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排序方式: 共有75条查询结果,搜索用时 31 毫秒
51.
52.
Tae Su OhAh Hyun Park Hyun JeongHun Kim Tae Hoon SeoYong Seok Lee Mun Seok JeongKang Jea Lee Eun-Kyung Suh 《Journal of Alloys and Compounds》2011,509(6):2952-2956
μ-Raman and μ-photoluminescence methods have been employed to investigate microscopic spatial stress distribution and optical properties of GaN films grown on the convex shape-patterned sapphire substrate (CSPSS). By comparison of the μ-Raman and μ-PL spectra, we found that significantly large difference, Δσxx ∼0.46 GPa, in biaxial compressive stress between the flat trench and convex regions in the side facet of the GaN film, around ∼2 μm below the surface whereas on the GaN surface, little difference with large residual stress was observed in both regions compared to those from the side facet. Temperature dependent and time-resolved photoluminescence spectra have shown that the GaN film grown on the CSPSS has improved crystal purity through the reduction of intrinsic point defects. 相似文献
53.
In this study,the authors proposed a new algorism which can simultaneously meets the strip shape control criterion and the strip crown control criterion.Based on the new algorism,the pass schedule is optimized to maximize the allowable PC angle range.To calculate the objective value for optimization of pass schedule,a slab method has been integrated with the roll stack deformation to simulate the strip profile. 相似文献
54.
Pressureless Sintering and Mechanical and Biological Properties of Fluor-hydroxyapatite Composites with Zirconia 总被引:2,自引:1,他引:1
Hae-Won Kim Young-Min Kong Young-Hag Koh Hyoun-Ee Kim Hyun-Man Kim Jea Seung Ko 《Journal of the American Ceramic Society》2003,86(12):2019-2026
Fluor-hydroxyapatite (FHA) fabricated by a reaction between fluorapatite (FA) and hydroxyapatite (HA) was mixed with ZrO2 to produce FHA–ZrO2 composites. When the relative amount of FA to HA increased, the decomposition of the composite was decreased gradually because of the formation of thermally stable FHA solid solutions. With such suppression of decomposition, the FHA–ZrO2 composites retained fully densified bodies. As a result, significant enhancements in mechanical properties, such as hardness, flexural strength, and fracture toughness, were achieved as the relative amount of FA to HA increased. The highest values in strength and toughness were 220 MPa and 2.5 MPa·m1/2 , respectively, with FHA–40 vol% ZrO2 composites. In vitro proliferation of osteoblast-like cells (MG63) on the composites showed behavior similar to that observed on pure HA and FHA. Alkaline phosphatase (ALP) activity of the growing cells (HOS) on the composites was slightly down-regulated compared with that on pure HA and FHA at prolonged periods. 相似文献
55.
Flexible Electronics: Improving Performance and Stability of Flexible Planar‐Heterojunction Perovskite Solar Cells Using Polymeric Hole‐Transport Material (Adv. Funct. Mater. 25/2016) 下载免费PDF全文
56.
Tae Su Oh Hyun JeongYong Seok Lee Tae Hoon SeoAh Hyun Park Hun KimKang Jea Lee Mun Seok JeongEun-Kyung Suh 《Thin solid films》2011,519(8):2398-2401
We investigated defect structures in the GaN film grown on a convex patterned sapphire substrate (CPSS) to determine the origin of structural improvement by transmission electron microscopy (TEM) and laser confocal scanning microscopy (LCSM). From the TEM results, we found that most of the threading dislocations (TDs) in the trench region of the CPSS were bent by lateral growth mode. Also the staircase-like TDs were observed near the curved slant region of the convex pattern; they converged at the top of the convex patterned region by staircase-upward propagation. This scenario seems to effectively prevent TDs from vertical propagation in the trench region. The photoluminescence mapping and spectra obtained by LCSM are consistent with these results from TEM observations. The generation of staircase-like TDs relates to the formation of a terraced surface during the growth, and suggests a probable mechanism that changes the propagation direction of TDs via the curved surface of the CPSS. The lateral growth and staircase-upward propagation of TDs are major factors on structural improvement of the GaN film grown on CPSS. 相似文献
57.
