Tsang J C, Freitag M, Perebeinos V, Liu J, Avouris Ph
IBM, T. J. Watson Research Center, Yorktown Heights, New York 10598, USA.
Nat Nanotechnol. 2007 Nov;2(11):725-30. doi: 10.1038/nnano.2007.321. Epub 2007 Oct 14.
We show that the Raman frequency associated with the vibrational mode at approximately 1,580 cm(-1) (the G mode) in both metallic and semiconducting carbon nanotubes shifts in response to changes in the charge density induced by an external gate field. These changes in the Raman spectra provide us with a powerful tool for probing local doping in carbon nanotubes in electronic device structures, or charge carrier densities induced by environmental interactions, on a length scale determined by the light diffraction limit. The G mode shifts to higher frequency and narrows in linewidth in metallic carbon nanotubes at large fields. This behaviour is analogous to that observed recently in graphene. In semiconducting carbon nanotubes, on the other hand, induced changes in the charge density only shift the phonon frequency, but do not affect its linewidth. These spectral changes are quantitatively explained by a model that involves the renormalization of the carbon nanotube phonon energy by the electron-phonon interaction as the carrier density in the carbon nanotube is changed.
我们表明，在金属和半导体碳纳米管中，与大约1580厘米⁻¹处的振动模式（G模式）相关的拉曼频率会随着外部栅极场诱导的电荷密度变化而发生偏移。拉曼光谱的这些变化为我们提供了一个强大的工具，用于在由光衍射极限确定的长度尺度上探测电子器件结构中碳纳米管的局部掺杂，或环境相互作用诱导的电荷载流子密度。在大场下，金属碳纳米管中的G模式向更高频率移动且线宽变窄。这种行为类似于最近在石墨烯中观察到的情况。另一方面，在半导体碳纳米管中，电荷密度的诱导变化仅使声子频率发生偏移，但不影响其线宽。这些光谱变化通过一个模型得到了定量解释，该模型涉及随着碳纳米管中载流子密度的变化，通过电子 - 声子相互作用对碳纳米管声子能量进行重整化。
