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In this work, we explain the origin and the mechanism responsible for the strong enhancement of the Raman signal of sulfur chains encapsulated by single-wall carbon nanotubes by running resonance Raman measurements in a wide range of excitation energies for two nanotube samples with different diameter distributions. The Raman signal associated with the vibrational modes of the sulfur chain is observed when it is confined by small-diameter metallic nanotubes. Moreover, a strong enhancement of the Raman signal is observed for excitation energies corresponding to the formation of excited nanotube-chain-hybrid electronic states. Our hypothesis was further tested by high pressure Raman measurements and confirmed by density functional theory calculations of the electronic density of states of hybrid systems formed by sulfur chains encapsulated by different types of single-wall carbon nanotubes.

Alignment of densely packed single-walled carbon nanotubes (SWNTs) largely preserves the extraordinary electronic properties of individual SWNTs in the alignment direction, while in transverse direction the films are very resistive due to large energy barriers for tunneling between adjacent SWNTs. We demonstrate that chromium atoms inserted between the sidewalls of parallel SWNTs effectively coordinate to the benzene rings of the nanotubes via hexahapto bonds that preserve the nanotube-conjugated electronic structure and serve as a conduit for electron transfer. The atomically interconnected aligned SWNTs exhibit enhanced transverse conductivity, which increases by ∼2100% as a result of the photoactivated organometallic functionalization with Cr. The hexahapto mode of bonding the graphitic surfaces of carbon nanotubes with transition metal atoms offers an attractive route to the reversible chemical engineering of the transport properties of aligned carbon nanotube thin films. We demonstrate that a device fabricated with aligned SWNTs can be reversibly switched between a state of high electrical conductivity (ON) by light and low electrical conductivity (OFF) by applied potential. This study provides a route to the design of novel nanomaterials for applications in electrical atomic switches, optoelectronic and spintronic devices.

We report the experimental realization of η6-complexes of group 6 transition metals with a single layer graphene using photo-activated reactions with organometallic compounds. The reaction progress was followed by in-situ measurements of the graphene conductivity. We observed that the chromium reagents exert the strongest effect on the electronic properties of graphene, leading to (η6-graphene)CrL [L = C6H6, (CO)3] complexes with enhanced conductivity. Thus, in the case of covalent functionalization of graphene with Cr(CO)6, the conductivity increased by a factor of 4, while the (η6- C6H6)Cr(CO)3 reagent doubled the conductivity producing the least enhancement. This mode of covalent bonding preserves the conjugation and the planarity of the graphene structure and offers a promising route for the preparation of a new class of graphitic materials functionalized with transition metals, which may find applications in optoelectronics, spintronics and magnetic nanodevices.

In this work, we examine the process of the quantum transfer of energy considering time-dependent dipole-dipole interaction in a dimer system characterized by two-level atom systems. By taking into account the effect of the acceleration and speed of the atoms in the dimer coupling, we demonstrate that the improvement of the probability for a single-excitation transfer energy extremely benefits from the incorporation of atomic motion effectiveness and the energy detuning. We explore the relevance between the population and entanglement during the time-evolution and show that this kind of nonlocal correlation may be generated during the process of the transfer of energy. Our work may provide optimal conditions to implement realistic experimental scenario in the transfer of the quantum energy. Keywords: Quantum energy transfer, Quantum acceleration and speed, Dipole-dipole interaction, Population, Dimer system, Two-level atom system, Quantum correlations

The presence of coherence phenomenon due to the interference of probability amplitude terms, is one of the most important features of quantum mechanics theory. Recent experiments show the presence of quantum processes whose coherence provided over suddenly large interval-time. In particular, photosynthetic mechanisms in light-harvesting complexes provide oscillatory behaviors in quantum mechanics due to quantum coherence. In this work, we investigate the coherent quantum transfer energy for a single-excitation and nonlocal correlation in a dimer system modelled by a two-level atom system with and without time-dependent coupling effect. We analyze and explore the required conditions that are feasible with real experimental realization for optimal transfer of quantum energy and generation of nonlocal quantum correlation. We show that the enhancement of the probability for a single-excitation transfer energy is greatly benefits from the combination of the energy detuning and time-dependent coupling effect. We investigate the presence of quantum correlations in the dimer using the entanglement of formation. We also find that the entanglement between the donor and acceptor is very sensitive to the physical parameters and it can be generated during the coherent energy transfer. On the other hand, we study the dynamical behavior of the quantum variance when performing a measurement on an observable of the density matrix operator. Finally, an interesting relationship between the transfer probability, entanglement and quantum variance is explored during the time evolution in terms of the physical parameters.

The unique two-dimensional structure and outstanding electronic, thermal, and mechanical properties of graphene have attracted the interest of scientists and engineers from various fields. The first step in translating the excellent properties of graphene into practical applications is the preparation of large area, continuous graphene films. Chemical vapour deposition (CVD) graphene has received increasing attention because it provides access to large-area, uniform, and continuous films of high quality. However, current CVD synthetic techniques utilize metal substrates (Cu or Ni) to catalyse the growth of graphene and post-growth transfer of the graphene film to a substrate of interest is critical for most applications such as electronics, photonics, and spintronics. Here we discuss recent advances in the transfer of as-grown CVD graphene to target substrates. The methods that afford CVD graphene on a target substrate are summarized under three categories: transfer with a support layer, transfer without a support layer, and direct growth on target substrates. At present the first two groups dominate the field and research efforts are directed towards refining the choice of the support layer. The support layer plays a vital role in the transfer process because it has direct contact with the atomically thin graphene surface, affecting its properties and determining the quality of the transferred graphene.

