Taguchi optimization of device parameters for fullerene and Poly (3-octylthiophene) based heterojunction photovoltaic devices

Photovoltaic devices were fabricated with the structure ITO/fullerene/Poly (3-octylthiophene)/Au and device parameters were optimized using Taguchi optimization technique. Optimized parameter such as fullerene and Poly (3-octylthiophene) film thickness, annealing temperature and annealing duration are found to be as 110 nm, 45 nm, 120° C and 15 min respectively. Fabricated device with optimized parameters shows short circuit current density (J_sc), open circuit voltage (V_oc) and fill factor (FF) as 2 × 10^− 4 mA/cm², 0.47 V and 0.25 respectively. Effect of solvent casting on C₆₀ layer was studied which shows formation of uneven surface providing large interfacial area.     

Phase transitions in single crystal tubes formed from C60 molecules under high pressure

Pure single crystal tubes formed from C₆₀ molecules, with a face-centered cubic (fcc) structure were fabricated by a liquid–liquid interfacial precipitation method using C₆₀ powder. A bulk transition from fcc to a simple cubic structure and a surface transition from (1 × 1) to (2 × 2) have been observed around 246 K (bulk transition temperature T_B) and 214 K (surface transition temperature T_S), respectively, during the measurement of the temperature dependence of electrical resistance. The initiation of the two transitions under pressure was investigated using a piston cylinder high pressure apparatus and it was found that both T_B and T_S increase with increasing pressure. And the C₆₀ molecules at the surface of the tube exhibit the same behavior of that in the bulk at a pressure of about 2.1 GPa.     

Mechanical properties of C58 materials and their dependence on thermal treatment

C₅₈ fullerene cages made by electron-impact induced fragmentation of C₆₀ fullerenes have been assembled into several micron thick solid films by low energy cluster beam deposition onto inert substrates held at room temperature under ultrahigh vacuum. The resulting as-prepared material, RT-C₅₈, behaves as an amorphous wide-band semiconductor. Nanoindentation was used to measure its mechanical properties revealing that RT-C₅₈ has a higher elastic modulus E and hardness H than the reference carbon allotropes solid C₆₀ and Highly Ordered Pyrolytic Graphite (HOPG): E(RT-C₅₈) = 14 GPa and H(RT-C₅₈) = 1.2 GPa. This effect can be explained by the unique intrinsic “functionalization” of C₅₈ cages: they comprise reactive surface sites constituted by annelated pentagon rings which give rise to covalently stabilized oligomers, –C₅₈–C₅₈–C₅₈, under our deposition conditions. Annealing, thick RT-C₅₈ films up to 1100 K in ultrahigh vacuum results in HT-C₅₈, a new material with considerably modified electronic and vibrational properties compared to the as-prepared RT-C₅₈ film. The associated molecular transformations, including also partial cage–cage coalescence reactions, raise the overall mechanical hardness of the material: H(HT-C₅₈) = 3.9 GPa.     

The effects of the post-annealing time on the growth mechanism of Bi2Sr2Ca1Cu2O8+∂ thin films produced on MgO (100) single crystal substrates by pulsed laser deposition (PLD)

Bi₂Sr₂Ca₁Cu₂O_8+∂ thin films were deposited on MgO (100) substrates by pulsed laser deposition (PLD). The effects of post-annealing time on the phase formation, the structural and superconducting properties of the films have been investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature dependent resistivity (R–T), atomic force microscopy (AFM), and DC magnetization measurements. The films deposited at 600 °C were post-annealed in an atmosphere of a gas mixture of Ar (93%) and O₂ (7%), at 860 °C for 10, 30, and 60 min. All films have demonstrated a mainly single phase of 2212 with a high crystallinity (FWHM≈0.159°) and c-axis oriented. The critical temperature, T_C, of the films annealed for 10, 30, and 60 min were obtained as 77, 78, and 78 K, respectively. The highest critical current density, J_C, was calculated as 3.34×10⁷ A/cm² for the film annealed at 860 °C for 30 min at 10 K.     

