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Electronic properties of wurtzite GaAs： A correlated structural, optical, and theoretical analysis of the same polytypic GaAs nanowire

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Nano Research 2018年第9期11卷 4708-4721页

作者： Alexander Senichev Pierre Corfdir Oliver Brandt Manfred Ramsteiner Steffen Breuer Jorg Schilling Lutz Geelhaar Peter Werner Max-Planck-lnstitut fur Mikrostrukturl)hysik Halle 06120 Germany PauI-Drude-lnstitut for Festkorperelektronik Berlin 10117 Germany Centre for Innovation Competence SiLi-nano Martin-Luther-Universitat Halle 06120 Germany present address: Birck Nanotechnology Center Purdue University West Lafayette Indiana 47907 USA present address: fraunhofer hhi Berlin 10587 Germany present address: ABB Corporate Research Baden-Dattwi15405 Switzerland

III-V compound semiconductor nanowires are generally characterized by the coexistence of zincblende and wurtzite structures. So far, this polytypism has impeded the determination of the electronic properties of the metastable wurtzite phase of GaAs, which thus remain highly controversial. In an effort to obtain new insights into this topic, we cross-correlate nanoscale spectral imaging by near-field scanning optical microscopy with a transmission electron microscopy analysis of the very same polytypic GaAs nanowire dispersed onto a Si wafer. Thus, spatially resolved photoluminescence spectra could be unambiguously assigned to nanowire segments whose structure is known with lattice-resolved accuracy. An emission energy of 1.528 eV was observed from extended zincblende segments, revealing that the dispersed nanowire was under uniaxial strain presumably due to interaction with its supporting substrate. These crucial information and the emission energy obtained for extended pure wurtzite segments were used to perform envelope function calculations of zincblende quantum disks in a wurtzite matrix as well as the inverse structure. In these calculations, we varied the fundamental bandgap, the electron mass, and the band offset between zincblende and wurtzite GaAs. From this multi-parameter comparison with the experimental data, we deduced that the bandgap between the F8 conduction and A valence band ranges from 1.532 to 1.539 eV in strain-free wurtzite GaAs, and estimated values of 1.507 to 1.514 eV for the F7-A bandgap.

关键词： nanowires crystal-phase quantumstructures wurtzite GaAs strain near-field scanning optical microscopy photoluminescence

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Surface tracking assessment and interaction in texture space

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Computational Visual Media 2018年第1期4卷 3-15页

作者： Johannes Furch Anna Hilsmann Peter Eisert fraunhofer hhi Berlin10587Germany Humboldt University Berlin10099Germany

In this paper, we present a novel approach for assessing and interacting with surface tracking algorithms targeting video manipulation in postproduction. As tracking inaccuracies are unavoidable,we enable the user to provide small hints to the algorithms instead of correcting erroneous results afterwards. Based on 2D mesh warp-based optical flow estimation, we visualize results and provide tools for user feedback in a consistent reference system, texture space. In this space, accurate tracking results are reflected by static appearance, and errors can easily be spotted as apparent change. A variety of established tools can be utilized to visualize and assess the change between frames. User interaction to improve tracking results becomes more intuitive in texture space, as it can focus on a small region rather than a moving *** show how established tools can be implemented for interaction in texture space to provide a more intuitive interface allowing more effective and accurate user feedback.

关键词： surface tracking assessment interaction mesh warp optical flow

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Predicting an Optimal Virtual Data Model for Uniform Access to Large Heterogeneous Data

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Data Intelligence 2024年第2期6卷 504-530页

作者： Chahrazed B.Bachir Belmehdi Abderrahmane Khiat Nabil Keskes LabRI-SBA Enterprise Information SystemsESI-SBA InstituteFraunhofer IAISAlgeriaGermany

