Tuning the field emission of graphene-diamond hybrids by pulsed methane flow CVD

Integrating different carbon allotropes, namely graphene and nanocrystalline diamond, into a hybrid structure is highly desirable for a synergistic approach envisaging a field emission material. In this work, this was accomplished by a simultaneous synthesis of both allotropes by microwave plasma CVD on copper substrates, using a CH4 pulsed flow modulation strategy. This approach enabled tailoring the density (from 1.01 x 10(6) to 4.48 x 10(6)/cm(2)) and diameter (from 1.06 to 3.09 mm) of nanocrystalline diamond clusters nucleated on the underlying graphene layer. Since morpho-structural aspects are critical regarding the field emission behavior, an exhaustive characterization was undertaken using scanning and transmission electron microscopy, Raman spectroscopy and optical profillometry. The field emission data were analyzed using the Fowler-Nordheim model and the electrical activation fields, ranging from similar to 4.6 to similar to 8.4 V/mu m, were found to decrease with increasing NCD cluster content. Two emission regimes were observed, each corresponding to a distinct field enhancement factor, reaching values as high as 2204. The dependency of these factors with the total NCD cluster surface area suggests emission from both the background graphene and the protruded NCD clusters. (C) 2017 Elsevier Ltd. All rights reserved.