By deposition of C60 on silicon at moderate temperatures (800°C … 900°C) the formation of thin epitaxial β-SiC-films on Si could be proved. C60 -molecules were deposited onto Si(001) and Si(111) in high-vacuum at constant deposition rates for some hours. The thickness and the composition of the formed layers are determined by Rutherford-Backscattering (RBS). The thickness of the layers varied between about 50nm and 200nm in dependence of the deposition parameters. From the shape of the RBS-spectra only β-SiC can be identified. SiC-grains with a mean size of about 500 nm have been observed by atomic force microscopy (AFM). X-ray diffraction (XRD) pole figure measurements demonstrate the heteroepitaxial growth of β-SiC on Si It can be shown by XRD that only the cubic structure (β-SiC) of the different polytypes of SiC was formed during the carbonization process. The formation of growth defects (twins) can be observed.

The lattice vibrations of crystalline solids are generally described by traveling elastic waves. However, the vibrations of fullerene solids are expected to be quite different from typical crystalline solids because of the large molecular mass. In fact, based on measurements of thermal conductivity and specific heat, it appears that the vibrations of compacted fullerene solids are best described as localized. Only below a few Kelvin has evidence for elastic waves been found in these solids where they exist along with the localized tunneling states that are characteristic of amorphous solids. In order to verify the existence of these tunneling defects, the low temperature internal friction of thin fullerene films deposited on a silicon substrate has been measured. Fullerene films were prepared under a variety of conditions with substrate temperatures ranging from 300 K to 500 K. Film grain sizes were characterized using atomic force microscopy, as well as, scanning tunneling microscopy. Grain sizes were found to range between 100 nm and 400 nm. We find that while localized tunneling defects appear to be present in these films, they do not appear to be intrinsic to the fullerene solid. Instead, the tunneling states may be the result of residual disorder that is present in the grain boundaries of the solids.

Fullerene C60 thin solid films have been fabricated on the (001) surfaces of alkali halides (NaCl, KCI and KBr) and muscovite by organic molecular beam deposition (OMBD) technique. Pure C60 powder was sublimated from the precisely temperature-controlled K-cell at low pressure (10−7 Torr) and deposited onto the substrates kept in the range 125 –300 °C. Increasing both the temperature of K-cell and the substrate temperature, fine crystals grow with different size, shape and distance between neighbors. The dependence of the size and density of island crystals on the deposition conditions revealed the mechanism of crystal growth and the effect of interaction between molecules and substrate surface.

As developed by Senturia and co-workers [1], microdielectrometry is a technique for measuring complex permittivity utilizing microfabrication technology to incorporate both the interdigital sensing electrodes and associated circuitry on the same microchip. By covering a microdielectrometer chip with a thin layer of C60, it is possible to dynamically monitor the film's frequency response and dielectric properties as a function of doping with selected gases and other species.

It is known that solid C60 has a substantial amount of interstitial volume. The presence of mobile ions in these spaces compromises the breakdown voltage and makes pure C60 unsuitable for applications requiring high-quality dielectric films. However, various immobile ions or neutral species (e.g. oxygen) can be made to fill the interstitial volume, changing the characteristics of the C60 films and, in some cases, improving the dielectric properties. In-situ microdielectric measurements of pristine and modified C60 films were performed for frequencies ranging from 0.005 Hz to 100 kHz. Based on the low-frequency behavior of the dielectric constant, a model is proposed for the mechanism of oxygen diffusion into the interstitial spaces of the fullerene material.

C60 films have been deposited using a partially ionized cluster beam deposition (PIBD) technique. The experimental results show that as Va. exceeds about 400 V almost all the C60 molecules fragmentate at collision with the substrate and the obtained films turn to be amorphous carbon layers at elevated Va, indicated by measurements of Raman spectra, X-ray diffraction, and ellipsometry.

C60 films, which are deposited by partially ionized beam deposition (PIBD), are doped by 100 keV boron ion implantation at dose ranging from 3*1014 to 1*1016 cm2 The implantation process has been studied using Fourier transform infrared spectroscopy (FTIR), Raman spectra and X-ray diffraction (XRD) analyses. Almost all C60 soccer-balls in the doped region in the films are found to be broken at dose of 1*1016 cm2, while at dose less than 6*1014 cm2 a few C60 molecules remain undestroyed and maintain the original structural properties.

