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, T.

doi:10.3390/nano12132220

Cited by 5 publications

(2 citation statements)

References 38 publications

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“…The width of the interaction volume for the X-ray generation of 15 kV electrons within matter was of the order of about 1 µm for GaAs and was similar for many transition metals. The X-ray detector was a 30 mm 2 Bruker X-Flash430 SDD (Bruker Nano Analytics, Berlin, Germany) mounted at a take-off angle of 22 • and equipped with an AP3.3 ultra-thin polymer window (MOXTEK, Inc., Orem, UT, USA) [32]. Bruker's Quantax70 software was used to acquire and analyze spectrum images that store complete X-ray data at 10 eV spectral resolution for each of the 640 × 480 data points.…”

Section: Methodsmentioning

confidence: 99%

Chemical Structure Comparison via Scanning Electron Microscopy of Spent Commercial Nickel–Metal Hydride Batteries

Walther

2023

Materials

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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.

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Section: Methodsmentioning

confidence: 99%

Chemical Structure Comparison via Scanning Electron Microscopy of Spent Commercial Nickel–Metal Hydride Batteries

Walther

2023

Materials

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“… Back-scattered electron SEM image in plan-view or top-down geometry (black & white) with overlaid X-ray map (coloured inset; blue represents Ga and yellow In L-line intensities) of nominally 1.5 ML InAs on GaAs(001). Reproduced from [ 30 ]. …”

Section: Figurementioning

confidence: 99%

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

Walther

2022

Nanomaterials

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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.

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Recent improvements in quantification of energy‐dispersive X‐ray spectra and maps in electron microscopy of semiconductors

Walther

2024

Applied Research

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This tutorial‐style article describes recent improvements in the quantitative application of energy‐dispersive X‐ray spectroscopy and mapping in electron microscopes to semiconductors, with a focus on spatial resolution, sensitivity and accuracy obtainable in characterising the chemical composition of thin layers, quantum wells and quantum dots. Various approaches applicable in scanning electron microscopy of bulk and (scanning) transmission electron microscopy of thin film samples are outlined. Applications to semiconductor quantum well systems, mainly based on indium gallium arsenide and silicon germanium studied in the author's laboratory, are provided as examples.

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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

Cited by 5 publications

References 38 publications

Chemical Structure Comparison via Scanning Electron Microscopy of Spent Commercial Nickel–Metal Hydride Batteries

Chemical Structure Comparison via Scanning Electron Microscopy of Spent Commercial Nickel–Metal Hydride Batteries

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

Recent improvements in quantification of energy‐dispersive X‐ray spectra and maps in electron microscopy of semiconductors

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