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  • 1.
    Eriksson, Johan
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Osiecki, Jacek
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Sakamoto, Kazuyuki
    Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan.
    Uhrberg, Roger
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Atomic and electronic structures of the ordered 2√3 × 2√3 andthe molten 1×1 phase on the Si(111):Sn surface2010Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 23, s. 235410-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Si(111) surface with an average coverage of slightly more than one monolayer of Sn, exhibits a 2√3 × 2√3 reconstruction below 463 K. In the literature, atomic structure models with 13 or 14 Sn atoms in the unit cell have been proposed based on scanning tunneling microscopy (STM) results, even though only four Sn atoms could be resolved in the unit cell. This paper deals with two issues regarding this surface. First, high resolution angle resolved photoelectron spectroscopy (ARPES) and STM are used to test theoretically derived results from an atomic structure model comprised of 14 Sn atoms, ten in an under layer and four in a top layer [Törnevik, et al., PRB 44, 13144 (1991)]. Low temperature ARPES reveals six occupied surface states. The calculated surface band structure only reproduces some of these surface states. However, simulated STM images show that certain properties of the four atoms that are visible in STM are reproduced by the model. The electronic structure of the Sn atoms in the under layer of the model does not correspond to any features seen in the ARPES results. New STM images are presented which indicate the presence of a different under layer consisting of eight Sn atoms, that is not compatible with the model. These results indicate that a revised model is called for. The second issue is the reversible transition from a 2√3 × 2√3 phase below 463 K to a 1×1 phase corresponding to a molten Sn layer, above that temperature. It is found that the surface band structure just below the transition temperature is quite similar to that at 100 K. The surface band structure undergoes a dramatic change at the transition. A strong surface state, showing a 1×1 periodicity, can be detected above the transition temperature. This state resembles parts of two surface states which, already before the transition temperature is reached, has begun a transformation and lost much of their 2√3×2√3 periodicities. Calculated surface band structures obtained from 1×1 models with 1 ML of Sn are compared with ARPES and STM results. It is found that the strong surface state present above the transition temperature shows a dispersion similar to that of a calculated surface band originating from the Sn-Si interface with the Sn atoms in T1 sites.

  • 2.
    Osiecki, Jacek
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Sohail, Hafiz Muhammad
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Eriksson, Johan
    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.
    Experimental and Theoretical Evidence of a Highly Ordered Two-Dimensional Sn/Ag Alloy on Si(111)2012Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, nr 5, s. 057601-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The existence of a highly ordered, two-dimensional, Sn/Ag alloy on Si(111) is reported in this study. We present detailed atomic and electronic structures of the one atomic layer thick alloy, exhibiting a 2 x 2 periodicity. The electronic structure is metallic due to a free-electron-like surface band dispersing across the Fermi level. By electron doping, the electronic structure can be converted into a semiconducting state. A rotated Sn trimer constitutes the key structural element that could be identified by a detailed analysis of constant energy contours derived from the free-electron-like band.

  • 3.
    Osiecki, Jacek
    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.
    Alloying of Sn in the surface layer of Ag(111)2013Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, nr 7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is found that 1/3 monolayer (ML) of Sn forms a surface alloy with 2/3 ML of Ag on Ag(111). This highly ordered alloy layer shows a √3×√3 structure. By employing experimental and theoretical tools (scanning tunneling microscopy [STM], angle resolved photoelectron spectroscopy, low-energy electron diffraction, and density functional theory), an atomic model has been obtained that reproduces the experimental electronic structure in both real and reciprocal space. Detailed surface band dispersions, constant energy contours, and STM images, obtained experimentally and theoretically, are compared in order to verify the model. Similar, 1-layer-thick alloys on Ag(111) with Pb, Bi, or Sb exhibit measurable spin–orbit interactions. However, no such spin split could be detected in the case of Sn in this study.

  • 4.
    Osiecki, Jacek
    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.
    Formation of a root 3 x root 3 surface on Si/Ge(111) studied by STM and LEED2009Inngår i: SURFACE SCIENCE, ISSN 0039-6028, Vol. 603, nr 16, s. 2532-2536Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have performed a detailed study of the formation and the atomic structure of a root 3 x root 3 surface on Si/Ge(111) using both scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Both experimental methods confirm the presence of a root 3 x root 3 periodicity but unlike the Sn/Ge(111) and the Sn/Si(111) surfaces, the Si/Ge(111) surface is not well ordered. There is no long range order on the surface and the root 3 x root 3 reconstruction is made up of double rows of silicon atoms separated by disordered areas composed of germanium atoms.

