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Taking advantage of the weak attraction forces between gold surface and silica zeolite colloids, selective growth of zeolite on silicon wafer over gold was exploited to fabricate continuous micropatterned b-oriented zeolite MFI monolayer film with excellent adhesion.

Despite theoretical predictions, the question of room-temperature magnetic order in graphene must be conclusively resolved before graphene can fully achieve its potential as a spintronic medium. Through scanning tunneling microscopy (STM) and point I-V measurements, the current study reveals that unlike pristine samples, graphene nanostructures, when functionalized with aryl radicals, can sustain magnetic order. STM images show 1-D and 2-D periodic super-lattices originating from the functionalization of a single sub-lattice of the bipartite graphene structure. Field-dependent super-lattices in 3-nm wide "zigzag" nanoribbons indicate local moments with parallel and anti-parallel ordering along and across the edges, respectively. Anti-parallel ordering is observed in 2-D segments with sizes of over 20 nm. The field dependence of STM images and point I-V curves indicates a spin polarized local density of states (LDOS), an out-of-plane anisotropy field of less than 10 Oe, and an exchange coupling field of 100 Oe at room temperature.

We report the use of chemically functionalized water-soluble single-walled carbon nanotubes (ws-SWCNTs) for the modulation of morpho-functional characteristics of astrocytes. When added to the culturing medium, ws-SWCNTs were able to make astrocytes larger and stellate/mature, changes associated with the increase in glial fibrillary acidic protein immunoreactivity. Thus, ws-SWCNTs could have more beneficial effects at the injury site than previously thought; by affecting astrocytes, they could provide for a more comprehensive re-establishment of the brain computational power.

Spin transport in carbon-based materials has stimulated much interest due to their ballistic conductance and a long phase coherence length. While much research has been conducted on individual carbon nanotubes, current growth and placement techniques are incompatible with large-scale fabrication. Here, we report on nonlocal spin injection and detection in single-walled carbon nanotube networks. We observe spin transport over a distance of 1 \ensuremath{\mu}m and extract a spin diffusion length of 1.6--2.4 \ensuremath{\mu}m with an injected spin polarization from CoFe into nanotube network of 18$%$--41$%$. Our observations demonstrate that spin transport is possible in carbon nanotube networks due to the formation of natural tunnel barriers between nanotubes and metallic contacts.

Organometallic hexahapto chromium metal complexation of single layer graphene, which involves constructive rehybridization of the graphene pi-system with the vacant chromium d orbital, leads to field effect devices which retain a high degree of the mobility with enhanced on-off ratio. This hexahapto mode of bonding between metal and graphene is quite distinct from the modification in electronic structure induced by conventional covalent sigma-bond formation with creation of sp3 carbon centers in graphene lattice and this chemistry is reversible., Comment: 18 pages, 10 figures, Adv. Mat. 2013, 25, 1131-1136

One for the half: recent work on atomic hydrogen and neutral radical heterocyclic molecules has moved the field of spin S=1/2 solids closer to the realization of synthetic intrinsic metals and superconductors. High-pressure experiments on hydrogen and chalcogenide-nitrogen molecules show evidence of metallic character. The molecular radicals exhibit a positive temperature coefficient of resistance under pressure-the classic signature of a metal.

Chemistry will play an increasingly important role in the realization of graphene applications. The chemical formation of covalent carbon–carbon bonds involving the basal plane carbon atoms offers an alternative approach to the control of the electronic properties of graphene, and potentially allows the generation of insulating and semiconducting regions in graphene wafers. This review summarizes recent progress in the covalent modification of epitaxial graphene and the effect that chemistry has on the electronic and magnetic properties of the material.

'A pioneer of modern anthropology', A. C. Haddon (1855–1940) contributed to the fields of embryology and evolutionary science before turning his interests to human civilisation and its history. In this work, first published in 1910, Haddon makes use of his wide-ranging knowledge of folk rituals and religious beliefs to introduce readers to basic principles of sympathetic magic, divination, talismanic powers and fetishism. A strong believer in the importance of preserving local religious practices and beliefs, Haddon uses the work to document customs from Britain to West Africa, America to Australia. Topics include forms of contagious magic, premised on a mutual influence between objects; amulets and talismans; magical names and words; and divination. In the second portion of the book, devoted to fetishism, Haddon offers an authoritative description of the fetish as a 'habitation, temporary or permanent, of a spiritual being', establishing basic definitions for an important field of cultural research.

Most of the interesting physics of graphene results from the singular electronic band structure at the so-called Dirac point, where the conduction and valence bands cross in momentum space. Although graphene is very stable thermodynamically, the electronic structure at the Dirac point facilitates basal plane chemistry including pericyclic reactions such as the Diels-Alder reaction. We have discovered a series of facile Diels-Alder reactions in which graphene can function either as a diene when paired with tetracyanoethylene and maleic anhydride or as a dienophile when paired with 2,3-dimethoxybutadiene and 9-methylanthracene. In this Account, we seek to rationalize these findings using simple arguments based on considerations of orbital symmetry and the frontier molecular orbital theory. The graphene conduction and valence bands (HOMO and LUMO) cross at the Dirac point, which defines the work function (W = 4.6 eV). Thus, the HOMO and LUMO form a degenerate pair of orbitals at this point in momentum space with the same ionization potential (IP) and electron affinity (EA). Based on the importance of the energies of the HOMO (-IP) and LUMO (-EA) in frontier molecular orbital (FMO) theory, graphene should be a reactive partner in Diels-Alder reactions due to the very high-lying HOMO and low-lying LUMO (energies of -4.6 eV). Inspection of the orbital symmetries of the degenerate pair of half-occupied band orbitals at the Dirac point confirms that with the appropriate orbital occupancies, both diene and dienophile reaction partners should undergo concerted Diels-Alder reactions with graphene that are allowed based on the Woodward-Hoffmann principles of orbital symmetry.

International audience; The authors report the effects of radical functionalization on the electrostatic force microscopy (EFM), the scanning tunneling spectra (STS), and Raman spectroscopy of epitaxial graphene. The EFM studies show the existence of layer dependent trapped charges in the pristine graphene. The uniform enhancement of energy gap is observed through STS. Raman spectra show nonuniformly distributed D-band intensities throughout the functionalized sample as a result of the inhomogeneous distribution of covalent bonds to the graphene sheets. The functionalization chemistry has a marked effect on the homogeneity of the electrostatic charge and leads to an increase of the energy of the band gap.

Thin-film multilayer structures with up to 20 repeat layers have been grown in a high-vacuum chamber by sequential deposition of aluminum (Al) and fullerene (${\mathrm{C}}_{60}$) onto room-temperature substrates. The periodicity of the layers is confirmed by x-ray-diffraction and in situ resistance measurements. The presence of underlying layers of ${\mathrm{C}}_{60}$ reduces the critical thickness at which Al becomes conducting from \ensuremath{\sim}35 to \ensuremath{\sim}20 \AA{}. In addition, there is a sudden increase in resistance that occurs when each Al layer is covered by a monolayer of ${\mathrm{C}}_{60}$. These observations, together with the measurement of a downward shift in frequency of a considerably broadened Raman-active ${\mathit{A}}_{\mathit{g}}$(2) pentagonal-pinch mode, imply that up to six electrons per ${\mathrm{C}}_{60}$ are transferred from the Al to the ${\mathrm{C}}_{60}$ layer. This demonstration of charge transfer across planar metal-${\mathrm{C}}_{60}$ interfaces suggests that multilayers may be a useful vehicle for forming fullerene interface compounds in two-dimensional structures.

