| 1. |
- Bovin, J O, et al.
(author)
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TEM-tomography of FAU-zeolite crystals containing Pt-clusters
- 1996
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In: Ultramicroscopy. - : Elsevier BV. - 0304-3991. ; 62:4, s. 81-277
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Journal article (peer-reviewed)abstract
- A method for preparing ultrathin sections (- 20 nm) of inorganic solids has been developed using ultramicrotomy of resin-embedded crystal fragments. Undamaged crystals, oriented along a crystallographic direction, could be imaged with transmission electron microscopy (TEM) at a resolution better than 0.5 nm. The true internal structure of the crystals could be investigated by imaging the second in a series of at least three consecutive ultrathin sections. Such TEM-tomography proved that Pt-ion exchanged FAU zeolite crystals, after reduction and oxidation, are occupied internally and randomly of large platinum clusters mainly in the {111-twin planes. TEM-tomography could be useful in man made nanostructures like semiconductors, epitaxial thin films, hard metal coatings, ceramics, catalysts, and biomaterials.
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| 2. |
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| 3. |
- Henning, P, et al.
(author)
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Compositional information from amorphous Si-Ge multilayers using high-resolution electron microscopy imaging and direct digital recording
- 1996
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In: Ultramicroscopy. - 0304-3991. ; 66:3-4, s. 221-235
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Journal article (peer-reviewed)abstract
- A simple method for extracting compositional information from high-resolution electron microscopy images of an amorphous two-element system using a slow-scan CCD camera has been developed. The method has been evaluated on amorphous Si/Ge multilayers. The characterisation of the multilayers provided information about thickness of the layers, maximum concentrations within the layers and elemental profiles across the boundaries. It was shown that the intensity profiles could be corrected for the wedge shape of the specimen and that the derived compositional profile was independent of average sample thickness variation within the range of the cross-section sample thickness.The results have been compared to analysis performed by Auger electron spectroscopy depth profiling on as-prepared multilayers as well as by energy-dispersive X-ray analysis and electron energy filtered images of cross-sections. The proposed HREM image contrast evaluation method gave spatial resolution in chemical analysis across the thin layers comparable in accuracy to the other methods, whereas the oscillation amplitude for the concentration is slightly less due to specimen preparation artifacts.
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| 4. |
- Hertz, H.M, et al.
(author)
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Optically trapped non-linear particles as probes for scanning near-field optical microscopy
- 1995
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In: Ultramicroscopy. - 0304-3991. ; 57:2-3, s. 309-312
-
Journal article (peer-reviewed)abstract
- We use the frequency doubled light from an optically trapped lithium niobate particle for non-intrusive scanning near-field optical microscopy. The detected power from this 50-100 nm diameter probe is currently tens of pW and is expected to approach nW with an improved detection system. The current experimental resolution is approximately 0.5 [mu]m, while the ultimate theoretical resolution is 70-90 nm. An acoustic trap which potentially allows higher resolution imaging is briefly described.
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| 5. |
- Wallenberg, LR, et al.
(author)
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Atomic-resolution study of structural rearrangements in small platinum crystals
- 1986
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991. ; 20:1-2, s. 71-75
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Journal article (peer-reviewed)abstract
- Structural rearrangements in small Pt crystals, which were initiated by the incident electron beam, have been studied in real time with a 400 kV high-resolution electron microscope equipped with TV image viewing and videorecording facilities. The phenomena of crystal growth, particle coalescence and atomic clouds above particular surfaces were recorded at the atomic level and have been analysed using frame-by-frame playback facilities.
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| 6. |
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| 7. |
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| 8. |
- Wallenberg, Reine, et al.
