Pavel V. Fedotov

Chiral-Selective Growth of Single-Walled Carbon Nanotubes on Lattice-Mismatched Epitaxial Cobalt Nanoparticles

Controlling chirality in growth of single-walled carbon nanotubes (SWNTs) is important for exploiting their practical applications. For long it has been conceptually conceived that the structural control of SWNTs is potentially achievable by fabricating nanoparticle catalysts with proper structures on crystalline substrates via epitaxial growth techniques. Here, we have accomplished epitaxial formation of monometallic Co nanoparticles with well-defined crystal structure, and its use as a catalyst in the selective growth of SWNTs. Dynamics of Co nanoparticles formation and SWNT growth inside an atomic-resolution environmental transmission electron microscope at a low CO pressure was recorded. We achieved highly preferential growth of semiconducting SWNTs (~90%) with an exceptionally large population of (6, 5) tubes (53%) in an ambient CO atmosphere. Particularly, we also demonstrated high enrichment in (7, 6) and (9, 4) at a low growth temperature. These findings open new perspectives both for structural control of SWNTs and for elucidating the growth mechanisms.

Predominant (6,5) Single-Walled Carbon Nanotube Growth on a Copper-Promoted Iron Catalyst

We have developed a magnesia (MgO)-supported iron-copper (FeCu) catalyst to accomplish the growth of single-walled carbon nanotubes (SWNTs) using carbon monoxide (CO) as the carbon source at ambient pressure. The FeCu catalyst system facilitates the growth of small-diameter SWNTs with a narrow diameter distribution. UV-vis-NIR optical absorption spectra and photoluminescence excitation (PLE) mapping were used to evaluate the relative quantities of the different (n,m) species. We have also demonstrated that the addition of Cu to the Fe catalyst can also cause a remarkable increase in the yield of SWNTs. Finally, a growth mechanism for the FeCu-catalyzed synthesis of SWNTs has been proposed.

Optical Properties of Graphene Nanoribbons Encapsulated in Single-Walled Carbon Nanotubes

We report the photoluminescence (PL) from graphene nanoribbons (GNRs) encapsulated in single-walled carbon nanotubes (SWCNTs). New PL spectral features originating from GNRs have been detected in the visible spectral range. PL peaks from GNRs have resonant character, and their positions depend on the ribbon geometrical structure in accordance with the theoretical predictions. GNRs were synthesized using confined polymerization and fusion of coronene molecules. GNR@SWCNTs material demonstrates a bright photoluminescence both in infrared (IR) and visible regions. The photoluminescence excitation mapping in the near-IR spectral range has revealed the geometry-dependent shifts of the SWCNT peaks (up to 11 meV in excitation and emission) after the process of polymerization of coronene molecules inside the nanotubes. This behavior has been attributed to the strain of SWCNTs induced by insertion of the coronene molecules.

Insights into chirality distributions of single-walled carbon nanotubes grown on different CoxMg1−xO solid solutions

Low-temperature chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWNTs) was achieved on two different types of CoxMg1−xO catalysts prepared by different techniques: atomic layer deposition (ALD) and impregnation. The chirality distribution of SWNTs grown on the ALD-prepared CoxMg1−xO catalyst is wider than that of SWNTs grown on the impregnation-prepared CoxMg1−xO catalyst. The different chirality distributions of SWNTs are related to their different growth modes. The ALD-prepared CoxMg1−xO catalyzes the growth of SWNTs by “tip growth” mode, as revealed by in situ environmental transmission electron microscopy studies. In contrast, SWNTs grow on the impregnation-prepared CoxMg1−xO by “base growth” mode. “Base growth” is attributed to strong metal–support interactions between the epitaxially formed Co nanoparticles and the underlying MgO support, accounting for the synthesis of SWNTs with high chiral-selectivity. In addition, impregnation-prepared CoxMg1−xO catalysts calcinated at different temperatures were systematically studied and their catalytic performances in synthesizing carbon nanotubes were elucidated. This work illustrates the influence of metal–support interactions and catalyst reducibility on the chirality-distribution of the synthesized SWNTs.

Copper chloride functionalization of semiconducting and metallic fractions of single-walled carbon nanotubes

Abstract. In this work, a separation of arc-grown single-walled carbon nanotubes (SWNTs) over conductivity type has been performed with an aqueous two-phase separation method. The separated fractions were used to synthesize copper chloride (CuCl) at SWNTs hybrid materials. These nanohybrids were studied using UV-vis-NIR optical absorption and Raman techniques. The changes in electronic and optical properties of functionalized SWNTs were revealed. A significant p-type doping of SWNTs by CuCl was considered as a main reason for modification of nanotube optical properties.

Laser synthesis and stability of one-dimensional polyynic carbon chains in liquid media

Abstract. The results on femtosecond laser formation of polyynic linear carbon chains (LCCs) are reported. To reduce the oxidation and degradation of carbon chains, the synthesis of LCCs was performed in liquid media. The flakes of graphite were suspended in water or in hexane and ultrasonicated to obtain a suspension of micron-size graphite particles. This suspension was irradiated by pulses of Ti:sapphire laser. The spectral lines at 189, 199, 215, 225, 262, 276, 284, 299, 323, 342, and 368 nm in the optical absorption spectrum of the irradiated graphite suspension were clearly distinguished. They were attributed to the absorption of polyynic carbon chains CnH2, where n=2 to 20. The stability of the synthesized one-dimensional carbon chains suspended in water and hexane was defined based on the intensity of the optical absorption bands. Its half-life time was estimated to be 20 h at room temperature for water, and 7 and 25 days for hexane at 60°C and 5°C, respectively.

Luminescence of 60B2O3-32CaF2-8Bi2O3 glasses codoped with chromium and neodymium

Abstract60B2O3-32CaF2-8Bi2O3 glasses codoped with chromium and neodymium have been prepared for the first time, and their luminescence properties have been studied. The glasses have been shown to contain chromium in two oxidation states. We have obtained luminescence spectra of Cr3+ in octahedral coordination and Cr4+ in tetrahedral coordination. Energy transfer from Bi3+ to Nd3+ and Cr3+ has been demonstrated.

Heat-induced transformations in coronene—single-walled carbon nanotube systems

Abstract. Coronene molecules are used as filler for single-walled carbon nanotubes. Variation of the synthesis temperature regimes leads to formation of different types of carbon nanostructures inside the nanotubes. Accurate determination of the structures by optical spectroscopy methods remains an important issue in composite materials. Clear distinction between adsorbed organic molecules on the surface of the tubes and filled structures may be accessed by Raman and photoluminescence spectroscopies. We perform additional heat treatment after the initial synthesis procedure and show the evolution of the optical spectral features corresponding to the filled structures and adsorbed materials on the surface of single-walled carbon nanotubes.

Linear and non-linear optical properties of filled single-wall carbon nanotubes

A new approach for modification of optical and electronic properties of single-wall carbon nanotube films via a gas phase filling of nanotubes with the stranger acceptor molecules (iodine, CuCl) is presented. The modified films are characterized by techniques of linear (UV-vis-NIR optical absorption and Raman scattering) and non-linear (pump-probe) optical spectroscopy.