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  • 3551.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Qadir, Muhammad Israr
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    One- and two-dimensional nanostructures for chemical- and biosensing2011In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 25, p. 745-748Article in journal (Refereed)
    Abstract [en]

    Nanostructures have been very popular for several years to do research on sensing. In this paper we will demonstrate the advantage of using nanowires of zinc oxide (ZnO) as one dimensional structure for potentiometric measurements in biological environments. The developed procedures show suitability for the accurate determination of most of the important metal ions and to characterize cells and thin bio-layers. We will also show how to use these structures for biosensing of glucose, cholesterol, and the application of extended gate metal oxide semiconductor field effect transistors as the signal transducer. In the second part, we will show how to use a two-dimensional nanostructure, specifically graphene, for cholesterol and glucose biosensing.

  • 3552.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Qadir, Muhammad Israr
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Rana, Sadaf Jamil
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Progress on one-dimensional zinc oxide nanomaterials based photonic devices2012In: Nanophotonics, ISSN 2192-8606, Vol. 1, no 1, p. 99-115Article in journal (Refereed)
    Abstract [en]

    One-dimensional nanostructures hold the most attractive and excellent physiochemical characteristics which exhibit the paramount influence on the fundamental and technological nanoelectronic as well as nanophotonic applications. In this review article, we present a detailed introduction to the diverse synthetic procedures which can be utilized for the fabrication of single-, planar- and three-dimensional ZnO nanostructures. More specifically, a thorough discussion regarding luminescence characteristics of the one-dimensional ZnO nanostructures is presented for ultraviolet and visible regions. We summarize the room temperature spontaneous emission and stimulated emission along with the interaction of the incident beam with material cavity to produce resonant optical modes and low-temperature time resolved photoluminescence studies. The most recent published results on the white light emitting diodes fabricated with the combination of ZnO nanotubes with p-GaN and ZnO nanorods with p-organic polymers on glass and disposable paper are discussed. Additionally, the significant results on optically and electrically pumped lasers are discussed; along with an overview on the future of ZnO nanostructures based photonic devices.

  • 3553.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Wadeasa, Amal
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Klason, Peter
    Gothenburg University, Sweden.
    Yang, Lili
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Beegum, Lubuna
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Raja, Shaffeq
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Zhao, Qiangxiang
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Light-emitting diodes based on n-ZnO nano-wires and p-type organic semiconductors2008In: Proc. SPIE 6895: Zinc Oxide Materials and Devices III, SPIE - International Society for Optical Engineering, 2008, p. 68950O-1-68950O-10Conference paper (Other academic)
    Abstract [en]

    After our recent successful demonstration of high brightness white light emitting diodes (HB-LEDs) based on high temperature grown n-ZnO nanowires on different p-type semiconductors, we present here LEDs fabricated on n-ZnO nano-wires and p-type organic semiconductors. By employing a low temperature chemical growth (≤ 90 °C) approach for ZnO synthesis combined together with organic p-type semiconductors, we demonstrate high quality LEDs fabricated on a variety of different substrates. The substrates include transparent glass, plastic, and conventional Si. Different multi-layers of p-type organic semiconductors with or without electron blocking layers have been demonstrated and characterized. The investigated p-type organic semiconductors include PEDOT:PSS, which was used as a anode in combination with other p-type polymers. Some of the heterojunction diodes also contain an electron blocking polymer sandwiched between the p-type polymer and the n-ZnO nano-wire. The insertion of electron blocking layer is necessary to engineer the device for the desired emission. Structural and electrical results will be presented. The preliminary I-V characteristics of the organic-inorganic hybrid heterojunction diodes show good rectifying properties. Finally we also present our findings on the origin of the green luminescence band which is responsible of the white light emission in ZnO is discussed.

  • 3554.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Wadeasa, Amal
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Yang, Lili
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Zhao,, Qingxiang
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Photonic devices in some low dimensional sysems2009In: ECS Transactions, ISSN 1938-5862, E-ISSN 1938-6737, Vol. 16, no 41, p. 17-30Article in journal (Refereed)
    Abstract [en]

    Results of using low temperature growth approach (lower than 100 oC) to control the growth of ZnO nanowires are presented. The effect of different parameters on the growth is highlighted. Time resolved low temperature photoluminescence (PL) was used to investigate surface recombination and its relation to the nanowires diameters. Finally hybrid light emitting diodes (LEDs) based on p-type polymers and n-ZnO nanowires grown on amorphous substrates is fabricated and characterized. This hybrid organic-inorganic technology can provide a suitable replacement of conventional lighting tubes.

  • 3555.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Zinc oxide nanostructures at the forefront of new white light- emitting technology2007Other (Other (popular science, discussion, etc.))
  • 3556. Wills, J.M.
    et al.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Teoretisk magnetism.
    Comment on 'Nature of non-magnetic strongly-correlated state in delta-Pu' by L.Pourovskii et al.''2006In: Europhysics letters, Vol. 76, p. 170-Article in journal (Refereed)
  • 3557.
    Wills, John M.
    et al.
    LANL, Los Alamos, USA.
    Eriksson, Olle
    Uppsala University.
    Andersson, Per
    FOI.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Grechnyev, Oleksiy
    Natl Acad Sci Ukraine, BI Verkin Inst Low Temp Phys & Engn, UA-61103 Kharkov, Ukraine.
    Alouani, Mebarek
    UdS CNRS, UMR 7504, Inst Phys & Chim Mat Strasbourg, F-67034 Strasbourg 2, France.
    Full-Potential Electronic Structure Method: Energy and Force Calculations with Density Functional and Dynamical Mean Field Theory2010Book (Other academic)
  • 3558. Winter, Johannes
    et al.
    Kuzmany, Hans
    Soldatov, Alexander
    Umeå University, Faculty of Science and Technology, Physics.
    Persson, Per-Axel
    Umeå University, Faculty of Science and Technology, Physics.
    Jacobsson, Per
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Charge transfer in alkali-metal-doped polymeric fullerenes1996In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 54, no 24, p. 17486-17492Article in journal (Refereed)
    Abstract [en]

    We present room-temperature Raman measurements of pressure-polymerized C60 and compare them with the spectra of RbC60 in the orthorhombic phase. Although both materials were prepared according to two completely different routes the spectra show a surprising similarity with respect to mode positions and line splitting. We concluded from this that both materials, the uncharged pressure-polymerized C60 and the rubidium-doped orthorhombic compound, have the same overall structure and the AC60 compounds can be considered as the doped species of the C60, polymerized using moderate low pressure and high temperatures. From a detailed comparison between both spectra mode shifting and line broadening as a consequence of the charge transfer was determined and electron-phonon coupling constants were estimated for the high-frequency Hg(7) and Hg(8) modes. The low values for the coupling constants compared to the ones in the K3C60 can explain the lack of superconductivity in the AC60 compounds.