CVD graphene has attracted a great deal of interest from both academia and industry. The strong motivation to commercialize high quality CVD graphene films and related devices has been restricted by the lack of a cheap, efficient, clean and reliable graphene transfer process. In this article, we report a novel graphene transfer technique which provides a route to high-throughput, reliable and economical transfer of graphene without introducing large cracks and residue contamination from polymers, such as PMMA or magnetic impurities. The transferred graphene was thoroughly characterized with Raman spectroscopy, Atomic Force Microscopy, and X-ray photoelectron spectroscopy. Fabricated large area graphene-based field effect transistors exhibited high mobilities, which were about 2 times higher than those for devices prepared with graphene transferred by the conventional wet transfer method. This new graphene transfer technique has the potential to expedite the large scale industrial utilization of CVD graphene in electronics, spintronics, catalysis and energy storage.

The unique properties of single-walled carbon nanotubes (SWCNTs) have made them interesting candidates for applications in biomedicine. There are diverse chemical groups that can be attached to SWCNTs in order for these tiny tubes to gain various functionalities, for example, water solubility. Due to the availability of these &ldquo, functionalization&rdquo, approaches, SWCNTs are seen as agents for a potential anti-cancer therapy. In this context, we tested different chemically-functionalized forms of SWCNTs to determine which modifications make them better combatants against glioblastoma (astrocytoma grade IV), the deadliest brain cancer. We investigated the effects that two types of water soluble SWCNTs, functionalized with polyethylene glycol (SWCNT-PEG) or tetrahydrofurfuryl-terminated polyethylene glycol (SWCNT-PEG-THFF), have on the morphology and vitality, that is, cell adhesion, proliferation and death rate, of the D54MG human glioblastoma cells in culture. We found that SWCNT-PEG-THFF solute, when added to culture media, makes D54MG cells less round (measured as a significant decrease, by ~23%, in the form factor). This morphological change was induced by the PEG-THFF functional group, but not the SWCNT backbone itself. We also found that SWCNT-PEG-THFF solute reduces the proliferation rate of D54MG cells while increasing the rate of cell death. The functional groups PEG and PEG-THFF, on the other hand, reduce the cell death rate of D54MG human glioma cells. These data indicate that the process of functionalization of SWCNTs for potential use as glioma therapeutics may affect their biological effects.

We report the synthesis of vulcanized polyisoprene (SPIP) nanowires and an investigation of the electrochemical lithiation mechanism of the covalently bonded sulfur bridges in SPIP. Electrochemical analysis demonstrates that the sulfur chains in SPIP have distinct electrochemical signatures from those that are characteristic of bulk elemental sulfur. The cyclic voltammetry and galvanostatic cycling data show a distinct multistep charge-transfer process and solid-state lithium–sulfur reaction behavior, and it is clear that this new material provides a promising basis for the development of cathodes for rechargeable batteries. Chemical changes due to the lithiation process are studied using Raman and X-ray photoelectron spectroscopy, on the basis of which new lithiation mechanisms of covalently bonded sulfur are proposed.

The Hammond Postulate and the Leffler analysis have provided a cornerstone in the understanding of reaction processes in organic chemistry for over 60 years, yet quantitative applications of these methodologies over the range of reactions envisaged in the original works remain elusive. In the present paper, we analyze a series of SN2 reactions in three solvents that lead to endothermic and exothermic reaction processes, and we show that within the hybridization reaction coordinate the SN2 reaction is fully consistent with both treatments. We give new presentations of the reaction energies as a function of reaction progress, which allow the generation of unified reaction coordinate diagrams that show a linear relationship between the hybridization metric of reaction progress and the relative energies of the stationary points on the potential surface as a function of structure and solvent as originally envisaged by Leffler and Hammond.

The formation of bis-hexahapto bonds between graphitic surfaces can electronically interconnect the surfaces of carbon materials containing the polybenzenoid ring system and increase the conductivity without introducing a strong perturbation to the in-plane electronic structure. In this paper, we report the use of organometallic chemistry to interconnect the surfaces of small scale graphene nanoplatelets by using a variety of metals and photochemically activated organometallic reagents.

We consider the covalent chemistry of the carbon allotropes with an emphasis on the newest member—graphene. We focus on the effect of such chemistry on the geometric and electronic structure of the functionalized materials and the way in which the conjugation is modified by such processes. We conclude that there are two limiting cases: (a) Conventional addition chemistry leading to the formation of σ-bonds to the graphitic surface in which there is full rehybridization of the derivatized carbon atoms from sp 2 to sp 3 ; thus these carbon atoms are effectively removed from conjugation and from the electronic band structure (referred to as destructive rehybridization). (b) Covalent chemisorption with formation of an organometallic hexahapto-metal bond that largely preserves the graphitic band structure (constructive rehybridization) and accompanies the formation of bis-hexahapto-metal bonds such as those in (η 6 -SWNT)Cr(η 6 -SWNT) which serve to interconnect adjacent graphitic surfaces and significantly reduces the internanotube junction resistance in SWNT networks. The formation of η 2 di-hapto bonds represent an intermediate case of covalent chemistry and is known to be important in carbon nanotubes and particularly the fullerenes but this situation has been treated in detail in previous publications.

