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  • 1.
    Amandusson, Helena
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Ekedahl, Lars-Gunnar
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Dannetun, Helen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Methanol induced hydrogen permeation through a Pd membrane1999Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 442, nr 2, s. 199-205Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dehydrogenation of methanol and the subsequent permeation of hydrogen through a 25 μm thick palladium film has been studied in a catalytic membrane reactor. At the temperature studied, 350°C, the decomposition pathway for methanol on clean palladium surfaces is believed to lead to Had and a carbonaceous overlayer. The released hydrogen can either desorb or permeate the palladium membrane. During a continuous supply of methanol hydrogen permeation is reduced and, eventually, totally quenched by the growing carbon monoxide/carbon coverage. Adding oxygen in the methanol supply can balance the increasing carbonaceous coverage through the production of carbon dioxide. In such a case, it is concluded that no CO bond scission occurs. The methanol/oxygen ratio is crucial for the hydrogen permeation rate. Isotope-labelled methanol, CH3OH, CH3OD, CD3OH and CD3OD, shows that it is preferentially the methyl (or methoxy) hydrogen that permeates the membrane.

  • 2.
    Castleton, Christopher
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Nokbin, S.
    Materials Chemistry, The Ångström Laboratory, Box 538, SE-751 21 Uppsala, Sweden, Laboratory for Computational and Applied Chemistry, Department of Chemistry, Kasetsart University, Bangkok, 10900, Thailand.
    Hermansson, K.
    Materials Chemistry, The Ångström Laboratory, Box 538, SE-751 21 Uppsala, Sweden.
    Correlations between magnetic properties and bond formation in Rh-MgO(0 0 1)2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 5, s. 1218-1230Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the results of first principles calculations for the magnetism of Rh adlayers on MgO(0 0 1), at three different adsorption sites and three different coverages, corresponding to 1, 1/2 and 1/8 monolayers. Finite magnetization is found in all cases except that of one Rh monolayer above the oxygen site, which is also the most stable. We examine how the magnetization changes as a function of the Rh-surface distance and relate this to changes in the real-space charge density and in the density of states (DOS) as the Rh adlayer interacts with the surface. We find that increasing either the Rh-Rh interaction strength or the Rh-surface interaction strength leads to reduced magnetization, while increasing the former drives a crossover from localized (atomic) to itinerant magnetism. Neither the magnetic transition itself, nor the localized-to-itinerant magnetism crossover, is found to be directly related to the formation of Rh-surface bonds. From a practical point of view, we predict that magnetism in the Rh-MgO(0 0 1) system is most likely to be found experimentally at reduced coverages and at low temperatures. © 2006 Elsevier B.V. All rights reserved.

  • 3.
    Chirita, Valeriu
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Münger, Peter
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Sundgren, J E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Reptation: a mechanism for cluster migration on (111) face-centered-cubic metal surfaces1999Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 436, nr 1-3, s. L641-L647Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Embedded-atom molecular-dynamics simulations were used to follow the diffusion dynamics of compact platinum clusters with up to 19 atoms on Pt(lll). The results reveal a cluster diffusion mechanism on (111) face-centered-cubic (fcc) surfaces involving successive shear translations of adjacent subcluster regions giving rise to reptation, a snake-like gliding motion. We show that for compact clusters with <7 atoms, this mechanism competes energetically with that of island diffusion through concerted motion. However, for cluster sizes of between 8 and similar or equal to 20 atoms, reptation becomes energetically favorable, especially for elongated clusters. Reptation is also shown to be an important migration mechanism for fractal (randomly ramified) and dendritic (symmetrically branched) islands. (C) 1999 Elsevier Science B.V. All rights reserved.

  • 4.
    Dannetun, Helen
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Lundström, Ingemar
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Petersson, L.-G.
    Dehydrogenation of acetylene and ethylene studied on clean and oxygen covered palladium surfaces1986Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 173, s. 148-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The interaction of acetylene and ethylene with a clean and oxygen covered Pd surface has been studied at a temperature of 473 K. The measurements were performed on a hydrogen sensitive Pd-MOS structure making it possible to obtain direct information on the dissociation of both hydrogen and oxygen containing species on a palladium surface. Desorption studies were also performed as well as ultraviolet photoelectron spectroscopy and work function measurements. The studies show that both acetylene and ethylene adsorb dissociatively at this temperature leaving mainly carbon on the surface. When an oxygen covered Pd surface is exposed to C2H2 or C2H4 carbon dioxide and water will be formed and desorb until the surface is oxygen free. In the case of acetylene the presence of preadsorbed oxygen does not block or prevent the C2H2 dissociation on the surface. For C2H4, a large preadsorbed oxygen coverage ( 0.45) will have an impeding effect on the dissociation. The CO2 desorption is oxygen coverage dependent contrary to the H2O desorption. This is due to the fact that hydrogen has a large lateral mobility on the surface while carbon has not. Both the CO2 and H2O reactions are, however, due to the same type of mechanisms.

  • 5.
    Dannetun, Helen
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Lundström, Ingemar
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Petersson, L.-G.
    Reactions between hydrocarbon and an oxygen covered palladium surface1988Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 193, s. 109-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Isothermic desorption studies where an oxygen covered polycrystalline Pd surface (T = 325–575 K) is exposed to small unsaturated hydrocarbons have been performed. The studied gases were acetylene, propene, propadiene, propyne, butene, butadiene, butyne, and also for comparison hydrogen. Electron energy loss spectroscopy (EELS) was available for adsorbate studies and a hydrogen sensitive Pd-MOS structure was used as a sample. The temperature limit for total dissociation is observed to decrease slightly for an oxygen covered surface compared to the clean surface. On an oxygen covered surface the dissociation is complete above 400 K and the reaction products are H2O, CO2, and adsorbed C. Varying the adsorption temperature, the carbon dioxide production is not detectable at room temperature, where all carbon is adsorbed and only water is formed, but increases to reach a constant level above 475 K. For temperatures above 400 K the licking coefficient is close to unity and there is no blocking due to preadsorbed oxygen (as there is for H2). Both the water and carbon dioxide formations are of Langmuir-Hinshelwood type but while the H2O desorption rate is found to depend only on impinging hydrocarbon flux the CO2 desorption rate depends also on the oxygen coverage.

  • 6.
    Dannetun, Helen
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Söderberg, Dennis
    Lundström, Ingemar
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Petersson, L.-G.
    The H2-O2 reaction on palladium studied over a large pressure range: Independence of the microscopic sticking coefficients on surface condition1985Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 152/153, s. 559-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied the H2---O2 reaction on Pd over a large pressure range by letting the reaction take place on the Pd gate of a Pd-MOS structure. By measuring shifts in the capacitance versus voltage (C(V)) curve of the structure, the variation of the “free” hydrogen atom concentration can be monitored during the reaction. By combining these results with surface potential measurements and with photoelectron spectroscopy, we find a critical ratio of 0.4 where the surface turns from being oxygen dominated to being hydrogen dominated. The critical ratio is independent of the absolute pressures and of surface condition and shows no significant temperature dependence in the temperature range 50–200°C. This implies that hydrogen and oxygen have similar sticking coefficients at both clean and technical Pd surfaces. The conclusion is drawn that hydrogen (and oxygen) dissociation on Pd is a property of the Pd atom or cluster of Pd atoms and is not critically dependent on any long-range order parameter such as the surface electronic density of states.

