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An organic material composed of neutral free radicals based on the spirobiphenalenyl system exhibits a room temperature conductivity of 0.3 siemens per centimeter and a high-symmetry crystal structure. It displays the temperature-independent Pauli paramagnetism characteristic of a metal with a magnetic susceptibility that implies a density of states at the Fermi level of 15.5 states per electron volt per mole. Extended Hückel calculations indicate that the solid is a three-dimensional organic metal with a band width of ∼0.5 electron volts. However, the compound shows activated conductivity (activation energy, 0.054 electron volts) and an optical energy gap of 0.34 electron volts. We argue that these apparently contradictory properties are best resolved in terms of the resonating valence-bond ground state originally suggested by Pauling, but with the modifications introduced by Anderson.

We report a systematic study of the purification of nitric acid treated single-walled carbon nanotubes (SWNTs) by centrifugation at constant pH. The progress of the purification procedure was followed by estimating the purity by solution-phase near-infrared spectroscopy, and it was found that the sediment obtained by centrifugation at pH 2 had the highest purity. The stability of the aqueous dispersions of SWNTs and carbonaceous impurities (CIMP) after nitric acid treatment was investigated by measuring their zeta potential and the concentration of acidic sites. We found that, at lower pH, the CIMP has a higher zeta potential than nitric acid treated SWNTs, and it is this factor that allowed the separation of the carbonaceous impurities via centrifugation and the concomitant purification of the SWNTs.

Poly(aminobenzene sulfonic acid) (PABS) and polyethylene glycol (PEG) were covalently attached to single-walled carbon nanotubes (SWNTs) to form water-soluble graft copolymers. Quantitative near-IR (NIR) spectroscopic studies of these SWNT graft copolymers indicate a water solubility of about 5 mg/mL, and atomic force microscopy studies show a fairly uniform length and diameter. On the basis of thermogravimetric analysis, the loading of SWNTs in the graft copolymers is estimated to be 30% for SWNT-PABS and 71% for SWNT-PEG. NIR spectroscopic studies of SWNT-PABS show that this graft copolymer has a ground state that is a hybrid of the electronic structures of the isolated PABS and SWNT macromolecules.

We report the preparation, crystallization, and solid-state characterization of the first members of a new family of spiro-bis-(1,9-diamino-substituted-phenalenyl)boron neutral radicals. The crystal structures show that the three radicals are monomeric and without close contacts in the crystal lattice. In all cases magnetic susceptibility measurements confirm the presence of free radicals with one unpaired spin per molecule. Two of the new radical compounds are among the most highly conducting neutral organic solids, with room-temperature conductivities reaching sigma(RT) = 4 x 10(-2) S/cm. The measured conductivities correlate with the closest intermolecular contacts in the solid state and with the calculated band dispersions, even though the bandwidths are much smaller than those found in other organic conductors.

We present a study on the electronic behavior of films of as-prepared and purified single-walled carbon nanotubes (SWNTs) and demonstrate the important role that chemical functionalization plays in modifying their electronic properties, which in turn throws further light on the mechanism of action of SWNT-based sensors. Films of electric arc SWNTs were prepared by spraying, and optical spectroscopy was used to measure the effective film thickness. The room-temperature conductivities (sigma(RT)) of thin films deposited from as-prepared and purified SWNTs are in the range sigma(RT) = 250-400 S/cm, and the nonmetallic temperature dependence of the conductivity indicates the presence of tunneling barriers, which dominate the film conductivity. Chemical functionalization of SWNTs with octadecylamine (ODA) and poly(m-aminobenzenesulfonic acid) (PABS) significantly decreases the conductivity; sigma(RT) = 3 and 0.3 S/cm for SWNT-ODA and SWNT-PABS, respectively.

Due to their electrical, chemical, mechanical and thermal properties, carbon nanotubes are one of the most promising materials for the electronics, computer and aerospace industries. Here, we discuss their properties in the context of future applications in biotechnology and biomedicine. The purification and chemical modification of carbon nanotubes with organic, polymeric and biological molecules are discussed. Additionally we review their uses in biosensors, assembly of structures and devices, scanning probe microscopy and as substrates for neuronal growth. We note that additional toxicity studies of carbon nanotubes are necessary so that exposure guidelines and safety regulations can be established in a timely manner.

We report the synthesis of a single-walled carbon nanotube (SWNT) graft copolymer. This polymer was prepared by the functionalization of SWNTs with polyethyleneimine (PEI). We used this graft copolymer, SWNT-PEI, as a substrate for cultured neurons and found that it promotes neurite outgrowth and branching.