(author)
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Vanadium Oxide on TiO2(B) - a HREM Study of Catalysis by Support Interaction
- 1990
-
In: Ultramicroscopy. - 0304-3991. ; 34:1-2, s. 33-40
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Journal article (peer-reviewed)abstract
- A model catalyst system with a loading range between 1/4 to 10 theoretical layers of vanadium oxide on TiO2(B ) support was tried for selective ammoxidation and oxidation of toluene. In the case of ammoxidation, a peak in conversion rate per unit surface area was found for a catalyst with a coverage of about 2 theoretical layers, indicating a strong interaction between the catalyst and the otherwise inactive support. The presence and amount of vanadium oxide on the support surface was verified by diffuse reflectance infrared spectroscopy, energy-dispersive elemental X-ray mapping and chemical analysis. By high resolution electron microscopy, the 32~ volume loss of the K2Ti409 support precursor on calcination was shown to be achieved by formation of microscopic, facetted voids ("negative crystals") in the bulk of the material. Initially, surfaces appeared dean and without any anomalous surface features. This can be explained by similar scattering power of V and Ti, and similar structure types. However, the active phase could be "developed" to visibility by prolonged exposure to the electron beam, which produced 1-2 am particles of reduced vanadium oxides on the surface.
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| 9. |
- Czigany, Zs., et al.
(author)
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Imaging of fullerene-like structures in CNx thin films by electron microscopy, Sample preparation artefacts due to ion-beam milling
- 2003
-
In: Ultramicroscopy. - 0304-3991 .- 1879-2723. ; 94:3-4, s. 163-173
-
Journal article (peer-reviewed)abstract
- The microstructure of CNx thin films, deposited by reactive magnetron sputtering, was investigated by transmission electron microscopy (TEM) at 200kV in plan-view and cross-sectional samples. Imaging artefacts arise in high-resolution TEM due to overlap of nm-sized fullerene-like features for specimen thickness above 5nm. The thinnest and apparently artefact-free areas were obtained at the fracture edges of plan-view specimens floated-off from NaCl substrates. Cross-sectional samples were prepared by ion-beam milling at low energy to minimize sample preparation artefacts. The depth of the ion-bombardment-induced surface amorphization was determined by TEM cross sections of ion-milled fullerene-like CNx surfaces. The thickness of the damaged surface layer at 5° grazing incidence was 13 and 10nm at 3 and 0.8keV, respectively, which is approximately three times larger than that observed on Si prepared under the same conditions. The shallowest damage depth, observed for 0.25keV, was less than 1nm. Chemical changes due to N loss and graphitization were also observed by X-ray photoelectron spectroscopy. As a consequence of chemical effects, sputtering rates of CNx films were similar to that of Si, which enables relatively fast ion-milling procedure compared to carbon compounds. No electron beam damage of fullerene-like CNx was observed at 200kV. © 2002 Elsevier Science B.V. All rights reserved.
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| 10. |
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| 11. |
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| 12. |
- McCaffrey, J.P., et al.
(author)
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Surface damage formation during ion-beam thinning of samples for transmission electron microscopy
- 2001
-
In: Ultramicroscopy. - 0304-3991 .- 1879-2723. ; 87:3, s. 97-104
-
Journal article (peer-reviewed)abstract
- All techniques employed in the preparation of samples for transmission electron microscopy (TEM) introduce or include artifacts that can degrade the images of the materials being studied. One significant cause of this image degradation is surface amorphization. The damaged top and bottom surface layers of TEM samples can obscure subtle detail, particularly at high magnification. Of the techniques typically used for TEM sample preparation of semiconducting materials, cleaving produces samples with the least surface amorphization, followed by low-angle ion milling, conventional ion milling, and focused ion beam (FIB) preparation. In this work, we present direct measurements of surface damage on silicon produced during TEM sample preparation utilizing these techniques. The thinnest damaged layer formed on a silicon surface was measured as 1.5nm thick, while an optimized FIB sample preparation process results in the formation of a 22nm thick damaged layer. Lattice images are obtainable from all samples. Copyright © 2001 Elsevier Science B.V.
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| 13. |
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| 14. |
- Stöger, M., et al.
(author)
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Separation of pure elemental and oxygen influenced signal in ELNES
- 2002
-
In: Ultramicroscopy. - 0304-3991 .- 1879-2723. ; 92:3-4, s. 285-292
-
Journal article (peer-reviewed)abstract
- The energy loss near edge structure (ELNES) of many elements is strongly influenced by the presence of oxygen or other elements at surfaces, grain boundaries, or in the bulk material. The presented investigation deals mainly with the influence of oxygen at the surface. A method for the separation of both, the pure bulk signal and the oxidized surface signal, was evaluated and tested on Al, Cu, Mg, and Si. A comparison of experimental data with ab initio bandstructure calculations and other proofs of the accuracy of ELNES separation are presented. Influences of error propagations were tested and are exemplarily given for Al and Si.
