jtaftoe

• Hansen, Vidar; Kosinskiy, Andrey & Taftø, Johan (2020). Distinguishing space groups by electron channelling: centrosymmetric full-Heusler or non-centrosymmetric half-Heusler? Acta Crystallographica Section A: Foundations and Advances. A76(2), s. 211–213. doi: 10.1107/S2053273319016942. Fulltekst i vitenarkiv Vis sammendrag

  X-ray emission under electron-channelling conditions is used to distinguish between a non-centrosymmetric half-Heusler and a centrosymmetric full-Heusler crystal. For TiCo1.5+xSn the space-group determination based on a Rietveld refinement procedure became challenging for increasing Co content (x > 0.2), while electron channelling proved successful for higher Co content (x = 0.35). This technique can be used on crystals as small as (10 nm)3.

• Hansen, Vidar; Echevarria-Bonet, Cristina; Minde, Mona Wetrhus & Taftø, Johan (2018). Determination of atomic positions and polar direction in half-Heusler material Sb1- xSnxTi1-y-zHfyZrzCo using electron channeling. AIP Advances. 8(12), s. 1–9. doi: 10.1063/1.5042816. Fulltekst i vitenarkiv Vis sammendrag

  Variation of electron-induced x-ray emission with the crystal direction of an incoming electron beam (channeling) is used to study the crystal site preference of different elements in a promising thermoelectric half-Heusler material. This material has Sb, Co and Ti as the main constituting elements, with lower contents of Hf, Zr and Sn. It is confirmed experimentally, in accordance with previous assumptions, that Sb and Sn occupy one of the octahedral sites, 4a (0, 0, 0), Ti, Zr and Hf the other octahedral site,4b(½, ½, ½),andCoatomsoccupythetetrahedralsite,4c(¼, ¼, ¼)inthecubic spacegroup F¯43m with lattice constant a = 0.598±0.001 nm. Furthermore, a strong asymmetry along the polar directions is observed, which is as it should be in a halfHeusler material, when the Co atoms have a strong preference for one of the two sets of tetrahedral sites. Such asymmetries can not be observed by kinematical diffraction according to Friedel’s law, thus demonstrating that the observation of element characteristic signals under channeling conditions is a unique technique for determining the sense of polar directions and distinguishing crystal symmetry alternatives in small crystal grains and nanocrystals.

• Sottmann, Jonas; Valset, Kjetil; Karlsen, Ole Bjørn & Taftø, Johan (2013). Synthesis and Measurement of the Thermoelectric Properties of Multiphase Composites: ZnSb Matrix with Zn4Sb3, Zn3P2, and Cu5Zn8. Journal of Electronic Materials. ISSN 0361-5235. 42(7), s. 1820–1826. doi: 10.1007/s11664-012-2441-7. Fulltekst i vitenarkiv
• Valset, Kjetil; Flage-Larsen, Espen; Stadelmann, P. & Taftø, Johan (2012). Electronic structure of Mg2Si by combining electron diffraction and first-principles calculations. Acta Materialia. ISSN 1359-6454. 60(3), s. 972–976. doi: 10.1016/j.actamat.2011.11.006. Fulltekst i vitenarkiv
• Song, Xin; Böttger, Paul Heinrich Michael; Karlsen, Ole Bjørn; Finstad, Terje & Taftø, Johan (2012). Impurity band conduction in the thermoelectric material ZnSb. Physica Scripta. ISSN 0031-8949. T148. doi: 10.1088/0031-8949/2012/T148/014001. Fulltekst i vitenarkiv
• Prytz, Øystein; Flage-Larsen, Espen; Gu, L.; Sigle, W.; Aken, Peter A van & Taftø, Johan (2012). Charge-ordered spinel AlV2O4: High-energy-resolution EELS and computational studies. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 85(19). doi: 10.1103/PhysRevB.85.195112. Fulltekst i vitenarkiv
• Valset, Kjetil; Böttger, Paul Heinrich Michael; Taftø, Johan & Finstad, Terje (2012). Thermoelectric properties of Cu doped ZnSb containing Zn3P2 particles. Journal of Applied Physics. ISSN 0021-8979. 111(2). doi: 10.1063/1.3675505. Fulltekst i vitenarkiv
• Rauwel, Protima; Løvvik, Ole Martin; Rauwel, Erwan Yann; Toberer, ES; Snyder, GJ & Taftø, Johan (2011). Nanostructuring in beta-Zn4Sb3 with variable starting Zn compositions. Physica status solidi. A, Applied research. ISSN 0031-8965. 208(7), s. 1652–1657. doi: 10.1002/pssa.201026613. Fulltekst i vitenarkiv
• Rauwel, Protima; Løvvik, Ole Martin; Rauwel, Erwan Yann & Taftø, Johan (2011). Nanovoids in thermoelectric beta-Zn4Sb3: A possibility for nanoengineering via Zn diffusion. Acta Materialia. ISSN 1359-6454. 59(13), s. 5266–5275. doi: 10.1016/j.actamat.2011.05.003. Fulltekst i vitenarkiv
• Valset, Kjetil; Taftø, Johan; Wu, L & Zhu, Y (2011). Anharmonic thermal motion of atoms in thermoelectric Mg2Si studied via convergent-beam electron diffraction. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 84(22). doi: 10.1103/PhysRevB.84.220301. Fulltekst i vitenarkiv
• Prytz, Øystein; Flage-Larsen, Espen; Toberer, E. S.; Snyder, G. J. & Taftø, Johan (2011). Reduction of lattice thermal conductivity from planar faults in the layered Zintl compound SrZnSb2. Journal of Applied Physics. ISSN 0021-8979. 109(4). doi: 10.1063/1.3549821. Fulltekst i vitenarkiv
• Valset, Kjetil & Taftø, Johan (2011). Bloch wave symmetries in electron diffraction: applications to Friedels law, Gjonnes-Moodie lines and refraction at interfaces. Ultramicroscopy. ISSN 0304-3991. 111(7), s. 854–859. doi: 10.1016/j.ultramic.2010.08.003. Fulltekst i vitenarkiv
• Foss, Steinar; Taftø, Johan & Haakenaasen, Randi (2010). A specimen preparation technique for plane-view studies of surfaces using transmission electron microscopy. Journal of Electron Microscopy. ISSN 0022-0744. 59(1), s. 27–31. doi: 10.1093/jmicro/dfp044. Fulltekst i vitenarkiv Vis sammendrag