We report a chemical processing technology that allows the continuous spinning of single-walled carbon nanotubes (SWNTs)-nylon 6 (PA6) fibers by the in-situ polymerization of caprolactam in the presence of SWNTs, which simultaneously optimizes the morphology of the composite. We show that caprolactam is an excellent solvent for carboxylic-acid-functionalized SWNTs (SWNT-COOH) and that this allows the efficient dispersal of the SWNTs and subsequent grafting of PA6 chains to the SWNTs through condensation reactions between the carboxylic-acid group on SWNT-COOH and the terminal amine group of PA6. The existence of a graft copolymer between the PA6 chains and the SWNTs is demonstrated by IR, TGA, and AFM studies, and we show that the solubility of the polymerized material in formic acid is controlled by the degree of graft copolymerization. The amount of grafted PA6 chains that are attached to the SWNTs can be adjusted by controlling the concentration of the initiator (6-aminocaproic acid). The process leads to a uniform dispersion of the SWNTs, and the presence of the graft copolymer increases the polymer/SWNT compatibility while strengthening the interfacial interaction between the nanotube and matrix. The Young's modulus, tensile strength, and thermal stability of the SWNT-reinforced composite fibers produced by this process are significantly improved.

9-Hydroxyphenalenone is a planar multicyclic beta-keto-enol that demonstrates C2V symmetry on the NMR timescale. Off-axis substitution breaks the molecular symmetry and results in tautomers. 1H and 13C NMR assignments were made for 9-hydroxyphenalenone and three methyl derivatives, and the solution-phase tautomers were determined.

Control of the conductivity of single wall carbon nanotubes (SWNTs) is crucial for the use of carbon nanotubes in molecular electronics. We report a new fundamental characteristic of semiconducting SWNTs: the persistent photoconductivity of chemically modified carbon nanotube films. Illumination of carboxylated semiconducting SWNTs with ultraviolet or visible light causes a persistent decrease in the conductivity of semiconducting films. The photoinduced conductivity persists in the dark with a characteristic half-life of 35 s to 1.2 × 103 s at room temperature and an activation energy of 0.35 eV. Infrared illumination restores the conductivity of SWNT films. Ultraviolet and visible light illumination partially refills empty valence band states of chemically modified SWNTs by electron injection from the dopant sites. Photoinduced injection of electrons is accompanied by a decrease of the conductivity of the p-doped SWNT film, because of neutralization of holes by injected electrons. Covalent attachment o...

A facile method for assembling carbon nanotubes (CNT) on ferromagnetic metal contacts is described. Multiwalled carbon nanotubes (MWNT) with a magnetic cap were fabricated by thermally evaporating nickel on top of a vertical array of MWNTs grown on silicon. Magnetic interaction between the magnets on the nanotubes and lithographically patterned ferromagnetic electrodes caused the relative alignment and directed placement of nanotubes. The lithographically patterned electrodes were further modified using electrochemical deposition to form asymmetric ferromagnetic electrodes as well as improve the electrical and magnetic interactions at the contacts. MWNTs thus assembled showed characteristics that have been established for various nanotube device configurations. This validates the assembling technique for exploring charge- and spin-based electronic devices.

This study demonstrates a novel approach toward development of advanced chemical sensors based on chemically functionalized single-walled carbon nanotubes (SWNTs). SWNTs with covalently attached poly(m-aminobenzene sulfonic acid), SWNT-PABS, have shown improved sensor performance for detection of NH3. Compared to purified SWNTs, devices fabricated with SWNT-PABS have shown more than 2 times higher change of resistance upon exposure to NH3. Importantly, the SWNT-PABS sensors rapidly recover their resistance when NH3 is replaced with nitrogen. Exposure to NH3 induces significant changes in the electronic structure of SWNT-PABS, which allow detection of NH3 at concentrations as low as 5 ppm. Thin film deposited between interdigitated electrodes was explored as a device configuration for development of gas sensors.

The influence of Ni−Y catalyst composition on the bulk scale synthesis of single-walled carbon nanotubes (SWNTs) is studied using solution phase near-infrared spectroscopy. We found that a wide ran...

UV illumination of semiconducting single wall carbon nanotubes (SWNTs) results in a substantial increase of the intensity of the first interband transition (S11) followed by dark or IR light induced restoration of the initial intensity. The intensity of the S11 transition could also be modulated by light-induced reversible conversion of spiropyran molecules attached to SWNTs from the spiro conformation to its merocyanine form. Both surface-located monomeric and end-located aggregated merocyanines were found in UV illuminated spiropyran-SWNT supramolecular conjugates.

The measurement of the bulk purity of single-walled carbon nanotubes (SWNTs) is an important outstanding problem. We report a solution-phase near-IR (NIR) spectroscopic study of a range of carbon materials with an emphasis on SWNTs, and we show that NIR spectroscopy is an extremely powerful tool in the assessment of the carbonaceous purity of SWNTs. We demonstrate the applicability of Beer's law for all of the carbon materials included in this study within a range of concentrations in dimethylformamide (DMF), and we are able to solve for the effective extinction coefficients. By analyzing the areal absorptivities of the second interband transition of semiconducting SWNTs for a number of samples of differing purities, we are able to derive an absolute molar extinction coefficient for the carbonaceous impurities in SWNT samples. We demonstrate significant progress toward the establishment of an absolute scale for the bulk carbonaceous purity of SWNTs.

