| 1. |
- Ali-Löytty, Harri, et al.
(författare)
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The role of (FeCrSi)2(MoNb)-type Laves phase on the formation of Mn-rich protective oxide scale on ferritic stainless steel
- 2018
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Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X. ; 132, s. 214-222
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Tidskriftsartikel (refereegranskat)abstract
- Microalloying of stainless steel with reactive elements increases oxidation resistance but makes the alloy prone to microstructural changes. XPS results reveal changes in the initial oxidation mechanism on Ti-Nb stabilized ferritic stainless steel (EN 1.4521) after 120 h heat treatment at 650 °C. Age-precipitation of (FeCrSi)2(MoNb)-type Laves phase resulted in less pronounced surface segregation and oxidation of microalloying elements. Si oxidizes preferentially at the Laves precipitate locations via outward diffusion forming diffusion barrier for the other scale forming elements. Most significantly the diffusion of Mn and the formation of low volatile (Mn,Cr)3O4 spinel oxide at the surface was strongly suppressed.
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| 2. |
- Bouhafs, Chamseddine, et al.
(författare)
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Synthesis of large-area rhombohedral few-layer graphene by chemical vapor deposition on copper
- 2021
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223. ; 177, s. 282-290
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Tidskriftsartikel (refereegranskat)abstract
- Rhombohedral-stacked few-layer graphene (FLG) displays peculiar electronic properties that could lead to phenomena such as high-temperature superconductivity and magnetic ordering. To date, experimental studies have been mainly limited by the difficulty in isolating rhombohedral FLG with thickness exceeding 3 layers and device-compatible size. In this work, we demonstrate the synthesis and transfer of rhombohedral graphene with thickness up to 9 layers and areas up to ∼50 μm2. The domains of rhombohedral FLG are identified by Raman spectroscopy and are found to alternate with Bernal regions within the same crystal in a stripe-like configuration. Near-field nano-imaging further confirms the structural integrity of the respective stacking orders. Combined spectroscopic and microscopic analyses indicate that rhombohedral-stacking formation is strongly correlated to the underlying copper step-bunching and emerges as a consequence of interlayer displacement along preferential crystallographic orientations. The growth and transfer of rhombohedral FLG with the reported thickness and size shall facilitate the observation of predicted unconventional physics and ultimately add to its technological relevance.
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| 3. |
- Cao, Wei, et al.
(författare)
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X-ray photoemission electron microscope determination of origins of room temperature ferromagnetism and photoluminescence in high co-content coxzn1-xo films.
- 2014
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Ingår i: Surface Review and Letters. - 0218-625X. ; 21:4
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we reported on the X-ray photoemission electron microscope (XPEEM) determination of magnetic and luminescence origins for two CoxZn1-xO films. The cobalt fraction x of radio frequency co-sputtered samples were 0.86(2) and 0.92(2), respectively. Films were ferromagnetic and semiconductive. Unique narrow green color lines beside the ZnO intrinsic emissions were found with a decay time in microsecond range at room temperature. Origins of magnetic and luminescence properties were determined with XPEEM. The X-ray absorption near edge structure at the CoL3-edge denoted that Co was partially oxidized, and phase-contrast images together with chemical composition identification further proved that Co and CoO co-existed in the samples. The ferromagnetism was attributed to ferromagnetism of Co clusters partially canceled by the antiferromagnetism of its oxide, and the photoluminescence to bound exciton in ZnO nanoclusters and defect related centers of ZnO nanoclusters in a Co-rich matrix. Present results show possibilities for adjusting magnetic and luminescence properties of Co-ZnO compounds by changing the cobalt concentration.
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| 4. |
- Cooil, S. P., et al.
(författare)
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Controlling the growth of epitaxial graphene on metalized diamond (111) surface
- 2015
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 107:18
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Tidskriftsartikel (refereegranskat)abstract
- The 2-dimensional transformation of the diamond (111) surface to graphene has been demonstrated using ultrathin Fe films that catalytically reduce the reaction temperature needed for the conversion of sp(3) to sp(2) carbon. An epitaxial system is formed, which involves the re-crystallization of carbon at the Fe/vacuum interface and that enables the controlled growth of monolayer and multilayer graphene films. In order to study the initial stages of single and multilayer graphene growth, real time monitoring of the system was preformed within a photoemission and low energy electron microscope. It was found that the initial graphene growth occurred at temperatures as low as 500 degrees C, whilst increasing the temperature to 560 degrees C was required to produce multi-layer graphene of high structural quality. Angle resolved photoelectron spectroscopy was used to study the electronic properties of the grown material, where a graphene-like energy momentum dispersion was observed. The Dirac point for the first layer is located at 2.5 eV below the Fermi level, indicating an n-type doping of the graphene due to substrate interactions, while that of the second graphene layer lies close to the Fermi level. (C) 2015 AIP Publishing LLC.
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| 5. |
- Cooil, Simon P., et al.