We present evidence for and study the properties of coreless Josephson vortices (parallel to the superconducting layers) in the organic superconductor (BEDT-TTF${)}_{2}$Cu(NCS${)}_{2}$, using ac susceptibility measurements in the mixed state. We observe (1) extremely weak-pinning restoring forces for flux motion parallel to the layers, due to the absence of the vortex normal core; (2) single vortex (noncollective) pinning, due to weak interactions between Josephson vortices; (3) the ``lock-in'' of the vortices parallel to the layers when the dc field is applied at an arbitrary angle; and (4) highly nonlinear response to the ac field h in the lock-in state, above a threshold of h\ensuremath{\sim}0.5 G. The behavior of tilted flux lines is dominated by the much stronger pinning and collective interactions of two-dimensional Abrikosov ``pancake'' vortices, and linear response is largely restored when the flux lines unlock from the layers. We measure the Josephson penetration depth to be ${\ensuremath{\lambda}}_{\mathrm{\ensuremath{\perp}}}$(T=5 K)\ensuremath{\sim}200 \ensuremath{\mu}m, yielding a penetration depth anisotropy of \ensuremath{\gamma}=${\ensuremath{\lambda}}_{\mathrm{\ensuremath{\perp}}}$/${\ensuremath{\lambda}}_{\mathrm{\ensuremath{\parallel}}}$\ensuremath{\sim}160-350.

Metal doped C60 compounds comprise a class of materials, which includes insulators, conductors and superconductors which exhibit record superconducting transition temperatures Tc for a molecularly based solid. The moderately high values of Tc originate from the interaction of the conduction electrons with high frequency intramolecular phonons, and from the high density of states at the Fermi level. The high density of states and narrow band width arise from the small orbital overlap between the C60 molecules. Hence, both electron-phonon and electron-electron interactions are expected to be important features of the of the electronic structure of metal doped fullerides. Whereas superconductivity is mediated by electron-phonon interactions in the A3C60 phases, we show that electron-electron interactions determine the low temperature transport properties. We compare the electronic properties of these materials with other classes of superconductors.

We report the two-dimensional angular-correlation-of-annihilation-radiation measurement of the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ (pair) momentum distribution in the organic superconductor \ensuremath{\kappa}-(BEDT-TTF${)}_{2}$Cu(NCS${)}_{2}$. Our data, when compared with tight-binding (H\"uckel) electronic-band calculations, show features consistent with predicted Fermi surfaces. The structure around Z in our spectrum supports the results from earlier de Haas--van Alphen and Shubnikov--de Haas measurements. In addition, our data show features consistent with the predicted open Fermi surface that runs nearly parallel to YM.

We report on the electrical resistivity of K[sub 3]C[sub 60] and Rb[sub 3]C[sub 60] thin films. These films, grown at elevated temperatures, are highly textured and consist of large single-crystal grains. The films exhibit metallic behavior up to 500 K, with residual resistivities of 1.2 m[Omega] cm. The low-temperature ([ital T]) resistivity exhibits a [ital T][sup 2] dependence. We suggest that it is dominated by electron-electron interactions, and we find quantitative agreement not only with estimates based on the electron density and the bandwidth, but also with other narrow band systems. The electron-phonon interactions only become important for the resistivity above room temperature, because these phonons correspond to high-frequency vibrations of the C[sub 60] molecule. Nevertheless, virtual excitations of these same high-energy phonons are responsible for the superconductivity. Using similar criteria of conventional organic superconductors, we find that these materials are dominated at all temperatures by electron-phonon interactions.

We report synthesis, structures and properties of strontium intercalated fullerite, SrxC60 compounds. This is identified as the only fulleride system where fcc and bcc phases compete in the same compositional range. In the vicinity of x=3, a bcc A15 phase coexists with a fcc phase with lattice constants 11.140 and 14.144 A, respectively. For Sr6C60, an Im 3 bcc phase with ao=10.975 A is observed. This phase becomes superconducting at T=4 K. These structural and electronic properties, being intermediate to grossly different calcium and barium intercalated fullerides, provide a unifying picture of all alkaline-earth intercalated fullerides.

