Tunable charge donation and spin polarization of metal adsorbates on graphene using an applied electric field

Parq, Jae-Hyeon; Yu, Jaejun; Kwon, Young–Kyun; Kim, Gunn

doi:10.1103/physrevb.82.193406

Cited by 13 publications

(8 citation statements)

References 25 publications

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“…Here, in the case of graphene grown on metals, the modulation of the linear dispersion is reported to depend strongly on the metal element used, according to both theoretical calculations 10,11 and experimental results. 12,13 The modulation in the electron dispersion relation occurs on a chemisorption group (e.g., Ni, Co, and Pd) and not on an adsorption group (e.g., Au, Ag, and Pt).…”

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confidence: 93%

The density of states of graphene underneath a metal electrode and its correlation with the contact resistivity

Ifuku

Nagashio

Nishimura

et al. 2013

Applied Physics Letters

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The density of states (DOS) of graphene underneath a metal is estimated through a quantum capacitance measurement of the metal/graphene/SiO 2 /n + -Si contact structure fabricated by a resist-free metal deposition process. Graphene underneath Au maintains a linear DOS -energy relationship except near the Dirac point, whereas the DOS of graphene underneath Ni is broken and largely enhanced around the Dirac point, resulting in only a slight modulation of the Fermi energy. Moreover, the DOS of graphene in the contact structure is correlated with the contact resistivity measured using devices fabricated by the resist-free process.To make the best use of the extremely high carrier mobility of graphene in electric devices, contact resistivity ( c ) should be seriously addressed 1,2 because it is necessary to be lowered by several orders of magnitude from the present status.1 Generally, the current injection from metal to graphene is proportional to the transmission probability and the density of states (DOS) in the metal and graphene. 3,4 In terms of the transmission probability, an intrinsic problem exists for momentum matching because the Dirac cone at the K point of the Brillouin zone boundary is generally lager than the Fermi wavenumber for typical metals. 5 The number of empty states in graphene as the final state is much smaller than the number of occupied states in the metal. This DOS bottleneck is considered to be the limiting factor in the total performance of graphene devices. 6,7 This limitation results from the inapplicability of conventional doping techniques such as ion implantation 8 because the thermodynamically stable C-C bonding prevents the substitutional doping of B or N for C. 9 The DOS of graphene in the contact structure, i.e., the metal/graphene/SiO 2 structure, could be different from the ideal linear relation because the electrical properties of graphene with monoatomic thickness are easily modulated by the environment. Therefore, determining the DOS of graphene in the contact structure provides information on the strength of the metal/graphene/SiO 2 interaction, which is key to setting guidelines to further reduce  c .Here, in the case of graphene grown on metals, the modulation of the linear dispersion is reported to depend strongly on the metal element used, according to both theoretical calculations 10,11 and experimental results. 12,13 The modulation in the electron dispersion relation occurs on a chemisorption group (e.g., Ni, Co, and Pd) and not on an adsorption group (e.g., Au, Ag, and Pt).10 Based on these reports, we selected Ni as a contact electrode to measure  c 1 because the DOS of graphene in the contact structure is expected to increase due to the strong -d coupling.14 However, in the graphene field effect transistors (FETs) fabricated using the conventional resist process, it has been shown that graphene underneath the Ni electrodes roughly maintains linear dispersion based on the transport measurements. 15This discrepancy could be caused by the resist residue in the devi...

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mentioning

confidence: 93%

The density of states of graphene underneath a metal electrode and its correlation with the contact resistivity

Ifuku

Nagashio

Nishimura

et al. 2013

Applied Physics Letters

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“…The demand for careful and systematic experimental adsorption studies on graphene is also underlined by the numerous first-principles calculations related to the effects of adsorbed atoms on graphene [15][16][17][18][19][20][21][22][23][24][25][26], to a large extent for transition metals. We believe it is fair to say that there is a considerable imbalance between calculations and experiments.…”

Section: Introductionmentioning

confidence: 99%

Phase coexistence of clusters and islands: europium on graphene

et al. 2012

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The adsorption and equilibrium surface phases of europium (Eu) on graphene on Ir(111) are investigated in the temperature range from 35 to 400 K and for coverages ranging from a small fraction of a saturated monolayer to the second layer by scanning tunnelling microscopy. Using density functional theory including 4f-shell Coulomb interactions and modelling of electronic interactions, excellent agreement with the experimental results for the equilibrium adsorbate phase, adsorbate diffusion and work function is obtained. Most remarkably, at 300 K in an intermediate coverage range a phase of uniformly distributed Eu clusters (size 10-20 atoms) coexists in two-dimensional equilibrium with large Eu-islands in a ( √ 3 × √ 3)R30 • structure. We argue that the formation of the cluster phase is driven by the interplay of three effects. Firstly, the metallic Eu-Eu binding leads to the local stability of ( √ 3 × √ 3)R30 • structures. Secondly, electrons lower their kinetic energy by leaving the Eu clusters, thereby doping graphene. Thirdly, the Coulomb energy penalty associated with the charge transfer from Eu to graphene is strongly reduced for smaller clusters.

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“…The ease with which graphene can be functionalized with hydrogen [3][4][5], oxygen [6][7][8], and metal atoms [9][10][11] has further added a new dimension into its potential for novel applications. Atomic layer deposition (ALD) is an efficient surface controlled thin film growth technique that is often used to deposit metal atoms on graphene [12].…”

Section: Introductionmentioning

confidence: 99%

Tailoring Li adsorption on graphene

et al. 2014

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The technological potential of functionalized graphene has recently stimulated considerable interest in the study of the adsorption of metal atoms on graphene. However, a complete understanding of the optimal adsorption pattern of metal atoms on a graphene substrate has not been easy because of atomic relaxations at the interface and the interaction between metal atoms. We present a partial particle swarm optimization technique that allows us to efficiently search for the equilibrium geometries of metal atoms adsorbed on a substrate as a function of adatom concentration. Using Li deposition on graphene as an example we show that, contrary to previous works, Li atoms prefer to cluster, forming four-atom islands, irrespective of their concentration. We further show that an external electric field applied vertically to the graphene surface or doping with boron can prevent this clustering, leading to the homogeneous growth of Li.

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Tunable charge donation and spin polarization of metal adsorbates on graphene using an applied electric field

Cited by 13 publications

References 25 publications

The density of states of graphene underneath a metal electrode and its correlation with the contact resistivity

The density of states of graphene underneath a metal electrode and its correlation with the contact resistivity

Phase coexistence of clusters and islands: europium on graphene

Tailoring Li adsorption on graphene

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