Journal of Materials Science (v.47, #4)

Preface to the Special Section E-MRS MACAN by Dominique Chatain; Wayne D. Kaplan; Mike Finnis; Chrisitina Scheu (1603-1604).

Au films are deposited onto line-patterned substrates, and the dewetting of the line-shaped films is studied. The results show that the line-patterned substrates can clearly lead to both, a decrease and an increase in the resulting particle size and particle spacing when compared to dewetting occurring on a flat substrate. The size and the spacing of the dewetted Au particles scale with the feature size of the line-shaped films in a Rayleigh-like way, but this scaling law ceases when the ratio of line width to film thickness reaches or exceeds a critical value.

Faceting mechanisms of Si nanowires and gold spreading by Laetitia Vincent; Rym Boukhicha; Cyrille Gardès; Charles Renard; Vy Yam; Frédéric Fossard; Gilles Patriarche; Daniel Bouchier (1609-1613).
We report detailed structural analysis of 〈111〉 oriented silicon nanowires (NWs) grown by UHV–CVD using the VLS process with a gold catalyst. STEM-HAADF observations have revealed an unexpected inhomogeneous distribution of gold nanoclusters on the NW surface. Gold is mainly distributed on three sides among the six {112}-sidewalls and is anchored on upward {111} facets. This original observation brought us a new comprehension of the faceting mechanisms. The stability of the 〈111〉 growth direction needs the formation of facets on {112}-sidewalls with energetically favorable planes. We demonstrate that the initial formation of covered facets with a three-fold symmetry is driven by the formation of {111} Au/Si interfaces between the nucleated Si NW and the Au droplet.

Atomic structure and reactivity of ferromagnetic Fe deposited on Si(001) by Nicoleta G. Gheorghe; Marius A. Husanu; George A. Lungu; Ruxandra M. Costescu; Dan Macovei; Cristian M. Teodorescu (1614-1620).
This study presents a correlated study of structural, reactivity, and magnetic properties of ultrathin Fe layers grown on Si(001) by molecular beam epitaxy in ultrahigh vacuum. The interface reactivity is characterized by Auger electron spectroscopy. The surface structure is characterized by low electron energy diffraction with spot profile analysis. The magnetism of the synthesized layers is investigated by magneto-optical Kerr effect. At room temperature, metal Fe layers with poor long-range order are synthesized; these layers are ferromagnetic with an extremely low coercitive field (below 1 Oe). The reactivity with Si is low in this case, with formation of an interface layer of about 8 Å Fe equivalent thickness with about 7 at.% Si diffused. Samples synthesized at higher temperatures (500 °C) exhibit better long-range order, though the Fe reactivity with Si is higher and leads to the formation of an interface compound whose approximate stoichiometry is very close to Fe3Si. Once this compound is formed (for an equivalent Fe thickness of about 14 monolayers), disordered metal Fe islands are developing with subsequent Fe deposition, which contain also about 8 at.% Si diffused. These structures exhibit a much lower ferrimagnetism, with saturation magnetization about one order of magnitude lower than in the case of the room temperature synthesis. In this case of high temperature synthesis, two phases are observed, a ferrimagnetic one and a superparamagnetic one.

In order to understand the influence of ductile metal interlayer on the overall deformation behavior of metal/nitride multilayer, different configurations of metal and nitride layers were deposited and tested under indentation loading. To provide insight into the trends in deformation with multilayer spacings, an FEM model with elastic-perfect plastic metal layers alternate with an elastic nitride on top of an elastic–plastic substrate. The strong strain mismatch between the metal and nitride layers significantly alters the stress field under contact loading leading to micro-cracking in the nitride, large tensile stresses immediately below the contact, and a transition from columnar sliding in thin metal films to a more uniform bending and microcracking in thicker coatings.

Structure of multilayer ZrO2/SrTiO3 by Wei Li Cheah; Michael W. Finnis (1631-1640).
Multilayered oxide heteroepitaxial systems, including that of a 1-nm-thick Y2O3-stabilised ZrO2 (YSZ) sandwiched between layers of SrTiO3 (STO) [1], have been a subject of much interest lately due to their significantly enhanced ionic conductivities as compared to the bulk materials. We aim to provide the foundation for understanding this increase in conductivity by considering the atomic configurations at the interfaces of such systems, specifically a ZrO2/STO multilayer system. Possible stable lattice structures of pure ZrO2 in the system are explored using a genetic algorithm in which the interatomic interactions are modelled by simple pair potentials. The energies of several of the more stable of these structures are then evaluated more accurately within density functional theory (DFT). We find that the fluorite ZrO2 phase is unstable as a coherently strained epitaxial layer in the multilayer system. Instead, anatase-, columbite-, rutile-, and pyrite-like ZrO2 epitaxies are found to be more stable, with the anatase-like epitaxy being the most stable structure over a wide range of chemical potential of the components. We also find a high energy metastable structure resembling the tetragonal fluorite structure which is predicted by DFT to be stabilised by SrO-terminated STO but not by TiO2-terminated STO.

Faceting–roughening of twin grain boundaries by B. B. Straumal; B. Baretzky; O. A. Kogtenkova; A. S. Gornakova; V. G. Sursaeva (1641-1646).
The coincidence site lattice (CSL) plays a similar role for grain boundaries (GB) as the crystal lattice plays for free surfaces. The most densely packed CSL is the twin-related CSL, characterized by an inverse density of coincidence sites Σ = 3. Phase diagrams in coordinates “relative temperature T/T m—misorientation angle θ—inclination angle φ” were constructed for the twin GBs in Cu, Al, and Mo having different stacking fault energy γ. At low γ the twin GB remains faceted at all φ values and the number of crystallographically different facets increases with decreasing temperature. With increasing γ asymmetric twin GBs become more and more rough, and fewer facets appear with decreasing temperature. Also, with increasing γ the facets start to degenerate of into the first order rough-to-rough ridges. The behavior of twin GBs in Cu, Al, and Mo is compared with that of twin GBs in Zn.

Equilibrium segregation of Ti to Au–sapphire interfaces by Elad Nussbaum; Hila Meltzman; Wayne D. Kaplan (1647-1654).
Equilibrium segregation of Ti to Au–sapphire interfaces was measured from dewetted Au(Ti) films on the (0001) surface of sapphire. Quantitative energy dispersive spectroscopy was used to determine a Ti excess at the Au–sapphire interface of 2.2 Ti atoms/nm2, which together with an excess of 4.6 Ti atoms/nm2 at the (0001) sapphire surface, is associated with a decrease in the solid–solid Au–sapphire interface energy. Quantitative high resolution transmission electron microscopy showed that the segregated Ti is distributed within a 1.54-nm thick intergranular film at the Au–sapphire interface, which is not a bulk phase but rather an equilibrium interface state. As a result, Ti segregation without the formation of a bulk reaction at the interface is associated with a decreased interface energy, improved wetting, and may be an important part of the total complex mechanism responsible for improved wetting and spreading in “reactive” braze systems.

