| 1. |
- Du, J., et al.
(författare)
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Probe of local impurity states by bend resistance measurements in graphene cross junctions
- 2016
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 27:24
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Tidskriftsartikel (refereegranskat)abstract
- We report on low-temperature transport measurements on four-terminal cross junction devices fabricated from high-quality graphene grown by chemical vapor deposition. At high magnetic fields, the bend resistance reveals pronounced peak structures at the quantum Hall plateau transition, which can be attributed to the edge state transport through the junctions. We further demonstrate that the bend resistance is drastically affected by the presence of local impurity states in the junction regions, and exhibits an unusual asymmetric behavior with respect to the magnetic field direction. The observations can be understood in a model taking into account the combination of the edge transport and an asymmetric scatterer. Our results demonstrate that a graphene cross junction may serve as a sensitive probe of local impurity states in graphene at the nanoscale.
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| 2. |
- Fan, Jin, et al.
(författare)
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Design of Novel Flat Bend Crossed Dipole for Wideband Phased Array Feed Applications
- 2019
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Ingår i: 2019 International Symposium on Antennas and Propagation, ISAP 2019 - Proceedings.
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Konferensbidrag (refereegranskat)abstract
- This paper presents a novel Phased Array Feed (PAF) element based on flat bend crossed dipole fed by 50-Ohm coaxial line. The PAF element is dual-polarized and made from all-metal to minimize Ohmic losses and simplify cryogenic integration. It is optimized for 4- 8 GHz band aiming to possible later integration in the SKA pathfinder PHAROS2. The proposed design can also be a good element candidate of PAF for the Five hundred meter Aperture Spherical Telescope (FAST) and Qi Tai Telescope (QTT) as well as other large radio telescopes.
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| 3. |
- Fan, Jin, et al.
(författare)
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Design of Octave-bandwidth Phased Array Feed for Large Radio Telescope
- 2019
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Ingår i: 13th European Conference on Antennas and Propagation, EuCAP 2019.
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Konferensbidrag (refereegranskat)abstract
- This paper presents design scenarios of Octave-bandwidth Phase Array Feed (PAF) based on a novel wideband dual polarized tightly-fed Bowtie antenna element. The PAF is optimized for the 4 - 8GHz band aiming to possible later integration in the SKA pathfinder PHAROS2. The proposed design can be a good candidate of PAF for the Five hundred meter Aperture Spherical Telescope (FAST) and Qi Tai Telescope (QTT) as well as other large radio telescopes.
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| 4. |
- Jing, Yumei, et al.
(författare)
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A Single-Electron Transistor Made of a 3D Topological Insulator Nanoplate
- 2019
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 31:42
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Tidskriftsartikel (refereegranskat)abstract
- Quantum confined devices of 3D topological insulators are proposed to be promising and of great importance for studies of confined topological states and for applications in low-energy-dissipative spintronics and quantum information processing. The absence of energy gap on the topological insulator surface limits the experimental realization of a quantum confined system in 3D topological insulators. Here, the successful realization of single-electron transistor devices in Bi2Te3 nanoplates using state-of-the-art nanofabrication techniques is reported. Each device consists of a confined central island, two narrow constrictions that connect the central island to the source and drain, and surrounding gates. Low-temperature transport measurements demonstrate that the two narrow constrictions function as tunneling junctions and the device shows well-defined Coulomb current oscillations and Coulomb-diamond-shaped charge-stability diagrams. This work provides a controllable and reproducible way to form quantum confined systems in 3D topological insulators, which should greatly stimulate research toward confined topological states, low-energy-dissipative devices, and quantum information processing.
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| 5. |
- Jing, Yumei, et al.
(författare)
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Weak antilocalization and electron-electron interaction in coupled multiple-channel transport in a Bi2Se3 thin film.
