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  • 51.
    Li, Cui
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Institute of Chemical and Physical Processes, Italy.
    Monti, Susanna
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Institute of Chemistry of Organometallic Compounds, Italy.
    Li, Xin
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Rinkevicius, Zilvinas
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Carravetta, V.
    Theoretical study of para-nitro-aniline adsorption on the Au(111) surface2016Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 649, s. 124-132Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic structure, bonding properties and dynamics of para-nitro-aniline (PNA) adsorbed on the Au(111) surface for a sub-monolayer coverge have been investigated by density-functional theory (DFT) static calculations and quantum molecular dynamics simulations. Four main adsorption geometries have been identified by DFT energy optimization with the gradient corrected PBE functional and accounting for the role of the van del Waals (vdW) interaction. Quantum dynamics calculations starting from the four different structures have been performed at room temperature to estimate the relative stability of the adsorbates and the presence of barriers for their interconversion. Quantum simulations suggest that the most stable adsorption geometry at room temperature is that of PNA with a slightly distorted molecular plane almost parallel to the Au(111) surface. In a second less populated configuration the PNA molecule interacts with the substrate by its NO2 group while the molecular plane is orthogonal to the surface. The N 1s electron photoemission spectrum has been simulated for the identified adsorbate geometries and a measurable variation of the absolute and relative chemical shift for the two nitrogen atoms in comparison with the known values for PNA in gas phase is predicted.

  • 52. Li, H. N.
    et al.
    Wang, X. X.
    He, Sailing
    Ibrahim, K.
    Qian, H. J.
    Su, R.
    Zhong, J.
    Abbas, M. I.
    Hong, C. H.
    Electronic state of C-60 monolayer on Ag(111) before and after Yb intercalation2005Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 586, nr 01-3, s. 65-73Artikkel i tidsskrift (Fagfellevurdert)
  • 53.
    Lousada, Cláudio M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Johansson, Adam Johannes
    Korzhavyi, Pavel A.
    Molecular and dissociative adsorption of water at a defective Cu(110) surface2017Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 658, s. 1-8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We performed a density functional theory (DFT) investigation of the molecular and dissociative adsorption of water at the perfect Cu(110) and at a defective Cu surface that provides a broad spectrum of adsorption sites in terms of coordination of Cu atoms, with the aim of understanding the role of surface defects in the dissociation of water molecules. The molecular adsorption of water is spontaneous at both surfaces but at the defective surface we found two stable molecular adsorption structures that differ slightly in the disposition of the O-atoms of H2O on the surface plane but differ considerably on the orientation of their H-atoms. Additionally we studied the dissociative adsorption of water accompanied with formation of H2(g). At the defective surface, starting from 1 ML of molecularly adsorbed H2O, the dissociation of 0.22 ML of H2O leading to 0.22 ML of HO, 0.78 ML H2O and H2(g) is exergonic but the dissociation of 0.44 ML or more H2O molecules is endergonic. These findings are discussed in terms of the two main factors that affect the adsorption energies: the existence of exposed adatoms provides an environment that facilitates the interaction with small adsorbates leading to stronger bonds between the surface and such adsorbates; and at the same time, the limited polarizability of the defect sites causes high coverages of adsorbates that drag electron density from the surface to be unfavorable. The overall effect is that at the defective Cu(110) formation of low coverages of HO groups is more favorable than at the perfect Cu(110) while forming coverages higher than 0.44 ML of HO is less favorable than at the perfect Cu(110). These effects have their origin in the extent of the polarization of the Cu–O bonds.

  • 54. 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 film2006Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, nr 12, s. L153-L157Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 55. 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 substrate2006Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, nr 13, s. L164-L168Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 56. Migas, D. B.
    et al.
    Bogorodz, V. O.
    Filonov, A. B.
    Borisenko, V. E.
    Skorodumova, N. V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Quasi-2D silicon structures based on ultrathin Me2Si (Me = Mg, Ca, Sr, Ba) films2018Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 670, s. 51-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By means of ab initio calculations with hybrid functionals we show a possibility for quasi-2D silicon structures originated from semiconducting Mg2Si, Ca2Si, Sr2Si and Ba2Si silicides to exist. Such a 2D structure is similar to the one of transition metal chalcogenides where silicon atoms form a layer in between of metal atoms aligned in surface layers. These metal surface atoms act as pseudo passivation species stabilizing crystal structure and providing semiconducting properties. Considered 2D Mg2Si, Ca2Si, Sr2Si and Ba2Si have band gaps of 1.14 eV, 0.69 eV, 0.33 eV and 0.19 eV, respectively, while the former one is also characterized by a direct transition with appreciable oscillator strength. Electronic states of the surface atoms are found to suppress an influence of the quantum confinement on the band gaps. Additionally, we report Sr2Si bulk in the cubic structure to have a direct band gap of 0.85 eV as well as sizable oscillator strength of the first direct transition. 

  • 57. Mitev, Pavlin D.
    et al.
    Hermansson, Kersti
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Surface properties of rutile TiO2(110) from molecular dynamics and lattice dynamics at 300 K: Variable-charge model results2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 23, s. 5359-5367Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Geometric structure, atomic vibrations and atomic charges and their thermally induced fluctuations have been calculated as a function of depth in, and thickness of, rutile TiO2(110) slabs, within the framework of the variable-charge potential of Swamy and Gale [V. Swamy, J.D. Gale, Phys. Rev. B 62 (2000) 5406] at 300 K. Molecular dynamics simulations and lattice dynamics calculations were performed with a 2D periodic slab model for slab thicknesses between 3 and 11 triple layers (approximately 9-35 angstrom). Odd-even oscillations with respect to the number of slab layers are found for the surface relaxation for very thin slabs, and for the (slowly converging) rumpling in the middle of the slab. The Ti and O atomic charges in the outermost three atomic layers differ from the rest of the slab (they are less ionic); the thermal vibrations do not alter this picture. The atomic mean-square amplitudes are some 50% larger (more for O, less for Ti) at the surface than in the middle of the slab and decay rather slowly to the bulk values. Comparisons with the results of a rigid-ion potential for titania [M. Matsui, M. Akaogi, Mol. Simul. 6 (1991) 238] are presented for non-electronic properties.

