Showing papers on "Amorphous solid published in 2001"

Encyclopedia of Materials: Science and Technology

Abstract: Subject areas: Functional Phenomena. Electrical and thermal transport in normal solids. Physics and application of superconductors. Lattice properties and thermodynamics. Metal-gas reactions and electrochemistry. Magnetism and electronic properties and bulk solids. Hard and soft magnetic materials, manufacturing and applications. Magneto-optical and optical recording. Magnetic recording magnetic fluids. Physical properties of thin films and artificial multilayers. Optical and dielectric phenomena. Fundamental Core Theory. Fundamentals of materials science. Amorphous materials. Nuclear materials and irradiation effects. Biomedical and dental materials. Natural products and biomimetics. Carbon. Wood and paper. Characterization of materials. Surfaces: structure and properties. Miscellaneous. Structural Materials. Metal extraction, melting and refining. Metal processing. Structure, transformations and properties, light metals. Structure, transformations and properties, ferrous metals. Ceramic processing. Structure, transformations, properties in ceramics. Composites: MMC, CMC, PMC. Applications: aerospace automotive, sports, other. Applications: building. Modeling: atomic, microscale, large scale. Materials selection, life cycle costs, environmental tradeoffs, etc. Corrosion. Structural Phenomena. Elasticity-residual stress. Brittle fracture. Plastic deformation in static loading. Microscopic models of plasticity. Deformation and damage under cyclic load. Creep, strength and fatigue at elevated temperature. Mechanical properties of surfaces and in micro-dimensions. Deformation-related processing. Mechanical testing and nondestructive inspection. Polymers and Materials Chemistry. Crystalline polymers. Glassy amorphous and liquid crystalline polymers. Conducting and semiconducting polymers and organics. Elastomers, networks and gels. Block copolymers. Industrial polymerization chemistry. New synthesis methods for speciality polymers. Polymer processing. Inorganic materials chemistry. Organic/inorganic hybrid materials. Self-assembling materials chemistry. Liquid crystals. Functional Materials. Physics and chemistry of semiconductors. Semiconducting devices. Defects in semiconductors. Evaluation of semiconductors. Crystal growth. Epitaxial growth. Semiconductor processing and IC fabrication. Nonlinear optical materials. Electroceramics. Packaging.

Amorphous transparent conductive oxide InGaO3(ZnO)m (m≤ 4): a Zn4s conductor

Abstract: With the purpose of creating ZnO-based amorphous transparent conductors, a range of amorphous films InGaoO3(ZnO)m (where m ≤ 4) was prepared using a pulsed-laser deposition method. The resulting films exhibited an optical bandgap of 2.8-3.0 eV, and an n-type electric conductivity of 170-400 Scm−1 at room temperature, displaying a slight dependence on the value of m, in which the carrier density was 1019-1020 cm−3 the electron mobili ty was 12-20 cm2 V−1 s−1 showing no p n anomaly between Hall and Seebeck coefficients. The conductivity displayed no significant dependence on the temperature ranging from 10 to 300 K. X-ray diffraction, transmission electron microscopy and extended X-ray absorption fine structure measurements confirmed that the films were amorphous phases. A combined use of bremsstrahlung isochromat spectroscopy and ultraviolet photoelectron spectroscopy revealed that the conduction band tail had a large dispersion and that the Fermi level was located at the conduction band edge. The...

Block copolymer thin films : Physics and applications

Abstract: ▪ Abstract A two-part review of research concerning block copolymer thin films is presented. The first section summarizes experimental and theoretical studies of the fundamental physics of these systems, concentrating upon the forces that govern film morphology. The role of film thickness and surface energetics on the morphology of compositionally symmetric, amorphous diblock copolymer films is emphasized, including considerations of boundary condition symmetry, so-called hybrid structures, and surface chemical expression. Discussions of compositionally asymmetric systems and emerging research areas, e.g., liquid-crystalline and A-B-C triblock systems, are also included. In the second section, technological applications of block copolymer films, e.g., as lithographic masks and photonic materials, are considered. Particular attention is paid to means by which microphase domain order and orientation can be controlled, including exploitation of thickness and surface effects, the application of external field...

