Enriched Single-walled Carbon Nanotubes Research Articles

Full Spectrum Raman Excitation Mapping Spectroscopy

A generalization of the Raman scattering (RS) spectrum, the Raman excitation map (REM) is a hyperspectral two-dimensional (2D) data set encoding vibrational spectra, electronic spectra and their coupling. Despite the great potential of REM for optical sensing and characterization with remarkable sensitivity and selectivity, the difficulty of obtaining maps and the length of time required to acquire them has been practically limiting. Here we show, with a simple setup using current optical equipment, that maps can be obtained much more rapidly than before (~ms to ~100 s now vs. ~1000 s to hours before) over a broad excitation range (here ~100 nm is demonstrated, with larger ranges straightforward to obtain), thus taking better advantage of scattering resonance. We obtain maps from different forms of carbon: graphite, graphene, purified single walled carbon nanotubes (SWCNTs) and chirality enriched SWCNTs. The relative speed and simplicity of the technique make REM a practical and sensitive tool for chemical analysis and materials characterization.

Nanoscale Excitation Dynamics of Carbon Nanotubes Probed with Photoinduced Force Microscopy

We perform time-resolved pump-probe measurements on heterogeneous samples of (6,5) enriched single-walled carbon nanotubes (SWCNTs), both at the ensemble level using transient absorption measuremen...

(Invited) Triplet Sensitizer Derived, Nanocarbon Bearing Donor-Acceptor Conjugates for High Potential, Long-Lived Charge Separation

Donor-acceptor conjugates capable of producing high potential, long-lived charge separated states are invaluable for artificial photosynthesis of converting light energy into either electricity or environmentally friendly fuels. The majority of the donor-acceptor conjugates designed for this purpose are derived mainly from singlet sensitizers.1,2 In such conjugates, charge separation from the singlet excited donor or acceptor due to rapid charge separation and recombination processes results in a short-lived charge separated state of singlet spin character. Utilization of high energy triplet sensitizers instead of the traditionally employed singlet sensitizers could be an elegant approach to generate long-lived charge separated states. The radical ion-pairs of triplet spin character charge recombine to the ground state slowly due to spin forbidden nature of the process. However, witnessing such a process purely from the triplet excited state without the interference of the singlet excited state and other competing photochemical events such as excitation energy transfer has been challenging to establish.3-5 In the present contribution, we summarize our efforts to derive and witness donor-acceptor conjugates where excited state electron transfer exclusively occurs from the triplet excited state. To achieve the goal, two triplet sensitizers, viz., palladium porphyrin and platinum porphyrin are covalently linked to either fullerene, C60 3-5 or (6,5) or (7,6) enriched single wall carbon nanotubes (SWCNTs).6 Using transient absorption spectral studies covering wide temporal and spatial regions, and time-resolved electron paramagnetic resonance (TR-EPR) studies, photoinduced electron transfer from 1MP* (M = Pd or Pt) to C60 in a series of dyads, leading to the formation of MP•+-C60 •- charge separated state of triplet spin character will be demonstrated. Similarly, the role of triplet sensitizers in promoting charge separation in PdP-SWCNT(6,5) and PdP-SWCNT(7,6) in solvents of different polarity will be highlighted. 1. C. B. KC, F. D’Souza, ‘Design and photochemical study of supramolecular donor-acceptor systems assembled via metal-ligand axial coordiation’ Coord. Chem. Rev. 2016, 322, 104-141.2. F. D’Souza, and O. Ito ‘Photosensitized electron transfer processes of nanocarbons applicable to solar cells’ Chem. Soc. Rev. 2012, 41, 86-96.3. C. Obondi, G. N. Lim, F. D’Souza, Triplet-Triplet Excitation Transfer in Palladium Porphyrin – Fullerene and Platinum Porphyrin – Fullerene Dyads’ J. Phys. Chem. C 2015, 119, 176-185.4. C. Obondi, G. N. Lim, B. Churchill, P. K. Poddutoori, A. van der Est, and F. D’Souza, ‘Modulating the generation of long-lived charge separated states exclusively from the triplet excited states in palladium porphyrin–fullerene conjugates’, Nanoscale, 2016, 8, 8333-8344.5. P. K. Poddutoori, Y. E. Kandrashkin, C. O. Obondi, F. D’Souza and A. van der Est, Triplet Electron Transfer and Spin Polarization in a Palladium Porphyrin–Fullerene Conjugate, Phys. Chem. Chem. Phys. 2018, 20, 28223-28231.6. L. M. Arellano, H. B. Gozebe, M. J. Gómez-Escalonilla, J. L. G. Fierro, F. D’Souza and F. Langa, Photoinduced charge separation in PdP-SWCNT(6,5) and PdP-SWCNT(7,6) donor-acceptor hybrids, manuscript in preparation.

