Abstract
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.
Highlights
Methods and SampleFew-layer graphene (FLG) samples were prepared from saturation potassium-doped spherical graphite powder (SGN18, Future Carbon) using dimethyl sulfoxide solvent for the wet chemical exfoliation as described elsewhere.[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 present in the sample.[29]
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
As the charge transfer is a monotonous function of the doping steps carried out, which is concluded from the conductivity data, the same monotonous fashion is assumed for the line width of the broader component
Summary
Few-layer graphene (FLG) samples were prepared from saturation potassium-doped spherical graphite powder (SGN18, Future Carbon) using dimethyl sulfoxide solvent for the wet chemical exfoliation as described elsewhere.[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 present in the sample.[29]. Prior to in situ measurements, the undoped FLG was heated to 400 C for 30 min in high vacuum (2 Â 10À6 mbar) to remove any residual solvents. The geometry is similar to the one used in the two-zone vapor phase intercalation technique.[9] The ampoule is sealed under a high vacuum (2 Â 10À6 mbar) Afterward, it is inserted into the microwave conductivity measurement setup (described later), where the in situ intercalation takes place. For every sample, an ESR measurement was performed to monitor the amount of conducting electrons in the system. Room temperature ESR measurements were performed after each doping step on a Bruker Elexsys E500 X-band spectrometer, without opening the sample ampoules. The latter can be performed when the spin diffusion time is smaller than the spin relaxation time (e.g., the so-called NMR limit), which is the usual case for porous materials
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