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  • 1. An, Wei
    et al.
    Baber, Ashleigh E.
    Xu, Fang
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Stacchiola, Dario
    Liu, Ping
    Mechanistic Study of CO Titration on CuxO/Cu(111) (x <= 2) Surfaces2014In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 6, no 8, p. 2364-2372Article in journal (Refereed)
    Abstract [en]

    The reducibility of metal oxides is of great importance to their catalytic behavior. Herein, we combined ambient-pressure scanning tunneling microscopy (AP-STM), X-ray photoemission spectroscopy (AP-XPS), and DFT calculations to study the CO titration of CuxO thin films supported on Cu(111) (CuxO/Cu(111)) aiming to gain a better understanding of the roles that the Cu(111) support and surface defects play in tuning catalytic performances. Different conformations have been observed during the reduction, namely, the 44 structure and a recently identified (5-7-7-5) Stone-Wales defects (5-7 structure). The DFT calculations revealed that the Cu(111) support is important to the reducibility of supported CuxO thin films. Compared with the case for the Cu2O(111) bulk surface, at the initial stage CO titration is less favorable on both the 44 and 5-7 structures. The strong CuxO <-> Cu interaction accompanied with the charge transfer from Cu to CuxO is able to stabilize the oxide film and hinder the removal of O. However, with the formation of more oxygen vacancies, the binding between CuxO and Cu(111) is weakened and the oxide film is destabilized, and Cu2O(111) is likely to become the most stable system under the reaction conditions. In addition, the surface defects also play an essential role. With the proceeding of the CO titration reaction, the 5-7 structure displays the highest activity among all three systems. Stone-Wales defects on the surface of the 5-7 structure exhibit a large difference from the 44 structure and Cu2O(111) in CO binding energy, stability of lattice oxygen, and, therefore, the reduction activity. The DFT results agree well with the experimental measurements, demonstrating that by adopting the unique conformation, the 5-7 structure is the active phase of CuxO, which is able to facilitate the redox reaction and the Cu2O/Cu(111)<-> Cu transition.

  • 2. Baber, Ashleigh E.
    et al.
    Xu, Fang
    Dvorak, Filip
    Mudiyanselage, Kumudu
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Senanayake, Sanjaya D.
    Sadowski, Jerzy T.
    Rodriguez, José A.
    Matolín, Vladimír
    White, Michael G.
    Stacchiola, Darío J.
    In Situ Imaging of Cu2O under Reducing Conditions: Formation of Metallic Fronts by Mass Transfer2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 45, p. 16781-16784Article in journal (Refereed)
    Abstract [en]

    Active catalytic sites have traditionally been analyzed based on static representations of surface structures and characterization of materials before or after reactions. We show here by a combination of in situ microscopy and spectroscopy techniques that, in the presence of reactants, an oxide catalyst's chemical state and morphology are dynamically modified. The reduction of Cu2O films is studied under ambient pressures (AP) of CO. The use of complementary techniques allows us to identify intermediate surface oxide phases and determine how reaction fronts propagate across the surface by massive mass transfer of Cu atoms released during the reduction of the oxide phase in the presence of CO. High resolution in situ imaging by AP scanning tunneling microscopy (AP-STM) shows that the reduction of the oxide films is initiated at defects both on step edges and the center of oxide terraces.

  • 3. Baber, Ashleigh E.
    et al.
    Yang, Xiaofang
    Kim, Hyun You
    Mudiyanselage, Kumudu
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Senanayake, Sanjaya D.
    Al-Mahboob, Abdullah
    Sadowski, Jerzy T.
    Evans, Jaime
    Rodriguez, Jose A.
    Liu, Ping
    Hoffmann, Friedrich M.
    Chen, Jingguang G.
    Stacchiola, Dario J.
    Stabilization of Catalytically Active Cu plus Surface Sites on TitaniumCopper Mixed-Oxide Films**2014In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 53, no 21, p. 5336-5340Article in journal (Refereed)
    Abstract [en]

    The oxidation of CO is the archetypal heterogeneous catalytic reaction and plays a central role in the advancement of fundamental studies, the control of automobile emissions, and industrial oxidation reactions. Copper-based catalysts were the first catalysts that were reported to enable the oxidation of CO at room temperature, but a lack of stability at the elevated reaction temperatures that are used in automobile catalytic converters, in particular the loss of the most reactive Cu+ cations, leads to their deactivation. Using a combined experimental and theoretical approach, it is shown how the incorporation of titanium cations in a Cu2O film leads to the formation of a stable mixed-metal oxide with a Cu+ terminated surface that is highly active for CO oxidation.

  • 4. Baraldi, Alessandro
    et al.
    Vesselli, Erik
    Bianchettin, Laura
    Comelli, Giovanni
    Lizzit, Silvano
    Petaccia, Luca
    de Gironcoli, Stefano
    Locatelli, Andrea
    Mentes, T. Onur
    Aballe, Lucia
    Weissenrieder, Jonas
    Lund University.
    Andersen, Jesper N.
    The (1x1)-> hexagonal structural transition on Pt(100) studied by high-energy resolution core level photoemission2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, no 16Article in journal (Refereed)
    Abstract [en]

    The (1 x 1)-> quasihexagonal (HEX) phase transition on a clean Pt(100) surface was investigated by monitoring the time evolution of the Pt4f(7/2) core level photoemission spectra. The spectral component originating from the atoms forming the (1 x .1) metastable unreconstructed surface was found at -570 +/- 20 meV with respect to the bulk peak. Ab initio calculations based on density functional theory confirmed the experimental assignment. At temperatures above 370 K, the (1 x 1) phase irreversibly reverts to the more stable HEX phase, characterized by a surface core level shifted component at -185 +/- 40 meV. By analyzing the intensity evolution of the core level components, measured at different temperatures in the range of 393-475 K, we determined the activation energy of the phase transformation, E=0.76 +/- 0.04 eV. This value is considerably lower than the one previously determined by means of low energy electron diffraction. Possible reasons for this discrepancy are discussed.

  • 5.
    Beaussant Törne, Karin Beaussant
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. Abbott, St Paul, MN USA.
    Khan, Fareed Ashraf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ornberg, Andreas
    Weissenrieder, Jonas
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zn-Mg and Zn-Ag degradation mechanism under biologically relevant conditions2018In: Surface Innovations, ISSN 2050-6252, E-ISSN 2050-6260, Vol. 6, no 1-2, p. 81-92Article in journal (Refereed)
    Abstract [en]

    Zinc (Zn) alloys form a promising new class of biodegradable metals that combine suitable mechanical properties with the favorable degradation properties of pure zinc. However, the current understanding of the influence of alloying elements on the corrosion of zinc alloys, in biologically relevant media, is limited. The authors studied the degradation of three alloys, zinc-4 wt% silver (Ag), zinc-0.5 wt% magnesium (Mg) and zinc-3 wt% magnesium by in situ electrochemical impedance spectroscopy (EIS). After exposure for 1 h or 30 d, the samples were characterized by infrared spectroscopy and scanning electron microscopy. The presence of secondary phases in the alloy microstructure induced selective corrosion and increased the degradation rate. EIS analysis revealed an increase in surface inhomogeneity already at short (hours) immersion times. The microgalvanic corrosion of the zinc-silver alloy resulted in enrichment of the AgZn3 phase at the sample surface. The enrichment of silver and potential release of AgZn3 particles may result in complications during the tissue regeneration. The zinc-magnesium alloy surface was depleted of the magnesium-rich phase after 8-12 d. The selective dissolution caused local precipitation of corrosion products and a thicker corrosion layer with larger pore size consistent with increased corrosion rate.