The use of neutral π-radicals as building blocks for molecular conductors holds both appeal and challenge. Such systems obviate the need for counterions, as charge transfer is not required to generate charge carriers. Essentially an array of π-radicals should function like atoms in an elemental metal, e.g., sodium, affording a half-filled energy band. Most radicals, however, tend to dimerize, and even when association can be suppressed the resulting low bandwidth W, coupled with a high on-site Coulomb repulsion U, leads to a Mott insulating state. We are pursuing the design and synthesis of stable heterocyclic thiazyl radicals, with a view to generating stable, crystalline materials with a high W/U ratio. The search for these new radicals, the molecular analogues of sodium, is the subject of this presentation.

The problems posed by the synthesis and purification of single-walled carbon nanotubes (SWNTs) have inhibited progress in the field. In this article, we review the methods available for measuring the purity of SWNTs and the current status of processes designed to purify them.We emphasize the hierarchy of the purification steps that must be developed in order to obtain high-quality material suitable for the full range of advanced applications that are envisioned for the ultimate carbon nanofiber.We review two strategies for SWNT purification, the assessment of SWNT purity by use of near-IR spectroscopy and its application to the thermal oxidation of thin films of SWNTs, as well as recent advances in the separation of metallic and semiconducting SWNTs. While substantial progress has been made in the purification and separation of SWNTs, we note the need for quality control and quality assurance within the industry. Much work remains before pure SWNTs of specific lengths, diameters, and chirality can be made available for applications.

A general synthetic route to the pyridine-bridged dithiazolodithiazolyl framework R2BPR1, involving N-alkylation of a 4-substituted 2,6-dichloropyridine, followed by amination and double Herz cyclization with S2Cl2, has been developed. The radicals R2BPMe (R2 = Me, Ph) have been prepared and characterized by EPR spectroscopy and cyclic voltammetry. Their crystal structures have been determined by X-ray crystallography. Both structures consist of undimerized slipped radical π-stacks. Lateral interactions in MeBPMe (space group P21/c) generate chainlike arrays with radicals linked by inversion centers; there are no close interchain S−S contacts. By contrast, in PhBPMe (space group P3121) the radical π-stacks are nested about 31 axes, so as to produce an extensive 2-dimensional network of intermolecular S−S interactions. Variable-temperature magnetic susceptibility measurements reveal that MeBPMe is essentially paramagnetic, whereas PhBPMe displays strong antiferromagnetic coupling. A value of J = −149 cm-1 ...

Single-walled carbon nanotube (SWNT) reinforced polymer composite membranes have been fabricated using the electrospinning technique. Nanofibers with a diameter in the range 50−100 nm were obtained by electrospinning SWNT-filled polystyrene composites. TEM observations revealed incorporation of small SWNT bundles oriented parallel to the nanofiber axis. As-prepared (AP) and ester (EST) functionalized SWNTs have been electrospun with polyurethane (PU) to demonstrate the effect of the chemical functionalization of SWNTs on the mechanical properties of SWNT-reinforced composites. The tensile strength of EST-SWNT-PU membranes is enhanced by 104% as compared to electrospun pure polyurethane membranes, while an increase of only 46% was achieved incorporating AP−SWNT in the polyurethane matrix. The tangent moduli of AP- and EST-SWNT-PU membranes were found to be respectively 215% and 250% higher than the control polyurethane membranes.

We report the preparation, crystallization, and solid-state characterization of a benzyl-substituted spirobiphenalenyl radical. The crystal structure shows that the radical is monomeric in the solid state, with the molecules packed in an unusual one-dimensional (1-D) fashion that we refer to as a pi-step stack. This particular mode of 1-D stacking is forced on the lattice arrangement by the presence of the orthogonal phenalenyl units that were specifically incorporated to prevent the crystallization of low-dimensional structures. The structure shows that this strategy is effective, and neighboring molecules in the stack can only interact via the overlap of one pair of active (spin-bearing) carbon atoms per phenalenyl unit, leading to the pi-step structure in which the remaining four active carbon atoms per phenalenyl unit do not interact with nearest neighbor molecules. The magnetic susceptibility data in the temperature range 4-360 K may be fit to an antiferromagnetic Heisenberg S = 1/2 linear chain model with intrachain spin coupling J = -52.3 cm(-1). Despite the uniform stacking, the material has a room temperature conductivity of 1.4 x 10(-3) S/cm and is best described as a Mott insulator.

Poly(m-aminobenzene sulfonic acid) (PABS), was covalently bonded to single-walled carbon nanotubes (SWNTs) to form a water-soluble nanotube–polymer compound (SWNT–PABS). The conductivity of the SWNT–PABS graft copolymer was about 5.6 × 10–3 S cm–1, which is much higher than that of neat PABS (5.4 × 10–7 S cm–1). The mid-IR spectrum confirmed the formation of an amide bond between the SWNTs and PABS. The 1H NMR spectrum of SWNT–PABS showed the absence of free PABS, while the UV/VIS/NIR spectrum of SWNT–PABS showed the presence of the interband transitions of the semiconducting SWNTs and an absorption at 17 750 cm–1 due to the PABS addend.

