Poly [2-(cinnamoyloxy)ethyl methacrylate-co-octamethacryl-POSS] nanocomposites: Synthesis and properties

Poly [2-(cinnamoyloxy)ethyl methacrylate-co-octamethacryl-POSS] nanocomposites were synthesized from octamethacryl-POSS and 2-(cinnamoyloxy)ethyl methacrylate (CEM) by free radical polymerization. The chemical structures and morphologies of these nanocomposites were determined by FTIR, ²⁹Si NMR, energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM) techniques. The XRD data showed that the materials were amorphous in nature, indicating that POSS formed an aggregate instead of a crystalline form in the polymer matrix. The POSS-CEM nanocomposites exhibited high thermal stability. Excitation and emission of the CEM-incorporated POSS nanocomposites, studied in the solid state, exhibited blue emission with CIE (x, 0.178; y, 0.137) coordinates, in addition to an emission intensity that increased with increasing CEM (monomer) concentration.     

The correlation of the electrical properties with electron irradiation and constant voltage stress for MIS devices based on high-k double layer (HfTiSiO:N and HfTiO:N) dielectrics

This paper describes the influence of e-beam irradiation and constant voltage stress on the electrical characteristics of metal-insulator-semiconductor structures, with double layer high-k dielectric stacks containing HfTiSiO:N and HfTiO:N ultra-thin (1 and 2 nm) films. The changes in the electrical properties were caused by charge trapping phenomena which is similar for e-beam irradiation and voltage stress cases. The current flow mechanism was analyzed on the basis of pre-breakdown, soft-breakdown and post-breakdown current-voltage (J-V) experiments. Based on α-V analysis (α=d[ln(J)]/d[ln(V)]) of the J-V characteristics, a non-ideal Schottky diode-like current mechanism with different parameters in various ranges of J-V characteristics is established, which limits the current flow in these structures independent of irradiation dose or magnitude of applied voltage during stress.     

The influence of electron-beam irradiation on electrical characteristics of metal-insulator-semiconductor capacitors based on a high-k dielectric stack of HfTiSiO(N) and HfTiO(N) layers

We describe the influence of electron irradiation (at 30 kV with a dose of up to 100 μC/cm²) on the electrical characteristics of metal-insulator-semiconductor structures based on a high-k dielectric stack of HfTiSiO(N) and HfTiO(N). The capacitance-voltage (C-V) and current-voltage characteristics were investigated after irradiation and compared to those of unirradiated samples. To better understand the irradiation effect, the capacitance-voltage (C-V) and current-voltage characteristics were also characterized for structures which were stressed at constant voltages. The irradiation induces a parallel shift of the C-V curves towards negative bias due to the introduction of positive charges in the bulk dielectric and semiconductor-dielectric interface. Annealing at 300 °C restored the C-V characteristics to those of the untreated state. A small decrease of the dielectric constant, from 11.7 to 10.7, was observed after irradiation. No measurable change in leakage current due to irradiation was observed.     

Design of an adaptive cache coherence protocol for large scalemultiprocessors

A large scale, cache-based multiprocessor that is interconnected by a hierarchical network such as hierarchical buses or a multistage interconnection network (MIN) is considered. An adaptive cache coherence scheme for the system is proposed based on a hardware approach that handles multiple shared reads efficiently. The new protocol allows multiple copies of a shared data block in the hierarchical network, but minimizes the cache coherence overhead by dynamically partitioning the network into sharing and nonsharing regions based on program behavior. The new cache coherence scheme effectively utilizes the bandwidth of the hierarchical networks and exploits the locality properties of parallel algorithms. Simulation experiments have been carried out to analyze the performance of the new protocol. The simulation results show that the new protocol gives 15% to 30% performance improvement over some existing cache coherence schemes on similar systems for a wide range of workload parameters     

Novel Nd2WO6-type Sm2−xAxM1−yByO6−δ (A = Ca, Sr; M = Mo, W; B = Ce, Ni) mixed conductors