Chirality enriched carbon nanotubes with tunable wrapping via corona phase exchange purification (CPEP).

Single-walled carbon nanotubes (SWCNTs) have unique photophysical properties and serve as building blocks for biosensors, functional materials and devices. For many applications it is crucial to use chirality-pure SWCNTs, which requires sophisticated processes. Purification procedures such as wrapping by certain polymers, phase separation, density gradient centrifugation or gel chromatography have been developed and yield distinct SWCNT species wrapped by a specific polymer or surfactant. However, many applications require a different organic functionalization (corona) around the SWCNTs instead of the one used for the purification process. Here, we present a novel efficient and straightforward process to gain chirality pure SWCNTs with tunable functionalization. Our approach uses polyfluorene (PFO) polymers to enrich certain chiralities but the polymer is removed again and finally exchanged to any desired organic phase. We demonstrate this concept by dispersing SWCNTs in poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6'-{2,2'-bipyridine})] (PFO-BPy), which is known to preferentially solubilize (6,5)-SWCNTs. Then PFO-BPy is removed and recycled, while letting the SWCNTs adsorb/agglomerate on sodium chloride (NaCl) crystals, which act as a toluene-stable but water-soluble filler material. In the last step these purified SWCNTs are redispersed in different polymers, surfactants and ssDNA. This corona phase exchange purification (CPEP) approach was also extended to other PFO variants to enrich and functionalize (7,5)-SWCNTs. CPEP purified and functionalized SWCNTs display monodisperse nIR spectra, which are important for fundamental studies and applications that rely on spectral changes. We show this advantage for SWCNT-based nIR fluorescent sensors for the neurotransmitter dopamine and red-shifted sp3 defect peaks . In summary, CPEP makes use of PFO polymers for chirality enrichment but provides access to chirality enriched SWCNTs functionalized in any desired polymer, surfactant or biopolymer.

Tuning of diameter and electronic type of CCVD grown SWCNTs: A comparative study on Co-Mo and Co-Ru bimetallic catalyst systems

Wafer-level catalytic chemical vapour deposition (CCVD) of semiconducting enriched single-walled carbon nanotubes (sc-SWCNTs) with high quality is of high interest for industrial realization of SWCNT-based sensor and electronic applications. While bimetallic catalysts systems are known to favor type-enriched growth of SWCNTs, surface morphological evolution of different bimetallic catalyst stacks during catalyst conditioning as well as its impact on SWCNTs growth is not clearly understood. Here, we present a systematic study on the effect of bimetallic catalyst composition, layer stack thickness configuration as well as CCVD process parameters on the composition of grown SWCNTs. Besides the well-known Co and Co-Mo system, the Co-Ru system was investigated. We found that in case of Co-Mo bimetallic system, highest degree of sc-SWCNTs content is achieved using bilayer configuration Co-Mo:0.2–0.1 nm processed at 810 °C and 20 kPa total pressure. In case of Co-Ru bimetallic system, highest degree of sc-SWCNTs content is achieved using Co-Ru:0.1–0.1 nm processed at 840 °C and 10 kPa total pressure.

