| 1. |
- Zhou, Yu, et al.
(författare)
-
Revealing the Contribution of Individual Factors to Hydrogen Evolution Reaction Catalytic Activity
- 2018
-
Ingår i: Advanced Materials. - : Wiley-VCH Verlagsgesellschaft. - 0935-9648 .- 1521-4095. ; 30:18
-
Tidskriftsartikel (refereegranskat)abstract
- For the electrochemical hydrogen evolution reaction (HER), the electrical properties of catalysts can play an important role in influencing the overall catalytic activity. This is particularly important for semiconducting HER catalysts such as MoS2, which has been extensively studied over the last decade. Herein, on-chip microreactors on two model catalysts, semiconducting MoS2 and semimetallic WTe2, are employed to extract the effects of individual factors and study their relations with the HER catalytic activity. It is shown that electron injection at the catalyst/current collector interface and intralayer and interlayer charge transport within the catalyst can be more important than thermodynamic energy considerations. For WTe2, the site-dependent activities and the relations of the pure thermodynamics to the overall activity are measured and established, as the microreactors allow precise measurements of the type and area of the catalytic sites. The approach presents opportunities to study electrochemical reactions systematically to help establish rational design principles for future electrocatalysts.
|
|
| 2. |
- Du, J., et al.
(författare)
-
Probe of local impurity states by bend resistance measurements in graphene cross junctions
- 2016
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 27:24
-
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.
|
|
| 3. |
- Jing, Yumei, et al.
(författare)
-
Weak antilocalization and electron-electron interaction in coupled multiple-channel transport in a Bi2Se3 thin film.
- 2016
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 8:4, s. 1879-1885
-
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.
|
|
| 4. |
- Li, Jiayu, et al.
(författare)
-
Charge transport and electron-hole asymmetry in low-mobility graphene/hexagonal boron nitride heterostructures
- 2018
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 123:6
-
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.
|
|
| 5. |
- Li, Jiayu, et al.
(författare)
-
Electron-Hole Symmetry Breaking in Charge Transport in Nitrogen-Doped Graphene
- 2017
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 11:5, s. 4641-4650
-
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.
|
|
| 6. |
- Ta, Huy Q., et al.
(författare)
-
Single Cr atom catalytic growth of graphene
- 2018
-
Ingår i: Nano Reseach. - : TSINGHUA UNIV PRESS. - 1998-0124 .- 1998-0000. ; 11:5, s. 2405-2411
-
Tidskriftsartikel (refereegranskat)abstract
- Single atoms are the ultimate minimum size limit for catalysts. Graphene, as an exciting, ultimately thin (one atom thick) material can be imaged in a transmission electron microscope with relatively few imaging artefacts. Here, we directly observe the behavior of single Cr atoms in graphene mono- and di-vacancies and, more importantly, at graphene edges. Similar studies at graphene edges with other elemental atoms, with the exception of Fe, show catalytic etching of graphene. Fe atoms have been shown to both etch and grow graphene. In contrast, Cr atoms are only observed to induce graphene growth. Complementary theoretical calculations illuminate the differences between Fe and Cr, and confirm single Cr atoms as superior catalysts for sp(2) carbon growth.
|
|
| 7. |
- Tong, Lianming, et al.
(författare)
-
Single gold-nanoparticle-enhanced Raman scattering of individual single-walled carbon nanotubes via atomic force microscope manipulation
- 2008
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:18, s. 7119-7123
-
Tidskriftsartikel (refereegranskat)abstract
- Investigating the electric field distribution around individual metallic nanoparticles is of significant importance for the understanding of the electromagnetic (EM) mechanism of surface-enhanced Raman scattering (SERS). We report single gold-nanoparticle-enhanced Raman scattering of individual single-walled carbon nanotubes (SWNTs) by atomic force microscope (AFM) manipulation. The distance between the gold nanoparticle (GNP) and the SWNT can be controlled by pushing the GNP with an AFM tip. The Raman signals increase when a single GNP is moved close to an individual SWNT, and the corresponding polarization dependence to the incident laser excitation at each GNP/SWNT distance is studied. The agreement of the experimental results with the theoretical model described in this paper suggests a rational modification of the EM enhancement model of SERS for one-dimensional "molecules", like nanotubes.
|
|
| 8. |
- Zhang, G. Q., et al.
(författare)
-
Low-field magnetotransport in graphene cavity devices
- 2018
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 29:20
-
Tidskriftsartikel (refereegranskat)abstract
- Confinement and edge structures are known to play significant roles in the electronic and transport properties of two-dimensional materials. Here, we report on low-temperature magnetotransport measurements of lithographically patterned graphene cavity nanodevices. It is found that the evolution of the low-field magnetoconductance characteristics with varying carrier density exhibits different behaviors in graphene cavity and bulk graphene devices. In the graphene cavity devices, we observed that intravalley scattering becomes dominant as the Fermi level gets close to the Dirac point. We associate this enhanced intravalley scattering to the effect of charge inhomogeneities and edge disorder in the confined graphene nanostructures. We also observed that the dephasing rate of carriers in the cavity devices follows a parabolic temperature dependence, indicating that the direct Coulomb interaction scattering mechanism governs the dephasing at low temperatures. Our results demonstrate the importance of confinement in carrier transport in graphene nanostructure devices.
|
|
| 9. |
- Zheng, Wenshan, et al.
(författare)
-
Patterning two-dimensional chalcogenide crystals of Bi2Se3 and In2Se3 and efficient photodetectors.
- 2015
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- Patterning of high-quality two-dimensional chalcogenide crystals with unique planar structures and various fascinating electronic properties offers great potential for batch fabrication and integration of electronic and optoelectronic devices. However, it remains a challenge that requires accurate control of the crystallization, thickness, position, orientation and layout. Here we develop a method that combines microintaglio printing with van der Waals epitaxy to efficiently pattern various single-crystal two-dimensional chalcogenides onto transparent insulating mica substrates. Using this approach, we have patterned large-area arrays of two-dimensional single-crystal Bi2Se3 topological insulator with a record high Hall mobility of ∼1,750 cm(2) V(-1) s(-1) at room temperature. Furthermore, our patterned two-dimensional In2Se3 crystal arrays have been integrated and packaged to flexible photodetectors, yielding an ultrahigh external photoresponsivity of ∼1,650 A W(-1) at 633 nm. The facile patterning, integration and packaging of high-quality two-dimensional chalcogenide crystals hold promise for innovations of next-generation photodetector arrays, wearable electronics and integrated optoelectronic circuits.
|
|
