First-principles molecular-dynamics calculations on chemical reactions and atomic structures induced by H radical impinging onto Si(001)2 x 1:H surface

Chemical reactions between hydrogen terminated Si(001)2 x 1 surface and impinging H radical are investigated by means of first-principles molecular-dynamics simulations. Reaction probabilities of abstraction of surface terminating H atom with H2 formation, adsorption onto Si surface and reflection of impinging H atom are analyzed with respect to the kinetic energy of incident H radical. The probabilities of abstraction and adsorption turn out to be ranging from 0.81 to 0.58 and from 0.19 to 0.42, respectively, while that of reflection almost zero. As initial kinetic energy of the impinging atom increases, the reaction probability of abstraction decreases and that of absorption increases. Metastable H-absorbed atomic configurations are also derived by optimizing the structures obtained in the impinging dynamics calculations. They are candidates of the so-called reservoir site which is a key to understand the unity hydrogen coverage observed after an exposure to gaseous H atom ambient despite existing residual vacant sites due to abstraction.     

Condensation and Collapse of Vapor Bubbles Injected in Subcooled Pool

We focus on condensation and collapse processes of vapor bubble(s) in a subcooled pool. We generate the vapor in the vapor generator and inject it/them to form vapor bubble(s) at a designated temperature into the liquid at a designated degree of subcooling. In order to evaluate the effect of induced flow around the condensing/collapsing vapor bubble, two different boundary conditions are employed; that is, the vapor is injected through the orifice and the tube. We also focus on interaction between/among the condensing/collapsing vapor bubbles laterally injected to the pool. Through this system we try to simulate an interaction between the vapor bubble and the subcooled bulk in a complex boiling phenomenon, especially that known as MEB (microbubble emission boiling) in which a higher heat flux than critical heat flux (CHF) accompanying with emission of micrometer-scale bubbles from the heated surface against the gravity is realized under a rather high subcooled condition.     

Purity-enhanced bulk synthesis of thin single-wall carbon nanotubes using iron-copper catalysts

We report high purity and high yield synthesis of single-wall carbon nanotubes (SWCNTs) of narrow diameter from iron-copper bimetal catalysts. The SWCNTs with diameter of 0.8-1.2 nm are synthesized using the zeolite-supported alcohol chemical vapour deposition method. Single metal and bimetal catalysts are systematically investigated to achieve both the enhancement of SWCNT yield and the suppression of the undesired formation of graphitic impurities. The relative yield and purity of SWCNTs are quantified using optical absorption spectroscopy with an ultracentrifuge-based purification technique. For the single metal catalyst, iron shows the highest catalytic activity compared with the other metals such as cobalt, nickel, molybdenum, copper, and platinum. It has been found that the addition of copper to iron results in the suppression of carbonaceous impurity formation without decreasing the SWCNT yield. The purity-enhanced SWCNT shows fairly low sheet resistance due to the improvement of inter-nanotube contacts. This scalable design of SWCNT synthesis with enhanced purity is therefore a promising tool for shaping future high performance devices.     

Exceptional plasticity of silicon nanobridges

The plasticity of covalently bonded materials is a subject at the forefront of materials science, bearing on a wide range of technological and fundamental aspects. However, covalent materials fracture in a brittle manner when the deformation exceeds just a few per cent. It is predicted that a macroscopically brittle material like silicon can show nanoscale plasticity. Here we report the exceptional plasticity observed in silicon nanocontacts ('nanobridges') at room temperature using a special experimental setup combining a transmission electron microscope and a microelectromechanical system. When accounting for surface diffusion, we succeeded in elongating the nanocontact into a wire-like structure, with a fivefold increase in volume, up to more than twenty times the original length. Such a large plasticity was caused by the stress-assisted diffusion and the sliding of the intergranular, amorphous-like material among the nanocrystals.     

Effect of the Chevron Angle on Cooling Heat Transfer Characteristics of Supercritical Pressure Fluids in Plate Heat Exchangers

ABSTRACT

For the development of industrial heat pump systems supplying a high-temperature heat source over 130°C, the authors have studied on cooling heat transfer of supercritical pressure fluids flowing in chevron-type plate heat exchangers (PHEs). In this study, to examine the effect of chevron angle on cooling heat transfer of supercritical pressure refrigerants, experiments were conducted for HFC134a and HFO1234ze(E) flowing in the PHEs with the chevron angles from 30° to 65°. In the experiments, cooling heat transfer coefficients were obtained in the wide range of bulk fluid enthalpy from vapor-like high temperature to liquid-like low temperature, changing the pressure in the reduced pressure range from 1.01 to 1.2 at the mass flow rates of 7 and 11 kg/min. Especially for the enthalpy region of the pseudo critical point and its vicinity in which good heat transfer appeared, the effect of chevron angle on heat transfer of supercritical pressure fluids was clarified based on the measurements. Furthermore, the effect of chevron angle was examined for the wide angle range from 0° to 90° with estimating the heat transfer coefficient for the angles 0° and 90° from appropriate correlations. Besides, the present data were compared with some conventional heat transfer correlations.     