Characterization of Transparent Conducting Carbon Nanotube Thin Films Prepared via Different Methods

The fabrication and characterization of transparent conductors based on single walled carbon nanotube (SWCNT) thin films were carried out in controlled environment and its performance compared. Here, we demonstrate the fabrication of thin, transparent, optically homogeneous, electrically conducting films of metallic enriched single-walled carbon nanotubes via three different deposition techniques namely dip coating, vacuum filtration and Langmuir Blodgett. Optical characterization showed that the maximum transmittance, TM, in Vis region is ~ 96.3% and minimum surface roughness, Ra ~ 4.87 nm achieved via Langmuir-Blodgett technique. I-V characteristics shows minimum sheet resistance, Rs ~ 3.62 × 103 Ω/sq and maximum conductivity, σ ~ 27.65 Ω-1cm-1 for vacuum filtration technique. It is shown that SWCNT deposition technique significantly affects the optical and electrical characteristics of resulting thin films. Langmuir Blodgett method produced film with the lowest surface roughness of Ra ~ 4.87 nm and uniform conductivity of σ ~ 0.025 Ω-1cm-1, whereas vacuum filtration method produced film with the highest surface roughness of Ra ~ 12.83 nm and non-uniform conductivity, σ, ranging from ~ 0.199 to ~0.017 Ω-1cm-1 depending on the film dimensions.

Near infrared nonlinear refractive index dispersion of metallic and semiconducting single-wall carbon nanotube colloids

Third-order nonlinear optical properties of different colloidal systems containing metallic and semiconducting enriched single wall carbon nanotubes have been investigated. Thermally managed Z-scan technique was performed to measure the nonlinear refractive index (n2) and estimate the absorption coefficient (β) of the colloidal systems. The n2 dispersion curve was obtained for both colloids in the range of 755–825nm, showing a considerable increase on the nonlinear refractive index for laser tuned at 800nm. The measurements also showed that the colloids nonlinear absorption coefficients were smaller than 8.5×10−10cm/W in this wavelength range. Analysis of the obtained figures of merit indicates that these systems are promising materials for all-optical switching applications.

Fluence-Dependent Singlet Exciton Dynamics in Length-Sorted Chirality-Enriched Single-Walled Carbon Nanotubes

We utilize individualized, length-sorted (6,5)-chirality enriched single-walled carbon nanotubes (SWNTs) having dimensions of 200 and 800 nm, femtosecond transient absorption spectroscopy, and variable excitation fluences that modulate the exciton density per nanotube unit length, to interrogate nanotube exciton/biexciton dynamics. For pump fluences below 30 μJ/cm(2), transient absorption (TA) spectra of (6,5) SWNTs reveal the instantaneous emergence of the exciton to biexciton transition (E11 → E11,BX) at 1100 nm; in contrast, under excitation fluences exceeding 100 μJ/cm(2), this TA signal manifests a rise time (τ rise ∼ 250 fs), indicating that E11 state repopulation is required to produce this signal. Femtosecond transient absorption spectroscopic data acquired over the 900-1400 nm spectral region of the near-infrared (NIR) region for (6,5) SWNTs, as a function of nanotube length and exciton density, reveal that over time delays that exceed 200 fs exciton-exciton interactions do not occur over spatial domains larger than 200 nm. Furthermore, the excitation fluence dependence of the E11 → E11,BX transient absorption signal demonstrates that relaxation of the E11 biexciton state (E11,BX) gives rise to a substantial E11 state population, as increasing delay times result in a concomitant increase of E11 → E11,BX transition oscillator strength. Numerical simulations based on a three-state model are consistent with a mechanism whereby biexcitons are generated at high excitation fluences via sequential SWNT ground- and E11-state excitation that occurs within the 980 nm excitation pulse duration. These studies that investigate fluence-dependent TA spectral evolution show that SWNT ground → E11 and E11 → E11,BX excitations are coresonant and provide evidence that E11,BX → E11 relaxation constitutes a significant decay channel for the SWNT biexciton state over delay times that exceed 200 fs, a finding that runs counter to assumptions made in previous analyses of SWNT biexciton dynamical data where exciton-exciton annihilation has been assumed to play a dominant role.