Electrochemistry of nitrated fullerene derivatives

Hexanitro[60]-fullerene was synthesized. Hexahydroxy[60]-fullerene was obtained by hydrolysis of the resulting hexanitro[60]-fullerene in situ. The electrochemical properties have been investigated by using cyclic voltammetry and controlled potential electrolysis technique. Two reduction peaks of C₆₀(OH)₆ with quasi-reversibility in DMF solution were observed. No electrochemical response was observed for the C₆₀(OH)₁₂ compound in a variety of solvent. An electrode following chemical reaction occurred for C₆₀(NO₂)₆ after the first reduction at ? 0.96 V. The trace amount residue of C₆₀(NO₂)₆ shows quasi-reversible redox behavior. The results from the controlled potential electrolysis show that the C₆₀(NO₂)₆ has six sequential electron transfer at ? 0.96 V (vs. Fc/Fc⁺) to produce free C₆₀ and NO₂^? anion.     

Anisotropic molecular packing of soluble C60 fullerenes in hexagonal nanocrystals obtained by solvent vapor annealing

We describe the self-assembly of soluble, chemically modified fullerene [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) into a new crystalline phase where the C₆₀ moieties are arranged in parallel layers. Minimum C₆₀ center-to-center distance is 10 Å within the layers, and up to 15 Å perpendicular to the layers. Highly anisotropic, mesoscopic hexagonal crystals of this material, with a lateral size of many microns and a thickness below 1 μm, are obtained from chloroform solution by solvent vapor annealing, and characterized by optical microscopy and X-ray diffraction. The crystalline structure is deduced combining experimental data with molecular modeling and ab initio calculations. The large difference in C₆₀–C₆₀ spacing indicates a high anisotropy in electrical and charge transport properties of this new phase.     

Mechanical properties of Si3N4 ceramics from an in-situ synthesized a-Si3N4/β-Si3N4 composite powder

Sintered Si₃N₄ ceramics were prepared from an ɑ-Si₃N₄/β-Si₃N₄ whiskers composite powder in-situ synthesized via carbothermal reduction at 1400–1550 °C in a nitrogen atmosphere from SiO₂, C, Ni, and NaCl mixture. Reaction temperatures and holding time for the composite powder, and mechanical properties of sintered Si₃N₄ were investigated. In the synthesized composite powder, the in-situ β-Si₃N₄ whiskers displayed an aspect ratio of 20–40 and a diameter of 60–150 nm, which was mainly dependent on the synthesis temperature and holding time. The flexural strength, fracture toughness and hardness of the sintered Si₃N₄ material reached 794±136 MPa, 8.60±1.33 MPa m^1/2 and 19.00±0.87 GPa, respectively. The in-situ synthesized β-Si₃N₄ whiskers played a role in toughening and strengthening by whiskers pulling out and crack deflection.     

Low-temperature preparation of Si3N4 whiskers bonded/reinforced SiC porous ceramics via foam-gelcasting combined with catalytic nitridation

Porous α-Si₃N₄ whiskers bonded/reinforced SiC (Si₃N_4(w)/SiC) ceramics were successfully prepared at as low as 1473 K for 2 h, via a combined foam-gelcasting and catalytic nitridation route using commercial Si and SiC powders containing some Fe impurity as the main raw materials. Small pores (0.03–5 μm) left by the packing of raw material particles and interlocking of in-situ formed Si₃N₄ whiskers coexisted with large ones (8–400 μm) resultant mainly from the foaming process. The impurity Fe from the raw materials Si and SiC acted as an internal catalyst, accelerating the nitridation of Si by increasing the bond length and weakening the bond strength in the N₂ molecules adsorbed on it. As-prepared Si₃N_4(w)/SiC porous ceramics contained 71.53% porosity and had flexural and compressive strengths of 5.60 ± 0.69 MPa and 12.37 ± 1.05 MPa, respectively.     