  • 6.
    Beaussant Törne, Karin
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Khan, Fareed Ashraf
    Örnberg, A.
    Weissenrieder, Jonas
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zn-Mg and Zn-Ag degradation mechanism under biologically relevant conditionsManuscript (preprint) (Other academic)
    Abstract [en]

    Zinc alloys form a promising new class of biodegradable metals that combine suitable mechanical properties with the favorable degradation properties of pure zinc. However, the current understanding of the influence of alloying elements on the corrosion of zinc alloys, in biologically relevant media, is limited. We studied the degradation of three alloys, Zn 4 wt% Ag, Zn 0.5 wt% Mg and Zn 3 wt% Mg by in situ electrochemical impedance spectroscopy (EIS). After exposure for 1h or 30 days the samples were characterized by infrared spectroscopy and scanning electron microscopy (SEM). The presence of secondary phases in the alloy microstructure induced selective corrosion and increased degradation rate. An increase in surface inhomogeneity was evident by EIS analysis both at short (hours) as well as long immersion times (days). The microgalvanic corrosion of the Zn-Ag alloy resulted in enrichment of the AgZn3 phase at the sample surface. The enrichment of Ag and potential release of AgZn3 particles may result in complications during the tissue regeneration. The Zn-Mg alloy surface was depleted of the Mg-rich phase after 8-12 days. The selective dissolution caused local precipitation of2corrosion products and a thicker corrosion layer with larger pore size consistent with increased corrosion rate.

  • 7.
    Beaussant Törne, Karin
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Örnberg, A.
    Weissenrieder, Jonas
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Characterization of the Protective Layer Formed on Zinc in Whole BloodManuscript (preprint) (Other academic)
    Abstract [en]

    The advantageous degradation properties of zinc in a biological environment are related to the presence of a protective corrosion layer composed of both organic and inorganic components. However, the mechanisms governing its formation and how the organic species influence its properties have not been established. Here we study the protective layer formation during anodic polarization in whole blood by in situ electrochemical impedance spectroscopy (EIS) as well as infrared spectroscopy and scanning electron microscopy. Simulated body fluid (m-SBF) was used as a reference media to discern the influence of the organic species present in whole blood. Protective zinc phosphate layers form on the Zn surface in both solutions, but of different nature and through diverse mechanisms. In m-SBF the passivating thin film formation occur already at open circuit potential, reducing the corrosion current compared to exposure in whole blood by a factor of 103. The high corrosion current in whole blood can be explained by a process including rapid protein adsorption preventing the initial formation of a protective phosphate layer. EIS analysis detected an inductive arc in whole blood at low overpotentials, before the onset of protective film formation, indicating the presence of adsorbed Zn2ions. The coverage of Zn ions approach 100% of the active surface at 110 mV. At this critical surface coverage a reaction between the adsorbed Zn ions and PO42- takes place which results in formation of a protective, porous, film of ~1 μm thickness. The inorganic component of the protective film formed in whole blood was characterized as Zn(PO4)2(OH)2·3H2O.

  • 8.
    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.
    Halldin Stenlid, Joakim
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Soldemo, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Marks, Kess
    Önsten, Anneli
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Johnson, Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Öström, Henrik
    Weissenrieder, Jonas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Dehydrogenation of methanol on Cu2O(100) and (111)2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 24Article in journal (Refereed)
    Abstract [en]

    Adsorption and desorption of methanol on the (111) and (100) surfaces of  Cu2O have been studied using high-resolution photoelectron spectroscopy in the temperature range 120–620 K, in combination with density functional theorycalculations and sum frequency generation spectroscopy. The bare (100) surfaceexhibits a (3,0; 1,1) reconstruction but restructures during the adsorption process into a Cu-dimer geometry stabilized by methoxy and hydrogen binding in Cu-bridge sites. During the restructuring process, oxygen atoms from the bulk that can host hydrogen appear on the surface. Heating transforms methoxy to formaldehyde, but further dehydrogenation is limited by the stability of the surface and the limited access to surface oxygen. The (√3 × √3)R30°-reconstructed (111) surface is based on ordered surface oxygen and copper ions and vacancies, which offers a palette of adsorption and reaction sites. Already at 140 K, a mixed layer of methoxy, formaldehyde, and CHxOy is formed. Heating to room temperature leaves OCH and CHx. Thus both CH-bond breaking and CO-scission are active on this  surface at low temperature. The higher ability to dehydrogenate methanol on (111) compared to (100) is explained by the multitude of adsorption sites and, in particular, the availability of surfaceoxygen.

  • 9.
    Cao, Lina
    et al.
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Dept Chem Phys, Hefei, Anhui, Peoples R China..
    Liu, Wei
    Univ Sci & Technol China, Natl Synchrotron Radiat Lab, Hefei, Anhui, Peoples R China..
    Luo, Qiquan
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Dept Chem Phys, Hefei, Anhui, Peoples R China..
    Yin, Ruoting
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Dept Chem Phys, Hefei, Anhui, Peoples R China..
    Wang, Bing
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Dept Chem Phys, Hefei, Anhui, Peoples R China..
    Weissenrieder, Jonas
    KTH, School of Engineering Sciences (SCI).
    Soldemo, Markus
    KTH, School of Engineering Sciences (SCI).
    Yan, Huan
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Dept Chem Phys, Hefei, Anhui, Peoples R China..
    Lin, Yue
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China..
    Sun, Zhihu
    Univ Sci & Technol China, Natl Synchrotron Radiat Lab, Hefei, Anhui, Peoples R China..
    Ma, Chao
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China..
    Zhang, Wenhua
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China..
    Chen, Si
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Dept Chem Phys, Hefei, Anhui, Peoples R China..
    Wang, Hengwei
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Dept Chem Phys, Hefei, Anhui, Peoples R China..
    Guan, Qiaoqiao
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Dept Chem Phys, Hefei, Anhui, Peoples R China..
    Yao, Tao
    Univ Sci & Technol China, Natl Synchrotron Radiat Lab, Hefei, Anhui, Peoples R China..
    Wei, Shiqiang
    Univ Sci & Technol China, Natl Synchrotron Radiat Lab, Hefei, Anhui, Peoples R China..
    Yang, Jinlong
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Dept Chem Phys, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Collaborat Innovat Ctr Chem Energy Mat iChEM, Hefei, Anhui, Peoples R China..
    Lu, Junling
    Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Dept Chem Phys, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, Collaborat Innovat Ctr Chem Energy Mat iChEM, Hefei, Anhui, Peoples R China.;Univ Sci & Technol China, CAS Key Lab Mat Energy Convers, Hefei, Anhui, Peoples R China..
    Atomically dispersed iron hydroxide anchored on Pt for preferential oxidation of CO in H-22019In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 565, no 7741, p. 631-635Article in journal (Refereed)
    Abstract [en]

    Proton-exchange-membrane fuel cells (PEMFCs) are attractive next-generation power sources for use in vehicles and other applications(1), with development efforts focusing on improving the catalyst system of the fuel cell. One problem is catalyst poisoning by impurity gases such as carbon monoxide (CO), which typically comprises about one per cent of hydrogen fuel(2-4). A possible solution is on-board hydrogen purification, which involves preferential oxidation of CO in hydrogen (PROX)(3-7). However, this approach is challenging(8-15) because the catalyst needs to be active and selective towards CO oxidation over a broad range of low temperatures so that CO is efficiently removed (to below 50 parts per million) during continuous PEMFC operation (at about 353 kelvin) and, in the case of automotive fuel cells, during frequent cold-start periods. Here we show that atomically dispersed iron hydroxide, selectively deposited on silica-supported platinum (Pt) nanoparticles, enables complete and 100 per cent selective CO removal through the PROX reaction over the broad temperature range of 198 to 380 kelvin. We find that the mass-specific activity of this system is about 30 times higher than that of more conventional catalysts consisting of Pt on iron oxide supports. In situ X-ray absorption fine-structure measurements reveal that most of the iron hydroxide exists as Fe-1(OH)(x) clusters anchored on the Pt nanoparticles, with density functional theory calculations indicating that Fe-1(OH)(x)-Pt single interfacial sites can readily react with CO and facilitate oxygen activation. These findings suggest that in addition to strategies that target oxide-supported precious-metal nanoparticles or isolated metal atoms, the deposition of isolated transition-metal complexes offers new ways of designing highly active metal catalysts.

