Field Emission Characterization of MoS2 Nanoflowers

Abstract

Nanostructured materials have wide potential applicability as field emitters due to their high aspect ratio. We hydrothermally synthesized MoS₂ nanoflowers on copper foil and characterized their field emission properties, by applying a tip-anode configuration in which a tungsten tip with curvature radius down to 30-100 nm has been used as the anode to measure local properties from small areas down to 1-100 µm². We demonstrate that MoS₂ nanoflowers can be competitive with other well-established field emitters. Indeed, we show that a stable field emission current can be measured with a turn-on field as low as 12 V/μm and a field enhancement factor up to 880 at 0.6 μm cathode-anode separation distance.

Keywords: MoS2; field emission; nanoflower; transition metal dichalcogenides.

Figure 1

(a) Schematic of the MoS₂ synthesis by the hydrothermal method; (b) Scanning electron microscope image of a MoS₂ nanoflower.

Figure 2

XPS Characterization of MoS₂ nanoflowers. Component peak-fitting of XPS spectra is shown for (a) C 1s region where C–C, C–OH, C–O–C, C=O, C=O(OH) and C–F are visible; (b) O 1s; (c) Mo 3d; (d) S 2p. Black solid lines represent the overall fit of experimental data (scattered points). The various peaks under the overall fitting curves represent the various components assumed to exist.

Figure 3

(a) Schematic of the FE measurement setup; (b) I-V characteristics measured by contacting both electrodes on the sample surface; (c) FE curve measured as first voltage sweep in a virgin area of the sample. Three successive regions of emission are identified. Black arrows indicate the turn-on voltage for each region. Black empty circles are experimental data measured in open circuit configuration. Black solid lines are the numerical simulations according to FN-theory (Equation (1)); (d) FN-plots for the different regions. Solid lines are the linear fittings; (e) FE curve measured in a different location after the initial electrical stress; (f) Three consecutive voltage sweeps measured in a third different location always after electrical stress to show the FE repeatability.

Figure 4

Effect of cathode–anode separation distance variation on the FE I-V characteristics. (a) Curves are measured for d = 800 nm and 1100 nm and are compared to theoretical FN behavior (solid lines). Inset: FN-plots and linear fittings. (b) Dependence of the turn-on field and of the field enhancement factor on the cathode–anode separation distance d in the range 600 nm–1100 nm.