C60 has been subjected to multiple micro-alloying passes by co-rolling together with Al and Mg. Complete amorphization has been found in samples of C60 with Al. However, the structural changes in the C60/Mg combination were more complex. Here, a chemical reaction occurred during which the C60 molecules were apparently broken up into amorphous carbon-like materials, while a Mg-containing oxidation reaction product formed.

We report here the results of our study on the properties of iodine-doped C60 thin films by IR and optical absorption, X-ray diffraction, and electrical conductivity measurements. The results show that there is no apparent structural change in the iodine-doped samples at room temperature in comparison with that of the undoped films. However, in the electrical conductivity measurements, an increase of more that one order of magnitude in the room temperature conductivity has been observed in the iodine-doped samples. In addition, while the conductivity of the undoped films shows thermally activated temperature dependence, the conductivity of the iodine-doped films was found to be constant over a fairly wide temperature range (from 20°C to 70°C) exhibiting a metallic feature.

Picosecond time resolved photoluminescence and photoconductivity measurements are performed to investigate the influence of high intensity illumination on the properties of Fullerene crystals. A highly nonlinear dependence of both the photoluminescence characteristics and the photoconductive response of the fullerenes is seen and temperature dependent measurements indicate that the nonlinear processes are associated with an insulatormetal-like phase transition in the material, and thus that the electronic properties of the excited state are dramatically altered at high excited state densities. The observed behaviour is compared and contrasted to the changes in the optical properties upon photochemical modification of the pristine material via Raman spectroscopy. Application of a simple phenomenological model to calculate the contribution of intermolecular exchange and correlation energies in the excited state supports the proposal that the observed phenomena originate from a Mott-like phase transition. A further manifestation of this behaviour is the emergence of a broadband electroluminescent emission above a critical injection current density.

The Raman spectrum of 13C enriched C60 samples is recorded and analyzed in comparison with that of undoped 12C60. Comparison with the isotopic effect in diamond and in other infinite solid networks is also made.

A frequency shift depending on the amount of 13C is observed for the C=C stretching vibration, without any splitting. This effect is unusual and is a proof that the C=C is not localized and its double bond character is not isolated but strongly coupled with other bonds in the cage. If the CC bond was independent as in small or non-spherical molecules such as organic compounds, an isotopic effect of Δv ≃ 30 cm-1 for 12C=13C and Δv ≃ 60 cm−1 for 13C=13C could be expected and a splitting could appear in the case of uncompleted 13C substitution and variable relative intensities could be observed. It is not the case of 13C60.

In isotopic C60, all C=C vibrations in the spherical network are stronglycoupled ; an average isotopic mass must be considered for the randomly distributed isotopic atoms in the material to interpret the experimental result. C60 has thus more solid than molecule behavior.

Reflectance (R) and trasmittance (T) of C60 single-crystals have been measured in the 400-5000 cm-1 range, at room temperature, by using micro-Fourier transform IR spectroscopy. The frequencies of the peaks, appearing in both R and T spectra, are compared with the IR active ones calculated for the simple cubic structure with the bond charge model. It appears that all modes which are expected from symmetry arguments to give a dipole activity are actually observed and the corresponding frequencies are in good agreement with the experimental findings.

A structural tranfsormation of C60 crystals has been induced by high fluence laser irradiation under various chemical environments. The role of oxygen in driving fullerene cage opening reactions is investigated. The resulting material, showing features typical of low density amorphous carbon, has been characterized by Raman spectroscopy. In order to provide an atomistic model of the damaged sample, we have simulated the irradiation process by a tight binding molecular dynamics calculation on a 240-atoms system. We have carefully investigated the structural and electronic properties. In particular, the short- and medium-range features have been related to the cage opening, which is here modeled as a sequence of bond breakings.