The use of multiwalled carbon nanotubes as a platinum support for proton exchange membrane fuel cells has been investigated as a way to reduce the cost of fuel cells through an increased utilization of platinum. Carbon nanotubes were selectively grown directly on the carbon paper by chemical vapor deposition with electrodeposited cobalt catalyzing the growth of the carbon nanotubes. The as-prepared carbon nanotubes were employed as the support for the subsequent platinum catalyst, which is electrodeposited on the carbon nanotubes. Physicochemical and electrochemical characterizations were conducted to identify the morphologies of the cobalt, the carbon nanotubes, and the electrodeposited platinum on the carbon nanotubes. The feasibility of a fuel cell using the carbon nanotube-based electrodes was demonstrated.

New synthetic routes to 1,2,3-dithiazolo-1,2,3-dithiazolylium salts, based on double Herz condensations of N-alkylated 2,6-diaminopyridinium salts with sulfur monochloride, have been developed. The two prototypal 1,2,3-dithiazolo-1,2,3-dithiazolyl radicals HBPMe and HBPEt have been prepared and characterized in solution by cyclic voltammetry and EPR spectroscopy. Measured electrochemical cell potentials and computed (B3LYP/6-31G) gas-phase disproportionation enthalpies favor a low on-site Coulombic repulsion energy U in the solid state. The crystal structures of HBPR (R = Me, Et) have been determined by X-ray crystallography (at 293 K). Both consist of slipped pi-stacks of undimerized radicals, with many close intermolecular S- - -S contacts. Magnetic, conductivity, and optical measurements have been performed and the results interpreted in light of extended Hückel band calculations. The crystalline materials are paramagnetic above 100 K, with room-temperature conductivities sigma(RT) of 10(-5)-10(-6) S cm(-1); the slightly greater conductivity of the R = Et compound can be associated with a more well developed band structure. We suggest a Mott-Hubbard insulator ground state for these materials, with an on-site Coulomb repulsion energy U of about 1.0 eV.

Electric-arc produced as-prepared single-walled carbon nanotube (AP-SWNT) films have been purified by a selective oxidation process. The purification is monitored by near-infrared (NIR) spectroscopy, which gives a quantitative estimate of relative purities. This technique also gives an estimate of the change in relative amounts of SWNTs and amorphous carbon impurities after each purification step, thereby providing accurate and selective control over the oxidation process. Oxidation was carried out by reaction in flowing oxygen at different temperatures and for different durations of time; the purity was evaluated after each oxidation step and compared to the starting as-prepared film. The purities and amounts of SWNTs and carbonaceous impurities were monitored as a function of oxidation temperature and time. Optimization of the process allowed a 3-fold improvement in the AP-SWNT purity with almost quantitative retention of the SWNT portion of the sample. A purification efficiency is defined, which is exp...

The nature of single-walled carbon nanotube (SWNT)−solvent interaction that is responsible for the stabilization of ultrasonicated dispersions was investigated using various techniques. It was found that the sonochemical decomposition and polymerization of o-dichlorobenzene (ODCB) is necessary for the stabilization of SWNTs in ODCB. The rate of decomposition of ODCB was shown to be dependent on the shape of the sonication vessel. The decomposition products of sonicated ODCB interact irreversibly with SWNTs. Under similar sonication conditions, N,N-dimethylformamide (DMF) did not induce discernible modification of the near-infrared spectrum of the dispersed SWNTs.

We report the crystal structure of a spiro-bis(1,9-disubstituted-phenalenyl)boron cation ( 2 + ) and by comparison with the structures of a series of radicals we conclude that the changes in bond lengths in the radicals compared to those of the corresponding cation can be qualitatively predicted by the sign of the partial bond order of the singly occupied molecular orbital (SOMO), which contains the additional electron. By use of this information, we can analyse the structures of the π-dimer radicals 1 and 2 and ascertain the location of the unpaired electron in these compounds. Where these radicals exist as paramagnetic π-dimers (high-temperature regime), the unpaired electrons reside mainly in the phenalenyl units not directly involved in the π-dimer interaction. At low temperatures, where the diamagnetic π-dimers exist, the electrons localise in the phenalenyl units directly involved in the π-dimer, but there still exists some degree of delocalisation of the electrons to the other halves of the molecules. We postulate that the increase in delocalisation of the unpaired electrons is related to the increase of the conductivity by about two orders of magnitude as the electrons spin pair.

We report the pressure dependence for the radial (omega R) and tangential (omega T) band frequencies in debundled single-walled carbon nanotubes (SWNTs) derived from laser-synthesized SWNT bundles. As previously described, a chemical procedure was used to prepare debundled SWNTs from as-prepared, large SWNT bundles. The normalized pressure coefficient for omega R in the debundled sample was compared with the corresponding value in the bundled sample to quantify the strength of van der Waals interactions between tubes in these nanotube materials. Furthermore, the pressure dependences for the radial (omega R) and tangential (omega T) band frequencies in debundled tubes were also compared with corresponding dependences predicted for isolated SWNTs, obtained with generalized tight binding molecular dynamic (GTBMD) simulations described in our previous work. The results presented here collectively suggest that the van der Waals interaction is still strong in the debundled sample studied here, which contained predominantly small bundles of SWNTs rather than isolated tubes.

