Abstract
We present the results of THz, infrared and magneto-optical measurements performed on graphite nanoplatelet films as a function of temperature (4.2–300 K) and magnetic field (0–17.5 T). An effective medium analysis of the low-energy spectral response indicates that the nanoplatelet material is well described by a Drude function plus two infrared absorption bands. Interestingly, the Drude plasma frequency (∼1675 cm− 1) decreases slowly with temperature, whereas the carrier scattering rate (∼175 cm− 1) is temperature independent. Furthermore, measurements in an applied magnetic field at 4.2 K show that a large portion of the Drude spectral weight is transferred to finite frequency features corresponding to various Landau-level transitions. Some of these transition energies scale as , as expected for Dirac-like quasi-particles in graphene and observed in other graphene-like materials. Thus, our results are consistent with recent theoretical calculations indicating that the spectrum of multilayer graphene can be decomposed into subsystems effectively identical to monolayer or bilayer graphene.
Highlights
ExperimentalHigh-density graphite nanoplatelet films were deposited onto high-resistivity (∼5000 cm) silicon substrates using a chemical process described elsewhere [20]
Graphite is converted into few-layer graphite nanoplatelets by a process of acid intercalation, thermal exfoliation, physical separation and dispersion [20]
The frequency dependence of the transmission of the graphite nanoplatelet film can be divided into two regions
Summary
High-density graphite nanoplatelet films were deposited onto high-resistivity (∼5000 cm) silicon substrates using a chemical process described elsewhere [20]. Raman spectra on the films are consistent with this fewlayer graphene character [21]–[23]. It is interesting to note the relatively even stacking of nanoplatelets in the film, consistent with a dense distribution over large areas of the substrate. THz and far-infrared transmission measurements were carried out at the U4IR beamline of the National Synchrotron Light Source at Brookhaven National Laboratory. A Bruker IFS 66v Fourier transform infrared spectrometer and a 1.5 K bolometer detector were used over the range 10–120 cm−1. Infrared studies in higher magnetic fields were carried out at the National High Magnetic Field Laboratory in Tallahassee, using a Bruker 113v spectrometer with custom light-pipe optics to carry the infrared radiation through a 20 T superconducting magnet and a 4.2 K bolometer detector. The unpolarized light was incident normal to the film, and the magnetic field B was applied either perpendicular (Faraday geometry) or parallel (Voigt geometry) to the film
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