Synthesis and nonlinear optical properties of novel Y-type polyurethanes with high thermal stability of dipole alignment

2,3-Di-(2′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3′-dimethoxy-4,4′-biphenylenediisocyanate to yield novel Y-type polyurethanes 4–5 containing 2,3-dioxy benzylidenemalononitrile group as a nonlinear optical (NLO)-chromophore, which constituted parts of the polymer backbones. Polyurethanes 4–5 were soluble in common organic solvents such as acetone and N,N-dimethylformamide. They showed a thermal stability up to 270 °C in thermogravimetric analysis thermograms and the glass-transition temperatures (T _g) obtained from differential scanning calorimetry thermograms were around 116–135 °C. The second harmonic generation (SHG) coefficients (d ₃₃) of poled polymer films at 106.4 mm⁻¹ fundamental wavelength were around 9.07 × 10⁻¹⁹ C (2.72 × 10⁻⁹ esu). The dipole alignment exhibited high thermal stability up to 10 °C higher than T _g, and there was no SHG decay below 145 °C due to the partial main-chain character of the polymer structure, which was acceptable for nonlinear optical device applications.     

Synthesis and characterization of arginine–glycine–aspartic peptides conjugated poly(lactic acid-co-<Emphasis Type="SmallCaps">l</Emphasis>-lysine) diblock copolymer

A biodegradable Copolymer of poly(lactic acid-co-lysine)(PLA–PLL) was synthesized by a modified method and novel Arginine–Glycine–Aspartic (RGD) peptides were chemical conjugated to the primary ε-amine groups of lysine components in four steps: I to prepare the monomer of 3-(N^ε-benzoxycarbonyl-l-lysine)-6-l-methyl-2,5-morpholinedione; II to prepare diblock copolymer poly(lactic acid-co-(Z)-l-lysine) (PLA–PLL(Z)) by ring-opening polymerization of monomer and l,l-lactide with stannous octoate as initiator; III to prepare diblock copolymer PLA–PLL by deprotected the copolymer PLA–PLL(Z) in HBr/HoAc solution; IV the reaction between RGD and the primary ε-amine groups of the PLA–PLL. The structure of PLA–PLL–RGD and its precursors were conformed by FTIR-Raman and ¹H NMR. Low weight average molecular weight (9,200 g/mol) of the PLA–PLL was obtained and its PDI is 1.33 determined by GPC. The PLA–PLL contained 2.1 mol% lysine groups as determined by ¹H NMR using the lysine protecting group’s phenyl protons. Therefore, the novel RGD-grafted diblock copolymer is expected to find application in drug carriers for tumor therapy or non-viral DNA carriers for gene therapy.     

A note on ‘ferroelectricity in polymer films containing TGS powder’

Ferroelectric polymer films have been made by dispersingtgs powder. The dielectric constant ε′ of the films has been measured. The thermal behaviour of ε′ is also reported. Data have been obtained from samples prepared with different weight concentrations (10–75%) oftgs.     

Study of the effect of thermal annealing on high k hafnium oxide thin film structure and electrical properties of MOS and MIM devices

The effect of rapid thermal annealing on structural and electrical properties of high k HfO₂ thin films is investigated. The films were initially deposited at pre-optimized sputtering voltage of 0.8 kV and substrate bias of 80 V in order to get optimized results for oxide charges and leakage current as a MOS device. The film properties were investigated for optimum annealing temperature in oxygen and optimum rapid thermal annealing temperature in nitrogen respectively to get the best electrical results as a MOS device structure. The film thickness, composition and microstructure is studied by Laser Ellipsometry, XRD and AFM and the effect of thermal annealing is shown. The electrical I–V and C–V characteristics of the annealed dielectric film were investigated employing Al-HfO₂-Si MOS capacitor structure. The flat-band voltage (V _fb) and oxide-charge density (Q _ox) were extracted from the high-frequency C–V curve. Dielectric study were further carried out on HfO₂ thin films having metal–insulator–metal (MIM) configuration over a wide temperature (300–500 K) and frequency (100 Hz to 1 MHz) range.     

