Influence of oligonucleotide interaction on electronic properties of single walled carbon nanotubes

Raman spectroscopy is a powerful tool to study molecular systems. The influence of the non‐covalent interactions of two different lengths of oligonucleotides, 10‐base and 25‐base, composed of polyA, polyT, polyG and polyC, on the electronic structure of single‐walled carbon nanotubes (SWCNTs) is first studied by means of Raman spectroscopy. Then, the possible changes in their electronic structure with chemical attachment of the oligonucleotides are investigated. The Raman data indicates that polyA with 10‐base wraps the SWCNTs at increased incubation time, while polyA with 25‐base wraps quickly, but increasing the incubation time reduces the efficient wrapping, possibly due to the self‐stacking. The polyT‐10 does not wrap around the SWCNTs very effectively even at increased incubation times, but the polyT‐25 wraps them effectively in 30 mins, but increasing the time again decreases the wrapping significantly. While polyG shows similar pattern to the case for the polyA, the polyC shows much higher affinity for the SWCNTs under all studied conditions. The chemical attachment of the same oligonucleotides does not alter the electronic properties of the SWCNTs significantly. These results suggest that oligonucleotides can be used to bring the SWCNTs into higher structures through DNA hybridization without significantly altering their unique properties. Copyright © 2012 John Wiley & Sons, Ltd.     

Y-branching of single walled carbon nanotubes

Y-branching was observed by scanning tunnelling microscopy (STM) in single wall carbon nanotubes grown by thermal decomposition of C₆₀ fullerene in the presence of transition metals. These novel carbon nanostructures may play an important role in carbon-based nanoelectronics. Received: 18 November 1999 / Accepted: 20 January 2000 / Published online: 8 March 2000     

Photocurrent in single walled carbon nanotubes

Carbon based nanomaterials have received a lot of attention due to their unique structural and physical properties. In this study, photoresponse in semiconducting single-walled carbon nanotubes is investigated using density functional theory. The photocurrent generated is found to increase with the increasing electrode voltage at a constant flux. In all models the current increases uniformly with applied voltage and maximum value of current is found in the pristine CNT model, however the magnitude of photocurrent decreases in the homogenously nitrogen and boron doped models. Moreover, the photocurrent increases with increase in flux showing photoresistive property in CNTs. The spectral peaks appear at different wavelengths in the three models paving way for wide range of applications in the futuristic optoelectronic devices.     

Chemical functionalization of single walled carbon nanotubes

Chemical modification has been performed on purified single walled carbon nanotubes. XPS spectrum shows that the peak corresponding to C (1s) centered at 284.38 eV in pure nanotubes (graphitic C) is 0.4 eV downshifted in chlorinated sample. Subsequent coupling reactions were carried out with diamine molecules to form intertube connections. Tripropylentetramine and phenylendiamine have been chosen as a molecular linker. End-to-side and end-to-end nanotube interconnections are formed and then observed by atomic force microscopy (AFM). Statistical analysis made from AFM images shows around 30% junctions in functionalized and less than 2% in pristine material. Remarkable features can be observed in the Raman spectra at different functionalization steps. Simple conductance measurements on bucky papers prepared from prestine nanotubes and from nanotubes modified at various steps have been made and are discussed.     

Encapsulation of methane molecules into carbon nanotubes

Methane gas (CH₄) is a chemical compound comprising a carbon atom surrounded by four hydrogen atoms, and carbon nanotubes have been proposed as possible molecular containers for the storage of such gases. In this paper, we investigate the interaction energy between a CH₄ molecule and a carbon nanotube using two different models for the CH₄ molecule, the first discrete and the second continuous. In the first model, we consider the total interaction as the sum of the individual interactions between each atom of the molecule and the nanotube. We first determine the interaction energy by assuming that the carbon atom and one of the hydrogen atoms lie on the axis of the tube with the other three hydrogen atoms offset from the axis. Symmetry is assumed with regard to the arrangement of the three hydrogen atoms surrounding the carbon atom on the axis. We then rotate the atomic position into 100 discrete orientations and determine the average interaction energy from all orientations. In the second model, we approximate the CH₄ molecule by assuming that the four hydrogen atoms are smeared over a spherical surface of a certain radius with the carbon atom located at the center of the sphere. The total interaction energy between the CH₄ molecule and the carbon nanotube for this model is calculated as the sum of the individual interaction energies between both the carbon atom and the spherical surface and the carbon nanotube. These models are analyzed to determine the dimensions of the particular nanotubes which will readily suck-up CH₄ molecules. Our results determine the minimum and maximum interaction energies required for CH₄ encapsulation in different tube sizes, and establish the second model of the CH₄ molecule as a simple and elegant model which might be exploited for other problems.     

