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  1. Article: Modelling and evaluation of material flow networks for recycling of discarded products /Grit Walther and Thomas Spengler

    Walther, Grit / Spengler, Thomas

    Logistik-Management : Prozesse, Systeme, Ausbildung ; mit 55 Tabellen

    2004  

    Language English
    Size graph. Darst
    Publisher Physica-Verl.
    Publishing place Heidelberg
    Document type Article
    Database ECONomics Information System

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  2. Article: Chemical Structure Comparison via Scanning Electron Microscopy of Spent Commercial Nickel-Metal Hydride Batteries.

    Walther, Thomas

    Materials (Basel, Switzerland)

    2023  Volume 16, Issue 17

    Abstract: Back-scattered electron imaging and X-ray elemental mapping were combined in a tabletop scanning electron microscope (SEM) to investigate cross-sections of three AA-type (mignon) nickel-metal hydride (NiMH) batteries from different manufacturers. All ... ...

    Abstract Back-scattered electron imaging and X-ray elemental mapping were combined in a tabletop scanning electron microscope (SEM) to investigate cross-sections of three AA-type (mignon) nickel-metal hydride (NiMH) batteries from different manufacturers. All batteries underwent 500-800 charge/discharge cycles and reached their end of lifetime after several years as they could no longer hold any significant electric charge (less than 20% of nominal charge capacity), but none showed any short-circuiting. The types of degradation observed in this field study included electrode swelling, metallic nickel formation and carbon incorporation into pores in the positive electrodes and, in the negative electrodes, metal alloy segregation of different elements such as nickel, lanthanum and, in one case, sodium, as well as grain break-up and pore formation. All these phenomena could readily be observed at rather small magnifications. This will be important for the improvement of NiMH batteries, for which new generations with nominally slightly increased charge capacities are being marketed all the time.
    Language English
    Publishing date 2023-08-23
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2487261-1
    ISSN 1996-1944
    ISSN 1996-1944
    DOI 10.3390/ma16175761
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article: Measuring Non-Destructively the Total Indium Content and Its Lateral Distribution in Very Thin Single Layers or Quantum Dots Deposited onto Gallium Arsenide Substrates Using Energy-Dispersive X-ray Spectroscopy in a Scanning Electron Microscope.

    Walther, Thomas

    Nanomaterials (Basel, Switzerland)

    2022  Volume 12, Issue 13

    Abstract: The epitaxial deposition of a precise number, or even fractions, of monolayers of indium (In)-rich semiconductors onto gallium arsenide (GaAs) substrates enables the creation of quantum dots based on InAs, InGaAs and indium phosphide (InP) for infrared ... ...

    Abstract The epitaxial deposition of a precise number, or even fractions, of monolayers of indium (In)-rich semiconductors onto gallium arsenide (GaAs) substrates enables the creation of quantum dots based on InAs, InGaAs and indium phosphide (InP) for infrared light-emitting and laser diodes and the formation of indium antimonide (InSb)/GaAs strained layer superlattices. Here, a facile method based on energy-dispersive X-ray spectroscopy (EDXS) in a scanning electron microscope (SEM) is presented that allows the indium content of a single semiconductor layer deposited on a gallium arsenide substrate to be measured with relatively high accuracy (±0.7 monolayers). As the procedure works in top-down geometry, where any part of a wafer can be inspected, measuring the In content of the surface layer in one location without destroying it can also be used to map the lateral indium distribution during quantum dot formation and is a method suitable as an in-situ quality control tool for epitaxy.
    Language English
    Publishing date 2022-06-28
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2662255-5
    ISSN 2079-4991
    ISSN 2079-4991
    DOI 10.3390/nano12132220
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article: Role of Interdiffusion and Segregation during the Life of Indium Gallium Arsenide Quantum Dots, from Cradle to Grave.

    Walther, Thomas

    Nanomaterials (Basel, Switzerland)

    2022  Volume 12, Issue 21

    Abstract: This article summarizes our understanding of the interplay between diffusion and segregation during epitaxial growth of InGaAs and InAs quantum dots. These quantum dots form spontaneously on flat GaAs (001) single-crystalline substrates by the so-called ... ...

