Size control for fullerene C60 nanocrystals during the high temperature and high pressure fluid crystallization process

The preparation and size control for mono-dispersed fullerene C₆₀ fine particles was successfully achieved during the high temperature and high pressure fluid (HTPL) crystallization process, in which acetone was used as the HTPL solvent and pure water or the mixture of acetone and water as the cooling solvent. The prepared fullerene C₆₀ particles had spherical shape and narrow size distribution with the average size ranging from 44 nm to 110 nm depending on the various experimental conditions, such as fluid temperature, solvent flow rate, system pressure and the ratio of acetone and water in cooling solvent. The products were characterized by using X-ray powder diffraction (XRD), scan electron microscopy (SEM), dynamic light scattering technique (DLS) and UV–VIS spectrum, respectively. And the size effect of such fullerene C₆₀ nanocrystals was confirmed.     

Surface potential measurement of organic photo-diode consisting of fullerene/copper phthalocyanine double layered device

We investigated the surface potential built across the electrode/fullerene (C₆₀) or copper phthalocyanine (CuPc) interface and C₆₀/CuPc interface as a function of the thickness of the semiconductor film in the dark condition and under illumination. The surface potential of C₆₀ on Au, Al and Mg changes negatively with the increment of film thickness and it saturates at − 0.25, − 1.0 and − 1.5 V within 20 nm. The Fermi level alignment at C₆₀/electrode interface is established within ∼ 20 nm from electrode, and very high electric field exists due to the displacement of negative electronic charges from electrode into C₆₀. On the other hand, the surface potential of CuPc on ITO changes to + 0.1 V, and the work functions of C₆₀ and CuPc were estimated as 5.0 eV and 4.7 eV. C₆₀ film also accepts electrons from CuPc at hetero-junction interface, and the Fermi-level alignment was again obtained at C₆₀/CuPc interface under illumination. The built-in potential of ca. 0.3 V formed at C₆₀/CuPc interface was considered as the origin of the reduction of open-circuit voltage in ITO/CuPc/C₆₀/Au device compared with the optimum value of 0.6 V. On the other hand, the very high electric field formed at C₆₀/Mg contact improved the photovoltaic properties.     

Reverse saturable absorption of fullerodendrimers in porous SiO2 sol–gel matrices

The non-linear absorption properties and the dynamics of porous sol–gel SiO₂ glasses, doped with fullerodendrimers, i.e., fullerene derivatives functionalized with dendritic branches have been investigated using a double-pump–probe technique. A frequency doubled mode locked Nd:YAG laser (25 ps (FHWM), 532 nm) was applied as irradiation source. A reverse saturable absorption (induced absorption) in the samples containing the fullerodendrimers has been observed. A similar induced absorption was also obtained in the pure C₆₀ samples. In addition, the dendritic branches, which prevent aggregation of the molecules, lead also to an increase of the triplet quantum yield due to a faster singlet–triplet relaxation.     

Optical and photoelectrical studies of gold nanoparticle-decorated C60 films

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 5 nm, 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.     

Deposition of unhydrogenated amorphous carbon films by sublimation of C60 fullerene in electron beam excited plasma

C₆₀ fullerene clusters are used as a carbon source to deposit unhydrogenated amorphous carbon films. C₆₀ clusters are sublimated by heating up to 850 °C. The sublimated fullerene powders are injected to an electron beam excited argon plasma and dissociated to be active species. Consequently, the carbon species condense as a thin film on the negatively biased substrates that are immersed in the plasma. Deposition rates of approximately 1.0 µm/h and the average surface roughness of 0.2 nm are achieved. X-ray diffraction pattern reveals that the microstructure of the film is amorphous while fullerene film deposited without the plasma shows crystal structure. Raman spectroscopic analysis shows that the films are one of the types of diamond-like carbon films. The nano-indentation technique is used for hardness measurement of the films and results in hardness up to about 20 GPa.     

XPS characterization of MWCNT and C60-based composites

X-ray photoelectron spectroscopy was used for characterization of MWNT-C₆₀ composites with assistance of scanning and transmission electron microscopy. The composites were received by immerison of nanotubes into fullerene solution in CS₂ with consequent processing with green laser irradiation at aproximately 10 W/cm². It was shown that C1s spectra of composites are different from simple addition of MWNT and C₆₀ features. It found that preliminary nanotube purification by oxidative treatment influences strongly the nature of fullerene-nanotube bonding. Hydrophilic surface of oxidized nanotube material has lower affinity to C₆₀ molecules and provides for concentration of C₆₀ molecules into clusters, which show differential charging effect in XPS spectra. The differential charging effect disappears after laser processing, which induces photopolymerization of fullerene clusters. The as-synthesized nanotubes form composites with more evenly distributed fullerene.     