We report a rapid, quantitative procedure for the evaluation of the carbonaceous purity of bulk quantities of as-prepared single-walled carbon nanotube (SWNT) soot by the utilization of solution-phase near-IR spectroscopy. The procedure starts with two steps of homogenization followed by solution/dispersion spectroscopy of a representative part of the bulk sample. The purity is evaluated against a reference sample by utilizing the region of the second interband transition (S22) for semiconducting SWNTs. The procedure is found to be capable of reliably analyzing the carbonaceous purity of a 10-g batch of SWNTs produced by the electric arc discharge method to within 3%.

A new class of phenalenyl-based neutral radical molecular conductors has recently been reported; a distinctive feature of these molecular solids is the absence of the well-defined conducting pathway(s) that are characteristic of the organic charge- transfer salts. These radicals do not stack in the solid state, and the requisite carbon- carbon contacts are all larger than the sum of the van der Waals distances. Magnetic susceptibility measurements show that these compounds usually exist as isolated free radicals with one spin per molecule (at least over some temperature range), apparently supporting the idea that there is little interaction between the molecules in the solid state. Nevertheless, these radicals show the highest conductivity (RT 0.05 S/cm) of any neutral organic solid and the conduction mechanism is at present unresolved. In this article we report a structurally related radical with a resistivity five orders of magnitude higher than that of the previously reported radicals. We analyze the crystallographic and electronic structure of this solid in detail and point out some of the challenges that remain in relating structure, magnetism, and conductivity in this new class of organic solids. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 853- 865, 2003

The passage of a current through a solid requires a pathway for the movement of electrons or holes. A new class of phenalenyl-based neutral radical molecular conductors has recently been reported; a distinctive feature of these molecular solids is the absence of any obvious conducting pathway(s). These radicals do not stack in the solid state, and the requisite carbon−carbon contacts are all larger than the sum of the van der Waals distances. Magnetic susceptibility measurements show that the first compound to be isolated behaves as a free radical with one spin per molecule, apparently supporting the idea that there is little interaction between the molecules in the solid state. Nevertheless, this radical shows the highest conductivity (σRT = 0.05 S/cm), of any neutral organic solid, and the conduction mechanism is presently unresolved. In the present study, we report a structurally related radical with a resistivity 4 orders of magnitude higher than that of the previously reported radicals. We analyze th...

Alkylation of the zwitterionic heterocycle 8-chloro-bis[1,2,3]dithiazolo[4,5-b:5',4'-e]pyridine (ClBP) with alkyl triflates affords 8-chloro-4-alkyl-4H-bis[1,2,3]dithiazolo[4,5-b:5',4'-e]pyridin-2-ium triflates [ClBPR][OTf] (R = Me, Et, Pr). Reduction of these salts with decamethylferrocene affords the corresponding ClBPR radicals as thermally stable crystalline solids. The radicals have been characterized in solution by cyclic voltammetry and EPR spectroscopy. Measured electrochemical cell potentials and computed (B3LYP/6-31G) gas-phase disproportionation enthalpies are consistent with a low on-site Coulombic barrier U to charge transfer in the solid state. The crystal structures of ClBPR (R = Me, Et, Pr) have been determined by X-ray crystallography (at 293 K). All three structures consist of slipped pi-stacks of undimerized radicals, with many close intermolecular S.S contacts. ClBPMe undergoes a phase transition at 93 K to a slightly modified slipped pi-stack arrangement, the structure of which has also been established crystallographically (at 25 K). Variable-temperature magnetic and conductivity measurements have been performed, and the results interpreted in light of extended Hückel band calculations. The room-temperature conductivities of ClBPR systems (sigma(RT) approximately 10(-)(5) to 10(-)(6) S cm(-)(1)), as well as the weak 1D ferromagnetism exhibited by ClBPMe, are interpreted in terms of weak intermolecular overlap along the pi-stacks. The latter is caused by slippage of the molecular plates, a feature necessitated by the steric size of the R and Cl groups on the pyridine ring.

The hydrofullerenes C(60)H(2) (1) and C(60)H(6) (2) have been prepared in (13)C-enriched form and 2D INADEQUATE NMR spectra were measured. These spectra have provided unambiguous (13)C assignments for 2, and nearly unambiguous assignments for 1. In both cases, the most downfield resonances are immediately adjacent to the sp(3) carbons, despite the fact that these carbons are the least pyramidalized carbons in the molecule. Typically, (13)C chemical shifts move downfield with increasing pyramidalization (THETA(p)), but in these systems there is no strong correlation between THETA(p) and delta. HF-GIAO calculations are able to predict the chemical shifts, but provide little chemical insight into the origin of these chemical shifts. London theory reveals a significant paramagnetic ring current in 1, a feature that helps explain the (1)H shifts in these compounds and may contribute to the (13)C chemical shifts as well.

Purification of single-walled carbon nanotubes by capillary electrophoresis (CE) is demonstrated. Real-time Raman spectroscopy of the separation process and single-wavelength UV/vis detection show the ability of CE to provide high-resolution separations of nanotube fractions with baseline separation. AFM images of collected fractions demonstrate that separations are based on tube length. The separation method is suggested to be based on alignment of the nanotubes along the separation field.

We report EHT calculations of the band electronic structure of substituted pentacene derivatives and the polymorphs of the parent compound. The results show that there are wide disparities among the bandwidths and electronic dimensionalities of these compounds. The parent pentacene polymorphs are 2-dimensional in their band electronic structure with moderate dispersions; the bandwidths in the 14.1 Å d-spacing polymorph are noticeably larger than for the 14.5 Å d-spacing polymorph, reported by Campbell. Whereas the parent pentacene polymorphs adopt the well-known herringbone packing, the new, substituted pentacenes are noticeably different in their solid state structures and this is reflected in the band electronic structures. TMS adopts a highly 1-dimensional structure that leads to a large bandwidth along the stacking direction; TIPS also adopts a stacked structure, but because the molecules are laterally interleaved in the fashion of bricks in a wall, this compound is strongly 2-dimensional.

Advances in the chemical vapor deposition (CVD) growth of graphene have made this material a very attractive candidate for a number of applications including transparent conductors, electronics, optoeletronics, biomedical devices and energy storage. The CVD method requires transfer of graphene on a desired substrate and this is most commonly accomplished with polymers. The removal of polymer carriers is achieved with organic solvents or thermal treatment which makes this approach inappropriate for application to plastic thin films such as polyethylene terephthalate substrates. An ultraclean graphene transfer method under mild conditions is highly desired. In this article, we report a naphthalene-assisted graphene transfer technique which provides a reliable route to residue-free transfer of graphene to both hard and flexible substrates. The quality of the transferred graphene was characterized with atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. Field effect transistors, based on the naphthalene-transfered graphene, were fabricated and characterized. This work has the potential to broaden the applications of CVD graphene in fields where ultraclean graphene and mild graphene transfer conditions are required.

Lithium-sulfur (Li-S) batteries are one of the most promising energy storage technologies because of the high theoretical capacity of sulfur as cathode. However, the high electrical resistivity of sulfur and the dissolution of lithium polysulfides into electrolytes are greatly limiting the performance of Li-S batteries. Interestingly, when the sulfur confinement size is smaller than 1 nm, different electrochemical behaviors and excellent cycle stabilities have been observed. However, the mechanism of sub-nano confinement of sulfur has not been investigated in details. Single-walled carbon nanotubes (SWCNTs) with their various pore size, uniform pore size distribution, and excellent electron conductivity are ideal hosts for studying the effect of different sulfur confinement sizes. In this study, we investigate the effect of sulfur confinement size by incorporating sulfur into both EA- (electric arc) and HiPco- (high-pressure carbon monoxide) SWCNTs with diameter of 1.55 ± 0.1 and 1.0 ± 0.2 nm, respectively. Interestingly, when sulfur is incorporated into HiPco-SWCNTs, the polymerized long chain sulfur molecules inside the tubes largely changes the Raman spectra. The giant Raman response from the sulfur provides an ideal opportunity to perform in situ studies on the lithiation-delithiation reactions of the confined sulfur. High-resolution TEM images confirm the chain structure of sulfur in EA- and HiPco-SWCNTs. Cyclic voltammetry and galvanostatic charge–discharge are performed by using different electrolytes, and sulfur in EA- and HiPco-SWCNTs show distinctively different electrochemical behaviors. In situ Raman spectra and ex situ XPS are measured during galvanostatic charge–discharge to investigate the lithiation-delithiation mechanism. A solid-state reaction mechanism was proposed when sulfur is in sub-nano confinement.

We report the crystallization of a subsitutionally doped organic conductor based on a host lattice composed of spiro-bis(phenalenyl)boron radicals. Co-crystallization of solutions of spiro-bis(9-oxidophenalenone)boron radical [PLY(O,O)]2B mixed with selected amounts of spiro-bis(9-oxidophenalenone)beryllium [PLY(O,O)]2Be leads to the formation of a series of solid-state solutions of composition [PLY(O,O)]2B(1-x)Be(x). The dopant molecules [PLY(O,O)]2Be serve to introduce holes into the lattice of spins provided by the [PLY(O,O)]2B radicals and lead to a systematic increase in the conductivity while decreasing the activation energy of the conduction process and leaving the solid-state structure relatively unperturbed. While the energies of the hole sites are expected to be high, the results are consistent with the interpretation of the electronic structure of [PLY(O,O)]2B in terms of the resonating valence bond model.

The formation of covalent bonds to single-walled carbon nanotube (SWNT) or graphene surfaces usually leads to a decrease in the electrical conductivity and mobility as a result of the structural rehybridization of the functionalized carbon atoms from sp(2) to sp(3). In the present study, we explore the effect of metal deposition on semiconducting (SC-) and metallic (MT-) SWNT thin films in the vicinity of the percolation threshold and we are able to clearly delineate the effects of weak physisorption, ionic chemisorption with charge transfer, and covalent hexahapto (η(6)) chemisorption on these percolating networks. The results support the idea that for those metals capable of forming bis-hexahapto-bonds, the generation of covalent (η(6)-SWNT)M(η(6)-SWNT) interconnects provides a conducting pathway in the SWNT films and establishes the transition metal bis-hexahapto organometallic bond as an electronically conjugating linkage between graphene surfaces.