    Abstract This article summarizes our understanding of the interplay between diffusion and segregation during epitaxial growth of InGaAs and InAs quantum dots. These quantum dots form spontaneously on flat GaAs (001) single-crystalline substrates by the so-called Stranski-Krastanow growth mechanism once a sufficient amount of indium has accumulated on the surface. Initially a perfectly flat wetting layer is formed. This strained layer then starts to roughen as strain increases, leading first to small, long-range surface undulations and then to tiny coherent islands. These continue to grow, accumulating indium both from the underlying wetting layer by lateral indium segregation and from within these islands by vertical segregation, which for InGaAs deposition results in an indium-enriched InGaAs alloy in the centre of the quantum dots. For pure InAs deposition, interdiffusion also results in an InGaAs alloy. Further deposition can lead to the formation of misfit dislocations that nucleate at the edges of the islands and are generally sought to be avoided. Overgrowth by GaAs or InGaAs alloys with low indium content commences preferentially between the islands, avoiding their strained edges, which initially leads to trench formation. Further deposition is necessary to cap these quantum dots effectively and to re-gain an almost flat surface that can then be used for subsequent deposition of multiple layers of quantum dots as needed for many optoelectronic devices.
    Language English
    Publishing date 2022-10-31
    Publishing country Switzerland
    Document type Journal Article ; Review
    ZDB-ID 2662255-5
    ISSN 2079-4991
    ISSN 2079-4991
    DOI 10.3390/nano12213850
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article ; Online: Preface to the special issue on Microscopy of Semiconducting Materials 2023.

    Walther, Thomas / Oliver, Rachel A

    Journal of microscopy

    2024  Volume 293, Issue 3, Page(s) 135–137

    Language English
    Publishing date 2024-01-28
    Publishing country England
    Document type Editorial
    ZDB-ID 219263-9
    ISSN 1365-2818 ; 0022-2720
    ISSN (online) 1365-2818
    ISSN 0022-2720
    DOI 10.1111/jmi.13265
    Database MEDical Literature Analysis and Retrieval System OnLINE

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    In stock of ZB MED Cologne/Königswinter

    Zs.A 838: Show issues Location:
    Je nach Verfügbarkeit (siehe Angabe bei Bestand)
    bis Jg. 1994: Bestellungen von Artikeln über das Online-Bestellformular
    Jg. 1995 - 2021: Lesesall (1.OG)
    ab Jg. 2022: Lesesaal (EG)

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  6. Article ; Online: Towards quantification of doping in gallium arsenide nanostructures by low-energy scanning electron microscopy and conductive atomic force microscopy.

    Guo, Ran / Walther, Thomas

    Journal of microscopy

    2024  Volume 293, Issue 3, Page(s) 160–168

    Abstract: We calculate a universal shift in work function of 59.4 meV per decade of dopant concentration change that applies to all doped semiconductors and from this use Monte Carlo simulations to simulate the resulting change in secondary electron yield for ... ...

    Abstract We calculate a universal shift in work function of 59.4 meV per decade of dopant concentration change that applies to all doped semiconductors and from this use Monte Carlo simulations to simulate the resulting change in secondary electron yield for doped GaAs. We then compare experimental images of doped GaAs layers from scanning electron microscopy and conductive atomic force microscopy. Kelvin probe force microscopy allows to directly measure and map local work function changes, but values measured are often smaller, typically only around half, of what theory predicts for perfectly clean surfaces.
    Language English
    Publishing date 2024-01-18
    Publishing country England
    Document type Journal Article
    ZDB-ID 219263-9
    ISSN 1365-2818 ; 0022-2720
    ISSN (online) 1365-2818
    ISSN 0022-2720
    DOI 10.1111/jmi.13263
    Database MEDical Literature Analysis and Retrieval System OnLINE

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    In stock of ZB MED Cologne/Königswinter

    Zs.A 838: Show issues Location:
    Je nach Verfügbarkeit (siehe Angabe bei Bestand)
    bis Jg. 1994: Bestellungen von Artikeln über das Online-Bestellformular
    Jg. 1995 - 2021: Lesesall (1.OG)
    ab Jg. 2022: Lesesaal (EG)

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  7. Article ; Online: Role of Interdiffusion and Segregation during the Life of Indium Gallium Arsenide Quantum Dots, from Cradle to Grave

    Thomas Walther

    Nanomaterials, Vol 12, Iss 3850, p

    2022  Volume 3850

    Abstract: This article summarizes our understanding of the interplay between diffusion and segregation during epitaxial growth of InGaAs and InAs quantum dots. These quantum dots form spontaneously on flat GaAs (001) single-crystalline substrates by the so-called ... ...