Size effect on doped single walled carbon nanotubes

Considering impurity doping in small sized carbon nanotubes of diameter around 0.4 nm, we have calculated the donor binding energy by increasing the dopant concentration through a screening function that includes the curvature effect. We could observe the sudden fall in donor binding energy and metallic behaviour of the smaller single walled carbon nanotubes around 10¹¹/cm² (0.0026%) of impurity concentration. This result is useful for nano electronic device application such as nano diodes and switches.     

Electronic properties of alkali-metal intercalated single walled carbon nanotubes

We present a comparative study of the electronic properties of sodium and lithium intercalated single walled carbon nanotubes in a bucky paper sample by electron energy loss spectroscopy and photoemission spectroscopy. We have found that at room temperature both sodium and lithium rapidly diffuse into the bulk of the sample while different magnitudes of charge transfer from Na and Li to the nanotube bundles have been observed. The maximum observed displacement of the Fermi level is almost the same for both alkali although Na and Li induce quite different changes in the carbon nanotube electronic structure. We interpret our results as a more covalent character of the Li-carbon nanotube interaction with respect to the ionic character of the Na-carbon nanotube interaction; the localization of the charge density along the Li-C bond is responsible for an intertube interaction within the carbon nanotube ropes.     

High yield incorporation and washing properties of halides incorporated into single walled carbon nanotubes

We describe here the high yield filling (i.e. >50%) of single walled nanotubes (SWNTs) with a variety of halides, achieved according to various modified filling procedures. Both bundles and discrete SWNTs can be filled continuously up to lengths of several hundred nm, often with filling yields approaching 60–70% or better. In addition some high yield filled SWNTs were subjected to long-term washing in either boiling or room temperature. aqueous media, which does not remove the filling from the tubules, but enables effective removal of water-soluble extraneous materials . Received: 10 May 2002 / Accepted: 25 October 2002 / Published online: 10 March 2003 RID="*" ID="*"Corresponding author. Fax: +44-1865/272-690, E-mail: jeremy.sloan@chem.ox.ac.uk     

Functionalization of silicon-doped single walled carbon nanotubes at the doping site: An ab initio study

We performed ab initio calculations on the cytosine-functionalized silicon-doped single walled carbon nanotubes (SWNT). The results show that silicon substitutional doping to SWNT can dramatically change the atomic and electronic structures of the SWNT. And more importantly, it may provide an efficient pathway for further sidewall functionalization to synthesize more complicated SWNT based complex materials, for example, our previously proposed base-functionalized SWNTs, because the doping silicon atom can improve the reaction activity of the tube at the doping site due to its preference to form sp3 hybridization bonding.     

Packing of linearly arranged benzene molecules inside single walled carbon nanotubes: The high pressure study

The high pressure behaviors and electronic properties of (C₆H₆)_n@SWCNT peapod structure with the different encapsulation densities are studied by the DFT calculation. The weak van der Waals interaction and electronic orbital hybridization interaction between the host and guest molecules are exhibited in the pressure lower and higher than 3 GPa, respectively. The encapsulation density of C₆H₆ molecules plays an important role in the structural deformation, the bonding behaviors, and the electronic orbital hybridization interaction of the considered four hybrid systems under the pressures.     

