The hidden constraints determining rheological evolution of graphene oxide under fragmentation are illustrated, reconciling the conflicting previous reports.

The direct observation of the structure of micrometer-sized vapor-deposited ice is performed at Pohang Accelerator Laboratory x-ray free electron laser (PAL-XFEL). The formation of micrometer-sized ice crystals and their structure is important in various fields, including atmospheric science, cryobiology, and astrophysics, but understanding the structure of micrometer-sized ice crystals remains challenging due to the lack of direct observation. Using intense x-ray diffraction from PAL-XFEL, we could observe the structure of micrometer-sized vapor-deposited ice below 150 K with a thickness of 2–50 μm grown in an ultrahigh vacuum chamber. The structure of the ice grown comprises cubic and hexagonal sequences that are randomly arranged to produce a stacking-disordered ice. We observed that ice with a high cubicity of more than 80% was transformed to partially oriented hexagonal ice when the thickness of the ice deposition grew beyond 5 μm. This suggests that precise temperature control and clean deposition conditions allow μm-thick ice films with high cubicity to be grown on hydrophilic Si3N4 membranes. The low influence of impurities could enable in situ diffraction experiments of ice nucleation and growth from interfacial layers to bulk ice.

The relativistic magnetron is one of the most attractive high‐power microwave sources, due to its compactness with high efficiency. It can generate hundreds of megawatts of microwave power in the L‐ and S‐bands. However, the efficiency of the magnetron is often limited due to the mode stability. In this Letter, three‐dimensional particle‐in‐cell simulation suggests even further increase of total efficiency of the magnetron can be realised via mode stabilisation using a self‐excited extended interaction in a collector region. A six‐vaned radial relativistic magnetron with a single radial output port powered by 400 kV, 900 MW with an efficiency of ∼48%. This improvement is attributed to the mode locking of operating π‐mode by a power‐boosted TE ₃₁₅ mode excited in the extended cavity.

The emission capability of as prepared reduced graphene oxide (rGO) and tungsten doped reduced graphene oxide (W-rGO) film field emitter (FE) cathodes are investigated experimentally. It is observed that W-rGO films showed a highest emission current density of ~ 800 A/cm ² at an applied DC electric field of 6.6 V/μm, which is far superior than the current density of ~ 390 A/cm ² from an as prepared rGO film. Short stability test also showed that emission current is much more stable than the rGO films. These excellent improvements can be attributed to the doping of tungsten into the rGO film, which helped to repair the broken bonds thus lowering the turn on field. Also, tungsten gives the film an excellent mechanical stability and higher thermal load handling capability, which is very important to achieve a stable, high performance operation and long life.

Uniform, highly conductive, thin film field emitters are in immense need for future development of high power compact terahertz(THz) vacuum electronic devices(VED). Reduced graphene oxide(rGO) based free standing film as high current sheet beam cathode is fabricated by hydrothermal method. This hydrothermal method facilitates highly conductive, thin, compact film. We achieved to get few micrometers to sub-micrometer thick film which is much thinner than conventional vacuum filtered film resulting in higher field enhancement factor, current density, and current. This approach can successfully establish a fabrication method for uniform, thin high current field emitter for high power THz VEDs.