The muon-spin-relaxation (\ensuremath{\mu}SR) technique has been used to study the internal field modulation dynamics of fluxons in crystals of \ensuremath{\kappa}-[BEDT-TTF${]}_{2}$Cu[NCS${]}_{2}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}10.5 K). The data exhibit a strong field dependence for applied fields in the range 129 Oe\ensuremath{\le}\ensuremath{\Vert}${\mathbf{H}}_{\mathrm{ext}}$\ensuremath{\Vert}\ensuremath{\le}4 kOe, which is attributed to a combination of vortex motion, finite core size effects, and pinning. In low fields (\ensuremath{\Vert}${\mathbf{H}}_{\mathrm{ext}}$\ensuremath{\Vert}=129 Oe), the data exhibit a flux-pinning transition at ${\mathit{T}}_{\mathit{x}}$\ensuremath{\sim}5 K, as evidenced by a peak in the second moment of the local field distribution at \ensuremath{\sim}5 K accompanied by an enhanced minimum in the first moment at the same temperature. In higher fields (\ensuremath{\Vert}${\mathbf{H}}_{\mathrm{ext}}$\ensuremath{\Vert}=750 Oe, 3 kOe, and 4 kOe), where the effects of motion and pinning are minimized, the symmetry of the underlying gap function is confirmed as s wave. Corrections for finite fluxon core, finite mean free path, and flux-lattice disorder were applied in determining the London penetration depth, ${\ensuremath{\lambda}}_{\mathit{L}}^{(\mathit{b}\mathit{c})}$(0)=7680\ifmmode\pm\else\textpm\fi{}700 \AA{}.

Previous high-resolution electron microscopy (HREM) observations of the carbon nanotubes have led to a "Russian doll" structural model that is based on hollow concentric cylinders capped at both ends. The structures of the carbon nanotubes and particles were characterized here by bulk physical and chemical property measurements. The individual nanostructure is as compressible as graphite in the c axis, and such nanostructures can be intercalated with potassium and rubidium, leading to a saturation composition of "MC 8 ." These results are counter to expectations that are based on a Russian doll structure. HREM after intercalation with potassium and deintercalation indicates that individual nanoparticles are a "paper-mache" of smaller graphite layers. Direct current magnetization and electron spin resonance measurements indicate that the electronic properties of the nanostructures are distinctly different from those of graphite. Although the nanostructures have distinct morphologies and electronic properties, they are highly defective and have a local structure similar to turbostratic graphite.

A new organic molecular conductor, based on a spiro-biphenalenyl neutral radical, simultaneously exhibits bistability in three physical channels: electrical, optical, and magnetic. In the paramagnetic state, the unpaired electrons are located in the exterior phenalenyl units of the dimer, whereas in the diamagnetic state the electrons migrate to the interior phenalenyl units and spin pair as a π-dimer. Against all expectations, the conductivity increases by two orders of magnitude in the diamagnetic state, and the band gap decreases. This type of multifunctional material has the potential to be used as the basis for new types of electronic devices, where multiple physical channels are used for writing, reading, and transferring information.

We report a 40% improvement of the thermal conductivity of graphite nanoplatelets–epoxy composites by chemical functionalization of graphite nanoplatelets utilizing nitric acid treatment, which also serves to enhance the spreadability of the material. FTIR and Raman spectroscopy confirmed the presence of a variety of oxygen functional groups at the edges and basal plane of the functionalized graphite nanoplatelets, which contributed to improved interaction with the polymer matrix. A comparative statistical analysis of the particle size distributions in pristine and functionalized graphite nanoplatelets based on scanning electron microscopy showed an increasing degree of exfoliation of the functionalized material. We compare the performance of the functionalized graphite nanoplatelets and carbon nanotubes as fillers in the polymer matrix and discuss the prospects for utilization of graphite nanoplatelets-based thermal interface materials in electronic packaging.

The zero-band-gap electronic structure of graphene enables it to function as either the diene or the dienophile in the Diels−Alder reaction, and this versatile synthetic method offers a powerful strategy for the reversible modification of the electronic properties of graphene under very mild conditions.