  • 5.
    Razado-Colambo, Ivy
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Osiecki, Jacek
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    STM studies of the Sn/Ge(111)√3x√3 and 3x3 surfacesManuskript (Annet vitenskapelig)
    Abstract [en]

    Scanning tunneling microscopy (STM) was used to study the room temperature (RT) √3x√3 and the low temperature (LT) 3x3 surfaces of Sn/Ge(111). The Sn/Ge(111)√3x√3 surface was prepared under different conditions. Nine sample preparations were performed with various Sn coverage and annealing treatments. The conditions that produced the best √3x√3 surface (low defect density and minimal area covered by islands and disorder) were: i) Sn coverage of 0.38 ML, ii) sample temperature slightly above that corresponding to the c(2x8) to 1x1 transition. This optimum preparation was used for the STM study of the LT 3x3 phase. The apparent height distribution of the Sn atoms in the 3x3 phase was analysed in detail and discussed in relation to the Sn 4d core-level line shape. Two peaks were observed in the apparent height distribution of the Sn atoms corresponding to the up and down atoms constituting the 3x3 reconstruction. Simulated Sn 4d core-level spectra were generated from the distribution by assuming a linear relation between the apparent height and the core-level binding energy. The simulated spectra are compared to experimental spectra appearing in the literature.

  • 6.
    Sakamoto, Kazuyuki
    et al.
    Chiba University, Japan .
    Kim, Tae-Hwan
    Pohang University of Science and Technology, South Korea .
    Kuzumaki, Takuya
    Chiba University, Japan .
    Mueller, Beate
    Chiba University, Japan .
    Yamamoto, Yuta
    Chiba University, Japan .
    Ohtaka, Minoru
    Chiba University, Japan .
    Osiecki, Jacek
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Miyamoto, Koji
    Hiroshima University, Japan .
    Takeichi, Yasuo
    University of Tokyo, Japan .
    Harasawa, Ayumi
    University of Tokyo, Japan .
    Stolwijk, Sebastian D.
    University of Munster, Germany .
    Schmidt, Anke B.
    University of Munster, Germany .
    Fujii, Jun
    CNRS, Italy .
    Uhrberg, Roger
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Donath, Markus
    University of Munster, Germany .
    Woong Yeom, Han
    Pohang University of Science and Technology, South Korea .
    Oda, Tatsuki
    Kanazawa University, Japan .
    Valley spin polarization by using the extraordinary Rashba effect on silicon2013Inngår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 4, nr 2073Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The addition of the valley degree of freedom to a two-dimensional spin-polarized electronic system provides the opportunity to multiply the functionality of next-generation devices. So far, however, such devices have not been realized due to the difficulty to polarize the valleys, which is an indispensable step to activate this degree of freedom. Here we show the formation of 100% spin-polarized valleys by a simple and easy way using the Rashba effect on a system with C-3 symmetry. This polarization, which is much higher than those in ordinary Rashba systems, results in the valleys acting as filters that can suppress the backscattering of spin-charge. The present system is formed on a silicon substrate, and therefore opens a new avenue towards the realization of silicon spintronic devices with high efficiency.

  • 7.
    Sohail, Hafiz Muhammad
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Osiecki, Jacek
    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.
    Electronic and atomic structures of a 3x3 surface formed by a binary Sn/Ag overlayer on the Ge(111)c(2x8) surface: ARPES, LEED, and STM studies2012Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, nr 20, s. 205409-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic and atomic structures of a well-ordered 3x3 periodicity of a binary Sn/Ag overlayer on Ge(111) have been studied. The ordered binary overlayer was formed by depositing 0.75 monolayer of Sn on an Ag/Ge(111) root 3x root 3 surface. Annealing at 330 degrees C resulted in a low-energy electron diffraction pattern that exhibited sharp spots. A detailed electronic structure investigation was performed by angle-resolved photoelectron spectroscopy. The Sn/Ag/Ge(111) 3x3 surface shows a rich band structure. There are seven bands which are positively identified as 3x3 surface bands, all within 1.5 eV below the Fermi level (E-F). The upper two bands disperse across E-F exhibiting steep almost linear dispersions down to a minimum energy of approximate to 0.40 eV below E-F at the (Gamma) over bar point (approximate to 0.30 eV at the (K) over bar point). Constant energy contours have been mapped in the 3x3 surface Brillouin zone (SBZ) in order to study an intriguing split observed in the band structure related to the two upper bands. It turned out that the two upper bands are degenerate along the (Gamma) over bar - (K) over bar and (M) over bar - (K) over bar symmetry lines of the 3x3 SBZ but separated along (Gamma) over bar - (M) over bar. Scanning tunneling microscopy images obtained at approximate to 40 K show essentially a hexagonal structure except for a honeycomb structure in a limited bias range imaging empty states. Core-level spectroscopy shows a narrow Sn 4d spectrum consistent with the high degree of structural order.