微孔对单壁纳米碳管储氢性能的影响

用巨正则蒙特卡罗分子模拟方法研究了单壁纳米碳管中的微孔即单壁纳米碳管基本孔-内管腔和管间孔对单壁纳米碳管储氢性能的影响.与低温下氮气吸附实验结果的比较发现单壁纳米碳管的内管腔是吸附的主要位置.分析单壁纳米碳管内管腔中吸附势的叠加和利用效率，发现管径为2nm左右时单壁纳米碳管内管腔的储氢容量最高.当单壁纳米碳管阵列的管间距增加时，单壁纳米碳管的管间孔也会成为有效的氢吸附位. 关键词： Monte Carlo方法 单壁纳米碳管 储氢 微孔     

An efficient route towards the covalent functionalization of single walled carbon nanotubes

A simple and efficient method of chemical functionalization of both single and multiwalled carbon nanotubes has been discussed to give enhanced water solubility by rapidly and efficiently generating an appreciable amount of hydrophilic functional groups using microwave radiation. Surface functionalization containing more than 30 wt% of oxygen has been achieved, resulting into solubility of 2–5 mg/mL. Further covalent functionalization of such soluble SWNTs provides a remarkable degree of aniline functionalization through amidation, where the formation of polyaniline has been avoided. Functionalization of SWNTs is confirmed by techniques like electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, Raman spectroscopy, cyclic voltammetry and impedance spectroscopy. Electrochemical analysis suggests an enhanced double layer capacitance (110 F/g) of nanotubes after microwave treatment. Aniline functionalization of SWNTs shows possible variations on the nanotube topography with concomitant formation of a dynamic polymer layer on the nanotube surface.     

Cutting of multi walled carbon nanotubes

Multi walled carbon nanotubes (MCNT) synthesized by CVD method have been successfully cut into different lengths by controlling H₂SO₄/HNO₃ (5:3) oxidation time. During the cutting process H₂SO₄ and HNO₃ were added independently and the oxidation processes were carried out at a lower temperature to void excess weight loss and damage to MCNT. The resulting shorted MCNT (s-MCNT) formed stable dispersion state in the polar solvents without the help of surfactants that provided possibility for further functionalization and application. Moreover, NaOH solution was used to determine the total percentage of acidic sites and the total percentage of acidic sites are about 0.2-1%.     

Interaction of alkanethiols with single-walled carbon nanotubes: First-principles calculations

We report the results of our first-principles study based on density functional theory on the interaction of alkanethiols with both defected and defect-free single-walled carbon nanotube (SWCNT). The adsorption energies are calculated for various configurations such as alkanethiol molecule approaching to defect sites heptagon, hexagon, and pentagon in defective tube, and another case where the alkanethiol approaching to hexagon in defect-free nanotube. The calculated results showed that alkanethiols are rather strongly bound to the outer surface of both the defected and defect-free carbon nanotubes with the binding energy of about −50.58 kcal/mol, consistent with the experimental result. We also find that alkanethiols prefer to be adsorbed on the hexagon ring site of defect-free nanotube. Furthermore, the effect of alkanethiols chain length on the adsorption of alkanethiols on carbon nanotubes has been investigated, and the obtained results reveal that the longer alkanethiols bind rather more strongly to the nanotube surface.     

Probing structural integrity of single walled carbon nanotubes by dynamic and static compression

We report on a first study of single walled carbon nanotubes (SWCNTs) after application of dynamic (shock) compression. The experiments were conducted at 19 GPa and 36 GPa in a recovery assembly. For comparison, an experiment at a static pressure of 36 GPa was performed on the material from the same batch in a diamond anvil cell (DAC). After the high pressure treatment the samples were characterized by Raman spectroscopy and transmission electron microscopy (TEM). After exposure to 19 GPa of shock compression the CNT material exhibited substantial structural damage such as CNT wall disruption, opening of the tube along its axis (“unzipping”) and tube shortening (“cutting”). Dynamic compression to 36 GPa resulted in essentially complete CNT destruction whereas at least a fraction of the nanotubes was recovered after 36 GPa of static compression though severely damaged. The results of these shock wave experiments underline the prospect of using SWCNTs as reinforcing units in material WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Resonant Raman excitation profiles of individually dispersed single walled carbon nanotubes in solution

