Photoconducive and photodielectric properties of heterostructures composed of poly-<Emphasis Type="Italic">N</Emphasis>-epoxypropylcarbazole and MEH-PPV films with a zinc octabutylphthalocyanine additive

The subject of investigation is poly-N-epoxypropylcarbazole and poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene] films with zinc 2,3,9,10,16,17,23,24-octabutylphthalocyanine additives. The photoconducive and photodielectric properties of these heterostructures are studied in the absorption range of the metal complex. The photosensitivity of the structures depends on the triplet state of photogenerated electron-hole pairs, their dissociation in an external electric field, and charge carrier trapping. The increased photosensitivity of the heterostructures compared with that of constituent films is explained by a higher efficiency of dissociation of the photogenerated electron-hole pairs and a reduced influence of non-equilibrium carrier traps at the interfaces.     

Characteristic features of the photoconductivity and spin conversion of electron-hole pairs in doped amorphous molecular semiconductors in the dye absorption region

The photoconductivity of doped poly-N-epoxypropylcarbazole films in the absorption region of a cationic polymethine dye is observed to increase when the BF ₄ ⁻ ion is replaced by Cl⁻ and I⁻. The effect of a magnetic field on the photoluminescence is investigated at room temperature. The photoconductivity is studied as a function of the electric field intensity and wavelength of light. The dependence of the photoconductivity on the nature of the anion can be explained by a change in the probability of intercombination conversion in ionic and electron-hole pairs. Fiz. Tverd. Tela (St. Petersburg) 41, 44–48 (January 1999)     

Effect of electric field on the optical absorption of amorphous molecular semiconductors doped with polymethine dyes

The effect of a dc electric field on the evolution of the electronic absorption spectra of poly(N-epoxypropylcarbazole) (PEPC), poly(styrene) (PS), and poly(vinyl butyral) (PVB) films doped with methine dyes is investigated. It is revealed that these spectra in the absorption range of the dye undergo transformations depending on the dipole moment and the symmetry of the π-electron structure of dye molecules. The inference is made that the electron density in the dye molecule is redistributed in an external electric field. This redistribution gives rise to the electric field-induced anisotropy in the spatial distribution function of photogenerated electron-hole pairs in amorphous molecular semiconductors.     

Effects of aggregation of squaryl dye on photogeneration of charges in amorphous molecular semiconductors based on poly-N-epoxypropyl carbazole

Peculiarities of photoconductivity, photoabsorption, and photoluminescence of poly-N-epoxypropyl carbazole films doped with an intraionic dye are investigated. The anomalous temperature dependences of the photoconductivity of the films in the dye absorption region are explained by studying the effect of the dye concentration, temperature, and external electric field on the liberation of captured charges from the traps formed in the films as a result of doping. It is concluded that an increase in the dye concentration enhances its aggregation, intensifies the photogeneration of triplet electron-hole pairs, and narrows the spatial distribution of traps for holes in the vicinity of the dye. The hole charges captured in such traps are connected through the Coulomb interaction with negatively charged fragments of dye molecules. The traps are destroyed through thermal activation.     

Modification of the surface and bulk electronic properties of ytterbium nanofilms under the action of adsorbed CO molecules

The modification of the surface and bulk electronic properties of ytterbium nanofilms under the action of adsorbed CO molecules has been investigated. It has been shown that adsorption of these molecules is accompanied by a fundamental rearrangement of the electronic structure of the films. This rearrangement is initiated by the formation of a donor-acceptor adsorption bond by a lone electron pair localized at the carbon atom of the CO molecule. The formation of this bond is accompanied by the lowering of the Yb 5d level below the Fermi level. After this lowering reaches a considerable value, the 4f electrons start to transfer to the 5d level; i.e., the 4f ¹⁴ → 4f ¹³ transition occurs. The transition opens a way to the N ₄₅ N ₆₇ N ₆₇ Koster-Kronig supertransition in the Auger spectra. As a result of these processes, the peaks observed in the spectra before adsorption of the CO molecules disappear and new peaks appear. Therefore, the adsorption of the CO molecules brings about qualitative changes in the Auger spectra of ytterbium. It has been found that the rearrangement of the ytterbium electronic structure due to the action of CO molecules involves both the surface of the ytterbium films and their near-surface layers. The thickness of these layers exceeds the Auger electron escape depth and can reach more than 11 monolayers.     