Synthesis and luminescence properties of Yb3+, Tm3+ and Ho3+ co-doped SrGd2(WO4)2(MoO4)2 nano-crystal

Novel up-conversion luminescent SrGd₂(WO₄)₂(MoO₄)₂: Yb³⁺/Tm³⁺/Ho³⁺ nano-crystals were synthesized by hydrothermal method. The composition ratio of rare earth had been investigated. It indicated that when C_Yb³⁺ = 10 mol% and C_Yb³⁺/C_Tm³⁺/C_Ho³⁺ = 10:1.5:2, the emission intensities were the highest. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and up-conversion luminescence spectra were used to characterize SrGd₂(WO₄)₂(MoO₄)₂: Yb³⁺/Tm³⁺/Ho³⁺ nano-crystals and they showed that the sample had high degree of crystallinity, the sample was tetragonal system, and the grain size of the sample was about 56 nm. Three emission peaks, including blue emission peak, green emission peak and red emission peak were observed at 477, 543 and 651 nm corresponding to ¹G₄ → ³H₆ and ¹G₄ → ³F₄ transitions of Tm³⁺, ⁵F₄ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions of Ho³⁺ respectively. All the emission peaks were observed by excitation of 980 nm semiconductor laser. The relationship between up-conversion intensity and excitation power revealed that blue emission at 477 nm was a three-photon absorption process, green emission at 543 nm and red emission at 651 nm was a two-photon absorption process. The quantum yields of the sample were near 3.2%.     

Langmuir-Blodgett films of C60 and C60O on Silicon: Islands, rings and grains

We show that monolayer-high islands of C₆₀ and C₆₀O can be transferred from Langmuir films on a water or phenol sub-phase to oxide-terminated Si(111) substrates. Faceted islands, in some cases incorporating a foam-like morphology reminscent of that previously observed for Langmuir films at the water-air interface using Brewster angle microscopy, are formed and transferred using small amounts (100-400 μl) of low concentration (of order 10^− 5M) solutions of C₆₀ (or C₆₀O) with low target pressures (~ 10 mN/m). However, worm-like monolayer domains are also observed under identical experimental conditions, indicating the key role that inhomogeneous solvent evaporation plays in the formation of two-dimensional fullerene aggregates on the subphase surface. While Langmuir-Blodgett multilayers of C₆₀ and C₆₀O are both granular, there are significant morphological differences observed between the molecular thin films. In particular, C₆₀O multilayers contain a relatively high density of ring (or “doughnut”) features with diameters in the 100-300 nm range which are not observed for C₆₀. We attribute the origin of these features to dipolar or hydrogen bonding-mediated interactions between the C₆₀O molecules at the water surface.     

Light Scattering Study of Aqueous Poly(Vinyl)pyrrolidone–Fullerene C70 Solutions

Abstract

It was shown by static and dynamic light scattering that poly(vinyl)pyrrolidone (PVP) molecules form large intermolecular complexes (clusters) with C₇₀ in aqueous solutions. The molecular weights and dimensions of PVP–C₇₀ clusters increase both with the increase of fullerene content and the molecular weight of the matrix PVP. However, two different diffusion coefficients were detected by dynamic light scattering. The slow mode was explained as diffusion of large PVP–C₇₀ clusters. The fast mode represents free PVP molecules in solution. Dimensions of clusters revealed in aqueous PVP–C₇₀ solutions are less than that for PVP–C₆₀ by factor of 2.5–3.     

Li and Ce doping of melt-textured YBCO: Improved jc at medium fields

The top seeded melt textured growth method was applied to a Ce doped YBCO material with a partial substitution of Cu with Li. The amount of Li in the samples varied from 0.25 to 0.05 at% relative to the copper atoms. The change of T_c and j_c compared to a reference sample was measured using SQUID magnetometer. Field induced pinning was indicated by elevated j_c in the j_c(B) curve. The peak effect at 77 K appeared in the moderate field region around 0.5 T. Optimal lithium content was determined to be at 0.05 at%. Final Li content in textured bulk material was verified with atomic absorption.     

FORMATION OF FULLERENES AND CARBON CLUSTERS BY LASER IRRADIATION OF POLYMERIC FULLERENE OXIDE (FULLERENE OZOPOLYMER)

ABSTRACT

Polymeric fullerene oxide (PFO) prepared by prolonged ozonation of C₆₀ fullerene has been laser irradiated and the resulting products formed have been studied by ion cyclotron resonance mass spectrometry. It has been found that PFO produces a complete set of carbon clusters from C₆₀ up to C₁₆₄. The mechanism of formation of this set of fullerenic clusters implies necessarily a laser-induced carbonization step of the PFO substrate. Once the PFO target has been changed into the opportune carbon nanostructure by the laser radiation, the sequence of fullerene carbon clusters has been produced.     