Conjugated polymer-controlled selective dispersion of single-walled carbon nanotubes and fabrication of network transistors

A family of polymers based on fluorene including homopolymers, alternating copolymers and two fourarmed polymers are synthesized by polycondensation. Their ability to selectively wrap specific (n, m) species using HiPco single-walled carbon nanotubes (SWNTs) as a raw material is investigated. Fluorescence, absorption and Raman spectroscopies are used to analyze SWNT species after addition to polymer suspensions. The results show separation of (n, m) SWNTs can be realized using an optimized polymer structure. The optimized polymer contains fluorene in the main chain to preferentially separate semiconducting nanotube species and hydrofluoric acid (HF)-degradable disilane groups so that it can be removed from the SWNTs after separation. We used the enriched SWNTs to prepare a solution-processed field-effect transistor with a random nanotube network in the active channel to demonstrate the selectivity of the polymer for (n, m) SWNTs. The device exhibits stable p-type semiconductor behavior in air with an on/off current ratio of 121 and hole mobility of 3.2 cm2V−1s−1. Open image in new window

The effect of single wall carbon nanotube metallicity on genomic DNA-mediated chirality enrichment

Achieving highly enriched single wall carbon nanotubes (SWNTs) is one of the major hurdles today because their chirality-dependent properties must be uniform and predictable for use in nanoscale electronics. Due to the unique wrapping and groove-binding mechanism, DNA has been demonstrated as a highly specific SWNT dispersion and fractionation agent, with its enrichment capabilities depending on the DNA sequence and length as well as the nanotube properties. Salmon genomic DNA (SaDNA) offers an inexpensive and scalable alternative to synthetic DNA. In this study, SaDNA enrichment capabilities were tested on SWNT separation with varying degrees of metallicity that were formulated from mixtures of commercial metallic (met-) and semiconducting (sem-) abundant SWNTs. The results herein demonstrate that the degree of metallicity of the SWNT sample has a significant effect on the SaDNA enrichment capabilities, and this effect is modeled based on deconvolution of the near-infrared (NIR) absorption spectra and verified with photoluminescence emission (PLE) measurements. Using molecular dynamics and circular dichroism, the preferential SaDNA mediated separation of the (6, 5) sem-tube is shown to be largely influenced by the presence of met-SWNTs.

Enhanced NMR Relaxation of Tomonaga-Luttinger Liquids and the Magnitude of the Carbon Hyperfine Coupling in Single-Wall Carbon Nanotubes

Recent transport measurements [Churchill et al. Nature Phys. 5, 321 (2009)] found a surprisingly large, 2-3 orders of magnitude larger than usual (13)C hyperfine coupling (HFC) in (13)C enriched single-wall carbon nanotubes. We formulate the theory of the nuclear relaxation time in the framework of the Tomonaga-Luttinger liquid theory to enable the determination of the HFC from recent data by Ihara et al. [Europhys. Lett. 90, 17,004 (2010)]. Though we find that 1/T(1) is orders of magnitude enhanced with respect to a Fermi-liquid behavior, the HFC has its usual, small value. Then, we reexamine the theoretical description used to extract the HFC from transport experiments and show that similar features could be obtained with HFC-independent system parameters.

Separation and/or selective enrichment of single-walled carbon nanotubes based on their electronic properties

Single-walled carbon nanotubes (SWNTs) possess unique electronic properties that make them very promising materials for use in both nano-electronics and thin film devices. However, SWNTs are always produced as a mixture of metallic and semiconducting nanotubes, which is a major roadblock to their widespread application. This tutorial review provides a brief summary of ways of separating single-walled carbon nanotubes into metallic and semiconducting fractions. Various methods including selective growth, selective removal, selective adsorption and band structure modulation--all of which aim to produce pure SWNTs with well-defined electronic properties--are systematically discussed. The main problems in this field, the outlook for separation techniques and some views of future developments are presented.

