Doping in Carbon Nanotubes Probed by Raman and Transport Measurements

Abstract

In situ Raman experiments together with transport measurements have been carried out on carbon nanotubes as a function of gate voltage. In metallic tubes, a large increase in the Raman frequency of the G(-) band, accompanied by a substantial decrease of its linewidth, is observed with electron or hole doping. In addition, we see an increase in the Raman frequency of the G(+) band in semiconducting tubes. These results are quantitatively explained using ab initio calculations that take into account effects beyond the adiabatic approximation. Our results imply that Raman spectroscopy can be used as an accurate measure of the doping of both metallic and semiconducting nanotubes.

Direct Observation of Born−Oppenheimer Approximation Breakdown in Carbon Nanotubes

“…Clean, defect-free single-walled carbon nanotubes (SWNTs) are systems which can be used to verify fundamental phenomena such as Wigner crystallization 7 and spin-orbit coupling 8 , and are ideal candidates for testing fundamental physical predictions. In nanotubes, the BO approximation is expected to break down because of the relatively short vibrational period of the longitudinal optical (LO) phonon and the relatively long electronic relaxation time 9,10 . This breakdown has been observed in semiconducting nanotube mats 9 , however, inhomogeneities broaden effects in such systems.…”

“…In nanotubes, the BO approximation is expected to break down because of the relatively short vibrational period of the longitudinal optical (LO) phonon and the relatively long electronic relaxation time 9,10 . This breakdown has been observed in semiconducting nanotube mats 9 , however, inhomogeneities broaden effects in such systems.…”

“…The Gband is broadened and downshifted (reduced in frequency), an effect arising from coupling to a continuum of electronic states 9,10,[12][13][14][15][16][17][18] . In other words, the LO phonon mode is damped by the free electrons near the Fermi energy 19,20 .…”

Kohn anomalies in graphene nanoribbons

“…[22][23][24][25][26][27] Recently, it has been shown that the frequencies and spectral widths of the ⌫ point optical phonons ͑called the G band in Raman spectra͒ depend on the position of the Fermi energy E F and the chirality of the metallic SWNT. [28][29][30][31] The Fermienergy dependence of the Raman spectra can be used to determine the position of the Fermi energy, and the chirality dependence of the Raman spectra provides detailed information on the electronic properties near the Fermi energy of metallic SWNTs. These dependences originate from the fact that the conduction electrons of a metal partly screen the electronic field of the ionic lattice.…”

Probing top-gated field effect transistor of reduced graphene oxide monolayer made by dielectrophoresis

“…This is achieved using solid polymer electrolyte (PEO + LiClO 4 ) and Pt wire [17,18,19,20] in top gate geometry where the Fermi level can be significantly shifted by applying small gate voltages (∼ 1V) due to large gate capacitance (∼ 1.5 µF/cm 2 ). The RGO single layer is characterized by 2D Raman band at 2687 cm -1 and temperature coefficient of resistance is ∼ -0.095 % C -1 , same as that of mechanically exfoliated monolayer graphene [21].…”