Doping in covalently functionalized carbon nanotubes: A Raman scattering study

Abstract

We experimentally investigate the effect of the structural and optoelectronic changes carbon nanotubes undergo after covalent functionalization. The carboxylation process alters the crystalline structure and the optical response of the tubes. We analyzed the intensity of disorder modes in the Raman spectra to estimate the structural degradation of the sp 2 network. After functionalization the bands associated with the G and 2D mode shift to higher frequency, indicating a change of the Fermi level DE F $ À0.5 and À0.65 eV in semiconducting and metallic nanotubes. This is also corroborated by the broadening of the semiconducting and narrowing of the metallic G mode phonons. Analysis of the luminescence correlated with absorption spectroscopy suggests that only the large-diameter tubes remain present after the functionalization procedure, whereas the small-diameter (d < 8.2 Å) ones get destroyed in the process. The spectral shifts of the E 11 transition energies indicate uniaxial strain of (e ¼ 0.18%) in the semiconducting nanotubes due to functionalization.

Fermi level shift in carbon nanotubes by dye confinement

“…The BWF line shape of the Raman G --band observed for non-defective tubes (green cross) and signing an important EPC [38], is strongly modified for defective nanotubes (black open circle). Considering that surface defects induce a p-type doping of the tube [39], the downshift of EF weakens the EPC, thus upshifting the Gmodes [26]. After 4T encapsulation (blue triangle), the peculiar BWF profile is recovered.…”

Advanced carbon nanotubes functionalization

“…[65]. Even mild covalent synthetic reaction conditions performed for very short times irreversibly destroy the emissive properties of the SWNTs [66]. Fig.…”

“…4 compares the emission of pristine nanotubes with the nanotubes prepared according the procedure of Ref. [66]: No emission can be observed from the majority of the tubes. This is the reason why it is dogmatically assumed by the nanotube community that covalent chemistry destroys the optoelectronic properties of SWNTs.…”

Light Control over Chirality Selective Functionalization of Substrate Supported Carbon Nanotubes

“…CNTs [20]. The D mode has been widely used in functionalized materials, [12,24] including aryl ring functionalization [17]. The increase of the D mode can therefore serve as a scale of the reaction product, since it is proportional to defects concentration.…”

“…intensity decrease is accompanied by a shift (0.5 cm −1 ) and broadening (0.7 cm −1 ) of the G mode due to doping induced by covalent functionalization. [24,33] The doping is a result of additional charge carriers shared by the functional moieties. The displacement of the G mode scales non-linearly with doping, [25,26] and therefore is not an ideal measure of the reaction product.…”