Microstructural engineering of ZnO-based varistor ceramics by Aleksander Rečnik; Slavko Bernik; Nina Daneu (1655-1668).
In ceramic materials, special boundaries play the key role in crystal growth. They introduce an abrupt structural and chemical anisotropy, which is readily reflected in an unusual microstructure evolution, whereas their local structure affects the physical properties of polycrystalline materials. These effects, however, can be exploited to tailor the electronic and optical properties of the materials, as demonstrated in this review. The presented topic is related to a preparatory stage of phase transformations, manifested through the evolution of chemically induced structural faults. In non-centrosymmetric structure of ZnO, inversion boundaries (IBs) are the most common type of planar faults that is triggered by the addition of the specific IB-forming dopants (Sb2O3, SnO2, TiO2). In addition to conventional TEM techniques, new methods were developed to resolve crystallography and atomic-scale chemistry of IBs. The absolute orientation of the polar c-axes on both sides of an IB was determined by micro-diffraction, providing the most reliable identification of crystal polarity in non-centrosymmetric crystals. To determine sub-monolayer quantities of dopants on the IB, we developed a special technique of analytical electron microscopy using concentric electron probe (CEP) in EDS or EELS mode, providing more accurate and precise results than any other technique. Knowing the local crystal chemistry of IBs, we were able to design experiments to identify their formation mechanism. IBs nucleate in the early stage of grain growth as a dopant-rich topotaxial 2D reaction product on Zn-terminated surfaces of ZnO grains. Soon after their nucleation, ZnO is epitaxially grown on the inherent 2D phase in an inverted orientation, which effectively starts to dictate anisotropic growth of the infected crystallite. In very short time, the grains with IBs dominate the entire microstructure via IB-induced exaggerated grain growth mechanism. This phenomenon was used to design physical properties of ZnO-based varistor ceramics, whereas the bottom-up approach demonstrated here provides the basic tool for microstructural engineering of functional materials in virtually any system that is prone to the formation of special boundaries.

Synthesis and characterization of CuInS2 thin film structures by Angela S. Wochnik; Christoph Heinzl; Florian Auras; Thomas Bein; Christina Scheu (1669-1676).
CuInS2 is a promising semiconductor material for solar cell applications. Here we use a mild solvothermal synthesis route to prepare CuInS2 films with different thicknesses and morphologies on fluorine-doped tin oxide coated glass. The microstructure of the films is studied in detail by scanning electron microscopy and transmission electron microscopy (TEM) and associated analytical techniques. For further characterization, we apply X-ray diffraction and UV/Vis absorption spectroscopy. Two different films are synthesized using different reagent stoichiometries and thermal treatments. The thicker film (25 μm) consists of three different regions. Close to the substrate a 600 nm thick densely packed layer occurs, on which a 1 μm thick flaky structure is found. On top of this structure, microspheres are located which possess a size of about 3 μm and are composed of numerous flakes. The thinner film consists of a 200 nm thick densely packed layer and a net-like structure built of individual flakes as well. In both films, TEM reveals that the flakes are adjacent to 10 nm thin branch-like rods. Energy dispersive X-ray spectroscopy of the densely packed layers indicates a Cu-rich composition which suggests them to be a p-type semiconductor. The rods and the flakes show a stoichiometric composition. Due to its high surface area, the thinner film offers a promising morphology for solar cell applications based on the large available area for the separation of electron–hole pairs, when the material is combined with a suitable electron conductor.

A phase field model of electrochemical impedance spectroscopy by W. Gathright; M. Jensen; D. Lewis (1677-1683).
A general phase field model for electrochemistry is presented in the context of simulating electrochemical impedance spectroscopy (EIS) experiments. The model tracks species, phases, and charge distribution. Governing partial differential equations are derived from a simple set of assumptions including ideal bulk solution thermodynamics, a method of interpolating between bulk phases, physical balance laws, and the second law of thermodynamics. A source term in the conservation of mass expression captures the behavior of the chemical reactions through the interface and in the bulk phases. Three example systems are given to demonstrate the variety of EIS behavior that can be simulated by this general model. These example systems show two-time constant transport, finite-length diffusion, and constant phase element behavior. Future versions of this model can be used to study the link between EIS and microstructure.

Interface structure of deposited GaSb on GaAs (001): Monte Carlo simulation and experimental study by N. Fazouan; E. Atmani; F. El Kasri; M. Djafari Rouhani; A. Esteve (1684-1689).
The growth of GaSb thin films by MBE on GaAs (001) is investigated experimentally, using TEM, and theoretically, using KMC simulations. The atomic scale mechanisms inherent to the growth are discussed and described in the KMC model in which the strain is introduced through an elastic energy term based on a valence force field approximation. We observe that the first two monolayers of the deposited films form strained three-dimensional clusters, but further deposition induces film relaxation and rough 3D growth with valley formation presenting (111) facets with unstable bottoms. We show that the roughening morphology and creation of grooves during growth are in agreement with experimental TEM observations.

Solubility of NiO in Pechini-derived ZrO2 examined with SQUID magnetometry by Joshua T. White; Ivar E. Reimanis; James R. O’Brien (1690-1696).
The solubility of NiO in ZrO2 was studied by X-ray diffraction, TEM, and SQUID magnetometry. Lattice parameter measurements from a similar, established oxide system, NiO−10YSZ, were first used to show that SQUID magnetometry can effectively measure solubility. ZrO2 specimens with 0, 0.5, 1, 2, 3, and 5 percent by mol NiO were prepared via the Pechini method. The specimens were calcined in air at 500, 600, and 1000 °C. The paramagnetic response of the specimens measured with SQUID magnetometry revealed that up to 5 percent by mol NiO is soluble in ZrO2 for specimens calcined at 500 and 600 °C. The relatively large solubility compared with NiO−10YSZ occurs due to the very fine grain size (5–10 nm). The fine grain size is also responsible for stabilizing the tetragonal phase of ZrO2. At the 1000 °C calcination temperature, the ZrO2 is entirely monoclinic, exhibits larger grains (>45 nm), and only dissolves about 0.5 percent by mol or less NiO. The correlations between grain size, ZrO2 polytype, and NiO addition are discussed.

Rare-earth-sesquioxide ceramics have been found to possess potential applications in solid-state lasers due to their excellent physical and chemical properties as well as low cost. In this paper, composite powders with the composition of Dy2(1−x)Tm2x O3 were prepared by ball milling method and corresponding ceramics were obtained using the pressureless sintering technique. Phase structure and vibrational spectra were investigated using X-ray diffraction, Raman spectrometer, and FT-IR spectrometer. It is shown that the mixture of Dy2O3 and Tm2O3 converts to an ordered solid solution of body-centered cubic structure after heat treatment at 1,100 °C for 4 h. It is also found that the cell constants of ceramics decrease linearly with the increase of Tm2O3 content. Raman spectra analysis demonstrates that bond length plays a major role in determining the frequencies of Raman bands at high-frequency range and that peak positions exhibit a blue shift with the increase of Tm2O3 content due to decreasing cell constant. Similar phenomenon is also observed in infrared spectra, which shows linearly increasing infrared band frequency with decreasing cell volume. The ball milling method used for preparing composite powders and vibrational spectra analysis in this work provide some important references for the study of laser ceramics containing Dy2O3 and Tm2O3.

Polyamide 66/organoclay nanocomposite fibers prepared by electrospinning by Li Wang; Yi-Bo Yan; Qing-Quan Yang; Jian Yu; Zhao-Xia Guo (1702-1709).
PA66/organoclay nanocomposite fibers have been prepared by electrospinning melt pre-compounded PA66/organoclay nanocomposites in hexafluoroisopropanol. The influences of solution concentration and organoclay loading on the morphology of the electrospun fibers have been studied by scanning electron microscopy. The dispersion of organoclay in PA66 fibers has been characterized by X-ray diffraction and transmission electron microscopy, showing that partial exfoliation and partial intercalation state of organoclay can be obtained when organoclay content is as high as 7.5 wt%. Organoclay platelets are oriented parallel to the axial direction of the fibers. The influences of organoclay loading on the crystallization behavior of PA66 and mechanical properties of the electrospun fiber mats have been investigated. Only α crystals of PA66 were observed in the fibers regardless of organoclay loading. Organoclay shows strong reinforcing effect, leading to a significant increase in tensile modulus.

