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A narrow energy distribution is a prominent characteristic of field-emission cold cathodes. When applied in a vacuum electronic device, the cold cathode is fabricated over a large area and works under a high current and current density. It is interesting to see the energy distribution of the field emitter under such a working situation. In this work, the energy distribution spectra of a single carbon nanotube (CNT) and a CNT film were investigated across a range of currents, spanning from low to high. A consistent result indicated that, at low current emission, the CNT film (area: 0.585 mm2) exhibited a narrow electron energy distribution as small as 0.5 eV, similar to that of a single CNT, while the energy distribution broadened with increased current and voltage, accompanied by a peak position shift. The influencing factors related to the electric field, Joule heating, Coulomb interaction, and emission site over a large area were discussed to elucidate the underlying mechanism. The results provide guidance for the electron source application of nano-materials in cold cathode devices. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) is an excellent field emission material. However, uniformity and stability are the key issues hampering its device application. In this work, a bimetallic W-Co alloy was adopted as the catalyst of CNT in chemical vapor deposition process. The high melting point and stable crystal structure of W-Co helps to increase the grown CNT diameter uniformity and homogeneous crystal structure. High-crystallinity CNTs were grown on the W-Co bimetallic catalyst. Its field emission characteristics demonstrated a low turn-on field, high current density, stable current stability, and uniform emission distribution. The Fowler–Nordheim (FN) and Seppen–Katamuki (SK) analyses revealed that the CNT grown on the W-Co catalyst has a relatively low work function and high field enhancement factor. The high crystallinity and homogeneous crystal structure of CNT also reduce the body resistance and increase the emission current stability and maximum current. The result provides a way to synthesis a high-quality CNT field emitter, which will accelerate the development of cold cathode vacuum electronic device application. [ABSTRACT FROM AUTHOR]

• Comprehensive utilization of solar energy to get hydrogen energy and fresh water was studied. • 2D lamellar membrane based on the semiconductor BiOCl nanosheet was designed. • PHE and PWE were closely related to the light-to-thermal conversion and water state. • The PWE rate of BOC-CNF@CNT lamellar membrane was up to 2.05 kg·m−2·h−1. Solar energy can help solve the energy and water shortage crisis. Developing a single material that can exhibit both photocatalytic hydrogen evolution (PHE) and photothermal water evaporation (PWE) represents a new concept to simultaneously realize green energy and fresh water supply. In this study, a series of 2D lamellar membranes (2DLMs) based on a conventional semiconductor BiOCl nanosheet was designed as an ensemble, and its combined application for PHE and PWE was explored, in which cellulose nanofibers (CNFs), carbon nanotubes (CNTs), and a self-assembly of CNF@CNT were also used. The PHE and PWE efficiencies are closely related to the conversion of solar energy and the state of the water molecules. Owing to the high light-to-thermal conversion, enhanced water transfer, and the low evaporation enthalpy of confined water, a composite made of BiOCl and CNF@CNT 2DLM (BOC-CNF@CNT) could rapidly reach a surface temperature of 46.6 °C, with its PWE rate reaching up to 2.05 kg·m−2·h−1. Moreover, owing to the high photogenerated carrier transport, strong photothermal effect, and the action of confined water, the PHE rate of BOC-CNF@CNT is 1.99-fold that of the composite made of BiOCl and CNF 2DLM (BOC-CNF) and 1.42-fold that of the composite made of BiOCl and CNT 2DLM (BOC-CNT). This work provides a new and effective strategy for a comprehensive utilization of solar energy to simultaneously produce clean hydrogen and fresh water. [ABSTRACT FROM AUTHOR]