  • 10. Evertsson, J.
    et al.
    Bertram, F.
    Zhang, Fan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Rullik, L.
    Merte, L. R.
    Shipilin, M.
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Ahmadi, Sareh
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Vinogradov, N.
    Carla, F.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Götelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Pan, Jinshan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Mikkelsen, A.
    Nilsson, J. -O
    Lundgren, E.
    The thickness of native oxides on aluminum alloys and single crystals2015In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 349, p. 826-832Article in journal (Refereed)
    Abstract [en]

    We present results from measurements of the native oxide film thickness on four different industrial aluminum alloys and three different aluminum single crystals. The thicknesses were determined using X-ray reflectivity, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. In addition, atomic force microscopy was used for micro-structural studies of the oxide surfaces. The reflectivity measurements were performed in ultra-high vacuum, vacuum, ambient, nitrogen and liquid water conditions. The results obtained using X-ray reflectivity and X-ray photoelectron spectroscopy demonstrate good agreement. However, the oxide thicknesses determined from the electrochemical impedance spectroscopy show a larger discrepancy from the above two methods. In the present contribution the reasons for this discrepancy are discussed. We also address the effect of the substrate type and the presence of water on the resultant oxide thickness.

  • 11. Fashandi, Hossein
    et al.
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Gothelid, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Eriksson, Jens
    Eklund, Per
    Spetz, Anita Lloyd
    Andersson, Mike
    Applicability of MOS structures in monitoring catalytic properties, as exemplified for monolayer-iron-oxide-coated porous platinum films2016In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 344, p. 583-590Article in journal (Refereed)
    Abstract [en]

    Metal Oxide Semiconductor (MOS) capacitor devices comprised of monolayer iron oxide-coated as well as non-coated polycrystalline Pt deposited on oxidized silicon carbide substrates have been fabricated and their usefulness as realistic model systems in catalyst studies development was evaluated. The CO oxidation characteristics of both iron oxide- and non-coated Pt catalysts were investigated using mass spectrometry, monitoring the carbon dioxide production rate for different combinations of carbon monoxide (CO) and oxygen concentrations at various temperatures. Additionally, the output capacitance of the MOS model catalysts was recorded for each individual CO oxidation activity. A low-temperature shift in CO oxidation characteristics for the monolayer-coated compared to the non-coated Pt catalysts was observed, similar to that previously reported for monolayer iron oxide grown on single-crystalline Pt substrates. A strong correlation between the output capacitance of the MOS structures and the CO oxidation characteristics was found for both monolayer- and non-coated model catalysts. Furthermore, the devices exhibit retained MOS electrical output and CO oxidation characteristics as well as an unaffected catalyst surface composition, as confirmed by photoelectron spectroscopy, even after 200 h of continuous model catalyst operation. In addition to the implications on practical applicability of monolayer iron oxide coating on widely used polycrystalline Pt films in real-world catalysts and sensors, the findings also point to new possibilities regarding the use of MOS model systems for in situ characterization, high throughput screening, and tailoring of e.g. catalyst- and fuel-cell-electrode materials for specific applications.

  • 12. Grinolds, Michael S.
    et al.
    Lobastov, Vladimir A.
    Weissenrieder, Jonas
    California Institute of Technology.
    Zewail, Ahmed H.
    Four-dimensional ultrafast electron microscopy of phase transitions2006In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 103, no 49, p. 18427-18431Article in journal (Refereed)
    Abstract [en]

    Reported here is direct imaging (and diffraction) by using 4D ultrafast electron microscopy (UEM) with combined spatial and temporal resolutions. In the first phase of UEM, it was possible to obtain snapshot images by using timed, single-electron packets; each packet is free of space-charge effects. Here, we demonstrate the ability to obtain sequences of snapshots (”movies”) with atomic-scale spatial resolution and ultrashort temporal resolution. Specifically, it is shown that ultrafast metal-insulator phase transitions can be studied with these achieved spatial and temporal resolutions. The diffraction (atomic scale) and images (nanometer scale) we obtained manifest the structural phase transition with its characteristic hysteresis, and the time scale involved (100 fs) is now studied by directly monitoring coordinates of the atoms themselves.

  • 13.
    Grinter, David
    et al.
    Brookhaven Natl Lab, Chem, Ridge, NY USA..
    Luo, Si
    Brookhaven Natl Lab, Chem, Ridge, NY USA.;SUNY Stony Brook, Chem, Stony Brook, NY 11794 USA..
    Soldemo, Markus
    KTH.
    Piazza, Luca
    KTH.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Senanayake, Sanjaya
    Brookhaven Natl Lab, Chem, Ridge, NY USA..
    Stacchiola, Dario
    Brookhaven Natl Lab, Chem, Ridge, NY USA..
    Rodriguez, Jose
    Brookhaven Natl Lab, Chem, Ridge, NY USA.;SUNY Stony Brook, Chem, Stony Brook, NY 11794 USA..
    Potassium promotion of a model Au/TiO2 catalyst2016In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 252Article in journal (Other academic)
  • 14. Guimond, S.
    et al.
    Abu Haija, M.
    Kaya, S.
    Lu, J.
    Weissenrieder, Jonas
    Fritz Haber Institute.
    Shaikhutdinov, S.
    Kuhlenbeck, H.
    Freund, H. -J.
    Doebler, J.
    Sauer, J.
    Vanadium oxide surfaces and supported vanadium oxide nanoparticles2006In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028, Vol. 38, no 1-3, p. 117-125Article in journal (Refereed)
    Abstract [en]

    The information obtained from the characterization of vanadium oxide single crystal surfaces is related to the study of vanadia nanoparticles supported on silica and alumina thin films, model systems for the so-called “supported monolayer vanadia catalysts”. It is found that these particles have properties similar to V2O3 surfaces, where the topmost V ions are involved in vanadyl groups and have a 5+ oxidation state. A vibrational spectroscopy investigation combined with DFT calculations show that the accepted interpretation of vibrational spectra from vanadia catalysts must be revised.

  • 15. Gustafson, J.
    et al.
    Resta, A.
    Mikkelsen, A.
    Westerstrom, R.
    Andersen, J. N.
    Lundgren, E.
    Weissenrieder, Jonas
    Lund university, Sweden.
    Schmid, M.
    Varga, P.
    Kasper, N.
    Torrelles, X.
    Ferrer, S.
    Mittendorfer, F.
    Kresse, G.
    Oxygen-induced step bunching and faceting of Rh(553): Experiment and ab initio calculations2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 3Article in journal (Refereed)
    Abstract [en]

    Using a combined experimental and theoretical approach, we show that the initial oxidation of a Rh(553) surface, a surface vicinal to (111), undergoes step bunching when exposed to oxygen, forming lower-index facets. At a pressure of about 10(-6) mbar and a temperature of 380 degrees C this leads to (331) facets with one-dimensional oxide chains along the steps, coexisting with (111) facets. Further increase of the pressure and temperature results in (111) facets only, covered by an O-Rh-O surface oxide. Our density functional theory calculations provide an atomistic understanding of the observed behavior.