Single-walled carbon nanotube (SWNT) thin films provide a unique platform for the development of electronic and photonic devices because they combine the advantages of the outstanding physical properties of individual SWNTs with the capabilities of large area thin film manufacturing and patterning technologies. Flexible SWNT thin film based field-effect transistors, sensors, detectors, photovoltaic cells, and light emitting diodes have been already demonstrated, and SWNT thin film transparent, conductive coatings for large area displays and smart windows are under development. While chirally pure SWNTs are not yet commercially available, the marketing of semiconducting (SC) and metallic (MT) SWNTs has facilitated progress toward applications by making available materials of consistent electronic structure. Nevertheless the electrical transport properties of networks of separated SWNTs are inferior to those of individual SWNTs. In particular, for semiconducting SWNTs, which are the subject of this Account, the electrical transport drastically differs from the behavior of traditional semiconductors: for example, the bandgap of germanium (E = 0.66 eV) roughly matches that of individual SC-SWNTs of diameter 1.5 nm, but in the range 300-100 K, the intrinsic carrier concentration in Ge decreases by more than 10 orders of magnitude while the conductivity of a typical SC-SWNT network decreases by less than a factor of 4. Clearly this weak modulation of the conductivity hinders the application of SC-SWNT films as field effect transistors and photodetectors, and it is the purpose of this Account to analyze the mechanism of the electrical transport leading to the unusually weak temperature dependence of the electrical conductivity of such networks. Extrinsic factors such as the contribution of residual amounts of MT-SWNTs arising from incomplete separation and doping of SWNTs are evaluated. However, the observed temperature dependence of the conductivity indicates the presence of midgap electronic states in the semiconducting SWNTs, which provide a source of low-energy excitations, which can contribute to hopping conductance along the nanotubes following fluctuation induced tunneling across the internanotube junctions, which together dominate the low temperature transport and limit the resistivity of the films. At high temperatures, the intrinsic carriers thermally activated across the bandgap as in a traditional semiconductor became available for band transport. The midgap states pin the Fermi level to the middle of the bandgap, and their origin is ascribed to defects in the SWNT walls. The presence of such midgap states has been reported in connection with scanning tunneling spectroscopy experiments, Coulomb blockade observations in low temperature electrical measurements, selective electrochemical deposition imaging, tip-enhanced Raman spectroscopy, high resolution photocurrent spectroscopy, and the modeling of the electronic density of states associated with various defects. Midgap states are present in conventional semiconductors, but what is unusual in the present context is the extent of their contribution to the electrical transport in networks of semiconducting SWNTs. In this Account, we sharpen the focus on the midgap states in SC-SWNTs, their effect on the electronic properties of SC-SWNT networks, and the importance of these effects on efforts to develop electronic and photonic applications of SC-SWNTs.

We spectroscopically analyze the effect of e-beam deposition of lanthanide metals on the electronic structure and conductivities of films of semiconducting (SC) single-walled carbon nanotubes (SWNTs) in high vacuum. We employ near-infrared and Raman spectroscopy to interpret the changes in the electronic structure of SWNTs on exposure to small amounts of the lanthanides (Ln = Sm, Eu, Gd, Dy, Ho, Yb), based on the behavior of the reference metals (M = Li, Cr) which are taken to exemplify ionic and covalent bonding, respectively. The analysis shows that while the lanthanides are more electropositive than the transition metals, in most cases they exhibit similar conductivity behavior which we interpret in terms of the formation of covalent bis-hexahapto bonds [(η(6)-SWNT)M(η(6)-SWNT), where M = La, Nd, Gd, Dy, Ho]. However, only M = Eu, Sm, Yb show the continually increasing conductivity characteristic of Li, and this supports our contention that these metals provide the first examples of mixed covalent-ionic bis-hexahapto bonds [(η(6)-SWNT)M(η(6)-SWNT), where M = Sm, Eu, Yb].

The solution phase reactions of single-walled carbon nanotubes (SWNTs) with Cr(CO)6 and benzene-Cr(CO)3 can lead to the formation of small chromium clusters. The cluster size can be varied from less than 1 nm to about 4 nm by increasing the reaction time. TEM images suggest that the clusters are deposited predominantly on the exterior walls of the nanotubes. TGA analysis was used to obtain the Cr content and carbon to chromium ratio in the Cr-complexed SWNTs. It is suggested that the carbon nanotube benzenoid structure templates the condensation of chromium atoms and facilitates the loss of carbon monoxide leading to well defined metal clusters.

