A Mo nanoscrew formed by crystalline Mo grains with high conductivity and excellent field emission properties

Abstract

A novel screw-like molybdenum nanostructure has been synthesized based on a simple thermal vapor deposition method. Each thread circle of the nanoscrews is formed by several crystalline Mo grains, which have a certain deflection with each other. The growth mechanism is described as a spiral growth mode, which depends heavily on the degree of supersaturation (σ) of deposited Mo vapors. The electrical property measurements and field emission properties on a single Mo nanoscrew show that their electrical conductivity should reach 3.44 × 10(4)-7.74 × 10(4) Ω(-1) cm(-1) and its maximum current should reach 15.8 μA. Mo nanoscrew film is also proved to have excellent field emission properties in different voltage driver modes. The largest emission current densities can reach 106.39 mA cm(-2) in the DC voltage driver mode and 0.66 A cm(-2) in the pulsed mode. A low turn-on field, good site distribution and remarkable emission stability is also recorded. These experimental results show that the highly conductive molybdenum nanoscrews should have potential applications as a cold cathode material for high current vacuum electron devices.

An Analytical Modeling of Field Electron Emission for a Vertical Wedged Ordered Nanostructure

“…Vertical wedged Mo nanowalls [27] and tapered Mo nanocones [25] were selected as our research object, and their structural para meters (as shown in Figure 7a,b) and measurement conditions were introduced into our models. The J-E curves in Figure 7c show that the simulation and experimental results reflect similar turnon field E to values: For Mo nanowalls, the simulated and experimental E to values are of 4.8 and 5.0 V µm −1 , respectively.…”

“…Using the structure models as shown in Figure 1, vertical wedged and tapered ordered nanostructure with the same length of 1 µm, radius of top curvature of 25 nm, and external electric field of 20 V µm −1 , have been set as different material compositions to do such a study. The chosen materials are some of the representative field emission materials, including carbon (with the surface work function φ of 5 eV), [38,39] zinc oxide (φ ≈ 5.2 eV), [40] silicon (φ ≈ 4.6 eV), [41] tungsten (φ ≈ 4.52 eV), [42] molybdenum (φ ≈ 4.24 eV), [25][26][27] and boron (φ ≈ 4.4 eV). [43] Figure 6 shows the comparison curves of the wedged ordered nanostructure and tapered nanostructure unit for different material compositions.…”

“…The surface work function φ of both models was set to 4.24 eV, assuming that the simulated material composition was molybdenum. [25][26][27] The applying voltage V was supposed to 2000 V, thus the external electrical field in this case was 20 V µm −1 . For the single wedged ordered nanostructure, the local electrical field intensities E local could be over 3000 V µm −1 in the middle locations on the top emission edge, and their corresponding distributions were relatively homogenous (Figure 2b).…”

“…On the one hand, such nanostructures have the advantages that their sharp tips, large lengths, and vertical alignment help to bring large field enhancement factor and low turn-on field, [23,24] and their robust bottoms contribute to reducing the resistance and improving heat dissipation at high applied electric field. [25] On the other hand, these nanostructures could be obtained through existing preparation methods, whether top-down microprocessing or the bottom-up self-assembled growth. Table 1 lists the representative vertical tapered structural field emission materials and their derivatives.…”

Fast identification of the conduction-type of nanomaterials by field emission technique

“…Nearly all of these nanomaterials were grown by chemical vapor deposition method 22,34–36 except Mo nanocones 25 (physical vapor deposition) and Si nano-apex 21 (electron beam lithography). Moreover, these one-dimensional nanomaterials were found to have identical morphology and uniformly distributed all over the substrate, which can eliminate the effect of nonuniformity on the physical property measurements and further assures the accuracy of the experimental results.…”