Transport in graphene tunnel junctions

Malec, C. E.; Davidović, Dragomir

doi:10.1063/1.3554480

Cited by 27 publications

(29 citation statements)

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“…In a technique referred to as gate-mapping tunneling spectroscopy [30,31], the differential conductance (dI/dV) was recorded as a function of tunneling sample bias, b , and gate voltage, For the present work we employ a mapping method [32], referred to as gate-averaged spectroscopy, where we calculate the average of all spectra that were recorded over our full gate These excitations are better discerned in IETS, where they appear as point symmetric peaks ћ and dips ћ with respect to zero bias. The latter identifies them as inelastic excitations.…”

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Strong Asymmetric Charge Carrier Dependence in Inelastic Electron Tunneling Spectroscopy of Graphene Phonons

et al. 2015

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†These authors contributed equally to this work Abstract:The observation of phonons in graphene by inelastic electron tunneling spectroscopy has been met with limited success in previous measurements arising from weak signals and other spectral features which inhibit a clear distinction between phonons and miscellaneous excitations. Utilizing a back gated graphene device that allows adjusting the global charge carrier density, we introduce an averaging method where individual tunneling spectra at varying charge carrier density are combined into one representative spectrum. This method improves the signal for inelastic transitions while it suppresses dispersive spectral features. We thereby map the total graphene phonon density of states, in good agreement with density functional calculations. Unexpectedly, an abrupt change in the phonon intensity is observed when the graphene charge carrier type is switched through a variation of the back gate electrode potential.This sudden variation in phonon intensity is asymmetric in carrier type, depending on the sign of the tunneling bias. The ability to detect phonons has been very important in many graphene applications.This has led, for example, to the routine application of Raman spectroscopy to graphene physics and devices [9]. IETS detects vibrational excitations without the stringent selection rules active in Raman spectroscopy [17], and it's employment in a scanning tunneling microscope (STM) brings about spatial mapping of inelastic processes [18]. Inelastic excitations appear in scanning tunneling spectroscopy as a set of steps in the differential tunneling conductance at the excitation energy ћ , and as a peak and dip pair at positive and negative sample biases, , in the second derivative [18]. Previously, IETS has had limited success in measuring phonons in graphene because of weak signals and spectral overlap with other miscellaneous excitations. To date only a few reports of phonons in graphene have been published [13][14][15][16]. Reference [13] characterized an excitation at 63 meV and assigned it to a K-point phonon, while reference [14] revealed an additional feature at 150 meV and also assigned it to a K-point phonon. Reference [15] detected an excitation at 360 meV, which was tentatively assigned to a breathing mode. followed by e-beam lithography to deposit Au contacts [19]. Measurements were performed with a custom-built low temperature STM, operating at 4.3 K and a base pressure better than 5 10 hPa [26,27]. All phonons were observed in repeated measurements, independent of sample location, and were unperturbed by the exposure of graphene to molecular hydrogen and deuterium. The latter gases were used to rule out false assignment of the observed features to background gas or contamination from device fabrication processes [24,28,29]. The graphene

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Strong Asymmetric Charge Carrier Dependence in Inelastic Electron Tunneling Spectroscopy of Graphene Phonons

et al. 2015

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“…Since metals will eventually be involved in some way in graphene circuits, as interconnects or gates, it is critical to understand their effect on the graphene. Theoretical 3,4 and experimental [5][6][7][8][9][10] publications have found that one of the major effects of a metal on graphene is doping. In addition to this, it is believed that some metals interact weakly, leaving the linear dispersion of graphene undisturbed, and thus it may be desirable to use such metals near regions where graphene properties are most important.…”

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“…These are resonances in the DOS caused by the disorder potential, and the slope dV g /dV p becomes slightly flatter at positive gate voltage, where the density of states is lower. This we interpret as a broadened Dirac point, 9 and its location at positive gate voltage means the graphene is hole doped. As the magnetic field is increased, these lines are seen to break up, and are replaced by lines with a staircase like structure of alternating high and low sloped lines.…”

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“…12,19 We can analyze the data despite the ZBA by inspecting how tunnel resonances in the spectra shift with V g . Those features that shift with gate voltage are related to the graphene DOS at energy eV p + E F (V p , V g ), and their slope is directly proportional to the DOS, 9 where E F (V p , V g ) is the Fermi level in graphene. By applying a gate or probe voltage, charge is added to or subtracted from the graphene.…”

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“…See Ref. 9 for additional details about fabrication. Narrow junctions (< 200 nm) were used to insure that the acid could partially penetrate the Cu/graphene interface before the lead was overetched.…”

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Evidence for incompressible states in a metal-graphene tunnel junction in high magnetic field

Malec

Davidović

2011

Phys. Rev. B

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We present transport measurements of tunnel junctions made between Cu and graphene in a magnetic field. We observe a transition to a Landau level like structure at high fields, as well as a set of sharp features in the tunneling spectra that shift with gate and tunnel probe voltage along the lines of constant charge density. We explain the sharp features with the formation of degeneracy split localized Landau levels, and addition of electrons to those levels one by one. A large capacitive coupling to the tunnel probe also increases the gate voltage spacing between the Landau levels.

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Applied Spectroscopy and the Science of Nanomaterials

Misra¹

2015

Progress in Optical Science and Photonics

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Transport in graphene tunnel junctions

Cited by 27 publications

References 35 publications

Strong Asymmetric Charge Carrier Dependence in Inelastic Electron Tunneling Spectroscopy of Graphene Phonons

Strong Asymmetric Charge Carrier Dependence in Inelastic Electron Tunneling Spectroscopy of Graphene Phonons

Evidence for incompressible states in a metal-graphene tunnel junction in high magnetic field

Applied Spectroscopy and the Science of Nanomaterials

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