  A method for preparing plane-view transmission electron microscope (TEM) samples is presented. With this inclined pseudo-plane-view technique, the undisturbed surface of the sample can be studied in plane view. Thus, nanostructures on the surface of a substrate can be studied with TEM in much the same way as with scanning electron microscopy (SEM), but in transmission at a much higher spatial resolution and with the opportunity of performing nanoscale diffraction. A glued sandwich with two surfaces facing each other was thinned at a low angle relative to the surfaces. The resultant construction contained thin wedges of the surfaces upon which it was possible to do TEM analysis. SEM analysis before and TEM analysis after such sample preparation was found to be consistent.

• Toberer, Eric S.; Rauwel, Protima; Gariel, S; Taftø, Johan & Snyder, G. Jeffrey (2010). Composition and the thermoelectric performance of beta-Zn4Sb3. Journal of Materials Chemistry. ISSN 0959-9428. 20(44), s. 9877–9885. doi: 10.1039/c0jm02011g. Fulltekst i vitenarkiv
• Flage-Larsen, Espen; Løvvik, Ole Martin; Prytz, Øystein & Taftø, Johan (2010). Bond analysis of phosphorus skutterudites: Elongated lanthanum electron buildup in LaFe4P12. Computational Materials Science. ISSN 0927-0256. 47(3), s. 752–757. doi: 10.1016/j.commatsci.2009.10.018. Fulltekst i vitenarkiv
• Sæterli, Ragnhild; Flage-Larsen, E.; Prytz, Ø.; Prytz, Øystein; Taftø, J. & Taftø, Johan [Vis alle 8 forfattere av denne artikkelen] (2009). Electron energy loss spectroscopy of the L2,3 edge of phosphorus skutterudites and electronic structure calculations. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 80(7), s. 075109-1–075109-7. doi: 10.1103/PhysRevB.80.075109. Fulltekst i vitenarkiv
• Prytz, Øystein; Gunnæs, Anette Eleonora; Karlsen, Ole Bjørn; Breivik, Tallak Harald; Toberer, E. S. & Snyder, G. J. [Vis alle 7 forfattere av denne artikkelen] (2009). Nanoscale inclusions in the phonon glass thermoelectric material Zn4Sb3. Philosophical Magazine Letters. ISSN 0950-0839. 89(6), s. 362–369. doi: 10.1080/09500830902950464. Fulltekst i vitenarkiv
• Prytz, Øystein; Saeterli, R; Sæterli, Ragnhild; Løvvik, Ole Martin & Taftø, Johan (2008). Comparison of the electronic structure of a thermoelectric skutterudite before and after adding rattlers: An electron energy loss study. Micron. ISSN 0968-4328. 39(6), s. 685–689. doi: 10.1016/j.micron.2007.10.012. Fulltekst i vitenarkiv Vis sammendrag

  Skutterudites, with rattler atoms introduced in voids in the crystal unit cell, are promising thermoelectric materials. We modify the binary skutterudite with atomic content Co8P24 in the cubic crystal unit cell by adding La as rattlers in all available voids and replacing Co by Fe to maintain charge balance, resulting in La2Fe8P24. The intention is to leave the electronic structure unaltered while decreasing the thermal conductivity due to the presence of the rattlers. We compare the electronic structure of these two compounds by studying the L-edges of P and of the transition elements Co and Fe using electron energy loss spectroscopy (EELS). Our studies of the transition metal white lines show that the 3d electron count is similar for Co and Fe in these compounds. As elemental Fe has one electron less than Co, this supports the notion that each La atom donates three electrons. The L-edges of P in these two skutterudites are quite similar, signalling only minor differences in electronic structure. This is in reasonable agreement with density functional theory (DFT) calculations, and with our multiple scattering FEFF calculations of the near edge structure. However, our experimental plasmon energies and dielectric functions deviate considerably from predictions based on DFT calculations.

• Diplas, Spyridon; Knutsen, T; Jørgensen, Sissel; Gunnæs, Anette Eleonora; Våland, T. & Norby, Truls [Vis alle 8 forfattere av denne artikkelen] (2008). An experimental study of the electronic structure of anodically grown films on an amorphous Ni78Si8B14 alloy. Surface and Interface Analysis. ISSN 0142-2421. 40(3-4), s. 826–829. doi: 10.1002/sia.2748. Fulltekst i vitenarkiv
• Prytz, Øystein; Sæterli, Ragnhild; Holmestad, Randi & Taftø, Johan (2008). Investigations of bonding in skutterudites by electron energy loss spectroscopy. I Hogan, T.P.; Yang, J.; Funahashi, R. & Tritt, T. (Red.), Materials Research Society Symposium Proceedings Vol. 1044: MateralsThermoelectric Power Generation. Materials Research Society. ISSN 9781558999879. Fulltekst i vitenarkiv
• Haakenaasen, Randi; Selvig, Espen; Foss, Steinar; Trosdahl-Iversen, Laila & Taftø, Johan (2008). Segmented nanowires of HgTe and Te grown by molecular beam epitaxy. Applied Physics Letters. ISSN 0003-6951. 92. doi: 10.1063/1.2898166. Fulltekst i vitenarkiv Vis sammendrag

