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.
"However, G−/ G+ modes being in-plane vibrations are less sensitive to environmental changes . Therefore, a rough estimation of the diameter (d) of CNTs deposited in the transistor was obtained by evaluating the splitting of the G− and G+ bands following an empirical formula recently proposed by Telg et al. . "
[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. DOI:10.1186/1556-276X-7-682 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we discuss the low-frequency range of the Raman spectrum of individual suspended index-identified single-walled (SWCNTs) and double-walled carbon nanotubes (DWCNTs). In SWCNTs, the role of environment on the radial breathing mode (RBM) frequency is discussed. We show that the interaction between the surrounding air and the nanotube does not induce a RBM upshift. In several DWCNTs, we evidence that the low-frequency modes cannot be connected to the RBM of each related layer. We discuss this result in terms of mechanical coupling between the layers which results in collective radial breathing-like modes. The mechanical coupling qualitatively explains the observation of Raman lines of radial breathing-like modes, whenever only one of the layers is in resonance with the incident laser energy.
[Show abstract][Hide abstract] ABSTRACT: The energy of ionic thermal motion presents universally, which is as high as
4 kJ\bullet kg-1\bullet K-1 in aqueous solution, where thermal velocity of ions
is in the order of hundreds of meters per second at room temperature1,2.
Moreover, the thermal velocity of ions can be maintained by the external
environment, which means it is unlimited. However, little study has been
reported on converting the ionic thermal energy into electricity. Here we
present a graphene device with asymmetric electrodes configuration to capture
such ionic thermal energy and convert it into electricity. An output voltage
around 0.35 V was generated when the device was dipped into saturated CuCl2
solution, in which this value lasted over twenty days. A positive correlation
between the open-circuit voltage and the temperature, as well as the cation
concentration, was observed. Furthermore, we demonstrated that this finding is
of practical value by lighting a commercial light-emitting diode up with six of
such graphene devices connected in series. This finding provides a new way to
understand the behavior of graphene at molecular scale and represents a huge
breakthrough for the research of self-powered technology. Moreover, the finding
will benefit quite a few applications, such as artificial organs, clean
renewable energy and portable electronics.
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