The electrical conductivity of single-walled carbon nanotube (SWNT) networks is strongly enhanced by the high vacuum e-beam deposition of transition metals. In the present communication we demonstrate that it is possible to accomplish the same chemical functionalization reactions at room temperature beginning with simple organometallic precursors. We show that the photochemically induced reactions of solutions of Cr(CO)6, Cr(η6-benzene)(CO)3, and Cr(η6-benzene)2 with thin films of semiconducting, metallic and non-separated SWNT films all lead to strongly enhanced conductivities which produce consistent results for each SWNT type among the three organometallic reagents. We conclude that all three of these reactions lead to the generation of covalent (η6-SWNT)Cr(η6-SWNT) interconnects which provide conducting pathways in the SWNT films and our results broaden the applicability of the transition metal bis-hexahapto-bond as an electronically conjugating linkage between graphene surfaces.

Polymorphism is an important issue for the application of organic semiconductors in field-effect transistors due to the dependence of device performance on crystal packing. Recently an organic semiconductor, 6,13-dichloropentacene (DCP), was shown to give a field-effect mobility as high as 9 cm2 V−1 s−1 when crystallized in the form of microribbons obtained by physical vapor transport (PVT), in contrast with the much lower mobilities found in crystals grown from solution. In the present manuscript we show that the crystals grown in the vapor phase are a polymorph of the structure reported for the crystals grown from solution. Both polymorphs show a π-stacking motif but differ in the interplanar distances and the displacement of the molecules along the long axes of the molecules. The DCP PVT structure compares favorably to that of rubrene, but DCP shows a much lower mobility. Band structure calculations show that the rubrene crystal exhibits greater band dispersion than DCP even though the long-axis displacement in rubrene is much greater. We conclude that the transport properties cannot be inferred simply by the magnitude of the intrastack long-axis displacement, but requires a consideration of the relative location of the HOMO/LUMO coefficients of the neighboring molecules in the stack.

Ultraviolet (UV) photodetectors based on heterojunctions of conventional (Ge, Si, and GaAs) and wide bandgap semiconductors have been recently demonstrated, but achieving high UV sensitivity and visible-blind photodetection still remains a challenge. Here, we utilized a semitransparent film of p-type semiconducting single-walled carbon nanotubes (SC-SWNTs) with an energy gap of 0.68 ± 0.07 eV in combination with a molecular beam epitaxy grown n-ZnO layer to build a vertical p-SC-SWNT/n-ZnO heterojunction-based UV photodetector. The resulting device shows a current rectification ratio of 103, a current photoresponsivity up to 400 A/W in the UV spectral range from 370 to 230 nm, and a low dark current. The detector is practically visible-blind with the UV-to-visible photoresponsivity ratio of 105 due to extremely short photocarrier lifetimes in the one-dimensional SWNTs because of strong electron–phonon interactions leading to exciton formation. In this vertical configuration, UV radiation penetrates the to...

This paper reports the successful fabrication of phenyl hydrazine chemical sensor based on CoAl07Fe13O4 ferrite nanoparticles. The CoAl07Fe13O4 ferrite nanoparticles were synthesized by simple and facile co-precipitation method and characterized in terms of their morphological, structural, compositional and electrical properties. The detailed characterizations confirmed that the prepared ferrite nanoparticles are grown in nanostructure, possessing CoAl07Fe13O4 composition and spinel structure of cubic phase. The fabricated phenyl hydrazine chemical sensor based on CoAl07Fe13O4 nanoparticles exhibited a high and reproducible sensitivity of ∼32342 Am M −1 cm −2 with the low experimental detection limit of 0.625 mM in a short response time of ∼100 s. The fabricated sensor shows a linear dynamic range from 0.625 mM to 10 mM. This presented work demonstrates that simply prepared CoAl07Fe13O4 ferrite nanoparticles are efficient electron mediators for the fabrication of robust and reliable chemical sensors for the detection of hazardous chemicals.

With the advent of many different forms of graphene (in addition to the long standing interest in fullerenes and carbon nanotubes), the characterization of carbon materials and their degree of conjugation is a particularly important topic in carbon science. We report the application of absorption spectroscopy and conductivity measurements to graphene derivatives and related carbon materials. Reduced graphene oxide (RGO) has been widely studied as a promising material for graphene applications because of its processability, and the same considerations apply to graphene functionalized with octadecylamine (ODA). This study utilizes a direct chemical modification of GO with ODA in the presence of dicyclohexylcarbodiimide to partially regenerate the graphene π-conjugation while producing a material (ODA-G) with excellent solubility in organic solvents. We show that the ODA-G exhibits optical absorptions, which are much stronger than those of GO, and comparable to liquid phase exfoliated graphene and reduced graphene oxide; the optical analysis is unified by the development of an analytical relationship between solid state absorption coefficients and solution state extinction coefficients, which allows the direct comparison of the electronic absorption spectroscopy of films and solutions of carbon materials. We further benchmark the regeneration of the graphenic structure in ODA-G with electrical conductivity measurements.

Porphyrins due to their unique and interesting physicochemical properties have been widely investigated as functional materials for chemical sensor fabrication. However, their poor conductivity is a major limitation toward the realization of porphyrin-based field-effect transistor/chemiresistor sensor. The issue of conductivity can be overcome by exploiting the excellent electrical property of single-walled carbon nanotubes (SWNTs) to make a SWNTs-based hybrid device in which SWNTs would act as a transducer and porphyrin as a sensory layer. The present attempt was to fabricate a SWNTs–poly(tetraphenylporphyrin) hybrid through electrochemical route and to evaluate its potential as a low-power chemiresistor sensor for sensing acetone vapor as a model for volatile organic compounds. Functionalization of SWNTs with porphyrin polymer by the electrochemical method resulted in a fuller coverage of SWNTs surface compared to a partial coverage by adsorption and thereby higher sensitivity. SWNTs were coated with po...