  • 7.
    Dannetun, Helen
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Wilzén, L.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Petersson, L.-G.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    The study of alcohol induced hydrogen permeation in a catalytic membrane reactor1996Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 357, s. 804-808Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied dehydrogenation and subsequent permeation of hydrogen from some small alcohols and hydrocarbons over a 20 μm thin Pd membrane at temperatures between 523 and 623 K. It is only for the smaller alcohols that significant amounts of hydrogen permeate the membrane. An addition of oxygen in the alcohol supply is needed to prevent a slow quenching of the permeation. The ratio of oxygen to alcohol is critical. For the right balance between methanol and oxygen permeation is very effective, and comparable to permeation caused by pure hydrogen. Studies of CH3OD and C2H5OD further show that the permeation is dependent on the hydrogen origin, i.e. the methyl and hydroxyl hydrogen have different reaction pathways and permeation probabilities.

  • 8.
    Edwards, NV
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Järrendahl, Kenneth
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Aspnes, DE
    NC State University, Box 8202, Raleigh, NC 26795, USA.
    Robbie, K
    NC State University, Box 8202, Raleigh, NC 26795, USA.
    Powell, GD
    NC State University, Box 8202, Raleigh, NC 26795, USA.
    Cobet, C
    Institut für Festkoeperphysik, Sekr. PN6-1, Technische Universität Berlin, Berlin, Germany.
    Esser, N
    Institut für Festkoeperphysik, Sekr. PN6-1, Technische Universität Berlin, Berlin, Germany.
    Richter, W
    Institut für Festkoeperphysik, Sekr. PN6-1, Technische Universität Berlin, Berlin, Germany.
    Madsen, LD
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Real-time assessment of selected surface preparation regimens for 4H-SiC surfaces using spectroscopic ellipsometry2000Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 464, nr 1, s. L703-L707Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spectroscopic ellipsometry (SE) was used to assess the removal of overlayer material from 4H-SiC (0001) and (0001) [Si- and C-face] surfaces in real time and, in particular, the critical final step of an otherwise standard RCA cleaning regimen commonly used to prepare SiC surfaces for contact formation. The treatments selected [buffered hydrofluoric acid (HF), concentrated HF, and dilute HF] removed 4-40 Angstrom of effective SiO2 overlayer thickness from these surfaces. The concentrated HF treatment yielded the best surface, i.e. that with the most abrupt transition region between bulk and surface and with the most oxide material removed. A fourth treatment regimen (sequential application of methanol, water, and 5% HF in methanol) was also developed for comparison with the full RCA clean. (C) 2000 Elsevier Science B.V. All rights reserved.

  • 9.
    Erdtman, Edvin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Kemi. Linköpings universitet, Tekniska fakulteten.
    Andersson, Mike
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad sensorvetenskap. Linköpings universitet, Tekniska fakulteten.
    Lloyd Spetz, Anita
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad sensorvetenskap. Linköpings universitet, Tekniska fakulteten.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Kemi. Linköpings universitet, Tekniska fakulteten.
    Simulations of the thermodynamics and kinetics of NH3 at the RuO2 (110) surface2017Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 656, s. 9s. 77-85Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ruthenium(IV)oxide (RuO2) is a material used for various purposes. It acts as a catalytic agent in several reactions, for example oxidation of carbon monoxide. Furthermore, it is used as gate material in gas sensors. In this work theoretical and computational studies were made on adsorbed molecules on RuO2 (110) surface, in order to follow the chemistry on the molecular level. Density functional theory calculations of the reactions on the surface have been performed. The calculated reaction and activation energies have been used as input for thermodynamic and kinetics calculations. A surface phase diagram was calculated, presenting the equilibrium composition of the surface at different temperature and gas compositions. The kinetics results are in line with the experimental studies of gas sensors, where water has been produced on the surface, and hydrogen is found at the surface which is responsible for the sensor response.

  • 10.
    Eriksson, Mats
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Kemiska och optiska sensorsystem. Linköpings universitet, Tekniska fakulteten.
    Ekedahl, Lars-Gunnar
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan. Tekniska högskolan.
    The catalytic oxidation of CO on polycrystalline Pd: Experiments and kinetic modelling1998Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 412/413, s. 430-440Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The catalytic oxidation of CO on a thin, polycrystalline Pd film has been studied. Even though the Pd film is expected to be dominated by (111) facets, some distinct differences compared to single crystalline Pd(111) are observed. A kinetic model for the CO oxidation reaction is presented. It gives good agreement with experiments, both in terms of CO2 reaction probability and CO coverage during reaction conditions. The model assumes a random distribution of the adsorbates, an activation energy for the reaction that decreases with increasing CO coverage, as well as a CO sticking coefficient that in a temperature dependent fashion depends on the oxygen coverage. Single crystal data available from the literature (initial sticking coefficients and heats of adsorption) were mainly used as input parameters. Thus, the model might also be a useful starting point when modeling the catalytic oxidation of CO on single crystal surfaces.

  • 11.
    Eriksson, Mats
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Kemiska och optiska sensorsystem. Linköpings universitet, Tekniska fakulteten.
    Petersson, Lars-Gunnar
    Spillover of hydrogen, oxygen and carbon monoxide in oxidation reactions on SiO2 supported Pd1994Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 311, nr 1-2, s. 139-152Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Oxidation of H2 and CO on large, oxygen preexposed Pd islands supported on SiO2, has been investigated in the temperature range 323 ⩽, T ⩽ 523 K. The results have been compared with the corresponding reactions on a polycrystalline Pd film. A maximum reactive sticking coefficient of 0.9 for H2 and an initial sticking coefficient for O2 of 0.8 on both structures is concluded. The maximum reactive sticking coefficient for CO is 0.85 on the film and apparently larger than unity on the island structure. The results obtained from the island structure can be rationalized if O2 and H2 dissociate on the Pd islands and have the possibility to spillover onto the oxide, while CO adsorbs and reacts both on the Pd islands and on the oxide. Spillover of oxygen occurs in a precursor state and is irreversible with an apparent activation energy of 0.1 eV for the forward reaction.

  • 12.
    Fahlman, Mats
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi.
    Salaneck, William R
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi.
    Surfaces and interfaces in polymer-based electronics2002Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 500, nr 1-3, s. 904-922Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Research on electronics applications such as light-emitting devices for flat-panel displays, transistors, sensors and even solid state lasers based on conducting polymers is presently under way and in some cases has reached the stage of prototype production. The mechanisms for charge injection and conduction in these materials are being studied, as are the physics of luminescence and its quenching. Lately, research into controlling film morphology through self-organizing techniques also has gained interest. Though the present interest in conducting polymers mainly concerns the pristine semiconducting state, doped conducting polymers are also studied for potential use in many applications. In this paper, we present an overview of some of the central issues in surface and interface science in the field, as well as provide our view on what may lie ahead in the future. Specifically, the importance of metal/polymer, polymer/metal and polymer/polymer interfaces is addressed. We illustrate these using polymer-based light-emitting devices, though the same type of issues appear in other polymer-based applications such as transistors and solar cells. © 2001 Elsevier Science B.V. All rights reserved.

  • 13.
    Fornander, H.
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Dannetun, Helen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Ekedahl, L.-G.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    A comparison of the CO and D2 oxidation reactions on Pd supported on MgO(100), MgO(110) and MgO(111)1999Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 440, nr 3, s. 375-386Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Oxidation of D2 and CO on oxygen pre-exposed 200 nm thick Pd films, epitaxially grown on MgO(100), MgO(110) and MgO(111), has been investigated in the temperature range 100–300°C. Oxygen initial sticking coefficients have been determined to be close to 1 for the 100 and 110 films, and around 0.8 for the 111 film. The sticking coefficient and reactive sticking coefficient for CO oxidation on Pd/MgO(100) is also close to 1, and the maximum reactive sticking coefficient for hydrogen oxidation is determined to be around 0.9 at temperatures above 200°C. It is shown that the reactivities for the different surfaces vary strongly with surface and oxygen coverage, and the consequence of this for supported particle catalysts is pointed out.