Raman excitation profiles were generated between 695 and 985 nm for individual carbon nanotubes dispersed in aqueous solution. We confirmed that previously published spectral assignments for semi-conducting and metallic carbon nanotubes are able to predict the location and resonant maxima of radial breathing mode features in the Raman spectrum. Three large diameter features were observed within the excitation space over the scan range and accurately predicted as metallic species. There was significant agreement between predicted and observed Raman modes. However, one discrepancy is noted with the (6,4) nanotubes. This species is not observed when excited at or near its absorption transition. We find that the Raman cross-sections in general, assuming a diameter-based distribution of nanotubes, are disproportionately smaller for mod(n-m,3)=1 semi-conducting nanotubes than their counterparts by at least an order of magnitude. These results have important implications for the use of Raman spectroscopy to effectively characterize the chirality distribution of carbon nanotube samples. PACS 61.46.+w; 73.22.-f; 78.30.-j     

Dynamic mechanical analysis of single walled carbon nanotubes/polymethyl methacrylate nanocomposite films

Dynamic mechanical properties of nanocomposite films with different ratios of single walled carbon nanotubes/polymethyl methacrylate(SWCNTs/PMMA) are studied. Nanocomposite films of different ratios(0, 0.5, 1.0, and2.0 weight percent(wt%)) of SWCNTs/PMMA are fabricated by using a casting technique. The morphological and structural properties of both SWCNT powder and SWCNTs/PMMA nanocomposite films are investigated by using a high resolution transmission electron microscope and x-ray diffractometer respectively. The mechanical properties including the storage modulus, loss modulus, loss factor(tan δ) and stiffness of the nanocomposite film as a function of temperature are recorded by using a dynamic mechanical analyzer at a frequency of 1 Hz. Compared with pure PMMA film, the nanocomposite films with different ratios of SWCNTs/PMMA are observed to have enhanced storage moduli, loss moduli and high stiffness, each of which is a function of temperature. The intensity of the tan δ peak for pure PMMA film is larger than those of the nanocomposite films. The glass transition temperature(T g) of SWCNTs/PMMA nanocomposite film shifts towards the higher temperature side with respect to pure PMMA film from 91.2?C to 99.5?C as the ratio of SWCNTs/PMMA increases from 0 to 2.0 wt%.     

Functionalized single-walled carbon nanotubes interacting with glycine amino acid: DFT study

We have investigated the adsorption of glycine on carbon nanotubes (CNTs) functionalized by various functional groups using density functional theory calculations. Compared with the pristine CNTs, the functionalized CNTs system has significantly higher binding energy value and shorter distance between the glycine and the nanotube surface. The calculations of electronic structures and charge Mulliken population indicate a strong physisorption process for the glycine adsorption on the functionalized CNTs. Therefore, functionalized CNT is expected to be a novel material for designing life science-related tools employing biological systems.     

Retracted: A comparative Raman study of graphite,single‐walled,and multi‐walled carbon nanotubes

Retraction: The following article from Journal of Raman Spectroscopy, ‘A comparative Raman study of graphite, single‐walled, and multi‐walled carbon nanotubes’, by Animesh K. Ojha and Arnulf Materny published online on 3 March 2009 in Wiley InterScience ( www.interscience.wiley.com ), has been retracted by agreement between the authors, the journal Editor in Chief, Wolfgang Kiefer, and the publisher John Wiley & Sons, Ltd. The retraction has been agreed due to lack of citation or acknowledgement of third party interests in certain data included in the article.     

Ab initio study of dielectric function of C-substituted single walled boron nanotubes

We report dielectric function related optical properties namely dielectric constant, static dielectric constant, and absorption coefficients of C-substituted hexagonal boron nanotubes. The optical properties were computed for parallel and perpendicular polarized light in the framework of density functional theory. In this regard, three models of BNTs namely armchair (3,3), zigzag (5,0), and chiral (4,2) have been undertaken for probing the effect of carbon impurity. Our calculations show high dielectric constant of armchair and chiral BNTs for parallel polarized light and magnitude becomes smaller for higher impurity concentration, while zigzag BNT exhibits reverse trend for high impurity concentration. For perpendicular polarized light, the magnitude of dielectric constant ε ₁(ω) is decreased and shifts at higher frequencies. The absorption is revealed highest for armchair followed by zigzag and chiral BNTs independent of impurity concentration. The intensity of absorption gets weaken for higher concentration. The chiral BNTs show smaller but uniform absorption in smaller frequency range results in uniform field emission. These findings are also compared with available experimental and theoretical results. These metallic nanotubes are promising candidate as interconnects for nanodevices as well as field emission devices.