Preparation and properties of in-situ mullite whiskers reinforced aluminum chromium phosphate wave-transparent ceramics

In-situ mullite whisker reinforced aluminum chromium phosphate wave-transparent ceramics were designed and prepared. The phase transformation, microstructure, mechanical and electrical properties of the ceramics were investigated, and the mechanisms of in-situ growth and toughening were discussed. Results indicated that the in-situ growth of mullite whisker significantly improved the mechanical properties of the matrix, especially the high temperature flexural strength. The room temperature flexural strength, 1000 °C flexural strength and fracture toughness of the ceramics were 135.60 MPa, 121.71 MPa and 4.52 MPa m^1/2. After sintering at 1500 °C, the optimum properties of ε^'_r, tanδ and microwave transmittance at region 8–12 GHz were <3.6, <0.03 and>80%, respectively. The sinterability of ACP matrix was improved by the in-situ process of high mullization above 1450 °C. Using ACP binder as the raw material can avoid the phase transformation from B-AlPO₄ to T-AlPO₄. The synthesized mullite whiskers played a role in toughening by whiskers fracture, crack deflection and whisker pulling out.     

Pulsed laser deposition of hard and superhard carbon thin films from C60 targets

In the present study, carbon films were deposited by a pulsed laser deposition method. A C₆₀ fullerene target has been irradiated by a frequency doubled Nd:YAG laser with a pulse duration of 7 ns. The carbon films grown on Si(111) substrates at different substrate deposition temperatures (30, 300 and 500 °C) were characterized by Raman, X-ray Photoelectron and X-ray Auger Electron Spectroscopies, Energy Dispersive X-Ray Diffraction, Scanning Electron and Atomic Force Microscopies, and Vickers microhardness technique. The composition, structure, morphology and mechanical properties of films were found to be strongly dependent on the substrate temperature. At 30 °C and 300 °C deposition temperature, superhard and hard diamond-like films have been obtained, respectively. In the case of 500 °C deposition, a hard film, composed of crystalline C₆₀ and diamond-like carbon, has been prepared.     

Room and high temperature flexural failure of spark plasma sintered boron carbide

Dense (95–98.6%) bulk boron carbide prepared by Spark Plasma Sintering (SPS) in Ar or N₂ atmospheres were subject to three-point flexural tests at room and at 1600 °C. Eight different consolidation conditions were used via SPS of commercially available B₄C powder. Resulting specimens had similar grain size not exceeding 4 µm and room-temperature bending strength (σ_25 °C) of 300–600 MPa, suggesting that difference in σ_25 °C is due to development of secondary phases in monolithic boron carbide ceramics during SPS processing. To explain such difference the composition of boron carbide and secondary phases observed by XRD and Raman spectroscopy. The variation in intensity of the Raman peak at 490 cm⁻¹ of boron carbide suggests modification of the boron carbide composition and a higher intensity correlates with a higher room-temperature bending strength (σ_25 °C) and Vickers hardness (HV). Secondary phases can modify the level of mechanical characteristics within some general trends that are not dependent on additives (with some exceptions) or technologies. Namely, HV increases, σ_25 °C decreases, and the ratio σ_1600 °C/σ_25 °C (σ_1600 °C – bending strength at 1600 °C) is lower when fracture toughness (K_IC) is higher. The ratio σ_1600 °C/σ_25 °C shows two regions of low and high K_IC delimited by K_IC=4.1 MPa m^0.5: in the low K_IC region, boron carbide specimens are produced in nitrogen.     

Syntheses,properties and biological activity of organogermanium substituted heteropolytungstates

Six new compounds [(RGe)XW₁₁O₃₉]ⁿ⁻ (R = HOOCCH₂CH₂, HOOCCH₂(m-NO₂C₆H₄)CH); X = Ge, Si, P) have been prepared and their Keggin structures determined by elementary analysis, IR, UV, ¹H NMR and ¹⁸³W NMR spectrometry. The results show that the complexes retain Keggin structure with organogermanium group grafting on the polyoxometalate surface. The complexes exhibit antitumoral activity in vitro as shown by MTT experiment.     