Power and gas pressure effects on properties of amorphous In–Ga–ZnO films by magnetron sputtering

Amorphous In–Ga–ZnO thin films were deposited on quartz glass substrate at room temperature utilizing radio frequency magnetron sputtering technique. Sputtering power and oxygen flow rate effects on the physical properties of the In–Ga–ZnO films were systematically investigated. It is shown the film deposition rate and the conductivity of the In–Ga–ZnO films increased with the sputtering power. The as-grown In–Ga–ZnO films deposited at 500 W exhibited the Hall mobility of 17.7 cm²/Vs. Average optical transmittance of the In–Ga–ZnO films is greater than 80% in the visible wavelength. The extracted optical band gap of the In–Ga–ZnO films increased from 3.06 to 3.46 eV with increasing the sputtering power. The electrical properties of the In–Ga–ZnO films are greatly dependent on the O₂/Ar gas flow ratio and post-growth annealing process. Increasing oxygen flow rate converted the In–Ga–ZnO films from semiconducting to semi-insulating, but the resistivity of the films was significantly reduced after being annealed in vacuum. Both the as-grown and annealed In–Ga–ZnO films show n-type electrical conductivity.     

Preparation of thick YBa2Cu3O7−δ films by dc magnetron sputtering

High-temperature superconducting films up to 3.6 μm thick were obtained and their properties requisite for the development of microwave devices were investigated. It is shown that YBa₂Cu₃O_7−δ films of thickness exceeding 3–5λ _L may be obtained for use in the microwave range. Pis’ma Zh. Tekh. Fiz. 24, 89–94 (October 12, 1998)     

Magnetic crystallographic anisotropy of Fe/GaAs(100) epitaxial films

An investigation was made of the anisotropic properties of Fe films obtained by molecular-beam epitaxy on GaAs(100) substrates. It is shown that at thicknesses t=40–50 Å the Fe films begin to exhibit cubic magnetic anisotropy. At thicknesses t>100 Å the first constant of cubic anisotropy K₁ has values similar to those for “bulk” Fe single crystals. Films of intermediate thickness 50<t<100 Å possess both isotropic and anisotropic phases. Pis’ma Zh. Tekh. Fiz. 25, 88–95 (January 26, 1999)     

On the thermal mechanism of microwave breakdown of high-temperature superconducting films

Theoretical arguments supporting the thermal nature of the microwave breakdown of high-temperature superconducting films are compared with experimental data. A comparison of the theoretical and experimental values of the threshold field for breakdown of a uniform film, B _f, and the threshold field for breakdown at nonsuperconducting defects, B _d, confirms the dependence corresponding to a thermal mechanism: B _f, B _d∝ (T _c-T ₀)^1/2. It is shown that the space-time picture of the observed breakdown is apparently due to overheating of the film near defects with a size of 10⁻⁵–10⁻⁶ m. The amplitude of the breakdown field may ultimately be limited by the abrupt decrease in the energy of critical disturbances for the initiation of breakdown. Pis’ma Zh. Tekh. Fiz. 24, 12–17 (June 12, 1998)     

Langmuir-Blodgett films made from C60 fullerene with grafted macromolecules

Langmuir-Blodgett films made from C₆₀ fullerene with grafted polymer chains —polystyrene and polyethylene oxide — are obtained for the first time. The Langmuir-Blodgett films are obtained by the transfer of Langmuir films onto substrates of single-crystal silicon. The Langmuir films and the single-layer Langmuir-Blodgett films of C₆₀ with grafted polystyrene are nonuniform over their thickness and form a network consisting of aggregates with a size of ≤6 μm. The Langmuir films of C₆₀ with grafted polyethylene oxide are much more uniform. They can easily be used to obtain Langmuir-Blodgett films containing up to 20 layers and having a surface that appears smooth under an optical microscope. Pis’ma Zh. Tekh. Fiz. 24, 88–94 (June 26, 1998)     

Synthesis and electrochemical polymerization of 9,9-bis(carbazolylalkyl)fluorene and characterization of its conducting polymer film with high tensile strength

Free-standing poly(9,9-bis(carbazolylalkyl)fluorene) (P2Cz-A-F, alkyl = hexyl or dodecyl) films with high tensile strength (185–200 kg cm⁻²) were electrochemically synthesized by direct anodic oxidation of the monomer 9,9-bis(carbazolylalkyl)fluorene (2Cz-A-F) in a mixed electrolyte of boron trifluoride diethyl etherate containing 30% CH₂Cl₂ (by volume). The electrochemical and physical properties show that the quality of P2Cz-A-F films are much better than that of polycarbazole (PCz) and polyfluorene (PF) films due to the specially designed structure consisting of stiff bicarbazyl chromophores linked by a flexible long alkyl spacer at the fluorene unit. The structure of free-standing P2Cz-A-F films was investigated by UV–visible and infrared spectroscopy. Thermal analysis shows that the polymer films have good thermal stability. Fluorescent spectral studies indicate that polymer films in the solid state are blue-light emitters, which may meet potential applications in polymer light-emitting diodes.     

