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• Lighter ions have better control in defect generation. • Proton microbeam induce ferromagnetic ordering at room temperature. • Moderate energy selection achieved utilizing SRIM simulation. • Controlled defect generation is useful in achieving ferromagnetic ordering by microbeam. We report tunable ferromagnetic properties of thin films of fullerene upon 1 MeV proton microbeam ion irradiation, by varying the ion fluence. Focused microbeam scanning of 1 MeV proton ions have been performed on the fullerene thin films. Consequently, a stable and significant ferromagnetic ordering at room temperature has been observed in the fullerene thin films. The proton microbeam irradiation induces a maximum magnetic ordering in fullerene with optimum dosage and subsequently higher fluence irradiations yield, diminishing effect upon the observed ferromagnetic ordering due to the higher degree of damages. The X-ray diffraction and Raman analysis confirm the damage due to proton microbeam irradiation. The reduction in the saturation magnetic moment induced, is very sharp as a result of exposure to the larger ion fluence. The approximate distance between defects has been simulated computationally, and its relation with observed ferromagnetism has been established. The irradiation has been performed at moderate ion flux (low microbeam current) to avoid the possible annealing effects of the ion irradiation. [ABSTRACT FROM AUTHOR]

Abstract: The many-electron response of a small-diameter conducting carbon nanotube, to the sudden creation of a 1s core state, is studied using density functional theory with different Gaussian basis sets and the generalized gradient approximation for exchange and correlation. Cluster computations are performed on carbon atoms located at a finite-size cylindrical network that is terminated by hydrogen atoms. Core-hole creation is simulated by replacing the 1s electron pair, localized at a central site of the structure, with effective pseudo-potentials for both neutral and ionized atomic carbon. The same approach is used to describe a neutral and core-ionized C60 fullerene molecule. The overlaps between the excited states of the ionized systems and the ground states of the neutral systems are combined in a Fermi's golden rule treatment yielding the shake-up spectra from the two clusters. The numerical response for the fullerene molecule is found in good agreement with the measured X-ray photoelectron spectrum from thick C60 films, including the low energy satellites at excitation energies below 4eV, within a peak position error of 0.3eV. The nanotube spectrum reveals features in common with X-ray photoelectron data from Bucky balls and Bucky papers. [Copyright &y& Elsevier]

Abstract: Nanostructured polymer–fullerene thin films are among the most prominent materials for application in high efficient polymer solar cells. Specifically, poly(3-hexylthiophene) (P3HT) and fullerene derivatives (PCBM) blends are used as the donor/acceptor materials forming a bulk heterojunction. Although P3HT:PCBM properties have been extensively studied, less light has been set on its nanomechanical properties, which affect the device service life. In this work Atomic Force Acoustic Microscopy (AFAM), Atomic Force Spectroscopy and Nanoindentation were used to study the effect of the fullerene presence and the annealing on the P3HT:PCBM nanomechanical behavior. The P3HT:PCBM thin films were prepared by spin coating on glass substrates and then annealed at 100°C and 145°C for 30min. Large phase separation was identified by optical and Atomic Force Microscopy (AFM) for the annealed samples. Needle-like PCBM crystals were formed and an increase of the polymer crystallinity degree with the increase of the annealing temperature was confirmed by X-ray diffraction. AFAM characterization revealed the presence of aggregates close to stiff PCBM crystals, possibly consisting of amorphous P3HT material. AFM force–distance curves showed a continuous change in stiffness in the vicinity of the PCBM crystals, due to the PCBM depletion near its crystals, and the AFM indentation provided qualitative results about the changes in P3HT nanomechanical response after annealing. [Copyright &y& Elsevier]

Abstract: We investigated the influence of thermal annealing on the structural and optical properties of two variations of organic nanocomposite materials; 1) poly [3-hexylthiophene] and [6,6]-phenyl C61 butyric acid methyl ester ( P3HT:PC61BM), and 2) poly [3-hexylthiophene] and [6,6]-phenyl C71 butyric acid methyl ester) (P3HT:PC71BM). The evolution of surface roughness and morphology was investigated using atomic force microscopy while device electrical properties were investigated by measuring current–voltage (I–V) characteristics. Upon thermal treatment, results show that P3HT:PC71BM nanocomposites produce a more homogeneous mixture of finer grain size than P3HT:PC61BM. Furthermore, stronger optical absorption in the visible region is observed in P3HT:PC71BM compared to P3HT:PC61BM. Since optical absorption is closely related to film crystallinity, it is inferred that P3HT:PC71BM composites undergo more extensive crystallization upon annealing. Photoluminescence spectra of both P3HT:PC61BM and P3HT:PC71BM nanocomposites (dissolved in chlorobenzene) show that each has excellent quenching effects. I–V characteristic curves show that P3HT:PC71BM registers higher current density under AM 1.5 illumination than does P3HT:PC61BM. For the devices described in this paper having active areas of approximately 12mm2, efficiency is approximately 33% better for C71-based solar cells than that observed for devices made using C61 fullerene. [Copyright &y& Elsevier]

