| 1. |
- Szamota-Leandersson, Karolina, et al.
(författare)
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Adsorption of Cs on InAs(111) surfaces
- 2006
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 252:15, s. 5267-5270
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Tidskriftsartikel (refereegranskat)abstract
- Caesiated InAs(111)B (1 x 1) and InAs(111)A (2 x 2) surfaces have been studied by photoelectron spectroscopy. On the InAs(111)B a new (root 3 x root 3)R30 degrees reconstruction was observed. During Cs evaporation remarkably small changes are observed in the lone pair states, and no sign of an accumulation layer at the surface can be observed. Instead, the additional charge provided by Cs is rapidly transported towards the bulk. On the InAs(111)A cesium behaves as a typical electropositive alkali metal donator that enhances the already existing accumulation layer.
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| 2. |
- Szamota-Leandersson, Karolina, et al.
(författare)
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Correlated development of a (2x2) reconstruction and acharge accumulation layer on the InAs(111)-Bi surface
- 2011
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 605:1-2, s. 12-17
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Szamota-Leandersson, Karolina, et al.
(författare)
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Electronic structure of bismuth terminated InAs(100)
- 2009
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 603:1, s. 190-196
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Agnarsson, Björn, et al.
(författare)
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Investigation on the role of indium in the removal of metallic gallium from soft and hard sputtered GaN (0001) surfaces
- 2009
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 517:21, s. 6023-6026
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Tidskriftsartikel (refereegranskat)abstract
- Cleaning of GaN by argon sputtering and subsequent annealing introduces metallic gallium on the GaN surface. Once formed, this metallic gallium can be difficult to remove. it has a strong influence on the Fermi level position in the band gap and poses a problem for subsequent epitaxial growth on the surface. We present a method of removing metallic gallium from moderately damaged GaN surfaces by deposition of indium, and formation of an In-Ga alloy that can be desorbed by annealing at similar to 550 degrees C. After the In-Ga alloy has desorbed, photoemission spectra show that the Ga3d bulk component becomes narrower indicating a smoother and more homogeneous surface. This is also reflected in a sharper low energy electron diffraction pattern. On heavily damaged GaN surfaces, caused by hard sputtering, larger amount of metallic gallium forms after annealing at 600 degrees C. This gallium readily alloys with deposited indium, but the alloy does not desorb until a temperature of 840 degrees C is reached and even then, traces of both indium and metallic gallium could be found on the surface.
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| 5. |
- Belopolski, Ilya, et al.
(författare)
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Observation of a linked-loop quantum state in a topological magnet
- 2022
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 604:7907, s. 647-652
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Tidskriftsartikel (refereegranskat)abstract
- Quantum phases can be classified by topological invariants, which take on discrete values capturing global information about the quantum state1–13. Over the past decades, these invariants have come to play a central role in describing matter, providing the foundation for understanding superfluids5, magnets6,7, the quantum Hall effect3,8, topological insulators9,10, Weyl semimetals11–13 and other phenomena. Here we report an unusual linking-number (knot theory) invariant associated with loops of electronic band crossings in a mirror-symmetric ferromagnet14–20. Using state-of-the-art spectroscopic methods, we directly observe three intertwined degeneracy loops in the material’s three-torus, T3, bulk Brillouin zone. We find that each loop links each other loop twice. Through systematic spectroscopic investigation of this linked-loop quantum state, we explicitly draw its link diagram and conclude, in analogy with knot theory, that it exhibits the linking number (2, 2, 2), providing a direct determination of the invariant structure from the experimental data. We further predict and observe, on the surface of our samples, Seifert boundary states protected by the bulk linked loops, suggestive of a remarkable Seifert bulk–boundary correspondence. Our observation of a quantum loop link motivates the application of knot theory to the exploration of magnetic and superconducting quantum matter.
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| 6. |
- Berntsen, Magnus H., et al.
(författare)
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A spin- and angle-resolving photoelectron spectrometer
- 2010
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 81:3
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Tidskriftsartikel (refereegranskat)abstract
- A new type of hemispherical electron energy analyzer that permits angle and spin resolved photoelectron spectroscopy has been developed. The analyzer permits standard angle resolved spectra to be recorded with a two-dimensional detector in parallel with spin detection using a mini-Mott polarimeter. General design considerations as well as technical solutions are discussed and test results from the Au(111) surface state are presented.
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| 7. |
- Bianchi, M., et al.