Alterations in glial fibrillary acidic protein (GFAP) levels accompany the changes in the morphology and proliferation of astrocytes induced by colloidal solutes and films of carbon nanotubes (CNTs). To determine if GFAP is required for the effects of CNTs on astrocytes, we used astrocytes isolated from GFAP null mice. We find that selected astrocytic changes induced by CNTs are mediated by GFAP, i.e., perimeter, shape, and cell death for solutes, and proliferation for films.

The electronic structure of single-walled carbon nanotubes (SWNTs) is investigated by transmission spectroscopy of thin films. Hole-doping of SWNTs, as a result of purification, leads to free carrier absorption in the far-IR spectral range. Thermal cycling de-dopes SWNTs, transferring spectral weight from the far-IR to the interband transitions in the near-IR spectral range. After the nanotubes are de-doped, a diameter dependent peak in the far-IR is apparent at ∼100 cm-1, which we ascribe to a curvature induced energy gap in the DOS of nonarmchair metallic SWNTs.

The preparation and crystal structure of 5-cyanofuran-2-[1,2,3,5-diselenadiazolyl], [RCN(2)Se(2)] (R = 5-cyanofuran), is reported. Crystal data for C(6)H(2)ON(3)Se(2): monoclinic, space group P2(1), a = 7.1121(7), b= 20.541(2), c =20.923(2) A, beta = 99.785(1) degrees, Z = 16. The crystal structure consists of diselenadiazolyl pi-dimer stacks running parallel to the x direction; the asymmetric unit consists of four pi-dimer units. The dimers are aligned into snakelike ribbons along the y direction, with consecutive dimers linked by head-to-tail CN-Se contacts. Each pi-dimer stack is bordered by two out-of-register stacks, but most interstack Se-Se contacts lie outside the van der Waals separation. Along the pi-dimer stacks, the intradimer Se-Se distances range from 3.183(10) to 3.294(1) A, and the interdimer Se-Se distances range from 3.826(1) to 3.945(1) A. Like other pi-dimer stacked diselenadiazolyls, [C(6)H(2)ON(3)Se(2)](2) is diamagnetic over the temperature range 4-380K. Variable temperature single-crystal conductivity measurements reveal a room-temperature conductivity near 10(-5) S cm(-1) and provide a calculated band gap of 0.72 eV. The structural results and transport properties are interpreted in the light of Extended Hückel band structure calculations.

By use of solution phase mid-IR spectroscopy we are able to obtain an estimate for the ratio of the carbon atoms in the single-walled carbon nanotube (SWNT) backbone to the carbon atoms in the end-groups and at defect sites of the octadecylamido (ODA) functionalized soluble SWNTs (s-SWNT-CONH(CH2)17CH3). This analysis shows that the weight percentage of the octadecylamido functionality in the s-SWNTs is about 50%.

X-ray photoelectron spectroscopy (XPS) has been used to investigate the surface chemical state of two carbon nanotube materials and determine the evidence of surface modification from a reaction with dichlorocarbene. Carbon and oxygen were the major elements observed on the surface of the pristine carbon nanotube produced by electric arc discharge. After reaction with dichlorocarbene, chlorine atoms amounting to about 1.6 at.% were detected and the peak position of Cl 2p was at 201.3 eV, which can be attributed to existence of organic chlorocarbons. A new intense peak addition to the peak at 285 eV for the elemental sp 2 and sp 3 carbon atoms appears at the binding energy of about 287.5 eV in the C 1s narrow scan spectrum. This binding energy is typical for C 1s ionization of sp 3 carbon in organic chlorocarbons. It was found that CC was the major carbon functional component in the surface modified carbon nanotube but other functional forms of carbon were also present such as CCl, CO, and OCO. With Ar + ion sputtering, the atomic percent concentration of chlorine decreased by 65%, the carbon concentration increased significantly and the oxygen surface concentration decreased from 20.7 to 5.5 at.%. The surface chemical treatment with dichlorocarbene has thus modified the surface of the carbon nanotube with localization of small amounts of chlorine atoms on the carbon surface without disrupting the single walled nanotube bundles.

We report the measurement of the acidic sites in three different samples of commercially available full-length purified single-walled carbon nanotubes (SWNTs) – as obtained from CarboLex (CLI), Carbon Solutions (CSI) and Tubes@Rice (TAR) – by simple acid–base titration methods. Titration of the purified SWNTs with NaOH and NaHCO3 solutions was used to determine the total percentage of acidic sites and carboxylic acid groups, respectively. The total percentage of acidic sites in full length purified SWNTs from TAR, CLI and CSI are about 1–3%.

We have measured the Raman spectrum of individual single walled carbon nanotubes in solution and compare it to that obtained from the same starting material where the tubes are present in ordered bundles or ropes. Interestingly, the radial mode frequencies for the tubes in solution are found to be approximately 10 cm (-1) higher than those observed for tubes in a rope, in apparent contradiction to lattice dynamics predictions. We suggest that there is no such contradiction, and propose that the upshift is due rather to a decreased energy spacing of the Van Hove singularities in isolated tubes over the spacings in a rope, thereby allowing the same laser excitation to excite different diameter tubes in these two samples.