Synthesis of nanocrystalline boron carbide from boric acid–sucrose gel precursor by Trinadha Raja Pilladi; K. Ananthasivan; S. Anthonysamy; V. Ganesan (1710-1718).
A novel method, based on the combustion of boric acid–sucrose xerogel was developed to synthesize nanocrystalline boron carbide powder. This xerogel was pyrolyzed at 1273 K. Boron carbide was obtained by heating this precursor at 1823 K. The yield of boron carbide was improved by the use of a novel graphite crucible designed for this purpose. The xerogel and the precursor were characterized by using Fourier transform infrared spectroscopy. The constituent phases were identified by using X-ray diffraction while their elemental composition was established with the help of chemical assay. The microstructure of the final product was examined with the help of scanning electron microscopy and transmission electron microscopy. This study demonstrates that the yield of boron carbide would be enhanced to about 48% while the free carbon content in the final product could be reduced to about 6 wt%. These are significant improvements over similar studies reported so far on the gel-based preparation of boron carbide.

X-ray diffraction pattern and AFM results confirm the nanostructure of p-ZnGa2Se4/n-Si. The unit cell lattice parameters, the crystallite size L, the dislocation density δ, and the main internal strain ε were calculated. The temperature and frequency-dependent electrical characteristics of the Al/p-ZnGa2Se4/n-Si/Al heterojunction diode (HJD) have been investigated to determine the interface states which are responsible for the non-ideal behavior of the characteristics of the diode. The capacitance–voltage (CV), conductance–voltage (GV), and series resistance–voltage (R sV) characteristics of the diode have been analyzed in the frequency range of 5 kHz–1 MHz and temperature range of 303–423 K. The interfaces states of the diode were determined using conductance–voltage technique. The interface state density profile for the diode was obtained as a function of temperature and frequency. The values of the built-in potential V bi, the doping concentration N d and the barrier height φ b(C–V) of the diode were calculated at different temperatures and frequencies. Our experimental results revealed that both the series resistance and interface state density values must be taken into account in studying the impedance spectroscopy of HJD to stand up their performance for electronic applications characteristics.

Vibrational and AFM studies of adsorption of glycine on DLC and silicon-doped DLC by M. Ahmed; A. J. Byrne; J. McLaughlin; A. Elhissi; D. A. Phoenix; W. Ahmed (1729-1736).
A better understanding of protein adsorption onto surfaces of materials is required to control biocompatibility and bioactivity. Diamond-like carbon (DLC) is known to have excellent biocompatibility. Various samples of a-C:H and silicon-doped a-C:H thin films (Si-DLC) were deposited onto silicon substrates using plasma-enhanced chemical vapour deposition (PECVD). Subsequently, the adsorption of the simplest amino acid glycine onto the surfaces of the thin films was investigated to elucidate the mechanisms involved in protein adhesion. The physicochemical characteristics of the surfaces, before and after adsorption of glycine, were investigated using Raman spectroscopy and atomic force microscopy (AFM). The Raman study highlighted a slight decrease in the I D/I G ratio with increasing the silicon dopant levels. Following exposure to glycine solutions, the presence of bands at ~1735 and ~1200 cm−1 indicates that the adsorption of glycine onto the surfaces has taken place. Glycine was bound to the surfaces via both deprotonated carboxyl and protonated amino groups whilst, as the silicon content in the DLC film increased the adsorption of glycine decreased. AFM analysis showed that the surface roughness increased following exposure to glycine. These results show that at low silicon doping the adsorption of the amino acid was enhanced whilst increased doping levels led to a reduced adsorption compared to undoped DLC. Therefore, doping of DLC may provide an approach to control the protein adsorption.

The preparation of carbon-encapsulated Fe/Co nanoparticles and their novel applications as bifunctional catalysts to promote the redox reaction for p-nitrophenol by Jun Xue; Houkui Xiang; Kaipeng Wang; Xiaorong Zhang; Shengjun Wang; Xuehua Wang; Hong Cao (1737-1744).
As a common organic pollutant in industrial and agricultural wastewater, p-Nitrophenol (p-NP) is difficult to be degraded naturally. Though, various methods have been developed for degradation of p-NP, the utilization of catalysts to electrochemically degrade p-NP became a novel effective way. In this article, two magnetic nanoparticles (carbon-encapsulated iron, Fe/C; carbon-encapsulated cobalt, Co/C) were prepared. Through a series of physical phase characterization, we found that the average dimension of the prepared magnetic nanoparticles arrived at 60 nm for Fe/C and 80 nm for Co/C, and within such small dimensions, the prepared nanoparticles might have some remarkable catalytic characters in electrochemical degradation of p-NP. Therefore, two novel types of Fe/C and Co/C modified glassy carbon electrodes were fabricated to investigate their catalytic activity for p-NP degradation. In our results, both of the two modified electrodes showed favorable stability and excellent electro-catalytic activity for p-NP degradation. In addition, two modified electrodes also exhibited favorable electro-catalytic reductive ability for p-NP. The electrochemical reactions on the surface of the two modified electrodes were all diffusion controlled processes. Therefore, Fe/C and Co/C were excellent bifunctional catalysts which could be considered as a practical way to be applied in industrial hydrogenation and oxidative degradation of organic compounds.

Correlation of crystallization mechanism with the structural and soft magnetic properties of FeSiBPCu nanocrystalline alloys has been investigated on the basis of Johnson–Mehl–Avrami kinetic model, transmission electron microscopy, and extended random anisotropy model. Pre-existent α-Fe clusters in melt-spun alloys with a size much smaller than critical nucleus size crystallize at a steadily increasing nucleation rate owing to the chain effect of rising constituent fluctuation. This unique crystallization mechanism leads to the formation of fine and uniform nanocrystallites and therefore superior soft magnetic properties. In contrast, pre-existent α-Fe clusters with a size approximate to the critical nucleus size nucleate gradually at the initial stage of crystallization process driven by thermal activation over the energy barrier of nucleation, and pre-existent α-Fe nanocrystallites with a size larger than critical nucleus size grow directly at the initial stage of crystallization process. Grains formed at the initial stage enlarge further in the subsequent crystallization process, which gives rise to a continuous decrease of the nucleation rate and the deterioration of soft magnetic properties.

The effect of severe plastic deformation on intermetallic particles was investigated using high-pressure torsion on an Al–1Mg–0.2Si–0.2Fe–0.3Mn alloy and an Al–3Mg–0.2Si–0.2Fe–0.3Mn (wt%) alloy. Extensive optical microscopy and scanning electron microscopy was performed to analyse the intermetallic particles using image analysis software. It was found that all the intermetallic particles decreased in size with increasing strain whilst their spatial distribution was homogenised. A greater decrease in size was found for the intermetallic particles present in Al–1Mg alloy and the possible causes are discussed. Even though the strain near the centre of the sample is close to zero, refinement of intermetallic particles is substantial at this location.

In order to improve the frequency range operation of Ni–Zn ferrites with the Ni0.7Zn0.3Fe2O4 stoichiometry in this study, they were doped with V2O3 at different concentrations (0, 0.25, 0.50, and 0.75 wt%). The samples were prepared by the solid-state reaction at 1250 °C for 24 h. The content and location of Vanadium in these ferrites allow us to determine its influence on their microstructure and magnetic properties. A single cubic spinel phase with lattice parameter variation was determined by the refinement of X-ray diffraction patterns. This refinement was achieved using the Rietveld method. The lattice parameter presents a slight enhancement with increasing Vanadium content up to 0.50 wt% of V2O3. The increase of intragrain porosity and the segregation of Vanadium at the grain boundary in samples with higher concentration of Vanadium show a narrow grain-size distribution that leads to a resonant character of the magnetic domain wall. A wide grain-size distribution determined in lower concentration of Vanadium results in a mixed resonant-relaxation dispersion. The use of V2O3 as a dopant in Ni–Zn ferrites increases the frequency operation and coercivity, H c, without abruptly degrading the saturation magnetization, M s. We, therefore conclude, that Vanadium may be used as a strong dopant for the preparation of ferrites for any particular high-frequency application.

