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  • 1.
    AlMotasem, Ahmed Tamer
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Gåård, Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Holleboom, Thijs
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Adhesion between ferrite iron-€“iron/cementite countersurfaces: A molecular dynamics study2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 103, p. 113-120Article in journal (Refereed)
    Abstract [en]

    The adhesive properties of Fe(110)/Fe(110) and Fe3C(001)/Fe(110) countersurfaces have been investigated by using classical molecular dynamics simulations. The simulation results show that Fe3C/Fe exhibits a relatively lower adhesion compared to the Fe/Fe. Additionally, the temperature dependence of the adhesive properties between 300–700 K has been examined. The results demonstrate that, with increasing the temperature, the values of the adhesion force and the work of adhesion continuously decrease in the case of Fe3C/Fe; they initially slightly increase up to 500 K then decrease in the case of Fe/Fe. Furthermore, the effect of lattice coherency between Fe/Fe has been examined and found to slightly reduce the adhesion. These results explain how carbides improve galling resistance of tool steel observed during dry sliding. 

  • 2.
    Almén, Anton
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Importance of atomic force microscopy settings for measuring the diameter of carbon nanotubes2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Carbon nanotubes (CNTs) have gathered a lot of interest because of their extraordinary mechanical, electrical and thermal properties and have potential applications in a wide variety of areas such as material-reinforcement and nano-electronics. The properties of nanotubes are dependent on their diameter and methods for determining this using atomic force microscopy (AFM) in tapping mode assume that the measured height of the tubes represent the real diameter. Based on early, faulty calculations, the forces in tapping mode were assumed to be much lower than in contact mode, however it was later shown that forces in tapping mode can at point of impact rival the forces present in contact mode. This means that there is a potential risk of tube deformation during tapping mode measurements, resulting in incorrectly determined diameters. This work studies CNTs deposited on a silicon-substrate to analyze the effect of three common AFM settings (tapping frequency, free oscillation amplitude and setpoint) to determine their effect on measured CNT diameters and recommendations for choosing settings are given.

  • 3.
    Ericsson, Leif K E
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Magnusson, Kjell
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Zhang, Hanmin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    AFM and STM Study of ZnO NanoplatesManuscript (preprint) (Other academic)
    Abstract [en]

    The surface morphology and electronic structure of hexagonal ZnO nanoplates have been studied by Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM). It was found that these nanoplates are terminated by their polar (0001) surfaces. The AFM investigation was performed in the ambient conditions with the nanocrystals “as grown”. Surprisingly, the AFM images of the top surfaces revealed an interesting triangular reconstruction, which was earlier observed only after cycles of sputtering and annealing of the ZnO(0001) surface in Ultra High Vacuum (UHV) systems. The surface atomic and electronic structures of these nanoplates have been further studied by STM and Scanning Tunneling Spectroscopy (STS) in UHV. The STM images also showed a triangular structure with single atomic steps. In addition, a 2x2 surface reconstruction has been observed with high resolution STM. This reconstruction agrees well with the recently proposed model that involves the removal of 1/4 of the topmost Zn atoms on the ZnO(0001) surface.

  • 4.
    Ericsson, Leif KE
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Growth and Characterization of ZnO Nanocrystals2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The understanding of surfaces of materials is of crucial importance to all of us. Considering nanocrystals (NCs), that have a large surface to bulk ratio, the surfaces become even more important. Therefore, it is important to understand the fundamental surface properties in order to use NCs efficiently in applications. In the work reported in this thesis ZnO NCs were studied.

    At MAX-lab in Lund, synchrotron radiation based Spectroscopic Photoemission and Low Energy Electron Microscopy (SPELEEM) and X-ray Photoelectron Spectroscopy (XPS) were used. At Karlstad University characterization was done using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Scanning Tunnelling Microscopy (STM), Auger Electron Spectroscopy (AES), and XPS.

    The fundamental properties of ZnO surfaces were studied using distributions of ZnO NCs on SiO2/Si surfaces. The conditions for distribution of ZnO NCs were determined to be beneficial when using ethanol as the solvent for ultrasonically treated dispersions. Annealing at 650 °C in UHV cleaned the surfaces of the ZnO NCs enough for sharp LEEM imaging and chemical characterization while no sign of de-composition was found. A flat energy band structure for the ZnO/SiO2/Si system was proposed after 650 °C. Increasing the annealing temperature to 700 °C causes a de-composition of the ZnO that induce a downward band bending on the surfaces of ZnO NCs.

    Flat ZnO NCs with predominantly polar surfaces were grown using a rapid microwave assisted process. Tuning the chemistry in the growth solution the growth was restricted to only plate-shaped crystals, i.e. a very uniform growth. The surfaces of the NCs were characterized using AFM, revealing a triangular reconstruction of the ZnO(0001) surface not seen without surface treatment at ambient conditions before. Following cycles of sputtering and annealing in UHV, we observe by STM a surface reconstruction interpreted as 2x2 with 1/4 missing Zn atoms.

  • 5.
    Ericsson, Leif
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Magnusson, Kjell
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Microwave assisted rapid growth of flat ZnO(0001) platelets2013Manuscript (preprint) (Other academic)
  • 6.
    Ericsson, Leif
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Magnusson, Kjell
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Preparation of ZnO nanocrystals for individual surface analysis2013Manuscript (preprint) (Other academic)
  • 7.
    Ericsson, Leif
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Zhang, Hanmin
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Magnusson, Kjell
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Photoemission study of ZnO nanocrystals: Thermal annealing in UHV and induced band bending2013In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 612, p. 10-15Article in journal (Refereed)
    Abstract [en]

    ZnO nanocrystals distributed by spin-coating on SiO2/Si surfaces were annealed in UHV and studied in situ by synchrotron radiation based X-ray Photoelectron Spectroscopy. Changes in chemical composition and electronic structure of ZnO nanocrystal surfaces were found with increasing annealing temperatures. Annealing at 650 °C reduces the surface contaminant levels without any observed de-composition of ZnO. After annealing at 700 °C an initial de-composition of ZnO together with further reduction of contaminants was observed. As a result, 650 °C is found to be the optimal annealing temperature for thermal cleaning of ZnO nanocrystals. Chemical changes and induced point defect formation cause changes in the band structure of the ZnO/SiO2/Si system. An upward band bending of 0.7 eV on the surfaces of the ZnO nanocrystals was found after annealing at 300 °C. The bands on the surfaces of ZnO nanocrystals gradually bend downwards with increasing annealing temperatures. A downward band bending of 1.4 eV is the result after annealing at 750 °C for 1 h. This large downward band bending is explained as due to the change in balance of oxygen vacancies and zinc vacancies on the surfaces of ZnO nanocrystals.

  • 8.
    Juteräng, David
    Karlstad University, Faculty of Technology and Science.
    STM Study of PTCDA on Pb/Si(111) 1×12012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The interaction and orbital energy levels of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) molecules on a Pb/Si(111) 1x1 substrate have been investigated. A Si(111) sample was annealed to form the 7x7 configuration. 1.5 monolayer of Pb was evaporated onto the surface, which was then annealed. 0.5 monolayer of PTCDA was applied to the substrate through molecular beam epitaxy (MBE). The surface configuration of the substrate was monitored step by step by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Scanning tunneling spectroscopy (STS) was used to pinpoint the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecules.

    It was found that the PTCDA molecules formed a herringbone pattern on the substrate. The PTCDA electronic energy levels corresponding to the HOMO and the LUMO were obtained. From these values the energy gap between these orbitals, the molecular bandgap of PTCDA on Pb/Si(111) 1x1, was determined.

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