  • 3559.
    Winters, M.
    et al.
    Chalmers, Sweden.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. University of Iceland, Iceland.
    Melios, C.
    National Phys Lab, England; University of Surrey, England.
    Kazakova, O.
    National Phys Lab, England.
    Strupinski, W.
    Institute Elect Mat Technology, Poland.
    Rorsman, N.
    Chalmers, Sweden.
    Characterization and physical modeling of MOS capacitors in epitaxial graphene monolayers and bilayers on 6H-SiC2016In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 6, no 8, article id 085010Article in journal (Refereed)
    Abstract [en]

    Capacitance voltage (CV) measurements are performed on planar MOS capacitors with an Al2O3 dielectric fabricated in hydrogen intercalated monolayer and bilayer graphene grown on 6H-SiC as a function of frequency and temperature. Quantitative models of the CV data are presented in conjunction with the measurements in order to facilitate a physical understanding of graphene MOS systems. An interface state density of order 2 . 10(12)eV(-1)cm(-2) is found in both material systems. Surface potential fluctuations of order 80-90meV are also assessed in the context of measured data. In bilayer material, a narrow bandgap of 260meV is observed consequent to the spontaneous polarization in the substrate. Supporting measurements of material anisotropy and temperature dependent hysteresis are also presented in the context of the CV data and provide valuable insight into measured and modeled data. The methods outlined in this work should be applicable to most graphene MOS systems. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

  • 3560.
    Winters, M
    et al.
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    Ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Zirath, H
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Rorsman, N
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    A temperature dependent measurement of the carrier velocity vs. electric field characteristic for as-grown and H-intercalated epitaxial graphene on SiC2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 19Article in journal (Refereed)
    Abstract [en]

    A technique for the measurement of the electron velocity versus electric field is demonstrated on as-grown and H-intercalated graphene. Van der Pauw, coplanar microbridge, and coplanar TLM structures are fabricated in order to assess the carrier mobility, carrier concentration, sheet resistance, and contact resistance of both epi-materials. These measurements are then combined with dynamic IV measurements to extract a velocity-field characteristic. The saturated electron velocity measurements indicate a value of 2.33 × 107cm/s for the as-grown material and 1.36 × 107cm/s for the H-intercalated material at 300 K. Measurements are taken as a function of temperature from 100 K to 325 K in order to estimate the optical phonon energy Eso of 4H-SiC by assuming an impurity scattering model. The extracted values of Eso are 97 meV for the as-grown sample and 115 meV for the H-intercalated sample. The H-intercalated result correlates to the anticipated value of 116 meV for 4H-SiC, while the as-grown value is significantly below the expected value. Therefore, we hypothesize that the transport properties of epitaxial graphene on SiC are influenced both by intercalation and by remote phonon scattering with the SiC substrate.

  • 3561.
    Wojek, Bastian M.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Comment on "Probing two- and three-dimensional electrons in MgB2 with soft x-ray angle-resolved photoemission"Manuscript (preprint) (Other academic)
    Abstract [en]

    A recent article by Sassa et al. [Phys. Rev. B 91, 045114 (2015)] reports on a soft-xray angle-resolved photoemission study of MgB2. The analysis and/or presentation of the collected data and the corresponding calculations appear to be partially inconsistent. The aim of this comment is to provide a guide to these inconsistencies and to discuss their influence on the presented conclusions.

  • 3562.
    Wolborski, Maciej
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Termination and passivation of Silicon Carbide Devices.2005Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Silicon carbide rectifiers are commercially available since 2001, and MESFET switches are expected to enter the market within a year. Moreover, three inch SiC wafers can be purchased nowadays without critical defects for the device performance and four inch substrate wafers are announced for the year 2005. Despite this tremendous development in SiC technology, the reliability issues like device degradation or high channel mobility still remain to be solved.

    This thesis focuses on SiC surface passivation and termination, a topic which is very important for the utilisation of the full potential of this semiconductor. Three dielectrics with high dielectric constants, Al2O3, AlN and TiO2, were deposited on SiC with different techniques. The structural and electrical properties of the dielectrics were measured and the best insulating layers were then deposited on fully processed and well characterised 1.2 kV 4H SiC PiN diodes. For the best Al2O3 layers, the leakage current was reduced to half its value and the breakdown voltage was extended by 0.5 kV, reaching 1.6 kV, compared to non passivated devices.

    As important as the proper choice of dielectric material is a proper surface preparation prior to deposition of the insulator. In the thesis two surface treatments were tested, a standard HF termination used in silicon technology and an exposure to UV light from a mercury lamp. The second technique is highly interesting since a substantial improvement was observed when UV light was used prior to the dielectric deposition. Moreover, UV light stabilized the surface and reduced the leakage current by a factor of 100 for SiC devices after 10 Mrad γ ray exposition. The experiments indicate also that the measured leakage currents of the order of pA are dominated by surface leakage.

  • 3563.
    Wolborski, Maciej
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Bakowski, Mietek
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Electrical characteristics of the epitaxial and Al implanted 4H-SiC PiN diodes with etched zone termination in the temperature range from 300K to 623K.Manuscript (Other academic)
  • 3564.
    Wu, Philip
    et al.
    Lund University.
    Paschoal Jr, Waldomiro
    Lund University.
    Kumar, Sandeep
    Lund University.
    Borschel, Christian
    Jena University.
    Ronning, Carsten
    Jena University.
    Canali, Carlo M.
    Linnaeus University, Faculty of Science and Engineering, School of Computer Science, Physics and Mathematics.
    Samuelson, Lars
    Lund University.
    Pettersson, Håkan
    Halmstad University.
    Linke, Heiner
    Lund University.
    Thermoelectric Characterization of Electronic Properties of GaMnAs Nanowires2012In: Journal of Nanotechnology, ISSN 1687-9503, E-ISSN 1687-9511, p. Article ID: 480813-Article in journal (Refereed)
    Abstract [en]

    Nanowires with magnetic doping centers are an exciting candidate for the study of spin physics and proof-of-principle spintronics devices. The required heavy doping can be expected to have a significant impact on the nanowires’ electron transport properties.

    Here, we use thermopower and conductance measurements for transport characterization of Ga0.95Mn0.05As nanowires over a broad temperature range. We determine the carrier type (holes) and concentration and find a sharp increase of the thermopower below temperatures of 120 K that can be qualitatively described by a hopping conduction model. However, the unusually large thermopower suggests that additional mechanisms must be considered as well.

  • 3565.
    Wu, Phillip M.
    et al.
    Division of Solid State Physics and the Nanometer Structure Consortium (NmC at LU), Lund University, P.O. Box 118, 221 00 Lund, Sweden.
    Paschoal Jr., Waldomiro
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Kumar, Sandeep
    Division of Solid State Physics and the Nanometer Structure Consortium (NmC at LU), Lund University, P.O. Box 118, 221 00 Lund, Sweden.
    Borschel, Christian
    Institute for Solid State Physics, Jena University, Max-Wien-Platz 1, 07743 Jena, Germany.
    Ronning, Carsten
    Institute for Solid State Physics, Jena University, Max-Wien-Platz 1, 07743 Jena, Germany.
    Canali, Carlo M.
    Division of Physics, School of Computer Science, Linnæus University, 39233 Kalmar, Sweden.
    Samuelson, Lars
    Division of Solid State Physics and the Nanometer Structure Consortium (NmC at LU), Lund University, P.O. Box 118, 221 00 Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Linke, Heiner
    Division of Solid State Physics and the Nanometer Structure Consortium (NmC at LU), Lund University, P.O. Box 118, 221 00 Lund, Sweden.
    Thermoelectric Characterization of Electronic Properties of GaMnAs Nanowires2012In: Journal of Nanotechnology, ISSN 1687-9503, E-ISSN 1687-9511, Vol. 2012, article id 480813Article in journal (Refereed)
    Abstract [en]

    Nanowires with magnetic doping centers are an exciting candidate for the study of spin physics and proof-of-principle spintronics devices. The required heavy doping can be expected to have a significant impact on the nanowires' electron transport properties. Here, we use thermopower and conductance measurements for transport characterization of Ga 0.95Mn 0.05As nanowires over a broad temperature range. We determine the carrier type (holes) and concentration and find a sharp increase of the thermopower below temperatures of 120 K that can be qualitatively described by a hopping conduction model. However, the unusually large thermopower suggests that additional mechanisms must be considered as well. © 2012 Phillip M. Wu et al.