In the present work, we have explored novel Nd₂WO₆-type structure Sm_2−xA_xM_1−yB_yO_6−δ (A = Ca, Sr; M = Mo, W; B = Ce, Ni) as precursor for the development of solid oxide fuel cells (SOFCs) anodes. The formation of single-phase monoclinic structure was confirmed by powder X-ray diffraction (PXRD) for the A- and B-doped Sm₂MO₆ (SMO). Samples after AC measurements under wet H₂ up to 850 °C changed from Nd₂WO₆-type structure into Sm₂MoO₅ due to the reduction of Mo^VI that was confirmed by PXRD and is consistent with literature. The electrical conductivity was determined using 2-probe AC impedance and DC method and was compared with 4-probe DC method. The total electrical conductivity obtained from these two different techniques was found to vary within the experimental error over the investigated temperature of 350-650 °C. Ionic and electronic conductivity were studied using electron-blocking electrodes technique. Among the samples studied, Sm_1.8Ca_0.2MoO_6−δ exhibits total conductivity of 0.12 S cm⁻¹ at 550 °C in wet H₂ with an activation energy of 0.06 eV. Ca-doped SMO appears to be chemically stable against reaction with YSZ electrolyte at 800 °C for 24 h in wet H₂. The ionic transference number (t_i) of Sm_1.9Ca_0.1MoO_6−δ in wet H₂ at 550 °C (pO₂ = 10^−25.5 atm) was found to be about 0.012 after subtraction of electrical lead resistance from the 2-probe AC data and showed predominate electronic conductors.     

Novel Fast Lithium Ion Conduction in Garnet-Type Li5La3M2O12 (M = Nb, Ta)

Lithium metal oxides with the nominal composition Li₅La₃M₂O₁₂ (M = Nb, Ta), possessing a garnetlike structure, have been investigated with regard to their electrical properties. These compounds form a new class of solid-state lithium ion conductors with a different crystal structure compared with all those known so far. The materials are prepared by solid-state reaction and characterized by powder XRD and ac impedance to determine their lithium ionic conductivity. Both the niobium and tantalum members exhibit the same order of magnitude of bulk conductivity (∼10⁻⁶ S/cm at 25°C). The activation energies for ionic conductivity (<300°C) are 0.43 and 0.56 eV for Li₅La₃Nb₂O₁₂ and Li₅La₃Ta₂O₁₂, respectively, which are comparable to those of other solid lithium conductors, such as Lisicon, Li₁₄ZnGe₄O₁₆. Among the investigated materials, the tantalum compound Li₅La₃Ta₂O₁₂ is stable against reaction with molten lithium. Further tailoring of the compositions by appropriate chemical substitutions and improved synthesizing methods, especially with regard to minimizing grain-boundary resistance, are important issues in view of the potential use of the new class of compounds as electrolytes in practical lithium ion batteries.     

Surface modification of CdS quantum dots using thiols-structural and photophysical studies

This study is aimed at identifying a suitable organic thiol for CdS by studying its structural, thermal and photophysical characteristics. Quantum dots of the II-VI semiconductor CdS, in the size regime of 2.0-3.3?nm, were prepared in the cubic phase by a wet chemical method. Five organic thiols were used for capping: (i) 1,4-dithiothreitol (DTT), (ii) 2-mercaptoethanol (ME), (iii)?cysteine (Cys), (iv)?methionine (Meth), and (v)?glutathione (GSH). Structural studies were carried out by x-ray diffraction (XRD) and transmission electron microscopy (TEM), which revealed the cubic phase of CdS. Optical properties were studied by FT-IR, UV-visible and fluorescence spectroscopic techniques, and a comparison was made between uncapped and capped CdS. FT-IR studies suggested two different bonding mechanisms of the capping agents with the CdS. GSH and DTT capped CdS showed significant decrease in absorption wavelengths. An increase in band gap was observed in two cases: when (i)?capped and (ii)?decreased in size. The band gap was increased from 2.50?eV for the uncapped to 2.77?eV for the DTT capped CdS. DTT was found to be the best capping agent for CdS among these five organic thiols in two aspects: (i)?yielding lower grain size in cubic phase, and (ii)?good fluorescence properties with efficient quenching of the surface traps.     