Anomalously high low-frequency effective permittivity in a system of metal nanoislands

The low-frequency effective permittivity in a system of Co, W, and FeNi metal nanoislands in an electric field is investigated. The permittivity of films is determined from analyzing the dependences of the susceptance of the films on the temperature and the electric field. It is found that the effective permittivity of the structures under investigation has an anomalously high positive value (10⁷–10⁸) and that an increase in the electric field leads to a decrease in the effective permittivity and an increase in the electrical conductivity of the films. The nature of the high effective permittivity of the structures is governed by the island structure of the metal films and associated with the polarization of dipoles formed by pairs of negatively and positively charged metal nanoislands.     

Rectification effect in poly-p-xylylene-cadmium sulfide graded nanocomposites

The hybrid poly-p-xylylene-cadmium sulfide nanocomposites characterized by gradients of concentrations and sizes of CdS nanoparticles along the lines of an applied electric field have been synthesized using the vapor deposition polymerization in an inhomogeneous electric field. The maximum concentration of cadmium sulfide can exceed 10 vol %, while the average effective sizes of the nanoparticles depend on the concentration and do not exceed 5 nm. The synthesized thin-film nanocomposites exhibit a quantum confinement effect. According to the estimates obtained from the shift of the absorption band edge, the radius of nanoparticles is 2.7 nm near the negative electrode and 3.5 nm near the positive electrode. It has been found that the sample formed in an electric field of 10 kV/cm manifests a rectification effect, which can be associated with the gradient of nanoparticle sizes. The measurements of current-voltage characteristics and photoconductivity have demonstrated that the synthesized samples possess high photoconductivity. The photocurrent in the sample prepared in an electric field of 10 kV/cm can exceed the dark current by two orders of magnitude, and the rectification effect in this case disappears.     

Investigation of piezoelectric effect in lithium tantalate crystals by high-resolution X-ray diffractometry

Lithium tantalate crystals under the action of an external electric field have been studied by x-ray diffractometry. Both single-domain samples and crystals with a regular domain structure have been investigated. In the case of a single-domain crystal, the angular position of the Bragg peak varies under the action of an external electric field due to the reverse piezoelectric effect. According to this variation, the corresponding tensor component of piezoelectric constants can be calculated. In the crystal with a regular domain structure, a surface relief appears under the action of an external electric field. Piezoelectric constants can also be calculated using this relief.     

Energy distributions of electrons emitted from tungsten tips covered by diamond-like films

The energy distribution of electrons emitted from the surface of diamond-like pointed cathodes under the action of a high electric field is reported. Diamond-like coatings are applied on thin tungsten tips by ion-beam evaporation in an ultrahigh vacuum. The structure of the carboniferous films covering the tungsten tips is examined by field-emission microscopy. The stability of the field-emission cathode current is considered, and the Fowler-Nordheim I-V characteristics are presented. Based on the results obtained, a model of field-emission cathode covered by a thin diamond-like coating that explains the energy distributions is suggested.     

Geminate recombination of long-lived electron-hole pairs in doped carbazole-containing amorphous molecular semiconductors

This paper reports an investigation into the features of geminate recombination of long-lived electron-hole pairs in films of poly(N-epoxypropylcarbazole) (PEPC) containing intramolecular charge transfer compounds as centers of photogeneration of charge carriers carried out by measuring the attenuation kinetics of isothermal recombination luminescence over a wide range of temperatures (4.2–300 K) for times t>1 s, along with the kinetics of photoinduced EPR signals. A study is made of how the presence of a potential barrier to the reverse transition of carriers to the recombination center and the initial triplet state of the charged pairs affects the geminate recombination. It is established that the kinetics of isothermal recombintation luminescence attenuation follow the law I(t)∝t ^−m for the times under study, where m takes values from 0.65 to 1.05. The first observations of a nonmonotonic change in m with temperature are reported (m passes through a minimum at a certain temperature), and a mechanism is proposed for recombination of charged pairs in PEPC containing intramolecular charge-transfer compounds as an explanation for this phenomenon. Fiz. Tverd. Tela (St. Petersburg) 39, 1183–1187 (July 1997)     

Fabrication of piezo-and pyrosensitive films of polyvinylidene fluoride by vacuum evaporation in an electric field