A combined photoemission and ab initio study of the electronic structure of (6,4)/(6,5) enriched single wall carbon nanotubes

AbstractDue to the growing number of applications of small diameter single wall carbon nanotubes (SWCNTs) in opto‐electronics and biological imaging, there is a strong need for a better understanding of their electronic properties. Because (6,5) tubes with a diameter of 0.75 nm are currently the strongest enriched in the CoMoCat synthesis process, they are one of the most studied carbon nanotubes. However, there is still a lack of knowledge on the electronic properties of these tubes. In this paper, we report on a detailed analysis of the electronic structure of (6,4)/(6,5) enriched nanotubes with a combined experimental and theoretical approach. From photoemission the detailed C1s and valence band response of these narrow diameter tubes is studied. The observed electronic structure is in sound agreement with state of the art ab initio calculations using density functional theory.

Solution-Phase Extraction of Ultrathin Inner Shells from Double-Wall Carbon Nanotubes

We present an efficient method to extract inner shells of double-wall carbon nanotubes (DWCNTs) in liquid phase. The extraction of inner from outer shells is achieved by cutting the DWCNTs with vigorous sonication in water containing surfactants. The extracted shells are perfectly isolated single-wall carbon nanotubes (SWCNTs) and can be separated using density gradient ultracentrifugation. Statistical analysis using high-resolution transmission electron microscopy reveals that the enrichment of SWCNTs with narrow diameter (0.62-1.0 nm) up to 100% is achieved from highly pure DWCNTs. Furthermore, the (5,4) SWCNTs, which have the diameter of 0.62 nm, are concentrated. Our findings provide a novel way to obtain very narrow, highly isolated SWCNTs with ultraclean surface that have not been obtained in conventional synthesis methods.

Optical Resolution and Diameter-Based Enrichment of Single-Walled Carbon Nanotubes through Simultaneous Recognition of Their Helicity and Diameter with Chiral Monoporphyrin

We have been developing host−guest methodology for separation of single-walled carbon nanotubes (SWNTs) with gable-type diporphyrins, designated as nanotweezers. In our previous works, chiral nanotweezers have been found to discriminate left- and right-handed structures (M and P forms, respectively, defined in our previous papers) as well as (n,m) structures through preferential extraction, giving optically active SWNTs with limited (n,m) forms. Herein, we report that chiral monoporphyrin also serves as a host molecule for separating SWNTs. When methanol was used as a solvent, chiral monoporphyrin extracted SWNTs through simultaneous recognition of their helicity and diameter, providing optically active SWNTs with enrichment of larger diameters. In ethylene glycol, on the other hand, a much larger amount of SWNTs was extracted through complexation with the chiral monoporphyrin, although the selectivity is lower than that in the case of methanol. Since the monoporphyrin can be prepared much more easily than diporphyrins, this finding may open up a practical route for large-scale separation of SWNTs through molecular recognition.

The effects of inhomogeneous isotope distribution on the vibrational properties of isotope enriched double walled carbon nanotubes

AbstractThe radial breathing mode in the Raman spectrum of 13C isotope enriched single walled carbon nanotubes is inhomogeneously broadened due to the random distribution of isotopes. We study this effect theoretically using density functional theory within the local density approximation and compare the result with experiments on isotope engineered double walled carbon nanotubes in which the inner tubes were grown from a mixture of 13C enriched fullerenes and natural fullerenes. As explained by the calculations, this synthesis procedure leads to an increased inhomogeneity compared to a case when only enriched fullerenes are used. The good agreement between the measurements and calculations shows the absence of carbon diffusion along the tube axis during inner tube growth, and presents a strong support of the theory that inner tube growth is governed by Stone–Wales transformations following the interconnection of fullerenes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enrichment of Single-Walled Carbon Nanotubes by Diameter in Density Gradients

The bulk enrichment and separation of single-walled carbon nanotubes (SWNTs) by diameter has been achieved through ultracentrifugation of DNA-wrapped SWNTs in aqueous density gradients. The separation is identified by the visual formation of colored bands of SWNTs in the density range of 1.11-1.17 g cm(-3). The optical absorbance spectra of the separated SWNTs indicate that SWNTs of decreasing diameter are increasingly more buoyant. This nondestructive and scalable separation strategy is expected to impact the fields of molecular electronics, optoelectronics, and sensing where SWNTs of a monodisperse band gap are essential.