Papers by Keyword: Bubble

Abstract: The amorphous silicon (a-Si) grown by plasma enhanced chemical vapor deposition (PECVD) has been widely applied in advanced semiconductor devices. However, it still suffers from the bubble defects when the deposition temperature goes above 450 °C. In this work, we have investigated the influence of underlying materials on the formation of bubbles of a-Si. The a-Si was deposited on different dielectric substrates, including silicon nitrides (SiN) and silicon dioxide (SiO₂), using PECVD technique at a substrate temperature of 500 °C. A large number of bubbles of the a-Si has been observed on the thermal ALD deposited SiN underlayer, and some of them even burst. In contrast, no bubble defects were observed at the a-Si grown on PECVD SiN and PECVD SiO₂ films. Such deviation may be attributed to the quality of the underlying material, which induces the H/H₂ diffusion during the growth of a-Si and results in bubbles. A solution based on the model has been used to suppress the formation of such bubbles. An inserting layer of SiO₂ was introduced in between SiN and a-Si to improve the density of the lower layer material and the adhesion between the two materials. As a result, there is no bubble defects at the surface of a-Si observed using optical microscope. Our work reveals the mechanism of the formation of bubble defects and paves a new method to eliminate the bubbles defects and to form high-quality a-Si, which shows potential in the manufacture of semiconductor devices.

Abstract: The effects of helium concentration and displacement damage on microstructural evolution at low dpa and low helium concentration were mainly investigated in specimens of austenitic stainless steel 316FR or SUS304 and a high chromium martensitic steel (HCM12A). The 316FR and HCM12A specimens were implanted uniformly with helium at 823 K up to 30 appm-He or 50 appm-He by 50 MeV cyclotron accelerator using energy degraders. After the helium implantation, the microstructures were examined by a transmission electron microscopy and positron annihilation lifetime measurements. Irradiation hardening behaviors were analyzed using SUS304 and HCM12A steels at 823 K implanted with He ion up to 100 appm with different He/dpa ratios in the HIT ion irradiation experiments and the hardening behaviors were examined by nano indentation method. In the irradiation and annealing specimens, these mechanical properties and microstructures were examined to understand the effects of helium production, displacement damage and annealing on microstructural development, and kinetic Monte Carlo (kMC) simulations were also performed to understand the microstructural development, and the results were compared with the results of TEM observation and positron annihilation lifetime measurements. Important some differences in the microstructural developments such as cavity formation and growth between austenitic stainless steel and martensitic steel were observed in low dpa and low helium concentration conditions.

Abstract: The present study describes ice characterization technique by utilizing light microscopy. Two different optical setups were used and compared. For ice structure characterization, ice was formed by adding water to an ice base layer: pouring hot water (+20 °C), pouring cold water (+3 °C) and spraying of hot water (+20 °C) water. Ice substrate specimens were made (20 x 30 x 20 mm prepared in a polypropylene mould) at -20 °C for 48 h. The heat flow direction governed the orientation of the air bubbles, and set the inner structure of ice. Pouring hot water onto ice slowly solidified the top layer and created channel-like pores perpendicular to the top surface, but cold water quickly solidified the top layer and created chaotically oriented air bubbles.

Abstract: Thermal damage of workpiece material induced by laser machining process can be reduced by using the underwater technique. This method requies the whole workpiece to be submerged in water while a laser beam strikes the work surface for ablation. Though water can cool the workpiece during the ablation, the dynamic features of water can adversely interfere the laser beam. The vapor bubbles created in water can scatter the laser beam and in turn attenuate the laser intensity at the work surface so as the ablation performance. In this paper, the bubble formation caused by laser machining of silicon in water was investigated and analyzed. The shadowgraph technique associated with the high speed camera was used to capture and measure the vapor bubble in water. The bubble size was found to increase with the laser pulse energy. After a number of laser pulses irradiated on the workpiece surface, the bubble was broken up into small ones which can significantly disturb the laser beam so as the ablation performance.

Abstract: The dissolution mechanism of air and formation mechanism of bubble in the scopic-scale Be based on VOF model,with the help of Fluent software,For the single bubble rising in the water by numerical simulation;The results show that liquid phase flow state is a key factor affecting the speed of the bubbles rise;Pressure difference is the main reason cause the jets and bubbles deformation.

Abstract: The dissolution mechanism of air and formation mechanism of bubble in the scopic-scale,and the change rule of the velocity and pressure of bubble in the rising process,made the theoretical analysis and explanation. Be based on VOF model,with the help of Fluent software,For the single bubble rising in the water by numerical simulation;The results show that liquid phase flow state is a key factor affecting the speed of the bubbles rise;Pressure difference is the main reason cause the jets and bubbles deformation.Through the above process in the rising process of the bubble velocity and pressure changes, and a detailed analysis of inquiry, the pressure and velocity of the bubble rising process show up more realistic.

Abstract: The bubbles in the liquid will scatter and absorb the ultrasound, therefore the existence of bubbles will seriously affect the ultrasound propagation in the liquid medium inside the pipeline. This paper analyzes the influence of bubbles in the liquid on the performance of the ultrasonic flow meter, and the gas-liquid two-phase flow rate measurement experiments are implemented. Experimental results show that with the increase of the bubble volume fraction in the liquid, the measurement error of the ultrasonic flow meter increases. When the bubble volume fraction exceeds 1%, the transit-time difference method of measuring the flow rate is nearly useless.

Abstract: When the bubble moves in the vicinity of a free surface, the movement will be affected by the buoyancy and the Bjerknes effect. Blake and Gibson proposed the criterion which determined the motion direction of the jet and the dynamics of bubble. They proposed the jet wouldn’t be formed in the condition that . Based on the potential flow theory, boundary element method (BEM) is used to calculate three typical examples in this paper in order to study the dynamics of the bubble under the combined action of the Bjerknes effect of the free surface and the buoyancy. It is found out during the analysis that the Blake criterion is applicable to predict the conditions that and .

Abstract: The breadmaking process can be defined by the succession of operations with operating conditions as input variables and dough properties as output ones, any output variable at step i being an input at step i+1. In this paper, we strive to show how the main properties of bread, density, porosity and alveolar structure (crumb), can be predicted from basic knowledge models (BKMs). So we have defined the variables of breadmaking, proposed BKMs for the two first operations, mixing and proofing, and underlined the needs to define them for shaping and baking, after a short review of existing models. The specific energy delivered during mixing is determined by a simple balance equation in order to predict gluten structuration and dough viscosity, the main output of mixing operation. Then an analysis of dough proofing at different structural scales, by rheology and imaging, allows to assess its alveolar structure, and to fit the kinetics of porosity and stability by phenomenological models. Finally we show how these BKMs could be integrated in order to help the design of baked products with target properties.

Abstract: Dynamic characteristics of micro bubble are the key for its applications. A thermal bubble is produced on the wall of microchannel with flowing fluid. Generation of bubble, including nucleation and growth, is observed and measured with different volume flow rates. The results show that nucleation becomes more difficult and instable with volume flow rate increasing. Bubble growth could be divided into three stages, while the second stage becomes shorter and even disappears as volume flow rate increasing. When volume flow rate increases suddenly, bubble shrinks, and it is more remarkable for larger volume flow rate. Furthermore it needs more time for bubble to reach and keep the minimum volume.