  • 16.
    Gustafsson, Oscar
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Karim, Amir
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Wang, Qin
    Reuterskiöld-Hedlund, Carl
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Ernerheim-Jokumsen, Christopher
    KTH.
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Persson, Sirpa
    Almqvist, Susanne
    Ekenberg, Ulf
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Noharet, Bertrand
    Asplund, Carl
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Andersson, Jan Y.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Photoluminescence and photoresponse from InSb/InAs-based quantum dot structures2012In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 19, p. 21264-21271Article in journal (Refereed)
    Abstract [en]

    InSb-based quantum dots grown by metal-organic vapor-phase epitaxy (MOVPE) on InAs substrates are studied for use as the active material in interband photon detectors. Long-wavelength infrared (LWIR) photoluminescence is demonstrated with peak emission at 8.5 mu m and photoresponse, interpreted to originate from type-II interband transitions in a p-i-n photodiode, was measured up to 6 mu m, both at 80 K. The possibilities and benefits of operation in the LWIR range (8-12 mu m) are discussed and the results suggest that InSb-based quantum dot structures can be suitable candidates for photon detection in the LWIR regime.

  • 17.
    Göthelid, Mats
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Tymczenko, Michael
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Chow, Winnie
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Ahmadi, Sareh
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Yu, Shun
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Bruhn, Benjamin
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Stoltz, Dunja
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    von Schenck, Henrik
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Sun, Chenghua
    Surface concentration dependent structures of iodine on Pd(110)2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 20, p. 204703-Article in journal (Refereed)
    Abstract [en]

    We use photoelectron spectroscopy, low energy electron diffraction, scanning tunneling microscopy, and density functional theory to investigate coverage dependent iodine structures on Pd(110). At 0.5 ML (monolayer), a c(2 x 2) structure is formed with iodine occupying the four-fold hollow site. At increasing coverage, the iodine layer compresses into a quasi-hexagonal structure at 2/3 ML, with iodine occupying both hollow and long bridge positions. There is a substantial difference in electronic structure between these two iodine sites, with a higher electron density on the bridge bonded iodine. In addition, numerous positively charged iodine near vacancies are found along the domain walls. These different electronic structures will have an impact on the chemical properties of these iodine atoms within the layer.

  • 18.
    Göthelid, Mats
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    von Schenck, Henrik
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Åkermark, B.
    Tkatchenko, A.
    Galvan, M.
    Adsorption site, core level shifts and charge transfer on the Pd(111)-I(root 3 x root 3) surface2006In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, no 15, p. 3093-3098Article in journal (Refereed)
    Abstract [en]

    We use core level photoelectron spectroscopy and density functional theory (DFT) to investigate the iodine-induced Pd(1 1 1)-I(root 3 x root 3) structure formed at 1/3 NIL coverage. From the calculations we find that iodine adsorbs preferentially in the fcc hollow site. The calculated equilibrium distance is 2.06 angstrom and the adsorption energy is 68 kcal/mol, compared to 2.45 angstrom and 54 kcal/mol in the atop position. The adsorption energy difference between fcc and hcp hollows is 1.7 kcal/mol. Calculated Pd 3d surface core level shift on clean Pd(1 1 1) is 0.30 eV to lower binding energy, in excellent agreement with our experimental findings (0.28-0.29 eV). On the Pd(1 1 1)-I(root 3 x root 3) we find no Pd 3d surface core level shift, neither experimentally nor, theoretically. Calculated charge transfer for the fcc site, determined from the Hirshfeld partitioning method, suggests that the iodine atom remains almost neutral upon adsorption.

  • 19.
    Halldin Stenlid, Joakim
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Johansson, A. J.
    Leygraf, Christofer
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Götelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Reactivity at the Cu2O(100):Cu-H2O interface: a combined DFT and PES study2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 44, p. 30570-30584Article in journal (Refereed)
    Abstract [en]

    The water-cuprite interface plays an important role in dictating surface related properties. This not only applies to the oxide, but also to metallic copper, which is covered by an oxide film under typical operational conditions. In order to extend the currently scarce knowledge of the details of the water-oxide interplay, water interactions and reactions on a common Cu2O(100):Cu surface have been studied using high-resolution photoelectron spectroscopy (PES) as well as Hubbard U and dispersion corrected density functional theory (PBE-D3+U) calculations up to a bilayer water coverage. The PBE-D3+U results are compared with PBE, PBE-D3 and hybrid HSE06-D3 calculation results. Both computational and experimental results support a thermodynamically favored, and H2O coverage independent, surface OH coverage of 0.25-0.5 ML, which is larger than the previously reported value. The computations indicate that the results are consistent also for ambient temperatures under wet/humid and oxygen lean conditions. In addition, both DFT and PES results indicate that the initial (3,0; 1,1) surface reconstruction is lifted upon water adsorption to form an unreconstructed (1 x 1) Cu2O(100) structure.

  • 20. Itoh, Y
    et al.
    Suzuki, T
    Birukawa, M
    Weissenrieder, Jonas
    KTH, Superseded Departments, Physics.
    Magnetic and magneto-optical properties of TbFeCo/(Pt,Pd) multilayers optimized for short wavelength recording1999In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 85, no 8 II A, p. 5091-5093Article in journal (Refereed)
    Abstract [en]

    Magnetic and magneto-optical properties of TbFeCo/Pt and TbFeCo/Pd multilayer films prepared by sputter deposition are discussed in conjunction with the multilayer structure. The magnetic behaviors in TbFeCo/Pt and TbFeCo/Pd multilayers are very similar to each other, and the saturation magnetization M-s at 298 K increases with thickness t of Pt and Pd up to t(Pt), t(Pd) =12 Angstrom. In TbFeCo/Pt multilayers, the contribution of Pt to the polar Kerr spectra is significant at ultraviolet photon energies. The Kerr rotation theta(K) and ellipticity eta(K) are enhanced with Pt layer thickness and become saturated at t(Pt) = 12 Angstrom. On the other hand, little contribution from Pd atoms is found in the TbFeCo/Pd multilayer.

  • 21. Itoh, Yusuke
    et al.
    Philips, G.N.
    Suzuki, T.
    Weissenrieder, Jonas
    KTH, Superseded Departments, Physics.
    Enhancement of Magneto-optical Effects through Polarized Pt and Pd in TbFeCo/(Pt, Pd) Multilayers1999In: Journal of the Magnetics Society of Japan, ISSN 0285-0192, Vol. 23, no s1, p. 55-58Article in journal (Refereed)
  • 22. Itoh, Yusuke
    et al.
    Weissenrieder, Jonas
    KTH, Superseded Departments, Physics.
    Suzuki, Takao
    Magnetic and Magneto-Optical Properties of TbFeCo/(Pt, Pd, NdCo) Multilayers1999In: Journal of the magnetics society of japan, ISSN 0285-0192, Vol. 23, no 4-2, p. 1081-1084Article in journal (Refereed)
  • 23.
    Janin, Emmanuelle
    et al.
    KTH, Superseded Departments, Physics.
    Ringler, Sandrine
    KTH, Superseded Departments, Physics.
    Weissenrieder, Jonas
    KTH, Superseded Departments, Physics.
    Åkermark, Torbjörn
    KTH, Superseded Departments, Physics.
    Karlsson, Ulf O.
    KTH, Superseded Departments, Physics.
    Göthelid, Mats
    KTH, Superseded Departments, Physics.
    Nordlund, D.
    Ogasawara, H.
    Adsorption and bonding of propene and 2-butenal on Pt(111)2001In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 482, p. 83-89Article in journal (Refereed)
    Abstract [en]

    The adsorption of propene and 2-butenal on the Pt(1 1 1) surface has been studied by high resolution photoelectron spectroscopy, both in the mono-and multi-layer regime. The results obtained indicate an involvement of both aliphatic and carbonyl groups in the bonding of 2-butenal with the platinum surface in the sub-monolayer regime.

