Effects of additive gases and plasma post-treatment on electrical properties and optical transmittance of ZnO thin films

A zinc oxide (ZnO) thin film as a channel layer in an oxide thin film transistor (TFT) has been characterized by investigating the effects of additive gases (such as hydrogen and oxygen) during growth and plasma treatment (using argon or hydrogen) after growth on its electrical, optical, and structural properties. By decreasing the additive gas ratio of O₂/H₂ or by increasing the treatment time of hydrogen plasma, the electrical resistivities of ZnO films were significantly reduced, and their transmittances and optical bandgap energies were blue-shifted in wavelength. These results were considered to be closely related to the passivation of oxygen vacancies as well as the formation of shallow donors that were induced by the injection of hydrogen in ZnO via gas addition and plasma treatment. In addition, the injection of hydrogen-including additive gas resulted in a decrease in grain size and crystallinity of ZnO films, whereas the plasma treatment hardly affected their crystalline structures.     

Behavior of strain at a thin Ge pile-up layer formed by dry oxidation of a Si0.7Ge0.3 film

The change of strain in Si_0.7Ge_0.3 films was investigated with medium energy ion scattering (MEIS). Si was removed in the films by selective oxidation at 800 °C, resulting in the formation of a Ge pile-up layer on the surface. The relaxation and the thickness of the pile-up layer were closely related to the oxidation time. MEIS data demonstrated that relaxation of the Ge layer in the depth direction occurred partially, and that the rates of relaxation decreased with depth. In addition, the rate of relaxation increased with the oxidation time. Lastly, the relaxation of the Ge layer affected the strain of the remaining Si_0.7Ge_0.3 substrate.     

Improved transmission of chirped signals from semiconductor opticaldevices by pulse reshaping using a fiber Bragg grating filter

Spectral filtering of chirped signals with an edge of a fiber grating filter improves propagation in nondispersion-shifted fiber. The improvement is due to a temporal shift of the frequency modulation with respect to the amplitude modulation. By filtering the chirped output of a semiconductor optical amplifier (SOA) wavelength converter with a fiber grating edge we obtain error-free transmission of converted data through 100 km of nondispersion-shifted fiber at 5 Gb/s     

Anisotropic etching characteristics of platinum electrode forferroelectric capacitor

The effect of etch parameters of platinum etching using Cl₂ /CO plasma on the etching properties and the etch profiles was investigated. The etching characteristics with respect to substrate temperature are different in two temperature regions below and above 210°C and significantly depended on Cl₂ concentration in each temperature region. The etch rates of Pt were enhanced suddenly at the substrate temperature of around 210°C when Cl₂ concentration is 50-80%. The etch rates of Pt below 210°C did not change much with increasing temperature. The selectivity of Pt over SiO ₂ was governed by the etch rate of SiO₂ in the lower temperature region but determined by the etch rates of Pt in the higher temperature region. The anisotropy of etch profiles was high enough to achieve vertical pattern without etch residues in the lower temperature region for the application in fabricating 1-Gbit era. In the higher temperature region, however, the slopes of etch profiles due to the volatile products of Pt were found. XPS was used to analyze the surface atomic compositions after various etching treatments     

Static strength analysis of CANDU-6 reactor fuel bundle

A static analysis, finite-element (FE) model was developed to simulate out-reactor fuel–string strength tests with use of the well-known, structural analysis computer code ABAQUS. The FE model takes into account the deflection of fuel elements, and stress and displacement in endplates subjected to hydraulic drag loads. It was adapted to the strength tests performed for CANFLEX 43-element bundles and the existing 37-element bundles. The FE model was found to be in good agreement with experiment results. With use of the FE model, the static behavior of the fuel bundle string, such as load transfer between ring elements, endplate rib effects, hydraulic drag load incurring plastic deformation in fuel string and hydraulic flow rate effects were investigated.     

Chronic inhibition of NOS does not prevent plasticity of rat somatosensory (S1) cortex following deafferentation

Nitric oxide (NO) has been proposed as an intercellular messenger mediating postsynaptic to presynaptic information transfer in the induction of long-term potentiation. A number of studies support the possible involvement of NO in synaptic plasticity. NO may have a role in synaptogenesis and synaptic plasticity in developing rat brain and may play a fundamental part in the process of regeneration, plasticity, and retargeting of axons following injury. We examined the possible role of NO on plasticity in the rat first somatosensory cortex with [14C]2-deoxyglucose (2-DG) autoradiography in rats treated daily with l-nitroarginine (l-NA) following neonatal unilateral vibrissae deafferentation. After 6 weeks of l-NA treatment, the local cerebral glucose utilization (LCGU) and the spatial extent of the metabolic activation following stimulation of the spared whisker was measured. NOS catalytic activity exhibited significant inhibition throughout the treatment period. Vibrissae deafferentation produced a small but not statistically significant increase of LCGU in the vibrissa activated C3 barrel, and l-NA treatment did not alter the activation of LCGU in the deafferented cortex following whisker stimulation. Additionally, l-NA treatment did not alter the area of metabolic activation on either the non-deafferented side or the deafferented side. Deafferentation produced a 298% increase in the metabolic representation of the spared C3 barrel following stimulation in the saline treated animals, a 257% increase in the chronically l-NA treated animals, and a 256% increase in the short-term treated animals, all with respect to the response in the non-deafferented cortex. Metabolic plasticity in the barrel cortex was not attenuated by l-NA treatment. These results show that nitric oxide does not play a major role on developmental cortical plasticity induced by vibrissae deafferentation in the rat.     

Application of upper bound method to the powder‐forging of cup‐shaped axisymmetric preforms for estimating punch load

This paper is concerned with the analytic derivation of the punch load required to forge cup‐shaped axisymmetric porous preforms. Splitting the two‐dimensional preform domain into three rectangular regions, we assumed the kinematically admissible velocity fields to apply the upper bound method. According to the resulting formulas, we developed an incremental numerical algorithm for computing time‐discretized step‐wise punch loads and preform volumes. In order to illustrate the validity of the proposed estimate, we compared the numerical results obtained by the present analysis with those by the finite element simulation. From the comparison made through different preform dimensions, we observed that the present analysis expects the reliable upper bounds of process step‐wise punch loads. Copyright © 2001 John Wiley & Sons, Ltd.     

Flexible cross‐linking by both pentaerythritol and polyethyleneglycol spacer and its impact on the mechanical properties and the shape memory effects of polyurethane

A series of polyurethane (PU) polymers cross‐linked laterally by pentaerythritol and polyethyleneglycol (PEG) spacers were compared with linear PU. The PU was composed of 4,4′‐methylenebis(phenylisocyanate) (MDI), poly(tetramethyleneglycol), 1,4‐butanediol (BD), pentaerythritol, and PEG‐200 as a spacer. PEG‐200 connected the pentaerythritol hydroxyl groups of two PU chains with MDI as a connecting agent. The phase separation between hard and soft segments was disrupted by the PEG crosslinking, and T_m did not change with an increase in cross‐linking content. Instead, the cross‐link density increased with an increase of pentaerythritol content. A significant increase in maximum stress compared with linear PU was attained, together with an increase in strain. The combination of both pentaerythritol and PEG‐200 in the PU resulted in the improvement of both stress and strain, unlike in the conventional cross‐linking method. The shape recovery increased to 90% and did not decrease after three test cycles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009