BiFeO3-modified lead-free piezoceramics Li0.05(Na0.515K0.485)0.95Nb0.8Ta0.2O3 (LKNNT) were successfully fabricated by conventional method to investigate its influences on phase structure and electricity as well as mechanical properties. A tiny amount of BiFeO3 (BF) changes the phase structure of LKNNT to tetragonal and further to pseudocubic, and also effectively improves the sintering ability and densification of LKNNT which enhances the mechanical property. The LKNNT piezoceramics with the addition of 1 mol% BF has the bulk density of 5.02 g/cm3 and an enhanced fracture strength of 142 MPa which is even higher than that of the sample of similar composition prepared by spark plasma sintering, also possesses room temperature electric properties of d 33* ~ 225 pm/V, k p ~ 36.3%, ε r ~ 1140, tgδ ~ 0.018, T c ~ 305 °C and Q m ~ 80. The d 33* remains constant up to 150 °C and the change ratio of dielectric property largely decreases over the temperature range of −50–150 °C, which can be attributed to the temperature-independent phase structure of LKNNT piezoceramics, making the ceramics as a promising candidate for actual applications.

Ceramics in the (1 − x)PbZrO3x[0.3Bi(Zn1/2Ti1/2)O3–0.7PbTiO3] solid solution system with 0.48 ≤ x ≤ 0.56 were investigated. A morphotropic phase boundary separating rhombohedral and tetragonal perovskite phases was identified at x = 0.52. This composition displays the maximum remanent polarization P r of 40.7 μC/cm2 and the best piezoelectric coefficient d 33 of 311 pC/N in the pseudo-binary system. However, the Curie temperature T c for this MPB composition is 291 °C, much lower than initially expected.

Pyroelectric properties of a ferroelectric superlattice with surface transition layers by Lian Cui; Quan Xu; Xu Xu; Yu Chun Li; Ze Long He; Ji Xin Che; Tian Quan Lü (1780-1786).
The transverse Ising model within the framework of the mean-field theory is used to investigate a ferroelectric superlattice composed of two different alternating ferroelectric slabs A and B, with the surface transition layer within each slab and an antiferroelectric interfacial coupling between two slabs. The combined influence of the surface transition layer and antiferroelectric interfacial coupling on the pyroelectric properties is discussed in detail. The results show that the pyroelectric properties of a ferroelectric superlattice present some interesting phenomena because of the existence of surface transition layer.

Discussion on the influence of DES content in CA-based polymer electrolytes by S. Ramesh; R. Shanti; Ezra Morris (1787-1793).
The degree of crystallinity in the matrix formed by cellulose acetate (CA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were reduced by embedding with deep eutectic solvent (DES) which is a type of ionic mixture synthesized from choline chloride and urea in a specific ratio. The fabrications of thin films were done by solution casting technique. The sample with composition of CA:LiTFSI:DES (28 wt%:12 wt%:60 wt%) appears as the highest conducting sample with the calculated value of 2.61 × 10−3 S cm−1 at ambient temperature. This high conducting sample possesses low relative viscosity so as to have high ion fluidity of 0.19. SEM micrographs were used to study the structural alternation that took place in the presence of DES at different ratio in the polymer electrolytes matrix. The dielectric loss tangent plot reveals the low relaxation time for high conducting sample which has immense movements of lithium conducting ion (Li+). The enhancement in the ionic conductivity of the DES plasticized samples with temperature obeys Arrhenius rule.

Piezo-resistance effect in composite based on cross-linked polydimethylsiloxane and polyaniline: potential pressure sensor application by T. del Castillo-Castro; M. M. Castillo-Ortega; J. C. Encinas; P. J. Herrera Franco; H. J. Carrillo-Escalante (1794-1802).
Composites that incorporate an electrically conducting filler, the hydrochloric polyaniline (PANI-Cl), into hydroxy-terminated polydimethylsiloxane (HO-PDMS) matrix were evaluated for DC electrical, mechanical, thermal, morphological and piezo-resistive properties. The main focus of the study was on the electrical–mechanical behavior of these composites in view of possible piezo-resistive sensor application. The percolation threshold of conductivity was determined to be around 11.5 wt% of PANI-Cl. Compression/expansion cyclic experiments showed that the filler content modified the stiffness, the magnitude of Mullins effect and the hysteresis behavior in elastomeric composites. The piezo-resistive response of composites differed depending on the sample composition and also, on the strain rate. Composites with concentration above the percolation threshold exhibited at least three-order change of its electrical resistance in a narrow interval of maximum 2% of deformation. The piezo-resistive sensitivity and the reproducibility of response suggested the possibility to use this material as a transducer in an electromechanical device.

The block copolymers of poly 2,2,3,4,4,4-hexafluorobutyl methacrylate-block-poly[3-(trimethyoxysilyl)propyl methacrylate] (PHFMA-b-PTMSPMA) were synthesized via atom transfer radical polymerization and used for the preparation of organic/inorganic hybrid materials by the sol–gel approach. The polymers were characterized by gel permeation chromatography, Fourier transform infrared and 1H nuclear magnetic resonance. The properties of the hybrid materials were investigated by Scanning electronic microscopy, contact angle, Scotch tape test, transmittances measurement, differential scanning calorimetry, and thermogravimetric analysis. The results were as follows: First, the hybrid materials had surface roughness, good hydrophobicity (>95° in contact angle with water), and could improve the contact angle of glass from 65.2° to 99.9° (the content of TMSPMA was 4.9 wt% in its polymer). Second, the adhesion of the hybrid materials to glass were enhanced by incorporating TMSPMA. Third, light transmittances of all the hybrid materials were above 90% in the visible range. Finally, the thermal stability of the hybrid materials were enhanced by incorporating silica moiety.

Pyreno-chalcone dendrimers as an additive in the redox couple of dye-sensitized solar cells by Perumal Rajakumar; Kathiresan Visalakshi; Shanmugam Ganesan; Pichai Maruthamuthu; Samuel Austin Suthanthiraraj (1811-1818).
Novel pyreno-chalcone dendrimers 1, 2, and 3 were synthesized and their ability to act as an additive in the redox couple (I/I3 ) of dye-sensitized nanocrystalline TiO2 solar cell has been tested. The redox couple doped with pyreno-chalcone dendrimer 3 gave a short circuit photocurrent density (J sc) of 7.40 mA/cm2, open circuit voltage (V oc) of 820 mV, and a fill factor of 0.51, corresponding to an overall conversion efficiency (η) of 7.89% under 40 mW/cm2 irradiation.

Synthesis and electrochemical performance of spherical FeF3/ACMB composite as cathode material for lithium-ion batteries by Li Liu; Meng Zhou; Xingyan Wang; Zhenhua Yang; Fanghua Tian; Xianyou Wang (1819-1824).
To improve the rate capability and cyclability of FeF3 cathode for Li-ion batteries, FeF3 has been modified by forming FeF3/ activated carbon microbead (ACMB) composite. The FeF3/ACMB composite is successfully achieved via a simple chemical route. The morphology and structural properties of the samples are investigated by X-ray diffraction and scanning electron microscopy (SEM). SEM observations demonstrate that FeF3/ACMB composite has a distinct spherical morphology. Electrochemical tests show that the FeF3/ACMB composite cathode has higher capacity, better cycleability, and better rate capability than pristine FeF3. Electrochemical impedance spectra indicate that the FeF3/ACMB composite electrode has low electrochemical resistance compared with pristine FeF3, indicating the enhanced conductivity of the FeF3/ACMB composite.

