| 1. |
- Fedotov, Pavel V., et al.
(författare)
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Optical Study of Nanotube and Coronene Composites
- 2013
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Ingår i: Journal of Nanoelectronics and Optoelectronics. - : American Scientific Publishers. - 1555-130X .- 1555-1318. ; 8:1, s. 16-22
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Forskningsöversikt (refereegranskat)abstract
- A novel nanomaterial, graphene nanoribbons encapsulated inside single-walled carbon nanotubes (GNR@SWNT), was studied by combined optical methods. This nanomaterial was found to have a bright photoluminescence both in IR and UV-Vis spectral ranges. Its spectral features have a complicated resonant structure different from the features of initial components: coronene molecules and SWNTs. The encapsulation ability appears to correlate strongly with the geometry of SWNTs. A weak interaction between nanotube walls and encapsulated species has been discovered: no evidence of charge or energy transfer has been registered.
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| 2. |
- Gorkina, Alexandra L, et al.
(författare)
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Transparent and conductive hybrid graphene/carbon nanotube films
- 2016
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 100, s. 501-507
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nanomaterials (carbon nanotubes (CNTs) and graphene) are promising materials for optoelectronic applications, including flexible transparent and conductive films (TCFs) due to their extraordinary electrical, optical and mechanical properties. However, the performance of CNT- or graphene-only TCFs still needs to be improved. One way to enhance the optoelectrical properties of TCFs is to hybridize CNTs and graphene. This approach leads to creation of a novel material that exhibits better properties than its individual constituents. In this work, the novel hybrid CNT-graphene nanomaterial was fabricated by graphene oxide deposition on top of CNT films. The graphene oxide was then reduced by thermal annealing at ambient atmosphere or in H2 atmosphere. At the final step the CNT-graphene hybrids were chemically doped using gold(III) chloride. As a result, we show that the hybrids demonstrate excellent optoelectrical performance with the sheet resistance as low as 73 Ω/□ at 90% transmittance.
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| 3. |
- Anoshkin, Ilya V., et al.
(författare)
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Freeze-Dried Carbon Nanotube Aerogels for High-Frequency Absorber Applications
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:23, s. 19806-19811
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Tidskriftsartikel (refereegranskat)abstract
- A novel technique for millimeter wave absorber material embedded in a metal waveguide is proposed. The absorber material is a highly porous carbon nanotube (CNT) aerogel prepared by a freeze-drying technique. CNT aerogel structures are shown to be good absorbers with a low reflection coefficient, less than -12 dB at 95 GHz. The reflection coefficient of the novel absorber is 3-4 times lower than that of commercial absorbers with identical geometry. Samples prepared by freeze-drying at -25 degrees C demonstrate resonance behavior, while those prepared at liquid nitrogen temperature (-196 degrees C) exhibit a significant decrease in reflection coefficient, with no resonant behavior. CNT absorbers of identical volume based on wet-phase drying preparation show significantly worse performance than the CNT aerogel absorbers prepared by freeze-drying. Treatment of the freeze-dried CNT aerogel with n- and p-dopants (monoethanolamine and iodine vapors, respectively) shows remarkable improvement in the performance of the waveguide embedded absorbers, reducing the reflection coefficient by 2 dB across the band.
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| 4. |
- Chernov, Alexander I, et al.
(författare)
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Optical properties of graphene nanoribbons encapsulated in single-walled carbon nanotubes
- 2013
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 7:7, s. 6346-6353
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Lioubtchenko, Dmitri V., et al.