We report the formation of chromium clusters on the outer walls of single-walled carbon nanotubes (SWNTs). The clusters were obtained by reacting purified SWNTs with chromium hexacarbonyl in dibutyl ether at 100 degrees C. The functionalized SWNTs were characterized by thermogravimetic analysis, XPS, and high-resolution TEM. The curvature of the SWNTs and the high mobility of the chromium moieties on graphitic surfaces allow the growth of the metal clusters and we propose a mechanism for their formation.

The occurrence of coherence phenomenon as a result of the interference of the probability amplitude terms is among the principle features of quantum mechanics concepts. Current experiments display the presence of quantum techniques whose coherence is supplied over large interval times. Specifically, photosynthetic mechanisms in light-harvesting complexes furnish oscillatory behaviors owing to quantum coherence. In this manuscript, we study the coherent quantum energy transfer for a single-excitation and nonlocal correlation in a dimer system (donor+acceptor) displayed by two-level systems (TLSs), interacting with a cavity field with a time-dependent coupling effect considering the realistic situation of coupling between each TLS and the cavity field. We analyze and explore the specific conditions which are viable with real experimental realization for the ultimate transfer of quantum energy and nonlocal quantum correlation. We show that the enhancement of the probability for a single-excitation energy transfer greatly benefits from the energy detuning, photon-number transition, classicality of the field, and the time-dependent coupling effect. We also find that the entanglement between the donor and acceptor is very sensitive to the physical parameters and it can be generated during the coherent energy transfer.

In this Perspective, we present an overview of recent fundamental studies on the nature of the interaction between individual metal atoms and metal clusters and the conjugated surfaces of graphene and carbon nanotube with a particular focus on the electronic structure and chemical bonding at the metal–graphene interface. We discuss the relevance of organometallic complexes of graphitic materials to the development of a fundamental understanding of these interactions and their application in atomtronics as atomic interconnects, high mobility organometallic transistor devices, high-frequency electronic devices, organometallic catalysis (hydrogen fuel generation by photocatalytic water splitting, fuel cells, hydrogenation), spintronics, memory devices, and the next generation energy devices. We touch on chemical vapor deposition (CVD) graphene grown on metals, the reactivity of its surface, and its use as a template for asymmetric graphene functionalization chemistry (ultrathin Janus discs). We highlight som...

We report the synthesis and properties of a series of spiro-bis(3,4,6,7-tetrachalcogenide-substituted-phenalenyl)boron salts and two of the corresponding tetrathioalkyl-substituted spiro-bis(phenalenyl)boron radicals [tetrathiomethyl (10) and tetrathioethyl (11)] in which all of the active positions of the phenalenyl (PLY) nucleus are functionalized. In the solid state, radicals 10 and 11 exist as a weak π-dimers due to the steric congestion of the thioalkyl groups in the superimposed PLY units. As a result, the spins are localized in the isolated (nonsuperimposed) PLY rings, and the structure, magnetic susceptibility measurements, and band structure calculations confirm that these PLY units are unable to undergo strong intermolecular interaction as a result of the orientation of the thioalkyl groups.

A simple two-terminal device containing a semiconducting single-walled-nanotube thin-film is reported that generates an extremely high density of holes when it comes in contact with an ionic liquid, inducing strong electromodulation of the interband and excitonic transitions as a result of the position-dependent shift of the single-walled-nanotube Fermi level.

In this Account, we discuss the chemistry of graphitic materials with particular reference to three reactions studied by our research group: (1) aryl radical addition, from diazonium precursors, (2) Diels-Alder pericyclic reactions, and (3) organometallic complexation with transition metals. We provide a unified treatment of these reactions in terms of the degenerate valence and conduction bands of graphene at the Dirac point and the relationship of their orbital coefficients to the HOMO and LUMO of benzene and to the Clar structures of graphene. In the case of the aryl radical addition and the Diels-Alder reactions, there is full rehybridization of the derivatized carbon atoms in graphene from sp(2) to sp(3), which removes these carbon atoms from conjugation and from the electronic band structure of graphene (referred to as destructive rehybridization). The radical addition process requires an electron transfer step followed by the formation of a σ-bond and the creation of a π-radical in the graphene lattice, and thus, there is the potential for unequal degrees of functionalization in the A and B sublattices and the possibility of ferromagnetism and superparamagnetism in the reaction products. With regard to metal functionalization, we distinguish four limiting cases: (a) weak physisorption, (b) ionic chemisorption, in which there is charge transfer to the graphitic structure and preservation of the conjugation and band structure, (c) covalent chemisorption, in which there is strong rehybridization of the graphitic band structure, and (d) covalent chemisorption with formation of an organometallic hexahapto-metal bond that largely preserves the graphitic band structure (constructive rehybridization). The constructive rehybridization that accompanies the formation of bis-hexahapto-metal bonds, such as those in (η(6)-SWNT)Cr(η(6)-SWNT), interconnects adjacent graphitic surfaces and significantly reduces the internanotube junction resistance in single-walled carbon nanotube (SWNT) networks. The conversion of sp(2) hybridized carbon atoms to sp(3) can introduce a band gap into graphene, influence the electronic scattering, and create dielectric regions in a graphene wafer. However, the organometallic hexahapto (η(6)) functionalization of the two-dimensional (2D) graphene π-surface with transition metals provides a new way to modify graphitic structures that does not saturate the functionalized carbon atoms and, by preserving their structural integrity, maintains the delocalization in these extended periodic π-electron systems and offers the possibility of three-dimensional (3D) interconnections between adjacent graphene sheets. These structures may find applications in interconnects, 3D-electronics, organometallic catalysis, atomic spintronics and in the fabrication of new electronic materials.

