Ordered water structure at hydrophobic graphite interfaces observed by 4D, ultrafast electron crystallography

Interfacial water has unique properties in various functions. Here, using 4-dimensional (4D), ultrafast electron crystallography with atomic-scale spatial and temporal resolution, we report study of structure and dynamics of interfacial water assembly on a hydrophobic surface. Structurally, vertically stacked bilayers on highly oriented pyrolytic graphite surface were determined to be ordered, contrary to the expectation that the strong hydrogen bonding of water on hydrophobic surfaces would dominate with suppressed interfacial order. Because of its terrace morphology, graphite plays the role of a template. The dynamics is also surprising. After the excitation of graphite by an ultrafast infrared pulse, the interfacial ice structure undergoes nonequilibrium “phase transformation” identified in the hydrogen-bond network through the observation of structural isosbestic point. We provide the time scales involved, the nature of ice-graphite structural dynamics, and relevance to properties related to confined water

4D electron diffraction reveals correlated unidirectional Behavior in zinc oxide nanowires

The confined electronic structure of nanoscale materials has increasingly been shown to induce behavior quite distinct from that of bulk analogs. Direct atomic- scale visualization of nanowires of zinc oxide was achieved through their unique pancake- type diffraction by using four- dimensional (4D) ultrafast electron crystallography. After electronic excitation of this wide- gap photonic material, the wires were found to exhibit colossal expansions, two orders of magnitude higher than that expected at thermal equilibrium; the expansion is highly anisotropic, a quasi- one- dimensional behavior, and is facilitated by the induced antibonding character. By reducing the density of nanowires, the expansions reach even larger values and occur at shorter times, suggesting a decrease of the structural constraint in transient atomic motions. This unanticipated ultrafast carrier- driven expansion highlights the optoelectronic consequences of nanoscale morphologies

Scanning ultrafast electron microscopy

Progress has been made in the development of four-dimensional ultrafast electron microscopy, which enables space-time imaging of structural dynamics in the condensed phase. In ultrafast electron microscopy, the electrons are accelerated, typically to 200 keV, and the microscope operates in the transmission mode. Here, we report the development of scanning ultrafast electron microscopy using a field-emission-source configuration. Scanning of pulses is made in the single-electron mode, for which the pulse contains at most one or a few electrons, thus achieving imaging without the space-charge effect between electrons, and still in ten(s) of seconds. For imaging, the secondary electrons from surface structures are detected, as demonstrated here for material surfaces and biological specimens. By recording backscattered electrons, diffraction patterns from single crystals were also obtained. Scanning pulsed-electron microscopy with the acquired spatiotemporal resolutions, and its efficient heat-dissipation feature, is now poised to provide in situ 4D imaging and with environmental capability

Simulation Studies Of Efficiency Enhancement Of Epitaxial Thin Film Silicon Solar Cell By Plasmonic Nanostructures

Kajian simulasi tentang kesan nanostruktur teras shell plasmonic ke atas prestasi sel solar filem nipis silikon dilaporkan. Enam nanostruktur teras shell yang dikaji ialah Ag nanoshell, Au nanoshell, Cu nanoshell, Ag-teras SiO 2-shell zarah, Au-teras SiO 2-shell zarah dan Cu-teras SiO 2-shell zarah. Simulation studies of the effects of plasmonic core-shell nanostructures on the performance of thin film silicon solar cell were reported. Six different core-shell nanostructures were studied

Direct role of structural dynamics in electron-lattice coupling of superconducting cuprates

The mechanism of electron pairing in high-temperature superconductors is still the subject of intense debate. Here, we provide direct evidence of the role of structural dynamics, with selective atomic motions (buckling of copper–oxygen planes), in the anisotropic electron-lattice coupling. The transient structures were determined using time-resolved electron diffraction, following carrier excitation with polarized femtosecond heating pulses, and examined for different dopings and temperatures. The deformation amplitude reaches 0.5% of the c axis value of 30 Å when the light polarization is in the direction of the copper–oxygen bond, but its decay slows down at 45°. These findings suggest a selective dynamical lattice involvement with the anisotropic electron–phonon coupling being on a time scale (1–3.5 ps depending on direction) of the same order of magnitude as that of the spin exchange of electron pairing in the high-temperature superconducting phase

Towards a High-order Godunov Method for Dispersive Wave Problems

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchive