Effect of C60 on the thermal stability of polyethylene glycol grafted to it

The thermal degradation of regular polymer networks, cross-linked by C₆₀ molecules along the end groups of polyethylene glycol, has been investigated by mass-spectrometric thermal analysis for the example of polyethylene glycol grafted to fullerene C₆₀. The character of the thermal degradation of the networks is substantially different from that of free polyethylene glycol and other polymer systems investigated earlier. The grafting to C₆₀ increases the thermal stability of polyethylene glycol. Pis’ma Zh. Tekh. Fiz. 23, 19–24 (September 26, 1997)     

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.     

Structure and mechanical properties of polyethylene-fullerene composites

The microhardness of films of fullerene-polyethylene composites prepared by gelation from semidilute solution, using ultrahigh molecular weight polyethylene (PE) (6×10⁶), has been determined. The composite materials were characterized by optical microscopy and X-ray diffraction techniques. The microhardness of the films is shown to increase notably with the concentration of fullerene particles within the films. In addition, a substantial hardening of the composites is obtained after annealing the materials at high temperatures (T _a=130 °C) and long annealing times (t _a=10⁵s). The hardening of the composites with annealing temperature has been identified with the thickening of the PE crystalline lamellae. Comparison of X-ray scattering data and the microhardness values upon annealing leads to the conclusion of phase separation of C₆₀ molecules from the polyethylene crystals within the material. The temperature dependence is discussed in terms of the independent contribution of the PE matrix of the C₆₀ aggregates to the hardness value.     

Effects of post-deposition annealing temperature and ambient on RF magnetron sputtered Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> gate on n-type silicon substrate

Samarium oxide (Sm₂O₃) thin films with thicknesses in the range of 15–30 nm are deposited on n-type silicon (100) substrate via radio frequency magnetron sputtering. Effects of post-deposition annealing ambient [argon and forming gas (FG) (90% N₂ + 10% H₂)] and temperatures (500, 600, 700, and 800 °C) on the structural and electrical properties of deposited films are investigated and reported. X-ray diffraction revealed that all of the annealed samples possessed polycrystalline structure with C-type cubic phase. Atomic force microscope results indicated root-mean-square surface roughness of the oxide film being annealed in argon ambient are lower than that of FG annealed samples, but they are comparable at the annealing temperature of 700 °C (Argon—0.378 nm, FG—0.395 nm). High frequency capacitance–voltage measurements are carried out to determine effective oxide charge, dielectric constant and semiconductor-oxide interface trap density of the annealed oxide films. Sm₂O₃ thin films annealed in FG have smaller amount of effective oxide charge and semiconductor-oxide interface trap density than those oxide films annealed in argon. Current–voltage measurements are conducted to obtain barrier heights of the annealed oxide films during Fowler–Nordheim tunneling.     

The effect of repeated annealing temperature on the structural,optical, and electrical properties of TiO<Subscript>2</Subscript> thin films prepared by dip-coating sol–gel method

In this study, we have studied the effect of repeated annealing temperatures on TiO₂ thin films prepared by dip-coating sol–gel method onto the glasses and silicon substrates. The TiO₂ thin films coated samples were repeatedly annealed in the air at temperatures 100, 200, and 300 °C for 5 min period. The dipping processes were repeated 5 to 10 times in order to increase the thickness of the films and then the TiO₂ thin films were annealed at a fixed temperature of 500 °C for 1 h period. The effect of repeated annealing temperature on the TiO₂ thin films prepared on glass substrate were investigated by means of UV–VIS spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM). It was observed that the thickness, average crystallite size, and average grain size of TiO₂ samples decreased with increasing pre-heating temperature. On the other hand, thickness, average crystallite size, and average grain size of TiO₂ films were increased with increasing number of the layer. Al/TiO₂/p-Si metal–insulator–semiconductor (MIS) structures were obtained from the films prepared on p-type single silicon wafer substrate. Capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements of the prepared MIS structures were conducted at room temperature. Series resistance (R _s) and oxide capacitance (C _ox) of each structures were determined by means of the C–V curves.     