Correlation between the morphology and photo-physical properties of P3HT:fullerene blends

The photo-induced charge transfer and optoelectronic efficiency of the solar cells correlated to the morphology and the structure of P3HT:C₆₀ blend was studied by means of photoluminescence and electron spin resonance (ESR). The occurrence of photo-induced charge transfer, well-known for blends of P3HT with fullerenes, was evidenced in blends of P3HT:C₆₀ (1:1 wt ratio) by a strong partially quenching of the P3HT luminescence. The ESR measurements allowed one to quantify the charge transfer between P3HT and C₆₀, which resulted in positive P3HT polarons. Wide-angle X-ray scattering (WAXS) and UV–vis spectroscopy showed that an inclusion of a C₆₀ fullerene in the P3HT matrix lead to lower peak intensities and dark Debye rings and a blue shift on the π–π* interband transition of the P3HT as well as a reduction in the absorption coefficient. Selected area electron diffraction patterns of a well-ordered sample of P3HT exhibit distinct diffraction rings indicating that the P3HT forms a polycrystalline film. The large-scale phase separation of P3HT and C₆₀ resulted from large C₆₀ agglomerations during spin coating lead to a low power conversion efficiency of 0.2 × 10⁻⁴%.     

Carbon Clusters Formation by Laser Irradiation of Carbonaceous Solids

Abstract

A laser ablation/Fourier‐transform ion cyclotron resonance mass spectrometry was used to generate fullerenes clusters from targets of carbonaceous material containing carbyne, C₆₀ photopolymer, graphite, diamond, C₆₀ fullerene crystals.     

Effect of copper doping on physical properties of nanocrystallized SnS zinc blend thin films grown by chemical bath deposition

SnS: Cu thin films have been successfully prepared on Pyrex substrates using low cost chemical bath deposition (CBD) technique with different copper doped concentration (y = [Cu]/[Sn] = 5%, 6%, 8%, 9% and 10%). The structure, the surface morphology and the optical properties of the SnS:Cu films were studied by X-ray diffraction (XRD), atomic force microscopy (AFM) and spectrophotometer measurements, respectively. To obtain a thickness of the order of 780 ± 31 nm for absorber material in solar cell devices, a system of multilayer has been prepared. It is found that the physical properties of tin sulphide are affected by Cu-doped concentration. In fact, X-ray diffraction study showed that better cristallinity in zinc blend structure with preferential orientations (111)^ZB and (200)^ZB, was obtained for y equal to 6%. According to the AFM analysis we can remark that low average surface roughness (RMS)value of SnS(ZB) thin film obtained with Cu-doped concentrations equal to y = 6%, is about of 54 nm. Energy dispersive spectroscopy (EDS) showed the existence of Cu in the films. Optical analyses by means of transmission T(λ) and reflection R(λ) measurements show 1.51 eV as a band gap value of SnS:Cu(6%) which is nearly equal to the theoretical optimum value of 1.50 eV for efficient light absorption. On the other hand, Cu-doped tin sulphide exhibits a high absorption coefficient up to 2 × 10⁶ cm⁻¹, indicating that SnS:Cu can be used as an absorber thin layer in photovoltaic structure such as SnS:Cu/ZnS/SnO₂:F and SnS:Cu/In₂S₃/SnO₂:F, where ZnS and In₂S₃ are chemically deposited in a previous studies.     

Synthesis of nanocrystalline LaF3 doped silica glasses by hydrofluoric acid catalyzed sol–gel process

Silica glasses doped with LaF₃ nanocrystals were prepared by HF-catalyzed sol–gel method. HF was used both as fluorine source and as catalyst of the sol–gel reaction, making it possible to shorten the processing time with reducing the concentration of SiOH groups to ～10¹⁸ cm^?3. The resultant glasses are transparent at visible spectral range, and the optical loss at the ultraviolet absorption edge is dominated by the Rayleigh scattering from LaF₃ crystallites. The size of LaF₃ crystallites increases with an increase in the sintering temperature and time, and is smaller than ～40 nm in samples showing good visible transparency. Green upconversion photoluminescence is observed in an Er³⁺-doped sample under excitation at 980 nm.     

