In this Communication we discuss how unimplanted and implanted films (Y and Au implanted) of C60, when hot isostatically pressed (HIPed) at a pressure of 170 MPa (1.7 kbar) of Ar and temperatures of 300 or 400 °C, show substantial uptake of Ar into the film. Rutherford backscattering (RBS) provides an effective method for elucidating film composition, showing the films to have ∼1.5 at.% of Ar, consistent with a stoichiometry close to Ar1 C60. The Ar was found to diffuse from the films when these were held in a vacuum at 300 °C. It could subsequently be reincorporated into the film by re-HIPing, with uptake of a similar amount of Ar. IR spectroscopy showed that the C60 IR absorptions remain unchanged throughout uptake of the Ar and its subsequent loss during heating at 300 °C. It appears that the Ar is trapped interstitially in the films outside the C60 cages.

The thermal expansion of CD4 solutions in the orientational glass C60 with molar concentration of deuteromethane 20 and 50% has been investigated in the temperature range 2.5–23K. The orientational glass CD4–C60 undergoes a first-order phase transition in the temperature interval 4.5–55K. This transition is manifested as hysteresis of the linear thermal expansion coefficient α as well as maxima in the temperature dependences α(T) and τ1(T), where τ1 is the characteristic thermalization time of the experimental samples. The characteristic re-orientation times of the C60 molecules and the characteristic phase transformations occurring in the experimental solutions are determined. The results of the present study are compared with the results of a similar study of the solution CH4–C60. It is concluded that tunneling rotation of the CH4 and CD4 molecules occupying interstitial positions in the fullerite C60 lattice occurs.

The radial thermal expansion coefficient (a)r of pure and Xe-saturated bundles of single-walled carbon nanotubes has been measured in the interval 2.2-120 K. The coefficient is positive above T = 5.5 K and negative at lower temperatures. The experiment was made using a low temperature capacitance dilatometer with a sensitivity of 2x10-9 cm and the sample was prepared by compacting a CNT powder such that the pressure applied oriented the nanotube axes perpendicular to the axis of the cylindrical sample. The data show that individual nanotubes have a negative thermal expansion while the solid compacted material has a positive expansion coefficient due to expansion of the intertube volume in the bundles. Doping the nanotubes with Xe caused a sharp increase in the magnitude of (a)r in the whole range of temperatures used, and a peak in the dependence (a)r (T) in the interval 50-65 K. A subsequent decrease in the Xe concentration lowered the peak considerably but had little effect on the thermal expansion coefficient of the sample outside the region of the peak. The features revealed have been explained qualitatively.

A new strategy for the preparation of well-dispersed clays in a polymer matrix by a spray-drying method is presented. Scanning electron microscopy and transmission electron microscopy measurements show that the spray-drying process produces clay/polymer microspheres in which the clay is trapped in a well-dispersed state throughout the polymer matrix. The microspheres have been successfully extruded into clay/poly(methyl methacrylate) nanocomposite bulk structures without any perturbation of the well-dispersed clay nanostructure in the original microspheres. Transmission electron microscopy and small-angle X-ray scattering show that the clay particles in the extruded materials range from single platelets to simple tactoids composed of a few stacked clay platelets, indicating an excellent degree of dispersion. The results show that sprayed microspheres are very good precursors for further processing such as extrusion or melt blending with other polymers for bulk nanocomposite fabrication. (c) 2008 Wiley Periodicals, Inc.

The temperature dependence of the linear thermal expansion coefficient α(T) is investigated in the temperature range of 2.5 to 23K for two different CH4–C60 solutions in which CH4 molecules occupy 24 and 50% of the octahedral interstitial sites of the C60 lattice. In both cases, α(T) exhibits hysteresis, suggesting the existence of two types of orientational glass associated with these solutions. The temperature of the first-order phase transition between these two glasses is estimated, and the behavior of these two glasses is compared. The characteristic times of thermalization τ1, reorientation of the C60 molecules τ2, and of the phase transformation between the glasses τ′, are estimated for these solutions. Both the temperature dependence of α(T) and the characteristic thermalization time τ1 are found to have features near the phase transition temperature, and an explanation is put forward to explain these observed features.

The lattice parameter a of fullerite C60 intercalated with N2 molecules is investigated in the temperature interval 6–295K by x-ray diffraction. It is found that the interstitial molecular N2 has a considerable effect on both the orientational phase transition temperature Tc and the orientational glass formation temperature Tg. Hysteresis of a(T) in the Tc and Tg regions is detected, along with an abrupt change in volume over the region defining Tc. Complete intercalation of C60 with N2 molecules results in a 0.2% increase in the lattice parameter, which persists over the whole temperature range. Evidence is also obtained that the interstitial guest molecular N2 induces a slight deformation of the cubic symmetry of the C60 host lattice.