Films of polyvinylidene fluoride with tetrafluoroethylene several micron thick were prepared by vacuum electron-beam evaporation in a static electric field. It is shown that a polymer deposited on a negative electrode possesses a structure similar to that of uniaxially stretched and polarized films and has a high (up to 85%) content of the piezoactive β phase. The electromechanical coupling coefficient k ₃₃ and the pyrosensitivity of these samples are substantially higher than those of layers deposited under the same conditions in the absence of a field. Zh. Tekh. Fiz. 68, 101–103 (December 1998)     

Solvatochromic behavior of dyes with dimethylamino electron‐donor and nitro electron‐acceptor groups in their molecular structure

Six dyes with N,N‐dimethylaminophenyl and 4‐nitrophenyl or 2,4‐dinitrophenyl groups in their molecular structures were prepared and characterized. These compounds have different conjugated bridges (C?C, C?N, and N?N) connecting the electron‐donor and the electron‐acceptor groups. All compounds are solvatochromic, with reverse solvatochromism occurring. The solvatochromic band observed in each spectrum for the dyes is due to a π ? π* transition, of an intramolecular charge transfer nature, which occurs from the electron‐donor N,N‐dimethylaminophenyl group to the electron‐acceptor group in the molecules, which is reinforced by the structures of the compounds optimized by applying density functional theory, which exhibit high planarity. The reverse solvatochromism was explained considering two resonance structures. The benzenoid form is better stabilized in less polar solvents and characterizes the region displaying positive solvatochromism, while the dipolar form is better stabilized in more polar solvents, in the region of negative solvatochromism. The Catalán multiparametric approach was used to study the contribution of solvent acidity, basicity, dipolarity, and polarizability to the solvatochromism exhibited by the compounds. These compounds are good candidates for the investigation of the polarizability and, to a lesser extent, the dipolarity of the medium, with very little interference from specific interactions of the solvent through hydrogen bonding. Copyright © 2014 John Wiley & Sons, Ltd.     

铁电薄膜底电极对薄膜结构与电性能的影响

研究了电极材料（Ｐｔ／Ｔｉ）对铁电ＰＬＺＴ（７．５／６５／３５）陶瓷薄膜结构和性能的影响．认为在Ｐｔ层厚度一定时，Ｔｉ层的厚度对铁电薄膜的结构和性能有显著影响．当Ｔｉ层过厚或过薄时，铁电薄膜的结构较差；而当Ｔｉ层的厚度适中时，则铁电薄膜的显向下微结构均匀，电性能较好，典型的剩余极化强度和矫顽场分别为２７．８μＣ·ｃｍ^-2和６５．１ｋＶ·ｃｍ^-1． 关键词：     

Thin ferroelectric films: Preparation and prospects of integration

The properties of (Ba,Sr)TiO₃ and BiFeO₃ thin films and related nanostructures have been considered. The films have been prepared by rf sputtering in an oxygen atmosphere at an elevated pressure, and the nanostructures have been produced using focused ion-beam etching. The electric field has been applied across a planar interdigital structure of electrodes. The structure, dielectric, electro-optical, and nonlinear optical properties of the prepared samples have been investigated over wide ranges of thicknesses and electric field frequencies. The high efficiency of the planar switching and its influence on the optical properties of the produced structures have been demonstrated. The nanostructuring makes it possible to change the dielectric and optical properties of the materials under investigation, thus increasing the range of switching of functional parameters.     

Athermal effects in ion implanted layers

Abstract

Defect structure and electrical characterization of boron and arsenic implanted layers has been investigated for implantation under athermal (light) excitation. This Photon Assisted (PA) implantation owes its specific properties to an additional electric field acting on charged particles including carriers and charged defects. It was shown that in case of n-type silicon this extra field draws charged vacancies and self-interstitials towards each other and, thus, diminishes transient diffusion of boron. This effect resulted in junctions which are about 20% shallower compared to conventionally processed reference wafers. Experiments using light of an Ar-ion laser and white light of a high pressure Xe arc lamp were compared. Some deactivation of carriers in the deeper laying parts of the p-region was always a by-product.     

