| 1. |
- Chaika, Alexander N., et al.
(författare)
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Rotated domain network in graphene on cubic-SiC(001)
- 2014
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 25:13
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Tidskriftsartikel (refereegranskat)abstract
- The atomic structure of the cubic-SiC(001) surface during ultra-high vacuum graphene synthesis has been studied using scanning tunneling microscopy (STM) and low-energy electron diffraction. Atomically resolved STM studies prove the synthesis of a uniform, millimeter-scale graphene overlayer consisting of nanodomains rotated by +/- 13.5 degrees relative to the < 110 >-directed boundaries. The preferential directions of the domain boundaries coincide with the directions of carbon atomic chains on the SiC(001)-c(2 x 2) reconstruction, fabricated prior to graphene synthesis. The presented data show the correlation between the atomic structures of the SiC(001)-c(2 x 2) surface and the graphene/SiC(001) rotated domain network and pave the way for optimizing large-area graphene synthesis on low-cost cubic-SiC(001)/Si(001) wafers.
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| 2. |
- Wu, Han-Chun, et al.
(författare)
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Large positive in-plane magnetoresistance induced by localized states at nanodomain boundaries in graphene
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Graphene supports long spin lifetimes and long diffusion lengths at room temperature, making it highly promising for spintronics. However, making graphene magnetic remains a principal challenge despite the many proposed solutions. Among these, graphene with zig-zag edges and ripples are the most promising candidates, as zig-zag edges are predicted to host spin-polarized electronic states, and spin-orbit coupling can be induced by ripples. Here we investigate the magnetoresistance of graphene grown on technologically relevant SiC/Si(001) wafers, where inherent nanodomain boundaries sandwich zig-zag structures between adjacent ripples of large curvature. Localized states at the nanodomain boundaries result in an unprecedented positive in-plane magnetoresistance with a strong temperature dependence. Our work may offer a tantalizing way to add the spin degree of freedom to graphene.
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| 3. |
- Chaika, Alexander N., et al.
(författare)
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Continuous wafer-scale graphene on cubic-SiC(001)
- 2013
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Ingår i: Nano Reseach. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 6:8, s. 562-570
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Tidskriftsartikel (refereegranskat)abstract
- The atomic and electronic structure of graphene synthesized on commercially available cubic-SiC(001)/Si(001) wafers have been studied by low energy electron microscopy (LEEM), scanning tunneling microscopy (STM), low energy electron diffraction (LEED), and angle resolved photoelectron spectroscopy (ARPES). LEEM and STM data prove the wafer-scale continuity and uniform thickness of the graphene overlayer on SiC(001). LEEM, STM and ARPES studies reveal that the graphene overlayer on SiC(001) consists of only a few monolayers with physical properties of quasi-freestanding graphene. Atomically resolved STM and micro-LEED data show that the top graphene layer consists of nanometersized domains with four different lattice orientations connected through the aOE (c) 110 >-directed boundaries. ARPES studies reveal the typical electron spectrum of graphene with the Dirac points close to the Fermi level. Thus, the use of technologically relevant SiC(001)/Si(001) wafers for graphene fabrication represents a realistic way of bridging the gap between the outstanding properties of graphene and their applications.
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| 4. |
- Walls, B., et al.
(författare)
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Nanodomain structure of single crystalline nickel oxide
- 2021
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Ingår i: Scientific Reports. - : Nature Portfolio. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- In this work we present a comprehensive study of the domain structure of a nickel oxide single crystal grown by floating zone melting and suggest a correlation between point defects and the observed domain structure. The properties and structure of domains dictate the dynamics of resistive switching, water splitting and gas sensing, to name but a few. Investigating the correlation between point defects and domain structure can provide a deeper understanding of their formation and structure, which potentially allows one to tailor domain structure and the dynamics of the aforementioned applications. A range of inhomogeneities are observed by diffraction and microscopy techniques. X-ray and low-energy electron diffraction reveal domains on the submicron- and nanometer-scales, respectively. In turn, these domains are visualised by atomic force and scanning tunneling microscopy (STM), respectively. A comprehensive transmission electron microscopy (TEM) study reveals inhomogeneities ranging from domains of varying size, misorientation of domains, variation of the lattice constant and bending of lattice planes. X-ray photoelectron spectroscopy and electron energy-loss spectroscopy indicate the crystal is Ni deficient. Density functional theory calculations-considering the spatial and electronic disturbance induced by the favourable nickel vacancy-reveal a nanoscale distortion comparable to STM and TEM observations. The different inhomogeneities are understood in terms of the structural relaxation induced by ordering of nickel vacancies, which is predicted to be favourable.
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| 5. |
- Wu, Han-Chun, et al.
(författare)
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Transport Gap Opening and High On-Off Current Ratio in Trilayer Graphene with Self-Aligned Nanodomain Boundaries.