The linear coefficients α(T) of N2–C60 solutions with 9.9% and 100% of the C60 lattice thermal expansion interstitials filled with N2 are investigated in the interval 2.2–24K. The dependence α(T) has a hysteresis suggesting co-existence of two types of orientational glasses in these solutions. The features of the glasses are compared. The characteristic times of phase transformations in the solutions and reorientation of C60 molecules are estimated.

The heat capacity Cm of polycrystalline fullerite C60 doped with nitrogen is measured in the temperature interval 2–13K. The contributions to the heat capacity from translational lattice vibrations (Debye contribution), from orientational vibrations of the C60 molecules (Einstein contribution), and from the motion of the N2 molecules in the octahedral cavities of the C60 lattice are estimated. However, no indications of the first-order phase transformation detected earlier in a dilatometric investigation of the N2–C60 orientational glass are found (beyond the experimental error limits). A possible explanation for this fact is proposed.

The Vickers microhardness of Xe-intercalated polycrystalline fullerite C60 (Xe C x 60, x 0.35) is measured in a moderately low temperature range of 77 to 300 K. A high increase in the microhardness of the material (by a factor of 2 to 3) as compared to that of pure C60 single crystals is observed. It is shown that the step-like anomaly in the temperature dependences of the microhardness of pure C60 single crystals recorded under the orientational fcc-sc phase transition (Tc 260 K) is also qualitatively retained for Xe C x 60, but its onset is shifted by 40 K towards lower temperatures and the step becomes less distinct and more smeared. This behavior of H T V( ) correlates with x-ray diffraction data, the analysis of which revealed a considerable influence of xenon interstitial atoms on the peculiar features of fullerite thermal expansion due to orientational phase transitions (see the paper by A.I. Prokhvatilov et al. in this issue).

In this section, we review research that shows strong evidence for rare-gas endohedral radiofullerene formation as a result of nuclear recoil that follows nuclear reactions. Pioneering neutron activation studies by Braun and Rausch, are described [1]. The subsequent discovery of stable rare gas interstitial fullerenes by Gadd et al. [19–21, 25], has enabled the gamma produced recoil mechanism of Braun and Rausch to be studied in greater detail [13, 14]. The preparation and thermal behaviour of rare gas interstitial fullerenes is briefly described as well as their behaviour to neutron irradiation. The results show the authenticity of Braun and Rausch’s earlier experimental work and an observed isotope effect indicates the unique nature of the endohedral formation process. Further neutron activation studies [15] of the rare gas interstitial Xe/C60, combined with the use of gamma spectroscopy and high pressure liquid chromatography (HPLC) shows strong evidence for an eluted fraction containing the radioactive endohedral fullerene, Xe@C60. The research of Ohtsuki et al. [10] is described, who have independently been studying an alternative nuclear activation process for producing rare gas radionuclides in the presence of fullerenes. Using HPLC, they have also found direct evidence for endohedral formation as a result of nuclear recoil. Important factors relating to the nuclear recoil mechanism of endohedral rare gas radiofullerene formation are discussed as well as the elegant state of the art ab initio molecular dynamics simulations by Ohtsuki et al. [10].

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The new intercalate compound C-60(N2O)(x) has been synthesised by hot isotatically pressing (HIPing) C-60 under 170 MPa of N2O. Neutron powder diffraction studies conducted on C-60(N2O)(x) between room temperature and 5 K have been analysed using Rietveld techniques and reveal a structural transition between a high-temperature (> similar to 250 K) Face-centred cubic (FCC) phase (Fm (3) over bar m, a = 14.215(2) Angstrom (298 K)) and a low-temperature (< similar to 150 K) simple cubic (SC) phase (Pa (3) over bar, a = 14.066(1) Angstrom (5 K)). (C) 2000 Elsevier Science B.V. All rights reserved.

The intercalate compound C-60(CO2)(x) has been synthesized by hot isostatically pressing C-60 under 170 MPa of CO2 and 350 degrees C. Neutron powder diffraction studies conducted on C-60(CO2)(x) between room temperature and 5 K have been analyzed using Rietveld techniques and reveal a structural transition between a high-temperature (greater than or similar to 250 K) face-centered cubic phase [Fm (3) over bar m, a=14.224(2) Angstrom (293 K)] and a low-temperature (less than or similar to 150 K) monoclinic phase [P2(1)/n, a=9.7438(9)Angstrom, b=9.7473(9)Angstrom, c=14.6121(11)Angstrom, beta = 90.390(6)degrees (5 K)]. The CO2 molecules occupy the octahedral interstices between the C-60 molecules and are oriented along the body diagonal of the high-temperature phase. In the low-temperature phase they are tilted slightly away from the c axis so as to place the oxygen atoms adjacent to the center of a pentagonal face on the C-60 molecules. [S0163-1829(98)05545-3].