(författare)
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W-band phase shifter based on optimized optically controlled carbon nanotube layer
- 2017
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Ingår i: 2017 IEEE MTT-S International Microwave Symposium (IMS). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509063604 ; , s. 1188-1191
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Konferensbidrag (refereegranskat)abstract
- Phase shifting in a dielectric rod waveguide (DRW), loaded with carbon nanotube (CNT) layers of different thickness, was studied experimentally under light illumination in the frequency range of 75-110 GHz. The dependence of efficiency of the phase shifting, in terms of phase shift per light intensity and millimeter wave attenuation, on the optical transparency of the CNT-layer is investigated in this paper. The best result, a phase shifter of 0-15° with less than 0.1 dB additional signal loss in the W-band was achieved for a 95% transparent CNT layer at 23 mW/mm2 light intensity of a tungsten halogen lamp (main radiation spectrum is 550-680 nm). The overall insertion loss of the phase shifter including two DRW tapering sections serving as transitions to rectangular waveguides are 3 to 5 dB in the W-band, about 2 dB is attributed to the CNT DRW section. This comprises, for the first time, an optically-controlled CNT-based DRW phase shifter with phase shift and insertion loss levels suitable for practical applications.
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| 6. |
- Nasibulina, Larisa I., et al.
(författare)
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Direct synthesis of carbon nanofibers on cement particles
- 2010
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2142, s. 96-101
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nanotubes (CNTs) and nanofibers (CNFs) are promising candidates for the next generation of high-performance structural and multifunctional composite materials. One of the largest obstacles to creating strong, electrically or thermally conductive CNT-CNF composites is the difficulty of getting a good dispersion of the carbon nanomaterials in a matrix. Typically, time-consuming steps are required in purifying and functionalizing the carbon nanomaterial. A new approach under which CNTs-CNFs are grown directly on the surface of matrix and matrix precursor particles is proposed. Cement was selected as the precursor matrix, since it is the most important construction material. A novel cement hybrid material (CHM) was synthesized in which CNTs and CNFs are attached to the cement particles by two different methods: screw feeder and fluidized bed reactors. CHM has been proved to increase the compressive strength by two times and the electrical conductivity of the hardened paste by 40 times.
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| 7. |
- Smirnov, Serguei, et al.
(författare)
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Optically controlled dielectric properties of single-walled carbon nanotubes for terahertz wave applications
- 2018
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 10:26, s. 12291-12296
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Tidskriftsartikel (refereegranskat)abstract
- Materials with tunable dielectric properties are valuable for a wide range of electronic devices, but are often lossy at terahertz frequencies. Here we experimentally report the tuning of the dielectric properties of single-walled carbon nanotubes under light illumination. The effect is demonstrated by measurements of impedance variations at low frequency as well as complex dielectric constant variations in the wide frequency range of 0.1-1 THz by time domain spectroscopy. We show that the dielectric constant is significantly modified for varying light intensities. The effect is also practically applied to phase shifters based on dielectric rod waveguides, loaded with carbon nanotube layers. The carbon nanotubes are used as tunable impedance surface controlled by light illumination, in the frequency range of 75-500 GHz. These results suggest that the effect of dielectric constant tuning with light, accompanied by low transmission losses of the carbon nanotube layer in such an ultra-wide band, may open up new directions for the design and fabrication of novel Terahertz and optoelectronic devices.
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| 8. |
- Talyzin, Alexandr, 1969-, et al.
(författare)
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Hydrogenation, Purification, and Unzipping of Carbon Nanotubes by Reaction with Molecular Hydrogen : Road to Graphane Nanoribbons
- 2011
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 5:6, s. 5132-5140
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of single-walled carbon nanotubes (SWNTs) with hydrogen gas was studied in a temperature interval of 400-550 degrees C and at hydrogen pressure of 50 bar. Hydrogenation of nanotubes was observed for samples treated at 400-450 degrees C with about 1/3 of carbon atoms forming covalent C-H bonds, whereas hydrogen treatment at higher temperatures (550 degrees C) occurs as an etching. Unzipping of some SWNTs Into graphene nanoribbons is observed as a result of hydrogenation at 400-550 degrees C Annealing in hydrogen gas at elevated conditions for prolonged periods of time (72 h) is demonstrated to result also in nanotube opening, purification of nanotubes from amorphous carbon, and removal of carbon coatings from Fe catalyst particles, which allows their complete elimination by acid treatment.
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| 9. |
- Talyzin, Alexandr V., et al.
