Detecting the local transport properties and the dimensionality of transport of epitaxial graphene by a multi-point probe approach

Barreto, Lucas; Perkins, Edward W; Johannsen, J.; Ulstrup, Søren; Fromm, Felix; Raidel, Christian; Seyller, Thomas; Hofmann, Philip

doi:10.1063/1.4789508

Cited by 11 publications

(10 citation statements)

References 28 publications

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“…Four-probe spectroscopy measurement with variable probe distances is the method of choice for studying materials where both surface and bulk contributions to electrical conduction are present. The common practice is to assume two decoupled conduction channels corresponding to the 2D conductance of surface states and the 3D conductance of bulk, − as schematically shown in Figure a, and deduce the dominant conduction mechanism through the dependence of the conductance with probe spacing. Such an assumption would only be valid if the potential profile across the surface were identical for both 2D and 3D conduction.…”

mentioning

confidence: 99%

Differentiation of Surface and Bulk Conductivities in Topological Insulators via Four-Probe Spectroscopy

et al. 2016

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We show a new method to differentiate conductivities from the surface states and the coexisting bulk states in topological insulators using a four-probe transport spectroscopy in a multiprobe scanning tunneling microscopy system. We derive a scaling relation of measured resistance with respect to varying interprobe spacing for two interconnected conduction channels to allow quantitative determination of conductivities from both channels. Using this method, we demonstrate the separation of 2D and 3D conduction in topological insulators by comparing the conductance scaling of Bi2Se3, Bi2Te2Se, and Sb-doped Bi2Se3 against a pure 2D conductance of graphene on SiC substrate. We also quantitatively show the effect of surface doping carriers on the 2D conductance enhancement in topological insulators. The method offers a means to understanding not just the topological insulators but also the 2D to 3D crossover of conductance in other complex systems.

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confidence: 99%

Differentiation of Surface and Bulk Conductivities in Topological Insulators via Four-Probe Spectroscopy

et al. 2016

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“…It is interesting to compare these results to those from epitaxial graphene grown on the silicon face of SiC, both because graphene is a similar Dirac-material but also because this system has been measured with the same 4STM and 12pp techniques. The reported results are remarkably similar.…”

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confidence: 99%

Surface-Dominated Transport on a Bulk Topological Insulator

et al. 2014

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Topological insulators are guaranteed to support metallic surface states on an insulating bulk, and one should thus expect that the electronic transport in these materials is dominated by the surfaces states. Alas, due to the high remaining bulk conductivity, surface contributions to transport have so-far only been singled out indirectly via quantum oscillations [1, 2], or for devices based on gated and doped topological insulator thin films, a situation in which the surface carrier mobility could be limited by defect and interface scattering [3][4][5][6]. Here we present the first direct measurement of surface-dominated conduction on an atomically clean surface of bulk-insulating Bi 2 Te 2 Se.Using nano-scale four point setups with variable contact distance, we show that the transport at 30 K is two-dimensional rather than three-dimensional and by combining these measurements with angle-resolved photoemission results from the same crystals, we find a surface state mobility of 390(30) cm 2 V −1 s −1 at 30 K at a carrier concentration of 8.71(7)×10 12 cm −2 .

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“…The graphene sample investigated in this work was produced following a well-documented synthesis method that provides high-quality monolayer graphene on the Siterminated face of SiC(0001). The graphene layer was decoupled from the substrate by hydrogen intercalation [36,37] such that the structural and electronic properties probed by transport, Raman and ARPES measurements closely approached pristine graphene [37][38][39][40]. The graphene is p-doped with a carrier concentration of ≈ 5 × 10 12 cm −2 that places the Dirac point 240 meV above the Fermi energy.…”

Section: Methodsmentioning

confidence: 99%

“…The graphene layer was decoupled from the substrate by hydrogen intercalation [36,37] such that the structural and electronic properties probed by transport, Raman and ARPES measurements closely approached pristine graphene [37][38][39][40]. The graphene is p-doped with a carrier concentration of ≈ 5 × 10 12 cm −2 that places the Dirac point 240 meV above the Fermi energy.…”

Section: Methodsmentioning

confidence: 99%

Ramifications of optical pumping on the interpretation of time-resolved photoemission experiments on graphene

Ulstrup¹,

Johannsen²,

Cilento³

et al. 2015

Journal of Electron Spectroscopy and Related Phenomena

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In pump-probe time and angle-resolved photoemission spectroscopy (TR-ARPES) experiments the presence of the pump pulse adds a new level of complexity to the photoemission process in comparison to conventional ARPES. This is evidenced by pump-induced vacuum space-charge effects and surface photovoltages, as well as multiple pump excitations due to internal reflections in the sample-substrate system. These processes can severely affect a correct interpretation of the data by masking the out-of-equilibrium electron dynamics intrinsic to the sample. In this study, we show that such effects indeed influence TR-ARPES data of graphene on a silicon carbide (SiC) substrate. In particular, we find a time-and laser fluence-dependent spectral shift and broadening of the acquired spectra, and unambiguously show the presence of a double pump excitation. The dynamics of these effects is slower than the electron dynamics in the graphene sample, thereby permitting us to deconvolve the signals in the time domain. Our results demonstrate that complex pump-related processes should always be considered in the experimental setup and data analysis.

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Detecting the local transport properties and the dimensionality of transport of epitaxial graphene by a multi-point probe approach

Cited by 11 publications

References 28 publications

Differentiation of Surface and Bulk Conductivities in Topological Insulators via Four-Probe Spectroscopy

Differentiation of Surface and Bulk Conductivities in Topological Insulators via Four-Probe Spectroscopy

Surface-Dominated Transport on a Bulk Topological Insulator

Ramifications of optical pumping on the interpretation of time-resolved photoemission experiments on graphene

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