Chiral index dependence of the G+ and G- Raman modes in semiconducting carbon nanotubes.
ABSTRACT Raman spectroscopy on the radial breathing mode is a common tool to determine the diameter d or chiral indices (n,m) of single-wall carbon nanotubes. In this work we present an alternative technique to determine d and (n,m) based on the high-energy G(-) mode. From resonant Raman scattering experiments on 14 highly purified single chirality (n,m) samples we obtain the diameter, chiral angle, and family dependence of the G(-) and G(+) peak position. Considering theoretical predictions we discuss the origin of these dependences with respect to rehybridization of the carbon orbitals, confinement, and electron-electron interactions. The relative Raman intensities of the two peaks have a systematic chiral angle dependence in agreement with theories considering the symmetry of nanotubes and the associated phonons.
- SourceAvailable from: Evgeniya Sheremet[show abstract] [hide abstract]
ABSTRACT: During the recent years, a significant amount of research has been performed on single-walled carbon nanotubes (SWCNTs) as a channel material in thin-film transistors (Pham et al. IEEE Trans Nanotechnol 11:44--50, 2012). This has prompted the application of advanced characterization techniques based on combined atomic force microscopy (AFM) and Raman spectroscopy studies (Mureau et al. Electrophoresis 29:2266--2271, 2008). In this context, we use confocal Raman microscopy and current sensing atomic force microscopy (CS-AFM) to study phonons and the electronic transport in semiconducting SWCNTs, which were aligned between palladium electrodes using dielectrophoresis (Kuzyk Electrophoresis 32:2307--2313, 2011). Raman imaging was performed in the region around the electrodes on the suspended CNTs using several laser excitation wavelengths. Analysis of the G+/G- splitting in the Raman spectra (Sgobba and Guldi Chem Soc Rev 38:165--184, 2009) shows CNT diameters of 2.5 +/- 0.3 nm. Neither surface modification nor increase in defect density or stress at the CNT-electrode contact could be detected, but rather a shift in G+ and G- peak positions in regions with high CNT density between the electrodes. Simultaneous topographical and electrical characterization of the CNT transistor by CS-AFM confirms the presence of CNT bundles having a stable electrical contact with the transistor electrodes. For a similar load force, reproducible current--voltage (I/V) curves for the same CNT regions verify the stability of the electrical contact between the nanotube and the electrodes as well as the nanotube and the AFM tip over different experimental sessions using different AFM tips. Strong variations observed in the I/V response at different regions of the CNT transistor are discussed.Nanoscale Research Letters 12/2012; 7(1):682. · 2.52 Impact Factor