Styryl silsesquioxane photoresist

There is a substantial need for photopattern‐able, heat resistant, and transparent materials that are applicable to electronic devices, such as imaging or display elements. Styryl silsesquioxane based photoresist forms thin micro patterns after i‐line exposure and alkaline development, and the resulting transparent film shows remarkable heat resistance. Radicals generated from a photoinitiator induce polymerization of styryl functionality in the photoresist film to form the micropatterns. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41459.     

Mechanical and thermal properties of potassium salts of poly(ethylene‐co‐ethylacrylate): Polyolefin ionomers in the absence of acid groups

The thermal and mechanical properties of ionomers prepared by partial saponification of poly(ethylene‐co‐ethylacrylate) (EEA) with potassium were investigated by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The Vicat softening temperature (VST) and bending modulus were also evaluated. Molecular design of the present EEA‐based ionomers eliminates acid groups, which affect ionic aggregates for conventional ionomers. The DSC results showed that the melting enthalpy and main crystallization temperature decreased as the ion content increased, whereas on the other hand, the crystal melting temperature at about 360 K did not depend on the ion content, and a secondary exothermal peak was observed in the cooling process. The variance of the VST increased as the crystallinity decreased. The temperature‐dependent curves of DMA data of the EEA‐based potassium ionomers with a higher ion content showed elastic plateau even at temperatures above their crystal melting points. Our results indicate the existence of strong cross‐linking mediated by ion aggregates. The quadratic increase of stiffness as a function of ion content, increasing VST with decreasing crystallinity, and elastic plateau of temperature‐dependent moduli above crystal melting temperature are significant characteristics of the EEA‐based potassium ionomers, which contain ionic aggregations without acid group presence. POLYM. ENG. SCI., 55:1843–1848, 2015. © 2014 Society of Plastics Engineers     

Understanding the final-state control from the standpoint of the model predictive control and its application to a three-dimensional trajectory control problem

Microsystem Technologies - In many motion control problems of mechatronic equipment, the control performance of the final-state of the control period is strictly important for positioning or...     

Development of Maximum Bubble Pressure Method for Surface Tension Measurement of High Viscosity Molten Silicate

A surface tension measurement method based on the maximum bubble pressure (MBP) method was developed in order to precisely determine the surface tension of molten silicates in this study. Specifically, the influence of viscosity on surface tension measurements was quantified, and the criteria for accurate measurement were investigated. It was found that the MBP apparently increased with an increase in viscosity. This was because extra pressure was required for the flowing liquid inside the capillary due to viscous resistance. It was also expected that the extra pressure would decrease by decreasing the fluid velocity. For silicone oil with a viscosity of \(1000\,\hbox {mPa}{\cdot }\hbox {s}\), the error on the MBP could be decreased to +1.7 % by increasing the bubble detachment time to \(300\,\hbox {s}\). However, the error was still over 1 % even when the bubble detachment time was increased to \(600\,\hbox {s}\). Therefore, a true value of the MBP was determined by using a curve-fitting technique with a simple relaxation function, and that was succeeded for silicone oil at \(1000\,\hbox {mPa}{\cdot } \hbox {s}\) of viscosity. Furthermore, for silicone oil with a viscosity as high as \(10\,000\,\hbox {mPa}{\cdot }\hbox {s}\), the apparent MBP approached a true value by interrupting the gas introduction during the pressure rising period and by re-introducing the gas at a slow flow rate. Based on the fundamental investigation at room temperature, the surface tension of the \(\hbox {SiO}_{2}\)–40 \(\hbox {mol}\%\hbox {Na}_{2}\hbox {O}\) and \(\hbox {SiO}_{2}\)–50 \(\hbox {mol}\%\hbox {Na}_{2}\hbox {O}\) melts was determined at a high temperature. The obtained value was slightly lower than the literature values, which might be due to the influence of viscosity on surface tension measurements being removed in this study.     

Strength and fracture surface energy of phase-separated glasses

Flexural strength and fracture surface energy were determined for lead borate glasses whose compositions lie in the immiscible region of the PbO-B₂O₃ system. The microstructural characterization indicated that the glasses are typical particulate composites which consist of two immiscible phases. For the glasses whose microstructure consists of PbO-rich particles/B₂O₃-rich matrix (B₂O₃-rich side of the miscibility gap), the fracture surface energy was found to decrease with increasing second-phase particles. To explain this behaviour, a crack propagation model in a brittle composite containing penetrable particles was proposed. On the other hand, for the glasses whose microstructure consists of B₂O₃-rich particles/PbO-rich matrix (PbO-rich side of the miscibility gap), an increase in fracture surface energy with volume fraction of dispersed particles was observed. This phenomenon could be best explained by Lange-Evans theory of fracture in brittle composites containing impenetrable particles. It was concluded that, when the critical crack size in a non-dispersed host glass is much larger than the particle size, the crack size in particulate composites is invariant with microstructure and also that the variation of strength results entirely from the variation of fracture toughness.