Morphology and activity of nanosized NdCl3 catalyst for 1,3‐butadiene polymerization

The binary lanthanide catalyst for 1,3‐butadiene was invented for 40 years ago. However, it has not been employed in commercial application due to its poor solubility and low activity. Nanosized neodymium chloride (NdCl₃) was prepared in tetrahydrofuran (THF) medium through dissolution, chelation, and colloidal formation steps. Anhydrous NdCl₃ was dissolved in THF, and ca. 1.5 THF molecules were coordinated. In the colloidal formation step, THF was slowly replaced with the addition of cyclohexane, and pale blue nuclei, nanosize below 200 nm, were formed. The structural studies for NdCl₃ · xTHF using X‐ray powder diffraction (XRD) and scanning electron microscope (SEM) indicate that high ordered crystallinity is decreased with reduced particle size from trigonal prismatic to porous sphere structure. Nano NdCl₃, obtained as colloidal state in cyclohexane, was activated with Al(iBu)₃ and Al(iBu)₂H at room temperature and employed for 1,3‐butadiene solution polymerization. The nanosized Nd catalysts showed high activity (1.0 ～ 1.3 × 10⁵ g/Nd mol · h), which is comparable to that of the ternary neodymium catalyst Nd(neodecanoate)₃/AlEt₂Cl/Al(iBu)₃. The microstructures of polybutadiene, cis, trans, and vinyl, are about 96.0, 3.5, and 0.5%, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1279–1283, 2005     

Low turn-on voltage and series resistance of polarization-induced InGaN-GaN LEDs by using p-InGaN/p-GaN superlattice

We have demonstrated high-performance InGaN-GaN multiple quantum-wells light-emitting diodes (LEDs) using polarization-induced (PI) p-InGaN-GaN superlattice. Electrical measurements show that PI LEDs produce much lower series resistance and turn-on voltage (at 20 mA) as compared to those of normal LEDs without the superlattice. It is also shown that the output power and photon wavelength of the PI LEDs remain electrically stable up to a high stress region of 200 mA. However, those of normal LEDs become electrically and optically degraded in excess of 120 mA. These results show that the use of the PI effect is very effective to the improvement of the electrical properties of LEDs.     

Ultraflat indium tin oxide films prepared by ion beam sputtering

Indium tin oxide (ITO) films with a smooth surface (root-mean-square roughness; R_rms=0.40 nm) were made using a combination of the deposition conditions in the ion beam-sputtering method. Sheet resistance was 13.8 Ω/sq for a 150-nm-thick film grown at 150 °C. Oxygen was fed into the growth chamber during film growth up to 15 nm, after which, the oxygen was turned off throughout the rest of the deposition. The surface of the films became smooth with the addition of ambient oxygen but electrical resistance increased. In films grown at 150 °C with no oxygen present, a rough surface (R_rms=2.1 nm) and low sheet resistance (14.4 Ω/sq) were observed. A flat surface (R_rms=0.5 nm) with high sheet resistance (41 Ω/sq) was obtained in the films grown with ambient oxygen throughout the film growth. Surface morphology and microstructure of the films were determined by the deposition conditions at the beginning of the growth. Therefore, fabrication of ITO films with a smooth surface and high electrical conductivity was possible by combining experimental conditions.     

Influence of Particle Velocity of Copper on Emitter Contact by Cold-Spray Method

In this study, we investigated cold-sprayed copper as a front contact for crystalline silicon solar cells. Copper powder was deposited on a monocrystalline silicon wafer with variation of the particle velocity during deposition. The particle velocity was varied by varying the heating temperature from 250 to 400 °C using a gas pressure of 0.45 MPa. The particle velocities were calculated using empirical equations, and were found to increase with an increase in the carrier gas temperature. Grid patterns were formed on a phosphorus-doped n-type emitter of a p-type silicon substrate. The electrode thickness increased with increasing particle velocity. The electrical properties of the grids were evaluated using the transfer length method. The specific contact resistance of the n-type emitter was in the range of 2.6-26.4 mΩ-cm². Damage to the p-n junction was investigated via minority carrier lifetime measurement of the substrate. The copper-silicon interface was evaluated using transmission electron microscopy. The contact properties were affected by the interface conditions.     