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| 15. |
- Ali, Hasan, 1985-, et al.
(author)
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An electron energy loss spectrometer based streak camera for time resolved TEM measurements
- 2017
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 176, s. 5-10
-
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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| 16. |
- Ali, Hasan, 1985-, et al.
(author)
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Noise-dependent bias in quantitative STEM-EMCD experiments revealed by bootstrapping
- 2024
-
In: Ultramicroscopy. - : Elsevier. - 0304-3991 .- 1879-2723. ; 257
-
Journal article (peer-reviewed)abstract
- Electron magnetic circular dichroism (EMCD) is a powerful technique for estimating element-specific magnetic moments of materials on nanoscale with the potential to reach atomic resolution in transmission electron microscopes. However, the fundamentally weak EMCD signal strength complicates quantification of magnetic moments, as this requires very high precision, especially in the denominator of the sum rules. Here, we employ a statistical resampling technique known as bootstrapping to an experimental EMCD dataset to produce an empirical estimate of the noise-dependent error distribution resulting from application of EMCD sum rules to bcc iron in a 3-beam orientation. We observe clear experimental evidence that noisy EMCD signals preferentially bias the estimation of magnetic moments, further supporting this with error distributions produced by Monte-Carlo simulations. Finally, we propose guidelines for the recognition and minimization of this bias in the estimation of magnetic moments.
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| 17. |
- Ali, Hasan, 1985-, et al.
(author)
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Quantitative EMCD by use of a double aperture for simultaneous acquisition of EELS
- 2019
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 196, s. 192-196
-
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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| 18. |
- Ali, Hasan, 1985-, et al.
(author)
-
Single scan STEM-EMCD in 3-beam orientation using a quadruple aperture
- 2023
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 251
-
Journal article (peer-reviewed)abstract
- The need to acquire multiple angle-resolved electron energy loss spectra (EELS) is one of the several critical challenges associated with electron magnetic circular dichroism (EMCD) experiments. If the experiments are performed by scanning a nanometer to atomic-sized electron probe on a specific region of a sample, the precision of the local magnetic information extracted from such data highly depends on the accuracy of the spatial registration between multiple scans. For an EMCD experiment in a 3-beam orientation, this means that the same specimen area must be scanned four times while keeping all the experimental conditions same. This is a non-trivial task as there is a high chance of morphological and chemical modification as well as non-systematic local orientation variations of the crystal between the different scans due to beam damage, contamination and spatial drift. In this work, we employ a custom-made quadruple aperture to acquire the four EELS spectra needed for the EMCD analysis in a single electron beam scan, thus removing the above-mentioned complexities. We demonstrate a quantitative EMCD result for a beam convergence angle corresponding to sub-nm probe size and compare the EMCD results for different detector geometries.
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| 19. |
- Angseryd, Jenny, 1979, et al.
(author)
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Quantitative APT analysis of Ti(C,N)
- 2011
-
In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 111:6, s. 609-614
-
Journal article (peer-reviewed)abstract
- A specially produced Ti(C,N) standard material, with a known nominal composition, was investigated with laser assisted atom probe tomography. The occurrence of molecular ions and single/multiple events was found to be influenced by the laser pulse energy, and especially C related events were affected. Primarily two issues were considered when the composition of Ti(C,N) was determined. The first one is connected to detector efficiency, due to the detector dead-time. The second one is connected to peak overlap in the mass spectrum. A method is proposed for quantification of the C content in order to establish the C/N ratio. A correction was made to the major C peaks, C at 6 and 12 Da, with the 13C isotopes, at 6.5 and 13 Da, according to the known natural abundance. In addition, a correction of the peak at 24 Da, where C and Ti overlap, is proposed based on the occurrence of single/multiple events for respective element. The results were compared to the results from other techniques such as electron energy loss spectroscopy, chemical analysis and X-ray diffraction. After applying the corrections, atom probe tomography results were satisfactory. Furthermore, the content of dissolved O in Ti(C,N) was successfully quantified. © 2011 Elsevier B.V.
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| 20. |
- Boll, Torben, 1979, et al.