- 2016
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 8:4, s. 1879-1885
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Tidskriftsartikel (refereegranskat)abstract
- The electron transport properties of a topological insulator Bi2Se3 thin film are studied in Hall-bar geometry. The film with a thickness of 10 nm is grown by van der Waals epitaxy on fluorophlogopite mica and Hall-bar devices are fabricated from the as-grown film directly on the mica substrate. Weak antilocalization and electron-electron interaction effects are observed and analyzed at low temperatures. The phase-coherence length extracted from the measured weak antilocalization characteristics shows a strong power-law increase with decreasing temperature and the transport in the film is shown to occur via coupled multiple (topological surface and bulk states) channels. The conductivity of the film shows a logarithmical decrease with decreasing temperature and thus the electron-electron interaction plays a dominant role in quantum corrections to the conductivity of the film at low temperatures.
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| 6. |
- Li, Jiayu, et al.
(författare)
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Charge transport and electron-hole asymmetry in low-mobility graphene/hexagonal boron nitride heterostructures
- 2018
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 123:6
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Tidskriftsartikel (refereegranskat)abstract
- Graphene/hexagonal boron nitride (G/h-BN) heterostructures offer an excellent platform for developing nanoelectronic devices and for exploring correlated states in graphene under modulation by a periodic superlattice potential. Here, we report on transport measurements of nearly 0°-twisted G/h-BN heterostructures. The heterostructures investigated are prepared by dry transfer and thermally annealing processes and are in the low mobility regime (approximately 3000 cm2 V-1s-1 at 1.9 K). The replica Dirac spectra and Hofstadter butterfly spectra are observed on the hole transport side, but not on the electron transport side, of the heterostructures. We associate the observed electron-hole asymmetry with the presence of a large difference between the opened gaps in the conduction and valence bands and a strong enhancement in the interband contribution to the conductivity on the electron transport side in the low-mobility G/h-BN heterostructures. We also show that the gaps opened at the central Dirac point and the hole-branch secondary Dirac point are large, suggesting the presence of strong graphene-substrate interaction and electron-electron interaction in our G/h-BN heterostructures. Our results provide additional helpful insight into the transport mechanism in G/h-BN heterostructures.
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| 7. |
- Li, Jiayu, et al.
(författare)
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Electron-Hole Symmetry Breaking in Charge Transport in Nitrogen-Doped Graphene
- 2017
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 11:5, s. 4641-4650
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Tidskriftsartikel (refereegranskat)abstract
- Graphitic nitrogen-doped graphene is an excellent platform to study scattering processes of massless Dirac Fermions by charged impurities, in which high mobility can be preserved due to the absence of lattice defects through direct substitution of carbon atoms in the graphene lattice by nitrogen atoms. In this work, we report on electrical and magnetotransport measurements of high-quality graphitic nitrogen-doped graphene. We show that the substitutional nitrogen dopants in graphene introduce atomically sharp scatters for electrons but long-range Coulomb scatters for holes and, thus, graphitic nitrogen-doped graphene exhibits clear electron-hole asymmetry in transport properties. Dominant scattering processes of charge carriers in graphitic nitrogen-doped graphene are analyzed. It is shown that the electron-hole asymmetry originates from a distinct difference in intervalley scattering of electrons and holes. We have also carried out the magnetotransport measurements of graphitic nitrogen-doped graphene at different temperatures and the temperature dependences of intervalley scattering, intravalley scattering, and phase coherent scattering rates are extracted and discussed. Our results provide an evidence for the electron-hole asymmetry in the intervalley scattering induced by substitutional nitrogen dopants in graphene and shine a light on versatile and potential applications of graphitic nitrogen-doped graphene in electronic and valleytronic devices.
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| 8. |
- Meng, Mengmeng, et al.
(författare)
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Strong spin-orbit interaction and magnetotransport in semiconductor Bi2O2Se nanoplates
- 2018
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 10:6, s. 2704-2710
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor Bi2O2Se nanolayers of high crystal quality have been realized via epitaxial growth. These two-dimensional (2D) materials possess excellent electron transport properties with potential application in nanoelectronics. It is also strongly expected that the 2D Bi2O2Se nanolayers can be an excellent material platform for developing spintronic and topological quantum devices if the presence of strong spin-orbit interaction in the 2D materials can be experimentally demonstrated. Herein, we report the experimental determination of the strength of spin-orbit interactions in Bi2O2Se nanoplates through magnetotransport measurements. The nanoplates are epitaxially grown by chemical vapor deposition, and the magnetotransport measurements are performed at low temperatures. The measured magnetoconductance exhibits a crossover behavior from weak antilocalization to weak localization at low magnetic fields with increasing temperature or decreasing back gate voltage. We have analyzed this transition behavior of magnetoconductance based on an interference theory, which describes quantum correction to the magnetoconductance of a 2D system in the presence of spin-orbit interaction. Dephasing length and spin relaxation length are extracted from the magnetoconductance measurements. Compared to the case of other semiconductor nanostructures, the extracted relatively short spin relaxation length of ∼150 nm indicates the existence of a strong spin-orbit interaction in Bi2O2Se nanolayers.