Tunable and selective formation of micropores and mesopores in carbide-derived carbon

Pore structure of carbide-derived carbon (CDC) was tunable by chlorination of Ti(C_1−xA_x) solid–solution carbides (A = O or N). High-energy ball milling method was used to synthesize various nanocrystalline Ti(C_1−xA_x) phases. We were able to obtain specific dimension of pore volumes in the range of micropore (<2 nm) or mesopore size (2–50 nm), depending on the compositions of the precursors. The substitutional atoms and their contents effectively modify the characteristics of pores i.e., pore size, volume and their distributions. The micropore volume density, total pore volume density and specific surface area (SSA) of Ti(C_0.7O_0.3) CDCs were found 1.55 cm³/g, 1.72 cm³/g and 3100 m²/g, respectively. In contrast, Ti(C_0.5N_0.5) CDCs showed enhancement of mesopore formation with 3.34 cm³/g, 3.45 cm³/g and 522 m²/g for mesopore volume density, total pore volume density and SSA, respectively.     

Different hydrolytic stabilities of some C,N-chelated germanium alkoxides

C,N-intramolecularly coordinated germanium(IV) methoxides Ar₃GeOMe (1) and (Ar′)₂Ge(OMe)₂ (2) [where Ar = [2-(Me₂NCH₂)C₆H₄]⁻, Ar′ = [2-(DipN = CH)C₆H₄]⁻, Dip = 2,6-(i-Pr)₂C₆H₃] were prepared by the reaction of the lithium precursors ArLi and Ar′Li with Ge(OMe)₄ in appropriate molar ratio. While the diorganogermanium(IV) compound 2 is air-stable specie, triorganogermanium(IV) compound is surprisingly smoothly hydrolyzed by air-moisture to corresponding triorganogermanol Ar₃GeOH (3). Studied compounds were characterized by the help of multinuclear NMR spectroscopy and in the case of 2 and 3 using single-crystal X-ray diffraction analysis.     

The production of carbon particles of different shapes produced by the chlorination of Cr(C5H5)2

Carbon particles have been obtained by the chlorination of chromocene (Cr(C₅H₅)₂). Changes in their morphology and micro-nanostructure have been monitored at two different temperatures. At 400 °C, filled materials (tubes and spheres) and agglomerated round particles are formed, whereas at 900 °C closed-end tubes, hollow and solid spheres were produced. Transmission electron microscopy shows that these particles are formed of highly disordered graphene-like layers, which is confirmed by the absence of the 2D and 2G bands in the Raman spectrum. The calculated in-plane correlation length of these graphene-like layers is 1.2 ± 0.1 nm. In all the carbon particles, electron energy-loss spectroscopy shows a very similar sp² carbon bonding content (89–98%) and mass density ranging from 1.6 to 1.8 g/cm³, both below standard graphite. Textural studies performed on the sample prepared at 900 °C show Type II adsorption isotherms with a surface area of 694 m²/g.     

Tuning of the Ba5Nb4O15 permittivity temperature coefficient

The Ba₅Nb₄O₁₅ ceramic offers attractive dielectric properties (ɛ_r ∼ 39, tan(δ) < 10⁻³, ρ_i ∼ 10¹² Ω cm) but exhibits a high permittivity temperature coefficient (τ_ɛ ∼ −171 ppm °C⁻¹). In order to tune this parameter, substitutions on the Ba and Nb sites by, respectively, Mg, Ca, Sr and V, Ta, Sn have been investigated. Two interesting formulations have been identified, Ba_2.5Mg_2.5Nb₄O₁₅ and Ba₅Nb₃SnO_14.5 as nominal compositions, with temperature coefficients of −44 and −30 ppm °C⁻¹, respectively. More attention has been paid to the Ba₅Nb₃SnO_14.5 compound (named 504Sn25) in which BaSnO₃ has been clearly identified as a secondary phase. BaSnO₃, having a positive and very high temperature coefficient (+393 ppm °C⁻¹), seems to be responsible for the τ_ɛ lowering of 504Sn25. Furthermore B₂O₃ addition as sintering aid has been successfully investigated for increasing the Ba₅Nb₃SnO_14.5 sample density. In terms of dielectric properties, it induces an increase of the permittivity and of the insulating resistivity, while the control of τ_ɛ is maintained. Finally, the formulation 504Sn25 + 15 mol% B₂O₃ sintered at 1200 °C has a value of 17.8 as dielectric constant and −1 ppm °C⁻¹ as τ_ɛ value, that evidences the potentiality of this material to be used as temperature stable capacitor.     

