Atomic-Scale Mapping of Thermoelectric Power on Graphene: Role of Defects and Boundaries

Park, Jewook; He, Guowei; Feenstra, R. M.; Li, An‐Ping

doi:10.1021/nl401473j

Cited by 57 publications

(57 citation statements)

References 41 publications

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“…The advantage of this method is the simultaneous imaging of the sample structure and thermoelectric signals with a spatial resolution of atomic‐scale. Since the Seebeck coefficient relies on the sample local density of states (LDOS) near the Fermi energy, and LDOS can be quite different in the presence of boundaries and disorders, thermoelectric imaging allows us to probe grain boundaries, wrinkles, defects, and impurities in graphene, which may not be reflected in topography images …”

Section: Thermoelectric Properties Of Graphenementioning

confidence: 99%

Thermal and Thermoelectric Properties of Graphene

Duan

2014

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The subject of thermal transport at the mesoscopic scale and in low-dimensional systems is interesting for both fundamental research and practical applications. As the first example of truly two-dimensional materials, graphene has exceptionally high thermal conductivity, and thus provides an ideal platform for the research. Here we review recent studies on thermal and thermoelectric properties of graphene, with an emphasis on experimental progresses. A general physical picture based on the Landauer transport formalism is introduced to understand underlying mechanisms. We show that the superior thermal conductivity of graphene is contributed not only by large ballistic thermal conductance but also by very long phonon mean free path (MFP). The long phonon MFP, explained by the low-dimensional nature and high sample purity of graphene, results in important isotope effects and size effects on thermal conduction. In terms of various scattering mechanisms in graphene, several approaches are suggested to control thermal conductivity. Among them, introducing rough boundaries and weakly-coupled interfaces are promising ways to suppress thermal conduction effectively. We also discuss the Seebeck effect of graphene. Graphene itself might not be a good thermoelectric material. However, the concepts developed by graphene research might be applied to improve thermoelectric performance of other materials.

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Section: Thermoelectric Properties Of Graphenementioning

confidence: 99%

Thermal and Thermoelectric Properties of Graphene

Duan

2014

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192

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“…Because Eq. (4) is an exact expression that does not involve any approximation, it can be generally applicable for other thermoelectric systems including noncontact STM setups [10,11,12]. …”

mentioning

confidence: 99%

Seebeck Effect at the Atomic Scale

et al. 2014

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The atomic variations of electronic wavefunctions at the surface and electron scattering near a defect have been detected unprecedentedly by tracing thermoelectric voltages given a temperature bias [Cho et al., Nature Mater. 12, 913 (2013)]. Because thermoelectricity, or Seebeck effect, is associated with heat-induced electron diffusion, how the thermoelectric signal is related to the atomic-scale wavefunctions and what the role of the temperature is at such a length scale remain very unclear. Here we show that coherent electron and heat transport through a point-like contact produces an atomic Seebeck effect, which is described by mesoscopic Seebeck coefficient multiplied with an effective temperature drop at the interface. The mesoscopic Seebeck coefficient is approximately proportional to the logarithmic energy derivative of local density of states at the Fermi energy. We deduced that the effective temperature drop at the tip-sample junction could vary at a sub-angstrom scale depending on atom-to-atom interaction at the interface. A computer-based simulation method of thermoelectric images is proposed, and a point defect in graphene was identified by comparing experiment and the simulation of thermoelectric imaging. 2The invention of the scanning tunneling microscope (STM) by Binnig and Rohrer [1,2] facilitated direct access to microscopic quantum mechanics [3]. This method provides realspace wavefunction images of a material surface by measuring the electrical tunneling currents across the vacuum gap. The microscopic imaging mechanism of atomically resolved wavefunctions in the tunneling microscopy is rather straightforward [4] because the tunneling current can be easily localized in space by controlling the vacuum gap.Heat, a measure of entropy, is largely perceived to be diffusive and transported incoherently by charge carriers (electrons and holes) and lattice vibrations (or phonons) in a material. Heat transport is therefore considered a challenging means of the local imaging of a material and its electronic states [5,6]. Very recently, however, Cho et al. [7] reported a series of atomic wavefunction images of epitaxial graphene, obtained while performing local thermoelectric imaging with a heat-based scanning probe microscope [6,7]. These counterintuitive heat-based real-space wavefunction images naturally generate one key question: how can one measure the atomic variation in the unit cell in a heat transport experiment? To answer this question, we must not only elucidate the imaging mechanism of the scanning thermoelectric microscope, but also re-evaluate the fundamental physics of thermoelectricity, or Seebeck effect, from conventional length scales to the atomic length scale.In this Letter, we present a theory of scanning thermoelectric microscopy with atomic resolution based on the mesoscopic electron and heat transport characteristics. This theory, beginning with the macroscopic general transport equation and electrostatic equations, illustrates the feasibility and mechanisms in play when o...

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“…Furthermore, as a result of the smooth scattering potential in the continuous top layer at the ML-BL boundary on SiC(0001) [30,44,45,47], only intravalleyscattering-induced long-wavelength Friedel oscillations can occur and intervalley-scattering-induced oscillations are absent [4,41,45]. Therefore, the energy gap considered here is opened by the long-wavelength (Q ¼ 2k F ) Friedel oscillation associated with intravalley scattering.…”

Section: Friedel Gaps In ML and Bl Graphenementioning

confidence: 92%

Energy Gap Induced by Friedel Oscillations Manifested as Transport Asymmetry at Monolayer-Bilayer Graphene Boundaries

Clark

Zhang

et al. 2014

Phys. Rev. X

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We show that Friedel charge oscillation near an interface opens a gap at the Fermi energy for electrons with wave vectors perpendicular to the interface. If the Friedel gaps on two sides of the interface are different, a nonequilibrium effect-shifting of these gaps under bias-leads to asymmetric transport upon reversing the bias polarity. The predicted transport asymmetry is revealed by scanning tunneling potentiometry at monolayer-bilayer interfaces in epitaxial graphene on SiC(0001). This intriguing interfacial transport behavior opens a new avenue toward novel quantum functions such as quantum switching.

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Atomic-Scale Mapping of Thermoelectric Power on Graphene: Role of Defects and Boundaries

Cited by 57 publications

References 41 publications

Thermal and Thermoelectric Properties of Graphene

Thermal and Thermoelectric Properties of Graphene

Seebeck Effect at the Atomic Scale

Energy Gap Induced by Friedel Oscillations Manifested as Transport Asymmetry at Monolayer-Bilayer Graphene Boundaries

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