Field emission characteristics of ZnO nanowires grown by catalyst-assisted MOCVD on free-standing inorganic nanomembranes

Abstract

ZnO field emitters on freely suspended inorganic nanomembranes (NMs) were synthesized by catalyst-assisted metal organic chemical vapor deposition (MOCVD) using the precursors zinc acetylacetonate hydrate and oxygen. The morphology and the possibly involved growth mechanisms of the randomly distributed ZnO nanostructures were investigated by scanning electron microscopy and by energy-dispersive x-ray spectroscopy. The findings indicate a growth process that involves the vapor–liquid–solid as well as the vapor–solid–solid mechanism. The field emission (FE) properties of such ZnO nanowire (NW) samples showed to be highly reproducible and independent of the investigated Si-based substrate types. Herein, a new type of flexible substrate for the MOCVD process has been introduced that allows for the direct growth of ZnO NWs on free-standing membranes for potential FE-based sensor applications. A turn-on field of 4.1 V µm−1 was detected for a macroscopic emission current density of 10 µA cm−2 and the stability test revealed fluctuations of only 9% around the mean emission current over a duration of 3 h proving a reliable and stable operation of such devices. Moreover, approaches were identified to further enhance the FE characteristics of the ZnO NWs by variation of the synthesis parameters and by enlargement of the NM area.