  • 3566. Wu, Weihua
    et al.
    Tang, Shaobin
    Gu, Junjing
    Cao, Xinrui
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Department of Physics, Institute of Theoretical Physics, Xiamen University, Xiamen, China.
    Realizing semiconductor to metal transition in graphitic ZnO and MoS2 nanocomposite with external electric field2015In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, no 120, p. 99153-99163Article in journal (Refereed)
    Abstract [en]

    First-principles calculations have been used to investigate the structural and electronic properties of graphitic ZnO and MoS2 (g-ZnO/MoS2) nanocomposites. It is found that the binding strength of g-ZnO/MoS2 exhibits strong dependence of atomic arrangement of g-ZnO relative to MoS2. The coupling interaction of g-ZnO/MoS2 obviously reduces the semiconducting band gaps, compared to both individual sheets, which are sensitive to its stacking orders. Interestingly, the vertical external electric field (E-field) can be applied to enhance the stability of g-ZnO/MoS2 and increase charge transfers between these two component. Furthermore, the E-field with the positive direction from MoS2 to g-ZnO can tune the band gap of g-ZnO/MoS2 nanocomposites, whereas this nanocomposites produce the semiconducting to metallic behavior transitions when the E-field changes from positive to negative direction, regardless of the stacking pattern. The tunable electronic properties of g-ZnO/MoS2 nanocomposites under the E-field are attributed to the changes in electrostatic potential difference between atom layer of MoS2 and interlayer region close to g-ZnO. Present results suggest that the g-ZnO/MoS2 heterojunction provides promising applications for MoS2-based optoelectronic and nanoelectronic devices, such as fabricating field effect transistor (FET).

  • 3567.
    Wutikuer, Otkur
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Fabrication and Characterization of 4H-SiC MOS Capacitors with Different Dielectric Layer Treatments2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    4H-SiC based Metal-Oxide Semiconductor(MOS) capacitors are promising key components for next generation power devices. For high frequency power applications, however, there is a major drawback of this type of devices, i.e. they have low inversion channel mobility that consequently affects the switching operation in MOS Field-Effect Transistors (MOSFETs). Carbon clusters or excess carbon atoms in the interface between the dielectric layer and SiC is commonly considered to be the carrier trapping and scattering centers that lower the carrier channel mobility. Based on the previous work in the research group, a new fabrication process for forming the dielectric layer with a lower density of the trap states is investigated. The process consists of standard semiconductor cleaning, pre-treatments, pre-oxidation, plasma enhanced chemical vapor deposition (PECVD) and post oxidation annealing. I-V measurements of the dielectric strength showed that the resulting layers can sustain proper working condition under an electric field of at least 5MV/cm. C-V characteristics measurements provided the evidence that the proposed method can effectively reduce the interfacial states, which are main culprit for a large flat band voltage shift of C-V characteristics, in particular under annealing at 900°C in nitrogen atmosphere.

  • 3568.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Goze-Bac, Christophe
    Röding, Robert
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Johnels, Dan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Kataura, Hiromichi
    Bernier, Patric
    13C NMR on intercalated 2D-polymerised C60 and modified peapods.2004In: Electronic Properties of Synthetic Nanostructures: Proceedings of the XVIII International Winter School/Euroconference on Electronic Properties of Novel Materials, Kirchhberg 2004, Melville, NY: American Institute of Physics (AIP) , 2004, p. 238-41Conference paper (Refereed)
    Abstract [en]

    We present 13C NMR results on the intercalated 2D C60-polymers Li4-xNaxC60 (x=0-4 with half integer steps) showing that while Li4C60 forms a tetragonal polymer with double polymer bonds between the molecules, Na4C60 form a monoclinic polymer with single polymer bonds. The chemical shift is much larger for Li-rich samples than for Na-rich samples, indicating perhaps a different type of interaction with the C60 molecules. The crossover between the two structures appears to be at the composition Li2.5Na1.5C60 . We also show NMR data on SWNT filled with C60 molecules, so called peapods, showing that the NMR line of C60 can not be observed when the C60 is inside the tubes. Weinterpret this as resulting from a very long relaxation time, indicating that the dynamics of the C60 molecule is hindered by the nanotube walls.

  • 3569.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Jacobsson, Per
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Comparative Raman study of photopolymerised and pressure-polymerised C60 films1999In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 60, no 7, p. 4535-4538Article in journal (Refereed)
    Abstract [en]

    We have made a Raman study of low-pressure polymerized and photopolymerized C60 films, polymerized in different ways, but otherwise initially identical. Although the structures developing in the films during polymerization are initially very similar, an analysis of characteristic features in the Raman spectra shows that photopolymerized material forms a more complex polymeric structure when the polymerization approaches saturation. We suggest that this complex structure contains branched polymeric chains and in particular that a mode near 1454 cm-1 in photopolymerized C60 is characteristic for this type of structure.

  • 3570.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Launois, Pascale
    Univ Paris II.
    Moret, Roger
    Univ Paris II.
    Huang, H
    Hong Kong Univ Sci & Technol,.
    Yang, SH
    Hong Kong Univ Sci & Technol,.
    Li, IL
    Hong Kong Univ Sci & Technol,.
    Tang, ZK
    Hong Kong Univ Sci & Technol,.
    Study by X-ray diffraction and Raman spectroscopy of a Dy@C82single crystal2003In: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 35, no 3, p. 371-375Article in journal (Refereed)
    Abstract [en]

    We report the first X-ray diffraction and Raman spectroscopy study of a single crystal of the rare-earth endohedral fullerene Dy@C-82. The lattice is found to be body-centered cubic (a = 25.79 Angstrom, space group I (4) over bar 3d) which is at variance with previous reports and confirms that several types of structures can be stabilized in Dy@C-82. X-ray diffraction/diffuse scattering methods reveal no low-temperature change down to 12 K for the present structure. The Raman spectroscopy data are comparable to those of other M@C-82 endohedral compounds. However, the Dy oxidation state and the force constant of the low-frequency metal-cage stretching mode do not follow the simple relationship observed before.

  • 3571.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Liu, Bin
    Natl Univ Singapore, Dept Chem & Biomol Engn.
    Orädd, Greger
    Umeå University, Faculty of Science and Technology, Chemistry.
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Chemistry.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Cationic polyfluorene: conformation and aggregation in a "good" solvent2009In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, ISSN 0014-3057, Vol. 45, no 11, p. 3228-3233Article in journal (Refereed)
    Abstract [en]

    The conjugated polyelectrolyte (CPE) poly{9,9'-bis[6 ''-(N,N,N-trimethylammonium)-hexylfluorene-alt-co-phenylene] dibromide} (PFPN+Br-) demonstrates a high solubility in methanol in comparison to other more hydrophilic or hydrophobic solvents. We have employed a combination of pulsed-field-gradient-NMR, photoluminescence (PL), and Raman spectroscopy to establish the conformation and aggregation behavior of PFPN+Br- in methanol, with the aim to attain information on how to design CPEs with a high solubility in a preferred solvent. We find that the diffusion coefficient and PL spectrum of PFPN+Br-, as well as the Raman-active methyl rocking mode of methanol, all exhibit a strong dependence on PFPN+Br- concentration. We rationalize our findings with a model in which PFPN+Br- forms aggregates via ∏-∏ interactions between main-chain segments, while the ionic side chains are surrounded and electrostatically screened by the methanol solvent. Accordingly, the notably high solubility of PFPN+Br- in methanol is rationalized by favorable interactions between the ionic side chains and the methanol molecules. We propose that an appropriate design of a high-solubility CPE should consider a matching of the mixed hydrophobic/hydrophilic character of the ionic side chain with that of the preferred solvent.

