Gate dependent Raman spectroscopy of graphene on hexagonal boron nitride

Abstract

Raman spectroscopy, a fast and nondestructive imaging method, can be used to monitor the doping level in graphene devices. We fabricated chemical vapor deposition (CVD) grown graphene on atomically flat hexagonal boron nitride (hBN) flakes and SiO2 substrates. We compared their Raman response as a function of charge carrier density using an ion gel as a top gate. The G peak position, the 2D peak position, the 2D peak width and the ratio of the 2D peak area to the G peak area show a dependence on carrier density that differs for hBN compared to SiO2. Histograms of two-dimensional mapping are used to compare the fluctuations in the Raman peak properties between the two substrates. The hBN substrate has been found to produce fewer fluctuations at the same charge density owing to its atomically flat surface and reduced charged impurities.

Ultrahigh-mobility graphene devices from chemical vapor deposition on reusable copper

“…For comparison, we also repeat the same procedure on a number of samples with CVD-grown graphene wet-transferred to SiO 2 or sandwiched between hBN flakes using the state-of-the-art wet etching technique ( 20 ). The obtained Γ 2D values for the wet-transferred samples are in agreement with literature ( 33 ). Remarkably, all heterostructures produced with the dry delamination method show a value of about 20 cm –1 , significantly smaller than what is observed in wet-transferred samples (see Fig.…”

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

“…57 Thus, the peculiar, nearly symmetric behaviors observed here and previously reported by others 7,8,41,[45][46][47] contrast strongly with the trends predicted if one only considers lattice expansion effects. This anomalous behavior has been originally predicted by Ando 56 and by Lazzeri and Mauri 57 as a consequence of the strong coupling between zone-center optical phonons and low-energy electronic excitations across the gapless bands of graphene.…”

“…42 Recently, electrochemically-gated graphene FETs have been successfully employed to investigate electron-phonon coupling, 41,[43][44][45][46][47] but also bandgap formation in bilayer graphene, 48,49 electron transport at high carrier density, 42,50,51 many-body phenomena, 6 as well as to electrically control the interaction between nano-emitters and graphene. 52,53 In such studies, an accurate determination of E F (hence of the gate capacitance) as a function of the gate voltage is a critical requirement.…”

Sensitive Raman Probe of Electronic Interactions between Monolayer Graphene and Substrate under Electrochemical Potential Control

“…Some (ω G , ω 2D ) values from references were also used, all of which were measured under electrochemical control or gating and only data of the zero-charge-density graphene were used. 9−11,13,14 The (ω G , ω 2D ) values spread between the strain lines of G/ITO and G/SiO 2 but did not lie on a straight line. Therefore, we assume that, if the measurements were all accurate, the discrepancy among our results and the references cannot be explained by charge doping or strain.…”

“…(a) ω 2D vs ω G of graphene on various substrates. Orange solid circles: CVD G/Cu foil; orange open circles: graphene transferred to Cu foil; red solid squares: CVD G/Au(111); red open squares: graphene transferred to Au(111); black diamonds: G/ITO; blue left triangles: G/SiO 2 ; green right triangles: micromechanical cleavage G/SiO 2 from refs (9−11, 13, 14). (b) ω 2D vs ω G of graphene during the synthesis of G/ITO.…”