  • 24.
    Janin, Emmanuelle
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    von Schenck, Hans
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Ringler, Sandrine
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Weissenrieder, Jonas
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Åkermark, Torbjörn
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Göthelid, Mats
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Adsorption and bonding of 2-butenal on Sn/Pt surface alloys2003In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 215, no 2, p. 245-253Article in journal (Refereed)
    Abstract [en]

    The adsorption of 2-butenal on the Pt(111), Pt(111)Sn-(2 x 2), and Pt(111)Sn-(root3 x root3)R30degrees surfaces has been studied by high-resolution photoelectron spectroscopy and DFT calculations. On Pt(111) 2-butenal adsorbs at a threefold hollow in a eta(3)(C,C,O) configuration. A similar geometry is observed for Pt(111)Sn-(2 x 2), although the oxygen coordinates to tin instead of platinum. As the surface coverage of tin increases, as for Pt(111)Sn-(root3 x root3)R30degrees, the most stable adsorption geometry changes to eta(1)(O), where the carbonyl oxygen once again coordinates to tin. The carbonyl bond thus retains an activated character as Pt/Sn alloys are formed. The alkene/surface interaction is, however, dramatically influenced at increasing surface concentrations of tin.

  • 25.
    Ji, Shaozheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Piazza, Luca
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Cao, Gaolong
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Park, S. T.
    Reed, B. W.
    Masiel, D. J.
    Weissenrieder, Jonas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Influence of cathode geometry on electron dynamics in an ultrafast electron microscope2017In: Structural Dynamics, ISSN 2329-7778, Vol. 4, no 5, article id 054303Article in journal (Refereed)
    Abstract [en]

    Efforts to understand matter at ever-increasing spatial and temporal resolutions have led to the development of instruments such as the ultrafast transmission electron microscope (UEM) that can capture transient processes with combined nanometer and picosecond resolutions. However, analysis by UEM is often associated with extended acquisition times, mainly due to the limitations of the electron gun. Improvements are hampered by tradeoffs in realizing combinations of the conflicting objectives for source size, emittance, and energy and temporal dispersion. Fundamentally, the performance of the gun is a function of the cathode material, the gun and cathode geometry, and the local fields. Especially shank emission from a truncated tip cathode results in severe broadening effects and therefore such electrons must be filtered by applying a Wehnelt bias. Here we study the influence of the cathode geometry and the Wehnelt bias on the performance of a photoelectron gun in a thermionic configuration. We combine experimental analysis with finite element simulations tracing the paths of individual photoelectrons in the relevant 3D geometry. Specifically, we compare the performance of guard ring cathodes with no shank emission to conventional truncated tip geometries. We find that a guard ring cathode allows operation at minimum Wehnelt bias and improve the temporal resolution under realistic operation conditions in an UEM. At low bias, the Wehnelt exhibits stronger focus for guard ring than truncated tip cathodes. The increase in temporal spread with bias is mainly a result from a decrease in the accelerating field near the cathode surface. Furthermore, simulations reveal that the temporal dispersion is also influenced by the intrinsic angular distribution in the photoemission process and the initial energy spread. However, a smaller emission spot on the cathode is not a dominant driver for enhancing time resolution. Space charge induced temporal broadening shows a close to linear relation with the number of electrons up to at least 10 000 electrons per pulse. The Wehnelt bias will affect the energy distribution by changing the Rayleigh length, and thus the interaction time, at the crossover.

  • 26. Kaya, S.
    et al.
    Baron, M.
    Stacchiola, D.
    Weissenrieder, Jonas
    Fritz Haber Institute.
    Shaikhutdinov, S.
    Todorova, T. K.
    Sierka, M.
    Sauer, J.
    Freund, H. -J
    On the geometrical and electronic structure of an ultra-thin crystalline silica film grown on Mo(112)2007In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, no 21, p. 4849-4861Article in journal (Refereed)
    Abstract [en]

    The atomic structure of a well-ordered silica film grown on a Mo(112) single crystal substrate is discussed in detail using the experimental and theoretical results available to date. New photoelectron spectroscopy results using synchrotron radiation and ultraviolet spectroscopy data are presented. The analysis unambiguously shows that the ultra-thin silica film consists of a two-dimensional network of corner-sharing [SiO4] tetrahedra chemisorbed on the unreconstructed Mo(112) surface. The review also highlights the important role of theoretical calculations in the determination of the atomic structure of the silica films and in interpretation of experimental data.

  • 27. Kaya, S.
    et al.
    Sun, Y. -N
    Weissenrieder, Jonas
    Fritz Haber Institute.
    Stacchiola, D.
    Shaikhutdinov, S.
    Freund, H. -J
    Ice-assisted preparation of silica-supported vanadium oxide particles2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 14, p. 5337-5344Article in journal (Refereed)
    Abstract [en]

    Vanadium oxide particles were prepared by physical vapor deposition of vanadium in oxygen ambient onto ice-precovered well-ordered silica thin films. Morphology, electronic structure, and vibrational properties of the vanadia deposits were studied by scanning tunneling microscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption, and infrared reflection absorption spectroscopy. The results show that the ice behaves as an oxidative agent, that favors vanadium oxidation up to V4+, and as a buffer layer that precludes strong interaction of the V adatoms with the silica film. At room temperature, upon desorption of the unreacted water, nanosized particles of vanadia hydroxide-like gel, containing V-OH and, to a lesser extent, vanadyl (VO) species, are formed. Vacuum annealing at 550 K leads to the total dehydration and partial reduction of the particles to V2O3, which expose the V-terminated surface. Subsequent reoxidation in 10(-6) mbar of O-2 irreversibly transforms the surface to the VO terminated, that is, the same as for the reactive deposition onto the clean silica surface. The results suggest that the structure of silica-supported vanadia catalysts is determined by a calcination step and should be considered under low oxygen pressure conditions as vanadium sesquioxide nanoparticles with the VO terminated surface.

  • 28. Kaya, S.
    et al.
    Weissenrieder, Jonas
    Fritz Haber Institute.
    Stacchiola, D.
    Shaikhutdinov, S.
    Freund, H. -J
    Formation of an ordered ice layer on a thin silica film2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 2, p. 759-764Article in journal (Refereed)
    Abstract [en]

    Adsorption of water on a thin silica film grown on a Mo(112) single crystal was studied by temperature-programmed desorption, infrared reflection absorption spectroscopy, and photoelectron spectroscopy using synchrotron radiation. Water does not dissociate on the defect-free oxygen-terminated silica surface. In contrast to adsorption at 100 K, where water follows a zero-order desorption kinetics, water adsorbed at 140 K exhibits a pseudo-first-order kinetics and induces a strong blue shift of the silica phonon. Even larger spectral changes were observed for D2O adsorption. The results were rationalized in terms of the formation of an amorphous solid water film at 100 K and a crystalline ice monolayer film at 140-150 K. This film is well-ordered as revealed by low-energy electron diffraction showing a c(2 x 2) superstructure with respect to the silica substrate.