(author)
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An APT investigation of an amorphous Cr-B-C thin film
- 2015
-
In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 159, s. 217-222
-
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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| 21. |
- 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
-
In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 173, s. 16-23
-
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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| 22. |
- Bäcke, Olof, 1984, et al.
(author)
-
Enhanced thermal stability of a polymer solar cell blend induced by electron beam irradiation in the transmission electron microscope
- 2017
-
In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 176:Spec. Issue, s. 23-30
-
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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| 23. |
- Calmels, Lionel, et al.
(author)
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Momentum-resolved EELS and EMCD spectra from the atomic multiplet theory : application to magnetite
- 2010
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 110:8, s. 1042-1045
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Journal article (peer-reviewed)abstract
- While the energy loss near edge structures of metallic crystals can be calculated with a good accuracy using density functional theory based codes, core-level spectra of transition metal oxides show pronounced multiplet effects which are better described by atomic multiplet codes. We describe the formalism which allows to calculate momentum-resolved electron energy loss spectra in the electric dipole approximation from the atomic multiplet theory, and we apply this formalism to the calculation of energy loss magnetic chiral dichroic spectra of magnetic transition metal oxides. Explicit results are given for magnetite Fe3O4.
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| 24. |
- Czigany, Zsolt, et al.
(author)
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Interpretation of electron diffraction patterns from amorphous and fullerene-like carbon allotropes
- 2010
-
In: Ultramicroscopy. - : Elsevier Science B.V., Amsterdam.. - 0304-3991 .- 1879-2723. ; 110:7, s. 815-819
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Journal article (peer-reviewed)abstract
- The short range order in amorphous and fullerene-like carbon compounds has been characterized by selected area electron diffraction (SAED) patterns and compared with simulations of model nanoclusters. Broad rings in SAED pattern from fullerene-like CNx at similar to 1.2, similar to 2, and similar to 3.5 angstrom indicate short-range order similar to that in graphite, but peak shifts indicate sheet curvature in agreement with high-resolution transmission electron microscopy images. Fullerene-like CPx exhibits rings at similar to 1.6 and 2.6 angstrom, which can be explained if it consists of fragments with short-range order and high curvature similar to that of C-20.
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| 25. |
- Davidsson, P, et al.
(author)
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DESIGN AND OPERATION OF A LOW-TEMPERATURE SCANNING TUNNELING MICROSCOPE SUITABLE FOR OPERATION BELOW 1-K
- 1992
-
In: Ultramicroscopy. - 0304-3991 .- 1879-2723. ; 42-44, s. 1470-1475
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Journal article (peer-reviewed)abstract
- A scanning tunneling microscope suitable for very low temperatures has been designed, and preliminary testing has been carried out. In order to improve cooling and temperature uniformity the instrument is arranged for operation immersed in the 3He-4He mixture inside the mixing chamber of a small dilution refrigerator. A discussion of the specific problems present in the design of this kind of an instrument is given as well as a description of our design. Special attention is given to the vacuum sealing and vibration-damping solutions required.
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| 26. |
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| 27. |
- Engberg, David, et al.
(author)
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Resolving mass spectral overlaps in atom probe tomography by isotopic substitutions – case of TiSi15N
- 2018
-
In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 184, s. 51-60
-
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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| 28. |
- 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
-
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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| 29. |
- Farahi, R. H., et al.
(author)
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Microscale Marangoni actuation : All-optical and all-electrical methods
- 2006
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 106:8-9, s. 815-821
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Journal article (peer-reviewed)abstract
- We present experimental results from an all-optical microfluidic platform that may be complimented by a thin film all-electrical network. Using these configurations we have studied the microfluidic convective flow systems of silicone oil, glycerol, and 1,3,5-trinitrotoluene on open surfaces through the production of surface tension gradients derived from thermal gradients. We show that sufficient localized thermal variation can be created utilizing surface plasmons and/or engaging individually addressable resistive thermal elements. Both studies manipulate fluids via Marangoni forces, each having their unique exploitable advantages. Surface plasmon excitation in metal foils are the driving engine of many physical-, chemical-, and bio-sensing applications. Incorporating, for the first time, the plasmon concept in microfluidics, our results thus demonstrate great potential for simultaneous fluid actuation and sensing. (c) 2006 Elsevier B.V. All rights reserved.