We have studied the nano and micro structure of the product resulting from high fluence laser irradiation of C60 single crystal. Raman spectra reveal that, in the presence of oxygen, amorphous carbon (a-C) is formed. The laser heating of the sample promotes fullerene o:ddation and cage opening reactions: the new carbon phase is originated by the coalescence of C60 fragments. The irradiance threshold tbr a-C tbrmation is discussed. Brillouin spectroscopy shows that the acoustic properties of the irradiated material are typical ofa higly porous material similar to carbon aerogels. Under irradiation in an inert environment C60 degradation is not observed, even for high power densities.

Modifications induced by laser heating of C60 single crystal are examined by scanning electron microscopy (SEM). The fullerite surface is etched in the presence of oxygen, whereas no substantial change is observed under inert atmosphere. The formation of three dimensional micro-structures is observed depending on laser annealing conditions. Energy dispersive X-ray (EDX) spectroscopy shows that oxygen concentration substantially increases in the irradiated regions.

Intermolecular vibrations in a variety of fullerene systems are reported that provide information on C60-C60 and alkali-metal - C60 interactions and disorder effects. Low frequency Raman scattering in laser polymerized C60 films are shown to exhibit additional modes not reported for bulk materials. This result is consistent with recent dimer calculations. Raman scattering and HREELS measurements are shown to provide complementary information on alkali-metal motions in K3C60. In FCC Na6C60 both octahedral site disorder effects and reduced Na-C bond lengths account for changes in the Raman spectrum relative to Na3C60.

High resolution 13C NMR has been used to investigate the properties of solid C60 after intercalation of molecular oxygen, which does not induce charge transfer with the host molecules. We show that, via the magnetic characteristics of the intercalant, information can be gained on its position and movement in the structure. In particular, molecular oxygen is found to occupy the middle of the octahedral site in the fcc structure of solid C60.

We have used 13C magic-angle spinning (MAS) nuclear magnetic resonance (NMR) to characterize the structure and rotational dynamics of C60 containing oxygen molecules located in the interstitial sites of the fcc lattice. Under normal conditions, a narrow peak at 143.7 ppm is observed for C60. When exposed to oxygen at moderate pressures, several additional resonances appear in the 13C MAS NMR spectrum. These secondary resonances are shifted downfield from the main peak at 143.7 ppm and are due to the Fermi-contact interaction of the paramagnetic oxygen molecules with the 13C nuclear spins. The presence of oxygen depresses the orientational ordering transition by ca. 20 K as observed by DSC. The spin-lattice relaxation time (T1) of each secondary peak shows a minimum near the ordering transition, indicating that this transition is not dependent on the number of oxygen molecules surrounding an individual C60 molecule. The T1 due to paramagnetic relaxation, normalized by the number of surrounding oxygen molecules, is constant. This observation demonstrates that within a given sample, the dynamics of C60 molecules are independent of the number of surrounding oxygen molecules.

We use ∼30 ps pulses at 532 nm to measure the complex excited-state molecular polarizability αe in a C60/benzene solution. We determine the imaginary part of αe by measuring the excited-state absorption cross-section in a pump-probe experiment. In a degenerate-four-wave-mixing (DFWM) experiment, we find that in delayed probing of the complex index gratings formed by ∼30 ps pulses, the thermal and the excited-state polarizability changes both contribute to these transient gratings.

Multiphoton ionization time-of-flight mass spectrosocopy is used as an on-line technique to investigate polycyclic aromatic hydrocarbons (PAH) and fullerenes in atmospheric pressure flames. We have recorded height profiles of neutral PAH and fullerenes in methane/argon diffusion flames. Fullerenes ranging from C32 to at least C150 are found in a region where PAH concentration starts to decrease. Uniformity of the profiles indicates that the fullerenes do not grow from smaller to larger ones. The influence of the amount of argon additive is discussed.

A survey of solvents with a wide variation of solubility for C60 and a broad variation in dielectric constant was investigated for possible red shifting of the linear absorbance spectra. Initial analysis shows that very small shifts are achieved. Molar extinction spectra were measured for C60 in each solvent in both the standard mode and with an integrating sphere. Comparison of the two methods has shown strong scattering effects. The UV-vis spectra revealed some broadening in the bands and in some cases supression of strong C60 bands. Fluorescence spectra also show broadening of bands and new fluorescence minima in some solvents indicating formation of complexes between the C60 and those solvents that contain nitrogen.