    Abstract This article summarizes our understanding of the interplay between diffusion and segregation during epitaxial growth of InGaAs and InAs quantum dots. These quantum dots form spontaneously on flat GaAs (001) single-crystalline substrates by the so-called Stranski-Krastanow growth mechanism once a sufficient amount of indium has accumulated on the surface. Initially a perfectly flat wetting layer is formed. This strained layer then starts to roughen as strain increases, leading first to small, long-range surface undulations and then to tiny coherent islands. These continue to grow, accumulating indium both from the underlying wetting layer by lateral indium segregation and from within these islands by vertical segregation, which for InGaAs deposition results in an indium-enriched InGaAs alloy in the centre of the quantum dots. For pure InAs deposition, interdiffusion also results in an InGaAs alloy. Further deposition can lead to the formation of misfit dislocations that nucleate at the edges of the islands and are generally sought to be avoided. Overgrowth by GaAs or InGaAs alloys with low indium content commences preferentially between the islands, avoiding their strained edges, which initially leads to trench formation. Further deposition is necessary to cap these quantum dots effectively and to re-gain an almost flat surface that can then be used for subsequent deposition of multiple layers of quantum dots as needed for many optoelectronic devices.
    Keywords electron microscopy ; InGaAs ; Stranski-Krastanow ; islands ; quantum dots ; Chemistry ; QD1-999
    Subject code 530
    Language English
    Publishing date 2022-10-01T00:00:00Z
    Publisher MDPI AG
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

    Full text online

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  8. Article ; Online: Measuring Non-Destructively the Total Indium Content and Its Lateral Distribution in Very Thin Single Layers or Quantum Dots Deposited onto Gallium Arsenide Substrates Using Energy-Dispersive X-ray Spectroscopy in a Scanning Electron Microscope

    Thomas Walther

    Nanomaterials, Vol 12, Iss 13, p

    2022  Volume 2220

    Abstract: The epitaxial deposition of a precise number, or even fractions, of monolayers of indium (In)-rich semiconductors onto gallium arsenide (GaAs) substrates enables the creation of quantum dots based on InAs, InGaAs and indium phosphide (InP) for infrared ... ...

    Abstract The epitaxial deposition of a precise number, or even fractions, of monolayers of indium (In)-rich semiconductors onto gallium arsenide (GaAs) substrates enables the creation of quantum dots based on InAs, InGaAs and indium phosphide (InP) for infrared light-emitting and laser diodes and the formation of indium antimonide (InSb)/GaAs strained layer superlattices. Here, a facile method based on energy-dispersive X-ray spectroscopy (EDXS) in a scanning electron microscope (SEM) is presented that allows the indium content of a single semiconductor layer deposited on a gallium arsenide substrate to be measured with relatively high accuracy (±0.7 monolayers). As the procedure works in top-down geometry, where any part of a wafer can be inspected, measuring the In content of the surface layer in one location without destroying it can also be used to map the lateral indium distribution during quantum dot formation and is a method suitable as an in-situ quality control tool for epitaxy.
    Keywords scanning electron microscopy (SEM) ; energy-dispersive X-ray spectroscopy (EDXS) ; InGaAs ; Stranski–Krastanov ; quantum dots ; Chemistry ; QD1-999
    Subject code 530
    Language English
    Publishing date 2022-06-01T00:00:00Z
    Publisher MDPI AG
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

    Full text online

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    Inter-library loan at ZB MED

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  9. Article: Measurement of Nanometre-Scale Gate Oxide Thicknesses by Energy-Dispersive X-ray Spectroscopy in a Scanning Electron Microscope Combined with Monte Carlo Simulations.

    Walther, Thomas

    Nanomaterials (Basel, Switzerland)

    2021  Volume 11, Issue 8

    Abstract: A procedure based on energy-dispersive X-ray spectroscopy in a scanning electron microscope (SEM-EDXS) is proposed to measure ultra-thin oxide layer thicknesses to atomic scale precision in top-down instead of cross-sectional geometry. The approach is ... ...

    Abstract A procedure based on energy-dispersive X-ray spectroscopy in a scanning electron microscope (SEM-EDXS) is proposed to measure ultra-thin oxide layer thicknesses to atomic scale precision in top-down instead of cross-sectional geometry. The approach is based on modelling the variation of the electron beam penetration depth and hence the depth of X-ray generation in the sample as a function of the acceleration voltage. This has been tested for the simple case of silica on silicon (SiO
    Language English
    Publishing date 2021-08-20
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2662255-5
    ISSN 2079-4991
    ISSN 2079-4991
    DOI 10.3390/nano11082117
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  10. Book: Thomas Mann und Hans Friedrich Blunck

    Blunck, Walther / Blunck, Hans Friedrich / Mann, Thomas

    Jahrbuch ... der Gesellschaft zur Förderung des Werkes von Hans Friedrich Blunck e.V. ; 1968

    Briefwechsel und Aufzeichnungen ; [zugleich eine Dokumentation]

    1969  

    Author's details Walther Blunck
    Language German
    Size 147 S., Ill.
    Publisher Troll-Verl
    Publishing place Hamburg
    Document type Book
    Database Former special subject collection: coastal and deep sea fishing

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