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| 30. |
- Flege, Jan Ingo, et al.
(author)
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Nanoscale analysis of the oxidation state and surface termination of praseodymium oxide ultrathin films on ruthenium(0001)
- 2017
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991. ; 183, s. 61-66
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Journal article (peer-reviewed)abstract
- The complex structure and morphology of ultrathin praseodymia films deposited on a ruthenium(0001) single crystal substrate by reactive molecular beam epitaxy is analyzed by intensity-voltage low-energy electron microscopy in combination with theoretical calculations within an ab initio scattering theory. A rich coexistence of various nanoscale crystalline surface structures is identified for the as-grown samples, notably comprising two distinct oxygen-terminated hexagonal Pr2O3(0001) surface phases as well as a cubic Pr2O3(111) and a fluorite PrO2(111) surface component. Furthermore, scattering theory reveals a striking similarity between the electron reflectivity spectra of praseodymia and ceria due to very efficient screening of the nuclear charge by the extra 4f electron in the former case.
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| 31. |
- Forsberg, Johan, et al.
(author)
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A versatile soft x-ray transmission system for time resolved in situ microscopy with chemical contrast
- 2009
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In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 109:9, s. 1157-1163
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Journal article (peer-reviewed)abstract
- We present the design and operation of a versatile soft X-ray transmission system for time resolved in situ microscopy with chemical contrast. The utility of the setup is demonstrated by results from following a corrosion process of iron in saline environment, subjected to a controlled humid atmosphere. The system includes a transmission flow-cell reactor that allows for in situ microscopic probing with soft X-rays. We employ a full field technique by using a nearly collimated X-ray beam that produces an unmagnified projection of the transmitted soft X-rays (below 1.1 keV) which is magnified and recorded by an optical CCD camera. Time lapse series with chemical contrast allow us to follow and interpret the chemical processes in detail. The obtainable lateral resolution is a few mu m, sufficient to detect filiform corrosion on iron.
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| 32. |
- Garbrecht, Magnus, et al.
(author)
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Quantitative atom column position analysis at the incommensurate interfaces of a (PbS)(1.14)NbS2 misfit layered compound with aberration-corrected HRTEM
- 2011
-
In: Ultramicroscopy. - : Elsevier. - 0304-3991 .- 1879-2723. ; 111:3, s. 245-250
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Journal article (peer-reviewed)abstract
- Aberration-corrected HRTEM is applied to explore the potential of NCSI contrast imaging to quantitatively analyse the complex atomic structure of misfit layered compounds and their incommensurate interfaces. Using the (PbS)(1.14)NbS2 misfit layered compound as a model system it is shown that atom column position analyses at the incommensurate interfaces can be performed with precisions reaching a statistical accuracy of +/- 6 pm. The procedure adopted for these studies compares experimental images taken from compound regions free of defects and interface modulations with a structure model derived from XRD experiments and with multi-slice image simulations for the corresponding NCSI contrast conditions used. The high precision achievable in such experiments is confirmed by a detailed quantitative analysis of the atom column positions at the incommensurate interfaces, proving a tetragonal distortion of the monochalcogenide sublattice. (C) 2010 Elsevier B.V. All rights reserved.
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| 33. |
- Grandfield, Kathryn, 1986-, et al.
(author)
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Three-dimensional structure of laser-modified Ti6Al4V and bone interface revealed with STEM tomography
- 2013
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In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 127, s. 48-52
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Journal article (peer-reviewed)abstract
- The early interaction between an implant's surface and bone is a leading factor for implant success, where multiple surface properties contribute to improved bone anchorage. An important parameter is surface topography, both on the micron and nanoscale. Laser-modification has been performed in the thread valleys of Ti6Al4V screws to alter their surface chemistry and topography to form a nanostructured surface titanium-dioxide. Implants were placed in the rabbit tibia, removed with surrounding bone after 8 weeks, fixated, dried and resin embedded. Focused ion beam milling (FIB) was used to prepare specimens from the resin blocks for transmission electron microscopy (TEM). Z-contrast electron tomography offered the possibility to explore the interfacial structure with high-resolution in three-dimensions. With this technique, collagen fibers of the surrounding bone appear to have been laid down parallel to the implant surface. Accordingly, visualization of the laser-modified interface with nanoscale three-dimensional resolution, as offered by Z-contrast electron tomography, gives new insights into bone bonding mechanisms between roughened titanium-dioxide surfaces and bone.
