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We report on some of the conditions during sublimation which promote single-shell carbon nanotube formation. Using as a catlyst a mixture of two metals (Co and Pt) in the anode, we observe a higher density of single-shell carbon nanotubes than that found with cobalt alone. Using other mixtures (Co and Fe), the nanotube yield is always lower, and their formation is even hindered (Co and Ru). First attempts of vacuum annealing at high temperature on samples containing cobalt-catalyzed single-shell carbon nanotubes suggest that this might be a good way to eliminate the catalyst particles. We present high-resolution transmission electron microscopy images of samples obtained by such procedures.

The different contributions which participate to the shift and broadening of an intramolecular mode in the plastic phase of C 60 are recalled. Especially, using a rotational diffusion model, we calculate the expected step of the linewidth of the A g and H g Raman modes related to the slowing down of the reorientational process at the order-disorder phase transition. For H g modes a value of the order of 2 cm -1 is calculated. On the other hand, we have performed a detailed analysis of the temperature dependence of the Raman spectrum of C 60 . We state that the slowing down of the reorientational process cannot explain alone the changes with temperature of the profile of the H g mode. We show that the room temperature spectrum of the 1426 cm -1 and 1575 cm -1 tangential H g modes results from the overlap of several components and changes with temperature of the profile of the H g mode are mainly related to an opposite temperature dependence of the intensity of these components and not to a dramatic narrowing of these modes.

We report interesting growth morphologies produced during the electric arc-discharge between a graphite cathode and a composite cobalt—graphite anode, which includes the abundant formation of single-shell carbon nanotubes of 1–2 nm diameter. As the pressure inside the chamber and the cobalt content of the electrode are varied these “carbon monotubes” are formed in bundles and in high density under certain conditions in the soot, webs and string-like structures that decorate the chamber and also on a collaret that forms around the conventional deposit containing multi-shell nanotubes. We present high-resolution transmission electron microscopy images of these structures and propose conditions that promote single-tube growth. We also notice, in some cases, novel formation of regularly spaced cobalt particles enclosed in graphitic capsules and surrounded by sheaths of soot.

We report the temperature and pressure dependence of 13 C nuclear spin-lattice relaxation time T 1 on K 3 C 60 in the normal state. Within the BCS electron-phonon pairing mechanism, we estimate the coupling strength and the relevant phonon mode involved to account for superconductivity.

Recent studies carried out on an organic superconductor, s-(BEDT-TTF) 2 I 3 , have shown the important role played by the 13 C isotope on the T c transition, when substitution is made on the central CC bond of the molecule. Simultaneously, Raman studies determined the frequency shifts observed in the CC stretching vibrations in the substituted samples and consequently, put in evidence the role of the intramolecular Ag vibrations. We have extended these studies to compounds of the new carbon family, the fullerenes, in which 82% of the carbon atoms were substituted with 13 C in C 60 . The superconducting transition measured on the same sample doped with potassium is lowered by 1.5 to 2K as compared to the standard material doped in similar conditions. In the Raman spectrum, the main Ag band measured at 1467 cm −1 in 12 C 60 is shifted to 1420 cm −1 in enriched 13 C 60 . Taking into account the ratio between the molecular weight of the enriched 13 C 60 and of the standard material, one predicts a theoretical value for this mode at 1418 cm −1 in the enriched sample. A preliminary analysis of the Raman spectrum will be presented.

EVOLVE simulation results of sputtering processes of Au films with 175 keV Ar ions are compared to available experimental results. Thicknesses of Au films are 23, 99 and 192 nm, which are small, comparable and large, respectively, compared to the range of Ar ions. As a result of dose-dependent analysis of Au films, a good agreement has been found if the displacement threshold energy of Au is assumed to be 12 eV. Reducing the surface binding energy of Au from 3.8 to 1.9 or even to 0.0 eV does not increase the sputtering yield as the elemental sputtering yield formula predicts. In fact, it has no significant effect at all on the sputtering yield if the elemental value, e.g. 36 eV, is used for the displacement threshold energy of Au. On the other hand, reducing the displacement threshold energy from 36 to 12 eV increases the sputtering yield by more than a factor of 2. The sputtering yield is expressed and discussed in terms of parametric relationships of the surface binding energy, displacement threshold energy, the film thickness and the fluence.

The interest in efficient intestinal delivery of health-promoting substances is increasing. However, the delivery of vulnerable substances such as enzymes requires specific attention. The transit through the stomach, where the pH is very low, can be detrimental to the enzymatic activity of the protein to be delivered. Here, we describe the microencapsulation of the model enzyme bile salt hydrolase (Bsh) using whey protein-gum arabic microencapsulates for food-grade and targeted enzyme delivery in the proximal region of the small intestine. Furthermore, the efficacy of enteric coating microencapsulates for site-specific enzyme delivery was compared in vitro with living Lactobacillus plantarum WCFS1 bacteria that endogenously produce the Bsh enzyme. Microencapsulates allowed highly effective protection of the enzyme under gastric conditions. Moreover, Bsh release under intestinal conditions appeared to be very efficient, although in the presence of pancreatin, the Bsh activity decreased in time due to proteolytic degradation. In comparison, L. plantarum appeared to be capable to withstand gastric conditions as well as pancreatin challenge. Delivery using encapsulates and live bacteria each have different (dis)advantages that are discussed. In conclusion, live bacteria and food-grade microencapsulates provide alternatives for dedicated enteric delivery of specific enzymes, and the choice of enzyme to be delivered may determine which mode of delivery is most suitable.

