In Situ Raman Probing of Graphene over a Broad Doping Range upon Rubidium Vapor Exposure

Abstract

We report in situ Raman scattering experiments on single-layer graphene (SLG) and Bernal bilayer graphene (BLG) during exposure to rubidium vapor. The G- and 2D-band evolutions with doping time are presented and analyzed. On SLG, the extended doping range scanned (up to about 10(14) electrons/cm(2)) allows the observation of three regimes in the evolution of the G-band frequency: a continuous upshift followed by a plateau and a downshift. Overall the measured evolution is interpreted as the signature of the competition between dynamic and adiabatic effects upon n-doping. Comparison of the obtained results with theoretical predictions indicates however that a substrate pinning effect occurs and inhibits charge-induced lattice expansion of SLG. At low doping, a direct link between electrostatic gating and Rb doping results is presented. For BLG, the added electrons are shown to be first confined in the top layer, but the system evolves with time toward a more symmetric repartition of the added electrons in both layers. The results obtained on BLG also confirm that the slope of the phonon dispersion close to the K point tends to be slightly reduced at low doping but suggest the occurrence of an unexpected increase of the phonon dispersion slope at higher electron concentration.

Resonance Raman Spectrum of Doped Epitaxial Graphene at the Lifshitz Transition

“…A similar observation was made in previous works that have also used artificially high temperatures 37 or Fermi level smearing 16 .…”

Raman spectroscopy of graphite intercalation compounds: Charge transfer, strain, and electron–phonon coupling in graphene layers

“…16a) has not yet been totally explained as its origin is more complex. The density charge observed to the boundary layers in GICs is shown to be above 4 × 10 13 /cm −3 , which for instance must lead to a frequency value in the order of ∼1611 cm −1 in agreement to electronic gated graphene [45,46], highly charged KC 24 [39], and theoretically addressed by Lazzeri et al [119]. Therefore, the calculated G c values for each GIC considered an arbitrary value of charged transfer frequency of 1611 cm −1 , minus its corresponding effective bi-axial strain (the same as the one considered for the G uc ) an almost perfect match of the resulting frequency is shown for the experimental G c in Fig.…”

“…This is the reason why this method is not accurate enough for surface sensitive methods like photoemission where in-situ UHV intercalation has been applied. More recently the use of new in-situ systems (process iv) in high-vacuum Raman doping cells allow the possibility to have a well controlled and consecutive in-situ intercalation [24,39] with an accurate stage determination in a systematic manner.…”

Raman spectroscopy of electrochemically gated graphene transistors: Geometrical capacitance, electron-phonon, electron-electron, and electron-defect scattering

“…Raman spectroscopy is also routinely employed to characterize unintentional doping in graphene [18][19][20] and to study the sensitivity of graphene to atmospheric 21 and chemical dopants. [22][23][24][25][26][27][28] Quantitative investigations of doped graphene are particularly relevant, since several interesting phenomena, such as superconductivity, [29][30][31] ferromagnetism, 32 charge or spin density waves, 33,34 as well as changes in the plasmon spectrum 35,36 are expected to occur in the strong doping regime (|E F | 1 eV). In practice, solid state graphene field-effect transistors (FETs), typically using a Si substrate as a back-gate and a SiO 2 epilayer as a gate dielectric, have been widely used to study the Raman response of graphene in the vicinity of the Dirac point (|E F | = 0 − 300 meV).…”

“…In practice, solid state graphene field-effect transistors (FETs), typically using a Si substrate as a back-gate and a SiO 2 epilayer as a gate dielectric, have been widely used to study the Raman response of graphene in the vicinity of the Dirac point (|E F | = 0 − 300 meV). 7,8,37,38 To access higher doping levels, other methodologies based on chemical doping [22][23][24][25][26][27][28] and electrochemical gating [39][40][41] have been introduced. The former is highly efficient, resulting in charge carrier concentrations exceeding 10 14 cm −2 , but is irreversible and little controllable.…”