Probing the Nature of Defects in Graphene by Raman Spectroscopy

Eckmann, Axel; Felten, Alexandre; Mishchenko, Artem; Britnell, L.; Krupke, Ralph; Новоселов, К. С.; Casiraghi, Cinzia

doi:10.1021/nl300901a

Cited by 1,864 publications

(1,710 citation statements)

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“…The intercalated layer demonstrates I D /I G ¼ 0.023 indicating low defect density. [23][24][25][26][27] Such a comparison is intractable in the as-grown sample because the D-peak is obscured by the CBL spectrum. 27 The increase in linewidth from 50 cm À1 to 68 cm À1 for the 2D peak upon H-intercalation is indicative of a transition from monolayer (plus CBL) to quasifree standing bilayer material, though there may be additional spectral broadening in both samples due to the presence of the BCB encapsulation layer.…”

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confidence: 99%

Graphene self-switching diodes as zero-bias microwave detectors

Westlund

Winters

Ivanov

et al. 2015

Applied Physics Letters

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Self-switching diodes (SSDs) were fabricated on as-grown and hydrogen-intercalated epitaxial graphene on SiC. The SSDs were characterized as zero-bias detectors with on-wafer measurements from 1 to 67 GHz. The lowest noise-equivalent power (NEP) was observed in SSDs on the hydrogen-intercalated sample, where a flat NEP of 2.2 nW/Hz 1 =2 and responsivity of 3.9 V/W were measured across the band. The measured NEP demonstrates the potential of graphene SSDs as zero-bias microwave detectors. Graphene exhibits electronic properties which are relevant for high-frequency applications 1 such as zero-bias detection in passive imaging arrays. 2 Detectors drawing zero bias current offer reduced 1/f-noise compared to biased detectors. Zero-bias detectors are today normally based on heterojunctions or Schottky diodes, reaching noise-equivalent power (NEP) below 20 pW/Hz 1 =2 beyond 100 GHz. 3,4 Zero-bias detection has been demonstrated in graphene field-effect transistors (FETs) with an NEP of 515 pW/Hz 1 =2 at 600 GHz. 5 Self-switching diodes (SSDs) offer a fundamentally different approach to zero-bias detection in which rectification and detection is achieved by a lateral field-effect. 6 Simulations have shown the feasibility of achieving rectification in graphene using SSD structures. 7,8 SSD detectors have previously been realized in other materials 9-12 with the most promising results for GaAs SSDs in which an NEP of 330 pW/Hz 1 =2 at 1.5 THz was observed. 13 In this work, detection with rectifying graphene SSDs at frequencies up to 67 GHz is demonstrated. The SSDs are realized in both as-grown (n-type) and hydrogen-intercalated (p-type) epitaxial graphene on SiC. Figure 1 shows a scanning electron micrograph of a single SSD channel fabricated in epitaxial graphene. The narrow graphene channel behaves as a lateral nanowire transistor. 6 The surrounding flanges act as lateral gates which are directly connected to the drain such that the drain voltage is simultaneously applied to the gates. This has the effect of modulating the carrier density in the nanowire channel generating a nonlinear current-voltage characteristic. 14 The inset shows an SSD design implemented for RF detection with nine nanowire channels acting in parallel to reduce resistance and NEP. 15 The SSDs were fabricated at the end of a 70 lm coplanar transmission line, in order to provide a partial RF match.Graphene was grown on the Si-face of two 20 Â 20 mm 2 nominally on-axis semi-insulating (SI) 4H-SiC substrates in a horizontal hot wall chemical vapor deposition (CVD) reactor. 16 Graphene growth was carried out at 1300 C to 1400 C in vacuum after an initial in-situ surface preparation of the substrates in a hydrogen/silane background. One of the samples was then intercalated in hydrogen at a temperature (pressure) of 800 C (500 mbar) in order to obtain quasi-free standing graphene. SSDs and supplementary test structures were fabricated on the graphene layers with and without H-intercalation. As-grown samples then consisted of a monolayer plus carbon buf...

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confidence: 99%

Graphene self-switching diodes as zero-bias microwave detectors

Westlund

Winters

Ivanov

et al. 2015

Applied Physics Letters

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“…The I(D)/I(D') ratio can be used to classify the type of defect. Eckmann et al [32] report a I(D)/I(D') ratio of 7 for vacancy-like defects and 13 for sp 3 hybridization. For water treated 6√3 we determine the ratio to be 8.…”

Section: Resultsmentioning

confidence: 99%

Buffer layer free graphene on SiC(0001) via interface oxidation in water vapor

Ostler

Fromm

Koch

et al. 2014

Carbon

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Intercalation of various elements has become a popular technique to decouple the buffer layer of epitaxial graphene on SiC(0001) from the substrate. Among many other elements, oxygen can be used to passivate the SiC interface, causing the buffer layer to transform into graphene. Here, we study a gentle oxidation of the interface by annealing buffer layer and monolayer graphene samples in water vapor. X-ray photoelectron spectroscopy demonstrates the decoupling of the buffer layer from the SiC substrate. Raman spectroscopy is utilized to investigate a possible introduction of defects. Angle-resolved photoemission spectroscopy shows that the electronic structure of the water vapor treated samples. Low-energy electron microscopy (LEEM) measurements demonstrate that the decoupling takes place without changes in the surface morphology. The LEEM reflectivity spectra are discussed in terms of two different interpretations.

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“…Raman spectroscopy is a widely used tool to study the vibrational modes of carbon based materials [13][14][15]. Because the normal modes of molecules are unique, they have their own set of Raman frequencies.…”

Section: Introductionmentioning

confidence: 99%

Vibrational properties of nanographene

Singh¹,

Peeters²

2013

Nanoscale Systems: Mathematical Modeling, Theory and Applications

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The eigenmodes and the vibrational density of states of the ground state configuration of graphene clusters are calculated using atomistic simulations. The modified Brenner potential is used to describe the carbon-carbon interaction and carbon-hydrogen interaction in case of H-passivated edges. For a given configuration of the C-atoms the eigenvectors and eigenfrequencies of the normal modes are obtained after diagonalisation of the dynamical matrix whose elements are the second derivative of the potential energy. The compressional and shear properties are obtained from the divergence and rotation of the velocity field. For symmetric and defective clusters with pentagon arrangement on the edge, the highest frequency modes are shear modes. The specific heat of the clusters is also calculated within the harmonic approximation and the convergence to the result for bulk graphene is investigated.

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Probing the Nature of Defects in Graphene by Raman Spectroscopy

Cited by 1,864 publications

References 47 publications

Graphene self-switching diodes as zero-bias microwave detectors

Graphene self-switching diodes as zero-bias microwave detectors

Buffer layer free graphene on SiC(0001) via interface oxidation in water vapor

Vibrational properties of nanographene

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