Determining charge state of graphene vacancy by noncontact atomic force microscopy and first-principles calculations

Liu, Y; Li, L

doi:10.1088/0957-4484/26/3/035702

Cited by 15 publications

(14 citation statements)

References 55 publications

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“…1e). This distinction is important for understanding the evolution of the spectra with charge and for identifying the supercritical regime.According to recent density functional theory (DFT) calculations 23 , the removal of a carbon atom from graphene and the subsequent lattice relaxation produces a positively charged …”

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Realization of a tunable artificial atom at a supercritically charged vacancy in graphene

et al. 2016

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Graphene's remarkable electronic properties have fuelled the vision of a graphene-based platform for lighter, faster and smarter electronics and computing applications. One of the challenges is to devise ways to tailor graphene's electronic properties and to control its charge carriers [1][2][3][4][5] . Here we show that a single-atom vacancy in graphene can stably host a local charge and that this charge can be gradually built up by applying voltage pulses with the tip of a scanning tunnelling microscope. The response of the conduction electrons in graphene to the local charge is monitored with scanning tunnelling and Landau level spectroscopy, and compared to numerical simulations. As the charge is increased, its interaction with the conduction electrons undergoes a transition into a supercritical regime [6][7][8][9][10][11] where itinerant electrons are trapped in a sequence of quasi-bound states which resemble an artificial atom. The quasi-bound electron states are detected by a strong enhancement of the density of states within a disc centred on the vacancy site which is surrounded by halo of hole states. We further show that the quasi-bound states at the vacancy site are gate tunable and that the trapping mechanism can be turned on and o , providing a mechanism to control and guide electrons in graphene.Supercriticality in atoms occurs when the Coulomb coupling, β = Zα, exceeds a critical value of order unity, where Z is the atomic number and α ∼ 1/137 is the fine structure constant. In this regime the electronic orbitals, starting with the 1S state, sink into the Dirac continuum until Z is reduced to the critical value. This process, known as atomic collapse (AC), is accompanied by vacuum polarization and the spontaneous generation of positrons 12,13 . But accessing this new physics requires ultra-heavy nuclei which do not exist in nature. In graphene, where the effective fine structure constant, α g = α(c/ν F ) ∼ 2, is much larger, the critical coupling, β c = (Z c /κ)α g = 0.5, can be reached for a relatively modest charge [6][7][8][9][10] (c is the speed of light, ν F the Fermi velocity and κ the effective dielectric constant). The transition to the supercritical regime in graphene is marked by the emergence of a sequence of quasi-bound states which can trap electrons. However, because graphene is a good conductor it is difficult to deposit and maintain a charge on its surface. Attempts to create charge by ionizing adatoms or donors with a scanning tunnelling microscope (STM) tip 14 showed that the charge decays when the field is removed. Alternatively, ions can be deposited directly on graphene, but because the charge transfer is inefficient 15 , attaining the critical Z requires piling up many ions, which, in the absence of a controllable mechanism to overcome the Coulomb repulsion, is very challenging 11 .Here we show that a vacancy in graphene can stably host a positive charge. The charge is deposited by applying voltage pulses with an STM tip and its gradual build-up is monitored with scanning tun...

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“…According to recent density functional theory (DFT) calculations 23 , the removal of a carbon atom from graphene and the subsequent lattice relaxation produces a positively charged…”

mentioning

confidence: 99%

Realization of a tunable artificial atom at a supercritically charged vacancy in graphene

et al. 2016

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“…This gate-controlled charging effect for defects has been demonstrated in a scanning tunneling microscopy study [21], in which not only a defect resonance state has been observed, but ionization of a defect by tip induced gating has been realized. A recent experimental study, combined with theoretical calculations, has also shown that defects are positively charged [30]. Therefore, on the hole side, where defects are ionized (charged), the long-range Coulomb potential can deflect carriers and reduce the scattering cross section of the short-range potential, leading to suppression of intervalley scattering.…”

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Electrical control of intervalley scattering in graphene via the charge state of defects

et al. 2016

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We study the intervalley scattering in defected graphene by low-temperature transport measurements. The scattering rate is strongly suppressed when defects are charged. This finding highlights "screening" of the short-range part of a potential by the long-range part. Experiments on calciumadsorbed graphene confirm the role of a long-range Coulomb potential. This effect is applicable to other multivalley systems, provided that the charge state of a defect can be electrically tuned. Our result provides a means to electrically control valley relaxation and has important implications in valley dynamics in valleytronic materials.

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“…6 Because of their relatively high formation energy, 27 graphene and graphite defect studies are typically limited to defects that are created by ion bombardment and irradiation. 6,25,28,29 As a stochastic process, the defect density and clustering produced by ion bombardment provide limited control. Native defects created during growth may allow for better control, but graphene grown in near-equilibrium conditions (such as CVD) is unlikely to exhibit native lattice defects, except at grain boundaries where independently nucleated growth regions meet.…”

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Native defects in ultra-high vacuum grown graphene islands on Cu(1 1 1)

Hollen

Tjung

Mattioli

et al. 2015

J. Phys.: Condens. Matter

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We present a scanning tunneling microscopy (STM) study of native defects in graphene islands grown by ultra-high vacuum (UHV) decomposition of ethylene on Cu(111). We characterize these defects through a survey of their apparent heights, atomic-resolution imaging, and detailed tunneling spectroscopy. Bright defects that occur only in graphene regions are identified as C site point defects in the graphene lattice and are most likely single C vacancies. Dark defect types are observed in both graphene and Cu regions, and are likely point defects in the Cu surface. We also present data showing the importance of bias and tip termination to the appearance of the defects in STM images and the ability to achieve atomic resolution.Finally, we present tunneling spectroscopy measurements probing the influence of point defects on the local electronic landscape of graphene islands.

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Determining charge state of graphene vacancy by noncontact atomic force microscopy and first-principles calculations

Cited by 15 publications

References 55 publications

Realization of a tunable artificial atom at a supercritically charged vacancy in graphene

Realization of a tunable artificial atom at a supercritically charged vacancy in graphene

Electrical control of intervalley scattering in graphene via the charge state of defects

Native defects in ultra-high vacuum grown graphene islands on Cu(1 1 1)

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