Deposition of WNxCy thin films for diffusion barrier application using the dimethylhydrazido (2) tungsten complex (CH3CN)Cl4W(NNMe2)

Tungsten nitride carbide (WN_xC_y) thin films were deposited by chemical vapor deposition using the dimethylhydrazido (2⁻) tungsten complex (CH₃CN)Cl₄W(NNMe₂) (1) in benzonitrile with H₂ as a co-reactant in the temperature range 300 to 700 °C. Films were characterized using X-ray diffraction (XRD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy and four-point probe to determine film crystallinity, composition, atomic bonding, and electrical resistivity, respectively. The lowest temperature at which growth was observed from 1 was 300 °C. For deposition between 300 and 650 °C, AES measurements indicated the presence of W, C, N, and O in the deposited film. The films deposited below 550 °C were amorphous, while those deposited at and above 550 °C were nano-crystalline (average grain size < 70 Å). The films exhibited their lowest resistivity of 840 µΩ-cm for deposition at 300 °C. WN_xC_y films were tested for diffusion barrier quality by sputter coating the film with Cu, annealing the Cu/WN_xC_y/Si stack in vacuum, and performing AES depth profile and XRD measurement to detect evidence of copper diffusion. Films deposited at 350 and 400 °C (50 and 60 nm thickness, respectively) were able to prevent bulk Cu transport after vacuum annealing at 500 °C for 30 min.     

Sol–gel synthesis,characterization and microwave absorbing properties of nano sized spherical particles of La0.8Sr0.2Mn0.8Fe0.2O3

LSMFO (La_0.8Sr_0.2Mn_0.8Fe_0.2O₃) nano sized powders were synthesized by modified EDTA assisted sol–gel synthesis using EDTA:metal ion = 0.5. Another new synthesis method, sol–gel self combustion using PVA, was also devised for the synthesis of LSMFO and the effects of the PVA mole ratio was investigated. The characterization techniques, XRD, FE-SEM, TG/DTA and ICP, confirmed the formation of the pure phase LSMFO by both the methods. The material attained spherical morphology instead of previously reported rod like structure. Sizes of synthesized powders vary from 14.5 nm to 23 nm. TG/DTA results suggest that LSMFO can be synthesized by the self combustion at temperatures as low as 200 °C. Synthesized LSMFO has excellent microwave absorbing properties in the range of 0.05–18 GHz and appreciable effective bandwidth, 2 GHz, with microwave absorption in excess of 10 dB and peak reflection loss of 25 dB which suggests that the materials can be used as effective microwave absorbers.     

Size-controlled recrystallization of fullerene by gas–antisolvent process

Gas–antisolvent (GAS) process using CO₂ successfully prepared crystals of fullerene (C₆₀) from a toluene solution through a precipitation. Particle sizes of precipitated C₆₀ could be easily controlled by changing the initial pressurization rate of CO₂, the temperature at the initial pressurization, and the quantity of C₆₀. Fullerene particles obtained by GAS method had regular octahedral shapes, whereas the particles obtained by adding liquid ethanol as an antisolvent to C₆₀ solution did not have such shape. Particle sizes could be changed in a range of 1.0–8.5 μm by GAS method; they were wider than the range of particles obtained by ethanol addition (0.7–1.8 μm).     

Nanostructure of laser pyrolysis carbon blacks: observation of multiwall fullerenes

A study of the nanostructure of both as-produced and thermally treated laser pyrolysis carbon blacks which comprise unusual types of nanoparticles and fullerenes is reported. It has been shown that those blacks are characterized by two-level nanostructure, i.e. they consist of amorphous nanoparticles 30–40 nm in size and C₆₀ clusters. Heat treatment at 3000°C causes restructurization with appearance of fullerene-like multishell nanoparticles of ∼20 nm size, higher fullerenes and multishell (cage-inside-cage) fullerenes. Transmission electron microscopy observation showed the occurrence of three different cage-inside-cage clusters: two-shell 1.4 nm size (C₆₀@C₂₄₀), two-shell 2.0 nm size (C₂₄₀@C₅₆₀) and three-shell 2.0 nm size (C₈₀@C₂₄₀@C₅₆₀).     

Preparation of a copper-polymer composite through the thermolysis of copper(II) succinate

A procedure has been proposed for the preparation of copper/polymer composites through Cu(C₄H₄O₄) · H₂O succinate thermolysis. Three types of copper nanoparticles have been incorporated into a fibrous carbon-polymer matrix of the composite: cubic (350 × 350 nm) and needle-like (40–80 nm in diameter and 4.5–5.5 μm in length) crystals and spherical copper particles (5 to 45 nm). We have compared copper succinate and copper maleate decomposition processes. The composites obtained through thermolysis have been shown to differ drastically.