Characteristic electron energy losses in organic PTCDA films

Studies are made of the characteristic energy losses of slow electrons during the formation of thin PTCDA films on a ZnO(0001) surface. It is shown that at low primary electron energies (<100 eV) the energy loss spectrum ( _n =3.0, 6.3, and 15 eV) reflects the structure of the transitions between the valence band and the conduction band. As the primary electron energy increases, energy losses to the excitation of plasma oscillations become dominant (ħω ₁=6 eV — excitation of a π-plasmon and ħω ₂=25 eV — excitation of a σ-plasmon). Pis’ma Zh. Tekh. Fiz. 25, 19–24 (October 26, 1999)     

Mechanism for thermal destruction of polystyrene grafted to fullerene C60

A model is proposed for the thermal destruction of polystyrene covalently bonded to C₆₀ and this is used to explain various characteristics of its experimental mass thermograms. Pis’ma Zh. Tekh. Fiz. 25, 25–30 (October 26, 1999)     

Influence of working gas pressure on the properties of thin films of high-temperature superconductors obtained by magnetron sputtering

The surface morphology, composition, microstructure, and electrical properties of thin films of YBa₂Cu₃O_7−x high-temperature superconductors, obtained by inverted magnetron sputtering, have been studied as a function of the pressure of the working gas mixture and results are presented. The main parameters of the magnetron discharge plasma near the substrate were determined by analyzing the characteristics of Langmuir probes. Changes in the properties of the films are considered to be caused by bombardment of the growing film with plasma ions accelerated in the floating potential field of the substrate. Films obtained at a pressure of 28 Pa and substrate temperature of 630 °C had a superconducting transition end temperature T _c ,off=89 K and a critical current density j _c =2 MA/cm² (at 77 K) and were free from secondary phase particles larger than 10 nm. Pis’ma Zh. Tekh. Fiz. 24, 80–85 (February 26, 1998)     

Corrosion of 20Kh13 steel in lead melts saturated with oxygen

We study the high-temperature interaction (650°C, 500 h) of 20Kh13 chromium steel with melts of stagnant lead saturated with oxygen (C _{O [Pb]} ≈ 6 · 10⁻³ wt.%). First (up to 200 h), separate islands of Me₃O₄ oxides (Me: Fe, Cr, Pb) are formed on the steel surface. In the course of time (for 500 h), these islands completely cover the steel surface as a result of lateral growth. The upper part of the oxide layer is formed by the (Fe_{1 − x} Pb_x) O · Fe₂ O₃ complex oxide growing from the initial “solid-metal—melt” interface toward the liquid-metal medium. The inner part of the oxide layer is spinel [(Fe_{1 − x} Pb_x) O · (Fe_{1 − y} Cr_y)₂O₃] enriched with chromium and formed on the basis of the matrix. Both layers symmetrically grow with respect to the initial “solid-metal—melt” interface. Lead does not penetrate into the steel matrix and is fixed only in the oxide layer. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 5, pp. 36–40, September–October, 2005.     

Thermal stability of gold-PS nanocomposites thin films

Low-temperature transmission electron microscopy (TEM) studies were performed on polystyrene (PS, M _w = 234 K) — Au nanoparticle composite thin films that were annealed up to 350°C under reduced pressure conditions. The composite thin films were prepared by wet chemical approach and the samples were then subsequently spin-coated on a carbon-coated copper grid for TEM measurements. TEM measurements were performed at liquid nitrogen temperatures to reduce the electron-beam-induced radiation damage. The results showed a marginal increase in Au nanoparticle diameter (2.3 nm–3.6 nm) and more importantly, an improved thermal stability of the polystyrene (PS) composite film much above its glass transition temperature.     