The development of novel molecules for the creation of nanometer structures with specific properties has been the current interest of this research. We have developed a set of molecules from hydrophobic ω- and α-amino acids by protecting the –NH2 with Boc (t-butyloxycarbonyl) group and –CO2H with para-nitroanilide such as BocHN–Xx–CONH–(p–NO2)·C6H4, where Xx is γ-aminobutyric acid (γ-Abu), (l)-isoleucine, α-aminoisobutyric acid, proline, etc. These molecules generate various nanometer structures, such as nanofibrils, nanotubes and nanovesicles, in methanol/water through the self-assembly of bilayers in which the nitro benzene moieties are stacked in the middle and the Boc-protected amino acids parts are packed in the outer surface. The bilayers can be further stacked one over the other through hydrophobic interactions to form multilayer structure, which helps to generate different kinds of nanoscopic structures. The formation of the nanostructures has been facilitated through the participation of various noncovalent interactions, such as hydrophobic interactions, hydrogen bonding and aromatic π-stacking interactions. Fluorescence microscopy and UV studies reveal that the nanovesicles generated from pro-based molecule can encapsulate dye molecules which can be released by addition of acid (at pH 2). These single amino acid based molecules are both easy to synthesize and cost-effective and therefore offer novel scaffolds for the future design of nanoscale structures.

Cu(In,Ga)Se2 thin films have been prepared by selenization of the evaporated metallic precursors on transparent and conductive ITO-coated as well as uncoated glass substrates, by starting from slightly Cu-rich or Cu-poor overall metallic proportions. The objective is to determine the influence of the Cu availability on the constituents distribution achieved after selenization, by means of data obtained at several film depths by grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy that have been related to the overall optical and structural characteristics of the material. This study points out the possibility of achieving homogeneous or graded absorber layers, showing for homogeneous samples an ITO/Cu(In,Ga)Se2 interface with ohmic electrical characteristics suitable to act as back contact for semitransparent photovoltaic devices.

Two new organic sensitizers (TP12) containing triarylamine donor and a cyanoacrylic acid acceptor bridged by alkoxy- or fluorine-substituted phenylene spacer have been synthesized and explored as a sensitizer in dye-sensitized solar cells (DSCs). The absorption spectra, electrochemical and photovoltaic properties of TP12 are extensively investigated. The DSC based on dye TP1 shows the best photovoltaic performance: a short-circuit photocurrent density (J SC) of 13.5 mA cm−2, an open-circuit photovoltage (V OC) of 702 mV, and a fill factor (ff) of 0.68, corresponding to an overall conversion efficiency of 6.4% under standard global AM1.5 solar light conditions. The results demonstrate that structural modification of substituting groups on π-spacer is importance for realizing a high efficiency DSC.

Fabrication and fluorescence properties of multilayered core–shell particles composed of quantum dot, gadolinium compound, and silica by Yoshio Kobayashi; Takuya Nozawa; Tomohiko Nakagawa; Kohsuke Gonda; Motohiro Takeda; Noriaki Ohuchi (1852-1859).
A preparation method for multilayered quantum dot/silica/gadolinium compound/silica (QD/Si/Gd/Si) core–shell particles is proposed. Silica (Si)-coated quantum dot (QD/Si) core–shell particles were prepared by a Stöber method at room temperature in water/ethanol solution with TEOS and NaOH in the presence of QD nanoparticles. Succeeding gadolinium compound (Gd)-coating of the QD/Si core–shell particles was performed by a homogeneous precipitation method using Gd(NO3)3, urea, and polyvinylpyrrolidone in the presence of the QD/Si particles, which resulted in production of multilayered QD/silica/gadolinium compound (QD/Si/Gd) core–shell particles. For Si-coating of the QD/Si/Gd particles, the Stöber method was performed at room temperature in water/ethanol solution with TEOS and NaOH in the presence of the QD/Si/Gd particles. Consequently, Si-coated QD/Si/Gd, i.e., multilayered QD/Si/Gd/Si, core–shell particles were obtained. The QD/Si/Gd/Si particles revealed strong fluorescence, which was almost comparable to the QD particles with no shells. These particles are expected to be harmless to living bodies, and have dual functions of magnetic resonance imaging and fluorescence.

Thermoluminescence properties of γ-irradiated KCaSO4Cl: X (X = Ce, Dy, Mn or Pb) by P. S. Thakre; S. C. Gedam; S. J. Dhoble (1860-1866).
A new phosphor KCaSO4Cl is very interesting for thermoluminescent properties. In this article, we present results concerning the main dosimetric properties of KCaSO4Cl activated by Ce, Dy, Mn, and Pb at various concentrations. Polycrystalline KCaSO4Cl: (Ce; Dy; Ce, Dy; Mn; Ce, Mn; Pb and Ce, Pb) phosphors prepared by solid state diffusion method have been studied for its thermoluminescence (TL) characteristics. The TL glow curves of γ-irradiated all KCaSO4Cl samples show strong single glow peaks indicating that only one type of trap can be formed. The intensity of the TL glow peaks increases with increase of the γ-ray dose to the samples but the intensity of the TL glow peaks increases with decrease of the concentration of the dopent. The sensitivity of all the phosphors presented here are more than that of CaSO4: Dy. The phosphors have a simple TL glow curve structure with a prominent peak at the lower temperature side. TL response, fading, reusability of the phosphors are also studied, and it is found that the phosphor is quite suitable for use in dosimetry of ionizing radiations.

The full exfoliation graphene oxide (GO) nanosheets were synthesized by an improved Hummers’ method. The phenylethynyl terminated thermosetting polyimide (PI) and PI/GO nanocomposites were prepared via a polymerization of monomer reactants process. Thermogravimetric analysis indicated that the incorporation of GO increased the thermal stability of the PI at low filling content. The friction and wear testing results of the PI and PI/GO nanocomposites under dry sliding condition against GCr15 steel showed that the addition of GO evidently improved the friction and wear properties of PI, which were considered to be the result of the formation of uniform transfer film and the increasing of load-carrying capacity. The friction and wear properties of the PI and PI/GO nanocomposites were investigated on a model ring-on-block test rig under dry sliding conditions against the GCr15 steel. Experimental results showed that the addition of GO evidently improved the friction and wear properties of PI, which were considered to be the result of the formation of uniform transfer film and the increasing of load-carrying capacity. The optimum GO content of nanocomposite for tribological properties is 3 wt%, which could be a potential candidate for tribo-material under dry sliding condition against GCr15 steel.

Co-sintering and microstructural characterization of steel/cobalt base alloy bimaterials by Céline Pascal; Aurélie Thomazic; Annie Antoni-Zdziobek; Jean-Marc Chaix (1875-1886).
The objective of this study is to process a bimaterial that combines the mechanical strength of a martensitic steel (X3CrNiMo13-4) and the wear and corrosion resistance of a cobalt base alloy (Stellite 6). The powder metallurgy route includes three steps: co-compaction, debinding, and pressureless co-sintering. The experimental approach consists in studying the compaction, the debinding and the sintering behavior of single materials (dimensional changes during sintering, microstructure, and hardness after sintering) before studying co-sintering. The co-sintering temperature range is defined from thermo-chemical calculations and single material sintering experiments especially for Stellite 6. Finally, the co-sintering ability is evaluated (green and final densities, shrinkage mismatch, coefficient of thermal expansion…) and the bimaterial sintering is studied. Despite the shrinkage mismatch of single materials, cohesion is achieved between the two materials through the infiltration of the supersolidus liquid from the Co base alloy to the steel and through the formation of an interdiffusion layer between the two materials characterized by a composition gradient.

Supramolecular morphology of two-step melt-spun poly(dioxanone) fibers by Yutaka Kawahara; Atsushi Nakayama; Masatoshi Shioya; Masaki Tsuji; Hideki Yamane; Tadahisa Iwata (1887-1892).
Structure of poly(dioxanone) (PPDX) fibers produced through a two-step melt-spinning process with an additional short-period annealing above the melting temperature of PPDX was investigated and the effect of annealing on the degradation behavior was discussed. The morphological study carried out by etching the fibers using a phosphate or permanganate solution suggested that the fibers take a skin–core structure, and both the skin layer and the core region consist of a bundle of microfibrils. The micro-beam X-ray diffraction analysis revealed that the short-period annealing in the production process only slightly promotes the crystallization in the skin layer but contributes to increasing the packing of amorphous chains near the skin, which seems to be the controlling factor of the hydrolytic degradation behavior of the fibers.

