Abstract 1. Bragg coherent diffraction imaging of single crystal defect dynamics in polycrystalline films (Braggcoherentdiffractiveimagingofsingle-graindefectdynamicsi...
1. Bragg Coherent Diffraction Imaging of Single Crystal Defect Dynamics in Polycrystalline Thin Films
(Bragg coherent diffractive imaging of single-grain defect dynamics in polycrystalline films)
The nature of a polycrystalline material depends on its crystallite distribution and interaction. In particular, grain boundaries and defects are critical to determining the response of a crystal to external excitation. Therefore, observing various grains, defects, and strain dynamics within functional materials is a long-standing challenge. Yau et al. reported a technique that reveals grain heterogeneity, including strain fields and single dislocations, which can be applied in in situ conditions in a reactive environment: grain Bragg coherent diffraction imaging ( gBCDI). Using a polycrystalline gold film that is subjected to heating, Yau et al. demonstrated how gBCDI resolves grain boundaries and dislocation dynamics in a single grain in three-dimensional detail with a spatial resolution of 10 nm and a sub-Elastoscopic displacement field resolution. These results paved the way for understanding the response of polycrystalline materials under external excitation and theoretically designing specific functions. (Science DOI: 10.1126/science.aam6168)
2. Elliptical polarized light excitation enhances the generation of higher harmonics in graphene
(High-harmonic generation in graphene enhanced by elliptically polarized light excitation)
Graphene has an electronic property that allows it to produce a range of nonlinear optical responses. One of the most desirable nonlinear optical processes is the generation of higher harmonics (HHG) from coherent electron motion caused by intense light fields. Yoshikawa et al. reported observations of up to nine harmonics in graphene excited by mid-infrared laser pulses at room temperature. The HHG in graphene is enhanced by elliptically polarized laser excitation, and the resulting harmonic radiation has a specific polarization. The observed ellipticity dependence is reproduced by the full quantum mechanical processing of HHG in the solid. The zero band gap property leads to the unique properties of HHG in graphene. The results of Yoshikawa et al. reveal the possibility of exploring the strong field and ultrafast dynamics and nonlinear characteristics of massless Dirac fermions. (Science DOI: 10.1126/science.aam8861)
3. Hydrolytically stable fluorinated metal-organic framework for energy efficient dehydration
(Hydrolytically stable fluorinated metal-organic frameworks for energy-efficient dehydration)
Natural gas must be dehydrated prior to shipping and use, however, conventional desiccants such as activated alumina or inorganic molecular sieves require a very energy intensive desiccant regeneration step. Cadiau et al. reported a hydrolytically stable metal fluoride-organic framework, AlFFIVE-1-Ni (KAUST-8), with a periodic array of open metal coordination sites and fluorine groups in a narrow square one-dimensional channel. The material selectively removes water vapor from a stream of typical higher hydrocarbons containing CO2, N2, CH4, and natural gas, and selectively removes H2O and CO2 in a gas stream containing N2. The complete desorption of water molecules adsorbed by the AlFFIVE-1-Ni adsorbent requires a relatively moderate temperature (~105 °C) and approximately half the energy input relative to the usual desiccant. (Science DOI: 10.1126/science.aam8310)
4. Three-dimensional Ca2+ imaging promotes understanding of astrocyte biology
(Three-dimensional Ca2+ imaging advances understanding of astrocyte biology)
Astrocyte communication is usually studied by two-dimensional calcium ion (Ca2+) imaging, but this method has not yet derived decisive data on the role of astrocytes in synaptic and vascular function. Bindocci et al. developed a three-dimensional two-photon imaging method and studied the Ca2+ kinetics of astrocytes in astrocyte-astral interactions throughout astrocytes. In awake mice and brain sections, it was found that Ca2+ activity in a single astrocyte was dispersed throughout the cell, mainly distributed between the regions, mainly in the region, and unevenly distributed in regions and regions. Both the process and the terminal show that calcium ions have frequent rapid activity in astrocytes, while the somatic cells are less active. Ca2+ activity in awake mice is higher than in brain sections, especially in the terminal and process, and shows occasional multifocal cellular activity. Astrocytes are locally responsive to minimal axonal emission of time-dependent Ca2+ points. (Science DOI: 10.1126/science.aai8185)
