| 1. |
- Ali, Hasan, 1985-, et al.
(author)
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An electron energy loss spectrometer based streak camera for time resolved TEM measurements
- 2017
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In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 176, s. 5-10
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Journal article (peer-reviewed)abstract
- We propose an experimental setup based on a streak camera approach inside an energy filter to measure time resolved properties of materials in the transmission electron microscope (TEM). In order to put in place the streak camera, a beam sweeper was built inside an energy filter. After exciting the TEM sample, the beam is swept across the CCD camera of the filter. We describe different parts of the setup at the example of a magnetic measurement. This setup is capable to acquire time resolved diffraction patterns, electron energy loss spectra (EELS) and images with total streaking times in the range between 100 ns and 10 μs.
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| 2. |
- Ali, Hasan, 1985-, et al.
(author)
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Quantitative EMCD by use of a double aperture for simultaneous acquisition of EELS
- 2019
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In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 196, s. 192-196
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Journal article (peer-reviewed)abstract
- The weak signal strength in electron magnetic circular dichroism (EMCD) measurements remains one of the main challenges in the quantification of EMCD related EELS spectra. As a consequence, small variations in peak intensity caused by changes of background intervals, choice of method for extraction of signal intensity and equally differences in sample quality can cause strong changes in the EMCD signal. When aiming for high resolution quantitative EMCD, an additional difficulty consists in the fact that the two angular resolved EELS spectra needed to obtain the EMCD signal are taken at two different instances and it cannot be guaranteed that the acquisition conditions for these two spectra are identical. Here, we present an experimental setup where we use a double hole aperture in the transmission electron microscope to obtain the EMCD signal in a single acquisition. This geometry allows for the parallel acquisition of the two electron energy loss spectra (EELS) under exactly the same conditions. We also compare the double aperture acquisition mode with the qE acquisition mode which has been previously used for parallel acquisition of EMCD. We show that the double aperture mode not only offers better signal to noise ratio as compared to qE mode but also allows for much higher acquisition times to significantly improve the signal quality which is crucial for quantitative analysis of the magnetic moments.
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| 3. |
- Boll, Torben, 1979, et al.
(author)
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An APT investigation of an amorphous Cr-B-C thin film
- 2015
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In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 159, s. 217-222
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Journal article (peer-reviewed)abstract
- A magnetron sputtered amorphous Cr-B-C thin film was investigated by means of atom probe tomography (APT). The film is constituted of two phases; a Cr-rich phase present as a few nanometer large regions embedded in a Cr-poor phase (tissue phase). The Cr-rich regions form columnar chains oriented parallel to the growth direction of the film. It was found that the Cr-rich regions have a higher B:C ratio than the Cr-poor regions. The composition of the phases was determined as approximately 35Cr-33B-30C and 15Cr-40B-42C (at%), respectively. The results suggest that this type of nanocomposite films has a more complex structure than previously anticipated, which may have an importance for the mechanical and electrical properties.
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| 4. |
- Bäcke, Olof, 1984, et al.
(author)
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Enhanced thermal stability of a polymer solar cell blend induced by electron beam irradiation in the transmission electron microscope
- 2017
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In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 173, s. 16-23
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Journal article (peer-reviewed)abstract
- We show by in situ microscopy that the effects of electron beam irradiation during transmission electron microscopy can be used to lock microstructural features and enhance the structural thermal stability of a nanostructured polymer:fullerene blend. Polymer:fullerene bulk-heterojunction thin films show great promise for use as active layers in organic solar cells but their low thermal stability is a hindrance. Lack of thermal stability complicates manufacturing and influences the lifetime of devices. To investigate how electron irradiation affects the thermal stability of polymer:fullerene films, a model bulk-heterojunction film based on a thiophene-quinoxaline copolymer and a fullerene derivative was heat-treated in-situ in a transmission electron microscope. In areas of the film that exposed to the electron beam the nanostructure of the film remained stable, while the nanostructure in areas not exposed to the electron beam underwent large phase separation and nucleation of fullerene crystals. UV–vis spectroscopy shows that the polymer:fullerene films are stable for electron doses up to 2000 kGy.
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| 5. |
- Bäcke, Olof, 1984, et al.