  Heterostructured nanowires consisting of alternating segments of HgTe and Te have been grown by molecular beam epitaxy. The cubic < 111 > HgTe and the hexagonal < 001 > Te directions are oriented along the wire. The 15-70 nm wide, 0.5-1.5 mu m long wires are nucleated at Au particles and grow laterally on Si substrates, but they are not epitaxially coupled to the substrates. An excess of Te relative to Hg during growth could explain the segmentation, as the bulk phase diagram then allows only HgTe and elemental Te. Alternating between these two phases is facilitated by the epitaxial match between the HgTe and Te segments. (C) 2008 American Institute of Physics.

• Diplas, S; Knutsen, Turid; Jørgensen, S; Gunnæs, Anette; Våland, Torstein & Norby, Truls [Vis alle 8 forfattere av denne artikkelen] (2008). An experimental study of the electronic structure of anodically grown films on an amorphous Ni78Si8B14 alloy. Surface and Interface Analysis. ISSN 0142-2421. 40(03.apr), s. 826–829. Fulltekst i vitenarkiv Vis sammendrag

  Films of Ni(OH)(2) and NiOOH grown on a rapidly solidified amorphous Ni78Si8B14 alloy by anodic polarisation were analysed with iPS and the results were compared with those of NiO and of films grown on polycrystalline Ni. SIMS performed on the polarised alloy showed enrichment of Ni at the outermost surface. Transmission electron microscopy (TEM) of cross-sectional samples showed an absence of crystallinity. The Ni 2p shake up satellite and valence band spectra suggested that NiOOH is characterised bya moreenhanced n-typesemi-conducting behaviour compared to Ni(OH)(2) in agreementwith earlier tunnelling current density measurements performed with scanning tunnelling spectroscopy (STS). Copyright (c) 2008 John Wiley & Sons, Ltd.

• Haakenaasen, R; Selvig, E; Hadzialic, Sanja; Skauli, T; Hansen, V & Tibballs, JE [Vis alle 12 forfattere av denne artikkelen] (2008). Nanowires in the CdHgTe material system. Journal of Electronic Materials. ISSN 0361-5235. 37, s. 1311–1317. doi: 10.1007/s11664-008-0414-7. Fulltekst i vitenarkiv
• Prytz, Øystein; Taftø, Johan; Ahn, Channing C. & Fultz, Brent (2007). Transition metal d-band occupancy in skutterudites studied by electron energy-loss spectroscopy. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 75. doi: 10.1103/PhysRevB.75.125109. Fulltekst i vitenarkiv
• Diplas, Spyridon; Prytz, Øystein; Karlsen, Ole Bjørn; Watts, JF & Taftø, Johan (2007). A quantitative study of valence electron transfer in the skutterudite compound CoP3 by combining x-ray induced Auger and photoelectron spectroscopy. Journal of Physics: Condensed Matter. ISSN 0953-8984. 19. doi: 10.1088/0953-8984/19/24/246216. Fulltekst i vitenarkiv
• Diplas, Spyridon; Jørgensen, Sissel; Taftø, Johan; Tønnessen, Trine; Knutsen, Turid & Lehrmann, Jens [Vis alle 9 forfattere av denne artikkelen] (2006). Probing the electronic structure of Ni-X, (X = B, S, P) catalysts with XPS. Surface and Interface Analysis. ISSN 0142-2421. 38, s. 238–242. Fulltekst i vitenarkiv Vis sammendrag

  Amorphous films of Ni-B, Ni-P and Ni-S were produced by electrodeposition on pure polycrystalline Ni. The films were studied with X-ray photoelectron spectroscopy (XPS). Changes in the Auger parameter (AP), peak energy shifts and changes in the Ni 2p shake up satellite intensity and energy were used to probe the electronic changes occurring upon alloying Ni with P, S and B. It is suggested that the Ni sites experience a higher electron density in the alloys than in the pure element and this could be the reason for the increased catalytic activity. Copyright (C) 2006 John Wiley & Sons, Ltd.

• Diplas, Spyridon; Jørgensen, Sissel; Taftø, Johan; Tønnessen, Trine; Knutsen, Turid & Lehrmann, J [Vis alle 9 forfattere av denne artikkelen] (2006). Probing the electronic structure of Ni-X, (X = B, S, P) catalysts with XPS. Surface and Interface Analysis. ISSN 0142-2421. 38. Fulltekst i vitenarkiv
• Prytz, Øystein; Løvvik, Ole Martin & Taftø, Johan (2006). Comparison of theoretical and experimental dielectric functions: electron energy-loss spectroscopy and density-functional calculations on skutterudites. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 74. doi: 10.1103/PhysRevB.74.245109. Fulltekst i vitenarkiv Vis sammendrag

  We explore the possibility of combining density functional theory DFT and electron energy loss spectroscopy EELS to determine the dielectric function of materials. As model systems we use the skutterudites CoP3, CoAs3, and CoSb3 which are prototypes for thermoelectric materials. We achieve qualitative agreement between the theoretically and experimentally obtained low energy-loss spectra and dielectric function. Some of the remaining discrepancies may be caused by the challenge of refining the experimental spectra before Kramers-Kronig analysis. However, contrary to what is the case for some crystals with less complicated electronic structure, the DFT calculated plasmon energies deviate significantly from the experimental values. The great accuracy with which the plasmon energy can be determined by EELS, suggests that this technique may provide valuable inputs in further efforts to improve DFT calculations. The use of EELS as the experimental technique may become particularly powerful in studies of small volumes of materials.