5. A solid state single photon filter
(A solid-state single-photon filter)
A strong limitation of linear optical quantum computing is the probability operation of a double qubit gate based on indistinguishable photon coalescence. One way to achieve deterministic operation is to utilize single photon nonlinearity of atomic transitions. Phase shifters, photon filters, and photon-photon gates have been confirmed with neutral atoms through atomic photon interaction regulation. The proof of concept for semiconductor quantum dots has been reported, but is still limited by inefficient atom-photon interfaces and phase distortion. Santis et al. report a large optical nonlinear high efficiency single photon filter at the single photon level near the optimal quantum dot cavity interface. When probed with a coherent optical band, the device exhibits an optimal nonlinear threshold of about 0.3 ± 0.1 incident photons. Santis et al. also demonstrated that 80% of the direct reflected light intensity consists of a single photon Fock state, and that the two and three photon components are strongly suppressed compared to a single photon. (Nature Nanotechnology DOI: 10.1038/NNANO.2017.85)
6. Energy-dependent dissipation paths in nanomechanical resonators
(Energy-dependent path of dissipation in nanomechanical resonators)
Energy attenuation plays a central role in many phenomena such as light emission, nuclear fission, and dissipation in quantum systems. Energy decay is often described as the system irreversibly leaking energy into the external environment. Güttinger et al. reported energy decay measurements in multilayer mechanical systems based on multilayer graphene. As the energy of the vibration mode decays freely, the rate of energy decay changes abruptly to a lower value. This finding can be explained by a model in which the measurement mode is mixed with other modes of the resonator at high energy. Below the threshold energy, the modes are separated, which results in a relatively low attenuation rate and a large mass factor of over 1 million. The work of Güttinger et al. opens up the manipulation of vibration states, the use of mechanical modes at completely different frequencies to regulate the mixing state, and the new possibilities of studying the collective motion of this highly adjustable system. (Nature Nanotechnology DOI: 10.1038/NNANO.2017.86)
7. Giant thermal Hall effect in multiferroic materials
(Giant thermal Hall effect in multiferroics)
The multi-ferromagnetic materials with dielectric and magnetic order coexistence and mutual coupling have re-emerged people's attention to their interrelated phenomena, providing a basic platform for studying many new functions. Basic excitations in systems such as electromagnetic vibrators and magnetocaloric heat transfer are strongly influenced by lattice-spin interactions. Ideue et al. reported the unprecedented coupling between magnetic and phonons in multiple systems, the giant thermal Hall effect. The thermal conduction of the insulated polar magnet (ZnxFe1-x)2Mo3O8 is controlled by phonons but is very sensitive to magnetic structures. In particular, large thermal Hall conductances observed in the ferrimagnetic phase indicate unconventional lattice-spin interactions and new mechanisms for Hall effect in insulators. The results show that the thermal Hall effect of multilayer materials can be an effective probe for strong lattice spin interaction and provide a new tool for magnetic current control of thermal current. (Nature Materials DOI: 10.1038/NMAT4905)
8. Printable Ag nanoparticle elastic conductor
(Printable elastic conductors by in situ formation of silver nanoparticles from silver flakes)
Printable elastomeric conductors are promising for use in large area stretchable sensors or actuator networks required by healthcare, wearable devices or robots. Elastomers with metal nanoparticles are one of the best ways to achieve high performance, but their large area utilization is limited by processing difficulties. Matsuhisa et al. reported a printable elastomeric conductor containing Ag nanoparticles that can be formed in situ only by mixing micron-sized Ag flakes, fluororubbers, and surfactants. The printable elastic composite exhibits a conductivity of more than 4000 Scm-1 (the highest value: 6,168 Scm-1) at 0% strain, and a conductivity of 935 Scm-1 when stretched to 400%. The formation of Ag nanoparticles is affected by the surfactant, the heating process, and the molecular weight of the elastomer, which can lead to a sharp increase in conductivity. Finally, they also demonstrated a fully printed sensor network for retractable robots that accurately detects pressure and temperature even when stretched over 250%. (Nature Materials DOI: 10.1038/NMAT4904)
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