(author)
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Enhanced thermal stability of a polymer solar cell blend induced by electron beam irradiation in the transmission electron microscope
- 2017
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In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 176:Spec. Issue, s. 23-30
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Journal article (peer-reviewed)abstract
- We show by in situ microscopy that the effects of electron beam irradiation during transmission electron microscopy can be used to lock microstructural features and enhance the structural thermal stability of a nanostructured polymer:fullerene blend. Polymer:fullerene bulk-heterojunction thin films show great promise for use as active layers in organic solar cells but their low thermal stability is a hindrance. Lack of thermal stability complicates manufacturing and influences the lifetime of devices. To investigate how electron irradiation affects the thermal stability of polymer:fullerene films, a model bulk-heterojunction film based on a thiophene-quinoxaline copolymer and a fullerene derivative was heat-treated in-situ in a transmission electron microscope. In areas of the film that exposed to the electron beam the nanostructure of the film remained stable, while the nanostructure in areas not exposed to the electron beam underwent large phase separation and nucleation of fullerene crystals. UV–vis spectroscopy shows that the polymer:fullerene films are stable for electron doses up to 2000 kGy.
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| 6. |
- Engberg, David, et al.
(author)
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Resolving mass spectral overlaps in atom probe tomography by isotopic substitutions – case of TiSi15N
- 2018
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In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 184, s. 51-60
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Journal article (peer-reviewed)abstract
- Mass spectral overlaps in atom probe tomography (APT) analyses of complex compounds typically limit the identification of elements and microstructural analysis of a material. This study concerns the TiSiN system, chosen because of severe mass-to-charge-state ratio overlaps of the 14 N + and 28 Si 2+ peaks as well as the 14N 2 + and 28 Si + peaks. By substituting 14 N with 15 N, mass spectrum peaks generated by ions composed of one or more N atoms will be shifted toward higher mass-to-charge-state ratios, thereby enabling the separation of N from the predominant Si isotope. We thus resolve thermodynamically driven Si segregation on the nanometer scale in cubic phase Ti 1- x Si x 15 N thin films for Si contents 0.08 ≤ x ≤ 0.19 by APT, as corroborated by transmission electron microscopy. The APT analysis yields a composition determination that is in good agreement with energy dispersive X-ray spectroscopy and elastic recoil detection analyses. Additionally, a method for determining good voxel sizes for visualizing small-scale fluctuations is presented and demonstrated for the TiSiN system.
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| 7. |
- Esmaily, Mohsen, 1987, et al.
(author)
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On the capability of in-situ exposure in an environmental scanning electron microscope for investigating the atmospheric corrosion of magnesium
- 2015
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In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 153, s. 45-54
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Journal article (peer-reviewed)abstract
- The feasibility of environmental scanning electron microscope (BEM) in studying the atmospheric corrosion behavior of 99.97% Mg was investigated. For reference, ex-situ exposure was performed. A model system was designed by spraying few salt particles on the metal surface and further promoting the corrosion process using platinum (Pt) deposition in the form of 1 x 1 x 1 pm(3) dots around the salt particles to create strong artificial cathodic sites. The results showed that the electron beam play a significant role in the corrosion process of scanned regions. This was attributed to the irradiation damage occurring on the metal surface during the BEM in-situ experiment. After achieving to a reliable process route, in a successful attempt, the morphology and composition of the corrosion products formed in-situ in the ESEM were in agreement with those of the sample exposed ex-situ.
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| 8. |
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| 9. |
- Koeck, Philip J. B.
(author)
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Annular dark field transmission electron microscopy for protein structure determination
- 2016
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In: Ultramicroscopy. - : Elsevier. - 0304-3991 .- 1879-2723. ; 161, s. 98-104
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Journal article (peer-reviewed)abstract
- Recently annular dark field (ADF) transmission electron microscopy (TEM) has been advocated as a means of recording images of biological specimens with better signal to noise ratio (SNR) than regular bright field images. I investigate whether and how such images could be used to determine the three-dimensional structure of proteins given that an ADF aperture with a suitable pass-band can be manufactured and used in practice. I develop an approximate theory of ADF-TEM image formation for weak amplitude and phase objects and test this theory using computer simulations. I also test whether these simulated images can be used to calculate a three-dimensional model of the protein using standard software and discuss problems and possible ways to overcome these.
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| 10. |
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