• Prytz, Øystein & Taftø, Johan (2005). Accurate determination of domain boundary orientation in LaNbO4. Acta Materialia. ISSN 1359-6454. 53. doi: 10.1016/j.actamat.2004.09.023. Fulltekst i vitenarkiv Vis sammendrag

  The orientation relationship between ferroelastic domains in LaNbO4 (with 0.5 at.% Sr) is studied by selected area electron diffraction and high-resolution electron microscopy. At room temperature the domains are related through a simple rotation of approximately 95 degrees about the monoclinic [0 1 0] axis, and the interface between two adjacent domains is highly ordered. The domain boundary is found to be the (2 0 5.10)/(5.10 0 2) planes of the two domains, in excellent agreement with our theoretical predictions. This orientation differs considerably from that predicted by more elaborate ferroelastic theory.

• Foss, Steinar; Nilsen, Ola; Olsen, Arne & Taftø, Johan (2005). Structure determination of MnO2 films grown on single crystal alpha-Al2O3 substrates. Philosophical Magazine. ISSN 1478-6435. 85, s. 2689–2705. Fulltekst i vitenarkiv
• Diplas, Spyridon; Lehrmann, J; Jørgensen, Sissel; Valand, T & Taftø, Johan (2005). (A) study of the alloying behaviour of Ni-B amorphous catalysts using Auger parameter measurements, and primary and secondary features of the XPS spectrum. Philosophical Magazine. ISSN 1478-6435. 85. Fulltekst i vitenarkiv
• Diplas, Spyridon; Lehrmann, J; Jørgensen, Sissel; Valand, T; Watts, JF & Taftø, Johan (2005). Characterization of Ni-B amorphous alloys with x-ray photoelectron and secondary ion mass spectroscopy. Surface and Interface Analysis. ISSN 0142-2421. 37, s. 459–465. Fulltekst i vitenarkiv
• Wu, L; Zhu, Y; Park, S; Shapiro, S; Shirane, G & Taftø, Johan (2005). Defect structure of the high-dielectric-constant perovskite CaCu3Ti4O12. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 71. Fulltekst i vitenarkiv
• Diplas, S; Lehrmann, Jens; Jørgensen, S; Våland, Torstein; Watts, J.F. & Taftø, Johan (2005). Characterization of Ni-B amorphous alloys with x-ray photoelectron and secondary ion mass spectroscopy. Surface and Interface Analysis. ISSN 0142-2421. 37(5), s. 459–465. Fulltekst i vitenarkiv Vis sammendrag

  Amorphous Ni-B alloys with nominal compositions 30 at.% B and 50 at.% B were produced via electrodeposition on pure Ni polycrystalline substrates. The surfaces of the alloys were characterized with x-ray photoelectron spectroscopy (XPS) and dynamic secondary ion mass spectrometry (DSIMS). Information on the compositional variation with depth was acquired with XPS both non-destructively, in angle-resolved mode (ARXPS), and destructively with argon ion etching, as well as with DSIMS. Boron oxide dominates the outermost surface of the alloys. Its presence also in the bulk of the alloys is attributed to oxidation during processing, whereas the presence of hydrogen detected with SIMS is attributed to adsorption occurring during processing. The Auger parameter concept and information from the primary and secondary structure of the XPS spectrum were employed to probe the electronic changes occurring upon alloying. It is suggested that the main electronic changes occurring are hybridization of the Ni spd states with the B sp states and an apparent increase of the electron density around the Ni sites. Copyright &COPY; 2005 John Wiley & Sons, Ltd. Amorphous NiB alloys with nominal compositions 30 at.% B and 50 at.% B were produced via electrodeposition on pure Ni polycrystalline substrates. The surfaces of the alloys were characterized with x-ray photoelectron spectroscopy (XPS) and dynamic secondary ion mass spectrometry (DSIMS). Information on the compositional variation with depth was acquired with XPS both non-destructively, in angle-resolved mode (ARXPS), and destructively with argon ion etching, as well as with DSIMS. Boron oxide dominates the outermost surface of the alloys. Its presence also in the bulk of the alloys is attributed to oxidation during processing, whereas the presence of hydrogen detected with SIMS is attributed to adsorption occurring during processing. The Auger parameter concept and information from the primary and secondary structure of the XPS spectrum were employed to probe the electronic changes occurring upon alloying. It is suggested that the main electronic changes occurring are hybridization of the Ni spd states with the B sp states and an apparent increase of the electron density around the Ni sites. Copyright © 2005 John Wiley & Sons, Ltd