Ionic conductivity in crystalline polymer electrolytes

Abstract: Polymer electrolytes are the subject of intensive study, in part because of their potential use as the electrolyte in all-solid-state rechargeable lithium batteries. These materials are formed by dissolving a salt (for example LiI) in a solid host polymer such as poly(ethylene oxide) (refs 2, 3, 4, 5, 6), and may be prepared as both crystalline and amorphous phases. Conductivity in polymer electrolytes has long been viewed as confined to the amorphous phase above the glass transition temperature, Tg, where polymer chain motion creates a dynamic, disordered environment that plays a critical role in facilitating ion transport. Here we show that, in contrast to this prevailing view, ionic conductivity in the static, ordered environment of the crystalline phase can be greater than that in the equivalent amorphous material above Tg. Moreover, we demonstrate that ion transport in crystalline polymer electrolytes can be dominated by the cations, whereas both ions are generally mobile in the amorphous phase. Restriction of mobility to the lithium cation is advantageous for battery applications. The realization that order can promote ion transport in polymers is interesting in the context of electronically conducting polymers, where crystallinity favours electron transport.

Hydrothermal synthesis of nanosized anatase and rutile TiO2 using amorphous phase TiO2

Abstract: Phase-pure TiO2 nanocrystallites with narrow particle-size distributions were selectively prepared by hydrothermal processes starting from amorphous TiO2. Autoclaving amorphous TiO2 in the presence of HF and HCl as cooperative catalysts led to the formation of narrow-sized anatase TiO2 with a regular crystalline surface. Use of nitric acid as a cooperative catalyst with HF also gave the anatase TiO2 with a narrow size distribution but with a rather irregular crystalline surface. On the other hand, amorphous TiO2 was converted to phase-pure rutile TiO2 nanocrystallites by autoclaving in the presence of citric and nitric acids. Chelation of TiO6 octahedra with citric acid and acidification with nitric acid are critical for the phase transition from amorphous to rutile. The shape of all rutile nanocrystallites was rod-like. The crystal growth of TiO2 to phase-pure anatase or rutile was proposed to proceed via respective face-sharing and edge-sharing processes through dissolution–precipitation of the dissolved TiO6 octahedra from the amorphous phase. The photocatalytic activity in the redox reaction of 2-propanol with oxygen was quite comparable among the synthesized anatase and rutile nanocrystallites.

Character of the glass transition in thin supported polymer films.

Abstract: We have used ellipsometry to study the thermal expansivity of thin polystyrene films on silicon substrates with thicknesses of 10--200 nm. We find well-defined glass transitions, and detailed analysis of the expansivities shows that for thinner films the transition width is broadened, while the strength of the transition, defined by the difference between the expansivities in the liquid and glassy state, is reduced; the expansivity in the glassy state is higher than in the bulk. These phenomena are consistent with the idea that a layer of roughly constant thickness, of order 10 nm, near the surface of the film has liquidlike thermal properties at all experimental temperatures.

Interface-limited injection in amorphous organic semiconductors

Abstract: We examine electron transport in the archetype amorphous organic material tris(8-hydroxyquinoline) aluminum $({\mathrm{Alq}}_{3}).$ It is established that for Al, LiF/Al, and Mg:Ag cathodes, injection processes at the metal/organic contact dominate the current-voltage characteristics. We find that transport is also injection-limited at low temperatures, but that the cathode dependence of current-voltage characteristics at $T=30$ K is substantially reduced, raising doubts over metal-to-organic injection models that depend on the cathode work function. Given that ultraviolet photoelectron spectroscopy measurements show a shift in the vacuum potential at the metal/${\mathrm{Alq}}_{3}$ interface of \ensuremath{\sim}1 eV, we investigate the impact of interfacial dipoles on adjacent molecules in the organic film. Consequently, we propose that injection is limited by charge hopping out of interfacial molecular sites whose energy distribution is broadened by local disorder in the interfacial dipole field. We derive a general analytic model of injection from interfacial states and find that it accurately predicts the current-voltage characteristics of transport in ${\mathrm{Alq}}_{3}$ over many orders of magnitude in current and over a wide range of temperatures. The model is extended to other amorphous organic semiconductors and is found to be applicable to both polymers and small molecular weight organic compounds.