  • 29. Kaya, S.
    et al.
    Weissenrieder, Jonas
    Fritz Haber Institute.
    Stacchiola, D.
    Todorova, T. K.
    Sierka, M.
    Sauer, J.
    Shaikhutdinov, S.
    Freund, H. -J
    Formation of one-dimensional molybdenum oxide on Mo(112)2008In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 602, no 21, p. 3338-3342Article in journal (Refereed)
    Abstract [en]

    The atomic structure of a reconstructed Mo(112)-O(2 x 3) surface has been revisited using photoelectron spectroscopy with synchrotron radiation, scanning tunneling microscopy, infrared reflection absorption spectroscopy and density functional theory. In contrast to previous models, the results are rationalized in terms of the formation of one-dimensional, Mo=O terminated molybdenum oxide involving corner sharing distorted [MoO(6)] octahedra on the (1 x 3) reconstructed Mo(112) surface.

  • 30. Kleber, C.
    et al.
    Weissenrieder, Jonas
    KTH, Superseded Departments, Materials Science and Engineering.
    Schreiner, M.
    Leygraf, Christofer
    KTH, Superseded Departments, Materials Science and Engineering.
    Comparison of the early stages of corrosion of copper and iron investigated by in situ TM-AFM2002In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 193, no 1-4, p. 245-253Article in journal (Refereed)
    Abstract [en]

    Tapping mode atomic force microscopy (TM-AFM) was used for the investigation of the early stages of atmospheric corrosion of pure copper and pure iron. The information obtained by this method is the change of the topography of the sample surfaces with emphasis on the. shape and lateral distribution of the corrosion products grown within the first 1300 min of weathering. Investigations were carried out in synthetic air at 80 and 90% relative humidity (RH) with additions of 250 ppb SO2 and 250 ppb NO2. On a polished copper surface the growth of corrosion products could be observed already at 80% RH and 250 ppb SO2, whereas an iron surface had to be exposed to 90% RH with 250 ppb SO2 and 250 ppb NO, to produce detectable changes on the surface.

  • 31. Lobastov, Vladimir A.
    et al.
    Weissenrieder, Jonas
    California Institute of Technology.
    Tang, Jau
    Zewail, Ahmed H.
    Ultrafast electron microscopy (UEM): Four-dimensional imaging and diffraction of nanostructures during phase transitions2007In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 7, no 9, p. 2552-2558Article in journal (Refereed)
    Abstract [en]

    Four-dimensional (4D) imaging during structural changes are reported here using ultrafast electron microscopy (UEM). For nanostructures, the phase transition in the strongly correlated material vanadium dioxide is our case study. The transition is initiated and probed in situ, in the microscope, by a femtosecond near-infrared and electron pulses (at 120 kell). Real-space imaging and Fourier-space diffraction patterns show that the transition from the monoclinic (P2(1)/c) to tetragonal (P4(2)/mnm) structure is induced in 3 +/- 1 ps, but there exists a nonequilibrium (metastable) structure whose nature is determined by electronic, carrier-induced, structural changes. For the particles studied, the subsequent recovery occurs in about 1 ns. Because of the selectivity of excitation from the 3d(II)-band, and the relatively low fluence used, these results show the critical role of carriers in weakening the V4+-V4+ bonding in the monoclinic phase and the origin of the nonequilibrium phase. A theoretical two-dimensional (2D) diffusion model for nanoscale materials is presented, and its results account for the observed behavior.

  • 32. Lu, J. -L
    et al.
    Kaya, S.
    Weissenrieder, Jonas
    Fritz Haber Institute.
    Gao, H. -J
    Shaikhutdinov, S.
    Freund, H. -J
    Low temperature CO induced growth of Pd supported on a monolayer silica film2006In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, no 12, p. L153-L157Article in journal (Refereed)
    Abstract [en]

    Nucleation, growth and sintering of Pd deposited on an ultra-thin silica film were studied by scanning tunneling microscopy and infrared reflection absorption spectroscopy. No preferential nucleation of Pd on the silica surface was observed both at 90 and 300 K deposition. When adsorbed on Pd clusters formed at 90 K, CO causes a strong sintering effect even at this temperature. The results are rationalized on the basis of a high mobility of Pd carbonyl-like species on the silica film. At a given Pd coverage, the extent of CO induced sintering cannot be achieved by annealing in vacuum. In addition, vacuum sintering, which commences above 700 K, goes simultaneously with interdiffusion of Pd and support.

  • 33. Lu, J. -L
    et al.
    Kaya, S.
    Weissenrieder, Jonas
    Fritz Haber Institute.
    Todorova, T. K.
    Sierka, M.
    Sauer, J.
    Gao, H. -J
    Shaikhutdinov, S.
    Freund, H. -J
    Formation of one-dimensional crystalline silica on a metal substrate2006In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, no 13, p. L164-L168Article in journal (Refereed)
    Abstract [en]

    We have observed formation of one-dimensional silica structures of 0.5 nm in width on Mo(112) single crystal surface. Combination of high-resolution scanning tunneling microscopy, photoelectron and infrared spectroscopy, and density functional theory provides strong evidence for formation of paired rows of corner sharing [SiO4] tetrahedra chemisorbed on a metal substrate.

  • 34. Lu, J. -L.
    et al.
    Weissenrieder, Jonas
    Fritz Haber Institute, Chemical Physics.
    Kaya, S.
    Gao, H. -J.
    Shaikhutdinov, S.
    Freund, H. -J.
    Structure, thermal stability, and CO adsorption properties of Pd nanoparticles supported on an ultra-thin SiO2 film2007In: Surface review and letters, ISSN 0218-625X, Vol. 14, no 5, p. 927-934Article in journal (Refereed)
    Abstract [en]

    Nucleation, growth, and thermal stability of Pd particles vapor-deposited on an ultra-thin crystalline silica film grown on Mo(112) have been studied by scanning tunneling microscopy, X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and temperature-programmed desorption of CO. No preferential nucleation of Pd on the silica film is found at room temperature deposition: the hemispherical Pd nanoparticles are homogenously dispersed on the support at all coverages studied (0.01-1ML(mono layer)). The Pd particles are resistant toward sintering up to 700K as judged by STM; however, CO adsorption studies have revealed surface chemical modification at temperatures as low as 550K. Strong morphological changes are observed above 800K (ultimately resulting in elongated rectangular islands at similar to 1000 K), which is accompanied by strong alterations of CO adsorption properties. The results are rationalized in terms of Pd and Mo substrate interdiffusion at elevated temperatures, while the silica film basically preserves its structure.

  • 35. Lundgren, E.
    et al.
    Gustafson, J.
    Resta, A.
    Weissenrieder, Jonas
    Maxlab.
    Mikkelsen, A.
    Andersen, J. N.
    Kohler, L.
    Kresse, G.
    Klikovits, J.
    Biederman, A.
    Schmid, M.
    Varga, P.
    The surface oxide as a source of oxygen on Rh(111)2005In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 144, no SI, p. 367-372Article in journal (Refereed)
    Abstract [en]

    The reduction of a thin surface oxide on the Rh(1 1 1) surface by CO is studied in situ by photoemission spectroscopy, scanning tunneling microscopy, and density functional theory. CO molecules are found not to adsorb on the surface oxide at a sample temperature of 100 K, in contrast to on the clean and chemisorbed oxygen covered surface. Despite this behavior, the surface oxide may still be reduced by CO, albeit in a significantly different fashion as compared to the reduction of a phase containing only chemisorbed on surface oxygen. The experimental observations combined with theoretical considerations concerning the stability of the surface oxide, result in a model of the reduction process at these pressures suggesting that the surface oxide behaves as a source of oxygen for the CO-oxidation reaction.