Synthesis of linear ZnO structures by a thermal decomposition method and their characterisation by K. K. Devarepally; D. C. Cox; A. T. Fry; V. Stolojan; R. J. Curry; M. Munz (1893-1901).
The semiconductor zinc oxide (ZnO) is a promising material for applications in optoelectronics, photochemistry and chemical sensing. Furthermore, ZnO structures can be grown with a large variety of sizes and shapes. Devices with ZnO rods or wires as their core elements can be used in solar cells, gas sensors or biosensors. In this article, an easy approach for the non-aqueous wet chemical synthesis of ZnO structures is presented that employs the solvent trioctylamine (TOA) and the surfactant hexamethylenetetramine (HMTA). Using the thermal decomposition method, rod-shaped structures were grown that are suitable for the fabrication of electrical devices. A detailed study was carried out to investigate the effects of various reaction parameters on the growth process. Both the concentration of the surfactant HMTA and the zinc precursor zincacetylacetonate (Zn(acac)2) were found to show strong effects on the resulting morphology. In addition to structural characterisation using XRD, SEM and TEM, also optical properties of rod-shaped ZnO structures were measured. Rod-shaped structures were obtained for the following conditions: reaction time 4 h, reaction temperature 70 °C, 1 mmol of Zn(acac)2, 4 mmol of HMTA and 25 mL of the solvent TOA. Photoluminescence and photoluminescence excitation spectroscopy of samples grown under these conditions provided information on levels of defect states that could be critical for chemical sensing applications. Two narrow peaks around 254 and 264 nm were found that are well above the band gap of ZnO.

Heterogeneous plastic deformation behavior of two bimodal ultrafine-grained nickel materials with different ultrafine-grained (UFG) and coarse-grained (CG) components fractions was investigated experimentally at the grain level. The prismatic specimens were deformed quasistatically up to 10% axial plastic strain using compression test at room temperature. The local microstructure of the initial and deformed samples was measured by electron backscattered diffraction pattern analysis in a scanning electron microscope. It was found that the plastic deformation of bimodal materials is highly heterogeneous and the degree of heterogeneity depends strongly on the grain size distribution and the volume fraction of the CG component. The large localized plastic strain within the coarse grains was observed during compression. The strain localization resulted in occurrence of debonding and cracks in the UFG region or in the interface between CG and UFG components.

Few-layer nano-graphene structures with large surface areas synthesized on a multifunctional Fe:Mo:MgO catalyst system by Enkeleda Dervishi; Alexandru R. Biris; Fumiya Watanabe; Jean L. Umwungeri; Thikra Mustafa; Joshua A. Driver; Alexandru S. Biris (1910-1919).
We present the synthesis of nano-graphene structures with large surface areas and high purity over a high-yield Fe:Mo:MgO catalytic system. Two different hydrocarbon sources, acetylene and methane, were used, and their role in determining the size and morphology of the few-layer graphene sheets was studied. In addition, varying the active metal loading of the catalyst system influenced the formation and type of the resulting carbon nano-structures, e.g., carbon nanotubes or few-layer graphene. Growth of nano-graphene sheets was detected after only 5-min reaction time over this multifunctional catalytic system. High purity and crystalline graphene structures were synthesized indicating another advantage of using this particular catalyst system. This catalytic chemical vapor deposition can be scaled up for large-scale few-layer graphene production.

Small-angle neutron scattering of multiphase secondary hardening steels by Mikaël Perrut; Marie-Hélène Mathon; Denis Delagnes (1920-1929).
Alloying secondary hardening steels with Ni and Al allows the precipitation of an intermetallic phase B2-NiAl in addition to the classical secondary carbides precipitation, adding up the advantages of both types of precipitation (Erlach et al. Mater Sci Eng A 429:96, 2006; Erlach et al. Int J Microstruct Mater Prop 3:373, 2008). Small-angle neutron scattering experiments were carried out to analyse the nanometric scale precipitation of a martensitic steel containing a double precipitation of carbides and intermetallic phase. The precipitates size, volume fraction and chemical composition for both carbides and intermetallic phases according to the tempering time were estimated and discussed. In addition, experimental cobalt-free grades containing a single precipitation or a double precipitation were manufactured and analysed. Relationship between measured tensile yield strengths and the nanometre-sized particles are suggested, showing that both populations of precipitates have a relevant impact on the mechanical properties.

Tunable plasmonic properties of silver nanorods for nanosensing applications by Jagmeet Singh Sekhon; S. S. Verma (1930-1937).
Localized surface plasmon resonance (LSPR) sensitivity to the surrounding medium refractive index has been studied for silver nanorods using Gans theory including the effect of retardation and surface scattering. The simulation results show the refractive index sensitivity (eV/RIU) maxima positions at width of 9, 6, and 4 nm for aspect ratios of 2, 3, and 4, respectively. Based on the sensing figure of merit (FOM), 9 nm is found to be a significant nanorod width, where the FOM dependence on width with respect to aspect ratio inverts. However, the optimal nanorod width for both the FOM and the modified figure of merit (MFOM) is about 6 nm for aspect ratios of 2, 3, and 4. A comparison with gold shows that silver nanorods exhibit relatively higher FOM and MFOM and thus, making them potential candidates for biochemical nanosensing applications.

Lead-free piezoelectric materials have grown in importance through increased environmental concern and subsequent EU and worldwide legislation, with the aspiration to reduce the use of Pb-based materials in all sectors. Integration of the next generation of lead-free piezoelectric materials with substrates to form functional micro devices has received less attention. Low temperature synthesis methods for K0.5Na0.5NbO3 (KNN) powder were developed to overcome the issue of poor purity of the final product during high temperature sintering. Molten hydroxide synthesis (MHS), derived from molten salt synthesis (MSS), has been developed to overcome a Na ion preference in the molten salt synthesis reaction that leads to NaNbO3 production instead of KNN when stoichiometric amounts of precursors are used. MHS makes use of a KOH molten reaction aid in place of the NaCl/KCl molten salt mix of the MSS. In a two stage reaction K rich intermediate niobates are produced and subsequent reactions with Na species produce KNN.

Structural and dielectric properties of Na1−x Ba x Nb1−x (Sn0.5Ti0.5) x O3 ceramics by H. Khelifi; A. Aydi; N. Abdelmoula; A. Simon; A. Maalej; H. Khemakhem; M. Maglione (1943-1949).
Lead-free (1 − x)NaNbO3/xBa(Ti0.5Sn0.5)O3 (x = 0.1, 0.125, 0.15, 0.175, 0.2, and 0.3) ceramics were elaborated by the conventional ceramic technique. Sintering has been made at 1523 K for 2 h. The crystal structure was investigated by X-ray diffraction with CuKα radiation at room temperature. As a function of composition, these compounds crystallize with tetragonal or cubic symmetry. Dielectric measurements show that the materials have a classical ferroelectric behavior for compositions in the range 0.10 ≤ x ≤ 0.15 and relaxor one for compositions in the range 0.15 < x ≤ 0.30. Temperatures T C or T m decrease as x content increases. The ferroelectric behavior has been confirmed by hysteresis characterization. For x = 0.1, a piezoelectric coefficient d 31 of 42.146 pC N−1 was obtained at room temperature. The evolution of the Raman spectra was studied as a function of temperature for x = 0.1.