  • 14.
    Fornander, H.
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Ekedahl, L.-G.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Dannetun, Helen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Structural effects of supported Pd particles in D2 and CO oxidation experiments1999Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 441, nr 2-3, s. 479-492Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the temperature range 100–300°C, isothermic D2 and CO titration experiments have been performed on oxygen pre-exposed 1.5, 4, 20 and 200 nm thick Pd films, epitaxially cube-on-cube grown on MgO(100). The oxygen pre-exposures varied from 0.2 to 150 L. The three thinnest films consisted of faceted particles, mainly bounded by Pd(111) and Pd(100) surfaces, while the 200 nm sample was a continuous, flat Pd(100) film with atomic steps. Atomic force microscopy demonstrated that the titration experiment did not affect the structure of the (large) Pd particles in the 20 nm film. The reaction behavior of the 1.5 nm film can be understood by assuming that the film consists of (111)-bounded Pd particles, where O2 and D2 dissociate and spill over to the oxide support, whereas CO adsorbs and reacts both on the Pd and on the oxide. The CO oxidation thus occurs in parallel on Pd and on MgO, while the D2 oxidation is sequential, first occurring on the Pd and then on the MgO. To explain the D2O desorption curves for the 4 and 20 nm films, spillover to the MgO support as well as reactions on the Pd(111) and Pd(100) facets have to be taken into account. The greater the oxygen pre-exposure, the higher the probability that the D2 molecules dissociate primarily on the Pd(111) surfaces.

  • 15.
    Gauthier, Y.
    et al.
    Institut Néel, UPR 2940 - CNRS, 25 av. des Martyrs, 38042 Grenoble, France.
    Zasada, I.
    Solid State Physics Department, University of Lodz, ul. Pomorska 149/153, 90-236 Lodz, Poland.
    De, Santis M.
    De Santis, M., Institut Néel, UPR 2940 - CNRS, 25 av. des Martyrs, 38042 Grenoble, France.
    Langlais, V.
    Institut Néel, UPR 2940 - CNRS, 25 av. des Martyrs, 38042 Grenoble, France, Universitat Autonoma de Barcelona, Departamento de Fisica, 08193 Bellaterra, Barcelona, Spain.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Surface structure and composition of the missing-row reconstruction of VC0.8(1 1 0): A LEED, GIXRD and photoemission study2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 16, s. 3383-3394Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Low energy electron diffraction, grazing incidence X-ray diffraction and photoemission were used to decipher the detailed structural arrangement and chemical composition of the surface region of a transition metal carbide, VC0.8(1 1 0). In agreement with previous scanning tunneling microscopy (STM) studies, we find that the surface reconstructs with a ridge-and-valley grating structure along the [1 over(1, ¯) 0] direction resulting from {0 0 1} faceting for the (3 × 1) and the (4 × 1) phases. Both superstructures terminate on the vacuum side with a nearly stoïchiometric VC region due to C segregation, in contrast with the conclusions drawn from this previous STM study. However, the present experiments clearly show that these phases are metastable, and slow cooling results in a (1 × 1) surface, which is highly C depleted, similarly to the (1 0 0) face. © 2007 Elsevier B.V. All rights reserved.

  • 16. Glans, P.-A.
    et al.
    Balasubramanian, T.
    MAX-Lab, Lund University, S-221 00, Lund, Sweden.
    Syväjärvi, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Johansson, Leif
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Core level and valence band photoemission study of the (1 1 1) and (1¯ 1¯ 1¯) surfaces of 3C-SiC2001Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 470, nr 3, s. 284-292Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A core level and valence band photoemission study of thick 3C-SiC(1 1 1) and 3C-SiC(1¯ 1¯ 1¯) epilayers grown by sublimation epitaxy is reported. The as introduced samples show threefold 1×1 low-energy electron diffraction patterns. For the Si face v3 and 6v3 reconstructed surfaces develop after in situ heating to 1100 °C and 1300 °C, respectively. For the C face a 3×3 reconstruction form after heating to 980 °C. A semiconducting behavior is observed for the v3 and 3×3 reconstructed surfaces while the 6v3 reconstruction show a Fermi edge and thus a metallic-like behavior. The surface state on the v3 surface is investigated and found to have ?1 symmetry and a total band width of 0.10 eV within the first surface Brillouin zone. For the Si2p and C 1s core levels binding energies and surface shifted components are extracted and compared to earlier reported results for 6H- and 4H-SiC.

  • 17. Glans, P.-A.
    et al.
    Johansson, Leif
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    SiC(0001)v3×v3 surface state2000Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 465, nr 1-2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An angle resolved photoemission study of the surface state on the 6H-SiC(0001) v3×v3 surface is reported. The symmetry of the surface state is determined and effects induced after oxygen and sodium exposures are investigated. The periodicity of the surface dispersion is investigated in two different azimuthal directions. The expected v3×v3 periodicity of a Mott-Hubbard ground state was not observed when going outside the first v3×v3 Surface Brillouin Zone.

  • 18.
    Hugosson, H.W.
    et al.
    Department of Physics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden, Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, S-100 44 Stockholm, Sweden.
    Eriksson, O.
    Department of Physics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden.
    Jansson, U.
    Department of Materials Chemistry, Ångström Laboratory, Uppsala University, S-751 21 Uppsala, Sweden.
    Abrikosov, Igor
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Surface segregation of transition metal impurities on the TiC(1 0 0) surface2005Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 585, nr 1-2, s. 101-107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The segregation energies of 3d (Sc-Cu), 4d (Y-Ag) and 5d (La-Au) transition metal impurities on the (1 0 0) surface of TiC have been obtained using first-principles electronic structure calculations. The results are in agreement with available experimental data and show that the difference in atomic size between the impurity and host species, as well as the difference in surface energies determines if the impurity will segregate towards the surface or not. The results indicate that the difference in size is the dominant factor for the trends in segregation of transition metal impurities towards the (1 0 0) surface of TiC. © 2005 Elsevier B.V. All rights reserved.

  • 19.
    Hugosson, H.W.
    et al.
    Uppsala University, and KTH.
    Eriksson, O.
    Uppsala University.
    Jansson, U.
    Uppsala University.
    Ruban, A.V.
    Technical University of Denmark.
    Souvatzis, P.
    Uppsala University.
    Abrikosov, Igor
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Surface energies and work functions of the transition metal carbides2004Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 557, nr 1-3, s. 243-254Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have performed an ab initio study of the surface energies, surface electronic structures and work functions for the (1 0 0) surface of the, existent and hypothetical, cubic 3d (Sc-Cu), 4d (Zr-Ag) and 5d (La-Au) transition metal carbides. The calculated surface energies have been compared to predictions using a so-called bond-cutting model and a model based on the so-called bonding energies. The absolute values and rough trends of the surface energies are fairly well predicted within the simple bond-cutting model, as compared to fully self-consistent calculations, while both trends and absolute values are well reproduced within the bonding energy model. The electronic structure (densities of states) of the transition metal carbides at the surface and in the bulk have been calculated. The trends are discussed in relation to the behavior of the surface energy and the work function across the series. © 2004 Elsevier B.V. All rights reserved.

  • 20. Jemander, S.T.
    et al.
    Lin, N.
    Kern Department, Max-Planck-Institute FKF, 70569, Stuttgart, Germany.
    Zhang, Hanmin
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Uhrberg, Roger
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Hansson, Göran
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    STM study of the surface defects of the (v3×v3)-Sn/Si(1 1 1) surface2001Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 475, nr 1-3, s. 181-193Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The (v3×v3)-Sn/Si(1 1 1) surface has been studied with scanning tunneling microscopy (STM) and Auger electron spectroscopy, and it is found that it contains basically five different types of defects originating from substitutional atoms and vacancies. The influence the defects have on their immediate neighbourhood is investigated and found to extend to the third nearest (v3×v3) adatom neighbour. Close to some defect constellations, a very local (3×3) periodicity in the apparent height in the STM images is found. This periodicity is shown to be a linear superposition of the perturbations generated by the individual defects in the constellations. The superposition of the height modulation is accurate and linear for a wide range of tip biases, as for combinations of different types of defects. Its linearity is explained in terms of small perturbations in the surface electronic structure. We also provide an explanation why the linearity breaks down when large perturbations are probed with small tip biases.

