Thermionic electron emission in the 1D edge-to-edge limit

Thermionic emission is a tunneling phenomenon, which depicts that electrons on the surface of a conductor can be pulled out into the vacuum when they are subjected to high electrical tensions while being heated hot enough to overtake their work functions. This principle has led to the great success of the so-called vacuum tubes in the early 20th century. To date, major challenges still remain in the miniaturization of a vacuum channel transistor for on-chip integration in modern solid-state integrated circuits. Here, by introducing nano-sized vacuum gaps (~200 nm) in a van der Waals heterostructure, we successfully fabricated a one-dimensional (1D) edge-to-edge thermionic emission vacuum tube using graphene as the filament. With the increasing collector voltage, the emitted current exhibited a typical rectifying behavior, with the maximum emission current reaching 200 pA and an On-Off ratio of 103. Besides, it is found that the maximum emission current was proportional to the number of the layers of graphene. Our results expand the studies of the nano-sized vacuum tube to an unexplored physical limit of 1D edge-to-edge emission, and hold great promise for future nano-electronic systems based on it.

A Case Study of Vacuum Tube-Well Dewatering Technology for Improving Deep Soft Soil in Yangtze River Floodplain

Deep soft soil of the Yangtze River floodplain in Nanjing has a special interlayer structure, which provides favorable conditions for the application of vacuum tube-well dewatering technology. This paper focuses on the design, construction and treatment effect of vacuum tube-well dewatering technology. The hydrological parameters and the hydraulic connections between the various layers of the site have been ascertained through two simple single-well multi-holes pumping tests. Moreover, the layout of vacuum tube-wells and depressurization wells in a test site with 84m length and 84m width was designed based on the above parameters. Field tests of vacuum tube-well dewatering technology were conducted on the test site. And the changes of groundwater level, ground settlement and pore water pressure during the test was monitored. The CPTU test technology was used to quickly evaluate the engineering properties of the site before and after treatment. Finally, combined with the settlement monitoring data, the hyperbolic method was used to predict the final settlement. The results indicated that consolidation efficiency of vacuum tube-well dewatering technology has obvious advantages. Implications of this study can provide a reference for the construction design of the site's ground improvement consolidation and other similar projects.

Low-Temperature Synthesis of Vanadium Dioxide Thin Films by Sol-Gel Dip Coating Method

The vanadium dioxide (VO2) thin films were synthesized by sol-gel dipping on a glass slide substrate at low temperature of 500°C in a vacuum tube furnace at a pressure of 2 × 10−3 mbar by 2-step calcination without an intermediate gas purging. Synthesis conditions, including temperature, vacuum pressure, and calcination steps in the vacuum tube furnace, were investigated to find the optimum condition that promoted the formation of VO2 phase. It was found that the 2nd calcination step was very important in realizing the monoclinic vanadium dioxide (VO2 (M)). The results of the valence electron analysis revealed the outstanding phase of VO2 and a small amount of V2O5 and V2O3 phases. The small crystallites of the VO2 were homogeneously distributed on the surface, and the grain was of an irregular shape of ∼220−380 nm in size. The film’s thickness was in a range of 69−74 nm. The film exhibited a metal-to-insulator transformation temperature of ∼68oC and good thermochromic property. Visible optical transmittance remained at ∼40−50% when the sample’s temperature changed from 25 to 80°C for a near infrared (NIR) region.