Showing papers by "Rodney S. Ruoff published in 1995"

Relationship between the Electron Affinities and Half-Wave Reduction Potentials of Fullerenes, Aromatic Hydrocarbons, and Metal Complexes

Abstract: Differences in energy for neutral molecule and negative ions upon going from the gas phase to solution. - {delta}{delta}G{sub sol}, have been calculated from gas phase electron affinites and half-wave reduction potentials for a series of fullerenes, aromatic hydrocarbons, metalloporphyrins, and metal complexes in dimethylformamide (DMF). For those compounds with similar charge delocalization, the value of -{delta}{delta}G{sub sol} is constant and equal to 1.76 {+-} 0.06 eV for the fullerenes, 1.99 {+-} 0.05 eV for the aromatic hydrocarbons and the metalloporphyrins, and 2.19 {+-} 0.14 eV for the metal acetylacetonates. The fullerenes form a new class of molecules in which the charge is highly delocalized, and this is demonstrated by the relatively low value of -{Delta}{Delta}{sub sol}. A procedure for determining adiabatic electron affinities from reduction potentials, and vice versa, is established. This procedure is applied to benzene to give an electron affinity of {minus}0.7 {+-} 0.14 eV, to La @ C{sub 82} to give an electron affinity of 3.21 {+-} 0.06 eV, and to Y @ C{sub 82} to give an electron affinity of 3.32 {+-} 0.06 eV. On the other hand, a value of E{sub 1/2} = 0.09 {+-} 0.14 V vs SCE is predicted for the reductionmore » of Ca@C{sub 60} in DMF based upon a reported electron affinity of 3.0 {+-} 0.1 eV. 36 refs., 4 figs., 3 tabs.« less

Selective and high-yield synthesis of higher fullerenes

Abstract: Fullerenes have been prepared by dc arc synthesis with graphite (anode) rods containing light elements such as B, Si, or Al in a series of concentrations. Furthermore, the influence of mixing N{sub 2} (g) with He(g) on the yield of higher fullerenes has been addressed. For each type of experiment, the relative fullerene yields are obtained from the relative peak areas in surface analysis by laser ionization-mass spectrometry (SALI-MS) spectra and the absolute yield of C{sub 60} and C{sub 70} from calibrated HPLC; the relative yields in SALI-MS represent closely the nascent distribution in the primary soots. We determine the approximate absolute yields of higher fullerenes, for which extinction coefficients are not yet available for HPLC analysis, by scaling the absolute C{sub 60} and C{sub 70} yields with the relative concentrations from SALI-MS. The most prominent increased higher fullerene yield was obtained with a 1% B-doped graphite rod with a 2:100 volume mixture of N{sub 2}(g): He(g); the absolute yield of C{sub 60} was reduced from 8.85% to 2.75%, and the yield of higher fullerenes such as C{sub 78} and C{sub 84} was increased by a factor of 2 over the pure C, pure He(g) case. We conclude that usingmore » a B-doped graphite rod and mixing in small amounts of N{sub 2}(g) into He(g) enhances both the absolute and relative yields of higher fullerenes. 18 refs., 4 figs., 3 tabs.« less

Excited Triplet and Reduced Forms of C84

Abstract: The triplet excited state behavior of C[sub 84] has been probed by the triplet - triplet energy transfer method using pulse radiolytically generated biphenyl triplets in benzene. The triplet excited state has a weak absorption in the UV (difference absorption maxima at 310 and 345 nm) but no significant absorption in the visible. The rate constants for energy transfer from [sup 3]BP* and [sup 3]C[sub 60]* are 4 [times] 10[sup 9] and 4.7 [times] 10[sup 9] M[sup [minus]1] s[sup [minus]1], respectively. Triplet excited state properties of [sup 3]C[sub 84]* are compared with other fullerenes. A photocatalytic method has also been successfully employed to reduce C[sub 84] in a UV-irradiated colloidal TiO[sub 2] suspension. 36 refs., 4 figs., 1 tab.

Scanning tunneling microscopy current-voltage characteristics of carbon nanotubes

Abstract: Scanning tunneling microscopy (STM) has been used to obtain images and current–voltage (I–V) curves of carbon nanotubes produced by arc discharge of carbon electrodes. The STM I–V curves indicate that carbon nanotubes with diameters from 2.0 to 5.1 nm have a metallic density of states. Using STM, we also observe nanometer‐size graphene sheets which are four graphite layers thick. The STM images of carbon nanotubes are in good agreement with transmission electron microscope images.

Sublimation of Higher Fullerenes and Their Interaction with Silicon (100) Surface

Abstract: The heat of sublimation of C{sub 60}, C{sub 70}, C{sub 78}, C{sub 84}, and C{sub 96} is measured by modulated molecular beam mass spectrometry (MMBMS) The scattering of C{sub 70} and C{sub 84} from Si(100) is also investigated by MMBMS The behavior of C{sub 84} is quite similar to that of C{sub 60} reported earlier by Hamza, Balooch, and Moalem, except that the onset of the surface decomposition of the fullerene occurs at 850 K, 150 K lower than for C{sub 60} When the surface temperature reaches 1000 K, total decomposition of the incident C{sub 84} is observed The behavior of C{sub 70} is surprisingly different from both C{sub 60} and C{sub 84} Twenty percent of the incident C{sub 70} decomposes at 1000 K, and the remaining 80% does not decompose until a target temperature of 1200 K is reached At surface temperatures below 800 K, for the interaction of C{sub 70} and C{sub 84} with silica, the dominent surface processes are adsorption with near perfect sticking probability, followed by surface diffusion to the edge of the specimen and desorption 20 refs, 6 figs

Street and ice hockey stick

Abstract: An ice, street or roller hockey stick (2) having a stick blade (4) that prevents excessive wear The stick includes a plurality of rods or members (12) inserted in the bottom edge (8) of the stick's blade (4) The rods or members (12) are made of a material exhibiting higher wear resistance characteristics than the material used to form the bottom edge (8) of the blade (4)

Excited Triplet and Reduced Forms of CM

Abstract: visible absorption spectra of c8429 and the reduction potentials of c8427-31 have already been reported. At least six reversible reductions have been characterized using cyclic v o l t a m r r ~ e t r y . ~ ~ ~ ~ Although distinctively different electronic properties of these two isomers were observed in electrochemical and ESR studies, the separation of the two isomers of c 8 4 has not yet been achieved. Consequently, a mixture of the two isomers has been used in this investigation. We report here, for the first time, experimental results which characterize triplet excited state properties of c84. We also report the photoelectrochemical reduction of c 8 4 in colloidal Ti02 suspension. Experimental Section Materials. Mass-pure C84 was obtained via selective solvent extraction followed by HPLC chromatography with a semipreparative Buckyclutcher column (Regis) run in recycling mode. Details of the selective solvent enrichment techniques will be published later.26a The purity of the sample was checked by surface analysis via laser ionization (SALI) mass spectrometry (MS), a technique that has been used extensively at SRI Intemational for analysis of fullerene samples.27b SALI-MS showed that the fullerene purity exceeded 99.5%, with the only impurity peaks belonging to c 8 2 and c86; in particular, no c60 or c 7 0 was present in the SALI-MS spectrum obtained. The