Cold cathode emission studies on topographically modified few layer and single layer MoS_2 films

摘要

Nanostructured materials, such as carbon nanotubes, are excellent cold cathode emitters. Here, we report comparative field emission (FE) studies on topographically tailored few layer MoS_2 films consisting of 〈0001〉 plane perpendicular (⊥) to c-axis (i.e., edge terminated vertically aligned) along with planar few layer and monolayer (1L) MoS_2 films. FE measurements exhibited lower turn-on field E_(to) (defined as required applied electric field to emit current density of 10μA/cm~2) ～4.5 V/μm and higher current density ～1 mA/cm~2, for edge terminated vertically aligned (ETVA) MoS_2 films. However, E_(to) magnitude for planar few layer and 1L MoS_2 films increased further to 5.7 and 11 V/μm, respectively, with one order decrease in emission current density. The observed differences in emission behavior, particularly for ETVA MoS_2 is attributed to the high value of geometrical field enhancement factor (β), found to be ～1064, resulting from the large confinement of localized electric field at edge exposed nanograins. Emission behavior of planar few layers and 1L MoS_2 films are explained under a two step emission mechanism. Our studies suggest that with further tailoring the microstructure of ultra thin ETVA MoS_2 films would result in elegant FE properties.