Composite sheets and nanotubes of different morphologies containing carbon, boron, and nitrogen were grown in the electric arc discharge between graphite cathodes and amorphous boron-filled graphite anodes in a nitrogen atmosphere. Concentration profiles derived from electron energy-loss line spectra show that boron and nitrogen are correlated in a one-to-one ratio; core energy-loss fine structures reveal small differences compared to pure hexagonal boron nitride. Boron and carbon are anticorrelated, suggesting the substitution of boron and nitrogen into the carbon network. Results indicate that singlephaase CyBxNx as well as separated domains (nanosize) of boron nitride in carbon networks may exist.

We report the vapor phase growth of partially filled graphitic fibers, 20-30 nm in diameter and up to a micron in length, during a manganese catalyzed carbon electric arc discharge. The fiber morphology resembles that of catalytic chemical vapor deposited carbon filaments but the inside hollow contains intermittent precipitates and continuous filling of Mn that at times occupy g50% of fiber lengths. Transmission electron microscopy and electron energy loss line spectra show that the fillings form as solid cores and may correspond to pure metal.

We report here interesting growth morphologies produced during the electric arc-discharge between a graphite cathode and different composite metal-graphite anodes: when the metal is pure cobalt powder, we obtain, under certain conditions of pressure and cobalt content in the electrode, many single-shell carbon nanotubes of 1–2 nm diameter which appear in the soot, webs, threads (in the reactor chamber) and also on a collaret that forms around the conventional deposit containing multi-shell nanotubes. When the metal is pure manganese powder, we obtain multi-layer hollow carbon fibers in the soot similar to the carbon fibers grown by catalytic chemical vapor deposition. Furthermore, many fibers have a good portion of the length filled with metal. We present here high-resolution transmission electron microscopy images of these structures.

The sputtering yield, joint polar and azimuthal angular distributions and the energy distribution of atoms sputtered from copper single crystals by 100 keV copper ions has been calculated as a function of crystal orientation using the cascade simulation code MARLOWE. The calculated yields and angular distributions are compared with experimental results for ions incident parallel to a close-packed axial channelling direction, parallel to a plane, and along a pseudo-random direction. Significant channeling effects are exhibited in both calculations and experiment. Strong peaking in the backscattered direction is calculated and observed for the axial irradiations alone. Primary range distributions and damage profiles are calculated for the three crystal orientations and compared with lattice damage measurements. The distributions of sputtered ions in both energy and angle are presented.

Copper targets were implanted with 125 keV gold and tantalum ions at selected incident angles of the beam relative to the target normal to examine the effect of the incident angle on the sputtering yields, the dose retained in the modified layer, and the atomic surface fractions. Sputtered particles were collected on aluminum foils to measure the angular distribution of the sputtered particles and to determine the partial sputtering yields of the beam and target species. A 1.5 MeV xenon beam implanted markers into the copper targets to determine the average sputtering yield for the surface during the implantation. Theoretical predictions from a surface binding energy correction model were compared with the experimental results. Although the predictions from the model were not exact, the trends of the data were in agreement with the model. The measured total sputtering yield increases with increasing incident beam angle, and, correspondingly, the fluence retained decreases with incident beam angle.

The sputtering yield and the angular distribution of sputtered atoms have been measured as a function of copper-ion-beam orientation with respect to copper single-crystal targets. Alpha-particle channeling has been employed to measure the lattice damage induced during the sputtering experiments. The experimental results have been compared with results from the cascade simulation program MARLOWE. Both planar and axial channeling of incident ions have been shown to significantly reduce the sputtering yield relative to a psuedo-random irradiation direction. Channeling of the incident particles also increases the depth to which lattice damage is produced. Surface preparation is found to strongly influence the orientation effects, with mechanical polishing reducing the channeling of incident ions, relative to electropolishing.

Self-ion sputtering yields were determined for copper, nickel, and aluminum at 60 keV, 90 keV, and 120 keV. The sputtering yields were determined by Rutherford backscattering measurements of the energy shifts of a deeply implanted xenon marker layer and by measuring the distribution and amount of sputtered material on a catcher foil using backscattering and particle induced X-ray emission. The effect of dose rate and net fluence on the yield were examined. Optical monitoring of the light intensity emitted by the sputtered particle confirmed no measurable change in the yield using self ion bombardment. The self-ion sputtering yields measured in this study are less than predicted by theory but are self consistent within experimental error independent of measurement technique. Additional measurement of self-ion sputtering yields in this energy range are needed for applications in materials modification.

In this paper the surface binding energy model proposed by Reynolds for a binary alloy has been extended to a ternary system. From this model extension the steady state atomic surface fractions were calculated for a ternary surface alloy to be prepared by ion implanting a binary alloy of known composition. These predictions were compared with the results of the subsequent ion implantation experiments. The total implantation process was monitored by the observation of light emitted through de-excitation processes from sputtered neutral atoms. The experimental results reported are for nickel-chromium alloy implanted with 90 keV copper and tantalum and were analyzed using Rutherford backscattering, particle induced X-ray emission, and Auger surface analysis. From these results the partial sputtering yield for each component, net sputtering yield and surface atomic fractions were determined, and then compared with the predicted values. The different analytical techniques show consistent agreement within experimental error and there is reasonable agreement between the experimental results and the predicted values.

The sputtering yields from thin Cu films of various thicknesses on aluminum backings, with 180 keV Ar+ ions, have been determined. The evolution of the ion-induced optical emission from the substrate, used to determine the ion dose necessary to sputter the film, was compared with predictions from the EVOLVE code for similar film thicknesses and sputtering conditions. The data and the predictions coincide for a 200 A film. For thicker films, they are similar but don't overlap. The sputtering process is well described by the EVOLVE code. For two of the films the experimental yield values are slightly lower than the predictions from the code, but the results, both experimental and from the simulation, are consistent with the idea that for very thin films the yield is smaller than that of infinitely thick targets and decreases as the film thickness decreases.