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| 9. |
- Meng, Mengmeng, et al.
(författare)
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Universal conductance fluctuations and phase-coherent transport in a semiconductor Bi2O2Se nanoplate with strong spin-orbit interaction
- 2019
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 11:22, s. 10622-10628
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Tidskriftsartikel (refereegranskat)abstract
- We report on phase-coherent transport studies of a Bi2O2Se nanoplate and on observation of universal conductance fluctuations and spin-orbit interaction induced reduction in fluctuation amplitude in the nanoplate. Thin-layered Bi2O2Se nanoplates are grown by chemical vapor deposition (CVD) and transport measurements are made on a Hall-bar device fabricated from a CVD-grown nanoplate. The measurements show weak antilocalization at low magnetic fields at low temperatures, as a result of spin-orbit interaction, and a crossover toward weak localization with increasing temperature. Temperature dependences of characteristic transport lengths, such as spin relaxation length, phase coherence length, and mean free path, are extracted from the low-field measurement data. Universal conductance fluctuations are visible in the low-temperature magnetoconductance over a large range of magnetic fields and the phase coherence length extracted from the autocorrelation function is consistent with the result obtained from the weak localization analysis. More importantly, we find a strong reduction in amplitude of the universal conductance fluctuations and show that the results agree with the analysis assuming strong spin-orbit interaction in the Bi2O2Se nanoplate.
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| 10. |
- Snyder, Gretchen L., et al.
(författare)
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Preclinical profile of ITI-214, an inhibitor of phosphodiesterase 1, for enhancement of memory performance in rats
- 2016
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Ingår i: Psychopharmacology. - : Springer Science and Business Media LLC. - 0033-3158 .- 1432-2072. ; 233:17, s. 3113-3124
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Tidskriftsartikel (refereegranskat)abstract
- Rationale: Therapeutic agents for memory enhancement in psychiatric disorders, such as schizophrenia, are urgently needed.Objective: The aim of this study is to characterize the preclinical profile of ITI-214, a potent inhibitor of phosphodiesterase 1 (PDE1).Methods: ITI-214 was assayed for inhibition of PDE1 versus other PDE enzyme families using recombinant human PDE enzymes and for off-target binding to 70 substrates (General SEP II diversity panel; Caliper Life Sciences). Effects of ITI-214 (0.1–10 mg/kg, po) on memory performance were assayed in rats using the novel object recognition (NOR) paradigm, with drug given at specified time points prior to or following exposure to objects in an open field. ITI-214 was evaluated for potential drug-drug interaction with risperidone in rats using conditioned avoidance response (CAR) and pharmacokinetic assessments.Results: ITI-214 inhibited PDE1A (Ki = 33 pmol) with >1000-fold selectivity for the nearest other PDE family (PDE4D) and displayed minimal off-target binding interactions in a 70-substrate selectivity profile. By using specific timing of oral ITI-214 administration, it was demonstrated in the NOR that ITI-214 is able to enhance acquisition, consolidation, and retrieval memory processes. All memory effects were in the absence of effects on exploratory behavior. ITI-214 did not disrupt the risperidone pharmacokinetic profile or effects in CAR.Conclusions: ITI-214 improved the memory processes of acquisition, consolidation, and retrieval across a broad dose range (0.1–10 mg/kg, po) without disrupting the antipsychotic-like activity of a clinical antipsychotic medication, specifically risperidone. Clinical development of ITI-214 is currently in progress.
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