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| 34. |
- Hebert, C., et al.
(author)
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Magnetic circular dichroism in electron energy loss spectrometry
- 2008
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In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 108:3, s. 277-284
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Journal article (peer-reviewed)abstract
- The measurement of circular dichroism in the electron microscope is a new, emerging method and, as such, it is subject to constant refinement and improvement. Different ways can be envisaged to record the signal. We present an overview of the key steps in the energy-loss magnetic chiral dichroism (EMCD) experiment as well as a detailed review of the methods used in the intrinsic way where the specimen is used as a beam splitter. Lateral resolution up to 20-30 nm can be achieved, and the use of convergent beam techniques leads to an improved SIN ratio. Dichroic effects are shown for Ni and Co single crystal; as a counterexample, measurements were carried also for a non-magnetic (Ti) sample, where no dichroic effect was found.
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| 35. |
- Holeňák, Radek, et al.
(author)
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Contrast modes in a 3D ion transmission approach at keV energies
- 2020
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In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 217
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Journal article (peer-reviewed)abstract
- We present options for visualizing contrast maps in 3D ion transmission experiments. Simultaneous measurement of angular distributions and flight time of ions transmitted through self-supporting, single-crystalline silicon foils allows for mapping of intensity and different energy loss moments. The transmitted projectiles were detected mainly for random beam-sample orientation using pulsed beams of He ions and protons with incident energies 50 and 200 keV. Differences in contrast, observed when varying the projectile type and energy, can be attributed to sample nuclear and electronic structure and bear witness to impact parameter dependent energy loss processes. Our results provide a base for interpretation of data obtained in prospective transmission studies when for example using a helium ion microscope.
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| 36. |
- Hug, G, et al.
(author)
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Orientation dependence of electron energy loss spectra and dielectric functions of Ti3SiC2 and Ti3AlC2
- 2010
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In: ULTRAMICROSCOPY. - : Elsevier Science B.V., Amsterdam.. - 0304-3991. ; 110:8, s. 1054-1058
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Journal article (peer-reviewed)abstract
- We employ monochromatized electron energy loss spectroscopy to study Ti3SiC2 and Ti3AlC2. By probing individual grains aligned along different axes in bulk polycrystalline Ti3SiC2 and Ti3AlC2, this approach enables determination of the anisotropy of the dielectric functions and an estimate of the free-electron lifetime in different orientations. The dielectric functions are characterized by strong interband transitions in the low energy region. The energies plasmon resonance were determined to be approximate to 5 eV and exhibit a strong orientation-dependence. Our measurements show that the free-electron lifetimes are also highly orientation-dependent. These results suggest that scattering of carriers in MAX phases is very sensitive to composition and orientation.
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| 37. |
- Jackman, Henrik, 1984-, et al.
(author)
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Image formation mechanisms in scanning electron microscopy of carbon nanotubes,and retrieval of their intrinsic dimensions.
- 2013
-
In: Ultramicroscopy. - : Elsevier. - 0304-3991. ; 124, s. 35-39
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Journal article (peer-reviewed)abstract
- We present a detailed analysis of the image formation mechanisms that are involved in the imaging of carbon nanotubes with scanning electron microscopy (SEM). We show how SEM images can be modelled by accounting for surface enhancement effects together with the absorption coefficient for secondary electrons, and the electron-probe shape. Images can then be deconvoluted, enabling retrieval of the intrinsic nanotube dimensions. Accurate estimates of their dimensions can thereby be obtained even for structures that are comparable to the electron-probe size (on the order of 2 nm). We also present a simple and robust model for obtaining the outer diameter of nanotubes without any detailed knowledge about the electron-probe shape.
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| 38. |
- Johnson, Lars, et al.