  • 3572.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Nyeanchi, Emmanuel B.
    Umeå University, Faculty of Science and Technology, Physics.
    Soldatov, Alexander
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    2D polymerization and doping of fullerenes under pressure2000In: High Pressure Research vol. 18: Proceedings of the XXXVII Meeting of the European High Pressure Research Group, Montpellier 1999 (EHPRG'99), Gordon & Breach , 2000, p. 139-143Conference paper (Refereed)
    Abstract [en]

    Tetragonal polymeric C60 has been studied by Raman spectroscopy and other methods. Attempts have been made to transform samples from the tetragonal to the orthorhom-bic phase and vice versa. The results suggest that the transformation is direct with no intermediate stage with free molecules. Tetragonal C60 has also been intercalated by potassium metal.

  • 3573.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Persson, Per-Axel
    Umeå University, Faculty of Science and Technology, Physics. Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Structural evolution of low-pressure polymerised C60 with polymerisation conditions1999In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 60, no 12, p. 1989-1994Article in journal (Refereed)
    Abstract [en]

    We show in this paper that characteristic features in the Raman spectra, especially the frequency of the pentagonal pinch mode, can give information about the polymeric structure of pressure polymerised C60. High-pressure treatment at 1 GPa below 510 K for 3 h results in the formation of a low fraction of dimers only, while treatment at the same pressure and time above 540 K affords a fully polymerised material. In the latter case, different relative fractions of dimers and polymer chains are obtained depending on whether the final reaction conditions were reached by isobaric or isothermal path. We suggest that this difference results from different reaction dynamics in the two cases. The polymerisation rate depends on T and p and on the rotational and orientational states of the molecules. At 1 GPa no polymerisation is observed in sc C60, while in “hexagon” oriented sc C60 at 1.7 GPa dimers are already formed 175 K below the fcc–sc transition and a fully polymerised material is obtained just below the transition to the fcc phase.

  • 3574.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Persson, Per-Axel
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Jacobsson, Per
    Umeå University, Faculty of Science and Technology, Physics.
    A Raman study of polymerised C601997In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 64, no 3, p. 223-226Article in journal (Refereed)
    Abstract [en]

    Results of Raman scattering studies on high pressure polymerized and photo polymerized C60 are reported. Although prepared according to different routes the Raman spectra of the two polymeric phases of C60 show a quantitative agreement with respect to mode positions and intensity. We conclude from this that both materials have the same structure at least in the short range order, i.e. the same type of bonding and co-ordination between neighbouring C60 molecules. An investigation of the time dependence of the thermal decomposition of high pressure polymerised C60 is also presented. The rate of decomposition of the polymeric phase is found to be multi-exponential at all temperatures investigated. From an Arrhenius-type analysis of the short time data and the long time data, respectively, the activation energy for thermal dissociation of polymeric bonds was found to increase with time.

  • 3575.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Persson, Per-Axel
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Jacobsson, Per
    Umeå University, Faculty of Science and Technology, Physics.
    Polymeric phases of C601997In: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, vol. 5: Proceedings of the 192nd Meeting of the Electrochemical Society, Paris 1997; Symposium Fullerenes: Chemistry, Physics, and New Directions, Pennington, NJ: The Electrochemical Society , 1997, p. 674-679Conference paper (Refereed)
    Abstract [en]

    We have investigated the "low" pressure region where C60 can be transformed into polymeric chains or clusters. To learn more about the polymerization process we have treated pristine C60 at several different temperatures under hydrostatic pressures in silicone oil. We found that the reaction rate varied with temperature. Above 520 K at 1.0 GPa similar and high polymer fractions were obtained in all samples, but at 497 K the polymer fraction was only 10% after three hours, as indicated by the shift of the intensity of the pentagonal pinch mode in the Raman spectrum. Also, samples treated at the same pressure and temperature but with different thermal pre-history showed different degrees of polymerization. We have also found a correlation between the shift of the pentagonal pinch mode in the Raman spectrum to 1463 /cm and the intermolecular vibrational mode at 97 /cm. We therefore make the conclusion that the shift of the pentagonal pinch mode to 1463 /cm corresponds to the presence of dimers in the sample.

  • 3576.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Soldatov, Alexander
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Spectroscopic study of phase transformations between orthorhombic and tetragonal C60 polymers2006In: The European Physical Journal B: Condensed Matter and Complex Systems, ISSN 1434-6028, Vol. 49, no 1, p. 59-65Article in journal (Refereed)
    Abstract [en]

    We present a detailed study of transformations between the orthorhombic and tetragonal polymeric states of C60. The transformations are characterised by Raman spectroscopy and X-ray diffraction. We show that the transformation from the orthorhombic (O) phase to the tetragonal (T) phase is very fast and our results indicate that the transformation goes via an intermediate dimer (D) state in a two-stage process, O↦D and, D↦T transformations, where the second process is slower than the first. On the other hand, the transformation from the tetragonal to the orthorhombic phase is significantly slower, indicating a high-energy threshold to break the polymer bonds at the temperatures used. The results also support earlier suggestions that the tetragonal phase contains disordered dimers that can be viewed as lattice defects in the formation of higher polymers.

  • 3577.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Stenmark, Patrik
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Structural aspects of two-dimensional polymers: Li4C60, Na4C60 and tetragonal C60. Raman spectroscopy and X-ray diffraction.2004In: Journal of Physics and Chemistry of Solids vol. 65, issue no. 2-3: Proceedings of the 12th International Symposium on Intercalation Compounds, ISIC-12, Poznan, Poland 2003, Amsterdam: Elsevier B.V. , 2004, p. 317-320Conference paper (Refereed)
    Abstract [en]

    We present an analysis of three different two-dimensional polymers, tetragonal C60, Li4C60, and Na4C60. Based on X-ray diffraction and Raman spectroscopy, we conclude that Li4C60 forms a tetragonal structure with intermolecular bonds formed by 2 plus 2 cycloaddition, in the same way as for tetragonal C60. Na4C60, on the other hand, forms a monoclinic structure with single C–C bonds between the molecules. Our Raman spectroscopy results can be interpreted in two ways: either the charge transfer to the C60 molecules is the same in both doped compounds with four electrons/molecule or the electron charge transfer is smaller from the Li ions than from the Na ions.

  • 3578.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Can two-dimensional fullerene polymers be intercalated?2000In: Molecular Crystals and Liquid Crystals vol. 340: Proceedings of the 10th International Symposium on Intercalation Compounds (ISIC 10), Okazaki 1999, Overseas Publishing Association, B.V. , 2000, p. 677-682Conference paper (Refereed)
    Abstract [en]

    Two-dimensional C60 polymers can be produced by treatment at high T and high p. Attempts have previously been made to intercalate these layered materials by alkali metals using the gas phase method but the polymers have always decomposed. We investigate here whether intercalated 2D polymers can be formed by other methods, such as by polymerization in the presence of alkali metals. Preliminary x-ray and Raman data can be interpreted to indicate the presence of an alkali metal intercalated tetragonal fullerene polymeric structure.

  • 3579.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Raman study of the two-dimensional polymers Na4C60 and tetragonal C60.2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 15, p. 155421-Article in journal (Refereed)
    Abstract [en]

    We present a Raman investigation of the monoclinic two-dimensionally polymerized phase Na4C60 and a comparison with the pure tetragonal C60 polymer and the doped K3C60 structure. The Raman spectrum of Na4C60 depends on the probing laser wavelength, and high wave-number modes are hard to observe with a low-energy laser excitation. The spectrum for Na4C60 is very rich with a pronounced splitting of the original Hg modes and a large number of new modes. Several modes at low wave numbers support the presence of intermolecular bonds and the line broadening observed for low-frequency Hg modes is typical for electron-phonon coupling in metallic fullerene systems. From the shift of the pentagonal pinch mode we deduce an unexpectedly low charge transfer of approximately three electrons per C60 molecule. The presence of a distinct mode around 980 cm-1 throws doubts on earlier assumptions that modes in this range are connected to vibrations in the intermolecular cyclobutane rings found in C60 polymers. No superconductivity is observed in Na4C60, although the electron-phonon interaction derived from the Raman spectrum is similar to that in K3C60.