  • 58. Nilekar, A. U.
    et al.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Mavrikakis, M.
    Surface segregation energies in low-index open surfaces of bimetallic transition metal alloys2009Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, nr 1, s. 91-96Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a database of 24 x 24 segregation energies of single transition metal impurities in low-index Surfaces of transition metal hosts, calculated using the localized self-consistent Green's function (LSGF) method, in combination with the atomic sphere approximation including a multipole correction to the electrostatic potential and energy. The surface energies of {1 0 0} facets for fcc and bcc transition ill eta Is, and the more stable of the two {1 0 (1) over bar 0} facets of hcp transition metals are also Calculated and compared with available theoretical results. Insights derived Should be useful for determining the nature of active sites in a variety of catalytic reactions employing bimetallic catalysts.

  • 59.
    Nilson, K.
    et al.
    Department of Physics, Uppsala University.
    Palmgren, Pål
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Åhlund, J.
    Department of Physics, Uppsala University.
    Schiessling, J.
    MAX-laboratory, University of Lund.
    Göthelid, E.
    Department of Physics, Uppsala University.
    Mårtensson, N.
    Department of Physics, Uppsala University.
    Puglia, C.
    Department of Physics, Uppsala University.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    STM and XPS characterization of Zinc Phthalocyanine on InSb(001)2008Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 602, nr 2, s. 452-459Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Zinc phthalocyanine (ZnPc) adsorbed on the InSb(0 0 1)-c(8 x 2) surface has been studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Coverages from sub-monolayer to monolayer (ML) have been investigated. The molecules form ordered structures on the reconstructed rows of the surface with the molecular plane parallel to the surface. A change in the electronic structure between the sub-ML and higher coverages has been observed. Moreover, in order to study the influence of annealing on the electronic and geometric structures, the samples have been heated to elevated temperatures (about 640 K). In addition, multi-layer ZnPc films have been characterized by XPS measurements.

  • 60. Nisar, J.
    et al.
    Araujo, Carlos Moyses
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Structural, electronic and energetic properties of water adsorbed on beta-Si3N4 (0001) surface: First-principles calculations2010Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 604, nr 5-6, s. 617-622Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Structural, energetic and electronic properties of water molecules adsorbed on beta-Si3N4 (0 00 1) surface, at various coverages, are investigated using density functional theory. At low coverages (0 <= 0.5), it is found that all H2O molecules undergo spontaneous dissociation forming hydroxyl (OH) and imino (NH) groups where the reactive sites are identified, a result shown for the first time using ab initio theory. For higher coverages (0 > 0.5), only partial dissociation takes place where some of the molecules stay intact being bound via H-bond in good agreement with experimental findings. The driving force for the water dissociation has been identified to be dangling bonds on lower coordinated N and Si surface atoms showing that not all surface atoms are reactive corroborating with previous experimental findings.

  • 61. Nokbin, S.
    et al.
    Limtrakul, J.
    Hermansson, Kersti
    KTH, Tidigare Institutioner                               , Bioteknologi.
    DFT plane-wave calculations of the Rh/MgO(001) interface2004Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 566, s. 977-982Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Rh/MgO(001) system has been studied by periodic plane-wave density functional calculations using the VASP code and PAW potentials. Four different adsorption sites (which were reduced to three after optimization) and three different surface coverages were investigated. For the most stable site, above O, the adhesion energy was found to decrease as a function of coverage (from 2.0 to 1.1 eV as the coverage increases from 1/8 to I ML), while the adsorption energy was found to increase with surface coverage. Electron density difference plots were calculated to display some of the electron rearrangement responsible for the Rh-oxide adhesion energy, and the features of the Mg and O adsorption sites were compared.

  • 62. OLSSON, LO
    et al.
    KHAZMI, YO
    KANSKI, J
    ILVER, L
    NILSSON, PO
    HAKANSSON, MC
    KARLSSON, Ulf O
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    SURFACE ELECTRONIC-STRUCTURE OF INSB(100)4X1 STUDIED BY ANGLE-RESOLVED PHOTOELECTRON-SPECTROSCOPY1995Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 331, s. 1176-1180Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The surface electronic structure of the In-rich InSb(100)4 X 1 surface has been studied by angle-resolved photoelectron spectroscopy. To determine the origin of different contributions in spectra, direct bulk interband transitions were first identified using a semi-empirical band structure calculation and assuming direct transitions into free electron-like final bands. Three surface-induced features were identified and their dispersions have been mapped along symmetry directions of the surface Brillouin zone.

  • 63. O'Shea, J. N.
    et al.
    Luo, Yi
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Schnadt, J.
    Patthey, L.
    Hillesheimer, H.
    Krempasky, J.
    Nordlund, D.
    Nagasono, M.
    Bruhwiler, P. A.
    Martensson, N.
    Hydrogen-bond induced surface core-level shift in pyridine carboxylic acids2001Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 486, nr 3, s. 157-166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Intermolecular hydrogen bonding in thick films of pyridine carboxylic acids (isonicotinic; picolinic and bi-isonicotinic acid) evaporated onto rutile TiO2(1 1 0) has been investigated with X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. These molecules are shown to be strongly H-bonded in the condensed phase, and a surface core-level shift is observed due to the presence of non-H-bonded nitrogen atoms in the surface layer. Density functional theory calculations are used to relate the experimental data to the proposed bonding configurations based on the surface termination of the known equilibrium solid-state structure. A kinetic barrier, attributed to the high degree of molecular orientation required for the formation of extended H-bonding networks, has also been investigated.