  • 21.
    Johansson, Leif
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Eickhoff, Th.
    Drube, W.
    A comparative photoemission study of polar and nonpolar SiC surfaces oxidized in N2O2004Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 552, nr 1-3, s. 251-259Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Photoemission studies of oxidized SiC samples grown ex situ in N 2O, at a temperature of 900 °C, on the (0001), (0001̄), (112̄0) and (101̄0) surfaces are reported. Angle resolved data from the Si 1s and Si 2p core levels and the Si KL2,3L2,3 Auger transitions are analyzed and compared to data from a sample grown in O2 on the (0001) surface. The results show oxide growth and no oxy-nitride formation. The growth rate is found to be smallest for the Si-terminated (0001) surface and highest for the nonpolar (101̄0) surface. The presence of two oxidation states, Si+4 and a suboxide, are required to explain and model recorded Si 1s, Si 2p and Si KLL spectra. The SiO2 shift is found to be smaller on the (0001) surface than on the other three surfaces, which is attributed to an oxide thickness dependence of the shift. A layer attenuation model describes satisfactorily the intensity variations observed in the core level components versus electron emission angle when assuming the suboxide at the interface. Estimates made of the thickness of the oxide layers show that the oxidation rate for the (0001) surfaces is about half of that for the (101̄0) surface and that the oxidation rate for the (112̄0) and (0001̄) surfaces are similar but somewhat smaller than for the (101̄0) surface. The amount of suboxide is found to be smaller on the nonpolar than on the polar surfaces. © 2004 Elsevier B.V. All rights reserved.

  • 22.
    Johansson, Leif
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Virojanadara, Chariya
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Eickhoff, Th.
    Institut für Experimentalphysik, Universität Hamburg, D-22761 Hamburg, Germany.
    Drube, W.
    Hamburger Synchrotronstrahlungslabor, Deutschen Elektronen-Synchrotron, D-22603 Hamburg, Germany.
    Properties of the SiO2/SiC interface investigated by angle resolved studies of the Si 2p and Si 1s levels and the Si KLL Auger transitions2003Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 529, nr 3, s. 515-526Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Angle resolved photoemission studies of the Si 2p and Si 1s core levels and the Si KL2,3L2,3 Auger transitions from SiO2/SiC samples are reported. Most samples investigated were grown in situ on initially clean and well ordered v3 × v3 reconstructed 4H-SiC(0 0 0 1) surfaces but some samples were grown ex situ using a standard dry oxidation procedure. The results presented cover samples with total oxide thicknesses from about 5 to 118 Å. The angle resolved data show that two oxidation states only, Si+1 and Si+4, are required to explain and model recorded Si 2p, Si 1s and Si KLL spectra. The intensity variations observed in the core level components versus electron emission angle are found to be well described by a layer attenuation model for all samples when assuming a sub-oxide (Si2O) at the interface with a thickness ranging from 2.5 to 4 Å. We conclude that the sub-oxide is located at the interface and that the thickness of this layer does not increase much when the total oxide thickness is increased from about 5 to 118 Å. The SiO2 chemical shift is found to be larger in the Si 1s level than in the Si 2p level and to depend on the thickness of the oxide layer. The SiO2 shift is found to be fairly constant for oxides less than about 10 Å thick, to increase by 0.5 eV when increasing the oxide thickness to around 25 Å and then to be fairly constant for thicker oxides. An even more pronounced dependence is observed in the Si KLL transitions where a relative energy shift of 0.9 eV is determined. The relative final state relaxation energy dR(2p) is determined from the modified Auger parameter. This yields a value of dR(2p) = -1.7 eV and implies, for SiO2/SiC, a "true" chemical shift in the Si 2p level of only ˜0.4 eV for oxide layers of up to 10 Å thick. © 2003 Elsevier Science B.V. All rights reserved.

  • 23.
    Karlsson, Fredrik
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Holtz, Per-Olof
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Moskalenko, Evgenii
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Monemar, Bo
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Schoenfeld, W.V.
    Garcia, J.M.
    Petroff, P.M.
    Effective tuning of the charge-state of single In(Ga)As/GaAs quantum dots by below barrier band gap excitation2003Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 532-535, s. 843-847Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The existence of a well-defined threshold energy, crucial for the charging of quantum dots (QDs), positioned between the barrier band gap and the wetting layer ground state is demonstrated. Optical excitation with energies above this threshold populates the QDs with extra electrons. The origin of the threshold is discussed in terms of acceptors in the GaAs barrier. ⌐ 2003 Elsevier Science B.V. All rights reserved.

  • 24.
    Karlsson, P.G.
    et al.
    Department of Physics, Uppsala University, Box 530, SE-75121 Uppsala, Sweden.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Richter, J.H.
    Department of Physics, Uppsala University, Box 530, SE-75121 Uppsala, Sweden.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Blomquist, J.
    Chemical Physics, Lund University, Box 118, SE-22100 Lund, Sweden.
    Uvdal, P.
    Chemical Physics, Lund University, Box 118, SE-22100 Lund, Sweden.
    Sandell, A.
    Department of Physics, Uppsala University, Box 530, SE-75121 Uppsala, Sweden.
    Ultrathin ZrO2 films on Si-rich SiC(0 0 0 1)-(3 × 3): Growth and thermal stability2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 11, s. 2390-2400Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The growth and thermal stability of ultrathin ZrO2 films on the Si-rich SiC(0 0 0 1)-(3 × 3) surface have been explored using photoelectron spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The films were grown in situ by chemical vapor deposition using the zirconium tetra tert-butoxide (ZTB) precursor. The O 1s XAS results show that growth at 400 °C yields tetragonal ZrO2. An interface is formed between the ZrO2 film and the SiC substrate. The interface contains Si in several chemically different states. This gives evidence for an interface that is much more complex than that formed upon oxidation with O2. Si in a 4+ oxidation state is detected in the near surface region. This shows that intermixing of SiO2 and ZrO2 occurs, possibly under the formation of silicate. The alignment of the ZrO2 and SiC band edges is discussed based on core level and valence PES spectra. Subsequent annealing of a deposited film was performed in order to study the thermal stability of the system. Annealing to 800 °C does not lead to decomposition of the tetragonal ZrO2 (t-ZrO2) but changes are observed within the interface region. After annealing to 1000 °C a laterally heterogeneous layer has formed. The decomposition of the film leads to regions with t-ZrO2 remnants, metallic Zr silicide and Si aggregates. © 2007 Elsevier B.V. All rights reserved.

  • 25. Kihlgren, T.
    et al.
    Balasubramanian, T.
    Wallden, L.
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    K/graphite: Uniform energy shifts of graphite valence states2006Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, nr 5, s. 1160-1164Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ultra-thin graphite overlayers prepared by heating SiC crystals can give highly resolved valence band photoemission spectra. This is exploited to monitor K deposition induced energy shifts of graphite valence band states. States near the corners of the Brillouin zone, responsible for the semimetal character of graphite, are observed to show shifts that are nearly equal to the shifts of the uppermost filled σ state and of an empty state 7.6 eV above E F. The results give credence to the rigid band shift model often used to discuss the electronic structure and charge transfer for graphite ad- and absorption systems. © 2006 Elsevier B.V. All rights reserved.