  • 36. Martynova, Y.
    et al.
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sachert, S.
    Polzin, S.
    Widdra, W.
    Shaikhutdinov, S.
    Freund, H. -J
    CO Oxidation Over Monolayer Manganese Oxide Films on Pt(111)2013In: Catalysis Letters, ISSN 1011-372X, E-ISSN 1572-879X, Vol. 143, no 11, p. 1108-1115Article in journal (Refereed)
    Abstract [en]

    Ultrathin manganese oxide films grown on Pt(111) were examined in the low temperature CO oxidation reaction at near atmospheric pressures. Structural characterization was performed by X-ray photoelectron spectroscopy, Auger electron spectroscopy, high-resolution electron energy loss spectroscopy, and temperature programmed desorption. The results show that the reactivity of MnOx ultrathin films is governed by a weakly bonded oxygen species, which may even be formed at low oxygen pressures (similar to 10(-6) mbar). For stable catalytic performance at realistic conditions the films required highly oxidizing conditions (CO:O-2 < 1:10), otherwise the films dewetted, ultimately resulting in the catalyst deactivation. Comparison with other thin films on Pt(111) shows, that the desorption temperature of weakly bonded oxygen species can be used as a benchmark for its activity in this reaction.

  • 37.
    Mazraati, Hamid
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Chung, Sunjae
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Houshang, Afshin
    Dvornik, Mykola
    Piazza, Luca
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Qejvanaj, Fatjon
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Jiang, Sheng
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Le, Tuan Q.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Low operational current spin Hall nano-oscillators based on NiFe/W bilayers2016In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, no 24, article id 242402Article in journal (Refereed)
    Abstract [en]

    We demonstrate highly efficient spin Hall nano-oscillators (SHNOs) based on NiFe/beta-W bilayers. Thanks to the very high spin Hall angle of beta-W, we achieve more than a 60% reduction in the auto-oscillation threshold current compared to NiFe/Pt bilayers. The structural, electrical, and magnetic properties of the bilayers, as well as the microwave signal generation properties of the SHNOs, have been studied in detail. Our results provide a promising path for the realization of low-current SHNO microwave devices with highly efficient spin-orbit torque from beta-W. Published by AIP Publishing.

  • 38. Mikkelsen, A.
    et al.
    Eriksson, J.
    Lundgren, E.
    Andersen, J. N.
    Weissenrieder, Jonas
    Lund University.
    Seifert, W.
    The influence of lysine on InP(001) surface ordering and nanowire growth2005In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 16, no 10, p. 2354-2359Article in journal (Refereed)
    Abstract [en]

    We report on high resolution photoelectron core level spectroscopy (HRCLS) and scanning tunnelling microscopy (STM) measurements of the decomposition of lysine adsorbed on InP(001) substrates. We find that components from the lysine can be present on the InP surface even after annealing to 600 degrees C and desorption of the native surface oxide. We further observe that while a crystalline surface phase can be observed on the epi-ready surface after annealing, the lysine treated surface still appears rough. We conclude that lysine residues inhibit the formation of a flat crystalline structure on the InP(001) surface. These results are discussed in terms of the lysine promotion of [001] nanowire growth.

  • 39.
    Palmgren, Pål
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Szamota-Leandersson, Katolina
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Chemical reaction and interface formation on InAs(111)-Co surfaces2005In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 574, no 2-3, p. 181-192Article in journal (Refereed)
    Abstract [en]

    We report a study of the initial interface formation of Co on InAs(1 1 1)A and B surfaces using high resolution photoelectron spectroscopy and scanning tunneling microscopy. We observe a strong chemical interaction between Co and, in particular, surface indium forming a metallic overlayer already below monolayer coverage. On annealed surfaces this overlayer agglomerates into islands, with a narrow size distribution. Furthermore, no two-dimensional electron gas is formed on InAs(1 1 1)A-Co in contrast to the clean surface.

  • 40. Sierka, M.
    et al.
    Todorova, T. K.
    Kaya, S.
    Stacchiola, D.
    Weissenrieder, Jonas
    Fritz Haber Institute.
    Lu, J.
    Gao, H.
    Shaikhutdinov, S.
    Freund, H. J.
    Sauer, J.
    Interplay between theory and experiment in the quest for silica with reduced dimensionality grown on a Mo(112) surface2006In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 424, no 1-3, p. 115-119Article in journal (Refereed)
    Abstract [en]

    The stability of ordered one- and two-dimensional silica structures formed on a Mo(112) surface as a function of silicon coverage and oxygen pressure (phase diagram) is derived from density functional theory. At elevated oxygen pressures formation of a new, previously not considered structure of two-dimensional silica film is predicted. It contains additional oxygen atoms adsorbed directly on the Mo(112) surface underneath a two-dimensional network of corner sharing [SiO4] tetrahedra. The existence of the new phase is confirmed experimentally using infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy.

  • 41. Sierka, Marek
    et al.
    Todorova, Tanya K.
    Sauer, Joachim
    Kaya, Sarp
    Stacchiola, Dario
    Weissenrieder, Jonas
    Fritz Haber Institute.
    Shaikhutdinov, Shamil
    Freund, Hans-Joachim
    Oxygen adsorption on Mo(112) surface studied by ab initio genetic algorithm and experiment2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 126, no 23Article in journal (Refereed)
    Abstract [en]

    Density functional theory in combination with genetic algorithm is applied to determine the atomic models of p(1x2) and p(1x3) surface structures observed upon oxygen adsorption on a Mo(112) surface. The authors’ simulations reveal an unusual flexibility of Mo(112) resulting in oxygen-induced reconstructions and lead to more stable structures than any suggested so far. Comparison of the stabilities of the predicted models shows that different p(1x2) and p(1x3) structures may coexist over a wide range of oxygen pressures. A pure p(1x2) structure can be obtained only in a narrow region of oxygen pressures. In contrast, a pure p(1x3) structure cannot exist as a stable phase. The results of simulations are fully supported by a multitude of experimental data obtained from low energy electron diffraction, x-ray photoelectron spectroscopy, and scanning tunneling microscopy.

  • 42. Sinner-Hettenbach, M.
    et al.
    Göthelid, Mats
    KTH, Superseded Departments, Physics.
    Weissenrieder, Jonas
    KTH, Superseded Departments, Physics.
    von Schenck, Henrik
    KTH, Superseded Departments, Physics.
    Weiss, T.
    Barsan, N.
    Weimar, U.
    Oxygen-deficient SnO2(110): a STM, LEED and XPS study2001In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 477, no 1, p. 50-58Article in journal (Refereed)
    Abstract [en]

    The reconstruction process of SnO2(110) was investigated by scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). The high-temperature 1 x 1 reconstruction could be identified as an intermediate face, transferable either to the 1 x 2 surface by annealing to higher temperature or back to the 4 x 1 reconstruction by annealing again at lower temperature. In this way, a new method to prepare well-ordered 4 x 1 terminated surfaces is introduced and the O/Sn ratio as well as the core-level positions of Sn 3d and O 1s were traced by XPS over a temperature range of 700-1200 K on freshly sputtered and on low-temperature long-time annealed SnO2(110). STM images of the 1 x 1 surface show a new structure of in-plane oxygen, ordered locally in zigzag rows that contribute to the LEED pattern as a very diffuse 2 x 1 intensity.