Traumatic spinal cord injury (SCI) induces tissue damage and results in the formation of a cavity that inhibits axonal regrowth. Filling this cavity with a growth-permissive substrate would likely promote regeneration and repair. Single-walled carbon nanotubes functionalized with polyethylene glycol (SWNT-PEG) have been shown to increase the length of selected neurites in vitro. We hypothesized that administration of SWNT-PEG after experimental SCI will promote regeneration of axons into the lesion cavity and functional recovery of the hindlimbs. To evaluate this hypothesis, complete transection SCI was induced at the T9 vertebral level in adult female rats. One week after transection, the epicenter of the lesion was injected with 25 μL of either vehicle (saline), or 1 μg/mL, 10 μg/mL, or 100 μg/mL of SWNT-PEG. Behavioral analysis was conducted before injury, before treatment, and once every 7 days for 28 days after treatment. At 28 days post-injection the rats were euthanized and spinal cord tissue was extracted. Immunohistochemistry was used to detect the area of the cyst, the extent of the glial scar, and axonal morphology. We found that post-SCI administration of SWNT-PEG decreased lesion volume, increased neurofilament-positive fibers and corticospinal tract fibers in the lesion, and did not increase reactive gliosis. Additionally, post-SCI administration of SWNT-PEG induced a modest improvement in hindlimb locomotor recovery without inducing hyperalgesia. These data suggest that SWNT-PEG may be an effective material to promote axonal repair and regeneration after SCI.

International audience; We report the enhanced photosensitivity of epitaxial graphene (EG) after electrochemical oxidation in nitric acid. The onset of photoconductivity appears at a photon energy of ~1.7 eV while the responsivity reaches 2.5 A/W at a wavelength of 470 nm (blue light, energy 2.64 eV) and further increases to 200 A/W in the UV spectral range (3.5 eV, 350 nm). The observed photoresponse is attributed to the formation of deep traps at the electro-oxidized EG interface, which release charge carriers under illumination and prolong the life time of the photocarriers. Potential applications of electro-oxidized EG in ultraviolet photodetection are discussed

Crystalline films of C60 with ~1 μm grain size and a preferred [111] texture have been doped with K and Rb to form superconducting compositions that have sharp zero-resistance transitions. The temperature dependence of the resistance above Tc for both K3C60 and Rb3C60 films reveals metallic behavior up to temperatures as high as 520 K without any evidence of saturation. For Rb3C60, electronic mean free paths significantly shorter than nearest-neighbor C60 distances and anomalously high values of the electron-phonon coupling strength are inferred. These results suggest that there is a strong interaction between the conduction electrons and the intramolecular vibrational modes and also bring into question the assumption that all of the donated charge (three electrons per C60) is itinerant.

Within the wr-orbital axis vector theory, the total rehybridization required for closure of the fullerenes is approximately conserved. This result allows the development of a structure-based index of strain in the fullerenes, and it is estimated that about 80 percent of the heat of formation of the carbon atoms in C60 may be attributed to a combination of v strain and steric inhibition of resonance. Application of this analysis to the geometries of structurally characterized organometallic derivatives of C60 and C70 shows that the reactivity exhibited by the fullerenes may be attributed to the relief of a combination of local and global strain energy. C60 is of ambiguous aromatic character with anomalous magnetic properties but with the reactivity of a continuous aromatic molecule, moderated only by the tremendous strain inherent in the spheroidal structure.

The irradiation of sublimed fullerene (C60 and C70) thin films with ultraviolet light in an oxygen-rich ambient has been found to lead to a substantially increased cohesive energy in the fullerene solid. The decreased solubility and lower vapor pressure of the phototransformed material enables wet (organic solvents) or dry (thermal or photon-induced sublimation) development of photo-defined negative images. One micrometer wide lines with good edge definition are demonstrated. X-ray, infrared, optical absorption, and high performance liquid chromatography reveal that photo-oxygenated C60 retains its fcc crystal structure but with a substantial fraction of the C60 molecules modified with carbonyl (C=O) bonds.