  • 26.
    Larsson, Mats
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Elfving, Anders
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Holtz, Per-Olof
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Hansson, Göran
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Ni, Wei-Xin
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Photoluminescence study of Si/Ge quantum dots2003Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 532-535, s. 832-836Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ge quantum dots embedded in Si are studied by means of photoluminescence (PL). The temperature dependent PL measurements show two different types of recombination processes related to the quantum dots. We ascribe a peak near 0.80 eV to the spatially indirect recombination in the type-II band lineup where the electron is located in the surrounding Si close to the interface and the hole in the Ge dot. Furthermore, a peak near 0.85 eV is attributed to the spatially direct recombination. We observe a transition from the spatially indirect to the spatially direct recombination as the temperature is increased. The measurements also show an up-shift of the Ge quantum dot emission energy with increasing excitation power density. The blueshift is primarily ascribed to an enhanced confinement of the electron associated with the increased band bending at the type-II Si/Ge interface at high carrier densities. Comparison is made with results, derived from measurements on uncapped samples. For these uncapped samples, no energy shifts due to excitation power or temperatures are observed in contrast to the capped samples. ⌐ 2003 Elsevier Science B.V. All rights reserved.

  • 27.
    Maleshlijski, S.
    et al.
    Ruhr University of Bochum, Germany; Karlsruhe Institute Technology, Germany; Heidelberg University, Germany.
    Sendra, G. H.
    Ruhr University of Bochum, Germany; Karlsruhe Institute Technology, Germany; Heidelberg University, Germany.
    Aldred, N.
    Newcastle University, England.
    Clare, A. S.
    Newcastle University, England.
    Liedberg, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Molekylär fysik. Linköpings universitet, Tekniska fakulteten. Nanyang Technology University, Singapore.
    Grunze, M.
    Karlsruhe Institute Technology, Germany; Heidelberg University, Germany.
    Ederth, Thomas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Molekylär fysik. Linköpings universitet, Tekniska fakulteten.
    Rosenhahn, A.
    Ruhr University of Bochum, Germany; Karlsruhe Institute Technology, Germany; Heidelberg University, Germany.
    Imaging SPR combined with stereoscopic 3D tracking to study barnacle cyprid-surface interactions2016Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 643, s. 172-177Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Barnacle larvae (cyprids) explore surfaces to identify suitable settlement sites. This process is selective, and cyprids respond to numerous surface cues. To better understand the settlement process, it is desirable to simultaneously monitor both the surface exploration behavior and any close interactions with the surface. Stereoscopic 3D tracking of the cyprids provides quantitative access to surface exploration and pre-settlement rituals. Imaging surface plasmon resonance (SPR) reveals any interactions with the surfaces, such as surface inspection during bipedal walking and deposition of temporary adhesives. We report on a combination of both techniques to bring together information on swimming behavior in the vicinity of the interface and physical interactions of the cyprid with the surface. The technical requirements are described, and we applied the setup to cyprids of Balanus amphitrite. Initial data shows the applicability of the combined instrument to correlate exploration and touchdown events on surfaces with different chemical termination. (C) 2015 Published by Elsevier B.V.

  • 28.
    Muhammad Sohail, Hafiz
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Uhrberg, Roger
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Umklapp induced surface band structure of Ag/Ge(111)6 x 62015Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 635, s. 55-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study focuses on the electronic structure of a 6 x 6 surface which is formed by 0.2 monolayer of Ag on top of the Ag/Ge(111) root 3 x root 3 surface. The 6 x 6 periodicity was verified by low energy electron diffraction. Angle resolved photoelectron spectroscopy was employed to study the electronic structure along the (Gamma) over bar-(M) over bar-(Gamma) over bar and (Gamma) over bar-(K) over bar-(M) over bar high symmetry lines of the 6 x 6 surface Brillouin zone. There are six surface bands in total. Out of these, three were found to be related to the 6 x 6 phase. The surface band structure of the 6 x 6 phase is significantly more complex than that of the,root 3 x root 3 surface. This is particularly the case for the uppermost surface band structure which is a combination of a surface band originating from the underlying root 3 x root 3 surface and umklapp scattered branches of this band. Branches centered at neighboring 6 x 6 SBZs cross each other at an energy slightly below the Fermi level. An energy gap opens up at this point which contains the Fermi level. The complex pattern of constant energy contours has been used to identify the origins of various branches of the surface state dispersions. (C) 2014 Elsevier B.V. All rights reserved.

  • 29.
    Münger, Peter
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Chirita, Valeriu
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Sundgren, J E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Adatom-induced diffusion of two-dimensional close-packed Pt-7 clusters on Pt(111)1996Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 355, nr 1-3, s. L325-L330Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular dynamics simulations were used to follow the dynamics of the motion of hexagonal Pt heptamers on Pt(111). Close packed Pt-7 clusters on fee sites were found to be very stable structures with reconfiguration or translation events occurring only rarely over simulation times >30 ns at 1000 K. The adsorption of a single adatom on the cluster surface, however, induced rapid intracluster bond breaking, reconfiguration, the introduction of stacking faults, and greatly enhanced cluster diffusion rates. Cluster migration occurred primarily through sequences of individual atom and concerted dimer jumps, but concerted cluster motion was also observed. The adatoms eventually descended to the terrace, predominantly through push-out/exchange reactions with cluster atoms at B edges.

  • 30.
    Münger, Peter
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Chirita, Valeriu
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik.
    Hultman, Lars
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik.
    Greene, J.E.
    Adatom/vacancy interactions and interlayer mass transport in small two-dimensional Pt clusters on Pt(1 1 1)2003Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 539, nr 1-3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use embedded-atom molecular dynamics simulations to follow the dynamics of adatoms, vacancies, and adatom/vacancy pairs on two-dimensional hexagonal Pt19 clusters on Pt(1 1 1) surfaces at 1000 K. All configurations are found to be quite stable and have essentially the same migration mobilities as compact hexagonal clusters. However, the presence of a single vacancy dramatically decreases the lifetime of an adatom on the cluster by a factor of three. This occurs primarily through an enhancement of the rate of push-out/exchange reactions at the outer cluster edge resulting from vacancy-induced softening of edge atom bonds. Overall, adatoms in the presence of vacancies descend to the terrace via vacancy filling 10% of the time, and through reactions with outer cluster edges the remaining 90%. Direct vacancy filling mechanisms are analogous to, and have similar activation energies with, those at outer cluster edges: adatom hopping over descending steps and push-out/exchange reactions. © 2003 Elsevier B.V. All rights reserved.

  • 31.
    Neidhardt, Jörg
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik.
    Högberg, Hans
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik.
    Hultman, Lars
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik.
    Arrhenius-type temperature dependence of the chemical desorption processes active during deposition of fullerene-like carbon nitride thin films2004Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 569, nr 1-3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The chemical desorption of carbon and nitrogen-containing species from the growth surface was investigated for the deposition of fullerene-like carbon nitride (FL CNx) thin solid films by reactive magnetron sputtering of a carbon target in a N2-containing atmosphere. The desorption of mainly C2N2 was suppressed by decreasing the substrate temperature for various N2 fractions in the discharge stepwise from 873 K down to cryogenic temperatures of 153 K. This approach enabled us to quantify the film-forming flux by determining the carbon and nitrogen incorporation rates by elastic recoil detection. The incorporation of both, carbon and nitrogen, was found to increase substantially at lower substrate temperatures, whereas this effect is most pronounced for the higher N 2 fractions. In turn, a modified Arrhenius-type rate equation was applied to extrapolate the total flux of the elements as well as their respective activation energies of desorption for the series at higher N 2 fractions. The reasonable fit indicates that the desorption process is mainly determined by the surface diffusion rate of adsorbed C xNy species as well as their structure and total number. The extrapolated fluxes of carbon and nitrogen atoms arriving as preformed species at the growth surface scaled strongly with the availability of N 2 in the discharge, while the obtained activation energies of 0.05-0.17 eV point towards a saturation of the process at elevated temperatures. Furthermore, the constant C/N ratio found in the film-forming flux leads to the notion that most of the nitrogen incorporated originates from preformed species instead of N atoms or ions. The FL structure evolution has to be seen as a sensitive interplay between the type and magnitude of preformed C xNy species in the deposition flux and the selectiveness of the preferential etching by means of the chemical desorption. © 2004 Elsevier B.V. All rights reserved.