  • 3580.
    Xia, Chao
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Johansson, Leif I
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Zakharov, A A
    MAX-lab, Lund University, Lund, Sweden.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Virojanadara, Chariya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Effects of Al on epitaxial graphene grown on 6H-SiC(0001)2014In: Materials Research Express, ISSN 2053-1591, Vol. 1, no 1, p. 1-13, article id 015606Article in journal (Refereed)
    Abstract [en]

    Aluminum was deposited on epitaxial monolayer-grown graphene on SiC(0001). The effects of annealing up to 1200 °C on the surface and interface morphology, chemical composition, and electron band structure were analyzed in situ by synchrotron-based techniques at the MAX Laboratory. After heating at around 400 °C, Al islands or droplets are observed on the surface and the collected Si 2p, Al 2p, and C 1s core levels spectra indicate Al intercalation at the graphene SiC interface. Also, the original single π -band splits into two, indicating decoupling of the carbon buffer layer and the formation of a quasi-free-standing bilayer-like electronic structure. Further heating at higher temperatures from 700 to 900 °C yields additional chemical reactions. Broader core level spectra are then observed and clear changes in the π -bands near the Dirac point are detected. More electron doping was detected at this stage since one of the π -bands has shifted to about 1.1 eV below the Fermi level. Different ordered phases of (7x7), (4x4), (1x1)Al , and (1x1)G were also observed on the surface in this temperature range. The original single π π-band was restored after heating at ~1200°C, although an Al signal was still able to be detected.

  • 3581.
    Xia, Chao
    et al.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Tal, Alexey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Johansson, Leif
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Olovsson, Weine
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Linköping University, National Supercomputer Centre (NSC).
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Virojanadara, Chariya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Effects of rhenium on graphene grown on SiC(0001)2018In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 222, p. 117-121Article in journal (Refereed)
    Abstract [en]

    We study the effects of Rhenium (Re) deposited on epitaxial monolayer graphene grown on SiC(0001) and after subsequent annealing at different temperatures, by performing high resolution photoelectron spectroscopy (PES) and angle resolved photoelectron spectroscopy (ARPES). The graphene-Re system is found to be thermally stable. While no intercalation or chemical reaction of the Re is detected after deposition and subsequent annealing up to 1200 degrees C, a gradual decrease in the binding energy of the Re 4f doublet is observed. We propose that a larger mobility of the Re atoms with increasing annealing temperature and hopping of Re atoms between different defective sites on the graphene sample could induce this decrease of Re 4f binding energy. This is corroborated by first principles density functional theory (DFT) calculations of the Re core-level binding energy shift. No change in the doping or splitting of the initial monolayer graphene electronic band structure is observed after Re deposition and annealing up to 1200 degrees C, only a broadening of the bands. (C) 2017 Elsevier B.V. All rights reserved.

    The full text will be freely available from 2019-08-07 00:01
  • 3582. Xiao, S.
    et al.
    Xiang, S.
    Yoon, Y.
    Kang, M. -G.
    Kida, M.
    Aoki, N.
    Reno, J. L.
    Ochiai, Y.
    Mourokh, L.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Bird, J. P.
    Talking Through the Continuum: New Manifestation of Fano-Resonance Phenomenology Realized With Mesoscopic Nanostructures2012In: Fortschritte der Physik, ISSN 0015-8208, E-ISSN 1521-3978, Vol. 61, no 2-3, p. 348-359Article in journal (Refereed)
  • 3583.
    Xiao, S.
    et al.
    Univ Buffalo, State Univ New York, Dept Elect Engn, Buffalo, NY 14260 USA..
    Yoon, Y.
    Univ Buffalo, State Univ New York, Dept Elect Engn, Buffalo, NY 14260 USA..
    Lee, Y. -H
    Bird, J. P.
    Univ Buffalo, State Univ New York, Dept Elect Engn, Buffalo, NY 14260 USA.;Chiba Univ, Grad Sch Adv Integrat Sci, Inage Ku, 1-33 Yayoi Cho, Chiba 2638522, Japan..
    Ochiai, Y.
    Chiba Univ, Grad Sch Adv Integrat Sci, Inage Ku, 1-33 Yayoi Cho, Chiba 2638522, Japan..
    Aoki, N.
    Chiba Univ, Grad Sch Adv Integrat Sci, Inage Ku, 1-33 Yayoi Cho, Chiba 2638522, Japan..
    Reno, J. L.
    Sandia Natl Labs, CINT, Dept 1131, MS 1303, Albuquerque, NM 87185 USA..
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Detecting weak coupling in mesoscopic systems with a nonequilibrium Fano resonance2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 16, article id 165435Article in journal (Refereed)
    Abstract [en]

    A critical aspect of quantum mechanics is the nonlocal nature of the wave function, a characteristic that may yield unexpected coupling of nominally isolated systems. The capacity to detect this coupling can be vital in many situations, especially those in which its strength is weak. In this work, we address this problem in the context of mesoscopic physics, by implementing an electron-wave realization of a Fano interferometer using pairs of coupled quantum point contacts (QPCs). Within this scheme, the discrete level required for a Fano resonance is provided by pinching off one of the QPCs, thereby inducing the formation of a quasibound state at the center of its self-consistent potential barrier. Using this system, we demonstrate a form of nonequilibrium Fano resonance (NEFR), in which nonlinear electrical biasing of the interferometer gives rise to pronounced distortions of its Fano resonance. Our experimental results are captured well by a quantitative theoretical model, which considers a system in which a standard two-path Fano interferometer is coupled to an additional, intruder, continuum. According to this theory, the observed distortions in the Fano resonance arise only in the presence of coupling to the intruder, indicating that the NEFR provides a sensitive means to infer the presence of weak coupling between mesoscopic systems.

  • 3584.
    Xiao, Xin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Influnence of boundary on hydrogen absorption in VManuscript (preprint) (Other academic)
  • 3585.
    Xiao, Xin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Thermodynamics of Hydrogen in Confined Lattice2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Three of the most important questions concerning hydrogen storage in metals are how much hydrogen can be absorbed, how fast it can be absorbed (or released) and finally how strongly the hydrogen is bonded. In transition metals hydrogen occupies interstitial sites and the absorption as well as desorption of hydrogen can be fast. The enthalpy of the hydride formation is determined by the electronic structure of the absorbing material, which determines the amount of energy released in the hydrogen uptake and the energy needed to release the hydrogen.

    This thesis concerns the possibility of tuning hydrogen uptake by changing the extension of the absorbing material and the boundary conditions of extremely thin layers. When working with extremely thin layers, it is possible to alter the strain state of the absorbing material, which is used to influence the site occupancy of hydrogen isotopes. Vanadium is chosen as a model system for these studies. V can be grown in the form of thin films as well as superlattices using MgO as a substrate. Special emphasis are on Fe/V(001) and Cr/V(001) superlattices as these can be grown as high quality single crystals on a routine basis. The use of high quality samples ensured well-defined conditions for all the measurements.

    In these experiments the hydrogen concentration is determined by the light transmittance of the thin films.  By changing the temperature and the pressure of the hydrogen gas, it is possible to determine the thermodynamic properties of hydrogen in the samples, from the obtained concentrations.  Measurements of the electrical resistivity is used to increase the accuracy in the measurements at low concentrations as well as to provide information on ordering at intermediate and high hydrogen concentrations. The thermodynamic properties and the electrical resistivity of VH are strongly affected by the choice of boundary layers. For example, when hydrogen is absorbed in V embedded by Fe, Cr or Mo in the form of superlattices, both the thermodynamic properties and the changes in the resistivity are strongly influenced.