p-type conductivity in CuCr1−xMgxO2 films and powders

Abstract: CuCr1−xMgxO2, a wide band gap semiconductor with the delafossite structure, has been synthesized in bulk and thin-film form. Bulk undoped CuCrO2 is almost black and has moderate conductivity with p-type carriers. Upon doping with 5% Mg, the conductivity increases by a factor of 1000. In films, the best p-type conductivity is 220 S cm−1 in CuCr0.95Mg0.05O2, a factor of 7 higher than previously reported for Cu-based p-type delafossites. Undoped films have a conductivity of order 1 S cm−1. Films are usually polycrystalline on amorphous substrates, but undoped films can be c-axis oriented if deposited at or above 650 °C. Optical and ultraviolet transmission data indicate a direct band gap of 3.1 eV.

Fragile-to-strong transition and polyamorphism in the energy landscape of liquid silica

Abstract: Liquid silica is the archetypal glass former, and compounds based on silica are ubiquitous as natural and man-made amorphous materials. Liquid silica is also the extreme case of a 'strong' liquid, in that the variation of viscosity with temperature closely follows the Arrhenius law as the liquid is cooled toward its glass transition temperature. In contrast, most liquids are to some degree 'fragile', showing significantly faster increases in their viscosity as the glass transition temperature is approached. Recent studies have demonstrated the controlling influence of the potential energy hypersurface (or 'energy landscape') of the liquid on the transport properties near the glass transition. But the origin of strong liquid behaviour in terms of the energy landscape has not yet been resolved. Here we study the static and dynamic properties of liquid silica over a wide range of temperature and density using computer simulations. The results reveal a change in the energy landscape with decreasing temperature, which underlies a transition from a fragile liquid at high temperature to a strong liquid at low temperature. We also show that a specific heat anomaly is associated with this fragile-to-strong transition, and suggest that this anomaly is related to the polyamorphic behaviour of amorphous solid silica.

Processing of silicate dust grains in Herbig Ae/Be systems

Abstract: We have analysed the 10 m spectral region of a sample of Herbig Ae/Be (HAEBE) stars. The spectra are dominated by a broad emission feature caused by warm amorphous silicates, and by polycyclic aromatic hydrocarbons. In HD 163296 we nd aliphatic carbonaceous dust, the rst detection of this material in a HAEBE star. The silicate band shows a large variation in shape, due to variable contributions of three components: (i) a broad shoulder at 8.6 m; (ii) a broad maximum at 9.8 m; and (iii) a narrow feature with a broad underlying continuum at 11.3 m. From detailed modeling these features can be identied with silica (SiO2), sub-micrometer sized amorphous olivine grains and micrometer sized amorphous olivine grains in combination with forsterite (Mg2SiO4), respectively. Typical mass fractions are 5 to 10 per cent of crystalline over amorphous olivine, and a few per cent of silica compared to the olivines. The detection of silica in emission implies that this material is heated by thermal contact with other solids that have a high absorptivity at optical to near-IR wavelengths. The observed change in peak position of the silicate band in HAEBE stars from 9.7 m to 11.3 m is dominated by an increase in average grain size, while changes in composition play only a minor r^ ole. The HAEBE stars, Pic and the solar system comet Halley form a sequence of increasing crystallinity. We nd that the abundance of SiO2 tends to increase with increasing crystallinity. This is consistent with the compositional changes expected from thermal annealing of amorphous grains in the inner regions of the disk. We conrm earlier studies that the timescale for crystallisation of silicates in disks is longer than that of coagulation. Our results indicate that the processes that governed grain processing in the proto-solar nebula, are also at work in HAEBE stars.

Very-low-operating-voltage organic light-emitting diodes using a p-doped amorphous hole injection layer

Abstract: We demonstrate the use of a p-doped amorphous starburst amine, 4, 4′, 4″-tris(N, N-diphenyl- amino)triphenylamine (TDATA), doped with a very strong acceptor, tetrafluoro- tetracyano-quinodimethane by controlled coevaporation as an excellent hole injection material for organic light-emitting diodes (OLEDs). Multilayered OLEDs consisting of double hole transport layers of p-doped TDATA and triphenyl-diamine, and an emitting layer of pure 8-tris-hydroxyquinoline aluminum exhibit a very low operating voltage (3.4 V) for obtaining 100 cd/m2 even for a comparatively large (110 nm) total hole transport layer thickness.

Pressure-induced amorphization and an amorphous–amorphous transition in densified porous silicon

Abstract: Crystalline and amorphous forms of silicon are the principal materials used for solid-state electronics and photovoltaics technologies. Silicon is therefore a well-studied material, although new structures and properties are still being discovered. Compression of bulk silicon, which is tetrahedrally coordinated at atmospheric pressure, results in a transition to octahedrally coordinated metallic phases. In compressed nanocrystalline Si particles, the initial diamond structure persists to higher pressure than for bulk material, before transforming to high-density crystals. Here we report compression experiments on films of porous Si, which contains nanometre-sized domains of diamond-structured material. At pressures larger than 10 GPa we observed pressure-induced amorphization. Furthermore, we find from Raman spectroscopy measurements that the high-density amorphous form obtained by this process transforms to low-density amorphous silicon upon decompression. This amorphous-amorphous transition is remarkably similar to that reported previously for water, which suggests an underlying transition between a high-density and a low-density liquid phase in supercooled Si (refs 10, 14, 15). The Si melting temperature decreases with increasing pressure, and the crystalline semiconductor melts to a metallic liquid with average coordination approximately 5 (ref. 16).

Surface Photovoltage Spectroscopy of Dye-Sensitized Solar Cells with TiO2, Nb2O5, and SrTiO3 Nanocrystalline Photoanodes: Indication for Electron Injection from Higher Excited Dye States

Abstract: The onset wavelengths of the surface photovoltage (SPV) in dye-sensitized solar cells (DSSCs) with different mesoporous, wide-band gap electron conductor anode materials, viz., TiO2 (anatase), Nb2O5 (amorphous and crystalline), and SrTiO3, using the same Ru bis-bipyridyl dye for all experiments, are different. We find a clear dependence of these onset wavelengths on the conduction band edge energies (ECB) of these oxides. This is manifested in a blue-shift for cells with Nb2O5 and SrTiO3 compared to those with TiO2. The ECB levels of Nb2O5 and SrTiO3 are known to be some 200−250 meV closer to the vacuum level than that of our anatase films, while there is no significant difference between the optical absorption spectra of the dye on the various films. We, therefore, suggest that the blue shift is due to electron injection from excited-state dye levels above the LUMO into Nb2O5 and SrTiO3. Such injection comes about because, in contrast to what is the case for anatase, the LUMO of the adsorbed dye in the s...

Structure-performance relations in nanocomposite coatings

Abstract: Properties of hard nanocomposite coatings, especially hardness, can be explained by their nanostructure. Hardness maxima are found for different nanocrystalline/amorphous materials deposited by different techniques at typically 20% of the amorphous phase. A zone model is proposed which correlates the hardness to the relative phase content. The hardness of nanocomposite coatings peaks at the common minimum of the grain size of the crystalline phase and the grain separation. For an adequate description of the performance of a coating, the thermal stability, oxidation behavior and frictional behavior should be included in addition to hardness. In a friction situation involving at least two friction partners, the overall behavior of the system is determined by many-body interactions. While thermal stability and oxidation properties as inherent material properties can be directly linked to the nanostructure of the coating, the frictional behavior of a coating cannot be generalized independent of the friction conditions.