Electrospinning of poly(dimethyl siloxane) by sol–gel method

Crosslinked poly(dimethyl siloxane) (PDMS) fibers were fabricated by electrospinning in combination with a sol–gel process followed by heat treatment. Before and after heat treatment, the changes in the chemical and thermal properties of the electrospun PDMS fibers were examined by differential scanning calorimetry (DSC), equilibrium swelling tests, and contact angle measurements. There was no significant change in morphology and average diameter of the as‐spun PDMS fibers after heat treatment. The tensile properties of the as‐spun PDMS fibers mat increased with increasing heat treatment temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication and characterization of TiO2/poly(dimethyl siloxane) composite fibers with thermal and mechanical stability

The mechanical stability of titania (TiO₂) nanofibers was improved by fabricating TiO₂/poly(dimethyl siloxane) (PDMS) composite fibers using a combination of hybrid electrospinning and sol‐gel methods, followed by heat treatment at 250°C for 3 h. The compositions (90/10, 80/20, and 70/30, w/w) of the TiO₂/PDMS composite fibers were varied by adjusting the flow rate of the PDMS sol with the flow rate of TiO₂ sol fixed. There was no significant change in morphology and average diameter of the as‐spun TiO₂/PDMS fibers after heat treatment. Both the tensile strength and modulus of the TiO₂/PDMS composite fibers increased gradually with increasing PDMS content up to 30 wt %. In addition, from the photo‐degradation reaction of methylene blue, the photocatalytic activity of TiO₂/PDMS composite fibers was strongly dependent on the TiO₂ content (%) in the composite fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fabrication and characterization of CdTe nano pattern on flexible substrates by nano imprinting and electrodeposition

Nano imprinting technology and the electrodeposition method were applied to make CdTe nano patterns on flexible substrates. An ammonia based aqueous solution was prepared at pH 10.7 and indium tin oxide (ITO)/polyethylene naphthalate (PEN) film with template was used as the working electrode. ITO thin film which was coated on PEN film had good electrical conductivity and optical transmittance. The template was manufactured by nano imprinting technology on ITO/PEN film. It was made from benzyl methacrylate and had nano rod arrays. It was used as the working electrode and for making CdTe nano pattern. CdTe nano pattern were analyzed by X-ray diffractometer, dual beam (DB)-focused ion beam (FIB)-scanning electron microscopy (SEM), Raman spectroscopy, and ultraviolet (UV)-visible (VIS) spectroscopy. The structure and optical properties of CdTe nano pattern on flexible substrates was analyzed. The crystalline size of nano pattern had 8.26 nm. The Te particles that were precipitated on CdTe surface seems to be exist. The absence of annealing process influenced to have low absorption coefficient and narrow band gap compared to bulk CdTe. However, nano pattern increased reflectance.     

Failure mechanism for metal cylinder under explosive loading

This paper presents the numerical study of dynamic fracture for metal cylinder under internal explosive loading. Also, the effects of fracture models and groove designs on fracture behavior are investigated. For the dynamic hardening behavior, the Lim-Huh model including the thermal softening effect is adopted [1, 2]. Also, the Lou-Huh fracture model considering the strain rate dependency is used for fracture prediction [3]. The tensile fracture occurs first at the outer surface, and the shear fracture is observed near the inner surface. In addition, finite element analyses are performed to study the effect of various groove designs on dynamic fracture; single U-groove and V-groove at the outer surface. The tensile and shear fracture lines are predicted near the groove tip and inner surface, respectively. It is concluded that the stress triaxiality parameter is one of the critical factors in the dynamic fracture prediction of the metal cylinder.

     

Comparative study of Al2O3, HfO2, and HfAlOx for improved self‐compliance bipolar resistive switching

The comparison of resistive switching (RS) storage in the same device architecture is explored for atomic layer deposition (ALD) Al₂O₃, HfO₂ and HfAlO_x‐based resistive random access memory (ReRAM) devices. Among them, the deeper high‐ and low‐ resistance states, more uniform V_SET‐V_RES, persistent R_OFF/R_ON (>10²) ratio and endurance up to 10⁵ cycles during both DC and AC measurements were observed for HfAlO_x‐based device. This improved behavior is attributed to the intermixing of amorphous Al₂O₃/HfO₂ oxide layers to form amorphous thermally stable HfAlO_x thin films by consecutive‐cycled ALD. In addition, the higher oxygen content at Ti/HfAlO_x thin films interface was found within the energy dispersive spectroscopy analysis (EDS). We believe this higher oxygen content at the interface could lead to its sufficient storage and supply, leading to the stable filament reduction‐oxidation operation. Further given insight to the RS mechanism, SET/RESET power necessities and scavenging effect shed a light to the enhancement of HfAlO_x‐based ReRAM device as well.