Key Engineering Materials Vols. 277-279

Abstract: The effects of grain-size in La0.7Ca0.3MnO3-δ (LCMO) system have been studied in connection with the magnetic and electronic properties. LCMO system prepared by the solid-state reaction was annealed in air at 1200, 1300 and 1400°C. The grain sizes of LCMO samples become larger with increasing of annealing temperature (TA ). The magnetization in LCMO samples increased while the coercive field decreased with increasing TA. The conductivity increased and the metal-insulator transition temperature TM-I decreased with increasing of TA. These physical properties are due to the oxygen deficiency caused by the increase of grain size. Finally, it was found that the grain size and the mechanical connection between grains play an important role in determining the electronic and magnetic properties.

Abstract: An electron stimulated desorption (ESD) experimental system consisting of a ultrahigh vacuum chamber, micro channel plate, electron gun, quadrupole mass spectrometer, liquid helium and liquid nitrogen cryostat, and a gas supply tube etc., was set up and evaluated in order to investigate desorption particles at the surface of rare gas solids (RGS). Ar was deposited on the copper sample for 200 seconds at a pressure of 6.3 x 10–4 Pa. Ion currents from the RGS during bombardment at various electron gun energies were measured. These increased proportionally with filament currents between 1.5 A and 1.75 A. With the electron gun turned on, the dominant residual species in the vacuum chamber were H2O, H2, C, O, N2, Ar, and CO2, as measured using a quadrupole mass spectrometer (QMS). The H2O partial pressure was almost 50 % of the total pressure, and that of the other gas species were lower than 20 %. Before starting the experiments, the ultimate base pressure of the ultrahigh vacuum chamber reached 10–8 Pa.

Abstract: Nanosize particle flow is significantly affected by inter-particle force. Due to the inter-particle force, the most significant characteristic of nanosize particle flow may become the formation of agglomerates or clusters which considerably affects the flow patterns. The formation of agglomerates or clusters results in a reduction in the number and an increase in the size of particles, both of which directly affect the frequency of inter-particle collisions and, in turn, the particle phase properties such as viscosity and pressure, as well as gas/particle drag force in gas/particle flow systems. In this present work, we focus our attention on the verification of nanosize particle flow behavior due to the formation of agglomerates or clusters under different fluctuation of flow and inelasticity of particle collision. By extending the application of the cohesive model using kinetic theory to nanosize particle flow system, we performed the homogeneous simple shear flow analysis using various fluctuation energy and restitution coefficient. The predicted flow properties, such as particle diameter growth, agreed well with the expected trends.

Abstract: This paper examines the development of nanotechnology in Asian countries and existing and potential ethical issues related to the changes coming about with the development in the pertinent area. The paper further explores strategies aiming to prevent the negative consequences of this development. Nanotechnology does not negatively affect human dignity and integrity. However, just like when dealing with any technology, some of its applications may present certain risks. More attentive monitoring and control has to be enforced in the fields where technology is interconnected with living environment.

Abstract: Polymer-coated cobalt nanocrystals were prepared in a polar solvent at high temperature through an organometallic thermal-decomposition route in the presence of poly (N-viny-2- pyrrolidone) as a protective polymer. The as-synthesized PVP-coated cobalt nanocrystals were 20 to 80 nm cubic/hexagonal shapes. HCP was further determined as a main phase in these samples. For comparison purposes, we have also prepared PVP-cobalt nanocrystals using the seed-mediated thermal decomposition method. It revealed that PVP plays a significant role in the synthesis of cubicstructured cobalt nanocrystals. It was also noted that the formation of Co nanocrystals and their magnetic properties were dependent not only on the PVP component but also in the synthetic route. The saturation magnetization (MS) determined from the seed-mediated sample is lower than that of the conventional sample. The coercivity of the former (610 Oe at 5 K), however, is double that of latter (300 Oe at 5 K), indicating that coercivity strongly depends on the crystallinity of the cobalt.

Abstract: We report the sonochemical synthesis of mercury telluride (HgTe) nanoparticles and the photocurrents of these nanoparticles and their organic hybrid system. The HgTe nanoparticles were about 5 nm in size and their lattice structure was cubic. Poly(N-vinylcarbazole)(PVK) was added to the HgTe nanoparticles for the formation of an inorganic(HgTe)-organic(PVK) hybrid system. The room-temperature photocurrents of the HgTe nanoparticles and the HgTe-PVK hybrid system were compared in this study. The photocurrent was significantly enhanced for the HgTe-PVK hybrid system.

Abstract: The reaction of EuX3 ·nH2O (X=Cl¯ , NO3¯ ), a- pyridoin anion (P) and 2,2¢-dipyridylamine in ethanol solution yields a hydroxo complex, EuP2(OH) 2(H2O) 2, which is characterized by NMR, IR, and elemental analyses. Europium complexes coordinated by nitrogen donating ligands such as 2,2¢-dipyridylamine or 2¢-hydroxypyridine are unstable in solution and are prone to decompose to europium hydroxo complex and pyridinium amine salt. The UV and PL spectra of europium complexes are reported and a decomposition mechanism is proposed.

Abstract: In this study, ZnO and CuO doped zinc oxide thin films were cathodically deposited in aqueous zinc chloride solutions in the presence of oxygen on a Pt/Ti/SiO2/Si substrate through an electrochemical reaction. A mercurous sulfate electrode was used as a reference electrode and the counter electrode was a Pt spiral wire. Deposition was carried out in solutions containing Zn2+ ions introduced as ZnCl2 salt at concentrations ranging from 5.0 x 10-4 to 5.0 x 10-2 M. The bath temperatures were controlled from 65°C to 80°C. The oxygen gas was introduced from argon/oxygen mixtures allowing its partial pressure to be fixed along with its concentration in the solution. Doping of CuO was carried out in cupric nitrate or a cupric chloride/0.1M KCl solution. The influence of the Cu/Zn concentration, deposition temperature of a solution, applied cathodic potential and deposition time were optimized. After the potential was applied, the cathodic current reached a steady state within 5 min. The composition, and the characterization of the surface of the films were investigated through X-ray diffractometry, X-ray photoelectron spectroscopy, atomic force microscopy and scanning electron microscopy.

Abstract: We investigate the growth of highly luminescent silicon nanocrystals by rapid thermal chemical vapor deposition (RTCVD), employing SiH4 and N2O as source gases. For [N2O]/[SiH4] = 7 ∼ 8 and a growth temperature of 650°C, we obtain the optimized deposition condition for silicon rich oxide (SRO) layer having highly luminescent Si nanocrystals after post-deposition annealing. The cross sectional transmission electron microscope investigation reveals the existence of Si nanocrystals in the SRO matrix. Thus, the photoluminescence (PL) from the SRO layer is attributed to the quantum confinement effect of carriers in Si nanocrystals. Based on a single layer growth study, we fabricate ultra-thin SRO/SiO2 superlattice having 25 periods on a 3-inch Si wafer. The superlattice has continuous thickness variation from the center to the edge positions of the Si wafer due to inherent wafer temperature variation during growth. Photoluminescence spectra show a systematic blue-shift from a thicker position (center position) to a thinner position (edge position) which is indicative of nanocrystal size control by SRO layer thickness in the superlattice.