    The critical temperature and H-H interactions of hydrogen in thin V(001) layers are found to increase with thickness of the thin films and superlattices. The observed finite size effects resemble same scaling with the thickness of the layers as does the magnetic ordering temperature. The results were validated by investigations of isotope effects in the obtained thermodynamic properties. Close to negligible effects are obtained when replacing hydrogen by deuterium, with respect to the thermodynamic properties. These observations are rationalised by an octahedral occupancy in the strained layers, as compared to tetrahedral occupancy in unstrained bulk. The octahedral site occupancy is found to strongly alter the diffusion coefficient of hydrogen in thin V layers.

     

  • 3586.
    Xiao, Xin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Johansson, Robert
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wolff, Max
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Hydrogen in V: isotope effects and site occupancyManuscript (preprint) (Other academic)
  • 3587.
    Xiaoqing, Li
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Mechanical Properties of Transition Metal Alloys from First-PrinciplesTheory2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The aim of the thesis is to investigate the alloying and temperature effects on the mechanical properties of body-centered cubic (bcc) random alloys. We employ the all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation. The second-order elastic constants reflect the mechanical properties of materials in the small deformation region, where the stress-strain relations are linear. Beyond the small elastic region, the mechanical properties of defect-free solids are described by the so called ideal strength. These two sets of physical quantities are the major topic of my investigations.

    In part one (papers I and II), the elastic constants and the ideal tensile strengths (ITS) are investigated as a function of Cr and Ti for the bccV-based random solid solution. We find that alloys along the equi-composition region exhibit the largest shear modulus and Young’s modulus, which is a resultof the opposite alloying effects obtained for the two cubic shear elastic constants C′ and C44. The classical Labusch-Nabarro solid-solution hardening (SSH) model extended to ternary alloys predicts a larger hardening effect in V-Ti than in V-Cr alloy. By considering a phenomenological expression for the ductile-brittle transition temperature (DBTT) in terms of Peierls stress and SSH, we show that the present theoretical results can account for the observed variations of DBTT with composition. Under uniaxial [001] tensile loading, the ITS of V is 12.4 GPa and the lattice fails by shear. Assuming isotropic Poisson contraction, the ITSs are 36.4 and 52.0 GPa for V in the [111] and [110] directions, respectively. For the V-based alloys, Cr increases and Ti decreases the ITS in all principal directions. Adding the same concentration of Cr and Ti to V leads to ternary alloys with similar ITS values as that of pure V. We show that the ITS correlates with the fcc-bcc structural energy difference and explain the alloying effects on the ITS based on electronic band structure theory.

    In part two (paper III), the alloying effect on the ITS of four bcc refractory HEAs based on Zr, V, Ti, Nb, and Hf is studied. Starting from ZrNbHf, we find that the ITS decreases with equimolar Ti addition. On the other hand, if both Ti and V are added to ZrNbHf, the ITS is enhanced by about 42%. An even more captivating effect is the ITS increase by about 170%, if Ti and V are substituted for Hf. We explain the alloying effect on the ITS based on the d-band filling. We explore an intrinsic brittle-to-ductile transition, which arises due to an alloying-driven change of the failure mode under uniaxial tension. Our results indicate that intrinsically ductile HEAs with high intrinsic strength can be achieved by controlling the proportion of group four elements to group five elements.

    In part three (papers IV and V), the ITS of bcc ferromagnetic Fe-based random alloys is calculated as a function of compositions. The ITS of Fe is calculated to be 12.6 GPa under [001] direction tension, which is in good agreement with the available theoretical data. For the Fe-based alloys, we predict that V, Cr, and Co increase the ITS, while Al and Ni decrease it. Manganese yields a weak non-monotonic alloying behavior. We show that the previously established ideal tensile strengths model based on structural energy differences for the nonmagnetic V-based alloys is of limited use in the case of Fe-bases alloys, which is attributed to the effect of magnetism. We find that upon tension all investigated solutes strongly alter the magnetic response of the Fe host from the unsaturated towards a stronger ferromagnetic behavior.

    In part four (paper VI), the temperature effect on the ITS of bcc Fe and Fe0.9Co0.1alloy is studied. We find that the ITS of Fe is only slightly temperature dependent below∼500K but exhibits large thermal gradients at higher temperatures. Thermal expansion and electronic excitations have an overall moderate effect, but magnetic disorder reduces the ITS with a pronounced 90% loss in strength in the temperature interval∼500 - 920K. Such a dramatic temperature effect far below the magnetic transition temperature has not been observed for other micro-mechanical properties of Fe. We demonstrate that the strongly reduced Curie temperature of the distorted Fe lattices compared to that of bcc Fe is primarily responsible for the onset of the drop of the intrinsic strength. Alloying additions, which have the capability to partially restore the magnetic order in the strained Fe lattice, push the critical temperature for the strength-softening scenario towards the magnetic transition temperature of the undeformed lattice. This can result in a surprisingly large alloying-driven strengthening effect at high temperature as illustrated in our work in the case of Fe-Co alloy

  • 3588.
    Xin, Xiao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Johansson, Robert
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Wolff, Max
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Hydrogen in vanadium: Site occupancy and isotope effects2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 13, article id 134107Article in journal (Refereed)
    Abstract [en]

    We discuss the influence of site occupancy on the absorption of the hydrogen isotopes H and D in thin V(001) layers. By growing V(001) under biaxial compressive strain in Fe/V(001) superlattices, the hydrogen (H as well as D) is forced to reside exclusively in octahedral (O-z) sites, even at the lowest concentrations. A weakening of the isotope effects is observed when hydrogen resides in octahedral as compared to tetrahedral sites.

  • 3589.
    Xu, Bo
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Sheibani, Esmaeil
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Liu, Peng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Zhang, Jinbao
    Tian, Haining
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. Uppsala University, Sweden.
    Vlachopoulos, Nick
    Boschloo, Gerrit
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. Dalian University of Technology (DUT)Dalian, China .
    Carbazole-Based Hole-Transport Materials for Efficient Solid-State Dye-Sensitized Solar Cells and Perovskite Solar Cells2014In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 38, p. 6629-6634Article in journal (Refereed)
    Abstract [en]

    (Graph Presented) Two carbazole-based small molecule hole-transport materials (HTMs) are synthesized and investigated in solid-state dye-sensitized solar cells (ssDSCs) and perovskite solar cells (PSCs). The HTM X51-based devices exhibit high power conversion efficiencies (PCEs) of 6.0% and 9.8% in ssDSCs and PSCs, respectively. These results are superior or comparable to those of 5.5% and 10.2%, respectively, obtained for the analogous cells using the state-of-the-art HTM Spiro-OMeTAD.

  • 3590.
    Xu, F.
    et al.
    Universit ̈at Konstanz, Germany.
    Holmqvist, Cecilia
    Norwegian University of Science and Technology, Norway.
    Belzig, W.
    Universit ̈at Konstanz, Germany.
    Over-bias light emission due to higher order quantum noise of a tunnel junction2015In: 2015 International Conference on Noise and Fluctuations (ICNF), IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    Understanding tunneling from an atomically sharp tip to a metallic surface requires to account for interactions on a nanoscopic scale. Inelastic tunneling of electrons generates emission of photons, whose energies intuitively should be limited by the applied bias voltage. However, experiments [Phys. Rev. Lett. 102, 057401 (2009)] indicate that more complex processes involving the interaction of electrons with plasmon polaritons lead to photon emission characterized by over-bias energies. We propose a model of this observation in analogy to the dynamical Coulomb blockade, originally developed for treating the electronic environment in mesoscopic circuits. We explain the experimental finding quantitatively by the correlated tunneling of two electrons interacting with an LRC circuit modeling the local plasmon-polariton mode. To explain the over-bias emission, the non-Gaussian statistics of the tunneling dynamics of the electrons is essential.

