286 research outputs found
Optimization of InGaAs Quantum Dots for Optoelectronic Applications
No full textSelf-assembled In_0.35Ga_0.65As/GaAs quantum dots with low indium content are grown under different growth temperature and investigated using contact atomic force microscopy(AFM). In order to obtain high density and high uniformityu of quantum dots, optimized conditions are concluded for MBE growth. Optimized growth condi-tions also compared with these of InAs/GaAs quantum dots. This will be very useful for InGaAs/GaAs QDs opto-electronic applications, such as quantum dots lasers and quantum dots infrared photodetectors
Single Layer Growth of Strained Epitaxy at Low Temperature
No full textContacting mode atomic force microscopy (AFM) is used to measure the In0.asGao.65As/GaAs epilayer grown at low temperature (460°C). Unlike the normal layer-by-layer growth (FvdM mode) or self-organized islands growth (SK mode) ,samples grown under 460 C are found to be large islands with atomic thick terraces. AFM measurements reveale near one monolayer high steps. This kind of growth is good between FvdM and SK growth modes and can be used to understand the evolution of strained epitaxy from FvdM to SK mode
Achievements and Prospects of Advanced Pavement Materials Technologies
No full textRoad transportation is a basic need for mobility and daily life. Currently, there are a number of challenges in dealing with distressed pavement and seeking new materials with sustainability in mind in pavement systems. Therefore, it is important to conduct further research in the following areas: (1) pavement structure, materials, and design; (2) pavement models as better solutions for pavement constructions; (3) pavement mechanics for improved understanding and mechanism analyses; (4) utilization of recycled materials for environmentally friendly solutions; (5) maintenance and rehabilitation for an extended life span of pavement; (6) intelligent construction for project management, energy conservation, and future constructions; and (7) innovative approaches to test and evaluate the performance of pavement materials. The purpose of this Special Issue “Achievements and Prospects of Advanced Pavement Materials Technologies” is to explore new research ideas for pavement materials as described above
Development of a material-machine cyber model for pavement paving compaction
No full textOver the past decades, extensive researches have taken attempts to improve the quality control of pavement compaction. Different methods such as conventional laboratory tests, practical in-situ experiments, image-based technologies, and numerical simulations, etc. have been taken into consideration to solve this issue. On the one hand, the research method must be accurate, reliable, repeatable. On the other, expected efficiency also requires time- and labour-saving. A proper way to improve the pavement compaction is based on the design conception, material selection, and the construction quality control. Furthermore, the practical way to guarantee the constructing quality is to optimize the working operations of the paver and compaction machine. In this case, the objective of this thesis is to propose a material-machine cyber model, to have a comprehensive understanding of compaction behavior, and to improve the compaction operations during paving compaction. The DEM simulation is proposed in this thesis, which can be applied to simulate the interaction between the granular materials and the machine. In repeated simulation experiments, the model parameters used in DEM must be validated prior to the numerical simulation. Laboratory tests provide the access to capture the physical parameters of the DEM model, and the real-time sensing technology makes it possible to acquire the movement of the aggregates during the whole compaction process. With these two practical ways, the DEM simulation can perform a practical and precise evaluation of the in-situ compaction, and provide a practical scenario to optimize the working operations of the pavement construction machine. This dissertation outlines the method to systematically investigate how to assess the material-machine interaction, and how to improve the pavement compaction quality control
Achievements and Prospects of Advanced Pavement Materials Technologies
No full textRoad transportation is a basic need for mobility and daily life. Currently, there are a number of challenges in dealing with distressed pavement and seeking new materials with sustainability in mind in pavement systems. Therefore, it is important to conduct further research in the following areas: (1) pavement structure, materials, and design; (2) pavement models as better solutions for pavement constructions; (3) pavement mechanics for improved understanding and mechanism analyses; (4) utilization of recycled materials for environmentally friendly solutions; (5) maintenance and rehabilitation for an extended life span of pavement; (6) intelligent construction for project management, energy conservation, and future constructions; and (7) innovative approaches to test and evaluate the performance of pavement materials. The purpose of this Special Issue “Achievements and Prospects of Advanced Pavement Materials Technologies” is to explore new research ideas for pavement materials as described above
Effect of InSb/In0.9Al0.1Sb superlattice buffer layer on the structural and electronic properties of InSb films
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High-Integrated-Photosensitivity Negative-Electron-Affinity GaAs Photocathodes with Multilayer Be-Doping Structures
No full textThe effect of changing Be doping concentration in GaAs layer on the integrated photosensitivity for nega- tive-electron-affinity GaAs photocathodes is investigated. Two GaAs samples with the monolayer structure and the muhilayer structure are grown by molecular beam epitaxy. The former has a constant Be concentration of 1 × 10^19 cm^-3, while the latter includes four layers with Be doping concentrations of 1 × 10^19, 7 × 10^18, 4 × 10^18, and 1 × 10^18 cm^-3 from the bottom to the surface. Negative-electron-affinity GaAs photocathodes are fabricated by exciting the sample surfaces with alternating input of Cs and O in the high vacuum system. The spectral response results measured by the on-line spectral response measurement system show that the integrated photosensitivity of the photocathode with the muhilayer structure enhanced by at least 50% as compared to that of the monolayer structure. This attributes to the improvement in the crystal quality and the increase in the surface escape probability. Different stress situations are observed on GaAs samples with monolayer structure and muhilayer structure, respectively
Influences of organic–inorganic interfacial properties on the performance of a hybrid near-infrared optical upconverter
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