Study on Pyramidal Molybdenum Nanostructures Cold Cathode with Large-Current Properties Based on Self-Assembly Growth Method

Abstract

In order to develop a field emission cold cathode for power vacuum electronic device applications, it is important to realize the properties of large-current and high current density. This requires the design and preparation of cold cathode materials with good crystallization, suitable geometric structure, and good contact interface. In this study, we report a pyramidal molybdenum nanostructure with single crystalline nature, which was self-assembly grown by a thermal evaporation method. We also report the optimization of the nanostructure, successfully sharpening its top end and reducing the thickness of the intermediate layer between the structure and the substrate (from 31.4 to 3.1 nm). By this way, the pyramidal molybdenum nanostructure exhibits high conductivity of about 1.8 × 10 5 Ω −1 cm −1 . The cold cathode composed by these nanostructures shows a large-current field emission performance, with the largest emission current of 47.62 mA as well as the highest current density of 2.38 A cm −2 , under a pulsed electric field as high as 28 V μm −1 . The proposed pyramidal molybdenum nanostructures provide a candidate for the large-current cold cathode of the power electronic devices.

Needle-Shaped Single-Crystalline Molybdenum Micro-Nano Structure with High Conductivity and Excellent Field Emission Properties: Implications for Large-Current Cold-Cathodes

“…The measured conductivity of 5 × 10 5 Ω –1 cm –1 makes it become one of the most conductive emitters, which is 2.5 times those from carbon-based nanomaterials, , 2.5–7 times those from other Mo-based nanostructures, ,, and more than one magnitude order higher than the typical metal-oxide semiconductor emitters. , Although this is not high compared to the LaB 6 nanowire (with an elongated geometry), its smaller body resistance and better heat transfer ability are easy to obtain large emission current. The measured maximum emission current (∼93.1 μA) of a continuous-type Mo needle is 5 times that from LaB 6 nanowire, 2 times that from carbon nanotube, almost one magnitude order larger than other Mo nanostructures ,, and two magnitude order larger than the metal-oxide semiconductor emitters, , besides that of vertical few-layer graphene which has a linear emission edge with more field emission sites. Both the excellent performances about the large current loading ability and the high electric transport capacity attribute to the high-quality single-crystalline nature, which needs to be realized in the proposed controllable self-assembly growth process.…”

“…54,55 Although this is not high compared to the LaB 6 nanowire (with an elongated geometry), 15 its smaller body resistance and better heat transfer ability are easy to obtain large emission current. The measured maximum emission current (∼93.1 μA) of a continuous-type Mo needle is 5 times that from LaB 6 nanowire, 15 2 times that from carbon nanotube, 56 almost one magnitude order larger than other Mo nanostructures 36,37,39 and two magnitude order larger than the metal-oxide semiconductor emitters, 54,55 besides that of vertical few-layer graphene 57 which has a linear emission edge with more field emission sites. Both the excellent performances about the large current loading ability and the high electric transport capacity attribute to the high-quality single-crystalline nature, which needs to be realized in the proposed controllable self-assembly growth process.…”

Tunable Broadband Photoresponse Electron‐Emission Nanostructure: Metasurface‐Extended Spectrum‐Selecting and Plasmon‐Enhanced Emitting

“…High‐melting Mo nanopyramids exhibit an appropriate geometry with a sharp top end and thick bottom, which is beneficial for excellent field‐emission properties, such as low turn‐on field‐ and large‐current emission. [ 17–19 ] Therefore, Mo nanopyramids were first designed into a metasurface emitter array ( Figure a). By selecting different geometric parameters of the pyramids, effective tunability of the frequency and amplitude of the broadband photoresponse can be realized.…”

“…Preparation and Characterization: A modified thermal evaporation technique was utilized to prepare single-crystalline Mo nanopyramids through the following reaction steps, which have been described in our previous work: [15][16][17][18][19] oxidation of the Mo source with residual oxygen in the cavity, disproportionation and decomposition of Mo oxides in the gas phase, condensation, and layered nucleation of Mo vapor atoms at specific temperatures. A piece of poly crystalline Mo bulk with high purity (%99.97%, ACHEMETAL Tungsten & Molybdenum Technology Co., Ltd., Luoyang) was placed as the evaporating Mo source, and the disc-shaped stainless steel substrates (#304, with diameter of %1.6 mm and area of %3.14 mm 2 ) were selected as the cathode platform considering the availability of electronic components.…”

“…High-melting metallic Mo has been demonstrated to be an attractive cold cathode material owing to its high conductivity, good thermal conductivity, and excellent high-temperature stability, and it has been successfully used in vacuum electron devices like traveling wave tubes, X-Ray tubes, and field-emission displays. [11][12][13] Recently, a series of Mo nanostructures based on self-assembly growth (e.g., nanowires, [14] nanowalls, [15] nanoscrews, [16] and nanopyramids [17] ) have been reported to exhibit excellent field-emission characteristics. In addition, self-assembled Mo-Mo microcavities have been experimentally demonstrated to exhibit strong localized light absorption and enhanced near-electromagnetic field under external light excitation, making Mo nanostructures a novel non-coinage-metal material for nanophotonics applications such as surface-enhanced Raman scattering (SERS).…”