Microstructural properties of electrochemically synthesized ZnSe thin films by T. Mahalingam; V. Dhanasekaran; R. Chandramohan; Jin-Koo Rhee (1950-1957).
In this study, we report the electrosynthesis of zinc selenide (ZnSe) thin films on indium-doped tin oxide-coated glass substrates. The deposited ZnSe thin films have been characterized for structural (X-ray diffraction), surface morphological (scanning electron microscopy), compositional (energy dispersive analysis by X-rays), photo luminescence property, and optical absorption analysis. Formation of cubic structure with preferential orientation along the (111) plane was confirmed from structural analysis. In addition, the influence of the deposition potential on the microstructural properties of ZnSe is plausibly explained. The optical properties of ZnSe thin films are estimated using the transmission spectrum in the range of 400–1200 nm. The optical band gap energy of ZnSe thin films was found to be in the range between 2.52 and 2.61 eV. Photoluminescence spectra were observed at blue shifted band edge peak. The morphological studies depict that the spherical and cuboid shaped grains are distributed evenly over the entire surface of the film. The sizes of the grains are found to be in the range between 150 and 200 nm. The ZnSe thin film stoichiometric composition was observed at optimized deposition condition.

Fluorinated polyimide–silica films with low permittivity and low dielectric loss by Yihe Zhang; Li Yu; Qingsong Su; Hong Zheng; Haitao Huang; H. L. W. Chan (1958-1963).
A sol–gel process was used to prepare polyimide–silica hybrid films from the fluorinated polyimide precursors (6FDA-ODA) and tetraethylorthosilicate (TEOS) in N,N-dimethyl acetamide. The hybrid film was then treated with hydrofluoric acid to remove the dispersed silica particles, leaving inside the film pores with diameters ranged from 80 nm to 1 μm, which depended on the size of the silica particles. The chemical structures and morphology of the hybrid and porous films were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The synthesized porous fluorinated polyimide films show low relative dielectric permittivity of 1.9, rendering them promising for microelectronic packaging materials.

A series of Zn-doped cadmium sulfide (CdS:Zn) nanopowders were prepared by a simple coprecipitation method at room temperature, mixing the stoichiometric amount of reactants in a Milli-Q water solvent. The composition of nanopowders was accurately adjusted by controlling the molar ratio of Cd, Zn acetate in the mixed reactants. Spectroscopic studies on as prepared nanopowders were investigated by using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy, Raman, UV–Vis absorption, Field emission–scanning electron microscope–energy-dispersive X-ray analysis, and photoluminescence. Broad nature of XRD peaks confirms that as prepared powders are in nanosize and cubic structure at room temperature. Doping with Zn in CdS does not lead to any structural phase transformation but introduces a decrease in the lattice constants. Raman spectrum of Zn-doped CdS nanopowders shifts slightly toward higher energy side compared with their pure CdS nanopowders. Exciton–phonon confinement factor (S) varies in between 0.3 and 0.4. At lower wavelength excitation, we observed a broad emission peak maximum centered at 404 nm is attributed to localized band edge emission.

In this study, we report a comparative study of the structural, morphological, and optical properties of the deposited ZnO thin films on Poly Propylene Carbonate (PPC) and glass substrates by direct current (DC) sputtering technique. X-ray diffraction (XRD) spectra of the films on PPC and glass substrates show mainly the ZnO (002) diffraction peaks at 2θ = 34.1 and 34.3o with full width at half maximum (FWHM) of 0.31 and 0.34o, respectively. Scanning electron microscopy (SEM) images show that both ZnO thin films have smooth surface. Photoluminescence (PL) spectra show two peaks, the first intense peak was found in the UV region. The second weak peak was observed in the visible region. The transmission and absorption spectra of the ZnO thin films deposited on both substrates showed that the films have good transmission in the visible region and a good absorption in the UV region. The optical energy gap (E g) values of the deposited ZnO thin films on PPC plastic and glass substrates were derived from absorption measurements and it found to be 3.38 and 3.40 eV, respectively.

A porous carbon foam prepared from liquefied birch sawdust by Rui Wang; Wei Li; Shouxin Liu (1977-1984).
Carbon foam was prepared by submitting birch sawdust to liquefaction, resinification, foaming, carbonization, and activation steps. The foam was characterized by TG and DTG, XRD, SEM, and nitrogen adsorption at 77 K. A mechanism for the formation of the porous carbon foam was proposed. Solid non-graphitized lightweight carbon foams with specific surface areas of 534–555 m2/g and cell sizes of 100–200 μm were obtained, depending on the carbonization or activation temperature used. The intermediate liquefied birch-based resin foam exhibits thermal stability superior to liquefied wood and inferior to phenolic resin, and decomposes rapidly in two stages, at 285.7 and 412.9 °C, respectively. Further activation of the carbon foam in a stream of nitrogen above 800 °C improves the pore structure and homogeneity of the cell size significantly. The matrix of the foams contains a large number of micropores, and the microstructure becomes more ordered as the activation temperature is increased.

Controlled fabrication of noble metal nanoparticles loaded on the surfaces of cyclotriphosphazene-containing polymer nanotubes by Jianwei Fu; Minghuan Wang; Chao Zhang; Qun Xu; Xiaobin Huang; Xiaozhen Tang (1985-1991).
We report on the fabrication of noble metal nanoparticles loaded on the surfaces of cross-linked poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) nanotubes of high stability. PZS nanotubes were first synthesized by precipitation polymerization between hexachlorocyclotriphosphazene and 4,4′-sulfonyldiphenol based on in situ template mechanism. Then the PZS nanotubes were directly used as scafford to load metal Au, Ag, and Pd nanoparticles, respectively, through cation complexation followed by gentle reduction. The structure and morphology of the metal/PZS nanocomposites were determined by means of Fourier transform infrared spectra, energy dispersive X-ray spectroscopy, elemental analysis, X-ray diffraction, scanning electron microscope, transmission electron microscope, and thermogravimetric analysis (TGA). Results showed that the metal/PZS nanocomposites possessed 460 °C of initial thermal decomposition temperature under air atmosphere and the loading amount of metal nanoparticles on the PZS nanotube surfaces could be controlled easily. As-fabricated metal/PZS nanocomposites are expected to have potential applications in catalysis.

Effect of chemical environments on palladium phthalocyanine thin film sensors for humidity analysis by Mohammad Javad Jafari; Mohammad Esmaeil Azim-Araghi; Samira Barhemat (1992-1999).
Chemiresistors based on palladium phthalocyanine (PdPc) thin films were investigated as humidity sensors. The samples were thermally evaporated onto gold electrodes with a thickness about 100 nm. Optical and electrical characteristics of PdPc thin films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrical measurements. The SEM image demonstrates PdPc (30–60 nm) nanosized particles, and XRD pattern shows that thin films are in α-phase at room temperature. Electrical measurements also confirm that PdPc exhibit semiconducting and photoconducting behaviors, and thermal activation energies of thin films were calculated. After that, the sensitivity and reversibility of devices were investigated on exposure to 20–90% RH in various chemical environments at 293 and 323 K. The response time (35–45 s) and recovery time (75–105 s) of sensors were measured at 293 K with respect to different chemical environments. At last, the stability of devices versus different RH% and chemical environments were tested. The sensors show very good stability on exposure to RH for a period of 2 months but their stability has been reduced in ethanol, acetone, and ammonia environments.

An investigation on hot-cracking mechanism of Sr addition into Mg–6Al–0.5Mn alloy by Shuang-Shou Li; Bin Tang; Xin-Yan Jin; Da-Ben Zeng (2000-2004).
The hot-tearing susceptibility of Mg–6Al–0.5Mn alloy decreased with the increasing Sr content (≤0.2 wt%). The related mechanism is described as follows: Sr refines the grain and reduces the tendency of divorced eutectic; Sr decreases the eutectic temperature and results in higher intergranular strength. Both of the above reasons could improve the filling capacity of the melt, resulting in the best hot-tearing-resistant property of the alloy.

