Pavel N. Gevko

Effect of annealing on the optical absorption spectra of single-walled carbon nanotubes

The thermal stability of initial and purified samples of single-walled carbon nanotubes prepared through gas-phase disproportionation of carbon monoxide CO in the presence of iron particles under high pressure (the HiPCO method) is investigated using optical absorption spectroscopy and thermogravimetry. An analysis of the optical absorption spectra demonstrates that thermal oxidation of the initial material proceeds rather rapidly and uniformly owing to the catalytic effect caused by the presence of iron particles in the sample. The destruction of the carbon nanotubes contained in the as-prepared and purified samples begins at temperatures of ∼250 and ∼300°C, respectively. It is shown that single-walled metallic nanotubes undergo faster oxidation as compared to the single-walled semiconducting nanotubes.

Optical absorption and raman spectroscopy study of the fluorinated double-wall carbon nanotubes

Abstract Double‐wall carbon nanotube (DWNT) samples have been fluorinated at room temperature with varied concentration of a fluorinating agent BrF3. Content of the products estimated from X‐ray photoelectron data was equal to CF0.20 and CF0.29 in the case of deficit and excess of BrF3. Raman spectroscopy showed considerable decrease of carbon nanotube amount in the fluorinated samples. Analysis of optical absorption spectra measured for pristine and fluorinated DWNT samples revealed a selectivity of carbon nanotube fluorination. Nanotubes with large chiral angle are more inert to the fluorinating agent used.

X-ray spectroscopy study of lithiated graphite obtained by thermal deposition of lithium

X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy are used for in situ studies of the electronic structure of lithiated natural graphite produced by thermal deposition of lithium upon graphite in a vacuum. By XPS and NEXAFS spectroscopy it is found that lithium vapor thermal deposition results in the formation of a lithiated graphite surface layer and a change in its electronic structure. Based on the quantum chemical simulation of the experimental СKα XES spectrum of lithiated graphite, it is found that lithium atoms are located mostly on the edges of graphite crystallites. Atomic force microscopy reveals that the size of natural graphite flakes varies from 50 nm to 200 nm.

Optical Absorption of Single‐Wall Carbon Nanotubes Produced by Arc‐Discharge Method with Different Concentration of Ni/Co Catalyst

Abstract Material containing single‐wall carbon nanotubes (SWNTs) was obtained by arc‐discharge method. The optical absorption spectra were measured. Several narrow absorption bands were observed in a range from 0.4 to 3 eV caused by optical transitions between van Hove singularities. Comparing the results of “tight‐binding” electronic structure calculation for SWNT with the experimental spectra we found that each feature of spectrum can be attributed to interband transition in SWNTs. We have also found that the total yield of SWNTs and their diameter distribution depend on the catalyst content.