(författare)
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One-dimensional spin texture of Bi(441): Quantum spin Hall properties without a topological insulator
- 2015
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 91:16
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Tidskriftsartikel (refereegranskat)abstract
- The high index (441) surface of bismuth has been studied using scanning tunneling microscopy (STM), angle resolved photoemission spectroscopy (APRES), and spin-resolved ARPES. The surface is strongly corrugated, exposing a regular array of (110)-like terraces. Two surface localized states are observed, both of which are linearly dispersing in one in-plane direction (k(x)), and dispersionless in the orthogonal in-plane direction (k(y)), and both of which have a Dirac-like crossing at k(x) = 0. Spin ARPES reveals a strong in-plane polarization, consistent with Rashba-like spin-orbit coupling. One state has a strong out-of-plane spin component, which matches with the miscut angle, suggesting its possible origin as an edge state. The electronic structure of Bi(441) has significant similarities with topological insulator surface states and is expected to support one-dimensional quantum spin Hall-like coupled spin-charge transport properties with inhibited backscattering, without requiring a topological insulator bulk.
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| 8. |
- Chernenk, Kirill, et al.
(författare)
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Performance and characterization of the FinEstBeAMS beamline at the MAX IV Laboratory
- 2021
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495. ; 28, s. 1620-1630
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Tidskriftsartikel (refereegranskat)abstract
- FinEstBeAMS (Finnish-Estonian Beamline for Atmospheric and Materials Sciences) is a multidisciplinary beamline constructed at the 1.5 GeV storage ring of the MAX IV synchrotron facility in Lund, Sweden. The beamline covers an extremely wide photon energy range, 4.5-1300 eV, by utilizing a single elliptically polarizing undulator as a radiation source and a single grazing-incidence plane grating monochromator to disperse the radiation. At photon energies below 70 eV the beamline operation relies on the use of optical and thin-film filters to remove higher-order components from the monochromated radiation. This paper discusses the performance of the beamline, examining such characteristics as the quality of the gratings, photon energy calibration, photon energy resolution, available photon flux, polarization quality and focal spot size.
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| 9. |
- Edwards, Brendan, et al.
(författare)
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Chemical Trends of the Bulk and Surface Termination-Dependent Electronic Structure of Metal-Intercalated Transition Metal Dichalcogenides
- 2024
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Ingår i: Chemistry of Materials. - 0897-4756. ; 36:15, s. 7117-7126
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Tidskriftsartikel (refereegranskat)abstract
- The addition of metal intercalants into the van der Waals gaps of transition metal dichalcogenides has shown great promise as a method for controlling their functional properties. For example, chiral helimagnetic states, current-induced magnetization switching, and a giant valley-Zeeman effect have all been demonstrated, generating significant renewed interest in this materials family. Here, we present a combined photoemission and density-functional theory study of three such compounds: Formula Presented, Formula Presented, and Formula Presented, to investigate chemical trends of the intercalant species on their bulk and surface electronic structure. Our resonant photoemission measurements indicate increased hybridization with the itinerant NbS2-derived conduction states with increasing atomic number of the intercalant, leading to pronounced mixing of the nominally localized intercalant states at the Fermi level. Using spatially and angle-resolved photoemission spectroscopy, we show how this impacts surface-termination-dependent charge transfers and leads to the formation of new dispersive states of mixed intercalant-Nb character at the Fermi level for the intercalant-terminated surfaces. This provides an explanation for the origin of anomalous states previously reported in this family of compounds and paves the way for tuning the nature of the magnetic interactions in these systems via control of the hybridization of the magnetic ions with the itinerant states.
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| 10. |
- Hedlund, E., et al.
(författare)
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A new test stand for heavy ion induced gas desorption measurements at TSL
- 2008
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 586:3, s. 377-381
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Tidskriftsartikel (refereegranskat)abstract
- In several experiments at CERN, GSI and BNL it has been found that the lifetime of highly energetic heavy ions in synchrotrons decreases with increasing number of injected ions. This phenomenon occurs due to the collisions of beam ions and residual gas molecules leading to the change of charge of the ions and their loss on the vacuum chamber walls, which in turn cause ion-induced gas desorption and further pressure increase. To gain a deeper understanding of the ion-induced desorption process in the energy range 5-45 MeV/u, a dedicated test stand was built at the end of the K beamline at The Svedberg Laboratory (TSL) in Uppsala, Sweden. The energy range was chosen due to the fact that the injection energy of the heavy ion synchrotron SIS18 at GSI will be 10 MeV/u, and that there are insufficient data in this energy range. A Test Particle Monte-Carlo model of the experimental set-up was build-up, run and analysed for different sample configurations. An important result is that for the same sample material the desorption yield from a flat sample causes a 1.58 times larger pressure increase than that of a tubular sample. A detailed explanation of the set-up is presented.
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