(författare)
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High-temperature transformations of coronene-based graphene nanoribbons encapsulated in SWNTs
- 2015
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:11, s. 2491-2495
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Tidskriftsartikel (refereegranskat)abstract
- Coronene-based graphene nanoribbons encapsulated inside single-walled carbon nanotubes (SWNTs) were prepared 440 degrees C under Ar and annealed at temperatures up to 825 degrees C. The structural modifications of coronene/SWNT samples were studied using Raman spectroscopy and transmission electron microscopy. Coronene and coronene-based graphene nanoribbons are hydrogen terminated and annealing at temperatures above the stability limit of C-H bonds were expected to result in formation of new products. Indeed, Raman spectroscopy revealed the appearance of new sharp peaks after annealing of samples above 650 degrees C. The possible nature of encapsulated products produced by annealing of hydrogen terminated nanoribbons inside SWNTs is discussed.
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| 10. |
- Talyzin, Alexandr V., et al.
(författare)
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Hydrogen-Driven Cage Unzipping of C-60 into Nano-Graphenes
- 2014
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:12, s. 6504-6513
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Tidskriftsartikel (refereegranskat)abstract
- Annealing of C-60 in hydrogen at temperatures above the stability limit of C H bonds in C60Hx (500-550 degrees C) is found to result in direct collapse of the cage structure, evaporation of light hydrocarbons, and formation of solid mixture composed of larger hydrocarbons and few-layered graphene sheets. Only a minor part of this mixture is soluble; this was analyzed using matrix-assisted laser desorption/ionization MS, Fourier transform infrared (FTIR), and nuclear magnetic resonance spectroscopy and found to be a rather complex mixture of hydrocarbon molecules composed of at least tens of different compounds. The sequence of most abundant peaks observed in MS, which corresponds to C2H2 mass difference, suggests a stepwise breakup of the fullerene cage into progressively smaller molecular fragments edge-terminated by hydrogen. A simple model of hydrogen-driven C-60 unzipping is proposed to explain the observed sequence of fragmentation products. The insoluble part of the product mixture consists of large planar polycyclic aromatic hydrocarbons, as evidenced by FTIR and Raman spectroscopy, and some larger sheets composed of few-layered graphene, as observed by transmission electron microscopy. Hydrogen annealing of C-60 thin films showed a thickness-dependent results with reaction products significantly different for the thinnest films compared to bulk powders. Hydrogen annealing of C-60 films with the thickness below 10 nm was found to result in formation of nanosized islands with Raman spectra very similar to the spectra of coronene oligomers and conductivity typical for graphene.
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| 11. |
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| 12. |
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| 13. |
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| 14. |
- Demchenko, P., et al.
(författare)
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Study of optical pumping influence on carbon nanotubes permittivity in THz frequency range
- 2018
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Ingår i: Journal of Physics. - : Institute of Physics Publishing.
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Konferensbidrag (refereegranskat)abstract
- Equivalent complex permittivity of carbon nanotubes (CNT) was measured with/without light illumination at the frequency range of 0.2-1 THz. It was shown that we can tune the dispersion of the CNT complex conductivity during varying of optical pumping (wavelength of 980 nm). These results mean that CNT is perspective candidate for development of THz tunable attenuators and phase shifters.
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| 15. |
- Gomon, D., et al.
(författare)
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Opticaly tunable conductivity of carbon nanotubes in terahertz frequency range
- 2018
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Ingår i: Optics InfoBase Conference Papers. - : OSA - The Optical Society. - 9781943580460
-
Konferensbidrag (refereegranskat)abstract
- Impact of infrared radiation illumination (980 nm) on the properties of carbon nanotubes (CNT), such as complex conductivity and permittivity, with different geometric parameters in the frequency range of 0.2-1.0 THz was studied.
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| 16. |
- Lyubchenko, Dmitri, et al.