  • 64. Ostrom, H
    et al.
    Nordlund, D
    Ogasawara, H
    Weiss, K
    Triguero, Luciano
    KTH, Tidigare Institutioner, KTH Syd.
    Pettersson, L G M
    Nilsson, A
    Geometric structure and chemical bonding of acetylene adsorbed on Cu(110)2004Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 565, nr 2-3, s. 206-222Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The chemical bonding and geometric structure of acetylene adsorbed on Cu(I 10) is analyzed using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) in combination with density functional theory (DFT) total energy geometry optimizations and spectral calculations. XPS reveals two different adsorbed species at liquid nitrogen temperature. The molecular alignment is deduced from angle-resolved XAS, revealing that in one site the molecules are aligned with the C-C axis along the [0 0 1] direction and in the other site with an average angle of 35degrees to the Cu rows. The position of the shape resonance is used to deduce a C-C bond length of 1.35 Angstrom, which is close to the values obtained from the DFT geometry optimizations. XES reveals strong sigma-pi mixing and new occupied states close to the Fermi level, originating from the out-of-plane pi* orbital, which becomes occupied upon adsorption in agreement with the Dewar-Chatt-Duncanson model of the bonding.

  • 65.
    Palmgren, Pål
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Claesson, Thomas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Önsten, Anneli
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Agnarsson, Björn
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Månsson, Martin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Tjernberg, Oscar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Band bending and structure dependent HOMO energy at the ZnO(0001)-titanyl phthalocyanine interface2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 18, s. 4222-4226Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated the initial stages of titanyl phthalocyanine (TiOPc) growth on single crystalline ZnO(0 0 0 1). This organic-semiconductor interface is self-organizing as a 2 x 1 pattern appears in a low energy electron diffraction upon deposition of the molecules. To achieve this pattern, the TiOPc is suggested to adsorb standing with the edge of the molecule along the substrate atomic rows. Photoelectron spectroscopy is used to further analyze the interface; a relatively large upwards band bending amounting to 0.5 eV is found and a splitting of the molecules highest occupied molecular orbital occurs after thermal treatment, indicating that the molecules are lying down.

  • 66.
    Palmgren, Pål
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Szamota-Leandersson, Katolina
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Claesson, Thomas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Tjernberg, Oscar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Karlsson, Ulf O.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Chemical reaction and interface formation on InAs(111)-Co surfaces2005Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 574, nr 2-3, s. 181-192Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 67. Papageorgiou, N.
    et al.
    Giovanelli, L.
    Faure, J. B.
    Layet, J. M.
    Göthelid, Mats
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Le Lay, G.
    Lead phthalocyanine thin films on InAs(100)-(4 x 2)/c(8 x 2) studied by synchrotron radiation photoelectron spectroscopy2001Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 482, s. 1199-1204Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We used synchrotron radiation photoelectron spectroscopy to study the interface between a thin film and an ordered single monolayer of lead phthalocyanine (PbPc) deposited on the clean InAs(1 0 0)-(4 x 2)/c(8 x 2) reconstructed surface. Analysis of the core level and valence band spectra gave information about the electronic properties of the interface, the interaction between the molecule and the substrate and the valence band offset of the heterojunction.

  • 68. Pasti, Igor A.
    et al.
    Baljozovic, Milos
    Skorodumova, Natalia V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering. Uppsala Univ, Dept Phys & Astron, Sweden.
    Adsorption of nonmetallic elements on defect-free MgO(001) surface - DFT study2015Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 632, s. 39-49Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Adsorption of 11 non-metals (H, B, C, N, O, F, Si, P, S, Cl and Br) on defect-free MgO(001) surface was investigate using DFT approach. Adsorption energies were found to be between -0.56 eV (hydrogen adsorption) and -2.63 eV (carbon adsorption). Charge transfer from substrate to adsorbate was observed to follow the periodicity in the Periodic Table of Elements, as increases from left to right and decreases from top to bottom. All investigated adsorbates prefer oxygen sites on MgO surface. The analysis of adsorbate-MgO(001) electronic structure suggested that the electronic structure of the O adsorption center and adsorbate atom is molecule-like and there is no strong interaction with MgO electronic bands. Based on the obtained dataset for adsorption energies of selected non-metallic adsorbates (X) the reactivity of MgO towards the bond cleavage in the cases of X-X, H-X and HO-X bonds was discussed. Obtained results point to weak reactivity of MgO(001) towards atomic adsorption and low activity for bond cleavage. However, these results can be used as a starting point for the functionalization of MgO, particularly in the cases where bond cleavage activity and surface-mediated stabilization of dissociation products are desired.

  • 69. Pentcheva, R.
    et al.
    Moritz, W.
    Rundgren, John
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Materialteori.
    Frank, S.
    Schrupp, D.
    Scheffler, M.
    A combined DFT/LEED-approach for complex oxide surface structure determination: Fe3O4(001)2008Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 602, nr 7, s. 1299-1305Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A combination of density functional theory (DFT) calculations and low energy electron diffraction (LEED) analysis is used to determine the surface structure of Fe3O4 0 00). We find that the surface is rich in oxygen and the observed (root 2- x root 2-)R45 degrees reconstruction is a result of a Jahn-Teller distortion as established by recent DFT-calculations [R. Pentcheva, F. Wendler, H.L. Meyerheim, W. Moritz, N. Jedrecy, M. Scheffler, Phys. Rev. Lett. 94 (2005) 126101]. The corresponding Pendry reliability factor is 0.34. Furthermore, we investigate the influence of the preparation conditions (temperature, oxygen pressure) on the LEED intensities of natural and synthetic samples. The electron scattering phase shifts used in the analysis of the LEED spectra are derived from two methods, one based on the DFT electron densities and another employing an overlap of atomic potentials with optimized muffin-tin radii. Both approaches lead to similar results.

  • 70. Pitkänen, H.
    et al.
    Alatalo, M.
    Puisto, A.
    Ropo, M.
    Kokko, K.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio study of the surface properties of austenitic stainless steel alloys2013Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 609, s. 190-194Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using ab initio calculations we investigated the surface energies of paramagnetic Fe1-c-nCrcNin random alloys within the concentration range of 0.12 <= c <= 032 and 0.04 <= n <= 0.32. These alloys crystallize mainly in the face centred cubic (fcc) structure and constitute the main building blocks of austenitic stainless steels. It is shown that all alloys have the lowest surface energies along the most close packed crystal orientation, namely the fcc (111) surfaces. The amount of Ni seems to have little effect on the surface energy, while almost all composition-driven change may be attributed to the changes in the Cr content. Within the studied compositional range, the change of the surface energy with the composition is of the order of 10%. Trends of the surface energy can be related to the magnetic structure of surfaces. Using the total energy as a function of the concentration, we determine the effective chemical potentials in bulk and at the surface, which can be used to estimate the surface segregation energies.