  • 32. Nilsing, M
    et al.
    Lunell, S
    Persson, P
    Ojamäe, Lars
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi.
    Phosphonic acid adsorption at the TiO2 anatase (101) surface investigated by periodic hybrid HF-DFT computations,2005Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 582, s. 49-60Artikkel i tidsskrift (Fagfellevurdert)
  • 33.
    Näslund, Lars-Åke
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan. SLAC National Accelerator Lab, CA USA .
    Reaction kinetics for the oxygen hydrogenation process on Pt(111) derived from temperature-programmed XPS2013Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 618, s. 42-48Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Oxygen hydrogenation under ultra high vacuum conditions at the platinum surface was explored using temperature-programmed X-ray photoelectron spectroscopy. Through modeling of the oxygen consumption, information on the reaction kinetics was obtained indicating that the reaction rate of the oxygen hydrogenation process depends on the hydrogen diffusion and on the lifetime of hydroxyl intermediates. The reaction rate is, however, enhanced when an autocatalytic process stabilizes the hydroxyl intermediates through hydrogen bonding to neighboring water molecules. The overall activation energy for the hydrogenation of atomic oxygen to form water was determined to be 0.20 eV with a frequency factor of only 10(3) s(-1).

  • 34.
    Pedersen, Henrik
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Söderlind, Fredrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Petoral, Rodrigo M.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Sensorvetenskap och Molekylfysik. Linköpings universitet, Tekniska högskolan.
    Uvdal, Kajsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Sensorvetenskap och Molekylfysik. Linköpings universitet, Tekniska högskolan.
    Käll, Per-Olov
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Ojamäe, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Fysikalisk Kemi. Linköpings universitet, Tekniska högskolan.
    Surface interactions between Y2O3 nanocrystals and organic molecules—an experimental and quantum-chemical study2005Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 592, nr 1-3, s. 124-140Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The surface interactions between Y2O3 nanocrystals and the organic molecules formic acid, diethylene glycol (DEG), and tetramethoxy silane (TMOS), have been studied experimentally and by quantum chemical calculations with the intent to elucidate the chemisorption characteristics such as adsorbate vibrational spectra and adsorption structures. Nanocrystal synthesis was performed by a colloidal method based on polyols and by a rapid combustion method. The products were experimentally characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS).

    In the quantum chemical calculations, the B3LYP hybrid density functional ab initio method was used to study the chemisorption of formic acid, DEG and TMOS at the surface of Y12O18 clusters. From a comparison of calculated and experimental vibrational spectra, the binding mode for formic acid on Y2O3 was inferred to be of bridge or bidentate type. The XPS and FT-IR experiments showed that DEG is chemisorbed on the particle surface. The experimental IR spectra of DEG chemisorbed on Y2O3 were consistent with an adsorption mode where the hydroxyl groups are deprotonated according to the quantum-chemical computations. The adsorption energy is of the order of 370 kJ mol−1 for formic acid, 550 kJ mol−1 for DEG, and 60 kJ mol−1 for TMOS, according to the quantum chemical calculations.

  • 35. Petersson, L-G
    et al.
    Dannetun, Helen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Karlsson, S.-E.
    Lundström, Ingemar
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Hydrogen dissociation on clean and contaminated Pd studied with a Pd-MOS structure.1982Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 117, s. 676-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We show how a new combination of methods can be used in order to gain information on hydrogen dissociation on Pd and on its dependence on the electronic structure. With this method we can also detect changes in hydrogen pressure of about 1×10−11 Torr H2 corresponding to hydrogen coverages on the Pd surface of about 0.001 of a monolayer.

  • 36. Petersson, L.-G.
    et al.
    Dannetun, Helen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Lundström, Ingemar
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    The water-forming reaction on Pd1985Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 161, s. 77-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The water-forming reaction on Pd has been studied on a Pd---SiO2---Si (Pd-MOS) structure in the temperature range 323–473 K. The reaction is found to be of the Langmuir-Hinshelwood type with the formation of OH beeing rate limiting. Since the Pd-MOS structure works as a sensitive hydrogen detector unique information on the behaviour of hydrogen during this catalytic reaction has been obtained. The reaction can be described in a model where the hydrogen atoms on the Pd surface have a large temperature activated lateral mobility and with no evidence of beeing in hot precursor states. At T = 473 K this means that for oxygen coverages 0.01 monolayers all hydrogen adsorbed will also react with oxygen. For smaller oxygen coverages unreacted hydrogen will not initially desorb towards the vacuum but towards the internal Pd surface of the Pd-MOS structure. Futhermore, hydrogen adsorption is blocked by adsorbed oxygen. The sticking coefficient for hydrogen on the bare Pd surface is, however, close to one and only weakly temperature dependent. An effect giving rise to a hysteresis in the work function versus oxygen coverage curve during oxygen adsorption - desorption is also discussed.

  • 37. Petersson, L.-G.
    et al.
    Dannetun, Helen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Lundström, Ingemar
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik. Linköpings universitet, Tekniska högskolan.
    Water production on palladium in hydrogen-oxygen atmospheres1985Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 163, s. 273-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied the water production on Pd in various oxygen-hydrogen atmospheres in combination with work function measurements, photoelectron spectroscopy and hydrogen sensitive measurements on a Pd---SiO2---Si structure. The existence of a critical oxygen to hydrogen pressure ratio is confirmed. Above the critical ratio, the water production rate decreases with increasing oxygen pressure and increases with increasing hydrogen pressure. Below the critical ratio, the water production rate is proportional to the oxygen pressure and independent of the hydrogen pressure. These features, together with the variations in oxygen and hydrogen coverage, are described by a simple Langmuir-Hinshelwood model, assuming that hydrogen has a large lateral mobility and that both hydrogen and oxygen adsorption-dissociation is blocked by adsorbed oxygen.

  • 38.
    Sakamoto, K.
    et al.
    Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japen.
    Takeyama, W.
    Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
    Zhang, Hanmin
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Uhrberg, Roger
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    High-resolution Si2p core-level and low-energy electron diffraction studies of the Ca/Si(1 1 1)-(3 × 2) surface2003Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 532-535, s. 628-632Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated the surface structure of the Ca/Si(1 1 1)-(3 × 2) surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. Weak ×2 streaks were observed in LEED at 300 K. After cooling the sample to 100 K, ×2 spots, which originate from both (3 × 2) and c(6 × 2) periodicities, appeared. By considering the energy shift and intensity of each surface component observed in the Si2p core-level spectra, we conclude that the structure of the (3 × 2) surface is basically the same as that of the honeycomb-chain-channel model with a Ca coverage of 1/6 ML. Further, we propose that the weak ×2 streaks at 300 K result from thermally induced disorder. © 2003 Elsevier Science B.V. All rights reserved.