The dynamic competition between stress generation and relaxation mechanisms during coalescence of Volmer–Weber thin films

Abstract: Real-time measurements of stress evolution during the deposition of Volmer–Weber thin films reveal a complex interplay between mechanisms for stress generation and stress relaxation. We observed a generic stress evolution from compressive to tensile, then back to compressive stress as the film thickened, in amorphous and polycrystalline Ge and Si, as well as in polycrystalline Ag, Al, and Ti. Direct measurements of stress relaxation during growth interrupts demonstrate that the generic behavior occurs even in the absence of stress relaxation. When relaxation did occur, the mechanism depended sensitively on whether the film was continuous or discontinuous, on the process conditions, and on the film/substrate interfacial strength. For Ag films, interfacial shear dominated the early relaxation behavior, whereas this mechanism was negligible in Al films due to the much stronger bonding at the Al/SiO2 interface. For amorphous Ge, selective relaxation of tensile stress was observed only at elevated temperatures...

Bulk amorphous and nanocrystalline alloys with high functional properties

Abstract: Recent progress of bulk amorphous, nanocrystalline and nanoquasicrystalline alloys in rod, sheet and ring forms produced by various casting processes has been reviewed by focusing on their formation, structure, mechanical strength, chemical properties, magnetic properties and applications. These bulk nonequilibrium alloys exhibit unique characteristics which cannot be obtained for conventional amorphous, crystalline and quasicrystalline alloys and have been commercialized in some application fields of electrodes and golf clubs, etc. The combination of new compositions, direct production to final material forms, novel structures and unique characteristics is promising for the future development of these nonequilibrium bulk alloys as basic science and engineering materials.

TEM-EDX study of mechanism of bonelike apatite formation on bioactive titanium metal in simulated body fluid.

Abstract: Bioactive titanium metal, which forms a bonelike apatite layer on its surface in the body and bonds to the bone through the apatite layer, can be prepared by NaOH and heat treatments to form an amorphous sodium titanate layer on the metal. In the present study, the mechanism of apatite formation on the bioactive titanium metal has been investigated in vitro. The metal surface was examined using transmission electron microscopy and energy dispersive X-ray spectrometry as a function of the soaking time in a simulated body fluid (SBF) and complemented with atomic emission spectroscopy analysis of the fluid. It was found that, immediately after immersion in the SBF, the metal exchanged Na(+) ions from the surface sodium titanate with H(3)O(+) ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after they were formed, incorporated the calcium ions in the fluid to form an amorphous calcium titanate. After a long soaking time, the amorphous calcium titanate incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate with a low Ca/P atomic ratio of 1.40. The amorphous calcium phosphate thereafter converted into bonelike crystalline apatite with a Ca/P ratio of 1.65, which is equal to the value of bone mineral. The initial formation of the amorphous calcium titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania, which are dissociated from the Ti-OH groups, with the positively charged calcium ions in the fluid. The amorphous calcium titanate is speculated to gain a positive charge and to interact with the negatively charged phosphate ions in the fluid to form the amorphous calcium phosphate, which eventually stabilizes into bonelike crystalline apatite.

Laser induced crystallization of amorphous Ge2Sb2Te5 films

Abstract: The crystallization behavior of Ge2Sb2Te5 thin films has been analyzed by atomic force microscopy and optical reflection measurements on various time scales in order to determine the crystallization kinetics including the crystallization mechanism, the corresponding activation barrier, and the Avrami coefficient. On the minute time scale, thin amorphous films were isothermally crystallized in a furnace under a protective Ar atmosphere. From these measurements the activation energy for crystallization was determined to be (2.0±0.2) eV, in close agreement with previous studies using different techniques. The isothermal measurements also revealed a temperature dependent incubation time for the formation of critical nuclei, which is compared with recent theories. On the nanosecond time scale, Ge2Sb2Te5 was locally crystallized with a focused laser. Either crystalline spots of submicron size were generated in an as deposited amorphous film or amorphous bits in an otherwise crystalline film were recrystallized. For the formation of crystalline spots in an as deposited amorphous film a minimum time of (100±10) ns was found, which is identified as the minimum incubation time for the formation of critical nuclei. In contrast, the complete crystallization of melt-quenched amorphous bits in a crystalline matrix was possible in 10 ns. This is attributed to the presence of quenched-in nuclei inside the amorphous bits. The combination of optical measurements with atomic force microscopy reveals the formation and growth of crystalline bits and shows that the crystal growth in vertical direction strongly affects the reflectivity changes.

