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  • 1.
    Besharat, Zahra
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Ghadami Yazdi, Milad
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Wakeham, Deborah
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Johnson, Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Rutland, Mark W.
    SP Technical Research Institute of Sweden, Sweden.
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Grönbeck, Henrik
    Se-C Cleavage of Hexane Selenol at Steps on Au(111)2018In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, no 8, p. 2630-2636Article in journal (Refereed)
    Abstract [en]

    Selenols are considered as an alternative to thiols in self-assembled monolayers, but the Se-C bond is one limiting factor for their usefulness. In this study, we address the stability of the Se-C bond by a combined experimental and theoretical investigation of gas phase-deposited hexane selenol (CH3(CH2)(5)SeH) on Au(111) using photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory (DFT). Experimentally, we find that initial adsorption leaves atomic Se on the surface without any carbon left on the surface, whereas further adsorption generates a saturated selenolate layer. The Se 3d component from atomic Se appears at 0.85 eV lower binding energy than the selenolate-related component. DFT calculations show that the most stable structure of selenols on Au(111) is in the form of RSe-Au-SeR complexes adsorbed on the unreconstructed Au(111) surface. This is similar to thiols on Au(111). Calculated Se 3d core-level shifts between elemental Se and selenolate in this structure nicely reproduce the experimentally recorded shifts. Dissociation of RSeH and subsequent formation of RH are found to proceed with high barriers on defect-free Au(111) terraces, with the highest barrier for scissoring R-Se. However, at steps, these barriers are considerably lower, allowing for Se-C bond breaking and hexane desorption, leaving elemental Se at the surface. Hexane is the selenol to selenolate formed by replacing the Se-C bond with a H-C bond by using the hydrogen liberated from transformation.

  • 2.
    Ghadami Yazdi, Milad
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    H. Moud, Pouya
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology. KTH.
    Marks, Kess
    Piskorz, Witold
    Öström, Henrik
    Hansson, Tony
    Kotarba, Andrzej
    Engvall, Klas
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Naphthalene on Ni(111): experimental and theoretical insights into adsorption, dehydrogenation and carbon passivationManuscript (preprint) (Other academic)
    Abstract [en]

    An attractive solution to mitigate tars and also to decompose lighter hydrocarbons in biomass gasification is secondary catalytic reforming, converting hydrocarbons to useful permanent gases. Albeit in use for long time in fossil feedstock catalytic steam reforming, the understanding of the catalytic processes is still limited. Naphthalene is typically present in the biomass gasification gas and to further understand the elementary steps of naphthalene transformation, we investigated the temperature dependent naphthalene adsorption, dehydrogenation and passivation on Ni(111). TPD (temperature programmed desorption) and STM (scanning tunneling microscopy) in ultra-high vacuum environment from 110 K up to 780 K, combined with DFT (density functional theory) were used in the study. Room temperature adsorption results in a flat naphthalene monolayer. DFT favors the di-bridge[7] geometry but the potential energy surface is rather smooth. DFT also reveals a pronounced dearomatization and charge transfer from the adsorbed molecule into the nickel surface. Dehydrogenation occurs in two steps, with two desorption peaks at approximately 450 K and 600 K. The first step is due to partial dehydrogenation generating active hydrocarbon species that at higher temperatures migrates over the surface forming graphene. The graphene formation is accompanied by desorption of hydrogen in the high temperature TPD peak. The formation of graphene effectively passivates the surface both for hydrogen adsorption and naphthalene dissociation. In conclusion, the obtained results on the model naphthalene and Ni(111) system, provides insight into elementary steps of naphthalene adsorption, dehydrogenation and carbon passivation, which may serve as a good starting point for rational design, development and optimization of the Ni catalyst surface, as well as process conditions, for the aromatic hydrocarbon reforming process.