(author)
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Blind deconvolution of time-of-flight mass spectra from atom probe tomography
- 2013
-
In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 132, s. 60-64
-
Journal article (peer-reviewed)abstract
- A major source of uncertainty in compositional measurements in atom probe tomography stems from the uncertainties of assigning peaks or parts of peaks in the mass spectrum to their correct identities. In particular, peak overlap is a limiting factor, whereas an ideal mass spectrum would have peaks at their correct positions with zero broadening. Here, we report a method to deconvolute the experimental mass spectrum into such an ideal spectrum and a system function describing the peak broadening introduced by the held evaporation and detection of each ion. By making the assumption of a linear and time-invariant behavior, a system of equations is derived that describes the peak shape and peak intensities. The model is fitted to the observed spectrum by minimizing the squared residuals, regularized by the maximum entropy method. For synthetic data perfectly obeying the assumptions, the method recovered peak intensities to within +/- 0.33 at%. The application of this model to experimental APT data is exemplified with Fe-Cr data. Knowledge of the peak shape opens up several new possibilities, not just for better overall compositional determination, but, e.g., for the estimation of errors of ranging due to peak overlap or peak separation constrained by isotope abundances. (C) 2013 Elsevier By. All rights reserved.
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| 39. |
- Khaliq, Muhammad Waqas, et al.
(author)
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GHz sample excitation at the ALBA-PEEM
- 2023
-
In: Ultramicroscopy. - 0304-3991. ; 250
-
Journal article (peer-reviewed)abstract
- We describe a setup that is used for high-frequency electrical sample excitation in a cathode lens electron microscope with the sample stage at high voltage as used in many synchrotron light sources. Electrical signals are transmitted by dedicated high-frequency components to the printed circuit board supporting the sample. Sub-miniature push-on connectors (SMP) are used to realize the connection in the ultra-high vacuum chamber, bypassing the standard feedthrough. A bandwidth up to 4 GHz with -6 dB attenuation was measured at the sample position, which allows to apply sub-nanosecond pulses. We describe different electronic sample excitation schemes and demonstrate a spatial resolution of 56 nm employing the new setup.
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| 40. |
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| 41. |
- Koeck, Philip J. B.
(author)
-
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
-
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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| 42. |
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| 43. |
- Koeck, Philip J. B.
(author)
-
Design of an Electrostatic Phase Shifting Device for Biological Transmission Electron Microscopy
- 2018
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In: Ultramicroscopy. - : Elsevier. - 0304-3991 .- 1879-2723. ; 187, s. 107-112
-
Journal article (peer-reviewed)abstract
- I suggest an electrostatic phase plate designed to broaden the contrast transfer function of a transmission electron microscope operated close to Scherzer defocus primarily in the low resolution direction. At higher defocus the low frequency behavior is equal to that close to Scherzer defocus, but CTF-correction becomes necessary to extend image interpretation to higher resolution. One simple realization of the phase plate consists of two ring shaped electrodes symmetrically surrounding the central beam. Since no physical components come into contact with the central beam and charge on the electrodes is controlled by an external voltage supply, problems with uncontrolled charging are expected to be reduced.
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| 44. |
- Koeck, Philip J. B.
(author)
-
Improved Hilbert phase contrast for transmission electron microscopy
- 2015
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 154, s. 37-41
-
Journal article (peer-reviewed)abstract
- Hilbert phase contrast has been recognized as a means of recording high resolution images with high contrast using a transmission electron microscope. This imaging mode could be used to image typical phase objects such as unstained biological molecules or cryo sections of biological tissue. According to the original proposal by (Danev et al., 2002) the Hilbert phase plate applies a phase shift of π to approximately half the focal plane (for example the right half excluding the central beam) and an image is recorded at Gaussian focus. After correction for the inbuilt asymmetry of differential phase contrast this image will have an almost perfect contrast transfer function (close to 1) from the lowest spatial frequency up to a maximum resolution determined by the wave length and spherical aberration of the microscope. In this paper I present theory and simulations showing that this maximum spatial frequency can be increased considerably almost without loss of contrast by using a Hilbert phase plate of half the thickness, leading to a phase shift of π/2, and recording images at Scherzer defocus. The maximum resolution can be improved even more by imaging at extended Scherzer defocus, though at the cost of contrast loss at lower spatial frequencies.
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| 45. |
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| 46. |
- Koelling, Sebastian, et al.
