Surface depth analysis for fluorinated block copolymer films by X-ray photoelectron spectroscopy using C60 cluster ion beam

X-ray photoelectron spectroscopy (XPS) using fullerene (C₆₀) cluster ion bombardment was applied to films of a fluorinated block copolymer. Spectra so obtained were essentially different from those using Ar ion beam. Structure in the surface region with the depth down to 60 nm drawn on the basis of XPS with C₆₀ beam was essentially the same as the one drawn by the result using dynamic secondary ion mass spectrometry, which is a well-established method for the depth analysis of polymers. This implies that XPS using C₆₀ beam enables one to gain access to the depth analysis of structure in polymer films with the depth range over the analytical depth of conventional XPS, that is, three times inelastic mean-free path of photoelectrons.     

Absorption Spectra of C<Subscript>60</Subscript> Fullerene Monomolecular Films

The absorption spectra of C₆₀ fullerene thin (from submonolayer to 5–6 monolayers) films deposited on different substrates have been studied. It has been shown that the spectra of the submonolayer and thick (more than 100 monolayers) films virtually coincide. The behavior of fullerene on the surface of different polymers can be judged from changes in the absorption spectra.     

Structure of C<Subscript>60</Subscript> polymer coatings deposited via electron-beam dispersion of fullerite

The structure and surface of thin coatings deposited via electron-beam dispersion of the C₆₀ fullerite have been investigated using IR and Raman spectroscopy, mass spectroscopy, and atomic-force microscopy. It has been demonstrated that layers with different contents of the polymerized phase, crystals of the tetragonal polymer phase, and three-dimensional polymeric forms of the C₆₀ fullerene are formed under the conditions providing for irradiation by secondary electrons in vacuum at a substrate temperature of 300 K.     

Determination of C60/C70 ratios in fullerene mixtures and film characterization by scanning tunneling microscopy

Fullerene powder mixtures with different C₆₀/C₇₀ ratios have been analyzed by a variety of techniques, and results have been compared. The fullerence mixtures have been characterized as solutions in n-hexane by high-pressure liquid chromatography (HPLC) and UV-VIS spectroscopy. Thin films of fullerenes on Au(111) have been prepared from the mixtures by sublimation. The sublimation process has been studied by simultaneous thermogravimetric and differential thermal analyses. Thin fullerene films on Au(111) have been investigated by scanning tunneling microscopy (STM). The STM images show primarily two types of ballshaped molecules arranged in a lattice with hexagonal symmetry (fcc(111) face, nearest neighbour distance: 1 nm). The two species differ in diameter. STM images of films made of mixtures of different C₆₀/C₇₀ ratios show that C₇₀ molecules display a larger apparent diameter (0.8 nm) and corrugation than C₆₀ molecules (0.7 nm). The C₆₀/C₇₀ ratios obtained by counting the corresponding molecular species in the STM images of the thin films are compared to the C₆₀/C₇₀ ratios determined by HPLC on hexane solutions of the mixtures. The observed differences might be explained by different rates of sublimation for the two species. The STM images reveal film defects (vacancies and boundaries) and dynamic processes (displacement of C₇₀ molecules and vacancies). In films prepared to have a C₆₀ coverage of less than one monolayer, stable structural units of the C₆₀(111) surface consisting of three or seven C₆₀ molecules are revealed by STM. Occasionally, substructure within individual fullerene molecules is observed.     

Polymerization of solid C<Subscript>60</Subscript> under C<Stack><Subscript>60</Subscript><Superscript>+</Superscript></Stack> cluster ion bombardment

The structure transformation occurring in fullerene film under bombardment by 50 keV C₆₀⁺ cluster ions is reported. The Raman spectra of the irradiated C₆₀ films reveal a new peak rising at 1458 cm⁻¹ with an increase in the ion fluence. This feature of the Raman spectra suggests linear polymerization of solid C₆₀ induced by the cluster ion impacts. The aligned C₆₀ polymeric chains composing about 5–10 fullerene molecules have been distinguished on the film surface after the high-fluence irradiation using atomic force microscopy (AFM). The surface profiling analysis of the irradiated films has revealed pronounced sputtering during the treatment. The obtained results indicate that the C₆₀ polymerization occurs in a deep layer situated more than 40 nm below the film surface. The deep location of the C₆₀ polymeric phase indirectly confirms the dominant role of shock waves in the detected C₆₀ phase transformation.     