Polyindole–CuO composite polymer electrolyte containing LiClO<Subscript>4</Subscript> for lithium ion polymer batteries

This study presents the preparation of a composite polymer electrolyte (CPE), polyindole-based CuO dispersed CPE containing lithium perchlorate by sol–gel method. Morphology and the structural studies were conducted by scanning electron microscopy and X-ray diffraction. The ionic conductivity of CPE was measured for different concentration of the monomer by impedance spectroscopy. CPE containing CuO/indole (2:1 w/w ratio) (CPE3) exhibited enhanced conductivity of 1.9498 × 10⁻⁵ S/cm at RT. This CPE showed a linear relationship between the ionic conductivity and the reciprocal of the temperature, indicative of the system decoupled from the segmental motion of the polymer.     

Li6ALa2Ta2O12 (A = Sr, Ba): Novel Garnet‐Like Oxides for Fast Lithium Ion Conduction

Oxides with the nominal chemical formula Li₆ALa₂Ta₂O₁₂ (A = Sr, Ba) have been prepared via a solid‐state reaction in air using high purity La₂O₃, LiOH·H₂O, Sr(NO₃)₂, Ba(NO₃)₂, and Ta₂O₅ and are characterized by powder X‐ray diffraction (XRD) in order to identify the phase formation and AC impedance to determine the lithium ion conductivity. The powder XRD data of Li₆ALa₂Ta₂O₁₂ show that they are isostructural with the parent garnet‐like compound Li₅La₃Ta₂O₁₂. The cubic lattice parameter was found to increase with increasing ionic size of the alkaline earth ions (Li₆SrLa₂Ta₂O₁₂: 12.808(2) Å; Li₆BaLa₂Ta₂O₁₂: 12.946(3) Å). AC impedance results show that both the strontium and barium members exhibit mainly a bulk contribution with a rather small grain‐boundary contribution. The ionic conductivity increases with increasing ionic radius of the alkaline earth elements. The barium compound, Li₆BaLa₂Ta₂O₁₂, shows the highest ionic conductivity, 4.0×10^–5 S cm^–1 at 22 °C with an activation energy of 0.40 eV, which is comparable to other lithium ion conductors, especially with the presently employed solid electrolyte lithium phosphorus oxynitride (Lipon) for all‐solid‐state lithium ion batteries. DC electrical measurements using lithium‐ion‐blocking and reversible electrodes revealed that the electronic conductivity is very small, and a high electrochemical stability (&#62; 6 V/Li) was exhibited at room temperature. Interestingly, Li₆ALa₂Ta₂O₁₂ was found to be chemically stable with molten metallic lithium.     

Chemical synthesis of Ca-doped CeO2—Intermediate temperature oxide ion electrolytes

Nano-crystalline fluorite-like structure CeO₂ and Ca-doped CeO₂ compounds were prepared in the temperature range of 220–400 °C using a precursor method which involves coprecipitation of Ca²⁺ and Ce⁴⁺ ions using oxalic acid from the aqueous calcium chloride and ammonium cerium nitrate solutions. The precipitated products were characterized by employing thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), infrared spectroscopy (IR), laser particle size analysis (LPSA) methods and scanning electron microscopy (SEM). TGA studies show two step weight loss in the temperature range: (i) room temperature to 200 °C and (ii) 200–400 °C for all the investigated precursors. The former loss is attributed to loss of water while the latter is due to decomposition of oxalates. The XRD study reveal a complex pattern for the as-precipitated powders, and surprisingly we see the formation of single-phase fluorite-like structure at about 220 °C for Ce_1−xCa_xO_2−x (0 < x < 0.20). However, XRD peaks were found to be very broad that sharpen with increasing temperature. The cubic fluorite-type lattice constant increases with increasing Ca-content, which is consistent with literature, and also follows the expected trend based on the ionic radii consideration. For purpose of comparison, Ce_1−xCa_xO_2−x (0 < x < 0.25) samples were also prepared by solid-state reaction using CeO₂ and CaCO₃, and lattice parameter is consistent with precipitation method samples within the experimental error. This result suggesting that doping of Ca is successful by coprecipitation. The particle size of parent and Ca-doped CeO₂ samples prepared by precipitated method was found to be in the range 10–85 nm (from PXRD) in the temperature range 400–1000 °C, while about order of higher size was observed for the ceramic method synthesized samples. The presently employed wet chemical method could be used to prepare ceria and doped materials with nano-sized particles for a large scale production at mild temperature.