Abstract: Optical and photoelectrical studies were performed on octane-1,8-dithiol cross-linked fullerene films, with supported gold nanoparticles (C60–DT–Au). According to high-resolution transmission electron microscopy observations, the average size of obtained gold nanoparticles was about 5nm, and the shape was spherical. The comparative investigation of optical properties of pristine and cross-linked with octane-1,8-dithiol C60 films, decorated with gold nanoparticles, found the difference in the extinction coefficient spectra, which was observed also in the photocurrent spectra of barrier heterostructure Au/C60/Si. The analysis of dark current–voltage characteristics for Au/C60/Si heterostructures showed that the model for them includes the barrier at the C60/Si interface and internal barriers in the C60 layer, caused by the trapping centers. The hopping mechanism of the current transport in the C60 layer was supplemented with the Poole–Frenkel emission process on these centers, with the barrier height greater for the fullerene C60 film cross-linked with octane-1,8-dithiol. [Copyright &y& Elsevier]

Abstract: Efficient photoinduced interlayer electron transfer from a phthalocyanine derivative, ZnPH4, to porphyrin cation of a porphyrin–fullerene donor–acceptor dyad was demonstrated by using time-resolved photovoltage technique. Multicomponent thin films with desired layer arrangements were constructed by the Langmuir–Blodgett and spin-coating methods in order to study charge transfer in solid state. As a contradiction to the photovoltage experiments, the dyad monolayer in the film structure did not enhance the current amplitude in electrochemical photocurrent measurements. This is associated with a weak electronic interaction between fullerene and aqueous electrolyte, reducing the photocurrent generation. The use of poly(3-hexylthiophene) as a hole conducting layer was shown to improve photocurrent yield of the device by forming efficient heterojunction together with the ZnPH4 layer. [Copyright &y& Elsevier]

Abstract: 4H-SiC (silicon carbide) films were grown on (0001) sapphire substrate at rather low temperatures(1000–1100°C) with relative high deposition rate by using fullerene (C60) and silicon solid sources molecular beam epitaxy with substrate nitridation and aluminum nitride (AlN) buffer layer deposition prior to the SiC deposition. The effects of substrate nitridation and AlN buffer layer to the adhesion of the SiC thin films on sapphire have been studied. X-Ray diffraction, pole figure, atomic force microscope, Fourier transform infrared spectroscopy and photoluminescence were employed for the analysis of composition, orientation of the film and surface morphology. Relative high deposition rate at ∼165nm/h was achieved. [Copyright &y& Elsevier]

The C 60 /glass, C 60 /Si, C 60 /porous Si/Si as well as porous Si/Si thin film structures for comparison were prepared and studied by photoluminescence spectroscopy at room temperature. Along with a broad-band low-energy emission at 1.774 eV in the photon energy range of the nominaly forbidden optical transitions, the C 60 films on glass substrate exhibit high-energy emissions at 2.115 eV and 2. 342 eV in the range of allowed dipole transititions. On the other hand, C 60 films on Si or porous Si/Si display only the 1.774 eV emission band. The intensity of this emission in C 60 /porous Si/Si is 200 times higher than that in C 60 /Si and at least 20 times exceeds the one for the emission observed on porous Si/Si. Such a dramatic increase in emission intensity is indicative of the relaxation of the selection rules for nominally forbidden optical transitions and suggests strong interaction of C 60 molecules with porous silicon walls. Molecular signatures of the C 60 films are clearly manifested by the vibronic transitions with 60 meV energy separation (A g -mode energy) between the irradiative levels, observed on 1.774 eV emission band in C 60 /porous Si/Si. The origin of the 2.115 and 2.342 eV emission bands is analyzed within a standard band insulator approach, together with the obtained ellipsometric data. The first corresponds to the band-to-band transitions at band gap. The appearance of the second can be related to the splitting of the valence band in the X point of the Brillouin zone of C 60 film due to the crystal field. The strength of the crystal field splitting is then ~ 200 meV. • C 60 fullerene layers on various substrates are obtained and thoroughly characterized. • C 60 thin film is a direct gap band insulator with band gap energy of 2.115 eV. • Vibronic levels of singlet Frenkel excitons are involved in emission below 2 eV. • 200 times enhanced emission below 2 eV is observed on C 60 film/porous Si/Si structures. [ABSTRACT FROM AUTHOR]