Bilateral bounds for the shear and torsion factors: comments on elementary derivations

This paper proposes a new simple derivation of bilateral bounds for the strain energy–based shear and torsion factors, χ _i , of an elastic beam together with some comments about the coherence of the current formulations. A rearrangement of the definition as a mean over the cross-section and an original decomposition of the shear stress in two parts—τ _eqv that is equivalent to the external force and a residual Δτ—allow (i) to interpret (χ − 1) as the mean quadratic deviation of the shear field with respect to the distribution τ _eqv and (ii) to easily evaluate an upper bound, using minimal information about the stress field. In this formulation, the lower bound becomes trivial. Several numerical examples illustrate the accuracy and suitability of the results obtained.     

Synthesis of novel ultraviolet stabilizers based on [60]fullerene and their effects on photo-oxidative degradation of polystyrene

Abstract

Two N-benzyl fulleropyrrolidines were synthesized via Prato reaction. The polystyrene (PS) films containing 0.5?wt% fullerene and N-benzyl fulleropyrrolidines were prepared from toluene via the solvent evaporation method. The photo-oxidative activities and thermostability of these films were determined by monitoring the average molecular weight and thermogravimetric curve. The changes in weight loss (%) and tensile strength with irradiation time were also tracked. After 480?h of illumination, the weight loss of PS films was 6.8%, while the corresponding index of PS with C₆₀ was 6.1%. The weight loss of PS with two fulleropyrrolidines was significantly lower than that before (3.8% and 2.7%). The results manifested the good ultraviolet (UV) stabilizing effect and thermostability of these complex films compared with PS. A probable mechanism was proposed to account for the stabilizing action of the [60]fullerene derivatives as multifunctional UV stabilizers.     

Dip-coated hydrotungstite thin films as humidity sensors

Thin films of a hydrated phase of tungsten oxide, viz. hydrotungstite, have been prepared on glass substrates by dipcoating method using ammonium tungstate precursor solution. X-ray diffraction shows the films to have a strongb — axis orientation. The resistance of the films is observed to be sensitive to the humidity content of the ambient, indicating possible applications of these films for humidity sensing. A homemade apparatus designed to measure the d.c. electrical resistance in response to exposure to controlled pulses of a sensing gas has been employed to evaluate the sensitivity of the hydrotungstite films towards humidity.     

Photoinitiated modifications of polymers: photocrosslinking, surface photografting and photolamination

 Based on extensive studies of photoinitiated reactions of synthetic polymers, processes for modification of sheets, films, filaments and yarn have been invented and developed. Using ultra violet irradiation, photocrosslinking of polyethylene melts as a continuous process on line with an extruder has been invented. Effective photocrosslinking has also been obtained for ethylene-propylene-diene (EPDM) elastomers and ultra high strength fibers of high density polyethylene (HDPE). A continuous process for surface modification of polymers by surface photografting has been invented and applied to strips of film, filaments and yarns. The inert surface of polyolefins, polyesters and polyamids, grafted with functional vinyl monomers, show decreased contact angle with water, increased adsorption of dyes and increased adhesion to other polymers. Photoinitiated lamination of polymer films and sheets has been invented and developed as a ”bulk surface photografting process”. Two or more films and sheets are interdispersed with reactive layers of monomer and initiator and then bonded together by photoinitiated grafting with ultraviolet irradiation. The crosslinked network formed is grafted to two adjacent polymer surfaces. This gives laminates of high lamination strength, high barrier properties, and promising commercial applications. Received: 8 April 1998 / Accepted: 22 May 1998     

Josephson Bicrystal Junctions on Sapphire Substrates for THz Frequency Application

Thin film metal oxide superconducting bicrystal junctions on sapphire substrates with I _c R _N products up to 2.5 mV at 4.2 K for width 4 μm and normal-state junction resistance 10–60 Ω were fabricated and characterized at dc and THz frequency. Three types of samples—one with broadband log-periodic antenna, another with double-slot antenna for 300 GHz and third one with double-slot antenna for 400 GHz—have been investigated at THz frequency. New design of antenna coupling with Josephson junction was elaborated for minimization of THz frequency losses in superconducting film. For a particular case of f=320 GHz double-slot antenna, a ratio for bandwidth Q = f/Δf ≈ 10 was measured.     