The possibility of π-electron ring currents in C 60 has been of interest since the initial identification of the fullerenes and the recent synthesis of these compounds has provided an experimental impetus to magnetic studies. We calculated a vanishingly small π-electron ring-current magnetic susceptibility for C 60 and this prediction has recently received experimental verification. We attributed this behavior to a near cancellation of the diamagnetic and Van Vleck paramagnetic terms. The higher fullerenes may become available for study in the near future and recent work by Diedrich et al. (Science, 252 (1991) 548) has led to the isolation of C 84 . Although the structure of this molecule has not yet been identified, Raghavachari and Rohlfing ( J. Phys. Chem., 95 (1991) 3457) have reported ab initio calculations of the structures of C 60 , C 70 and two isomers of C 84 . We therefore decided to study these structures with the three-dimensional finite-field London theory previously employed to study C 60 and C 70 with idealized geometries. The π-electron ring-current magnetic susceptibilities of the fullerenes included in the present study do not monotonically increase toward the graphite value. Both isomers of C 84 show small average diamagnetic susceptibilities. There is a large anisotropy associated with the π-electron diamagnetic susceptibility of C 84 ( D 6 h ). With the exception of C 70 , all of the molecules show a strongly enhanced diamagnetism in the 6-state and a weak diamagnetism in the 12-state.

The reactions of N,N,N[prime]-tris(trimethylsilyl)formamidine with ECl[sub 2] (E = S, Se) afford 1,2,3,5-dithia- and 1,2,3,5-diselenadiazolium chloride, which can be reduced with triphenylantimony to the corresponding dithia- and diselenadiazolyl radicals [HCN[sub 2]E[sub 2]]. The solid state structure of the cofacial dimer [HCN[sub 2]S[sub 2]][sub 2] has been determined by X-ray diffraction; crystals of [HCN[sub 2]S[sub 2]][sub 2] belong to the monoclinic space group P2[sub 1]/n, with a = 6.833(6), b = 16.463(4), c = 19.161(4) A, [beta] = 93.57(4)[degrees], FW = 210.30, Z = 12. The crystal structure consists of stacked dimers, with three dimers in the asymmetric unit. Along the stacking axis the mean intradimer S---S contact is 3.11 A; the mean interdimer contact is 3.76 A. Ab initio calculations with split-valence and larger basis sets have been employed to evaluate the structures and energies of both the gas phase radicals and their dimers. Minor changes in geometry are predicted upon association of the monomers; this relative structural invariance is consistent with low binding energies, the best predictions (including zero point vibrational energy corrections) being ca. 4 kcal/mol (for E = S) and ca. 10 kcal/mol (for E = Se). 30 refs., 6 figs., 9 tabs.

We report the observation and assignment of the doping-induced features in the UV-visible and near-IR optical spectra of ${\mathrm{C}}_{60}$ thin films and their direct correlations with electrical resistivity. A pronounced bleaching and several induced absorptions are observed upon doping with the alkali metals, potassium and rubidium. The absence of a strong dependence of the induced spectra upon intercalant suggests that the induced features observed are intrinsic to the host fullerene film. The evolution of these transitions, as doping proceeds from pristine ${\mathrm{C}}_{60}$ to ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$, is consistent with a two-domain picture for the formation of the metallic state. As the intercalation proceeds beyond the resistance minimum, an overall change in spectral shape begins to occur and energy shifts of many of the features become apparent. These observations indicate changes in the electronic bands accompanying the structural phase transformations from ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ to ${\mathrm{K}}_{6}$${\mathrm{C}}_{60}$. There is no spectral evidence for the presence of ${\mathrm{K}}_{4}$${\mathrm{C}}_{60}$ during doping.