• Wu, L; Schofield, MA; Zhu, Y & Taftø, Johan (2004). A unique determination of boundary condition in quantitative electron diffraction: Application to accurate measurements of mean inner potentials. Ultramicroscopy. ISSN 0304-3991. 98(2-4), s. 135–143. Fulltekst i vitenarkiv
• Wu, LJ; Zhu, YM; Vogt, T; Su, HB; Davenport, JW & Taftø, Johan (2004). Valence-electron distribution in MgB2 by accurate diffraction measurements and first-principles calculations. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 69(6), s. 064501–064505. Fulltekst i vitenarkiv
• Foss, Steinar; Olsen, Arne; Simensen, Christian J. & Taftø, Johan (2003). Determination of the crystal structure of the pi-AlFeMgSi phase using symmetry- and site- sensitive electron microscope techniques. Acta Crystallographica Section B: Structural Science. ISSN 0108-7681. B 59, s. 36–42. Fulltekst i vitenarkiv
• Klie, Robert F.; Zhu, Yimei; Schneider, Gerald & Taftø, Johan (2003). Experimental probing of the anisotropy of the empty p states near the Fermi level in MgB2. Applied Physics Letters. ISSN 0003-6951. 82, s. 4316–4318. Fulltekst i vitenarkiv
• Taftø, Johan (2003). Electron channeling, structure factor phases, polarity and atom site determination in crystals. Micron. ISSN 0968-4328. 34, s. 157–166. Fulltekst i vitenarkiv
• Zhu, Yimei; Wu, L.J. & Taftø, Johan (2003). Accurate measurements of valence electron distribution and interfacial lattice displacement using quantitative electron diffraction. Microscopy and Microanalysis. ISSN 1431-9276. 9, s. 442–456. Fulltekst i vitenarkiv
• Perkov, Igor V.; Chukanov, Nikita V.; Larsen, Alf Olav; Merlino, Stefano; Pasero, Marco & Pushcharovsky, Dmitriy Yu. [Vis alle 12 forfattere av denne artikkelen] (2003). Sphaerobertrandite, Be3SiO4(OH)2: redefinition, new data, crystal structure and genesis. European journal of mineralogy. ISSN 0935-1221. 15(1), s. 157–166. Fulltekst i vitenarkiv
• Wu, L.J.; Zhu, Yimei; Taftø, Johan; Welch, D. O. & Suenaga, M. (2002). Quantitative analysis of twist boundaries and stacking faults in Bi-based superconductors by parallel recording of darkfield images with a coherent electron source. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 66(104), s. 51701–51713. Fulltekst i vitenarkiv Vis sammendrag

  Study of grain boundaries by quantitative electron microscope techniques.

• Foss, Steinar; Simensen, Christian J.; Olsen, Arne & Taftø, Johan (2002). Crystal structure of the pi phase in the Al-Si-Mg-Fe system studied by electron channneling. Philosophical Magazine Letters. ISSN 0950-0839. 82(12), s. 681–686. Fulltekst i vitenarkiv Vis sammendrag

  Revision of the crystal structure of the pi-phase by electron channeling

Se alle arbeider i NVA

• Delimitis, Andreas; Hansen, Vidar Folke; Symeou, Elli; Kyratsi, Theodora; Minde, Mona Wetrhus & Taftø, Johan (2019). DETERMINATION OF HOST AND DOPANT ION DISTRIBUTION IN MG2SI1-XSNX THERMOELECTRIC MATERIALS BY ELECTRON CHANNELING. Acta Crystallographica Section A: Foundations and Advances. 75, s. e321–e321. doi: 10.1107/S2053273319092350. Fulltekst i vitenarkiv Vis sammendrag

  Detailed structure studies by electron microscopy methods have been widely exploited due to the unique capabilities electrons provide. Precise identification of atomic positions is feasible by employing spectroscopy techniques in an analytical transmission electron microscope. In this aspect, methods such as energy dispersive Xray spectroscopy (EDS) are utilised, under strong channelling conditions, where the yield of element characteristic X-ray emission can be modified and manipulated, dependent upon crystallographic directions of the incident beam. These channelling effects are powerful in determining atomic site locations in crystals and techniques such as ALCHMI (Atom Location by Channeling Enhanced MIcroanalysis) have been developed and evaluated. Structural analyses employing electron channelling have a recent focus in systems for renewable technologies and energy harvesting, such as thermoelectric (TE) materials. TEs based on Mg2Si1-xSnx have gained increased interest, due to inexpensive production costs, abundancy and a toxic nature of raw materials, especially for power generation applications within the intermediate temperature range (500–900 K). Synthesis of Mg2Si1-xSnx in nanocrystal morphologies, often coupled by incorporation of dopants in their host matrix is exploited, with a scope to efficiently reduce thermal conductivity, particularly for Sn-rich or Bi doped Si-rich compounds. Previous studies confirmed the multiplicity of phases in this system, however, the precise distribution of host and dopant ions location is still controversial. Application of the electron channelling technique is therefore more than essential in order to accurately determine and refine their structural characteristics. Experimental outcomes will be demonstrated and discussed.

• Delimitis, Andreas; Hansen, Vidar Folke; Symeou, Elli; Kyratsi, Theodora; Minde, Mona Wetrhus & Taftø, Johan (2019). Determination of host and dopant ion distribution in Mg2Si1-xSnx thermoelectric materials by electron channeling. Fulltekst i vitenarkiv Vis sammendrag

  Detailed structure studies by electron microscopy methods have been widely exploited due to the unique capabilities electrons provide. Precise identification of atomic positions is feasible by employing spectroscopy techniques in an analytical transmission electron microscope. In this aspect, methods such as energy dispersive X-ray spectroscopy (EDS) are utilised, under strong channeling conditions, where the yield of element characteristic X-ray emission can be modified and manipulated, dependent upon crystallographic directions of the incident beam. These channeling effects are powerful in determining atomic site locations in crystals and techniques such as ALCHEMI (Atom Location by CHanneling Enhanced MIcroanalysis) have been developed and evaluated. Structural analyses employing electron channeling have a recent focus in systems for renewable technologies and energy harvesting, such as thermoelectric (TE) materials. TEs based on Mg2Si1-xSnx have gained increased interest, due to inexpensive production costs, abundancy and atoxic nature of raw materials, especially for power generation applications within the intermediate temperature range (500–900 K). Synthesis of Mg2Si1-xSnx in nanocrystal morphologies, often coupled by incorporation of dopants in their host matrix is exploited, with a scope to efficiently reduce thermal conductivity, particularly for Sn-rich or Bi doped Si-rich compounds. Previous studies confirmed the multiplicity of phases in this system, however, the precise distribution of host and dopant ions location is still controversial. Application of the electron channeling technique is therefore more than essential in order to accurately determine and refine their structural characteristics. Experimental outcomes will be demonstrated and discussed.

