| 1. |
- Boerrnert, Felix, et al.
(författare)
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Single-wall-carbon-nanotube/single-carbon-chain molecular junctions
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:8, s. 085439-1-085439-5
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Tidskriftsartikel (refereegranskat)abstract
- Stable junctions between a single carbon chain and two single-wall carbon nanotubes were produced via coalescence of functionalized fullerenes filled into a single-wall carbon nanotube and directly imaged by in situ transmission electron microscopy. First principles quantum chemical calculations support the observed stability of such molecular junctions. They also show that short carbon chains bound to other carbon structures are cumulenes and stable semiconductors due to Peierls-like distortion. Junctions like this can be regarded as archetypical building blocks for all-carbon molecular electronics.
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| 2. |
- Gooth, Johannes, et al.
(författare)
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Local Magnetic Suppression of Topological Surface States in Bi2Te3 Nanowires
- 2016
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Ingår i: ACS Nano. - Washington : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 10:7, s. 7180-7188
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Tidskriftsartikel (refereegranskat)abstract
- Locally induced, magnetic order on the surface of a topological insulator nanowire could enable room-temperature topological quantum devices. Here we report on the realization of selective magnetic control over topological surface states on a single facet of a rectangular Bi2Te3 nanowire via a magnetic insulating Fe3O4 substrate. Low-temperature magnetotransport studies provide evidence for local time-reversal symmetry breaking and for enhanced gapping of the interfacial 1D energy spectrum by perpendicular magnetic-field components, leaving the remaining nanowire facets unaffected. Our results open up great opportunities for development of dissipation-less electronics and spintronics.
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| 3. |
- Pohl, Darius, et al.
(författare)
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Atom size electron vortex beams with selectable orbital angular momentum
- 2017
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- The decreasing size of modern functional magnetic materials and devices cause a steadily increasing demand for high resolution quantitative magnetic characterization. Transmission electron microscopy (TEM) based measurements of the electron energy-loss magnetic chiral dichroism (EMCD) may serve as the needed experimental tool. To this end, we present a reliable and robust electron-optical setup that generates and controls user-selectable single state electron vortex beams with defined orbital angular momenta. Our set-up is based on a standard high-resolution scanning TEM with probe aberration corrector, to which we added a vortex generating fork aperture and a miniaturized aperture for vortex selection. We demonstrate that atom size probes can be formed from these electron vortices and that they can be used for atomic resolution structural and spectroscopic imaging - both of which are prerequisites for future atomic EMCD investigations.
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| 4. |
- Pohl, Darius, et al.
(författare)
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Electron vortex beams prepared by a spiral aperture with the goal to measure EMCD on ferromagnetic films via STEM
- 2015
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 150, s. 16-22
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Tidskriftsartikel (refereegranskat)abstract
- X-ray magnetic circular dichroism is a well established method to study element specific magnetic properties of a material, while electron magnetic circular dichroism (EMCD), which is the electron wave analogue to XMCD, is scarcely used today. Recently discovered electron vortex beams, that carry a discrete orbital angular momentum (OAM) L, are also predicted to reveal dichroic signals. Since electron beams can be easily focused down to sub-nanometer diameters, this novel technique promises the possibility to quantitatively determine local magnetic properties with unrivalled lateral resolution. As the spiralling wave front of the electron vortex beam has an azimutally growing phase shift of up to 2 pi and a phase singularity in its axial center, specially designed apertures are needed to generate such non-planar electron waves. We report on the preparation and successful implementation of spiral apertures into the condenser lens system of an aberration-corrected FEL Titan(3) 80-300 transmission electron microscope (TEM). This setup allows to perform scanning TEM (STEM) with vortex beams carrying user-selected OAM. First experiments on the interaction of the vortex beam with a poly-crystalline sample are presented. Within the achieved signal to noise ratio no EMCD signal has been detected. This finding is supported by simulations of inelastic scattering of a beam generated by spiral aperture.
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| 5. |
- Schneider, Sebastian, et al.
(författare)
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Magnetic properties of single nanomagnets : Electron energy-loss magnetic chiral dichroism on FePt nanoparticles
- 2016
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 171, s. 186-194
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Tidskriftsartikel (refereegranskat)abstract
- Electron energy-loss magnetic chiral dichroism (EMCD) allows for the quantification of magnetic properties of materials at the nanometer scale. It is shown that with the support of simulations that help to identify the optimal conditions for a successful experiment and upon implementing measurement routines that effectively reduce the noise floor, EMCD measurements can be pushed towards quantitative magnetic measurements even on individual nanoparticles. With this approach, the ratio of orbital to spin magnetic moments for the Fe atoms in a single Ll(0) ordered FePt nanoparticle is determined to be m(l)/m(s) = 0.08 +/- 0.02. This finding is in good quantitative agreement with the results of XMCD ensemble measurements. (C) 2016 Elsevier B.V. All rights reserved.
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| 6. |
- Schneider, Sebastian, et al.