  • 71.
    Punkkinen, Marko P. J.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Laukkanen, P.
    Ahola-Tuomi, M.
    Pakarinen, J.
    Kuzmin, M.
    Tukiainen, A.
    Perala, R. E.
    Lang, J.
    Ropo, M.
    Kokko, K.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Pessa, M.
    Vayrynen, I. J.
    Core-level shifts of InP(100)(2 x 4) surface: Theory and experiment2009Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, nr 16, s. 2664-2668Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Surface core-level shifts (SCLSs) of the (2 x 4)-reconstructed InP(100) surface with the established mixed In-P dimer structure have been investigated by first-principles calculations and photoelectron spectroscopy. Theoretical values were calculated using both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation energy functional. The obtained theoretical values are quite similar within both approximations. The found differences originate in the tiny structural differences. It is concluded that the expansion or contraction of the crystal lattice has smaller effect on the SCLSs than the geometrical details of the reconstruction, which suggests that the Madelung potential has the dominant effect on the SCLSs. The results support the presence of a P 2p peak at higher binding energy (BE) compared to bulk peak, as proposed with recent measurements [P. Laukkamen, J. Pakarinen, M. Ahola-Tuomi, M. Kuzmin, R. E. Perala, I. J. Vayrynen, A. Tukiainen, V. Rimpilainen, M. Pessa, M. Adell, J. Sadowski, Surf. Sci. 600 (2006) 3022], and reveal several hitherto not reported SCLSs. The calculated SCLSs reproduce the measured spectra within reasonable accuracy. Furthermore, the atomic origins of the InP(100)(2 x 4) SCLSs are solved. In particular, it is shown that the lowest SCLS of P 2p, of the InP(100)(2 x 4) arises from the topmost In-P dimers.

  • 72.
    Punkkinen, Marko P. J.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Laukkanen, P.
    Lång, J.
    Kuzmin, M.
    Dahl, J.
    Zhang, Hualei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Pessa, M.
    Guina, M.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kokko, K.
    Structure of ordered oxide on InAs(100) surface2012Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 606, nr 23-24, s. 1837-1841Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It was recently found that oxygen induces ordered reconstructions on several III-V surfaces. The most oxygen-rich reconstruction shows (3x1) periodicity. Based on first-principles investigations, a detailed atomic model is presented for this reconstruction. The uncommon periodicity is attributed to the highly stable In - O - In trilayer below surface which also leads to stabilizing additional bonds within the surface layer. The strain induced by the trilayer is more effectively accommodated within the (3 x 1) reconstruction than within the competing (2 x 1) reconstruction due to smaller number of dimers. It is proposed that the experimentally found semiconductivity is reached by substitutional atoms within the surface layer. Suitable substitution preserves the magnitude of the bulk band gap.

  • 73. QU, H
    et al.
    KANSKI, J
    NILSSON, PO
    KARLSSON, Ulf O
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    SURFACE ELECTRON-STRUCTURE OF INP(110) STUDIED WITH ANGLE-RESOLVED PHOTOELECTRON-SPECTROSCOPY1991Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 255, nr 3, s. 237-244Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The surface electron structure of InP(110) has been studied by means of synchrotron radiation excited angle-resolved photoelectron spectroscopy. After identifying the bulk-related spectral structures, the surface-induced energy bands have been mapped along symmetry directions. The polarization dependence of the surface-related structures is discussed.

  • 74.
    Rad, Goshtasbi
    et al.
    KTH, Tidigare Institutioner, Materialvetenskap.
    Göthelid, Mats
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Le Lay, G.
    Karlsson, Ulf O.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Cerium-induced reconstructions on the Si(111) surface2004Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 558, nr 03-jan, s. 49-56Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Scanning tunnelling microscopy has been used to investigate cerium-induced reconstructions on Si(1 1 1). Room temperature deposition of submonolayers of Ce is reactive and produces an intricate two layer silicide structure: a root7 x root7 phase on top of a 2root3 x 2root3 reconstruction, co-existing with the bare Si(1 1 1)-7x7 surface. Annealing the submonolayer-covered surface at 600degreesC generates a one-dimensional (5x2) structure comprising both Cc and Si adatoms. This structure coexists with the bare 7x7 and a 2x3 structure with cerium adatoms in alternating H-3 and T-4 positions.

  • 75. Rad, M. G.
    et al.
    Göthelid, Mats
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Le Lay, G.
    Karlsson, U. O.
    Grehk, T. M.
    Sandell, A.
    Influence of charged impurities on the surface phases of Sn/Ge(111)2001Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 477, nr 03-feb, s. 227-234Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The root3 alpha and 3 x 3 reconstructions on the Ge(111)-Sn surface have been perturbed by small amounts of iodine and potassium to test the spectral response in the course of a synchrotron radiation photoemission study. We demonstrate the inadequacy of the static model of the root3 alpha phase at room temperature and of the surface charge density wave model of the 3 x 3 phase at low temperature. Instead, the influence of the charged impurities is consistently explained when considering that dynamical fluctuations in the tin adatom positions are frozen in upon passing the phase transition temperature.

  • 76. Ropo, M.
    et al.
    Kokko, K.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kollar, J.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    The chemical potential in surface segregation calculations: AgPd alloys2006Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, nr 4, s. 904-913Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We put forward a technique for calculating the surface segregation profile in substitutional disordered alloys. The surface internal energy and the effective bulk and surface chemical potentials are calculated using the full charge density exact muffin-tin orbitals method, combined with the coherent potential approximation. The application of our approach is demonstrated to the close-packed surface of AgcPd1-c random alloys with 0 < c < 1. The surface concentration profile, surface energy and segregation energy are investigated as functions of bulk composition. The present results are compared with former theoretical and experimental data. It is found that at low temperature, Ag segregates to the surface layer for the entire bulk composition range. At 0 K, the subsurface layer contains 100% Pd for c <= 0.4, and somewhat more than (2c - 1) Ag in alloys with c > 0.5. The temperature dependence of the segregation profile is significant for I'd rich alloys and for alloys with intermediate concentrations. At temperatures >= 600 K, the subsurface layer is obtained to be almost bulk like.