Kyoung Il Lee Uk Yeong Kim Suck Hwan Kang Jea Keun Lee Woo Hyun Kim 《Chemical engineering science》2007,62(24):7060-7067
Dispersion characteristics of low density fluidized particles such as polyethylene and polypropylene were investigated by using the stochastic method in three-phase inverse fluidized beds with viscous liquid medium ( in height). To establish the relationship between the pressure drop variation and the particle dispersion in test section, the histogram of pressure drop fluctuations were also measured and analyzed. Effects of operating variables such as gas and liquid velocities, liquid viscosity and media particle kind (density) on the fluctuating frequency, dispersion coefficient and exiting rate of media particles from the test section were determined. The fluctuating frequency and dispersion coefficient of particles increased with increasing gas or liquid velocity, but decreased considerably with increasing liquid viscosity in three-phase inverse fluidized beds. The dispersion coefficient of media particles of relatively higher density exhibited a value higher than that of lower density particles. The dispersion coefficients of particles were well correlated with operating variables in terms of dimensionless groups. 相似文献
58.
Somasundara A.A. Kansal A. Jea D.D. Estrin D. Srivastava M.B. 《Mobile Computing, IEEE Transactions on》2006,5(8):958-973
We discuss the use of mobility to enhance network performance for a certain class of applications in sensor networks. A major performance bottleneck in sensor networks is energy since it is impractical to replace the batteries in embedded sensor nodes post-deployment. A significant portion of the energy expenditure is attributed to communications and, in particular, the nodes close to the sensor network gateways used for data collection typically suffer a large overhead as these nodes must relay data from the remaining network. Even with compression and in-network processing to reduce the amount of communicated data, all the processed data must still traverse these nodes to reach the gateway. We discuss a network infrastructure based on the use of controllably mobile elements to reduce the communication energy consumption at the energy constrained nodes and, thus, increase useful network lifetime. In addition, our approach yields advantages in delay-tolerant networks and sparsely deployed networks. We first show how our approach helps reduce energy consumption at battery constrained nodes. Second, we describe our system prototype, which utilizes our proposed approach to improve the energy performance. As part of the prototyping effort, we experienced several interesting design choices and trade-offs that affect system capabilities and performance. We describe many of these design challenges and discuss the algorithms developed for addressing these. In particular, we focus on network protocols and motion control strategies. Our methods are tested using a practical system and do not assume idealistic radio range models or operation in unobstructed environments. 相似文献
59.
Chloride Passivation of ZnO Electrodes Improves Charge Extraction in Colloidal Quantum Dot Photovoltaics 下载免费PDF全文
Jongmin Choi Younghoon Kim Jea Woong Jo Junghwan Kim Bin Sun Grant Walters F. Pelayo García de Arquer Rafael Quintero‐Bermudez Yiying Li Chih Shan Tan Li Na Quan Andrew Pak Tao Kam Sjoerd Hoogland Zhenghong Lu Oleksandr Voznyy Edward H. Sargent 《Advanced materials (Deerfield Beach, Fla.)》2017,29(33)
The tunable bandgap of colloidal quantum dots (CQDs) makes them an attractive material for photovoltaics (PV). The best present‐day CQD PV devices employ zinc oxide (ZnO) as an electron transport layer; however, it is found herein that ZnO's surface defect sites and unfavorable electrical band alignment prevent devices from realizing their full potential. Here, chloride (Cl)‐passivated ZnO generated from a solution of presynthesized ZnO nanoparticles treated using an organic‐solvent‐soluble Cl salt is reported. These new ZnO electrodes exhibit decreased surface trap densities and a favorable electronic band alignment, improving charge extraction from the CQD layer and achieving the best‐cell power conversion efficiency (PCE) of 11.6% and an average PCE of 11.4 ± 0.2%. 相似文献
60.
Wael Z. Tawfik Gil Yong Hyun Seong Jea Lee Sang-Wan Ryu Jun-Seok Ha June Key Lee 《Journal of Materials Science》2018,53(12):8878-8886
InGaN/GaN multi-quantum well light-emitting diodes (LEDs) are conventionally grown on a sapphire substrate due to a lack of compatible substrates with a high compressive strain. This is a result of the relatively large lattice, and thermal expansion coefficient mismatches between GaN and sapphire. The compressive strain is considered to be a major obstacle to further improve next-generation high-performance GaN-based LEDs. In this paper, we have designed, electroplated, and tested an efficient substrate using a patterned copper (Cu) layer on the backside of sapphire to relax the compressive strain in a GaN epilayer. The patterned Cu layer has a significant function in that it supports the GaN/sapphire LEDs with an external tensile stress. The external tensile stress is capable of compensating for the compressive strain in the GaN/sapphire LEDs by controlling the curvature of the wafer bowing. This patterned Cu layer, when applied to the GaN/sapphire LEDs, suppresses the compressive strain by up to 0.28 GPa. The GaN-based LEDs on this innovative and effective sapphire/Cu substrate offer improved optical and electrical performance. 相似文献