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| 2. |
- Gray, A. X., et al.
(författare)
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Ultrafast terahertz field control of electronic and structural interactions in vanadium dioxide
- 2018
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 98:4
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Tidskriftsartikel (refereegranskat)abstract
- Vanadium dioxide (VO2), an archetypal correlated-electron material, undergoes an insulator-metal transition near room temperature that exhibits electron-correlation-driven and structurally driven physics. Using ultrafast temperature- and fluence-dependent optical spectroscopy and x-ray scattering, we show that multiple interrelated electronic and structural processes in the nonequilibrium dynamics in VO2 can be disentangled in the time domain. Specifically, following intense subpicosecond terahertz (THz) electric-field excitation, a partial collapse of the insulating gap occurs within the first picosecond. At temperatures sufficiently close to the transition temperature and for THz peak fields above a threshold of approximately 1 MV/cm, this electronic reconfiguration initiates a change in lattice symmetry taking place on a slower timescale. We identify the kinetic energy increase of electrons tunneling in the strong electric field as the driving force, illustrating a promising method to control electronic and structural interactions in correlated materials on an ultrafast timescale.
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| 3. |
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| 4. |
- Henighan, T., et al.
(författare)
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Generation mechanism of terahertz coherent acoustic phonons in Fe
- 2016
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Ingår i: PHYSICAL REVIEW B. - 2469-9950. ; 93:22
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Tidskriftsartikel (refereegranskat)abstract
- We use femtosecond time-resolved hard x-ray scattering to detect coherent acoustic phonons generated during ultrafast laser excitation of ferromagnetic bcc Fe films grown on MgO(001). We observe the coherent longitudinal-acoustic phonons as a function of wave vector through analysis of the temporal oscillations in the x-ray scattering signal. The width of the extracted strain wave front associated with this coherent motion is similar to 100 fs. An effective electronic Gruneisen parameter is extracted within a two-temperature model. However, ab initio calculations show that the phonons are nonthermal on the time scale of the experiment, which calls into question the validity of extracting physical constants by fitting such a two-temperature model.
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| 5. |
- Li, Guowei, et al.
(författare)
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Carbon-Tailored Semimetal MoP as an Efficient Hydrogen Evolution Electrocatalyst in Both Alkaline and Acid Media
- 2018
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Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 8:24
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Tidskriftsartikel (refereegranskat)abstract
- The electrolysis processes such as hydrogen evolution reaction (HER) require high efficient catalysts with robust surface stability. A high conductivity is also necessary to speed up the charge transport between the catalyst and the electrolyte. Recently, the observation of exceedingly high conductivity in the topological semimetal MoP, has provided a model catalyst to investigate the correlation between the electrical transport and the electrocatalytic activity for the HER. Thus, MoP is encapsulated in a Mo, P codoped carbon layer (MoP@C). This composite material exhibits outstanding HER performance, with an extremely low overpotential of 49 mV at a current density of 10 mA cm(-2) and a Tafel slope of 54 mV dec(-1) in an alkaline medium. In addition, electron transport analysis indicates that MoP exhibits high conductivity and mobility due to the existence of triple-point fermions and a complex Fermi surface. Furthermore, the presence of P-C and Mo-C bonds at the interface between the carbon layer and the MoP particles modulates the band structure of MoP@C and facilitates fast electron transfer, accumulation, and subsequent delocalization, which are in turn responsible for the excellent HER activity.
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| 6. |
- Li, Guowei, et al.
(författare)
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Dirac Nodal Arc Semimetal PtSn4: An Ideal Platform for Understanding Surface Properties and Catalysis for Hydrogen Evolution
- 2019
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Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773.
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Tidskriftsartikel (refereegranskat)abstract
- Conductivity, carrier mobility, and a suitable Gibbs free energy are important criteria that determine the performance of catalysts for a hydrogen evolution reaction (HER). However, it is a challenge to combine these factors into a single compound. Herein, we discover a superior electrocatalyst for a HER in the recently identified Dirac nodal arc semimetal PtSn4. The determined turnover frequency (TOF) for each active site of PtSn4 is 1.54 H-2 s(-1) at 100 mV. This sets a benchmark for HER catalysis on Pt-based noble metals and earth-abundant metal catalysts. We make use of the robust surface states of PtSn4 as their electrons can be transferred to the adsorbed hydrogen atoms in the catalytic process more efficiently. In addition, PtSn4 displays excellent chemical and electrochemical stabilities after long-term exposure in air and long-time HER stability tests.
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| 7. |
- Malinowski, R., et al.
(författare)
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Dynamic Control of Particle Deposition in Evaporating Droplets by an External Point Source of Vapor
- 2018
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:3, s. 659-664
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Tidskriftsartikel (refereegranskat)abstract
- The deposition of particles on a surface by an evaporating sessile droplet is important for phenomena as diverse as printing, thin-film deposition, and self-assembly. The shape of the final deposit depends on the flows within the droplet during evaporation. These flows are typically determined at the onset of the process by the intrinsic physical, chemical, and geometrical properties of the droplet and its environment. Here, we demonstrate deterministic emergence and real-time control of Marangoni flows within the evaporating droplet by an external point source of vapor. By varying the source location, we can modulate these flows in space and time to pattern colloids on surfaces in a controllable manner.
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