  • 43.
    Soldemo, Markus
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Halldin Stenlid, Joakim
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Besharat, Zahra
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Ghadami Yazdi, Milad
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Önsten, Anneli
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Leygraf, Christofer
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    The Surface Structure of Cu2O(100)2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 8, p. 4373-4381Article in journal (Refereed)
    Abstract [en]

    Despite the industrial importance of copper oxides, the nature of the (100) surface of Cu2O has remained poorly understood. The surface has previously been subject to several theoretical and experimental studies, but has until now not been investigated by atomically resolved microscopy or high-resolution photoelectron spectroscopy. Here we determine the atomic structure and electronic properties of Cu2O(100) by a combination of multiple experimental techniques and simulations within the framework of density functional theory (DFT). Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) characterized the three ordered surface structures found. From DFT calculations, the structures are found to be energetically ordered as (3,0;1,1), c(2 x 2), and (1 x 1) under ultrahigh vacuum conditions. Increased oxygen pressures induce the formation of an oxygen terminated (1 x 1) surface structure. The most common termination of Cu2O(100) has previously been described by a (3 root 2 x root 2)R45 degrees unit cell exhibiting a LEED pattern with several missing spots. Through atomically resolved STM, we show that this structure instead is described by the matrix (3,0;1,1). Both simulated STM images and calculated photoemission core level shifts compare favorably with the experimental results.

  • 44.
    Soldemo, Markus
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Johansson, Niclas
    Besharat, Zahra
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Önsten, Anneli
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Knudsen, Jan
    Schnadt, Joachim
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Cuprous oxide surfaces exposed to sulfur dioxide and near-ambient pressures of waterManuscript (preprint) (Other academic)
    Abstract [en]

    The interaction of sulfur dioxide with Cu2O(100) and Cu2O(111) at ultra-high vac-uum is studied. It is found that on both surfaces, the sulfur dioxide moleculesbind as SO3-species. Dosing water in UHV does not impact the SO3-species at thedoses used. When dosing water at near-ambient pressure conditions, however, itis observed that the sulfur in the SO3-species shifts to Cu2S when monitoring thePES S 2p-region.

  • 45.
    Soldemo, Markus
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Jonas, Weissenrieder
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Oxidation of Fe(100) in oxygen gas at 400 °CManuscript (preprint) (Other academic)
    Abstract [en]

    The oxidation of Fe(100) was studied at an oxygen gas pressure of 1×10−6mbarand a temperature of 400°C. The main findings is that the oxide film, beyond oxy-gen adsorbate structure, is formed by layer-by-layer growth and has a Fe3O4(100)termination.

  • 46.
    Soldemo, Markus
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Lundgren, E.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Oxidation of Fe(110) in oxygen gas at 400 °c2016In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 644, p. 172-179Article in journal (Refereed)
    Abstract [en]

    The initial oxidation of Fe(110) in oxygen gas at 400 °C beyond initial adsorbate structures has been studied using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM). Formation of several ordered phases of surface oxides is observed at oxygen coverages between approximately 2.3 and 3.5 oxygen atoms/Fe(110) surface atom. Initially, a FeO(111)-like film is formed with a parallelogram-shaped moiré pattern. It has two mirror domains that are formed symmetrically around the growth direction of a zigzag-shaped adsorbate structure. With increased local oxygen coverage, the moiré structure transforms into a ball-shaped form. Both these moiré structures have equal atomic stacking at the surface and equal apparent height in STM, suggesting oxygen ions diffusing into the film upon oxidation and that the oxide growth takes place at the iron-iron oxide interface. The FeO(111)-like film turns into a Fe3O4(111)-like film with a triangular bistable surface termination as the oxidation proceeds further. The FeO(111)-like film growth proceeds according to the Frank-van der Merwe mechanism while the Fe3O4(111)-like film grows according to the Stranski-Krastanov mechanism.

  • 47.
    Soldemo, Markus
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Niu, Yuran
    Zakharov, Alexei
    Lundgren, Edvin
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    A well-ordered surface oxide on Fe(110)2015In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 639, p. 13-19Article in journal (Refereed)
    Abstract [en]

    A well-ordered surface oxide grown on Fe(110) has been studied using scanning tunneling microscopy (STM), low energy electron diffraction, low energy electron microscopy, and core level photoelectron spectroscopy. The iron oxide film exhibits wide terraces and is formed after exposure to 100-1000 L at 1 x 10(-6) mbar O-2 and 400 degrees C. Two domains, mirror symmetric in the Fe(110)-lattice mirror symmetry planes but otherwise equal, are observed. The surface oxide forms a relatively large coincidence surface unit cell (16.1 angstrom x 26.5 angstrom). Imaging by STM reveals a strong bias dependence in the apparent height within the surface unit cell. The oxygen terminating atomic layer has a hexagonal atomic structure, FeO(111)-like, with the atomic sparing of 3.2 angstrom, that is expanded by similar to 63% relative to bulk FeO(111).

  • 48.
    Soldemo, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Vandichel, Matthias
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Competence Ctr Catalysis, SE-41296 Gothenburg, Sweden.;Aalto Univ, Dept Chem & Mat Sci, Sch Chem Engn, Sch Sci, Espoo 02150, Finland.;Aalto Univ, Dept Appl Phys, Sch Chem Engn, Sch Sci, Espoo 02150, Finland..
    Gronbeck, Henrik
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Competence Ctr Catalysis, SE-41296 Gothenburg, Sweden..
    Weissenrieder, Jonas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Initial Fe3O4(100) Formation on Fe(100)2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 26, p. 16317-16325Article in journal (Refereed)
    Abstract [en]

    The initial oxidation of Fe(100) at 400 degrees C has been studied by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and low-energy electron diffraction, in combination with density functional theory calculations. The first observed well-ordered surface oxide is formed at a coverage of similar to 3 oxygen atoms per unreconstructed surface Fe(100) atom. STM shows that this surface oxide is terminated by straight atomic rows exhibiting a p(2 X 1) periodicity. However, already for oxide films with a coverage of similar to 4 oxygen atoms (corresponding to one Fe3O4 unit cell thickness), wiggly atomic rows appear similar to the c(2 X 2) reconstructed Fe3O4 (100)-surface with the Fe3O4 unit vectors rotated 45 degrees to Fe(100). The wiggly rows are a consequence of subsurface cation iron vacancies, which previously have been observed for bulk surfaces. The formation of subsurface vacancies is supported by the XPS O is signature, which is modeled by considering the core-level shifts for all oxygen atoms in the film. Throughout the oxidation series, the microscopy results reveal a layer-by-layer (Frank-van der Merwe) growth.

  • 49.
    Soldemo, Markus
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sulfur dioxide interaction with oxidized low-index iron surfacesManuscript (preprint) (Other academic)
    Abstract [en]

    Sulfur dioxide was dosed on thin iron oxides grown on Fe(100) and Fe(110) (fromPaper 1 and Paper 2). It is found that the sulfur dioxide molecules adsorb as SO4-species at room temperature and that some of the adsorbed molecules dissociateupon adsorption and forming FeS2. The oxides corresponding to the lowest dosesof oxygen gas in Paper 1 and Paper 2 were annealed after the sulfur dioxide dos-ing, resulting in increased amount of dissociated molecules. The thicker oxides, onboth surfaces were exposed to another dose of sulfur dioxide, the change of sulfurcoverages show that the surfaces are almost saturated.

  • 50. Stacchiola, D. J.
    et al.
    Baron, M.
    Kaya, S.
    Weissenrieder, Jonas
    Fritz Haber Institute.
    Shaikhutdinov, S.
    Freund, H. -J.
    Freund, J.
    Growth of stoichiometric subnanometer silica films2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 1Article in journal (Refereed)
    Abstract [en]

    We present a method to grow stoichiometric SiO(2) films of only similar to 0.6-0.9 nm in thickness on a metal substrate. Based on photoelectron and infrared spectroscopy studies, we conclude that the similar to 0.6-nm-thick silica films exhibit characteristics only observed for > 2.0-nm-thick films grown on conventional Si substrates. The films can be used as model oxides for fundamental studies and may have implications on the further miniaturization of metal-oxide-semiconductor transistors.

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