  • 77. Salomon, E.
    et al.
    Angot, T.
    Thomas, C.
    Layet, J. M.
    Palmgren, Pål
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Nlebedim, C. I.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Etching of silicon nanowires on Ag(110) by atomic hydrogen2009Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, nr 23, s. 3350-3354Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Scanning Tunnelling Microscopy, High Resolution Electron Energy Loss Spectroscopy and High Resolution X-Ray Photoelectron Spectroscopy have been used to study the adsorption of atomic hydrogen onto Si nanowires grown on Ag(1 1 0). We demonstrate that the hydrogen strongly interacts with the Si nanowires modifying their structural and electronic properties. Hydrogen atoms etch the Si nanowires and eventually lead to their complete removal from the Ag(1 1 0) surface.

  • 78.
    Schaefer, A.
    et al.
    Lund Univ, Dept Synchrotron Radiat Res, POB 118, SE-22100 Lund, Sweden.;Chalmers Univ Technol, Competence Ctr Catalysis, S-41296 Gothenburg, Sweden..
    Lanzilotto, V.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    Cappel, Ute B.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Tillämpad fysikalisk kemi. Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden.
    Uvdal, P.
    Lund Univ, Dept Chem, Chem Phys, POB 124, SE-22100 Lund, Sweden..
    Borg, A.
    NTNU Norwegian Univ Sci & Technol, Dept Phys, NO-07491 Trondheim, Norway..
    Sandell, A.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    First layer water phases on anatase TiO2(101)2018Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 674, s. 25-31Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The anatase TiO2(101) surface and its interaction with water is an important topic in oxide surface chemistry. Firstly, it benchmarks the properties of the majority facet of TiO2 nanoparticles and, secondly, there is a controversy as to whether the water molecule adsorbs intact or deprotonates. We have addressed the adsorption of water on anatase TiO2(101) by synchrotron radiation photoelectron spectroscopy. Three two-dimensional water structures are found during growth at different temperatures: at 100 K, a metastable structure forms with no hydrogen bonding between the water molecules. In accord with prior literature, we assign this phase to chains of disordered molecules. Growth 160 K results in a metastable structure with expressed hydrogen bonding between the water molecules. At 190 K, the water molecules become disordered as the thermal energy is too high and hence the hydrogen bonds break. The result is a structure with isolated monomers. Partial dissociation is observed for all three growths, with the molecular state only slightly favored in energy (20-40 meV) over the dissociated state. Heating of a thick film leads to more dissociation compared to a bilayer, when formed at 100 K. Thus, extending the water network facilitates proton transport and hence dissociation. The results reconcile apparent conflicting experimental results previously obtained by scanning tunneling microscopy (STM) and core level photoelectron spectroscopy.

  • 79. Sinner-Hettenbach, M.
    et al.
    Göthelid, Mats
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Weiss, T.
    Barsan, N.
    Weimar, U.
    von Schenck, H.
    Giovanelli, L.
    Le Lay, G.
    Electronic structure of SnO2(110)-4 x 1 and sputtered SnO2(110) revealed by resonant photoemission2002Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 499, nr 1, s. 85-93Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The surface properties of SnO2(1 1 0)-4 x 1 and sputtered SnO2(1 1 0) were studied comparatively by resonant photoemission of the valence band states in a photon energy range of 60-130 eV. Resonating energetic levels could be observed on the 4 x I reconstructed surface and the resonance behavior could be switched off by sputter treatment. Additionally, the Sn 4d core-levels were recorded at two photon energies in order to allow a statement about the surface's stoichiometry. A tentative explanation of the observed resonance and of the discrepancy between ordered and sputtered surface is given with regard to recent STM results on similar prepared surfaces.

  • 80. Sinner-Hettenbach, M.
    et al.
    Göthelid, Mats
    KTH, Tidigare Institutioner, Fysik.
    Weissenrieder, Jonas
    KTH, Tidigare Institutioner, Fysik.
    von Schenck, Henrik
    KTH, Tidigare Institutioner, Fysik.
    Weiss, T.
    Barsan, N.
    Weimar, U.
    Oxygen-deficient SnO2(110): a STM, LEED and XPS study2001Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 477, nr 1, s. 50-58Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 81.
    Soldemo, Markus
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Lundgren, E.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Oxidation of Fe(110) in oxygen gas at 400 °c2016Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 644, s. 172-179Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 82.
    Soldemo, Markus
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Niu, Yuran
    Zakharov, Alexei
    Lundgren, Edvin
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    A well-ordered surface oxide on Fe(110)2015Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 639, s. 13-19Artikkel i tidsskrift (Fagfellevurdert)
    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).

  • 83.
    Stoltz, Dunja
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Stoltz, S. E.
    Johansson, L. S. O.
    Surface resonance on the (6 root 3 x 6 root 3)-R30 degrees-reconstructed 5 ML Au on (root 3 x root 3)-R30 degrees-4H-SiC(0001)2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 12, s. 2508-2511Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we present evidence for a surface resonance on the (6v root 3 x 6 root 3)-R30 degrees-reconstruction obtained on 5 monolayers (ML) of An deposited on the (root 3 x root 3)-R30 degrees-4H-SiC(0001) and subsequently annealed. We use synchrotron radiation-based angle resolved photoelectron spectroscopy to show that this resonance has no k(parallel to)-dispersion, but a parabolic-like kil-dispersion of 0.4 eV around Gamma. Its electronic localization in the (6 root 3- x 6 root 3-)-R30 degrees surface reconstruction is documented by comparison with the (2 root 3- x 2 root 3-)-R30 degrees structure, obtained at a slightly lower annealing temperature after 5 ML Au deposition on the (root 3- x root 3)-R30 degrees-4H-SiC(0001) substrate.