Dependence of the empirical model parameters of the surface resistance of a high-temperature superconducting film on the parameters of the technological process

The dependence of the surface resistance on the substrate heater temperature has been investigated for the purpose of optimizing the conditions for preparing YBa₂Cu₃O_7−δ films. It is shown that the resistance R _sur is highly sensitive to the accuracy of maintaining the substrate holder temperature to minimize the surface resistance of the films and maximize the parameter γ, which determines the temperature-dependent curves σ(t) and λ_L(t). Pis’ma Zh. Tekh. Fiz. 23, 79–84 (August 12, 1997)     

Influence of low-temperature annealing on the properties of Y1Ba2Cu3O7−δ thin films

The influence of annealing at 180 °C on the structure, critical temperature, and electrical resistivity of Y₁Ba₂Cu₃O_7−δ thin films has been investigated. It is shown that films grown at reduced temperatures are sensitive to this annealing, which can substantially alter these film parameters. Pis’ma Zh. Tekh. Fiz. 24, 55–58 (January 12, 1998)     

Investigation of inhomogeneities in thin films of high-temperature superconductors by scanning probe microscopy

Scanning tunneling microscopy and atomic force microscopy were used to study inhomogeneities in thin films of Y-Ba-Cu-O high-temperature superconductors caused by secondary-phase precipitates. It was established that Y-Ba-Cu-O films with high global critical parameters may constitute a complex heterogeneous system containing regions of different thickness and electrical properties. It is shown that these inhomogeneities may strongly influence the parameters of devices formed using these films. Pis’ma Zh. Tekh. Fiz. 25, 68–73 (February 26, 1999)     

Growth of GaN by molecular-beam epitaxy with activation of the nitrogen by a capacitive rf magnetron discharge

It is shown that GaN films can be grown by molecular-beam epitaxy with plasma activation of the nitrogen by a magnetron rf discharge in a specially constructed coaxial source with capacitive coupling. A growth rate of ∼0.1 μm/h is obtained on GaAs and sapphire substrates, and ways are found for optimizing the design of the plasma source in order to increase the growth rate. The electrophysical and luminescence properties of undoped epitaxial films are investigated at temperatures ranging all the way to room temperature. Pis’ma Zh. Tekh. Fiz. 24, 30–35 (June 26, 1998)     

Variation of electrical properties in sepiolite during dehydration

The dielectric constant (K), loss (tanδ) andac conductivity of a sepiolite sample have been measured as a function of frequency in the range 10²-10⁷ Hz and in the temperature region 30–400°C. Thedc conductivities of hot pressed pellets were measured in the temperature range 30–550°C.K and tanδ of these samples decrease with increasing frequency. Results of these measurements have been correlated with the structural transformation accompanying dehydration, making use ofdta, ir and x-ray data. The moderately large value of activation energy (∼ 2·2 eV) in the intrinsic range suggests that the conduction process is most probably associated with ions.     

Electrochemical copolymerization of benzanthrone and 3-methylthiophene and characterization of their fluorescent copolymer

Poly(3-methylthiophene-co-benzanthrone), a novel copolymer, was successfully achieved by electrochemical oxidation of the monomer mixtures of 3-methylthiophene (3MeT) and benzanthrone in the binary solvent system containing boron trifluoride diethyl etherate and acetonitrile. A series of experiments with different monomer feed ratios were carried out to investigate the influence of monomer feed ratio on the electrochemical copolymerization and the overall properties of the copolymer films. The resulting copolymer possesses the advantages of both polybenzanthrone and poly(3-methylthiophene), such as considerable fluorescence property, good redox activity, high thermal stability, and relatively high electrical conductivity. Ultraviolet–visible, FT-IR, and thermal analysis were used to characterize and investigate the structure and thermal stability of the copolymers. Fluorescence spectroscopic studies revealed that the copolymer dissolved in common organic solvents was a good green or yellow-green light emitter, with a strong emission at 499 nm in doped state and 529 nm in dedoped state.     