• Løvvik, Ole Martin; Song, Xin; Valset, Kjetil; Flage-Larsen, Espen; Fjeld, Harald & Graff, Joachim Seland [Vis alle 15 forfattere av denne artikkelen] (2014). Thermoelectric materials from first principles to final applications: Basic and applied thermoelectrics in Oslo. Fulltekst i vitenarkiv
• Song, Xin; Persson, Clas; Norby, Truls; Flage-Larsen, Espen; Karlsen, Ole Bjørn & Hansen, Vidar [Vis alle 16 forfattere av denne artikkelen] (2014). Conversion of Heat and Energy: Thermoelectrics. Fulltekst i vitenarkiv
• Valset, Kjetil; Prytz, Øystein; Hansen, Vidar & Taftø, Johan (2012). Quantitative study of structure factors at large reciprocal vectors using convergent beam electron diffraction: Application to anharmonicity of the thermal motion in Mg2Si. Fulltekst i vitenarkiv
• Holmestad, Randi; Walmsley, John Charles; Prytz, Øystein; Soleim, Bjørn Gunnar; Helvoort, Antonius Van & Olsen, Arne [Vis alle 18 forfattere av denne artikkelen] (2012). NORTEM – ambitions and plans. Fulltekst i vitenarkiv
• Løvvik, Ole Martin; Valset, Kjetil; Rauwel, Protima; Prytz, Øystein; Flage-Larsen, Espen & Song, Xin [Vis alle 12 forfattere av denne artikkelen] (2012). Thermoelectricity in Oslo. Fulltekst i vitenarkiv
• Qureishy, Thomas; Hansen, Vidar; Karlsen, Ole Bjørn; Gunnæs, Anette Eleonora & Taftø, Johan (2012). Superstructures in Mg2Si1-xSnx. Fulltekst i vitenarkiv
• Song, Xin; Valset, Kjetil; Böttger, Paul Heinrich Michael; Karlsen, Ole Bjørn; Finstad, Terje & Taftø, Johan (2011). Structure and Thermoelectric Properties of Cr and Mn Doped ZnSb. Fulltekst i vitenarkiv
• Song, Xin; Karlsen, Ole Bjørn; Taftø, Johan; Böttger, Paul Heinrich Michael & Finstad, Terje (2011). Electrical and structural characterization of thermoelectric material ZnSb with additions of Mn and Cr. Fulltekst i vitenarkiv
• Flage-Larsen, Espen; Prytz, Øystein & Taftø, Johan (2011). The Lorenz function; its scattering properties and the validity of the parabolic approximation. Fulltekst i vitenarkiv
• Flage-Larsen, Espen; Prytz, Øystein & Taftø, Johan (2011). Material-specific Lorenz numbers: Electronic and lattice parts of the thermal conductivity. Fulltekst i vitenarkiv
• Valset, Kjetil; Böttger, Paul Heinrich Michael; Taftø, Johan & Finstad, Terje (2011). High mobility Cu-doped ZnSb containing particles of Zn3P2. Fulltekst i vitenarkiv
• Løvvik, Ole Martin; Flage-Larsen, Espen; Rauwel, Protima; Prytz, Øystein & Taftø, Johan (2010). Solubility and mobility of Zn in Zn4Sb3 - a combined computational and experimental study. Fulltekst i vitenarkiv
• Rauwel, Protima; Martin, Løvvik Ole; Rauwel, Erwan Yann; Toberer, Erik; Snyder, Jeffery & Taftø, Johan (2010). Nanostructuring in thermoelectric Zn4Sb3 with varying Zn concentrations. Fulltekst i vitenarkiv
• Valset, Kjetil & Taftø, Johan (2010). Bloch wave description of refraction at interfaces. Fulltekst i vitenarkiv
• Prytz, Øystein; Toberer, E. S.; May, A. F.; Flage-Larsen, Espen; Snyder, G. J. & Taftø, Johan (2010). Transmission electron microscopy studies of nanostructures in SrZnSb2: reduced thermal conductivity through defect scattering. Fulltekst i vitenarkiv
• Flage-Larsen, Espen & Taftø, Johan (2010). Transport properties in light of analytic band generation: the potential of energy filtering and the validity of the parabolic approximation. Fulltekst i vitenarkiv
• Prytz, Øystein; Flage-Larsen, Espen; Gu, L.; Sigle, W. & Taftø, Johan (2009). The charge-ordered spinel AlV2O4: EELS and DFT studies. Fulltekst i vitenarkiv
• Bording, Jan Kåre; Prytz, Øystein; Hansen, Vidar & Taftø, Johan (2009). Improved thermoelectric materials through nanostructuring: implications for energy savings. Fulltekst i vitenarkiv
• Valset, Kjetil; Böttger, Paul Heinrich Michael; Karlsen, Ole Bjørn & Taftø, Johan (2009). Microstructure and thermoelectric property studies of ZnSb with Sb and Zn4Sb3 inclusions. Fulltekst i vitenarkiv