(author)
-
Characteristics of cross-sectional atom probe analysis on semiconductor structures
- 2011
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 111:6, s. 540-545
-
Journal article (peer-reviewed)abstract
- The laser-assisted Atom Probe has been proposed as a metrology tool for next generation semiconductor technologies requiring sub-nm spatial resolution. In order to assess its potential for the analysis of three-dimensional semiconductor structures like FinFETs, we have studied the Atom Probes lateral resolution on a silicon, silicon–germanium multilayer structure. We find that the interactions of the laser with the semiconductor materials in the sample distort the sample surface. This results in transient errors of the measured dimensions of the structure. The deformation of the sample furthermore leads to a degradation of the lateral resolution. In the experiments presented in this paper, the Atom Probe reaches a lateral resolution of 1-1.8 nm/decade. In this paper we will discuss the reasons for the distortions of the tip and demonstrate that with the present state of data reconstruction severe quantification errors limit its applicability for the quantitative analysis of heterogeneous semiconductor structures. Our experiments show that reconstruction algorithms taking into account the time dependent nanostructure of the tip shape are required to arrive at accurate results.
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| 47. |
- Koelling, S., et al.
(author)
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Optimal laser positioning for laser-assisted atom probe tomography
- 2013
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 132, s. 70-74
-
Journal article (peer-reviewed)abstract
- Laser-assisted atom probe tomography is a material analysis method based on field evaporating ions from a tip-shaped sample by a combination of a standing electric held and a short (pico- or lemtosecond) laser pulse. The laser-pulse thereby acts as a starting signal for a time-of-flight mass analysis of the ions whereby the thermal energy deposited in the tip by the laser pulse temporarily enables the evaporation of ions from the surface of the tip. Here we will use simulations of the laser absorption on a silicon tip to find the optimal position of the laser spot in order to maximize the mass resolution achieved during the experiments. We will confirm our simulations by showing that the experimentally observed mass resolution indeed changes as predicted by the simulations.
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| 48. |
- Lidbaum, Hans, et al.
(author)
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Reciprocal and real space maps for EMCD experiments
- 2010
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 110:11, s. 1380-1389
-
Journal article (peer-reviewed)abstract
- Electron magnetic chiral dichroism (EMCD) is an emerging tool for quantitative measurements of magnetic properties using the transmission electron microscope (TEM), with the possibility of nanometer resolution. The geometrical conditions, data treatment and electron gun settings are found to influence the EMCD signal. In this article, particular care is taken to obtain a reliable quantitative measurement of the ratio of orbital to spin magnetic moment using energy filtered diffraction patterns. For this purpose, we describe a method for data treatment, normalization and selection of mirror axis. The experimental results are supported by theoretical simulations based on dynamical diffraction and density functional theory. Special settings of the electron gun, so called telefocus mode, enable a higher intensity of the electron beam, as well as a reduction of the influence from artifacts on the signal. Using these settings, we demonstrate the principle of acquiring real space maps of the EMCD signal. This enables advanced characterization of magnetic materials with superior spatial resolution.
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| 49. |
- Liu, Fang, 1975, et al.
(author)
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Atom probe tomography of thermally grown oxide scale on FeCrAl
- 2013
-
In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 132, s. 279-284
-
Journal article (peer-reviewed)abstract
- Thermally grown Al2O3 scales formed on a FeCrAl alloy were successfully analyzed using pulsed green laser atom probe tomography. Two types of atom probe tomography specimens, the “thin oxide” type: a thin Al2O3 layer (
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| 50. |
- Liu, Fang, 1975, et al.
(author)
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Effects of laser pulsing on analysis of steels by atom probe tomography
- 2011
-
In: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 111:6, s. 633-641
-
Journal article (peer-reviewed)abstract
- When performing atom probe tomography analysis, laser pulsing was found very helpful for some types of steels, which are prone to premature sample failure under voltage pulsing. Rather accurate chemical compositions for both matrix and precipitates were obtained by voltage- and laser-pulsed mode. Some special issues on the effects of laser are discussed. A simple correction based on the 13 C n+ and 10 B n+ peak was used to quantify C in the carbide (M 23 C 6 , M = Fe, Cr, Mo) and B in the boride (M 3 B 2 , M = Mo, Fe, Cr, V). The mass resolution in laser mode is sufficient to resolve 56 Fe 2+ and 14 N 1 2 + at 28 Da. Small peak shifts were found in the spectrum due to reflectron aberrations. © 2010 Elsevier B.V.
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