Influence of Y on the phase composition and mechanical properties of as-extruded Mg–Zn–Y–Zr magnesium alloys by Jingfeng Wang; Pengfei Song; Shan Gao; Yiyun Wei; Fusheng Pan (2005-2010).
The influence of Y on the microstructure, phase composition and mechanical properties of the extruded Mg–6Zn–xY–0.6Zr (x = 0, 1, 2, 3 and 4, in wt%) alloys has been investigated and compared by optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer and tensile testing. The increase in Y content has shown grain refinement effects on the microstructure morphologies of the extruded alloys. However, when the content of Y exceeds 2.2 wt%, the grain refinement effect of the Y is not obvious any more with the increase of the Y content. The quasicrystal I-phase (Mg3YZn6), face-centred cubic structure W-phase (Mg3Y2Zn3) and a long period stacking ordered (LPSO) X-phase (Mg12YZn) can precipitate in different ranges of Y/Zn ratio (in at.%) when the Y content in the Mg–Zn–Y–Zr alloys is varied. Comparison of the mechanical properties of the alloys showed that the different ternary Mg–Zn–Y phases have different strengthening and toughening effects on the Mg–Zn–Y–Zr alloys in the following order: X-phase > I-phase > W-phase > MgZn2.

X-ray absorption spectroscopy (XAS) and impedance spectroscopy have been used to study the oxidation state of chromium in (Na0.5Bi0.5TiO3)(1−x)(BiCrO3) x solid solution. XAS measurements reveal that chromium ion occupies the octahedral site in Na0.5Bi0.5TiO3 (NBT). The increase in chromium content increases the distortion in chromium-oxygen octahedral. No shift in the Cr–K edge was observed with increase in chromium content. The XAS measurements suggest that chromium exists either as +3 or +5 state in (Na0.5Bi0.5TiO3)(1−x)(BiCrO3) x . The impedance measurements show a considerable increase in the electrical conductivity with increase in chromium content. The activation energy for conduction mechanism was found to lie between 0.50 and 0.7 eV for all the samples. These measurements indicate that main contribution to the conductivity is because of oxygen defects generated by the incorporation of chromium at B-site of NBT.

Carbon black–clay hybrid nanocomposites based upon EPDM elastomer by Asish Malas; Chapal Kumar Das (2016-2024).
The present study explored the effect of nanoclay on the properties of the ethylene–propylene–diene rubber (EPDM)/carbon black (CB) composites. The nanocomposites were prepared with 40 wt% loading of fillers, where the nanoclay percentage was kept constant at 3 wt%. As the modified nanoclay contains the polar groups and the EPDM matrix is nonpolar, a polar rubber oil extended carboxylated styrene butadiene rubber (XSBR), was used during the preparation of nanocomposites to improve the compatibility. Primarily the nanoclay was dispersed in XSBR by solution mixing followed by ultrasonication. After that EPDM-based, CB–clay hybrid nanocomposites, were prepared in a laboratory scale two roll mill. The dispersion of the different nanoclay in the EPDM matrix was observed by wide-angle X-ray diffraction (WAXD) and high resolution transmission electron microscopy. It was found that the mechanical properties of the hybrid nanocomposites were highly influenced by the dispersion and exfoliation of the nanoclays in the EPDM matrix. Thermo gravimetric analysis, scanning electron microscopy and dynamic mechanical thermal analysis was carried out for each nanocomposite. Among all the nanocomposites studied, the thermal and mechanical properties of Cloisite 30B filled EPDM/CB nanocomposite were found to be highest.

Growth of aligned ZnO nanorods on transparent electrodes by hybrid methods by M. F. Meléndrez; K. Hanks; Francis Leonard-Deepak; F. Solis-Pomar; E. Martinez-Guerra; E. Pérez-Tijerina; M. José-Yacaman (2025-2032).
The fabrication of ZnO (80 nm) thin film was achieved by hybrid atomic layer deposition (ALD) to prevent the reaction between the reactants and conductive layer of the substrates. ZnO nanorods (ZnO-NRs) growth over the substrates was performed by wet chemical procedure in which Zn(NO3)2 and hexamethylenetetramine were used as the precursors. HR-TEM, SAED, FE-SEM, X-ray diffraction (XRD), and UV–Vis spectroscopy were employed to characterize the ZnO-NRs samples on the substrates. XRD and HR-TEM analyses confirmed that the ZnO nanorod structure is hexagonal wurtzite type with growth in the [0001] direction. Length and thickness of the ZnO-NRs ranged between 45  and 90 nm and 480  and 600 nm, respectively. It was observed that the growth rate of NRs in [0001] direction is 10 times higher than in [1000] direction. The growth mechanism and resulted dimensions of nanorods are function of the synthesis parameters (in hybrid ALD process) such as reaction time, temperature, precursor molar ratio, and thickness of ZnO film.

Structure and magnetic properties of soft organic ZnAl-LDH/polyimide electromagnetic shielding composites by Fengzhu Lv; Yueying Wu; Yihe Zhang; Jiwu Shang; Paul K. Chu (2033-2039).
The imidization mechanism, structure, and magnetic properties of organic modified Zinc-aluminum layered double hydroxides/polyimide composites are investigated. During imidization, organic modified Zinc-aluminum layered double hydroxides lose the hydroxyl group and sodium dodecyl sulfate modifier decomposes partly resulting in a loose contact between PI and oxidized Zinc-aluminum layered double hydroxides. The thermal properties of composites are slightly decreased with increasing organic modified Zinc-aluminum layered double hydroxides but the wettability varies oppositely. Comparing to organic modified Zinc-aluminum layered double hydroxides, the saturated magnetization of heated organic modified Zinc-aluminum layered double hydroxides is enhanced slightly due to structural improvement in Fe3O4 crystalline domain. Therefore, the magnetic properties are not affected by imidization procedure. The soft magnetic composites have large potential in electromagnetic shielding.

Well-defined microcapsules with polyamide–polyurea as a hybrid shell have been described for biomedical applications. Interfacial polymerization method with surfactant and cosurfactant was developed for the preparation of the hybrid microcapsules. After reaction, centrifugation, and freeze drying processes, the polyamide–polyurea hybrid microcapsules with porous membranes were successfully fabricated. Compared with previous researches of the single polyamide or polyurea microcapsules, experimental data showed that the hybrid microcapsules have a thicker shell and excellent mechanical property. Various diameters and morphologies for the hybrid microcapsules can be obtained by changing the stirring rate, drying method, and surfactant content.

A casein-polysaccharide hybrid hydrogel cross-linked by transglutaminase for drug delivery by Wenwen Yin; Rongxin Su; Wei Qi; Zhimin He (2045-2055).
A protein-polysaccharide hydrogel was reported as a biocompatible, biodegradable, and non-toxic material that had biomedical applications such as drug delivery. The hydrogel, composed of 10% casein and 1% konjac glucomannan (KGM), was formed with 0.4 wt% transglutaminase (MTG) as the cross-linker. The physicochemical properties of the protein-polysaccharide hydrogel were investigated by SEM observation, FT-IR analysis, swelling ratio test, and stability test. The results of the stability test proved that the hydrogel with KGM had an obviously improved stability. Its degradation rate also decreased from 100% to less than 60% compared with the hydrogel without KGM at the end of the test. The results of the swelling ratio test demonstrated that the addition of KGM restricted the mobility of the chains, and decreased the swelling ratio of the hydrogel. The results of the FT-IR revealed hydrogen bond interactions during the gelation process upon the addition of KGM. To investigate in vitro release behavior, docetaxel was chosen as a model drug incorporated into the casein/KGM hydrogels. The hydrogel with 1% KGM exhibited a good drug release behavior.