We report the preparation, crystallization, and solid-state characterization of ethyl (3)- and butyl (4)-substituted spiro-biphenalenyl radicals. Both of these compounds are found to be conducting face-to-face pi-dimers in the solid state but with different room-temperature magnetic ground states. At room temperature, 4 exists as a diamagnetic pi-dimer (interplanar separation of approximately 3.1 A), whereas 3 is a paramagnetic pi-dimer (interplanar separation of approximately 3.3 A), and both compounds show phase transitions between the paramagnetic and diamagnetic forms. Electrical resistivity measurements of single crystals of 3 and 4 show that the transition from the high-temperature paramagnetic pi-dimer form to the low-temperature diamagnetic pi-dimer structure is accompanied by an increase in conductivity by about 2 orders of magnitude. This behavior is unprecedented and is very difficult to reconcile with the usual understanding of a Peierls dimerization, which inevitably leads to an insulating ground state. We tentatively assign the enhancement in the conductivity to a decrease in the on-site Coulombic correlation energy (U), as the dimers form a super-molecule with twice the amount of conjugation.

Full-length single-walled carbon nanotubes (SWNTs) were rendered soluble in common organic solvents by noncovalent (ionic) functionalization of the carboxylic acid groups present in the purified SWNTs. Atomic force microscopy (AFM) showed that the majority of the SWNTs ropes were exfoliated into small ropes (2−5 nm in diameter) and individual nanotubes with lengths of several micrometers during the dissolution process. The combination of multiwavelength laser excitation Raman scattering spectroscopy and solution-phase visible and near-infrared spectroscopies was used to characterize the library of SWNTs that is produced in current preparations. The average diameter of metallic nanotubes was found by Raman spectroscopy to be smaller than that of semiconducting nanotubes in the various types of full-length SWNT preparations. This observation sheds new light on the mechanism of SWNT formation.

The absorption properties of optical protein memories, comprised of Bacteriorhodopsin (BR) monolayer films, were studied for the first time to better understand the underlying read/write processes. We demonstrate that 755 nm light provides the greatest difference between the bR and Q photostates in 2D BR films. This implicates 755 nm as an optimal wavelength for probing the state of monolayer BR. A Cary 5000 spectrometer was used to observe state changes via absorption measurements following LED irradiation of BR coated samples.

In multi-layer printed wiring boards (PWBs), electrical connections between different layers are accomplished with plated through holes (PTHs). The reliability of the PTH barrel and the PTH-inner plane (IP) connection depends not only on the design but also on the conditions of manufacturing and assembly processes of the board. The concerns associated with manufacturing arise from drilling which heats up and smears the surrounding epoxy onto the copper inner plane surfaces and also from subsequent chemical hole-clean operations which desmear the drilled holes. Good adhesion of the PTH copper to the desmeared PTH wall and to the copper inner planes is important for the reliability of the PTHs during assembly and field service. PWB coupons consisting of resin-glass bundle areas as well as resin filled clearance areas surrounding the PTH have been considered for a series of experiments and tests. On these coupons, accelerated stress tests and failure analysis of the PTHs at the end of these tests have been conducted. An elasto-plastic finite element analysis of the PTH strains for a temperature excursion of 102°C has been carried out for signal PTHs without and with IP connections. A peel test, using a micro-mechanical tester, has also been carried out to assess the adhesion of PTH copper to different regions along the drilled hole. All of the testing techniques have been supplemented by suitable analytical techniques for studying the distribution of smear on the copper inner planes. A birefringence technique to estimate the temperature of the hole wall during drilling has been described. All of the fails observed during stress testing are in the form of cracks in the PTH barrel, the plane of the crack being perpendicular to the barrel axis. The cracks are localized near the glass bundle-resin rich interface. It has also been observed in the failure analysis that the PTH/IP connections are not susceptible to failure during the accelerated stress testing conditions considered. These observations are also supported by the results of stress analysis. The results of stress analysis show that the interior clearance holes show higher strains than those closer to board surfaces, suggesting that the PTH barrel failure is likely to occur at the clearance hole and that the likelihood of failure at the interior clearance holes is higher than those closer to the PWB surfaces. The results of the peel test reveal that in the glass bundle-resin regions, the adhesion along the PTH wall is determined by the mechanical interlocking between the plated copper and the glass bundles and is relatively insensitive to desmear operations. However, adhesion in the resin-rich areas is a strong function of the desmear operation, which enhances the adhesion of the PTH to the resin. Finally, it is shown that the birefringence technique may be used effectively to estimate the drilling temperature and, hence, the degree of smearing and PTH quality. It is concluded that while smear may play an important role in the failure of PTHs in PWBs, for thick packaging boards with high aspect ratio PTHs, the predominant failure mechanism is less likely to be smear related. Such a failure mechanism would be preceded by failure in the PTH barrels as a result of the large strain concentrations imposed at specific locations within the cross-section.