铝诱导非晶硅薄膜的场致低温快速晶化及其结构表征

铝诱导非晶硅薄膜晶化可以降低退火温度、缩短退火时间，是制备多晶硅薄膜的一种重要方法.在此基础上，通过在退火过程中加入电场加速了界面处硅、铝原子间的互扩散，实现了非晶硅薄膜的快速低温晶化.实验结果表明，外加电场，退火温度为400℃，退火时间为60min时，薄膜的晶化率大于60％；退火温度为450℃退火时间为30min时，薄膜已经呈现明显的晶化现象；退火温度为500℃退火时间为15min时，薄膜的x射线多晶峰强度与非晶峰强度之比为未加电场的3—4倍. 关键词： 非晶硅薄膜 多晶硅薄膜 外加电场     

Effect of an in-situ applied electric field on growth of Bi4Ti3O12 films by sol-gel

Bi₄Ti₃O₁₂ (BIT) films were prepared on Pt/TiO₂/SiO₂/Si substrates by the sol-gel method. A low electric field was in-situ applied to BIT films during rapid thermal annealing (RTA). It was first found that a bias electric field has great influence on the structure, orientation, and morphology of BIT films at proper temperatures. Under the electric field of very low V/cm, BIT films show highly c-axis-oriented growth with second phase of bismuth oxide at 600 and 650 °C. The possible origin is proposed. On one hand, the electrostatic energy provides an extra driving force and the co-interaction of the electrostatic energy and interface energy promotes the c-axis-oriented growth of the BIT grains. On the other hand, the second phase of bismuth oxide produced during RTA in an electric field also plays an important role in the control of film orientation.     

Experimental analysis of current conduction through thermally grown SiO<Subscript>2</Subscript> on thick epitaxial 4H-SiC employing Poole-Frenkel mechanism

Electrical properties of SiO₂ grown on the Si-face of the epitaxial 4H-SiC substrate by wet thermal oxidation technique have been experimentally investigated in metal oxide-silicon carbide (MOSiC) structure with varying oxide thicknesses employing Poole-Frenkel (P-F) conduction mechanism. The quality of SiO₂ with increasing thickness in MOSiC structure has been analysed on the basis of variation in multiple oxide traps due to effective P-F conduction range. Validity of Poole-Frenkel conduction is established quantitatively employing electric field and the oxide thickness using forward I–V characteristics across MOSiC structures. From P-F conduction plot (ln(J/E) vs. E ^1/2), it is revealed that Poole-Frenkel conduction retains its validation after a fixed electric field range. The experimental methodology adopted is useful for the characterization of oxide films grown on 4H-SiC substrate.     

Optical, electrical, and photophysical properties of films of polycomplexes of azobenzene derivatives with cobalt

The absorption spectra, photoconductivity, and electrical conductivity of films of new polycomplexes of 4-methacyloyloxy-(4′-carboxy-3′-oxy)azobenzene and 4-methacryloyloxy-2-nitro-(4′-carboxy-3′-oxy)azobenzene with cobalt were investigated with switched-off and switched-on external electric fields. The effect of an external electric field on the transmission of linearly polarized light through films near the long-wavelength absorption edge is revealed. It is shown that the change in the light transmission under the action of an external electric field is due to the spatial reorientation of the dipole moments of azobenzene groups photoinduced by polarized light in an external electric field. The effect of an electric field on the light transmission is explained by the formation of forces acting on the dipole moments of azobenzene groups and on metal ions. The increase in the dipole moments of azobenzene groups as a result of introduction of nitro groups into their composition decreases the effect of cobalt ions on the electro-optical properties of polycomplex films.     

Characteristics of SrBi2Ta2O9 ferroelectric films in an in situ applied low electric field prepared by metalorganic decomposition

SrBi₂Ta₂O₉ (SBT) films were prepared on Pt/TiO₂/SiO₂/Si substrates at 750 °C in oxygen by metalorganic decomposition method. A low electric field was in situ applied during the film crystallization. It was first found that a low electric field and its direction have significant influence on the microstructures and ferroelectric properties of SBT films. Under a positive electric field (assuming that the bottom electrode is electrically grounded), the films show stronger c-axis-preferred orientation than without electric field and under a negative electric field. As a possible origin is proposed that the interface-induced nucleation growth between SBT and Pt coated substrate with application of low electric field plays a key role. Above all, an in situ applied low electric field during the film crystallization is a promising technique controlling film orientation for film preparation by wet chemical method.