  • 8.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Osiecki, Jacek
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Syväjärvi, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Uhrberg, Roger
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Johansson, Leif
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Zakharov, A A
    Lund University.
    Substrate orientation: A way towards higher quality monolayer graphene growth on 6H-SiC(0001)2009Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, nr 15, s. L87-L90Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of substrate orientation on the morphology of graphene growth on 6H-SiC(0 0 0 1) was investigated using low-energy electron and scanning tunneling microscopy (LEEM and STM). Large area monolayer graphene was successfully furnace-grown on these substrates. Larger terrace widths and smaller step heights were obtained on substrates with a smaller mis-orientation from on-axis (0.03 degrees) than on those with a larger (0.25 degrees). Two different types of a carbon atom networks, honeycomb and three-for-six arrangement, were atomically resolved in the graphene monolayer. These findings are of relevance for various potential applications based on graphene-SiC structures.

  • 9.
    Wang, Weimin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Sohail, Hafiz Muhammad
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Osiecki, Jacek
    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.
    Broken symmetry induced band splitting in the Ag2Ge surface alloy on Ag(111)2014Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 12, s. 125410-1-125410-6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report a study of the atomic and electronic structures of the ordered Ag2Ge surface alloy containing ⅓ monolayer of Ge. Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES) data reveal a symmetry breaking of the expected √3 × √3 periodicity, which is established for other Ag2M alloys (M = Bi, Sb, Pb, and Sn). The deviation from a simple √3 × √3 structure manifests itself as a splitting of diffraction spots in LEED, as a striped structure with a 6× periodicity including a distortion of the local hexagonal structure in STM, and as a complex surface band structure in ARPES that is quite different from those of the other Ag2M alloys. These results are interesting in view of the differences in the atomic and electronic structures exhibited by different group IV elements interacting with Ag(111). Pb and Sn form √3 × √3 surface alloys on Ag(111), of which Ag2Pb shows a surface band structure with a clear spin-orbit split. Si and C form silicene and graphene structures, respectively, with linear band dispersions and the formation of Dirac cones as reported for graphene. The finding that Ag2Ge deviates from the ideal (√3 × √3) Ag2Sn and Ag2Pb surface alloys makes Ge an interesting “link” between the heavy group IV elements (Sn, Pb) and the light group IV elements (Si, C).

  • 10.
    Watcharinyanon, Somsakul
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Osiecki, Jacek
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Zakharov, A A
    Lund University.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Uhrberg, Roger
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif I
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Hydrogen intercalation of graphene grown on 6H-SiC(0001)2011Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 605, nr 17-18, s. 1662-1668Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Atomic hydrogen exposures on a monolayer graphene grown on the SiC(0001) surface are shown to result in hydrogen intercalation. The hydrogen intercalation induces a transformation of the monolayer graphene and the carbon buffer layer to bi-layer graphene without a buffer layer. The STM, LEED, and core-level photoelectron spectroscopy measurements reveal that hydrogen atoms can go underneath the graphene and the carbon buffer layer and bond to Si atoms at the substrate interface. This transforms the buffer layer into a second graphene layer. Hydrogen exposure results initially in the formation of bi-layer graphene islands on the surface. With larger atomic hydrogen exposures, the islands grow in size and merge until the surface is fully covered with bi-layer graphene. A (root 3 x root 3)R30 degrees periodicity is observed on the bi-layer areas. ARPES and energy filtered XPEEM investigations of the electron band structure confirm that after hydrogenation the single pi-band characteristic of monolayer graphene is replaced by two pi-bands that represent bi-layer graphene. Annealing an intercalated sample, representing bi-layer graphene, to a temperature of 850 degrees C. or higher, re-establishes the monolayer graphene with a buffer layer on SiC(0001).

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