Study of the Initial Stage of Fluorinated C<Subscript>60</Subscript>F<Subscript>18</Subscript> Fullerene Adsorption on the Cu(001) Surface

The dynamics of the adsorption and evolution of fluorinated C₆₀F₁₈ fullerene molecules on the Cu(001) surface are studied by real-time ultra-high vacuum scanning tunneling microscopy. Fluorinated fullerene molecules are shown to decompose with time on the Cu(001) surface transforming to C₆₀ molecules. The decay rate depends on the initial molecular coverage. The rapid decay of fluorinated fullerene molecules is observed when the coverage is no higher than 0.2 single layers. As a result, two-dimensional islands consisting of pure C₆₀ molecules are formed on the Cu(001) surface. 2D islands consisting of fluorinated fullerene molecules are formed when the initial molecular coverage is higher than 0.5 single layers. The molecules inside these islands also tend to decompose with time. It is found experimentally that fluorine atoms are removed completely from the initial C₆₀F₁₈ molecules adsorbed on the Cu(001) surface after 250 h when the initial molecular coverage is 0.6 single layers.     

Effect of C60 fullerene, fullerene-containing soot, and other carbon materials on the sliding edge friction of metals

A comparative study of different carbon materials (C₆₀ fullerene; soot, both with and without fullerenes; graphite; and industrial carbon black) as additives to industrial lubricating oils has been carried out for copper-steel and steel-steel sliding couples. The soot containing fullerene and the powder of pure fullerene produce a noticeable improvement in the antifriction and antiwear properties of steel-steel and steel-copper couples, especially under heavy loads and pressures at the contact. The greatest improvement was observed for the steel-steel couple. Structural-mechanical studies were carried out for copper riders and it has been demonstrated by several methods that the addition of the C₆₀ fullerene (pure fullerene or as a fullerene-containingsoot) creates a fullerene-polymer film on the frictional surface about 1000 Å thick, which has a protective effect.     

Epitaxial growth of C<Subscript>60</Subscript> thin films on the Bi(0001)/Si(111) surface

The morphology and atomic structure of C₆₀ fullerene films on the Bi(0001)/Si(111)?7 × 7 surface with different coverages have been studied by scanning tunneling microscopy and spectroscopy and low-energy electron microscopy in high vacuum. It is shown that the most favorable sites for nucleation of C₆₀ islands are double steps and domain boundaries on the surface of epitaxial Bi film.     

Low-dimensional nanostructures and fullerene films on semiconductor surface

The morphology and atomic structures of C₆₀ fullerene films on a Bi(0001)/Si(111)-7 × 7 surface and adsorption of fluorofullerene C₆₀F _x molecules on a Si(111)-7 × 7 surface have been studied by scanning tunneling microscopy/spectroscopy and low-energy electron microscopy under ultra high-vacuum conditions. It has been shown that initial nucleation of C₆₀ islands on the surface of an epitaxial Bi film occurs on double steps and domain boundaries, while tunnel spectra do not exhibit any significant charge transfer to the lowest unoccupied molecular orbital states. Fluorofullerene molecules allow local (at the nanoscale level) modification of Si surface through local etching.     

Scanning and friction-force microscopy of thin C60 films on GeS(001)

The surface morphology of thin C₆₀ films grown epitaxially under ultra-high vacuum conditions on layered GeS(001) substrates has been studied by scanning force microscopy. The individual C₆₀ layers were imaged down to molecular resolution. The growth mechanism was found to be of layer-by-layer type at the initial stages of growth, but seems to be very sensitive to the substrate temperature. The tribological properties of these films have been probed simultaneously by means of lateral force microscopy. The frictional coefficient of the C₆₀ layers was determined to be significantly smaller than the frictional coefficient of the GeS substrate. This demonstrates that well-ordered C₆₀ films can have even better lubricating properties than a layered material.     