Transport properties of cross-linked fullerenol–PVA membranes

Polyhydroxy fullerenes such as fullerenol C₆₀(OH)_22–24 have helped to bridge the gap between fullerenes and their innate solubility issues, where fullerenol solubility in water is 50 mg/ml whereas C₆₀ solubility is 1.3 × 10⁻¹¹ mg/ml. The improved solubility of these fullerene derivatives allows them to be better integrated into composite materials. Here we investigated the transport properties of cross-linked fullerenol–polyvinyl alcohol membranes with the addition of maleic acid for increased stability. High humidity causes the mechanical properties of polyvinyl alcohol to decrease. Using fullerenol as a cross-linker, we were able to decrease the sorption of water with these PVA membranes.     

Synthesis of Na0.5Bi0.5TiO3 whiskers and their nanoscale piezoelectricity

The perovskite structured lead-free system Na_0.5Bi_0.5TiO₃ (NBT) whiskers were synthesized from whiskers of layered tunnel structured Na₂Ti₆O₁₃ (NT), using a topochemical route. Both NT and NBT whiskers show high aspect ratios with an average length of 15 µm and diameter of 1 µm. By prolonging the reaction time from 2 h to 6 h at 900 °C, NT whiskers with monoclinic phase completely transformed to NBT whiskers with pseudocubic phase. Typical strip-like nanodomains are observed in a NBT whisker, which are parallel to each other. The piezoelectric response amplitude for a NBT whisker indicates a large electric field induced strain, corresponding to a S_max/E_max value of as high as 300 pm/V. This work provides an in-depth instruction to prepare pure NBT whiskers, and gives the detailed piezoelectricity of NBT whiskers to promote their applications in energy harvesting and micro-electromechanical systems.     

Improvement of structural and superconducting properties of Bi-2212 textured rods by substituting sodium

In this paper, the physical and superconducting properties of Bi₂Sr₂Ca_1−xNa_xCu₂O_8+δ with x=0.0, 0.05, 0.075, 0.1, and 0.20 textured superconducting fiber rods prepared by a laser floating zone (LFZ) technique were studied. The effects of Na⁺¹ substitution for Ca²⁺ have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transport measurements, dc-magnetization, magnetic hysteresis and magnetic critical current density. The powder XRD patterns of samples have indicated that Bi-2212 phase is the major one, independently of Na content. The best critical temperature, T_C, has been found as 93.3 K from M–T data for the sample with 0.075 Na substitution. The maximum magnetic J_C value has been calculated as 1.35×10⁵ A/cm² at 10 K for the 0.10 Na sample. The maximum transport critical current density has directly been measured as 1.3×10³ A/cm² at 77 K for the 0.05Na sample.     

Ca(BH4)2 as a simple tool for the preparation of thorium and uranium metallocene borohydride complexes: First synthesis and crystal structure of (C5Me5)2Th(η3-H3BH)2

Calcium borohydride allows for the high-yielding synthesis of (C₅Me₅)₂An(η³-H₃BH)₂ (An = Th, U) by reaction with (C₅Me₅)₂AnCl₂ (An = Th, U). While a preparative synthesis of (C₅Me₅)₂U(η³-H₃BH)₂ has been previously reported in the literature using K(C₅Me₅) and U(BH₄)₄, the use of Ca(BH₄)₂ is higher yielding and mild. Full characterization of the novel compound (C₅Me₅)₂Th(η³-H₃BH)₂ is presented.