Optical properties of electrochromic materials can be controlled by the application of an electric field allowing recent development of new applications such as smart windows technology for indoor climate control and energy conservation. We report the fabrication of a single-walled nanotube (SWNT) thin film based electro-optical modulator controlled by ionic liquid polarization in which the active electrochromic layer is made of a film of semiconducting (SC-) SWNTs and the counter-electrode is composed of a film of metallic (MT-) SWNTs. Optimization of this electro-optical cell allows the operations with an optical modulation depth of 3.7 dB and a response time in the millisecond range, which is thousands of times faster than typical electrolyte-controlled devices. In addition, a dual electro-optical device was built utilizing electro-optically active SC-SWNT films for each electrode that allowed increasing modulation depth of 6.7 dB while preserving the speed of the response.

Graphite nanoplatelets (GNPs) were reacted with transition metal (M) carbonyls followed by annealing and compaction to remove the CO ligands and form bis-hexahapto bonds between the GNP surfaces. The M-GNP films (M = Cr, W, Mo) were characterized with Raman spectroscopy and conductivity measurements. It was observed that interconnection of the graphitic faces of GNPs by bis-hexahapto metal coordination resulted in a decrease of electrical conductivity. The complexes offer promise as catalysts and in the fabrication of new 3-D electronic materials.

The development of selective high precision chemical functionalization strategies for device fabrication, in conjunction with associated techniques for patterning graphene wafers with atomic accuracy would provide the necessary basis for a post-CMOS manufacturing technology. This requires a thorough understanding of the principles governing the reactivity and patterning of graphene at the sub-nanometer length scale. This article reviews our quest to delineate the principles of graphene chemistry - that is, the chemistry at the Dirac point and beyond, and the effect of covalent chemistry on the electronic structure, electrical transport and magnetic properties of this low-dimensional material in order to enable the scalable production of graphene-based devices for low- and high-end technology applications.

We report the preparation of organometallic side-wall complexes of single-walled carbon nanotubes (SWNTs) under conditions, which allow the study of both mono- and bis-hexahapto SWNT coordination compounds [(η6-SWNT)Cr(CO)3, (η6-SWNT)Cr(η6-C6H6), (η6-SWNT)2Cr]. The results are interpreted in terms of exohedral and endohedral binding of chromium to the SWNT sidewalls and ligand competition reactions suggest that endohedral binding provides a very stable and kinetically inert mode of organometallic bonding. We demonstrate that the electrical conductivity of SWNT thin films are significantly enhanced by side-wall bonding to Group 6 transition metals (M = Cr, Mo, and W), which serve to reduce the inter-carbon nanotube junction electrical resistance by the formation of SWNT interconnects [(η6-SWNT)2M].

A high energy density supercapacitor device is reported that utilizes hybrid carbon electrodes and the ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) as an electrolyte. The hybrid electrodes are prepared from reduced graphite oxide (rGO) and purified single-walled carbon nanotubes (SWCNTs). A simple casting technique gives the hybrid structure with optimum porosity and functionality that provides high energy and power densities. The combination of SWCNTs and rGO in a weight ratio of 1:1 is found to afford a specific capacitance of 222 F g−1 and an energy density of 94 Wh kg−1 at room temperature.

We report the preparation, crystallization, and solid state characterization of a new benzannulated phenalenyl radical; a distinctive feature of this molecular solid is the absence of any well defined conducting pathway(s). In the solid state, the radicals exist as π-dimer and the requisite C···C contacts between dimers are all larger than the sum of the van der Waals distances. The magnetic susceptibility measurement indicates that, in the solid state, the radical remains paramagnetic and the fraction of Curie spins is 0.55 per molecule. Pressed pellet conductivity measurements indicate a value of σRT = 0.5 × 10−6 S/cm. The conductivity value is comparable with those of similarly packed phenalenyl based neutral radicals. Copyright © 2012 John Wiley & Sons, Ltd.