The previous study [G. E. Gadd and T. G. Slanger, J. Chem. Phys. 92, 2194 (1990)] of the upsilon = 0-6 levels of the NO(B 2-PI) valence state has been extended to the upsilon = 7 level, which is of particular interest because it lies at the first dissociation limit of the molecule, and also in a region where strong homogeneous mixing with the C 2-PI Rydberg state manifests itself. Thus, the upsilon = 7 radiative lifetime can be affected by both these interactions, which are dependent on rotational level. It has often been argued that the B 2-PI-3/2 spin-orbit component interacts strongly with C 2-PI-1/2,3/2, whereas the B 2-PI-1/2 component is unperturbed. We show here that "unperturbed" is a relative term and that a sensitive way to demonstrate that even the B 2-PI-1/2 levels are mixed with the C 2-PI state is to measure the intensity branching in the B-X 7-upsilon" vibrational progression from fluorescent spectra, for different rotational levels. In the present study, excitation of these levels is carried out on the B-X 7-0 band at 191-192 nm. We have investigated the lifetimes of both spin-orbit components of B 2-PI (upsilon = 7) and find that the decreasing interaction with the C 2-PI state with increasing rotational level, in spite of the increasing energy above the dissociation limit, leads to a steady increase in radiative lifetime. The value reached at high J is 350-400 ns, whereas the lifetimes of the OMEGA = 1/2 levels that lie below the dissociation limit approach a value of 600-700 ns, consistent with the extrapolation of lifetime data for upsilon = 0-6.

The previous study [G. E. Gadd and T. G. Slanger, J. Chem. Phys. 92, 2194 (1990)] of the v=0–6 levels of the NO(B 2Π) valence state has been extended to the v=7 level, which is of particular interest because it lies at the first dissociation limit of the molecule, and also in a region where strong homogeneous mixing with the C 2Π Rydberg state manifests itself. Thus, the v=7 radiative lifetime can be affected by both these interactions, which are dependent on rotational level. It has often been argued that the B 2Π3/2 spin–orbit component interacts strongly with C 2Π1/2,3/2, whereas the B 2Π1/2 component is unperturbed. We show here that ‘‘unperturbed’’ is a relative term and that a sensitive way to demonstrate that even the B 2Π1/2 levels are mixed with the C 2Π state is to measure the intensity branching in the B–X 7–v″ vibrational progression from fluorescent spectra, for different rotational levels. In the present study, excitation of these levels is carried out on the B–X 7–0 band at 191–192 nm. We have investigated the lifetimes of both spin–orbit components of B 2Π(v=7) and find that the decreasing interaction with the C 2Π state with increasing rotational level, in spite of the increasing energy above the dissociation limit, leads to a steady increase in radiative lifetime. The value reached at high J is 350–400 ns, whereas the lifetimes of the Ω=1/2 levels that lie below the dissociation limit approach a value of 600–700 ns, consistent with the extrapolation of lifetime data for v=0–6.

A note on surface tension effects on breaking bow waves - In their interesting recent paper [1], Grosenbaugh and Yeung show that the forward extent of a breaking bow wave in front of a two-dimensional body can be significantly affected by the addition of surfactants to reduce surface tension. However, although they note that contaminants such as dust can also affect the surface flow, they appear to be unaware of the possibility that dynamic effects on surface tension, particularly when surfactants are present, may play an important role, as discussed in reference [2]. As shown by Davies [3], surface films can damp eddies at a free surface of a turbulent liquid. The mechanism is due to the so-called Marangoni effect; that is, where a surface film is locally stretched, the surface contaminant concentration is momentarily reduced, leading to an increase in surface tension which tends to contract the local surface region again. This is why a soap bubble is so much more stable than one formed in pure water. Similarly, upwelling flows associated with turbulence at a water surface cause local stretching and contraction which will tend to be opposed by the presence of the surface contaminant.

Photodissociation of NO has been investigated in the energy region between 8.89 eV, the energy required to produce N(2D)+O(3 P), and 9.26 eV, the ionization limit. Using the technique of resonance-enhanced multiphoton ionization (REMPI), we have demonstrated that there are areas in this energy region in which there are large yields of N(2D), and others where the yields are small. Localized concentrations, from 2-hν dissociation of NO at 270 nm, are an order of magnitude greater than can be obtained from a discharge in N2.