  • 3591.
    Xu, F.
    et al.
    Universität Konstanz, Germany.
    Holmqvist, Cecilia
    Universität Konstanz, Germany.
    Belzig, W.
    Universität Konstanz, Germany.
    Overbias Light Emission due to Higher-Order Quantum Noise in a Tunnel Junction2014In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 113, article id 066801Article in journal (Refereed)
    Abstract [en]

    Understanding tunneling from an atomically sharp tip to a metallic surface requires us to account for interactions on a nanoscopic scale. Inelastic tunneling of electrons generates emission of photons, whose energies intuitively should be limited by the applied bias voltage. However, experiments [G. Schull et al., Phys. Rev. Lett. 102, 057401 (2009)] indicate that more complex processes involving the interaction of electrons with plasmon polaritons lead to photon emission characterized by overbias energies. We propose a model of this observation in analogy to the dynamical Coulomb blockade, originally developed for treating the electronic environment in mesoscopic circuits. We explain the experimental finding quantitatively by the correlated tunneling of two electrons interacting with a LRC circuit modeling the local plasmon-polariton mode. To explain the overbias emission, the non-Gaussian statistics of the tunneling dynamics of the electrons is essential.

  • 3592.
    Xu, F.
    et al.
    Univ Konstanz, Germany.
    Holmqvist, Cecilia
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Rastelli, G.
    Univ Konstanz, Germany.
    Belzig, W.
    Univ Konstanz, Germany.
    Dynamical Coulomb blockade theory of plasmon-mediated light emission from a tunnel junction2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 24, article id 245111Article in journal (Refereed)
    Abstract [en]

    Inelastic tunneling of electrons can generate the emission of photons with energies intuitively limited by the applied bias voltage. However, experiments indicate that more complex processes involving the interaction of electrons with plasmon polaritons lead to photon emission with overbias energies. We recently proposed a model of this observation in Phys. Rev. Lett. 113, 066801 (2014), in analogy to the dynamical Coulomb blockade, originally developed for treating the electromagnetic environment in mesoscopic circuits. This model describes the correlated tunneling of two electrons interacting with a local plasmon-polariton mode, represented by a resonant circuit, and shows that the overbias emission is due to the non-Gaussian fluctuations. Here we extend our model to study the overbias emission at finite temperature. We find that the thermal smearing strongly masks the overbias emission. Hence, the detection of the correlated tunneling processes requires temperatures k(B)T much lower than the bias energy eV and the plasmon energy h omega(0), a condition which is fortunately realized experimentally.

  • 3593.
    Xu, Weidong
    et al.
    Soochow University, Peoples R China.
    McLeod, John A.
    Soochow University, Peoples R China.
    Yang, Yingguo
    Chinese Academic Science, Peoples R China.
    Wang, Yimeng
    Soochow University, Peoples R China; Beijing University of Technology, Peoples R China; Beijing University of Technology, Peoples R China.
    Wu, Zhongwei
    Soochow University, Peoples R China.
    Bai, Sai
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Yuan, Zhongcheng
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Song, Tao
    Soochow University, Peoples R China.
    Wang, Yusheng
    Soochow University, Peoples R China; Beijing University of Technology, Peoples R China; Beijing University of Technology, Peoples R China.
    Si, Junjie
    Zhejiang University, Peoples R China.
    Wang, Rongbin
    Soochow University, Peoples R China.
    Gao, Xingyu
    Chinese Academic Science, Peoples R China.
    Zhang, Xinping
    Beijing University of Technology, Peoples R China; Beijing University of Technology, Peoples R China.
    Liu, Lijia
    Soochow University, Peoples R China.
    Sun, Baoquan
    Soochow University, Peoples R China.
    Iodomethane-Mediated Organometal Halide Perovskite with Record Photoluminescence Lifetime2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 35, p. 23181-23189Article in journal (Refereed)
    Abstract [en]

    Organometallic lead halide perovskites are excellent light harvesters for high-efficiency photovoltaic devices. However, as the key component in these devices, a perovskite thin film with good morphology and minimal trap states is still difficult to obtain. Herein we show that by incorporating a low boiling point alkyl halide such as iodomethane (CH3I) into the precursor solution, a perovskite (CH3NH3PbI3-xClx) film with improved grain size and orientation can be easily achieved. More importantly, these films exhibit a significantly reduced amount of trap states. Record photoluminescence lifetimes of more than 4 mu s are achieved; these lifetimes are significantly longer than that of pristine CH3NH3PbI3-xClx films. Planar heterojunction solar cells incorporating these CH3I-mediated perovskites have demonstrated a dramatically increased power conversion efficiency compared to the ones using pristine CH3NH3PbI3-xClx. Photoluminescence, transient absorption, and microwave detected photoconductivity measurements all provide consistent evidence that CH3I addition increases the number of excitons generated and their diffusion length, both of which assist efficient carrier transport in the photovoltaic device. The simple incorporation of alkyl halide to enhance perovskite surface passivation introduces an important direction for future progress on high efficiency perovskite optoelectronic devices.

  • 3594. Xu, Xing-Dong
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Chen, Hongzhong
    Qu, Qiuyu
    Zhao, Lingzhi
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhao, Yanli
    Host-Guest Interaction-Mediated Construction of Hydrogels and Nanovesicles for Drug Delivery2015In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 11, no 44, p. 5901-5906Article in journal (Refereed)
  • 3595.
    Yablonskikh M. V., M. V.
    et al.
    Uppsala University.
    Yarmoshenko, Yu. M.
    Russian Academy of Sciences-Ural Division, Yekaterinburg .
    Solovyev, I. V.
    Russian Academy of Sciences-Ural Division, Yekaterinburg .
    Kurmaev, E. Z.
    Russian Academy of Sciences-Ural Division, Yekaterinburg .
    Duda, L.-C.
    Uppsala University.
    Schmitt, Thorsten
    Uppsala University.
    Magnuson, Martin
    Uppsala University.
    Nordgren, Joseph
    Uppsala University.
    Moewes, Alexander
    University of Saskatchewan, Saskatoon, Canada .
    Resonant L_alpha,betha X-ray emission and L2,3 X-ray absorption spectra of 3d metals in Co2MnZ (Z=Al,Ga,Sn,Sb) Heusler alloys as an element-selectve probe of spin character of valence band2005In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 144-147, p. 765-769Article in journal (Refereed)
    Abstract [en]

    The 3d metal resonant X-ray emission spectra (RXES) and L3,2 X-ray absorption spectra (XAS) of the Co2MnZ (Z=Al, Ga, Sn, Sb) alloys were measured using linearly polarized soft X-rays. The Mn and Co spectra are compared with results of spin-polarized calculations of Mn 3d and Co 3d partial densities of states performed for each alloy. It is found that a satellite observed at the high-energy side of Mn spectra is due to the localized Mn 3d states located above the Fermi energy. It is shown that the presence of the same satellite structure indicates a higher degree of spin-polarization of Mn 3d states than Co 3d states.