• Böttger, Paul Heinrich Michael; Valset, Kjetil; Flage-Larsen, Espen; Prytz, Øystein; Bording, Jan Kåre & Karlsen, Ole Bjørn [Vis alle 10 forfattere av denne artikkelen] (2009). An overview of our basic and applied thermoelectric research activity. Fulltekst i vitenarkiv
• Prytz, Øystein; Gunnæs, Anette Eleonora; Breivik, Tallak Harald; Toberer, E. S.; Snyder, G. J. & Taftø, Johan (2009). Nanostructured thermoelectric materials, reduction of thermal conductivity in Zn4Sb3. Fulltekst i vitenarkiv
• Sæterli, Ragnhild; Flage-Larsen, Espen; Prytz, Øystein; Taftø, Johan; Marthinsen, Knut & Holmestad, Randi (2009). Electron energy loss near edge structure of phosphorus L2,3 edges in skutterudites. Fulltekst i vitenarkiv
• Taftø, Johan (2008). CBED with the electron beam cross-over at and above the specimen level. Fulltekst i vitenarkiv
• Prytz, Øystein; Gunnæs, Anette Eleonora; Toberer, Eric; Snyder, Jeff & Taftø, Johan (2008). Transmission electron microscopy search for defects and disorder causing the low thermal conductivity of Zn4Sb3. Fulltekst i vitenarkiv
• Prytz, Øystein; Gunnæs, Anette Eleonora; Breivik, Tallak Harald; Toberer, Eric; Snyder, Jeff & Taftø, Johan (2008). Transmission Electron Microscopy Studies of Nanostructure in ß-Zn4Sb3. Fulltekst i vitenarkiv
• Flage-Larsen, Espen; Prytz, Øystein; Løvvik, Ole Martin; Wu, L.; Zhu, Y. & Taftø, Johan (2007). Bonding and valence electron distribution in thermoelectric skutterudites. Fulltekst i vitenarkiv
• Flage-Larsen, Espen; Prytz, Øystein; Løvvik, Ole Martin & Taftø, Johan (2007). Calculation of valence electron distribution and thermoelectric coefficients in skutterudies. Fulltekst i vitenarkiv
• Sæterli, Ragnhild; Prytz, Øystein; Vullum, Per Erik; Marthinsen, Knut; Holmestad, Randi & Taftø, Johan (2007). Convergent beam electron diffraction experiments on thermoelectric skutterudites. Fulltekst i vitenarkiv
• Sæterli, Ragnhild; Prytz, Øystein; Holmestad, Randi; Marthinsen, Knut & Taftø, Johan (2007). The local electronic structure of phosphorus in skutterudites studied by electron energy-loss spectroscopy. Fulltekst i vitenarkiv
• Sæterli, Ragnhild; Prytz, Øystein; Holmestad, Randi; Marthinsen, Knut & Taftø, Johan (2007). The local electronic structure of phosphorus in skutterudites studied by electron energy-loss spectroscopy. Fulltekst i vitenarkiv
• Prytz, Øystein; Sæterli, Ragnhild; Holmestad, Randi & Taftø, Johan (2007). Investigations of bonding in skutterudites by electron energy loss spectroscopy. Fulltekst i vitenarkiv
• Sæterli, Ragnhild; Prytz, Øystein; Vullum, Per Erik; Friis, Jesper; Marthinsen, Knut & Holmestad, Randi [Vis alle 7 forfattere av denne artikkelen] (2007). Convergent beam electron diffraction experiments on thermoelectric skutterudites. Fulltekst i vitenarkiv
• Prytz, Øystein; Sæterli, Ragnhild; Randi, Holmestad & Taftø, Johan (2007). Investigations of bonding in skutterudites by electron energy loss spectroscopy. Fulltekst i vitenarkiv
• Prytz, Øystein; Flage-Larsen, Espen; Karlsen, Ole Bjørn; Diplas, Spyridon; Finstad, Terje & Taftø, Johan [Vis alle 11 forfattere av denne artikkelen] (2007). Electronic structure of thermoelectric skutterudites; combining spectroscopic techniques, precision electron diffraction and density functional theory. Fulltekst i vitenarkiv
• Sæterli, Ragnhild; Prytz, Øystein; Marthinsen, Knut; Holmestad, Randi & Taftø, Johan (2007). EELS study of phosphorus L-edges of skutterudites. Fulltekst i vitenarkiv
• Taftø, Johan; Prytz, Øystein; Wu, Lijun & Zhu, Yimei (2007). Valence electron distribution studied by electron diffraction. Fulltekst i vitenarkiv
• Sæterli, Ragnhild; Prytz, Øystein; Vullum, Per Erik; Taftø, Johan & Holmestad, Randi (2007). EELS and CBED studies of skutterudites. Fulltekst i vitenarkiv
• Prytz, Øystein; Løvvik, Ole Martin & Taftø, Johan (2005). Experimental and theoretical studies of plasma resonance and the electronic structure of binary skutterudites. Fulltekst i vitenarkiv Vis sammendrag