  • 84. Stoltz, S. E.
    et al.
    Popovic, D.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    A high-resolution core-level study of Ni-catalyzed absorption and desorption of hydrogen in Mg-films2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 6, s. 1507-1512Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ultra-thin magnesium and magnesium-nickel films grown on Mo(110) under ultra-high vacuum (UHV) conditions are hydrogenated at room temperature with atomic H and studied by high-resolution core-level photoelectron spectroscopy (PES). For the Mg-film a layer of hydride is formed at the Mg/Mo interface and a sub-mono layer of hydride is formed at the surface, while an intermediate region remained non-hydrogenated. For the Mg-Ni-film a thick layer of surface hydride was detected, showing that Ni enhances formation of Mg-hydride at the surface. During the heat-up of the hydrogenated Mg-Ni-film hydrogen desorption started at 400 K.

  • 85.
    Szamota-Leandersson, Karolina
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Bugoi, R.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Le Lay, G.
    Karlsson, Ulf O.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Pb induced charge accumulation on InAs(111)B2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 15, s. 3246-3252Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Pb/InAs(111)B interface has been studied by synchrotron radiation photoelectron spectroscopy (SR-PES) of valence band and ln4d, As3d and Pb5d core levels. Room temperature deposition of similar to 1 ML of Pb on InAs(I I I)B leads to an ordered overlayer that induces a metallic channel at the surface, as seen through a weak emission in the vicinity of the Fermi level. Its narrow localization in reciprocal space supports the formation of a two-dimensional free electron gas (2DEG) in the surface region. It is proposed that the adsorbed metal layer swaps the initial polarisation of the surface and thus pulls electrons back to the surface. This charge re-arrangement increases the charge density in the accumulation layer and reduces the screening length and thus the depth of the potential well at the surface.

  • 86.
    Szamota-Leandersson, Karolina
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Leandersson, Mats
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Karlsson, Ulf O.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Correlated development of a (2x2) reconstruction and acharge accumulation layer on the InAs(111)-Bi surface2011Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 605, nr 1-2, s. 12-17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied the formation of a Bi induced (2x2) reconstruction on the InAs(111)Bsurface. In connection to the development of the (2x2) reconstruction, a two dimensionalcharge accumulation layer located in the bottom of the InAs conduction band appears as seenthrough a photoemission structure at the Fermi level. Not well ordered Bi layers do not inducea charge accumulation. The Bi induced reconstruction reduces the polarisation of the pristinesurface and changes the initial charge distribution. InAsBi alloying occurs below the surfacewhere Bi act as charge donor leading to the charge accumulation layer.

  • 87.
    Szamota-Leandersson, Karolina
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Leandersson, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Palmgren, Pål
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Karlsson, Ulf O.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Electronic structure of bismuth terminated InAs(100)2009Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, nr 1, s. 190-196Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Deposition of Bi onto (4 x 2)/c(8 x 2)-InAs(1 0 0) and subsequent annealing results in a (2 x 6) surface reconstruction as seen by low electron energy diffraction. The Bi condensation eliminates the original (4 x 2) Surface reconstruction and creates a new Structure including Bi-dimers. This Surface is metallic and hosts a charge accumulation layer seen through photoemission intensity near the Fermi level. The accumulation layer is located in the bulk region below the surface, but the intensity of the Fermi level structure is strongly dependent oil the Surface order.

  • 88. TORNEVIK, C
    et al.
    GOTHELID, M
    HAMMAR, M
    KARLSSON, Ulf O
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    NILSSON, NG
    FLODSTROM, SA
    WIGREN, C
    OSTLING, M
    ADSORPTION OF SN ON SI(111)7X7 - RECONSTRUCTIONS IN THE MONOLAYER REGIME1994Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 314, nr 2, s. 179-187Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Different monolayer phases of Sn on Si(111)7 x 7 have been studied by means of scanning tunneling microscopy (STM), core-level photoelectron spectroscopy (XPS), and Rutherford backscattering spectrometry (RBS). The STM results show that square-root 3 x square-root 3 reconstructions are obtained for room-temperature deposition of 1/3 ML of Sn followed by sample annealing in a broad temperature range. A T4 Sn adatom square-root 3 x square-root 3 phase is formed for temperatures between 500 and 800-degrees-C, with a concentration of defects that is strongly dependent on the temperature and which is as high as 25% for the lowest temperatures. Above 825-degrees-C a second square-root 3 x square-root 3 adatom reconstruction is formed, a mosaic-like phase with a 1: 1 mixture of Si and Sn atoms in T4 positions. The results from investigations of the higher coverage 2 square-root 3 x 2 square-root 3 reconstruction by XPS and RBS support the theory that this phase is a two-layer epitaxial Sn structure with all Si(111) dangling bonds saturated. The Sn coverage for this phase was determined to be between 1 and 1.2 ML.

  • 89. Varekamp, P R
    et al.
    Bjorkqvist, M
    Gothelid, M
    Karlsson, Ulf O
    Observation of true c(8x2) symmetry in scanning tunnelling microscopy images of the clean InSb(001) surface1996Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 350, nr 1-3, s. L221-L226Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Filled and empty state scanning tunnelling microscopy images of the sputtered and annealed InSb(001) surface are presented. The sputter-anneal preparation generates a surface with two distinct phases. The dominant phase possesses a unit cell with true c(8 x 2) symmetry, whereas the other phase is attributed to an asymmetric 1 x 3 reconstruction. The presence of a c(8 x 2) unit cell in filled state images is in contrast to previous reports, which identified only a 4 x 1 unit cell. The true c(8 x 2) symmetry further indicates, if the available structural model is used as a guide, that the current interpretation of features in filled state images is incorrect. This result may necessitate a reevaluation of the structural model for the InSb(001)-c(8 x 2) surface.

