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- Iwasaki, Takayuki, et al.
(författare)
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Formation and structural analysis of twisted bilayer graphene on Ni(111) thin flims
- 2014
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 625, s. 44-49
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Tidskriftsartikel (refereegranskat)abstract
- We synthesized twisted bilayer graphene on single crystalline Ni(111) thin films to analyze the statistical twist angle distribution on a large scale. The twisted bilayer graphene was formed by combining two growth methods, namely the catalytic surface reaction of hydrocarbons and carbon segregation from Ni. Low energy electron diffraction (LEED) investigations directly revealed dominant twist angles of 13 degrees, 22 degrees, 38 degrees, and 47 degrees. We show that the angle distribution is closely related to the sizes of Moire superlattices which form at commensurate rotation angles. In addition to the commensurate angles, quasi-periodic Moire structures were also formed in the vicinity of the dominant angles, confirmed by microscopic observations with low energy electron microscopy and scanning tunneling microscopy (STM). The quasi-periodic Moire patterns are presumably caused by insufficient mobility of carbon atoms during the segregation growth while cooling. Micro-LEED studies reveal that the size of single twisted domains is below 400 nm. Atomic-scale characterization by STM indicates that the twisted layer grown by segregation is located underneath the layer grown by surface reaction, i.e. between the Ni surface and the top single-crystal graphene layer. (C) 2014 Elsevier B.V. All rights reserved.
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| 2. |
- Krumrein, Marcel, et al.
(författare)
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Precise Characterization of a Waveguide Fiber Interface in Silicon Carbide
- 2024
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Ingår i: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022.
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Tidskriftsartikel (refereegranskat)abstract
- Spin-active optical emitters in silicon carbide are excellent candidates toward the development of scalable quantum technologies. However, efficient photon collection is challenged by undirected emission patterns from optical dipoles, as well as low total internal reflection angles due to the high refractive index of silicon carbide. Based on recent advances with emitters in silicon carbide waveguides, we now demonstrate a comprehensive study of nanophotonic waveguide-to-fiber interfaces in silicon carbide. We find that across a large range of fabrication parameters, our experimental collection efficiencies remain above 90%. Further, by integrating silicon vacancy color centers into these waveguides, we demonstrate an overall photon count rate of 181 kilo-counts per second, which is an order of magnitude higher compared to standard setups. We also quantify the shift of the ground state spin states due to strain fields, which can be introduced by waveguide fabrication techniques. Finally, we show coherent electron spin manipulation with waveguide-integrated emitters with state-of-the-art coherence times of T-2 similar to 42 mu s. The robustness of our methods is very promising for quantum networks based on multiple orchestrated emitters.
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