    Both the intensity of the satellite structure in Mn spectra and the /, peak ratio are increased and follow the atomic number of Z element. The effect is especially strong when excitating slightly above the L3 and L2 threshold energies as well as at resonance. We observe a correlation between these spectral parameters and the magnitude of local magnetic moment. The changes occurring in the Mn RXES are in good agreement with a predicted decrease in p–d hybridization (between the atoms of Z element and Mn atoms). The calculated local density of Mn 3d states at the Fermi energy follows the same trend as the hybridization. This suggests that RXES of 3d metals can be used to monitor the degree of spin-polarization of the valence band states and the local density of states at the Fermi level. Note that neither the Mn L2,3 absorption nor the Co L2,3 and Co emission spectra of the alloys are affected by the different composition (different Z elements).

  • 3596.
    Yablonskikh M. V., M. V.
    et al.
    Uppsala University.
    Yarmoshenko, Yu. M.
    Russian Academy of Sciences-Ural Division, Yekaterinburg .
    Solovyev, I. V.
    Russian Academy of Sciences-Ural Division, Yekaterinburg .
    Kurmaev, E. Z.
    Russian Academy of Sciences-Ural Division, Yekaterinburg .
    Duda, L.-C.
    Uppsala University.
    Schmitt, Thorsten
    Uppsala University.
    Magnuson, Martin
    Uppsala University.
    Nordgren, Joseph
    Uppsala University.
    Moewes, Alexander
    University of Saskatchewan, Saskatoon, Canada .
    Resonant L_alpha,betha X-ray emission and L2,3 X-ray absorption spectra of 3d metals in Co2MnZ (Z=Al,Ga,Sn,Sb) Heusler alloys as an element-selectve probe of spin character of valence band2005In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 144-147, p. 765-769Article in journal (Refereed)
    Abstract [en]

    The 3d metal resonant X-ray emission spectra (RXES) and L3,2 X-ray absorption spectra (XAS) of the Co2MnZ (Z=Al, Ga, Sn, Sb) alloys were measured using linearly polarized soft X-rays. The Mn and Co spectra are compared with results of spin-polarized calculations of Mn 3d and Co 3d partial densities of states performed for each alloy. It is found that a satellite observed at the high-energy side of Mn spectra is due to the localized Mn 3d states located above the Fermi energy. It is shown that the presence of the same satellite structure indicates a higher degree of spin-polarization of Mn 3d states than Co 3d states.

    Both the intensity of the satellite structure in Mn spectra and the /, peak ratio are increased and follow the atomic number of Z element. The effect is especially strong when excitating slightly above the L3 and L2 threshold energies as well as at resonance. We observe a correlation between these spectral parameters and the magnitude of local magnetic moment. The changes occurring in the Mn RXES are in good agreement with a predicted decrease in p–d hybridization (between the atoms of Z element and Mn atoms). The calculated local density of Mn 3d states at the Fermi energy follows the same trend as the hybridization. This suggests that RXES of 3d metals can be used to monitor the degree of spin-polarization of the valence band states and the local density of states at the Fermi level. Note that neither the Mn L2,3 absorption nor the Co L2,3 and Co emission spectra of the alloys are affected by the different composition (different Z elements).

  • 3597.
    Yadav, Manoj K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    First-principles study of thermoelectric properties of CuI2014In: MATERIALS RESEARCH EXPRESS, ISSN 2053-1591, Vol. 1, no 1, article id 015708Article in journal (Refereed)
    Abstract [en]

    Theoretical investigations of the thermoelectric properties of CuI have been carried out employing first-principles calculations followed by the calculations of transport coefficients based on Boltzmann transport theory. Among the three different phases of CuI, viz. zinc-blende, wurtzite and rock salt, the thermoelectric power factor is found to be the maximum for the rock salt phase. We have analysed the variations of Seebeck coefficients and thermoelectric power factors on the basis of calculated electronic structures near the valence band maxima of these phases.

  • 3598.
    Yadav, Manoj Kumar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Nepal Acad Sci & Technol, Unit Phys Sci, Khumaltar, Lalitpur, Nepal..
    Vovusha, Hakkim
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. King Abdullah Univ Sci & Technol, Phys Sci & Engn PSE Div, Thuwal, Saudi Arabia..
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Adsorption and dissociation of dinitrogen on transition metal (Ta, W and Re) doped MgO surface2016In: Computational and Theoretical Chemistry, ISSN 2210-271X, E-ISSN 2210-2728, Vol. 1090, p. 165-170Article in journal (Refereed)
    Abstract [en]

    The adsorption and dissociation of dinitrogen on transition metal (Ta, W and Re) doped MgO(100) surface has been studied employing density functional theory. It is found that all these transition metals (TM) on MgO(100) surface are capable of adsorbing dinitrogen (N-2), however there is no dissociative adsorption of N-2 on single transition metal dopant. When two TM atoms are doped on MgO(100) surface, dissociative adsorption of dinitrogen occurs in all the three cases. Whether the dissociation is spontaneous or is it associated with activation barrier depends on the orientation of N-2 molecule approaching the dopant site.

  • 3599.
    Yakhshi Tafti, Mohsen
    KTH, School of Information and Communication Technology (ICT).
    Microwave Assisted Organometallic Synthesis,Structural Characterization and ThermoelectricEvaluation of Cu2SeManuscript (preprint) (Other academic)
    Abstract [en]

    In this article we report a highly efficient synthesis route for fabrication of nanostructured bulk thermoelectric (TE) copper selenide (Cu2Se) nanopowders. Using Microwave (MW) assisted synthesis and through bottom-up synthesis approach, copper selenide nanopowders were fabricated. The nanopowders then underwent an optimized SPS compaction generated with the aim of high compaction density as well as the overall thermoelectric figure of merit ZT. The structural and thermoelectric transport property evaluation was performed and a ZT of 2.1 at 900 K was achieved. The high ZT value was attributed to the dramatically reduced thermal conductivity which reached values of as low as 0.38 W/mK. Detailed process, structural evaluation and TE transport property measurements of the prepared samples are presented.IntroductionThermoelectric

  • 3600.
    Yakhshi Tafti, Mohsen
    KTH, School of Information and Communication Technology (ICT).
    Nanostructured Bulk Thermoelectrics: Scalable Fabrication Routes, Processing and Evaluation2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Current fossil fuel based energy sources have a huge shortcoming when one discusses their efficiency. The conversion efficiency of fossil fuel-based technologies is less than 40% in best cases. Therefore, until the renewable energy section is mature enough to handle all the energy demand one has to research and develop the technologies available to harvest the energy from the waste heat generated in fossil fuel-based supply sources. One of these emerging technologies is the use of thermoelectric (TE) devices to achieve this goal, which are solid-state devices capable of directly interconverting between heat and electrical energy. In the past decade there has been a significant scientific and financial investment within the field to enhance their properties and result in time/energy efficient fabrication processes of TE materials and devices for a more sustainable environment.

    In this thesis with use of chemical synthesis routes for nanostructured bulk thermoelectric materials iron antimonide (FeSb2), skutterudites (based on general formula of RzMxCo1-xSb3-yNy) and copper selenide (Cu2Se) are developed. These materials are promising candidates for use in thermoelectric generators (TEG) or for sensing applications. Using chemical synthesis routes such as chemical co-precipitation, salt melting in marginal solvents and thermolysis, fabrication of these TE materials with good performance can be performed with high degree of reproducibility, in a much shorter time, and easily scalable manner for industrial processes. The TE figure of merit ZT of these materials is comparable to, or better than their conventional method counterparts to ensure the applicability of these processes in industrial scale.

    Finally, through thorough investigation, optimized consolidation parameters were generated for compaction of each family of materials using Spark Plasma Sintering technique (SPS). As each family of TE nanomaterial investigated in this thesis had little to no prior consolidation literature available, specific parameters had to be studied and generated. The aim of studies on compaction parameters were to focus on preservation of the nanostructured features of the powder while reaching a high compaction density to have positive effects on the materials TE figure of merit.

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