  • 3.
    Ghadami Yazdi, Milad
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Lousada, Claudio M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Evertsson, J.
    Rullik, L.
    Soldemo, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Bertram, F.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Weissenrieder, J.
    Lundgren, E.
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Structure dependent effect of silicon on the oxidation of Al(111) and Al(100)2019In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 684, p. 1-11Article in journal (Refereed)
    Abstract [en]

    The effect of sub-monolayer silicon on the oxidation of Al(111) and Al(100) surfaces was investigated using X-ray Photoelectron Spectroscopy (XPS) and density functional theory (DFT) calculations. On both surfaces the adatom site is preferred over substituting Si into the Al-lattice; on Al(100) the four fold hollow site is vastly favored whereas on Al(111) bridge and hollow sites are almost equal in energy. Upon O 2 exposure, Si is not oxidized but buried at the metal/oxide interface under the growing aluminum oxide. On Al(111), Si has a catalytic effect on both the initial oxidation by aiding in creating a higher local oxygen coverage in the early stages of oxidation and, in particular, at higher oxide coverages by facilitating lifting Al from the metal into the oxide. The final oxide, as measured from the Al2p intensity, is 25–30% thicker with Si than without. This observation is valid for both 0.1 monolayer (ML) and 0.3 ML Si coverage. On Al(100), on the other hand, at 0.16 ML Si coverage, the initial oxidation is faster than for the bare surface due to Si island edges being active in the oxide growth. At 0.5 ML Si coverage the oxidation is slower, as the islands coalesce and he amount of edges reduces. Upon oxide formation the effect of Si vanishes as it is overgrown by Al 2 O 3 , and the oxide thickness is only 6% higher than on bare Al(100), for both Si coverages studied. Our findings indicate that, in addition to a vanishing oxygen adsorption energy and Mott potential, a detailed picture of atom exchange and transport at the metal/oxide interface has to be taken into account to explain the limiting oxide thickness.

  • 4.
    Marks, Kess
    et al.
    Stockholm Univ, Fysikum, Dept Phys, S-10691 Stockholm, Sweden..
    Ghadami Yazdi, Milad
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Piskorz, Witold
    Jagiellonian Univ Krakow, Fac Chem, Gronostajowa 2, PL-31387 Krakow, Poland..
    Simonov, Konstantin
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Stefanuik, Robert
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Sostina, Daria
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland..
    Guarnaccio, Ambra
    CNR, ISM, Tito Scalo Unit, I-85050 Potenza, Italy..
    Ovsyannikov, Ruslan
    Helmholtz Zentrum Berlin Mat & Energie, Inst Methods & Instrumentat Synchrotron Radiat Re, ISRR, D-12489 Berlin, Germany..
    Giangrisostomi, Erika
    Helmholtz Zentrum Berlin Mat & Energie, Inst Methods & Instrumentat Synchrotron Radiat Re, ISRR, D-12489 Berlin, Germany..
    Sassa, Yasmine
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden..
    Bachellier, Nicolas
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland..
    Muntwiler, Matthias
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland..
    Johansson, Fredrik O. L.
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Lindblad, Andreas
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Hansson, Tony
    Stockholm Univ, Fysikum, Dept Phys, S-10691 Stockholm, Sweden..
    Kotarba, Andrzej
    Jagiellonian Univ Krakow, Fac Chem, Gronostajowa 2, PL-31387 Krakow, Poland..
    Engvall, Klas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Process Technology.
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Harding, Dan J.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Ostrom, Henrik
    Stockholm Univ, Fysikum, Dept Phys, S-10691 Stockholm, Sweden..
    Investigation of the surface species during temperature dependent dehydrogenation of naphthalene on Ni(111)2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, no 24, article id 244704Article in journal (Refereed)
    Abstract [en]

    The temperature dependent dehydrogenation of naphthalene on Ni(111) has been investigated using vibrational sum-frequency generation spectroscopy, X-ray photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory with the aim of discerning the reaction mechanism and the intermediates on the surface. At 110 K, multiple layers of naphthalene adsorb on Ni(111); the first layer is a flat lying chemisorbed monolayer, whereas the next layer(s) consist of physisorbed naphthalene. The aromaticity of the carbon rings in the first layer is reduced due to bonding to the surface Ni-atoms. Heating at 200 K causes desorption of the multilayers. At 360 K, the chemisorbed naphthalene monolayer starts dehydrogenating and the geometry of the molecules changes as the dehydrogenated carbon atoms coordinate to the nickel surface; thus, the molecule tilts with respect to the surface, recovering some of its original aromaticity. This effect peaks at 400 K and coincides with hydrogen desorption. Increasing the temperature leads to further dehydrogenation and production of H-2 gas, as well as the formation of carbidic and graphitic surface carbon. 