Encapsulation of sulfur in HiPCO-SWNTs leads to large changes in the Raman spectra with the appearance of new peaks at 319, 395, and 715 cm–1 which originate from the sulfur species within the SWNTs, while the high frequency SWNT bands (ν > 1200 cm–1) are decreased in intensity. The encapsulated species also shifts the near-IR interband electronic transitions to lower energy by more than 10%. These effects seem to originate with the van der Waals interaction of the confined sulfur species with the walls of the SWNTs which are not expected to be significant in the case of the previously studied large diameter SWNTs. We suggest that sulfur in the small diameter SWNTs exists as a helical polymeric sulfur chain that enters the SWNT interior in the form of S2 (3Σg–) molecules which undergo polymerization to linear diradicals. Fil: Li, Guanghui. University of California; Estados Unidos Fil: Fu, Chengyin. University of California; Estados Unidos Fil: Oviedo, María Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. University of California; Estados Unidos Fil: Chen, Mingguang. University of California; Estados Unidos Fil: Tian, Xiaojuan. University of California; Estados Unidos Fil: Bekyarova, Elena. University of California; Estados Unidos Fil: Itkis, Mikhail. University of California; Estados Unidos Fil: Wong, Bryan. University of California; Estados Unidos Fil: Guo, Juchen. University of California; Estados Unidos Fil: Haddon, Robert. University of California; Estados Unidos

Single-walled carbon nanotubes (SWCNTs) were purified by treatment with concentrated nitric acid and then subjected to Soxhlet extraction with tetrahydrofuran (THF). The THF extract of low molecular weight carboxylated carbons was derivatized with (trimethylsilyl)diazomethane and the resulting methylated material was separated with column chromatography and thin layer chromatography and several fractions were identified by GC–MS and 1H NMR. The fractions were shown to include small benzopolycarboxylic acids and organic nitro compounds.

Large-area mono- and bilayer graphene films were synthesized on Cu foil (~ 1 inch(2)) in about 1 min by a simple ethanol-chemical vapor deposition (CVD) technique. Raman spectroscopy and high resolution transmission electron microscopy revealed the synthesized graphene films to have polycrystalline structures with 2-5 nm individual crystallite size which is a function of temperature up to 1000°C. X-ray photoelectron spectroscopy investigations showed about 3 atomic% carboxylic (COOH) functional groups were formed during growth. The field-effect transistor devices fabricated using polycrystalline graphene as conducting channel (L(c)=10 μm; W(c)=50 μm) demonstrated a p-type semiconducting behavior with high drive current and Dirac point at ~35 V. This simple one-step method of growing large area polycrystalline graphene films with semiconductor properties and easily functionalizable groups should assist in the realization of potential of polycrystalline graphene for nanoelectronics, sensors and energy storage devices.

Chemical functionalization is a promising route to band gap engineering of graphene. We chemically grafted nitrophenyl groups onto exfoliated single-layer graphene sheets in the form of substrate-supported or free-standing films. Our transport measurements demonstrate that nonsuspended functionalized graphene behaves as a granular metal, with variable range hopping transport and a mobility gap ∼0.1 eV at low temperature. For suspended graphene that allows functionalization on both surfaces, we demonstrate tuning of its electronic properties from a granular metal to a semiconductor in which transport occurs via thermal activation over a transport gap ∼80 meV from 4 to 300 K. This noninvasive and scalable functionalization technique paves the way for CMOS-compatible band gap engineering of graphene electronic devices.

We report the synthesis, crystallization, and solid-state characterization of the 3,7-ethoxy-substituted spirobiphenalenyl-boron neutral radical 22. The radical is distinguished by its low disproportionation energy and one-dimensional structure. We show that our strategy of substitution of OEt group at the active positions of the phenalenyl units changes the crystal packing from its previously known OMe analogue and the solid-state properties are dictated by the partial π-stack structure and the oxygen atoms at the 3,7-positions and can be best rationalized in terms of the resonating valence bond model. Magnetic susceptibility measurements show that in the solid state the radical remains paramagnetic but there is significant spin-spin interaction between the molecules. Band structure calculations reflect efficient overlap between the molecules along the π stack and show evidence of interactions between the spin-bearing oxygen atoms. The room temperature electrical conductivity (σ(RT)=2.0×10(-2) S cm(-1)) of 22 is higher than that observed in previously known one-dimensional phenalenyl radicals.

We present an experimental study on ultra-dense 3-D non-volatile magnetic universal logic gates with reconfigurable AND and OR functions. A four-layer magnetic structure with a net thickness of less than 30 nm is employed as a study illustration of a highly scalable magnetic logic device. In the device, the magnetic state of the top output "soft" layer depends on the magnetic states of the remaining three "hard" layers used as two input and one reset layers, respectively. To build vertically oriented magnetic devices with a gradient of the coercivity and the magnetization across the thickness, we use Co/Pd multilayers sputter-deposited via a combinatorial synthesis. Through a focused magneto-optical Kerr effect (F-MOKE) study, we relate input and output states in the 4-layer logic device to shoulders on major and minor M-H hysteresis loops. We use magnetic force microscopy (MFM) to identify magnetic logic operations.

International audience; Graphene displays unprecedented electronic properties including room-temperature ballistic transport and quantum conductance, and because of its small spin-orbit interaction, graphene has the potential to function as the building block of future spintronic devices. Theoretical calculations indicate that a defective graphene sheet will be simultaneously semiconducting and magnetic; thus it would act as a room-temperature magnetic semiconductor. Recently, ferromagnetic ordering at room temperature has been observed by magnetometry measurements on bulk samples of reduced graphene oxide.