A new stable compound ${\mathrm{Ba}}_{3}$${\mathrm{C}}_{60}$ is reported in the Ba-${\mathrm{C}}_{60}$ phase diagram. Rietveld refinement of x-ray powder diffraction data shows that this compound has the A15 structure with a lattice constant of 11.34 \AA{}. The Pm3\ifmmode\bar\else\textasciimacron\fi{}n space group implies a perfect alternating orientational order for the ${\mathrm{C}}_{60}$ molecules, not previously observed in doped fullerite structures. The relative stability of the A15 phase over the fully intercalated fcc structure can be explained by a simple model involving the Madelung energy differences, orientation dependence of the ${\mathrm{C}}_{60}$-cation interaction energy, and distortion-induced relaxational energy gains.

C 60 has not yet been detected in primitive meteorites, a finding that could demonstrate its existence in the early solar nebular or as a component of presolar dust. However, other allotropes of carbon, diamond and graphite, have been isolated from numerous chondritic samples. Studies of the isotopic composition and trace element content and these forms of carbon suggest that they condensed in cireumstellar environments. Diamond may also have been produced in the early solar nebula and meteorite parent bodies by both low-temperature—low-pressure processes and shock events. Evidence for the occurrence of another carbon allotrope, with sp hybridized bonding, commonly known as carbyne, is presented.

Within the neighbourhood of the Sun, a number of highly evolved stars are carbonrich in the sense that they have more carbon than oxygen so their outer atmospheres contain molecules such as CN, CH and C 2 H 2 . These stars are cool with atmospheric temperatures near 3000 K and they are also luminous, typically 10 4 times more powerful than the Sun. The outer envelopes of these stars are tenuously bound, and they all are losing mass at a very high rate, in some cases more than 10 -5 M@ a -1 (where M@ denotes the mass of the Sun). These high luminosity carbon stars remain in this phase for a time, very approximately, near 105 years. They exhibit a large amount of carbon in their atmospheres because the products of the nuclear burning that occurs in the very centre of the star, including the synthesis of carbon, appear on the surface. In the extended envelopes around these stars, there is a very active chemistry, and the gas is sufficiently cool that nucleation of solid dust grains occurs. These solid particles may grow to sizes as large as 1 pm although a more typical size is near 0.05 pm. We therefore can identify both relatively small carbon-bearing molecules (for example HC 7 N) and much larger carbon-containing dust grains in the outflows. The amount of intermediate size particles or molecules, such as C 60 , and their possible role in the circumstellar chemistry is not yet well understood. At least in the envelope of the well studied carbon star IRC +10216, there appears to be more carbon in CO and solid grains than in polycyclic aromatic hydrocarbons.

The chemistry by which the closed-cage carbon clusters, C 60 and C 70 , can be formed in high yield out of the chaos of condensing carbon vapour is considered. Several mechanisms for this process that have been proposed are critically discussed. The two most attractive are the ‘pentagon road’ where open sheets grow following the alternating pentagon rule and the ‘fullerene road’ where smaller fullerenes grow in small steps in a process which finds the buckminsterfullerene (C 60 ) local deep energy minimum and to a lesser extent the C 70 ( D 5h ) minimum. A clear choice between the two does not seem possible with available information.

Conjugation in C 60 is not as extensive as was originally anticipated because, for various reasons, the pentagon rings avoid containing double bonds. As a consequence, there is extensive bond localization and the molecule, which is quite reactive, and displays superalkene rather than superaromatic properties. C 70 behaves in a similar fashion; other fullerenes may follow suit. Additions predominate and C 60 is particularly susceptible to nucleophilic attack. Added groups may also be readily replaced by nucleophiles, although the reaction mechanism is uncertain at present: The functionalized molecule tends to revert to the parent fullerene at moderate temperatures, and characterization of reaction products by mass spectrometry is thus particularly difficult. This fact, coupled with the complexity of the addition products, makes work with fullerenes exacting. A selection of reactions studied to date and the progress made towards identifying various patterns of addition are described.