  • 39.
    Sakamoto, Kazuyuki
    et al.
    Graduate School of Advanced Integrated Science Chiba University, Japan.
    Eriksson, Johan
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Ueno, Nobuo
    Spectroscopy, Applied Physics Chiba University.
    Uhrberg, Roger
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Photoemission study of the thallium induced Si(111)-´`3x´`3 surface2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 22, s. 5258-5261Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated the surface electronic structure of the Tl induced Si (1 1 1) - (sqrt(3) × sqrt(3)) surface by using angle-resolved photoelectron spectroscopy. Three semiconducting surface states were observed in the gap of the bulk band projection. Of these three states, the one, whose binding energy is approximately 0.3 eV, hardly disperses. Regarding the two other states, we discuss their properties by comparing their dispersion behaviors with those of the surface states of the other group III metal (Al, Ga and In) induced (sqrt(3) × sqrt(3)) reconstructions. The split observed at the over(G, -) point and the smaller dispersion widths of these two states indicate that the origins of the surface states of the Tl induced (sqrt(3) × sqrt(3)) reconstruction are not the same as those of the Al, Ga and In induced (sqrt(3) × sqrt(3)) reconstructions. These results support the idea that the atomic structure of the Tl / Si (1 1 1) - (sqrt(3) × sqrt(3)) surface is different from that of the (sqrt(3) × sqrt(3)) reconstructions induced by other group III metals, which was proposed in the literature.

  • 40.
    Sangiovanni, Davide
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Edström, Daniel
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Petrov, Ivan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan. University of Illinois, Urbana, USA.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan. University of Illinois, Urbana, USA.
    Chirita, Valeriu
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Ab-initio and classical molecular dynamics simulations of N2 desorption from TiN(001) surfaces2014Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 624, s. 25-31Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ab initio molecular dynamics simulations based on density functional theory show that N adatoms are chemisorbed in threefold sites close to a N surface atom and between the two diagonally opposed neighboring Ti surface atoms on TiN(001). The most probable N adatom reaction pathway, even in the presence of nearby N adatoms, is for the N adatom and N surface atom pair to first undergo several exchange reactions and then desorb as a N2 molecule, resulting in a surface anion vacancy, with an activation barrier Edes of 1.37 eV and an attempt frequency Ades = 3.4 × 1013 s− 1. Edes is essentially equal to the N adatom surface diffusion barrier, Es = 1.39 eV, while As is only three to four times larger than Ades, indicating that isolated N adatoms migrate for only short distances prior to N2 desorption. The probability of N2 desorption via recombination of N adatoms on TiN(001) is much lower due to repulsive adatom/adatom interactions at separations less than ~ 3 Å which rapidly increase to ~ 2 eV at a separation of 1.5 Å. We obtain good qualitative and quantitative agreement with the above results using the modified embedded atom method potential to perform classical molecular dynamics simulations.

  • 41.
    Sangiovanni, Davide
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Edström, Daniel
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Petrov, Ivan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan. University of Illinois, Urbana, USA.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan. University of Illinois, Urbana, USA.
    Chirita, Valeriu
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Ti adatom diffusion on TiN(001): Ab initio and classical molecular dynamics simulations2014Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 627, s. 34-41Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ab initio and classical molecular dynamics (AIMD and CMD) simulations reveal that Ti adatoms on TiN(001) surfaces migrate between neighboring fourfold hollow sites primarily along in-plane less than100greater than channels. less than100greater than and less than110greater than single jumps, as well as less than100greater than double jump rates, obtained directly from MD runs as a function of temperature, are used to determine diffusion activation energies Ea, and attempt frequencies A, for the three preferred Ti adatom migration pathways on TiN(001). From transition rates Aexp[-Ea / (k(B)T)], we determine adatom surface distribution probabilities as a function of time, which are used to calculate adatom diffusion coefficients D(T). AIMD and CMD predictions are consistent and complementary. Using CMD, we investigate the effect on the adatom jump rate of varying the phonon wavelength degrees of freedom by progressively increasing the supercell size. We find that long-wavelength phonons significantly contribute to increasing adatom mobilities at temperatures less than= 600 K, but not at higher temperatures. Finally, by directly tracking the Ti adatom mean-square displacement during CMD runs, we find that Ti adatom jumps are highly correlated on TiN(001), an effect that yields lower D-s values (D-s(corr)) than those estimated from uncorrelated transition probabilities. The temperature-dependent diffusion coefficient is D-s(corr) (T) = (4.5 x 10(-4) Cm-2 s(-1)) exp[-0.55 eV / (k(B)T)].

  • 42.
    Sangiovanni, Davide
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Tasnadi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Petrov, Ivan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. University of Illinois, USA.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. University of Illinois, USA.
    Chirita, Valeriu
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    N and Ti adatom dynamics on stoichiometric polar TiN(111) surfaces2016Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 649, s. 72-79Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use molecular dynamics (MD) based on the modified embedded atom method (MEAM) to determine diffusion coefficients and migration pathways for Ti and N adatoms (Ti-ad and N-ad) on TiN(111). The reliability of the classical model-potential is verified by comparison with density functional theory (DFT) results at 0 K. MD simulations carried out at temperatures between 600 and 1800 K show that both Ti-ad and N-ad favor fcc surface sites and migrate among them by passing through metastable hcp positions. We find that N-ad species are considerably more mobile than Ti-ad on TiN(111); contrary to our previous results on TiN(001). In addition, we show that lattice vibrations at finite temperatures strongly modify the potential energy landscape and result in smaller adatom migration energies, E-a = 1.03 for Ti-ad and 0.61 eV for N-ad, compared to 0 K values E-aOK = 1.55 (Ti-ad) and 0.79 eV (N-ad). We also demonstrate that the inclusion of dipole corrections, neglected in previous DFT calculations, is necessary in order to obtain the correct formation energies for polar surfaces such as TiN(111). (C) 2016 Elsevier B.V. All rights reserved.

  • 43.
    Sohail, Hafiz Muhammad
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Uhrberg, Roger I. G.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Electronic and atomic structures of a Sn induced 3√3x3√3 superstructure on the Ag/Ge(111) √3x√3 surface2016Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 644, s. 29-33Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated sub-monolayer coverages of Sn on the Ag/Ge(111)  surface. It was found that ≈0.45 monolayer (ML) resulted in a new, well-defined, reconstruction with a periodicity. The periodic structure of the surface atoms was verified by low energy electron diffraction and scanning tunneling microscopy. The electronic structure was studied in detail using angle resolved photoelectron spectroscopy and core level spectroscopy at a temperature of 100 K. Several surface bands were identified and their dispersions are presented along the  and  high symmetry lines of the  surface Brillouin zone (SBZ). The  surface has a metallic character since there is a strong surface band crossing the Fermi level near -points coinciding with -points of the 1×1 SBZ. The Fermi contour of the metallic band showed a hexagonal shape in contrast to the circular shaped Fermi contour of the initial  surface. Both empty and filled state STM images showed a hexagonal arrangement of protrusions which show a local  periodicity and a superimposed modulation of the apparent heights with a  periodicity.

  • 44.
    Sohail, Hafiz Muhammad
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Uhrberg, Roger I. G.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Electronic and atomic structures of the Ag induced √3x√3 superstructure on Ge(111)2014Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 625, s. 23-29Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Ag/Ge(111) surface together with Ag/Si(111) constitutes a set of surfaces that is ideally suited for fundamental studies related to low dimensional physics. We here focus on the atomic and electronic structures of the two-dimensional superstructure induced by Ag on Ge(111), a surface that is significantly less studied than the Si counterpart. Extensive information on the surface band structure obtained by angle resolved photoelectron spectroscopy (ARPES) is presented, complemented by atomic information from scanning tunneling microscopy (STM). The results reveal new findings that are important for the understanding of the Ag induced structure, acting as a prototype for semiconductor/metal interfaces. i) We have identified a new occupied surface band near the -point of the surface Brillouin zone. ii) The Ag/Ge(111) surface exhibits a partially occupied surface band, S1, with a parabolic-like shape at Γ¯. At low temperature (≈ 100 K) this band splits into two bands, S1U and S1D. The identification of two bands is significantly different from the case of Ag/Si(111) for which just one band has been reported. Besides these specific results, our extensive ARPES study reveals four surface bands at room temperature (RT), while five surface bands were identified at ≈ 100 K (LT). Room temperature empty state STM images show, depending on the tunneling bias, both honeycomb and hexagonal periodicities which are consistent with the honeycomb chained trimer and the in-equivalent trimer models, respectively.

