Manipulation and Characterization of Aperiodical Graphene Structures Created in a Two-Dimensional Electron Gas

We demonstrate that Dirac fermions can be created and manipulated in a two-dimensional electron gas (2DEG). Using a cryogenic scanning tunneling microscope, we arranged coronene molecules one by one on a Cu(111) surface to construct artificial graphene nanoribbons with perfect zigzag (ZGNRs) or arm-chairedges and confirmed that new states localized along the edges emerge only in the ZGNRs. We further made and studied several typical defects, such as single vacancies, Stone-Wales defects, and dislocation lines, and found that all these defects introduce localized states at or near the Dirac point in the quasiparticle spectra. Our results confirm that artificial systems built on a 2DEG provide rigorous experimental verifications for several long-sought theoretical predications of aperiodic graphene structures.

Figure 1

(a) STM image of an artificial pristine graphene structure of a triangular array consisting of 300 coronene molecules. Top inset: chemical structure of coronene; bottom inset: simulation model (the red discs are 1.0 eV potentials). Scale bar: 5 nm. (b) Experimental $dI/dV$ (solid) and simulated DOS spectrum (dashed). (c) Power function along $\mathrm{\Gamma }K$ (left) and $\mathrm{\Gamma }M$ (right) directions resolved by 2D FTLDOS. Dashed curves are simulated band dispersions along the defined directions. (d) Simulated FTLDOS.

Figure 2

(a)–(d) An artificial 6-ZGNR. (a) STM image (left part) and simulation model (right part). (b) STS map acquired at $-0.26\mathrm{V}$ (left part) and simulated LDOS map at $-0.24\mathrm{V}$ (right part). (c) Experimental row-averaged $dI/dV$ spectra and calculated LDOS. Black dashed line indicates the Dirac point. (d) The amplitude of the edge state (We use the term “amplitude of the edge state” to refer to the modulus squared of the wave function in the calculation, and to the $dI/dV$ value at the position and bias voltage of the edge state in the experiment.) as a function of row index. Experimental (calculated) results are shown in solid (open) symbols. (e)–(g) An artificial 7-AGNR. (e) STM image (left part) and simulation model (right part). (f) STS map acquired at $-0.23\mathrm{V}$. (g) Experimental row-averaged $dI/dV$ spectra and calculated LDOS. Scale bars: 5 nm.

Figure 3

(a) STM image (upper) and simulation model (lower) of an artificial 558 defect line. (b) STS map acquired at $-0.23\mathrm{V}$ (upper) and simulated LDOS map at $-0.21\mathrm{V}$ (lower). (c) Experimental column-averaged $dI/dV$ spectra and calculated LDOS. (d) Calculated LDOS intensity (upper) measured LDOS amplitude (lower) at $-0.22\mathrm{V}$ as a function of column index. Scale bars: 5 nm.

Figure 4

(a)–(d) An artificial single vacancy. (a) STM image. (b) Experimental (left) and simulated (right) $dI/dV$ spectra acquired at sites $A_1$ and $B_1$ [marked as the black and red dots in (a)]. (c) Experimental (upper) and simulated (lower) $dI/dV$ maps at $-0.23\mathrm{V}$. (d) Experimental (solid) and simulated (open) $-0.23\mathrm{V}$ LDOS amplitude as a function of sites. (e)–(g). An artificial Stone-Wales defect. (e) STM image. (f) Experimental (left) and simulated (right) $dI/dV$ spectra (Red: acquired with the tip located at the red dot marked in (e); Black: from the unmodified sites). (g) Experimental (left) and simulated (right) $dI/dV$ maps at $-0.23\mathrm{V}$. Scale bars: 5 nm.