Molecular simulation of C60 adsorption onto a TiO2 rutile (1 1 0) surface

A Monte Carlo molecular simulation study is presented on the adsorption and growth of C₆₀ films on the surface of the (1 1 0) face of rutile. Simulations are performed for a temperature of 600 K using atomistic models both for the fullerene molecules and the TiO₂ surface. It is found in this work that C₆₀ is adsorbed preferably in an ordered arrangement along the surface depressions over the exposed undercoordinated Ti cations. At low densities adsorption occurs preferably at alternate rows, with locations in consecutive rows being occupied appreciably only at higher C₆₀ densities. At low densities, the fullerene molecules tend to aggregate into islands in the surface plane. Additional layers of C₆₀ form only as the density increases, and do so before a monolayer is completed in all consecutive rows. Full monolayer capacity obtained at the highest densities is about 0.9 C₆₀ molecules per nm², but this is only achieved by completing the packing of molecules in interstices at a slightly upper level. The fraction of the molecules that lie closest to the surface only amounts to 0.6 molecules per nm².     

Structure of phase-inversion membranes from small-angle neutron scattering data

The structure of gradient-porous (asymmetric) membranes based on polyamide imide at different conditions of their formation has been investigated using small-angle neutron scattering. It has been shown that the membranes consist of rigid porous networks with well-defined interfaces between the polymer and the pores. It has been found that there are differences in the packings of structural elements of porous membranes-spherical pores with radii from 4 to 100 nm—depending on the membrane preformation time, drying regime, and the presence of fullerene C₆₀ for modifying the mechanical and selective properties of membranes. The membranes also contain larger pores of micrometer sizes. Differences in the rates of saturation of membranes with water and their limiting swelling ratios are found, which can be explained by the structure of the dense layers of membranes (skin layer) and their different hydrophilities (depending on the fullerene content).     

Processing of C<Subscript>60</Subscript> thin films by Matrix-Assisted Pulsed Laser Evaporation (MAPLE)

Thin films of fullerenes (C₆₀) were deposited onto silicon using matrix-assisted pulsed laser evaporation (MAPLE). The deposition was carried out from a frozen homogeneous dilute solution of C₆₀ in anisole (0.67 wt%), and over a broad range of laser fluences, from 0.15 J/cm² up to 3.9 J/cm². MAPLE has been applied for deposition of fullerenes for the first time and we have studied the growth of thin films of solid C₆₀. The fragmentation of C₆₀ fullerene molecules induced by ns ablation in vacuum of a frozen anisole target with C₆₀ was investigated by matrix-assisted laser desorption/ionization (MALDI). Our findings show that intact fullerene films can be produced with laser fluences ranging from 0.15 J/cm² up to 1.5 J/cm².     

Gold cluster formation on C60 surfaces observed with scanning tunneling microscopy: Au-cluster beads and self-organized structures

The growth mechanism of Au-clusters on fullerene layers has been investigated by scanning tunneling microscopy in ultrahigh vacuum at room temperature. The fullerene layers, which serve as substrates, are formed on a graphite surface and exhibit the typical combination of round and fractal shapes, and small sections of the original graphite substrate are exposed. The immobile Au-clusters are concentrated on the C₆₀ terminated surface section, and the original fullerene island structures are preserved. A preferential nucleation of Au-clusters is observed at the C₆₀-graphite edges while the C₆₀-C₆₀ edges remains undecorated. These Au-clusters are placed directly on the edge and shared by the graphite and fullerene layer. They form bead-like structures, which densely populate this edge, while the first layer C₆₀ islands are clearly depleted of Au-clusters. A roughness analysis of the fullerene surface indicates the presence of Au atoms (or very small clusters), which are embedded in the fullerene surface, and likely situated in the troughs in between the large molecules. These Au atoms are highly mobile and cannot be individually resolved at room temperature. The analysis of the spatial and size distributions of Au-clusters provides the basis for the development of a qualitative model, which describes the relevant surface processes in the Au-fullerene system. The simultaneous deposition of Au and fullerene on graphite leads to the formation of highly organized structures, in which Au-clusters are embedded in a ring of fullerene molecules with a constant width of about 4 nm. The mechanism for the formation of these structures is highly speculative at present and further experiments will be pursued in the near future. A comprehensive analysis of the Au-C₆₀ system is presented, which contributes to the advancement in our understanding of the metal-fullerene interaction and furthers the development of composite materials of interest in the synthesis of solar cells and metal contacts to organic materials.     