Characterization of biodegradable poly(butylene adipate-co-terephtalate)/sodium caseinate films loaded with an alkyl furanoside as antimicrobial agent

A biodegradable material was prepared by blending sodium caseinate (NaCAS) with poly(butylene adipate-co-terephtalate) (PBAT). The best composition was selected from mechanical testing of PBAT/NaCAS blends for further manufacture of a partially biobased film able to deliver a bioactive compound. From stress–strain testing, it was determined that the best mechanical properties while keeping maximum NaCAS content were obtained for 80/20 w/w PBAT/NaCAS blends plasticized with 10 % Glycerol (Gly). The surfactant octyl-β-d-galactofuranoside was used as an antitubercular agent and directly incorporated in the blend during hot mixing. The biodegradable films containing 1–5 % by weight of galactofuranoside were observed by SEM and showed crystalline structures on their surface. From X-ray diffraction studies, it was demonstrated that on the surface, the octyl galactofuranoside crystallized orthorhombic with space group P2₁2₁2₁. The molecular packing calculated from X-ray data showed bilayer structures with interdigitated octyl chains. Finally, the mycobacteriostatic properties of Gly-plasticized PBAT/NaCAS films were evaluated from a modified Kirby-Bauer test.     

Preparation and investigation of films of (Zn1−x Cdx)3(P1−y Asy)2 solid solutions

Pulsed laser evaporation was used to prepare thin films of (Zn_1−x Cd_x)₃(P_1−y As_y)₂ solid solutions. It was shown that varying the flux density of the laser radiation and the substrate temperature allows films to be obtained whose composition, structure, and electrical properties are similar to those of the bulk samples. Pis’ma Zh. Tekh. Fiz. 24, 85–88 (October 12, 1998)     

Percolation threshold for electrical resistivity of Ag-nanoparticle/titania composite thin films fabricated using molecular precursor method

To find the percolation threshold for the electrical resistivity of metallic Ag-nanoparticle/titania composite thin films, Ag-NP/titania composite thin films, with different volumetric fractions of silver (0.26 ≤ φ_Ag ≤ 0.68) to titania, were fabricated on a quartz glass substrate at 600 °C using the molecular precursor method. Respective precursor solutions for Ag-nanoparticles and titania were prepared from Ag salt and a titanium complex. The resistivity of the films was of the order of 10⁻² to 10⁻⁵ Ω cm with film thicknesses in the range 100–260 nm. The percolation threshold was identified at a φ_Ag value of 0.30. The lowest electrical resistivity of 10⁻⁵ Ω cm at 25 °C was recorded for the composite with the Ag fraction, φ_Ag, of 0.55. X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and transmission electron microscopic (TEM) evaluation of the effect of the morphology and the nanostructures of the Ag nanoparticles in the composite thin films on the electrical resistivity of the film revealed that the films consist of rutile, anatase, and metallic Ag nanoparticles homogeneously distributed in the titania matrix. It could be deduced that the electrical resistivity of the thin films formed at 600 °C was unaffected by the anatase/rutile content within the thin film, whereas the shape, size, and separation distance of the Ag nanoparticles strongly influenced the electrical resistivity of the Ag-nanoparticle/titania composite thin films.     

Films of a-Si:H doped with erbium from the metalorganic compound Er(HFA)3*DME, emitting at 1.54 μm

For the first time standard low-temperature (< 300 °C) plasma-enhanced chemical vapor deposition technology has been used to obtain a-Si(Er):H films emitting at 1.54 μm at room temperature. The fluorine-containing metalorganic compound Er(HFA)₃*DME, exhibiting enhanced volatility and fairly good thermal stability, was used for the first time as the Er source. The establishment of photoconduction in the synthesized samples indicates that they are of satisfactory electronic quality and potentially useful for developing light-emitting diodes at 1.54 μm. Pis’ma Zh. Tekh. Fiz. 24, 8–13 (July 12, 1998)