  We determine the plasmon energies of the skutterudites CoP3, CoAs3 and CoSb3 by electron energy loss spectroscopy, and compare with calculated values from the Drude model and density functional theory (DFT). For these compounds, whose doped versions have potential applications as thermoelectric materials, there is a relatively large discrepancy between experiment and theory based on the Drude model as well as the DFT-calculations. We also study the transitions from occupied to unoccupied states near the Fermi-level that show up at energies lower than the plasmon energies. The features observed are in general agreement with the DFT-calculations.

• Prytz, Øystein & Taftø, Johan (2005). Accurate determination of orientation relationships between ferroelastic domains: the tetragonal to monoclinic transition in LaNbO4 as an example. Fulltekst i vitenarkiv Vis sammendrag

  LaNbO4 crystallizes in a tetragonal high-temperature phase with space group I41/a, which transforms to a monoclinic phase upon cooling below 500 °C. The low-temperature phase has space group I2/a (C2/c) with a monoclinic angle b=94.1°. This system serves as a useful model of a ferroelastic transition of the 4/mF2/m type using the notation of Aizu [1]. This transition produces ferroelastic domains, the boundaries between which are parallel to the monoclinic baxis. The orientation of these boundaries relative to the monoclinic a- and c-axes has been predicted by Sapriel [2] for all 94 ferroelastic species, and calculations specifically for the LaNbO4 system have been presented by Jian and Wayman [3]. We present an accurate determination of the boundary orientation in LaNbO4 using selected area electron diffraction. The boundary planes are parallel to the (2 0 5.10)/(5.10 0 2) planes of the two domains, as opposed to the predictions of Jian and Wayman which indicate that the domain boundaries should be oriented parallel to the (2 0 -4.04)/(4.04 0 2) planes. Our experimental results are in good agreement with the results of a previous study [4]. Furthermore, we present a simple geometric model for calculating the boundary orientation based only on the unit cell parameters of the monoclinic phase. This model gives a boundary orientation in excellent agreement with our experimental determination.

• Taftø, Johan (2004). Beyond locating the atoms towards addressing the electronic structure of crystals using advanced transmission electron microscopy. Fulltekst i vitenarkiv
• Taftø, Johan (2004). Quantitive electron diffraction in studies of electron distribution in crystals. Fulltekst i vitenarkiv
• Knutsen, Turid; Hansen, Vidar; Håkansson, B; Gunnæs, Anette; Jørgensen, Sissel & Våland, Torstein [Vis alle 7 forfattere av denne artikkelen] (2003). A Study of Amorphous and Crystalline Ni78Si8B14. Fulltekst i vitenarkiv
• Zhu, Yimei; Wu, L.J.; Taftø, Johan; Schofield, M.A.; Volkov, V.V. & Beleggia, M. [Vis alle 7 forfattere av denne artikkelen] (2003). Understanding spatial distribution of electrostatic and magnetic potentials in materials. Fulltekst i vitenarkiv
• Jahren, Jens; Sørbrøden, Erik; Gunnæs, Anette E.; Taftø, Johan & Aagaard, Per (2003). SEM, STEM and EELS of Fe-hydroxide from the Langøya Gypsum Landfill. Fulltekst i vitenarkiv
• Knutsen, Turid; Hansen, Vidar; Håkansson, B.; Gunnæs, Anette Eleonora; Jørgensen, Sissel & Våland, T. [Vis alle 7 forfattere av denne artikkelen] (2003). A study of amorphous and crystalline Ni78Si8B14. Fulltekst i vitenarkiv
• Foss, Steinar & Taftø, Johan (2003). Investigation of fast electrons propagating nearly parallel to interfaces. Fulltekst i vitenarkiv
• Jahren, Jens; Sørbrøden, Erik; Gunnæs, Anette Eleonora; Taftø, Johan & Aagaard, Per (2003). SEM, TEM and EELS of Fe-hydroxide from the Langøya gypsum landfill. Fulltekst i vitenarkiv
• Taftø, Johan; Klie, Robert F. & Zhu, Yimei (2003). Electronic structure information from EELS using the anisotropic superconductor MgB2 as an example. Fulltekst i vitenarkiv
• Prytz, Øystein; Sørbrøden, Erik; Norby, Truls Eivind & Taftø, Johan (2003). Twin Boundaries in LaNbO4. Fulltekst i vitenarkiv
• Sørbrøden, Erik; Hansen, Vidar; Olsen, Arne; Holme, Børge & Taftø, Johan (2002). Imaging of hardening particles in an Al-Mg-Zn alloy using plasmon electron energy losses. Fulltekst i vitenarkiv
• Taftø, Johan; Wu, L.J. & Zhu, Yimei (2002). Exploring Valence Electron Distribution in High Temperature Superconductors with a Focused Electron Probe. Fulltekst i vitenarkiv Vis sammendrag

  Study of the valence electron distribution in superconductors by precision electron diffraction techniques.

• Taftø, Johan (2002). Characteristic energy losses of channeled electrons; reciprocity and double alignment. Fulltekst i vitenarkiv Vis sammendrag

  Channeling of fast electrons in crystals monitored by detecting element characteristic energy losses.

• Zhu, Yimei; Wu, L.J. & Taftø, Johan (2002). A Challenging to Characterization of Superconductors: Accurate Measurements of Charge Distribution and Interfacial Displacement. Fulltekst i vitenarkiv Vis sammendrag

  Maasurements of lattice displacements with picometer accuracy by coherent electron diffraction.

• Taftø, Johan; Foss, Steinar; Olsen, Arne & Simensen, Christian J. (2002). Locating atoms in small crystals by combining convergent beam electron diffraction and electron channeling. Fulltekst i vitenarkiv Vis sammendrag

  Study of the crystal structure of microcrystals by electron channeling

• Prytz, Øystein; Taftø, Johan; Fjellvåg, Helmer & Finstad, Terje (2007). Electronic structure and bonding in thermoelectric skutterudites. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  The present work is a study of the electronic structure and bonding of the class of materials often called skutterudites. These materials have received much attention during the past decade, largely because their thermoelectric properties are rather easily modified and improved. Most investigations have been into synthesizing materials and measuring their thermoelectric properties. There have also been several theoretical studies of their electronic structure. However, there have been fewer experimental studies of the bonding of these materials. In this thesis, electron energy-loss spectroscopy and x-ray photoelectron and Auger spectroscopy have been used together with density functional calculations to study the electronic structure of skutterudites. This combination of experimental and theoretical methods may be mutually beneficial, and the aim of this thesis is to bridge the gap between theoretical considerations and experimental investigations of the bonding.

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