ELECTRON SPIN RESONANCE CHARACTERISTICS OF NITROGEN-DOPED FULLERENE

The nitrogen-doped fullerene has been obtained by arc discharge between two high-purity graphite rods in the atmosphere of N₂ and He, The electron spin resonance(ESR) characteristics of N-doped fullerene have been investigated. The results show that the ESR spectra of N-doped fallerene axe composed of two parts, a paramagnetic signal of N-center and a paramagnetic signal of C-center, For comparing with N-doped fullerene, we have also studied ESR spectra of C₆₀ powder, C₆₀ sublimed film and H-doped C₆₀ film. For C₆₀ powder and H-doped C₆₀ film, their in situ ESR. measurements are carried out at various temperatures, and reasonable explanations are proposed.     

Intercalation of C60 fullerene crystals with alkali and alkaline-earth metals through self-propagating high-temperature synthesis

A method for rapidly intercalating C₆₀ fullerene crystals has been implemented using self-propagating high-temperature synthesis. The method has been used to intercalate C₆₀ fullerene crystals with alkali (K, Rb) and alkaline-earth (Ca, Ba) metals. The superconducting transition temperatures of the prepared compounds have been measured. The C₆₀ fullerene crystals intercalated with calcium have been investigated using X-ray diffraction.     

Comparative study of optical parameters of fullerene C60 film at different temperatures

Fullerene C₆₀ thin films on glass substrate (around 2000 ? thickness) were prepared by thermal evaporation technique. The structural, surface morphology and optical properties of the films were studied. The optical properties of fullerene C₆₀ were investigated in the spectral range 200 nm to 900 nm using a UV-Vis spectrophotometer at room temperature as well as at liquid nitrogen temperature (77 K). The optical band gap at room temperature is found to be 2.30 eV, which gradually decreases with lowering the temperature and reaches to 2.27 at 77 K. The thickness and refractive index of fullerene C₆₀ film were calculated by ellipsometry. From the X-ray analysis, we have calculated the grain size, dislocation density, number of crystallite per unit area, and strain of the film at room temperature. The surface morphology of film was analyzed by scanning electron microscope (SEM). The present result show that the fullerene C₆₀ film becomes more conducting at low temperature.     

Deposition of fullerene films from the ablation plasma generated by high-power ion beams on graphite targets

A possibility of deposing carbon films with a high content of C₆₀ and C₇₀ fullerenes from an ablation plasma generated as a result of irradiation of graphite targets by pulsed high-power ion beams is shown. The relative contents of the crystalline diamond-like carbon phase, crystalline fullerene phase, and amorphous carbon phase have been determined by X-ray diffraction analysis for different deposition conditions. The nanohardness and Young’s modulus of the deposited films and their adhesion to the single-crystal silicon substrate have been measured.     

Molecular dynamics simulation of the low-energy interaction between Cu<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>@C<Subscript>60</Subscript> endofullerenes and the surface of a copper crystal

A molecular dynamics simulation of the low-energy interaction of C₆₀ fullerenes and Cu₁@C₆₀, Cu₆@C₆₀, and Cu₁₃@C₆₀ endofullerenes with a Cu(100) surface was performed. The effects of a copper cluster encapsulated in a fullerene and of a fullerene’s translational motion and rotation energy on its penetration into a surface were investigated. It was shown that the presence of an encapsulated cluster has a positive effect on fullerene penetration into a surface with preservation of the fullerene’s structure. The optimal conditions for fullerene penetration into a copper crystal surface were determined.     

Computer-aided design of nanostructured materials containing trisaza-bridged [60]fullerene

A novel fullerene-based building block for the synthesis of nanostructured materials has been designed with the aid of electronic structure theory calculations and molecular modeling. The building block consists of four trisaza-bridged C₆₀ fullerene molecules linked to a central cubane (C₈) unit. Each C₆₀ unit is located on the vertex of a tetrahedron with edge of 2.2 nm. One possible packing mode of the building blocks to yield the nanostructured material is suggested.