The synthesis and microwave study of linear cyanopolyynes, HC 5 N and HC 7 N, in the mid-1970s was followed by the unanticipated detection of these, and longer chains (HC 9 N and HC 11 N), in space. To gain insight into the way in which such species and carbon clusters in general might form, an experiment was devised in 1985 to simulate conditions in carbon stars, involving the laser vaporization of graphite in a supersonic nozzle and detection of the resulting carbon species by mass spectrometry. This initiative resulted in the serendipitious discovery of an entirely new allotrope of carbon, C 60 , named buckminsterfullerene after the inventor of the geodesic dome. Five to seven years later, C 60 and other members of what is now know as the fullerene family have been isolated in macroscopic amounts, however, these exciting developments have tended to overshadow fundamental problems associated with the aggregation of carbon atoms in which acetylenes, and polyynes in particular, may play a key role.

The gaseous, solution and solid state experimental evidence for electron addition to the fullerenes is reviewed and it is shown that this class of molecules function as powerful electron acceptors. The topological character of C 60 as described by Hückel molecular orbital theory suggests that the molecule will undergo facile reduction, but comparisons with planar conjugated hydrocarbons show that this feature alone cannot account for the very low half-wave reduction potential of C 60 . Because of the curvature of the surface, fullerene hybridization falls between graphite (sp 2 ) and diamond (sp 3 ) and these new carbon allotropes are therefore of intermediate , and perhaps variable hybridization. According to POAV1 theory the carbon atoms in C 60 are of sp 2.28 hybridization. It is concluded that rehybridization plays an important role in determining the electronic structure of the fullerenes and it is the combination of topology and rehybridization that together account for the extraordinary ability of C 60 to accept electrons.

The preparation and solid-state characterization of the 1,3,5-triazine-bridged tris(1,2,3,5-ditliiadiazolyl) complex 4,4',4''-(2,4,6-(1,3,5-triazinetriyl))tris(1,2,3,5-dithiadiazolyl) [N 3 C 3 (CN 2 S 2 ) 3 ] are described. The crystals belong to the monoclinic space group C2/c, with a=20.759(7) A, b=10.525(3) A, c=17.554(3) A, β=140.18(4) o , fw=390.5, Z=8, and V=2456.2(12) A 3 . The crystal structure consists of layers of interlocked dimers. Alternate layers are oriented in an antiparallel fashion, thereby precluding a stacked structure similar to that found in the related 1,3,5-benzene-based triradical. There are two dimerization environments

Van der Waals forces that bind C[sub 60] molecular solids are found to be sufficiently strong to allow the reproducible fabrication of free-standing C[sub 60] membranes on (100) silicon wafers. Membranes, 2,000 to 6,000 angstroms thick, were fabricated by a modified silicon micromachining process and were found to be smooth, flat, and mechanically robust. An important aspect of the silicon-compatible fabrication procedure is the demonstration that C[sub 60] films can be uniformly and nondestructively thinned in a CF[sub 4] plasma. Young's modulus and fracture strength measurements were made on membranes with areas larger than 6 millimeters by 6 millimeters. It may be possible to use C[sub 60] membranes for physical property measurements and applications. 20 refs., 5 figs.

A formulation within the London approximation of magnetic ring currents is applied to C60, C70, and their hexa-anions. Contrary to previous approaches, this formulation does not require the identification of closed loops and can therefore be applied to these molecules despite their topological complexity. Knowledge of the ring currents provides a better understanding of their magnetic ring-current susceptibilities. Probe dipoles are used to investigate local spatial variations of the magnetic field induced by the ring currents. In an attempt to evaluate how the carbon chemical shifts are affected by the ring currents, we separate the current into a component circulating above and one below the molecular surface. Assuming a displacement of the negatively charged electronic clouds towards the outside of the molecule, we axe able to understand the relative positions of the carbon NMR lines of C60 and C60(6-).

Electrical resistance measurements show that uniform intercalation of Ba into C60 films is much more difficult to achieve than in the case of the other alkaline earths (AE), Ca and Sr. BaxC60 films studied after annealing at 220°C show a resistivity minimum between 1