The growth of generated data in the industry requires new efficient big data integration approaches for uniform data access by end-users to perform better business *** virtualization systems,including Ontology-Based Data Access(ODBA)query data on-the-fly against the original data sources without any prior data *** approaches by design use a fixed model e.g.,TABULAR as the only Virtual Data Model-a uniform schema built on-the-fly to load,transform,and join relevant *** other data models,such as GRAPH or DOCUMENT,are more flexible and,thus,can be more suitable for some common types of queries,such as join or nested *** queries are hard to predict because they depend on many criteria,such as query plan,data model,data size,and *** address the problem of selecting the optimal virtual data model for queries on large datasets,we present a new approach that(1)builds on the principal of OBDA to query and join large heterogeneous data in a distributed manner and(2)calls a deep learning method to predict the optimal virtual data model using features extracted from SPARQL ***-implementation of our approach currently leverages state-of-the-art Big Data technologies,Apache-Spark and Graphx,and implements two virtual data models,GRAPH and TABULAR,and supports out-of-the-box five data sources models:property graph,document-based,e.g.,wide-columnar,relational,and tabular,stored in Neo4j,MongoDB,Cassandra,MySQL,and CSV *** experiments show that our approach is returning the optimal virtual model with an accuracy of 0.831,thus,a reduction in query execution time of over 40%for the tabular model selection and over 30%for the graph model selection.

关键词： Data Virtualization Big Data OBDA Deep Learning

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An efficient geosciences workflow on multi-core processors and GPUs:a case study for aerosol optical depth retrieval from MODIS satellite data

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International Journal of Digital Earth 2016年第8期9卷 748-765页

作者： Jia Liu Dustin Feld Yong Xue Jochen Garcke Thomas Soddemann Peiyuan Pan Key Laboratory of Digital Earth Science Institute of Remote Sensing and Digital EarthChinese Academy of SciencesBeijingChina Faculty of Life Sciences and Computing London Metropolitan UniversityLondonUK fraunhofer Institute for Algorithms and Scientific Computing SCAI Sankt AugustinGermany Institute for Numerical Simulation University of BonnBonnGermany University of Chinese Academy of Sciences BeijingChina Department of Computer Science University of CologneCologneGermany

Quantitative remote sensing retrieval algorithms help understanding the dynamic aspects of Digital ***,the Big Data and complex models in Digital Earth pose grand challenges for computation *** this article,taking the aerosol optical depth(AOD)retrieval as a study case,we exploit parallel computing methods for high efficient geophysical parameter *** present an efficient geocomputation workflow for the AOD calculation from the Moderate Resolution Imaging Spectroradiometer(MODIS)satellite *** to their individual potential for parallelization,several procedures were adapted and implemented for a successful parallel execution on multicore processors and Graphics Processing Units(GPUs).The benchmarks in this paper validate the high parallel performance of the retrieval workflow with speedups of up to 5.x on a multi-core processor with 8 threads and 43.x on a *** specifically address the time-consuming model retrieval part,hybrid parallel patterns which combine the multicore processor’s and the GPU’s compute power were implemented with static and dynamic workload distributions and evaluated on two systems with different CPU–GPU *** is shown that only the dynamic hybrid implementation leads to a greatly enhanced overall exploitation of the heterogeneous hardware environment in varying circumstances.

关键词： Digital earth highperformance computing GPU multi-core hybrid parallel pattern aerosol optical depth retrieval workflow

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Digital holography in production:an overview

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Light(Advanced Manufacturing) 2021年第3期2卷 1-13页

作者： Markus Fratz Tobias Seyler Alexander Bertz Daniel Carl fraunhofer Institute for Physical Measurement Techniques IPM Georges-Köhler-Allee 30179110 FreiburgGermany

Many challenging measurement tasks in production simultaneously have high requirements for accuracy,measurement field size,lateral sampling,and measurement *** this paper,we provide an overview of the current state of the art in digital holography for surface topography measurements and present three applications from completely different productions with no alternative to digital holography;we describe the HoloTop sensor family,which has been designed specifically for industrial use,and present the most recent results achieved in reallife industrial *** applications address measurement tasks that could not be solved until now,either by optical or tactile *** start with a description of the first-ever inline integration of a digital holographic measurement system that inspects precision turned parts for the automotive *** proceed by presenting measurements performed with a compact sensor that can be placed inside a tooling machine and operated fully *** this case,the tool holder was used to position the sensor *** into a tooling machine places high demands on both robustness and ***,the quality control of electronic interconnectors such as microbumps with the highest demand for accuracy and repeatability is *** of these applications illustrate the major advantages of digital holographic systems:it is possible to measure a relatively large field of view with interferometric precision and very short acquisition ***,both reflective and matt surfaces can be measured *** end this publication with an assessment of the future potential of this technology and the necessary development steps involved.

关键词： holographic steps topography

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