(författare)
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Millimeter Wave Beam Steering Based on Optically Controlled Carbon Nanotube Layers
- 2018
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Konferensbidrag (refereegranskat)abstract
- In this paper, the dielectric constant changing of thin carbon nanotube layers under light illumination was used for phase shifter development in dielectric rod waveguides. This designed phase shifter was introduced to the dielectric rod waveguide dual-antenna array. The measurements of the beam steering at 90 GHz of the dielectric rod antenna array, covered with carbon nanotubes, were carried out.
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| 17. |
- Nasibulina, Larisa I., et al.
(författare)
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Effect of carbon nanotube aqueous dispersion quality on mechanical properties of cement composite
- 2012
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Ingår i: Journal of Nanomaterials. - : Hindawi Limited. - 1687-4110 .- 1687-4129. ; 2012
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Tidskriftsartikel (refereegranskat)abstract
- An effect of the quality of carbon nanotube (CNT) dispersions added to cement on paste mechanical properties has been studied. High-quality dispersions of few-walled CNT (FWCNTs) were produced in two steps. First, FWCNTs were functionalized in a mixture of nitric and sulfuric acids (70wt. and 96wt., resp.) at 80°C. Second, functionalized FWCNTs were washed out by acetone to remove carboxylated carbonaceous fragments (CCFs) formed during CNT oxidation. Mechanical test results showed 2-fold increase in the compressive strength of the cement paste prepared from the dispersion of acetone-washed functionalized FWCNTs, which is believed to occur due to the chemical interaction between cement matrix and functional groups (-COOH and -OH). Utilisation of unwashed FWCNTs led to a marginal improvement of mechanical properties of the cement pastes, whereas surfactant-treated functionalized FWCNT dispersions only worsened the mechanical properties. Copyright © 2012 Larisa I. Nasibulina et al.
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| 18. |
- Smirnov, Serguei, et al.
(författare)
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Carbon Nanotube Layer Modeling for Computer Simulation of Optically Controlled Phase Shifters
- 2018
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Konferensbidrag (refereegranskat)abstract
- We propose an approach for efficient modeling of thin carbon nanotube layers for full-wave device simulations without increasing the number of simulation mesh cells. A surface impedance, used in computer simulations, is calculated from the dielectric constant of the material. The dielectric constant is modeled by a Drude–Lorentz resonance, fitted to experimental results. The approach allowed to study the nanotube-induced losses and finite-size resonance effects in optically-controlled, dielectric rod waveguide-based phase shifters. The correctness of the model was verified both by the simulated and the measured S-parameters in the W-band.
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| 19. |
- Smirnov, Serguei, et al.
(författare)
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Millimeter Wave Phase Shifter Based on Optically Controlled Carbon Nanotube Layers
- 2018
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Konferensbidrag (refereegranskat)abstract
- Surfaces with tunable impedance are usually lossy at high frequencies, which limits the design of millimeter wave and Terahertz devices. This work experimentally demonstrates a phase shifter based on single-walled carbon nanotubes and dielectric rod waveguides in the 220–330 GHz frequency range. Thin carbon nanotube layers are used as a tunable impedance surface with the dielectric properties optically controlled by laser illumination.
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| 20. |
- Smirnov, Serguei, et al.
(författare)
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Wavelength-dependent photoconductivity of single-walled carbon nanotube layers
- 2019
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Ingår i: RSC Advances. - : RSC Publishing. - 2046-2069. ; 9:26, s. 14677-14682
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Tidskriftsartikel (refereegranskat)abstract
- A number of electronic devices such as phase shifters, polarizers, modulators, and power splitters are based on tunable materials. These materials often do not meet all the requirements namely low losses, fast response time, and technological compatibility. Novel nanomaterials, such as single-walled carbon nanotubes, are therefore widely studied to fill this technological gap. Here we show how the dielectric constant of single-walled carbon nanotube layers can be substantially modified by illuminating them due to unique light–matter interactions. We relate the optical excitation of the nanotube layers to the illumination wavelength and intensity, by resistance and capacitance measurements. The dielectric constant is modified under laser illumination due to the change of material polarization and free carrier generation, and is shown to not be temperature-related. The findings indicate that SWCNT layers are a prospective tunable optoelectronic material for both high and low frequency applications.
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