Magnetic Studies of Spin Wave in Fe/Ag Multilayer Films

Magnetic properties of Fe/Ag multilayer films are investigated and examined versus Fe layer thickness t _Fe. As a result, spontaneous magnetization M(T) temperature dependence has been revealed to be well described by a T ^3/2 law in all multilayer films (7 ?≤t _Fe≤60 ?). Spin-wave theory based on anisotropic ferromagnetic system has been also used to explain magnetization temperature dependence. For Fe layer thickness, approximate values for J ₀ bulk exchange interaction and J _s surface exchange interaction have been estimated. First principle calculations based on density functional theory (DFT) and Korringa–Kohn–Rostoker (KKR)—coherent potential approximation (CPA) method—combined with Local Spin Density Approximation (LSDA), are performed as well. Magnetic moment, in fcc Ag_1−x Fe _x and bcc Fe_1−x Ag _x systems, versus x is presented and discussed in terms of Fe content on magnetic coupling. Reasonable agreement between experimental data and theoretical calculations is highlighted.     

Structural Characterization of Selected MxC60 Phases (M=Li,Na, K) Synthesized Electrochemically in All-Solid-State Cells

Abstract

Electroreduction of C₆₀ was carried out in all-solid-cells operating with polymer electrolytes composed of polyethylene oxide (PEO), and salts like LiClO₄, NaCF3SO₃ or KCF₃SO₃. Some selected reduced phases of C₆₀ were isolated and characterized by electron diffraction microscopy.     

P-type semiconducting Cu2O–NiO thin films prepared by magnetron sputtering

P-type semiconducting thin films consisting of a new multicomponent oxide composed of Cu₂O and NiO were deposited on glass substrates by r.f. magnetron sputtering using Cu₂O–NiO mixed powder targets. The multicomponent oxide thin films deposited in an Ar atmosphere with a Ni content (Ni/(Cu + Ni) atomic ratio) in the range from 0 to 100 at.% were found to be p-type semiconductors. As the Ni content was increased in the range from 0 to about 30 at.%, the energy bandgap of the resulting films gradually increased as well as the obtained resistivity increased from 70 to 4 × 10⁴ Ω cm, a consequence of decreases in both the Hall mobility and the hole concentration. The films prepared with a Ni content of about 30–50 at.% exhibited a relatively constant resistivity and energy bandgap. The resistivity and the energy bandgap of films prepared with a Ni content above about 60 at.% considerably increased as the Ni content was increased. Furthermore, a pn thin-film heterojunction prepared by depositing undoped n-ZnO and p-multicomponent oxide (Ni content of 50 at.%) thin films exhibited a rectifying I–V characteristic.     

Electronic structure and electrical transport characteristics of C60, 2C60 and 4C60 fullerene molecules

The extended Hückel method and the Green’s function method were used to calculate the electronic structure and electrical transport of Au electrode-C₆₀, 2C₆₀ or 4C₆₀ fullerene-Au electrode systems. Furthermore, their electronic structure and electrical transport characteristics were compared and analyzed. The results show that (i) owing to the contact with the Au electrodes, the C₆₀, 2C₆₀ and 4C₆₀ molecules change in their electronic structures significantly, and their energy gaps between LUMO and HOMO are narrow; (ii) the bonding between C₆₀, 2C₆₀ or 4C₆₀ fullerene and Au electrodes is partially covalent and partially electrovalent; and (iii) the conductance of the three fullerenes conforms to the order of C₆₀ > 2C₆₀ > 4C₆₀. Translated from Journal of Materials Science and Engineering, 2006, 24(1): 53–56 [译自: 材料科学与工程学报]     

Component composition and strain of barium-strontium titanate ferroelectric films

The effect of the ratios of the cationic components and internal strains on the critical temperature T _c and the dielectric characteristics of BSTO ferroelectric films grown on α-Al₂O₃ [1012] and LaAlO₃ substrates were investigated. Ion backscattering diagnostics revealed a barium deficiency in the surface layer of the films and showed that the films differ in structural quality. Pis’ma Zh. Tekh. Fiz. 25, 50–60 (October 12, 1999)