  • 5.
    Suvanam, Sethu Saveda
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Usman, M.
    KTH, School of Information and Communication Technology (ICT). Experimental Physics Laboratories, National Centre for Physics, Quaid-i-Azam University, Islamabad, Pakistan.
    Martin, D.
    Yazdi, Milad G.
    KTH, School of Information and Communication Technology (ICT).
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT).
    Tempez, A.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT).
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT).
    Improved interface and electrical properties of atomic layer deposited Al2O3/4H-SiC2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 433, p. 108-115Article in journal (Refereed)
    Abstract [en]

    In this paper we demonstrate a process optimization of atomic layer deposited Al2O3 on 4H-SiC resulting in an improved interface and electrical properties. For this purpose the samples have been treated with two pre deposition surface cleaning processes, namely CP1 and CP2. The former is a typical surface cleaning procedure used in SiC processing while the latter have an additional weak RCA1 cleaning step. In addition to the cleaning and deposition, the effects of post dielectric annealing (PDA) at various temperatures in N2O ambient have been investigated. Analyses by scanning electron microscopy show the presence of structural defects on the Al2O3 surface after annealing at 500 and 800 °C. These defects disappear after annealing at 1100 °C, possibly due to densification of the Al2O3 film. Interface analyses have been performed using X-ray photoelectron spectroscopy (XPS) and time-of-flight medium energy ion scattering (ToF MEIS). Both these measurements show the formation of an interfacial SiOx (0 < x < 2) layer for both the CP1 and CP2, displaying an increased thickness for higher temperatures. Furthermore, the quality of the sub-oxide interfacial layer was found to depend on the pre deposition cleaning. In conclusion, an improved interface with better electrical properties is shown for the CP2 sample annealed at 1100 °C, resulting in lower oxide charges, strongly reduced flatband voltage and leakage current, as well as higher breakdown voltage.

  • 6.
    Tissot, Heloise
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Wang, Chunlei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Stenlid, Joakim Halldin
    Stockholm Univ, Albanova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden..
    Panahi, Mohammad
    Koc Univ, TUPRAS Energy Ctr KUTEM, TR-34450 Istanbul, Turkey.;Koc Univ, Chem Dept, TR-34450 Istanbul, Turkey..
    Kaya, Sarp
    Koc Univ, TUPRAS Energy Ctr KUTEM, TR-34450 Istanbul, Turkey.;Koc Univ, Chem Dept, TR-34450 Istanbul, Turkey..
    Soldemo, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Ghadami Yazdi, Milad
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Brinck, Tore
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Weissenrieder, Jonas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Interaction of Atomic Hydrogen with the Cu2O(100) and (111) Surfaces2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 36, p. 22172-22180Article in journal (Refereed)
    Abstract [en]

    Reduction of Cu2O by hydrogen is a common preparation step for heterogeneous catalysts; however, a detailed understanding of the atomic reaction pathways is still lacking. Here, we investigate the interaction of atomic hydrogen with the Cu2O(100):(3,0;1,1) and Cu2O(111):(root 3 x root 3)R30 degrees surfaces using scanning tunneling microscopy (STM), low-energy electron diffraction, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). The experimental results are compared to density functional theory simulations. At 300 K, we identify the most favorable adsorption site on the Cu2O(100) surface: hydrogen atoms bind to an oxygen site located at the base of the atomic rows intrinsic to the (3,0;1,1) surface. The resulting hydroxyl group subsequently migrates to a nearby Cu trimer site. TPD analysis identifies H-2 as the principal desorption product. These observations imply that H-2 is formed through a disproportionation reaction of surface hydroxyl groups. The interaction of H with the (111) surface is more complex, including coordination to both Cu+ and O-CUS sites. STM and XPS analyses reveal the formation of metallic copper clusters on the Cu2O surfaces after cycles of hydrogen exposure and annealing. The interaction of the Cu clusters with the substrate is notably different for the two surface terminations studied: after annealing, the Cu clusters coalesce on the (100) termination, and the (3,0;1,1) reconstruction is partially recovered. Clusters formed on the (111) surface are less prone to coalescence, and the (root 3 x root 3)R30 degrees reconstruction was not recovered by heat treatment, indicating a weaker Cu cluster to support interaction on the (100) surface.

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