  • 90. Varekamp, P R
    et al.
    Hakansson, M C
    Kanski, J
    Kowalski, B J
    Olsson, L O
    Ilver, L
    He, Z Q
    Yarmoff, J A
    Karlsson, Ulf O
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Angle-resolved photoemission spectroscopy of the 1x1 ordered overlayers on iodine-saturated GaAs(001) and InAs(001)1996Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 352, s. 387-390Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Angle-resolved valence band photoelectron spectra are collected from 1 X 1 ordered overlayers on I-2-saturated GaAs(001)-4 x 1, -c(2 X 8), and InAs(001)-c(8 x 2). A high-intensity dispersive surface state, located approximately 4.4 eV below the valence band maximum, is observed in each case. The state passes through an open lens in the projected bulk density of states and disperses symmetrically around the surface Brillouin zone edge. For all surfaces studied, the state is stronger when excited with the electric field polarized in the [110], as compared to the <(1)over bar 10>], azimuth. Since the state is independent of the termination of the initial surface, and since iodine bonds primarily to the outermost element, the state must result from delocalization of the electron states in the overlayer, and is not related to bonding with the substrate.

  • 91.
    Vincent, Jonathan
    et al.
    Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University.
    Olsen, R.A.
    Baerends, E.J.
    Kroes, G. J.
    Dissociative chemisorption of H 2 on Pt(111): isotope effect and effects of the rotational distribution and energy dispersion2004Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 573, nr 3, s. 433-445Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Six-dimensional quantum dynamics calculations on dissociative scattering of H2 and D2 from Pt(111) are performed.The six-dimensional potential energy surface used was generated using density functional theory employingthe generalized gradient approximation. The isotope effect, the effect of widening the rotational distribution on the dissociationprobability and the effect of the energy dispersion are investigated, as they are possible reasons for a discrepancybetween previous theoretical work and molecular beam experiments. It was found that these effects cannot explainthe differences between the theoretical and experimental results.

  • 92. von Schenck, H.
    et al.
    Janin, E.
    Tjernberg, Oscar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Svensson, M.
    Göthelid, Mats
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    CO bonding on tin modified Pt(110)-(1 x 2)2003Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 526, nr 02-jan, s. 184-192Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of tin on the bonding of CO to Pt(l 10) has been studied using high-resolution electron energy loss spectroscopy, density functional theory and photoelectron spectroscopy. CO binds on-top to platinum at all investigated tin and CO coverages. Bonding of CO in Sn-Pt alloy rows is weakened compared to clean Pt(l 10). However, several different adsorption sites in Pt-only rows, inequivalent with regard to their coordination environment, show very similar characteristics with respect to CO adsorption.

  • 93. Wadsak, M.
    et al.
    Schreiner, M.
    Aastrup, T.
    Leygraf, Christofer
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Combined in-situ investigations of atmospheric corrosion of copper with SFM and IRAS coupled with QCM2000Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 454, s. 246-250Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Scanning force microscopy (SFM) and infrared reflection absorption spectroscopy (IRAS) coupled with quartz crystal microbalance (QCM) were used for in-situ investigations of the atmospheric corrosion of pure copper. Based on chemical and kinetic studies obtained by IRAS/QCM, tapping mode atomic force microscopy (TM-AFM) and phase detection imaging (PDI) were applied to gain information about the topography changes of the sample surface with emphasis on the shape and lateral distribution of the corrosion products. Investigations were carried out in synthetic air with 60 and 80% relative humidity (RI-I). At 60% RH, small features partly covering the surface could be observed with TM-AFM. These features were identified as cuprous oxide with IRAS. Contrary to these results, a fast formation of a layer of cuprous oxide entirely covering the sample surface was observed at 80% RH with TM-AFM. QCM investigations showed a higher formation rate of cuprous oxide at 80% than at 60% RH but in both cases, a high corrosion rate at the beginning of the exposure, which decreases with progressing time.

  • 94.
    Weissenrieder, Jonas
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Göthelid, Mats
    KTH, Tidigare Institutioner, Fysik.
    Le Lay, G.
    Karlsson, Ulf O.
    KTH, Tidigare Institutioner, Fysik.
    Investigation of the surface phase diagram of Fe(110)-S2002Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 515, nr 1, s. 135-142Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reconstructions and overlayer structures of the Fe(110) surface at different sulfur (S) coverage are presented by atomically resolved scanning tunneling microscopy combined with Auger electron spectroscopy and low energy electron diffraction investigations. S overlayers were obtained by annealing a Fe(110) single crystal to 700 degreesC in order to induce S segregation from the bulk. Fe(110)c(6 x 4), (3 x 1) and (1 x 1) reconstructions were found at sub or monolayer S coverage. At S coverage above one monolayer a (2 x 1) super structure was formed on top of the Fe(110)(1 x 1)-S structure. When increasing the coverage further, S grow in a zigzag formation from step edges across the terraces. These zigzag rows grow in the [1 (1) over bar1] and [001] directions and form a quasi-ordered parallelogram structure.

  • 95.
    Weissenrieder, Jonas
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Göthelid, Mats
    KTH, Tidigare Institutioner, Fysik.
    Månsson, Martin
    KTH, Tidigare Institutioner, Fysik.
    von Schenck, Henrik
    KTH, Tidigare Institutioner, Fysik.
    Tjernberg, Oscar
    KTH, Tidigare Institutioner, Fysik.
    Karlsson, Ulf O.
    KTH, Tidigare Institutioner, Fysik.
    Oxygen structures on Fe(110)2003Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 527, nr 03-jan, s. 163-172Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adsorption of oxygen on a Fe(110) single crystal has been studied by means of high resolution photoelectron spectroscopy (HRPES) and scanning tunneling microscopy (STM). Core level spectra were analyzed in detail on both clean and adsorbate covered surfaces. A shoulder on the high binding energy side of the Fe 2p core level indicates a structure comprising multiple components interpreted as an exchange split of the final state due to interaction between the 2p and 3d electrons. After adsorption of oxygen, (2 x 5), (2 x 2) and (3 x 1) reconstructions were observed with atomically resolved STM. The iron surface was further exposed to gradually higher doses of oxygen. Deconvolution of the O 1s HRPES spectra revealed two components separated approximately by 0.4 eV. The component at lower binding energy dominates at low coverage, while the high binding energy component increases in intensity with increasing O coverage. The formation of oxides was observed in the Fe 2p spectrum in the region between 708 and 710 eV. Further, well ordered iron oxides were grown by exposure to oxygen at 250 degreesC. The O 1s core level contained a single component with a binding energy similar to that of the high energy component in the just discussed O 1s spectrum. Low energy electron diffraction and STM images of this structure showed a large moire pattern with a 22.1 Angstrom x 30.9 Angstrom unit cell.