- 2015
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 9:9, s. 8967-8975
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Tidskriftsartikel (refereegranskat)abstract
- Trilayer graphene exhibits exceptional electronic properties that are of interest both for fundamental science and for technological applications. The ability to achieve a high on-off current ratio is the central question in this field. Here, we propose a simple method to achieve a current on-off ratio of 10(4) by opening a transport gap in Bernal-stacked trilayer graphene. We synthesized Bernal-stacked trilayer graphene with self-aligned periodic nanodomain boundaries (NBs) on the technologically relevant vicinal cubic-SiC(001) substrate and performed electrical measurements. Our low-temperature transport measurements clearly demonstrate that the self-aligned periodic NBs can induce a charge transport gap greater than 1.3 eV. More remarkably, the transport gap of ∼0.4 eV persists even at 100 K. Our results show the feasibility of creating new electronic nanostructures with high on-off current ratios using graphene on cubic-SiC.
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| 6. |
- Lubben, Olaf, et al.
(författare)
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Self-assembly of Fe nanocluster arrays on templated surfaces
- 2012
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 111:7
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Tidskriftsartikel (refereegranskat)abstract
- The growth of Fe nanoclusters on the Ge(001) and MoO2/Mo(110) surfaces has been studied using low-temperature scanning tunneling microscopy (STM) and X-ray magnetic circular dichroism (XMCD). STM results indicate that at low coverage Fe atoms self-assemble on both surfaces into well-separated nanoclusters, which nucleate at equivalent surface sites. Their size, shape, and the observed spatial separation are dictated by the substrate and depend on preparation conditions. Annealing the Fe nanoclusters on Ge(001) at 420 K leads to the formation of linear nanocluster arrays, which follow the Ge dimer rows of the substrate, due to cluster mobility at such temperature. In turn, linear Fe nanocluster arrays are formed on the MoO2/Mo(110) surface at room temperature at a surface coverage greater than 0.5 monolayer. This is due to the more pronounced row pattern of the MoO2/Mo(110) surface compared to Ge(001). These nanocluster arrays follow the direction of the oxide rows of the strained MoO2/Mo(110) surface. The Fe nanoclusters formed on both surfaces show a superparamagnetic behavior as measured by XMCD. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676207]
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| 7. |
- Luebben, Olaf, et al.
(författare)
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Fe Nanoclusters on the Ge(001) Surface Studied by Scanning Tunneling Microscopy, Density Functional Theory Calculations and X-Ray Magnetic Circular Dichroism
- 2011
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Ingår i: Nano Reseach. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 4:10, s. 971-978
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Tidskriftsartikel (refereegranskat)abstract
- The growth of Fe nanoclusters on the Ge(001) surface has been studied using low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. STM results indicate that Fe nucleates on the Ge(001) surface, forming well-ordered nanoclusters of uniform size. Depending on the preparation conditions, two types of nanoclusters were observed having either four or sixteen Fe atoms within a nanocluster. The results were confirmed by DFT calculations. Annealing the nanoclusters at 420 K leads to the formation of nanorow structures, due to cluster mobility at such temperature. The Fe nanoclusters and nanorow structures formed on the Ge(001) surface show a superparamagnetic behaviour as measured by X-ray magnetic circular dichroism.
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| 8. |
- Murphy, Barry E., et al.
(författare)
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Homolytic Cleavage of Molecular Oxygen by Manganese Porphyrins Supported on Ag(111)
- 2014
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 8:5, s. 5190-5198
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen binding and cleavage are important for both molecular recognition and catalysis. Mn-based porphyrins in particular are used as catalysts for the epoxidation of alkenes, and in this study the homolytic cleavage of O-2 by a surface-supported monolayer of Mn porphyrins on Ag(111) is demonstrated by scanning tunneling microscopy, X-ray absorption, and X-ray photoemission. As deposited, {5,10,15,20-tetraphenylporphyrinato}Mn(III)CI(MnCITPP) adopts a saddle conformation with the average plane of its macrocyde parallel to the substrate and the axial CI ligand pointing upward, away from the substrate. The adsorption of MnCITPP on Ag(111) Is accompanied by a reduction of the Mn oxidation state from Mn(III) to Mn(II) due to charge transfer between the substrate and the molecule. Annealing the Mn(II)CITPP monolayer up to 510 K causes the chlorine ligands to desorb from the porphyrins while leaving the monolayer intact. The Mn(II)TPP is stabilized by the surface acting as an axial ligand for the metal center. Exposure of the Mn(11)TPP/Ag(111) system to molecular oxygen results in the dissociation of O-2 and forms pairs of Mn(111)OTPP molecules on the surface. Annealing at 445 K reduces the Mn(111)OTPP complex back to Mn(II)TPP/Ag(111). The activation energies for Cl and 0 removal were found to be 0.35 +/- 0.02 eV and 0.26 +/- 0.03 eV, respectively.
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