(författare)
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Simple method for optimization of classical electron magnetic circular dichroism measurements : The role of structure factor and extinction distances
- 2018
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:11
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Tidskriftsartikel (refereegranskat)abstract
- Electron magnetic circular dichroism (EMCD), the electron wave analog of x-ray magnetic circular dichroism (XMCD), allows for the element specific measurement of the spin and orbital magnetic moments with up to nanometer resolution. However, due to dynamical diffraction effects, the signal-to-noise ratios of EMCD spectra are often very low. We describe a simple set of rules, how to set up a geometry for a classical EMCD experiment on an arbitrary crystal structure to get a maximum dichroic signal. The procedure is based on an evaluation of the structure factor and extinction distances. Proof-of-concept simulations and experiments on a FeGe crystal present a successful test of these guidelines.
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| 7. |
- Ta, Huy Q., et al.
(författare)
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Single Cr atom catalytic growth of graphene
- 2018
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Ingår i: Nano Reseach. - : TSINGHUA UNIV PRESS. - 1998-0124 .- 1998-0000. ; 11:5, s. 2405-2411
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Tidskriftsartikel (refereegranskat)abstract
- Single atoms are the ultimate minimum size limit for catalysts. Graphene, as an exciting, ultimately thin (one atom thick) material can be imaged in a transmission electron microscope with relatively few imaging artefacts. Here, we directly observe the behavior of single Cr atoms in graphene mono- and di-vacancies and, more importantly, at graphene edges. Similar studies at graphene edges with other elemental atoms, with the exception of Fe, show catalytic etching of graphene. Fe atoms have been shown to both etch and grow graphene. In contrast, Cr atoms are only observed to induce graphene growth. Complementary theoretical calculations illuminate the differences between Fe and Cr, and confirm single Cr atoms as superior catalysts for sp(2) carbon growth.
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| 8. |
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| 9. |
- Thersleff, Thomas, 1980-, et al.
(författare)
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The interface and defect structure of superconducting Ba(Fe1-xCox)2As2 thin films
- 2011
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Ingår i: Microscopy Conference 2011, 28 August – 02 September 2011, Kiel, Germany.
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Konferensbidrag (refereegranskat)abstract
- Essential to the understanding of key fundamental properties in the newly discovered iron-based superconductors as well as critically assessing their potential for applications and devices is their fabrication into very high quality thin films. Thin films of the Ba(Fe1-xCox)2As2 phase – discovered by Sefat et al. [1] and commonly referred to as “Ba-122” – are particularly interesting since this compound appears to be resilient against oxidation and degradation due to water vapor [2], it is considerably easier to deposit compared to other iron-based superconductors, and it has a relatively high critical temperature of 25.5 K. The search for optimal thin film growth parameters is currently the subject of a number of international research groups. [2 – 11]. However, difficulties overcoming the poor metal/oxide bond at the interface of many substrates has necessitated the need for significant optimization of the deposition parameters [9,10] as well as the use of various intermediate layers [8] to produce well-textured films. In spite of these efforts, nearly all of these films contain an unintentional amorphous or iron-containing layer at the interface. While the nature of this interface is not yet fully understood, the disruption of local crystallographic ordering associated with it precludes the use of these films for interface-sensitive applications such as multilayers or heterostructures where coherent and chemically inert phase boundaries are required. A detailed investigation into the nature of this interface on both STO and LSAT substrates reveals that it is characterized by the presence of an interdiffusion layer. Ba diffuses approximately 2 nm into both substrates and is mass-balanced by the previously mentioned amorphous layer of unknown composition (figure 1). This amorphous layer is rich in iron and, on LSAT, even contains significant amounts of textured iron [9]. The nature of this interface is the first topic of this contribution. Additionally, the current transport properties of these thin films are observed to be strongly dependent on the type and concentration of defects present. An overview of the defects observed in this system constitutes the second topic of this contribution. Finally, it has been shown that, by using a metallic iron buffer layer, a highly coherent and chemically inert interfacial bond can take place [12-14]. The effect of such an interface on the defect landscape and, subsequently, the macroscopic superconducting properties of the Ba-122 thin films will be discussed in detail. [1] A. Sefat, et al., Phys. Rev. Lett. 101, 117004 (2008)[2] H. Hiramatsu, et al., Phys. Rev. B 80, 052501 (2009)[3] H. Hiramatsu, et al., Appl. Phys. Express 1, 101702 (2008)[4] E. -M. Choi, et al., Appl. Phys. Lett. 95, 062507 (2009)[5] T. Katase, et al., Solid State Commun. 149, 2121 (2009)[6] S. Lee, et al., Appl. Phys. Lett. 95, 212505 (2009)[7] K. Iida, et al., Appl. Phys. Lett. 95, 192501 (2009)[8] S. Lee, et al., Nature Mater. 9, 397 (2010)[9] K. Iida, et al., Phys. Rev. B 81, 100507(R) (2010)[10] T. Katase, et al., Appl. Phys. Lett. 96, 142507 (2010)[11] T. Katase, et al., Appl. Phys. Express 3, 063101 (2010)[12] T. Thersleff, et al., Appl. Phys. Lett. 97, 022506 (2010)[13] K. Iida, et al., Appl. Phys. Lett. 97, 172507 (2010)[14] K. Iida, et al., Appl. Phys. Express 4, 013103 (2011)
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