  • 96.
    Westerberg, Staffan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik (Stängd 20120101), Halvledarmaterial, HMA (Stängd 20120101). University of California Berkeley, United States.
    Wang, C.
    Somorjai, G. A.
    Heat of adsorption of CO on Pt(1 1 1) obtained by sum frequency generation vibrational spectroscopy: A new technique to measure adsorption isotherms2005Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 582, nr 1-3, s. 137-144Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    CO adsorption on Pt(1 1 1) was studied at temperatures between 373 K and 463 K in a pressure range of 1 × 10-8-3 × 10-5 Torr. Adsorption isotherms were obtained using sum frequency generation, (SFG). By correlating the normalized SFG signal to the surface coverage, the obtained isotherms are in satisfactory agreement with Langmuir adsorption, which is suitable for coverages up to a monolayer. Close to saturation coverage the heat of adsorption was determined to 113(±15) kJ/mol, which is in close agreement to values obtained by single crystal adsorption calorimetry, low energy electron diffraction (LEED) and temperature programmed desorption (TPD) [Y.Y. Yeo, L. Vattuone, D.A. King, J. Chem. Phys. 106 (1997) 392; G. Ertl, M. Neumann, K.M. Streit, Surf. Sci. 64 (1977) 393].

  • 97. WIGREN, C
    et al.
    ANDERSEN, JN
    NYHOLM, R
    KARLSSON, Ulf O
    EPITAXIAL SILICIDE FORMATION IN THE MG/SI(111) SYSTEM1993Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 289, nr 3, s. 290-296Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The silicide formation has been studied in the Mg/Si(111) system by IOW energy electron diffraction (LEED) and photoelectron spectroscopy. It has been found that an epitaxial Mg2Si silicide is responsible for the (2/3 square-root e x 2/3 square-root 3)R30-degrees reconstruction in this system. The thickness of the silicide is limited due to the very low formation temperature for this silicide. The Fermi level is positioned 0.59 +/- 0.06 eV above the valence band maximum in the Si substrate and the valence band maximum in the epitaxial silicide is positioned 0.3 +/- 0.1 eV below the Fermi level.

  • 98. WIGREN, C
    et al.
    ANDERSEN, JN
    NYHOLM, R
    KARLSSON, Ulf O
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    FORMATION OF SM SILICIDES ON SI(111) - COMPOSITION AND EPITAXY1993Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 293, nr 3, s. 254-259Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The formation of Sm silicides on Si(111) by means of solid phase epitaxy has been studied with low energy electron diffraction, Auger electron spectroscopy and photoelectron spectroscopy of the Sm 4f level and Si 2p level. A limited reaction is found to occur already at room temperature whereas at higher temperatures a strongly intermixed Sm/Si layer showing some long range order is formed. The Sm atoms of this intermixed phase are found to be completely trivalent in accordance with expectations. The intermixed layer consists of two silicides with different compositions, one of them being SmSi2-x, the other being tentatively ascribed to SmSi.

  • 99. Yang, Zongxian
    et al.
    Woo, Tom K.
    Hermansson, Kersti
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Adsorption of NO on unreduced and reduced CeO2 surfaces: A plane-wave DFT study2006Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, nr 22, s. 4953-4960Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adsorption of NO on the (111) and (110) surfaces of ceria (CeC2) was studied using projector-augmented wave (PAW) method based density-functional theory within the generalized gradient approximation (GGA). Several adsorption sites for NO on the stoichiometric surfaces are found, all with weak molecule-surface interaction. The adsorption on the reduced surfaces is much stronger. The O-ends of the adsorbed NO molecules fill the oxygen vacancies and the N-O bonds are elongated. If two such adsorbed NO molecules, residing at neighbouring sites, meet, their N-ends will form a strong N-N bond with little or no barrier. This is an intermediate step towards dissociation of free N-2 which is calculated to be strongly thermodynamically driven.

  • 100. Zhukovskii, Y. F.
    et al.
    Kotomin, E. A.
    Herschend, B.
    Hermansson, Kersti
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Jacobs, P. W. M.
    The adhesion properties of the Ag/alpha-Al2O3(0001) interface: an ab initio study2002Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 513, nr 2, s. 343-358Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ab initio computer simulations of the atomic and electronic structure of the Ag/alpha-Al2O3(0 0 0 1) (corundum) interface have been performed for a periodic two-dimensional slab model using the Hartree-Fock method and a posteriori electron correlation corrections. We have considered both Al- and O-terminated corundum substrate surfaces. The dependence of the adhesion energy on the interfacial distance has been analyzed for the two most favorable Ag adsorption positions over corundum and for two different metal coverages (a 1/3 monolayer (NIL) of the Ag(l 1 1) crystallographic plane and a full Ag(I 1 1) monolayer). The two different terminations (Al- and O-) give rise to qualitatively different results. The former case corresponds to the most stable termination of the pure corundum (0 0 0 1) substrate where small adhesion energies per Ag atom (0.15-0.25 eV for I ML and 0.40-0.55 eV for 1/3 NIL) are accompanied by minor interfacial charge transfer, indicating physisorption, which may be explained by a weak atomic polarization. In contrast, for O-terminated corundum, substantial adhesion energies (3-5 eV per Ag atom at I ML coverage and 6-11 eV for 1/3 ML) combined with noticeable charge transfer from silver atoms towards the substrate (0.5e to 0.9e) are clear indications of a strong interfacial ion bonding. For both terminations, the observed difference in Ag adhesion energies for 1/3 NIL and I NIL coverages arises from a transition from directed Ag-O bonding towards a more delocalized electron density distribution in the complete monolayer. The results of our calculations are compared with available experimental studies and theoretical simulations for various Me/Al2O3 interfaces.

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