Transport, magnetic and vibrational properties of chemically exfoliated few-layer graphene

Chacón-Torres

et al. 2019

Sci Rep

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An efficient route to synthesize macroscopic amounts of graphene is highly desired and bulk characterization of such samples, in terms of the number of layers, is equally important. We present a Raman spectroscopy-based method to determine the typical upper limit of the number of graphene layers in chemically exfoliated graphene. We utilize a controlled vapour-phase potassium intercalation technique and identify a lightly doped stage, where the Raman modes of undoped and doped few-layer graphene flakes coexist. The spectra can be unambiguously distinguished from alkali doped graphite, and modeling with the typical upper limit of the layers yields an upper limit of flake thickness of five layers with a significant single-layer graphene content. Complementary statistical AFM measurements on individual few-layer graphene flakes find a consistent distribution of the layer numbers.

Section: Methodsmentioning

confidence: 95%

Characterizing the maximum number of layers in chemically exfoliated graphene

Szirmai

Chacón-Torres

et al. 2019

Sci Rep

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“…Prior to in situ measurements, the undoped FLG was heated to 400 °C for 30 min in high vacuum (2 × 10 −6 mbar) to remove any residual solvents. It was shown previously in the previous studies [ 28,29 ] that this does not affect the morphology of the starting FLG.…”

Section: Methods and Sample Preparationmentioning

confidence: 62%

“…[25][26][27] Chemical exfoliation was finalized using ultrasound tip sonication, as it is known to produce the best quality. [28,29] The properties of the starting material are well characterized by atomic force microscopy and Raman spectroscopy, which revealed that the restacked FLG is also present in the sample. [29] The dominant portion (90%) of the material consists of five layers or less, including monolayer content.…”

Section: Methods and Sample Preparationmentioning

confidence: 99%

“…The undoped material exhibits two symmetric Lorentzian peaks, as noted earlier. [20,28] The presence of these signals is due to the remaining solvent, dangling bonds, or other localized lattice defects. Even after the first intercalation step, two, different Dysonian features [35] appear with a gradually higher intensity.…”

Section: Spin Propertiesmentioning

confidence: 99%

“…The undoped FLG has two, symmetric components due to the presence of localized defects, as seen before. [20,28] After potassium intercalation, two, different asymmetric lines appear. These lines are identified as Dysonians [35] as an indication of the presence of conducting electrons.…”

Section: Spin Propertiesmentioning

confidence: 99%

See 2 more Smart Citations

Tuning Conductivity and Spin Dynamics in Few‐Layer Graphene via In Situ Potassium Exposure

Physica Status Solidi (b)

Sági

Kollarics

et al. 2020

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Chemical modification such as intercalation or doping of novel materials is of great importance for exploratory material science and applications in various fields of physics and chemistry. Herein, the systematic intercalation of chemically exfoliated few‐layer graphene with potassium is reported while monitoring the sample resistance using microwave conductivity. It is found that the conductivity of the samples increases by about an order of magnitude upon potassium exposure. The increased number of charge carriers deduced from the electron spin resonance (ESR) intensity also reflects this increment. The doped phases exhibit two asymmetric Dysonian lines in ESR, a usual sign of the presence of mobile charge carriers. The width of the broader component increases with the doping steps; however, the narrow components seem to have a constant line width.

Electronic and Magnetic Properties of Black Phosphorus

Physica Status Solidi (b)

Simón

Nagy

et al. 2017

Self Cite

Black phosphorus (bP) has emerged as the next member in the graphene inspired two‐dimensional materials family. Its electronic and magnetic properties are studied herein using electron and nuclear magnetic resonance techniques (ESR and NMR) and microwave conductivity measurement. The latter is a unique technique to study conductivity on air sensitive samples. The ESR study indicates the absence of free charge carriers and no sign of paramagnetic defects are found. 31P NMR shows the presence of a characteristic Pake doublet structure due to the interaction between I = 1/2 nuclei. Microwave conductivity shows, in accordance with the ESR results, that black phosphorus behaves as a semiconductor and we identify extrinsic and intrinsic charge carrier contributions to the conductivity and extracted the sizes of the gaps. ESR measurement also yields that bP might find applications as a microwave absorbent.