Properties of high κ gate dielectrics Gd2O3 and Y2O3 for Si

Abstract: We present the materials growth and properties of both epitaxial and amorphous films of Gd2O3 (κ=14) and Y2O3 (κ=18) as the alternative gate dielectrics for Si. The rare earth oxide films were prepared by ultrahigh vacuum vapor deposition from an oxide source. The use of vicinal Si (100) substrates is key to the growth of (110) oriented, single domain films in the Mn2O3 structure. Compared to SiO2 gate oxide, the crystalline Gd2O3 and Y2O3 oxide films show a reduction of electrical leakage at 1 V by four orders of magnitude over an equivalent oxide thickness range of 10–20 A. The leakage of amorphous Y2O3 films is about six orders of magnitude better than SiO2 due to a smooth morphology and abrupt interface with Si. The absence of SiO2 segregation at the dielectric/Si interface is established from infrared absorption spectroscopy and scanning transmission electron microscopy. The amorphous Gd2O3 and Y2O3 films withstand the high temperature anneals to 850 °C and remain electrically and chemically intact.

Rietveld quantitative amorphous content analysis

Abstract: A procedure for Rietveld quantitative amorphous content analysis (RQACA) is outlined, in which the effects of systematic errors in the powder patterns are studied. The method derives the amorphous content from the small overestimation of an internal crystalline standard in a Rietveld refinement of an appropriate mixture. Of several standards studied, Al2O3 gave the best results. The statistical analysis of standard mixtures with a known amount of amorphous content indicated that this is a precise and accurate tool. It enables the measurement of the amorphous content with an accuracy close to 1%. Sample preparation and Rietveld analysis need to be optimized in order to minimize the systematic errors. The analysis of samples with phases displaying strong preferred orientation effects gives very high errors in the amorphous content. Samples with different absorption coefficients have also been studied in order to evaluate the importance of microabsorption. This plays an important role but it can be adequately corrected if the absorption coefficients of the standard and the sample are not very different. RQACA has been applied to tricalcium silicate, C3S, which is the main component of Portland cement. The average amorphous content of C3S, after microabsorption correction using two standards of higher and lower absorption coefficients, was found to be 19%.

A second distinct structural “state” of high-density amorphous ice at 77 K and 1 bar

Abstract: High-density amorphous ice (HDA), further densified on isobaric heating from 77 K to 165 (177) K at 1.1 (1.9) GPa, relaxes at 77 K and 1 bar to the same structural “state” with a density of 1.25 ± 0.01 g cm−3. Its density is higher by ≈9% than that of HDA, and thus it is called very-high-density amorphous ice (VHDA). X-ray diffractogram and Raman spectrum of VHDA clearly differs from that of HDA, and the hydrogen-bonded O–O distance increases from 2.82 A in HDA to 2.85 A in VHDA. Implications for the polyamorphism of the amorphous forms of water are discussed.

Systematic Conductivity Behavior in Conducting Polymers: Effects of Heterogeneous Disorder

Abstract: The conduction process in conducting polymers has some unusual features. Even for highly conducting samples, the electronic transport properties show a mixture of metallic and non-metallic character, which is most easily explained in terms of the heterogeneous morphology of the polymers. The Figure shows the characteristic temperature dependence of conductivity as doping level is increased. A key feature of the conductivity of the organic conducting polymers is its surprisingly large magnitude for materials with low carrier density and considerable disorder. For polyacetylene the inferred conductivity of the highly conducting crystalline regions can be greater than that of copper. However, the temperature dependence of the conductivity shows non-metallic sign over a wide range of temperatures in virtually all conducting polymers—a change to metallic sign occurs only at higher temperatures and only in some polymers. This behavior is compared and contrasted with that of carbon nanotubes (which can also be regarded as conducting polymers) and of amorphous conventional metals. The measured conductivities of organic polymers and single-wall carbon nanotube networks are analyzed in terms of a heterogeneous model that gives a good account of the data. The granularity of the superconductivity recently discovered in polythiophene films is also consistent with this heterogeneous model.

