Effects of tip induced carrier density in local tunnel spectra of graphene

Choudhary, S.; Gupta, Anjan K.

doi:10.1063/1.3555344

Cited by 9 publications

(21 citation statements)

References 23 publications

(17 reference statements)

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“…The local quantity V D g is the gate voltage at which the Fermi level of graphene is also aligned with the latter energy levels. It includes the influence of the local gating produced by the tip on the local Dirac point due to both the tip-sample work function mismatch and the bias voltage [8,18]. In the absence of capacitive coupling to the tip, one would find the spatially averaged V D g to coincide with V 0 g found from transport experiments.…”

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confidence: 94%

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Charge Puddles in Graphene near the Dirac Point

et al. 2016

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The charge carrier density in graphene on a dielectric substrate such as SiO_{2} displays inhomogeneities, the so-called charge puddles. Because of the linear dispersion relation in monolayer graphene, the puddles are predicted to grow near charge neutrality, a markedly distinct property from conventional two-dimensional electron gases. By performing scanning tunneling microscopy and spectroscopy on a mesoscopic graphene device, we directly observe the puddles' growth, both in spatial extent and in amplitude, as the Fermi level approaches the Dirac point. Self-consistent screening theory provides a unified description of both the macroscopic transport properties and the microscopically observed charge disorder.

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mentioning

confidence: 94%

“…The number of graphene layers and the absence of surface contamination are confirmed from combined optical, Raman and ex-situ AFM characterization. Using a mechanical mask [8], we deposit the metallic source and drain contacts to form a 4 µm long graphene junction ( Fig. 1a).…”

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confidence: 99%

Charge Puddles in Graphene near the Dirac Point

et al. 2016

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“…The evolution of the two minima with V g in local spectra shows significant variation even on a given SLG device, which cannot be modeled by simple tip-gating effect 32 as discussed further. V g dependence of the local tunnel-spectra has been studied and modeled by several STM groups [31,32,34] using tip-gating effect. In this model the primary minima position shows v F |V g − V D g | dependence on V g with v F as the Fermi velocity of graphene and V D g is a local constant dependent on local doping as described later.…”

Section: Resultsmentioning

confidence: 99%

“…It can be found by V g required to make E F coincide with the DP. In addition, incorporating the effect of tipgating [32], we get,…”

Section: Effect Of Interface States On Tunnel Spectramentioning

confidence: 99%

“…Electronic inhomogeneities in graphene as arising from charge disorder due to interface and defect states have been investigated by several STM groups [29][30][31] . Since the carrier density in graphene is small near DP, the tip-gating effect on the spectra is significant 31,32 . Additional tipgating related effects such as ionization of impurities on graphene 33 , quantum confinement effects 34 , have also been reported.…”

Section: Introductionmentioning

confidence: 99%

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Inhomogeneous screening of gate electric field by interface states in graphene FETs

Singh¹,

Gupta²

2017

J. Phys.: Condens. Matter

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The electronic states at graphene-SiO2 interface and their inhomogeneity is investigated using the back-gate-voltage dependence of local tunnel spectra acquired with a scanning tunneling microscope. The conductance spectra show two, or occasionally three, minima that evolve along the bias-voltage axis with the back gate voltage. This evolution is modeled using tip-gating and interface states. The energy dependent interface states' density, Dit(E), required to model the back-gate evolution of the minima, is found to have significant inhomogeneity in its energy-width. A broad Dit(E) leads to an effect similar to a reduction in the Fermi velocity while the narrow Dit(E) leads to the pinning of the Fermi energy close to the Dirac point, as observed in some places, due to enhanced screening of the gate electric field by the narrow Dit(E).

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Scanning Tunneling Microscope‐Characterization of Chemical Vapor Deposition‐Graphene: Ripples and Twisted Bi‐layers at Multiple Scales

Tyagi,

Tiwari,

Mathew

et al. 2024

Physica Status Solidi (b)

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Despite numerous limitations, graphene characterization using scanning tunneling microscopy is an important aspect of graphene research. In the present study, an ambient, large effective field of view scanning tunneling microscope (A‐LEF‐STM) is used as a more practical extension of a standard STM for analyzing chemical vapor deposited (CVD)‐graphene: A rigid sample stage, which allows the tip to be relocated to any point over an area of 3.5 × 3.5 mm, is attached to the latter. This simple enhancement allows rough patches spanning hundreds of nanometers on any sample to be easily circumnavigated, almost always without damaging the tip. Ripples and multi‐layer regions including those with twisted bi‐layers, in a graphene sheet grown on a copper foil using CVD, are located using the augmented manoeuvrability, and imaged in high‐definition from micron to angström scales. Insights relating to the resolution with which surfaces of varying roughness can be imaged are developed using simulations and a careful analysis of the scanning process. The enhanced field of view is also utilized to verify the extent of graphene coverage over the entire sample area. The acquired images of single and multi‐layer depositions are carefully interpreted. The applicability of this end‐to‐end characterization process for other samples is also discussed. Overall, this study demonstrates the potential benefits of the A‐LEF‐STM as an eminent characterization tool, complementary to a Raman spectrometer, for CVD‐graphene and other two‐dimensional materials.

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Effects of tip induced carrier density in local tunnel spectra of graphene

Cited by 9 publications

References 23 publications

Charge Puddles in Graphene near the Dirac Point

Charge Puddles in Graphene near the Dirac Point

Inhomogeneous screening of gate electric field by interface states in graphene FETs

Scanning Tunneling Microscope‐Characterization of Chemical Vapor Deposition‐Graphene: Ripples and Twisted Bi‐layers at Multiple Scales

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