The carbon nanotube−polyethylene glycol (PEG) graft copolymer was synthesized by covalent functionalization of electric arc single-walled carbon nanotubes (SWNTs) with the monofunctional, tetrahydrofurfuryl-terminated polyethylene glycol PEG-THFF (MW∼200), to give a material composed of 80 wt % SWNTs. We show that the sequential processing of the resulting material by ultrasonication and high-shear mixing provides a means to disperse the SWNT-PEG-THFF macromolecules on two different length scales and leads to highly viscous solutions; at a concentration of 10 mg/mL the kinematic viscosity (ν) of an aqueous SWNT-PEG-THFF dispersion reaches a value of ν > 1000 cSt (for water ν ∼ 1 cSt). Analysis of this procedure by means of viscosity measurements and atomic force microscopy (AFM), shows that ultrasonication is effective in disrupting the SWNT bundles, while the high shear mixing disperses the individual SWNTs. The kinematic viscosity of aqueous dispersions of SWNT-PEG-THFF was measured as a function of nan...

We report the synthesis, crystallization, electrochemistry, X-ray structure and electron density distribution of a methoxy-substituted-tris-phenalenyl based neutral radical (18); the cyclic voltammogram of the compound shows that the strategy of oxygen substitution at 3,7-positions and the utilization of tris-phenalenyls within the silicon complex reduce the electrochemical disproportionation potentials. The crystal structure shows that the radical exists as a 1D π-chain of partially superimposed phenalenyl rings with intermolecular carbon⋯carbon contacts that fall within van der Waals atomic separation. A bond length–bond order regression analysis of the experimental structures shows that the electron density is distributed over two out of the three phenalenyl units.

We demonstrate an unusual electrochemical reaction of sulfur with lithium upon encapsulation in narrow-diameter (subnanometer) single-walled carbon nanotubes (SWNTs). Our study provides mechanistic insight on the synergistic effects of sulfur confinement and Li+ ion solvation properties that culminate in a new mechanism of these sub-nanoscale-enabled reactions (which cannot be solely attributed to the lithiation-delithiation of conventional sulfur). Two types of SWNTs with distinct diameters, produced by electric arc (EA-SWNTs, average diameter 1.55 nm) or high-pressure carbon monoxide (HiPco-SWNTs, average diameter 1.0 nm), are investigated with two comparable electrolyte systems based on tetraethylene glycol dimethyl ether (TEGDME) and 1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5). Electrochemical analyses indicate that a conventional solution-phase Li-S reaction occurs in EA-SWNTs, which can be attributed to the smaller solvated [Li(TEGDME)]+ and [Li(15-crown-5)]+ ions within the EA-SWNT diameter. In stark contrast, the Li-S confined in narrower diameter HiPco-SWNTs exhibits unusual electrochemical behavior that can be attributed to a solid-state reaction enabled by the smaller HiPco-SWNT diameter compared to the size of solvated Li+ ions. Our results of the electrochemical analyses are corroborated and supported with various spectroscopic analyses including operando Raman, X-ray photoelectron spectroscopy, and first-principles calculations from density functional theory. Taken together, our findings demonstrate that the controlled solid-state lithiation-delithiation of sulfur and an enhanced electrochemical reactivity can be achieved by sub-nanoscale encapsulation and one-dimensional confinement in narrow-diameter SWNTs. Fil: Fu, Chengyin. University Of California Riverside; Estados Unidos Fil: Oviedo, María Belén. University Of California Riverside; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Zhu, Yihan. Zhejiang University Of Technology; China Fil: von Wald Cresce, Arthur. U. S. Army Research Laboratory; Estados Unidos Fil: Xu, Kang. U. S. Army Research Laboratory; Estados Unidos Fil: Li, Guanghui. University Of California Riverside; Estados Unidos Fil: Itkis, Mikhail E.. University Of California Riverside; Estados Unidos Fil: Haddon, Robert C.. University Of California Riverside; Estados Unidos Fil: Chi, Miaofang. Oak Ridge National Laboratory; Estados Unidos Fil: Han, Yu. King Abdullah University Of Science And Technology; Arabia Saudita Fil: Wong, Bryan M.. University Of California Riverside; Estados Unidos Fil: Guo, Juchen. University Of California Riverside; Estados Unidos

Treatment of carbon nanotubes by oxidizing acids is extensively used to dissolve metal residues from raw nanotube samples. The effect of acid treatment on the tubes themselves is twofold: it introduces uniform carboxylic sidegroups on the tube ends and defects, and it increases the overall charge concentration on the nanotube walls, thereby p-doping the material. Wide-range optical spectroscopy is an ideal tool to characterize both effects from one type of measurement: vibrational signatures indicate the presence of the sidegroups, the increase in far-infrared absorption signals the presence of free carriers, and the disappearance of interband transitions is the consequence of the depletion of Van Hove singularities when introducing holes. We have subjected carbon nanotube samples to two kinds of acid treatment: mild (in HNO(3) vapor at room temperature) and aggressive (high-temperature reflux). We found that on mild treatment, electronic doping occurs without defect oxidation to carboxylic groups, while the aggressive procedure leads to both doping and defect oxidation. Our spectroscopic data unambiguously prove that the changes in electrical conductivity on acid doping are intrinsic, and not just a result of improving the contact between nanotubes. Refereed/Peer-reviewed