(författare)
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In Situ Patterning of Ultrasharp Dopant Profiles in Silicon
- 2017
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 11:2, s. 1683-1688
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Tidskriftsartikel (refereegranskat)abstract
- We develop a method for patterning a buried two-dimensional electron gas (2DEG) in silicon using low kinetic energy electron stimulated desorption (LEESD) of a monohydride resist mask. A buried 2DEG forms as a result of placing a dense and narrow profile of phosphorus dopants beneath the silicon surface; a so-called δ -layer. Such 2D dopant profiles have previously been studied theoretically, and by angle-resolved photoemission spectroscopy, and have been shown to host a 2DEG with properties desirable for atomic-scale devices and quantum computation applications. Here we outline a patterning method based on low kinetic energy electron beam lithography, combined with in situ characterization, and demonstrate the formation of patterned features with dopant concentrations sufficient to create localized 2DEG states.
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| 6. |
- Forti, Stiven, et al.
(författare)
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Semiconductor to metal transition in two-dimensional gold and its van der Waals heterostack with graphene
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of two-dimensional (2D) transition metals has attracted growing attention for both fundamental and application-oriented investigations, such as 2D magnetism, nanoplasmonics and non-linear optics. However, the large-area synthesis of this class of materials in a single-layer form poses non-trivial difficulties. Here we present the synthesis of a large-area 2D gold layer, stabilized in between silicon carbide and monolayer graphene. We show that the 2D-Au ML is a semiconductor with the valence band maximum 50 meV below the Fermi level. The graphene and gold layers are largely non-interacting, thereby defining a class of van der Waals heterostructure. The 2D-Au bands, exhibit a 225 meV spin-orbit splitting along the Γ K ¯ direction, making it appealing for spin-related applications. By tuning the amount of gold at the SiC/graphene interface, we induce a semiconductor to metal transition in the 2D-Au, which has not yet been observed and hosts great interest for fundamental physics.
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| 7. |
- Greco, Rossella, et al.
(författare)
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Activation of 2D cobalt hydroxide with 0D cobalt oxide decoration for microplastics degradation and hydrogen evolution
- 2023
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Ingår i: Chemical Engineering Journal. - 1385-8947. ; 471
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Tidskriftsartikel (refereegranskat)abstract
- The 2D semiconductors are important players in environmental and energy fields due to their unique catalytic and physical properties defined by their dimensionality. Versatile functionalities on one 2D matrix will enlarge its application scopes but require dedicated engineering paths. In this work, we present a cross-dimensional strategy by decorating 0D Co3O4 onto 2D Co(OH)2 to form a multifunctional photocatalyst. The one-pot hydrothermally synthesized Co3O4@Co(OH)2 composite is capable of degrading polystyrene microplastics with an efficiency of 40% under 0.495 W white LED illumination. In a separated experiment, H2 evolution reaction from water splitting was evaluated in absence of sacrificial agents leading to 43 μmol g−1 and to an apparent quantum efficiency of 3.48% at 420 nm. The study of the energy band diagrams by UV–Visible and ambient photoemission spectroscopy and the analysis of the radicals involved in the reaction of photocatalytic degradation allow to unveil the mechanisms for both the processes herein studied. Finally, we could confirm that the heterostructure benefits the redox potentials of 2D and 0D counterparts and facile electron transfers when crossing two different dimensions. These results provide guidelines and inspiration for cross-dimensional activations of low-dimensional materials for versatile functionalities.
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| 8. |
- Head, Ashley R., et al.
(författare)
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In situ characterization of the deposition of anatase TiO2 on rutile TiO2(110)
- 2018
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Ingår i: Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 36:2
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Tidskriftsartikel (refereegranskat)abstract
- Growing additional TiO2 thin films on TiO2 supstrates in ultrahigh vacuum (UHV)-compatible chambers have many applications for sample preparation, such as smoothing surface morphologies, templating, and covering impurities. However, there has been little study into how to control the morphology of TiO2 films deposited onto TiO2 supstrates, especially using atomic layer deposition (ALD) precursors. Here, the authors show the growth of a TiO2 film on a rutile TiO2(110) surface using titanium tetraisopropoxide (TTIP) and water as the precursors at pressures well below those used in common ALD reactors. X-ray absorption spectroscopy suggests that the relatively low sample temperature (175 °C) results in an anatase film despite the rutile template of the supstrate. Using ambient pressure x-ray photoelectron spectroscopy, the adsorption of TTIP was found to be self-limiting, even at room temperature. No molecular water was found to adsorb on the surface. The deposited thickness suggests that an alternate chemical vapor deposition growth mechanism may be dominating the growth process. This study highlights the possibility that metal oxide film deposition from molecular precursors is an option for sample preparations in common UHV-compatible chambers.
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| 9. |
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| 10. |
- Höcker, Jan, et al.
(författare)
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Growth and structure of ultrathin praseodymium oxide layers on ruthenium(0001)
- 2016
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Ingår i: Physical Chemistry Chemical Physics. - 1463-9076.
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Tidskriftsartikel (refereegranskat)abstract
- The growth, morphology, structure, and stoichiometry of ultrathin praseodymium oxide layers on Ru(0001) were studied using low-energy electron microscopy and diffraction, photoemission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. At a growth temperature of 760 [degree]C, the oxide is shown to form hexagonally close-packed (A-type) Pr2O3(0001) islands that are up to 3 nm high. Depending on the local substrate step density, the islands either adopt a triangular shape on sufficiently large terraces or acquire a trapezoidal shape with the long base aligned along the substrate steps.
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