate band gap in a graphene monolayer is a very important but rather difficult task. A rare working solution of this problem is to cut it into one-dimensional (1D) nanometer-wide ribbons. Here we show that, instead of cutting the graphene monolayer, a wide band gap can be created in a unique 1D strained structure, i.e., a wrinkled graphene-nanoribbon-like (GNR-like) structure, of a continuous graphene sheet via strong hybridization between the graphene and the metal substrate. The wrinkled GNR-like structures with widths of only a few nanometers are observed in a continuous graphene sheet grown on a Rh foil by using thermal strain engineering. Spatially resolved scanning tunneling spectroscopy revealed a band-gap opening of a few hundred meV in the GNR-like structure in an otherwise continuous metallic graphene sheet, directly demonstrating the realization of a metallic-semiconducting-metallic junction entirely in a graphene monolayer.

Figure 1

A (chiral) zigzag-GNR-like structure in a continuous graphene sheet on a Rh foil. (a) A $30\times 30\mathrm{n}{\mathrm{m}}^2$ STM image of a graphene monolayer ($V_{\mathrm{sample}}=800\mathrm{mV}$ and $I=0.3\mathrm{nA}$) on a Rh foil. (b) A $10\times 10\mathrm{n}{\mathrm{m}}^2$ STM image of the graphene area within the black frame in (a). To relax the in-plane compressive strains induced by the substrate, a (chiral) zigzag-GNR-like structure with a width of about 5.2 nm is formed. (c) The profile line of the (chiral) zigzag-GNR-like structure showing a flat region between the two bending boundaries, which are almost parallel. (d) and (e) show atomic resolution STM images of the two bending boundaries of the (chiral) zigzag-GNR-like structure taken from the area marked with the red and blue frames, respectively, in (b). The atomic structures of graphene are overlaid onto the STM images. Obviously, the bending boundaries are almost along the zigzag direction of graphene.

Figure 2

Energy gaps in the (chiral) zigzag-GNR-like structures. (a) A typical STM image ($V_{\mathrm{sample}}=800\mathrm{mV}$ and $I=0.3\mathrm{nA}$) and profile line of a (chiral) zigzag-GNR-like structure with a width of $W\sim 6.2\mathrm{nm}$ in a continuous graphene layer on the Rh foil. (b) Spatially resolved STS spectra recorded at different positions from 1 to 3 in (a). (c) Typical STS spectra taken on (chiral) zigzag-GNR-like structures with different widths, and these samples exhibit different energy gaps as marked by two arrows. (d) The observed energy gaps as a function of the width in the (chiral) zigzag-GNR-like structures.

Figure 3

Geometry and electronic structure of a zigzag-GNR-like structure on a Rh(111) surface. (a) and (b) The top and side views of the atomic structure of a zigzag-GNR-like structure on a Rh (111) surface (gray balls: carbon atoms and blue balls: Rh atoms). $W$ denotes the width of the flat graphene region, and $d$ denotes the distance between the bending graphene region and the Rh(111) surface. The red dashed frame indicates the supercell in the calculation. (c) Band structure of the zigzag-GNR-like structure on a Rh(111) surface with $W=18.22$ and $d=2\AA$. The red solid circles illustrate the bands contributed by carbon atoms.

Figure 4

Electronic structures of the buckled graphene on a Rh(111) surface with (a) $W=14.14$ and $d=2\AA$, (b) $W=22.63$ and $d=2\AA$, (c) $W=18.22$ and $d=1.8\AA$, and (d) $W=18.22$ and $d=2.2\AA$. The red solid balls illustrate the energy bands contributed by carbon atoms.