  • 45.
    Sohail, Hafiz Muhammad
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Uhrberg, Roger I. G.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Experimental studies of an In/Pb binary surface alloy on Ge(111)2016Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 649, s. 146-151Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, we present a binary In/Pb surface alloy on Ge(111) formed by evaporating0.85 monolayer (ML) of In on the Pb/Ge(111)  surface with 1.33 ML of Pb. A welldefined3×3 periodicity is formed after annealing at a temperature of ≈200 °C, as verified by bothlow energy electron diffraction (LEED) and scanning tunneling microscopy (STM). OverviewSTM images, obtained at 50 K, show a clear 3×3 periodicity. Detailed STM images reveal thatthe protrusions consist of atomic sized features with a local hexagonal arrangement. Each 3×3unit cell contains nine such features indicating a structure with 9 atoms per 3×3 cell. Based onangle resolved photoelectron spectroscopy (ARPES) data, we have identified five surface bandswithin the bulk band gap. Four of them cross the Fermi level leading to a metallic character of thesurface. The dispersions of these bands have been mapped in detail along the high symmetrydirections of the 3×3 surface Brillouin zone. Fermi contours, mapped in 2D k-space, showinteresting features. In particular, the occurrence of two differently rotated hexagon like contoursis discussed.

  • 46. Svedberg, EB
    et al.
    Jemander, TS
    Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden.
    Lin, N
    Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden.
    Erlandsson, Ragnar
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik.
    Hansson, Göran
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Birch, Jens
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik.
    Sundgren, JE
    Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden.
    Epitaxial growth of UHV magnetron sputtered Mo thin films on MgO(001) substrates, oxygen segregation and surface reconstructions1999Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 443, nr 1-2, s. 31-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Studies of epitaxial growth of Mo thin films on MgO(001) substrates by ultrahigh Vacuum (UHV) d.c. magnetron sputter deposition have shown independently by in situ low energy electron diffraction (LEED), scanning tunnelling microscopy (STM) and time-resolved in situ reflection high-energy electron diffraction (RHEED) measurements that oxygen is present on the Mo surface during the initial stages of growth. Oxygen induced reconstructions are only found for films thinner than similar to 50 nm, and it is shown that the oxygen originates from the MgO substrate. The oxygen is causing the growing film surface to continuously reconstruct with the (root 5 x root 5)R26 degrees 33', p(2 x 2) and c(2 x 2) structures indicating O coverages ranging from similar to 0.8-1.0 ML. STM measurements confirm earlier X-ray diffraction (XRD) and STM measurements of the (root 5 x root 5)R26 degrees 33' reconstruction and show for the first time STM images of the surface structures where p(2 x 2) and c(2 x 2) reconstructions are present. Based on our STM data we suggest surface models for the p(2 x 2) and c(2 x 2) reconstructions. The STM measurements also revealed surfaces randomly interspersed with apparent 2x2 'holes' not visible by techniques such as LEED due to their non-periodic nature. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

  • 47.
    Söderberg, Hans
    et al.
    Luleå University of Technology.
    Birch, Jens
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik.
    Hultman, Lars
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik.
    Odén, Magnus
    Luleå University of Technology.
    RHEED studies during growth of TiN/SiNx/TiN trilayers on MgO(001)2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, s. 2352-2356Artikkel i tidsskrift (Fagfellevurdert)
  • 48.
    Tholander, Christopher
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Tasnádi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Greene, Joseph E.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Effect of Al substitution on Ti, Al, and N adatom dynamics on TiN(001), (011), and (111) surfaces2014Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 630, s. 28-40Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Substituting Al for Ti in TiN(001), TiN(011), and N- and Ti-terminated TiN(111) surfaces has significant effects on adatom surface energetics which vary strongly with the adatom species and surface orientation. Here, we investigate Ti, Al, and N adatom surface dynamics using density functional methods. We calculate adatom binding and diffusion energies with both a nudged elastic band and grid-probing techniques. The adatom diffusivities are analyzed within a transition-state theory approximation. We determine the stable and metastable Ti, Al, and N binding sites on all three surfaces as well as the lowest energy migration paths. In general, adatom mobilities are fastest on TiN(001), slower on TiN(111), and slowest on TiN(011). The introduction of Al has two major effects on the surface diffusivity of Ti and Al adatoms. First, Ti adatom diffusivity on TiN(001) is significantly reduced near substituted Al surface atoms; we observe a 200% increase in Ti adatom diffusion barriers out of fourfold hollow sites adjacent to Al surface atoms, while Al adatom diffusivity between bulk sites is largely unaffected. Secondly, on TiN(111), the effect is opposite; Al adatoms are slowed near the substituted Al surface atom, while Ti adatom diffusivity is largely unaffected. In addition, we note the importance of magnetic spin polarization on Ti adatom binding energies and diffusion path. These results are of relevance for the atomistic understanding of Ti1-xAlxN alloy and Ti1-xAlxN/TiN multilayer thin-film growth processes.

  • 49.
    Virojanadara, Chariya
    et al.
    Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
    Hetzel, M.
    Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Choyke, W.J.
    Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, United States.
    Starke, U.
    Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
    Electronic and atomic structure of the 4 H-SiC (1 over(1, ¯) 0 2) -c (2 × 2) surface2008Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 602, nr 2, s. 525-533Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The (1 over(1, ¯) 0 2) orientated plane of hexagonal silicon carbide of the 4H polytype consists of a periodic arrangement of stripes with alternating bond configuration on a nanometer scale. The two stripe configurations of the bulk truncated surface have an atomic structure very close to the carbon-face SiC basal plane and the cubic SiC(1 0 0) surface, respectively. The structural and electronic properties of the c(2 × 2) reconstruction on the 4 H-SiC (1 over(1, ¯) 0 2) surface were investigated using photoemission spectroscopy (PES), scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). The core level photoemission spectra reveal two surface shifted Si2p components and one shifted C1s component in addition to the SiC bulk peaks. In accordance with the periodicity observed in LEED, atomically resolved STM micrographs show a c(2 × 2) arrangement of bright features which are accounted as Si adatoms. The electronic structure of this SiC (1 over(1, ¯) 0 2) -c (2 × 2) phase is experimentally determined by angle resolved PES studies of the valence band revealing four surface states. Based on the experimental observations and a comparison to similar phases on other SiC surfaces, a tentative surface model can be developed which consists of Si adatoms in so-called H3 sites on the basal-plane type stripes and carbon dimers in Si bridging configuration on the cubic stripes of the bulk truncated surface. © 2007 Elsevier B.V. All rights reserved.

  • 50.
    Virojanadara, Chariya
    et al.
    Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany.
    Hetzel, M.
    Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany.
    Riedl, C.
    Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany.
    Johansson, Leif I.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Choyke, W. J.
    Department of Physics and Astronomy, University of Pittsburgh, United States.
    Starke, U.
    Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany.
    Silicon adatom chains and one-dimensionally confined electrons on 4H-SiC(1-102): The (2x1) reconstruction2008Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 602, nr 22, s. 3506-3509Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic and atomic structure of the 4H-SiC surface was investigated. Photoemission data indicate that the surface contains about 2 Si layers on top of the bulk layers. Scanning tunneling microscopy images show that these adlayers are terminated by an ordered array of adatom chains separated by the unit cell size. An electronic surface state located at a binding energy of 0.8 eV shows one-dimensional confinement with dispersion only along the chains. Based on the experimental observations, a tentative (2 × 1) surface model is derived with the surface terminated by alternating chains of Si adatoms and Si dimers in between.

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