Control of amorphous solid water morphology using molecular beams. I. Experimental results

Abstract: The adsorption of N2 was used to investigate the porosity/morphology of thin films of amorphous solid water. Molecular beams were used to vapor deposit amorphous solid water films on a Pt(111) crystal at a variety of incident growth angles. The amount of N2 adsorbed by the amorphous solid water depends very sensitively on the growth angle and thermal history of the film. For normal and nearly normal incidence growth, the water films are relatively dense and smooth and adsorb only a small amount of N2. For larger growth angles, the films are porous and adsorb large quantities of N2 with apparent surface areas as high as ∼2700 m2/g. The physical and chemical properties of amorphous solid water are of interest because of its presence in astrophysical environments. The observations have important implications for laboratory studies which use vapor deposited amorphous solid water films as analogs for astrophysical icy bodies such as comets.

Sonochemical synthesis of amorphous Cu andnanocrystalline Cu2O embedded in a polyaniline matrix

Abstract: Composite materials containing amorphous Cu nanoparticles and nanocrystalline Cu2O embedded in polyaniline matrices have been prepared by a sonochemical method. These composite materials were obtained from the sonication of copper(II) acetate when aniline or 1% v/v aniline–water was used as solvent. Mechanisms for the formation of these products are proposed and discussed. The physical and thermal properties of the as-prepared composite materials are presented. A band gap of 2.61 eV is estimated from optical measurements for the as-prepared Cu2O in polyaniline.

EPR Study of the Surface Characteristics of Nanostructured TiO2 under UV Irradiation

Abstract: Nanostructured TiO2 samples with primary particle size in the 4−20 nm range were prepared by either hydrothermal (H) or thermal (T) treatment of an amorphous precursor, and their behavior under UV illumination at 77 K was studied by means of EPR spectroscopy. The samples of the H series present the smallest crystallite size and after irradiation in a vacuum show some Ti3+ centers. In contrast, under these conditions only weak signals associated with oxygenated radicals are observed for the T samples. However, when oxygen is preadsorbed, several oxygenated complexes (O-, O2-, O2H•, and O3-) are photogenerated in proportions that depend on the characteristics of the material. Subsurface O- species are exclusively detected in the case of the samples of the H series, whereas ozonide radicals and surface O- are stabilized on materials with larger crystalline domains. These oxygenated complexes are thermally unstable, and they disappeared after warming to room temperature in the case of the T samples, but they ...

Controlled p-type doping of polycrystalline and amorphous organic layers: Self-consistent description of conductivity and field-effect mobility by a microscopic percolation model

Abstract: We present a systematic study on p-type doping of zinc-phthalocyanine by tetrafluoro-tetracyano-quinodimethane as an example of controlled doping of thin organic films by cosublimation of matrix and dopant. The zinc-phthalocyanine layers are prepared both in polycrystalline and amorphous phase by variation of the sublimation conditions. The films are electrically characterized in situ by temperature dependent conductivity and Seebeck and field-effect measurements. In addition to previous work, we show that also amorphous phthalocyanine layers can be doped, i.e., their conductivity increases and their Seebeck coefficient decreases indicating a shift of the Fermi level towards the hole transport level. The field-effect mobility of the polycrystalline samples is in the range of ${10}^{\ensuremath{-}4}--{10}^{\ensuremath{-}3} {\mathrm{cm}}^{\ensuremath{-}2}/\mathrm{Vs}$ and increases with increasing dopant concentration. Adapting a percolation model presented by Vissenberg and Matters [Phys. Rev. B, 57, 12 964 (1998)], which assumes hopping transport within a distribution of localized states, we can quantitatively describe the conductivity (in different organic layers) and the field-effect mobility.