Abstract
We report on the improved field emission performance of graphene foam (GF) following transient exposure to hydrogen plasma. The enhanced field emission mechanism associated with hydrogenation has been investigated using Fourier transform infrared spectroscopy, plasma spectrophotometry, Raman spectroscopy, and scanning electron microscopy. The observed enhanced electron emissionhas been attributed to an increase in the areal density of lattice defects and the formation of a partially hydrogenated, graphane-like material. The treated GF emitter demonstrated a much reduced macroscopic turn-on field (2.5 V μm-1), with an increased maximum current density from 0.21 mA cm-2 (pristine) to 8.27 mA cm-2 (treated). The treated GFs vertically orientated protrusions, after plasma etching, effectively increased the local electric field resulting in a 2.2-fold reduction in the turn-on electric field. The observed enhancement is further attributed to hydrogenation and the subsequent formation of a partially hydrogenated structured 2D material, which advantageously shifts the emitter work function. Alongside augmentation of the nominal crystallite size of the graphitic superstructure, surface bound species are believed to play a key role in the enhanced emission. The hydrogen plasma treatment was also noted to increase the emission spatial uniformity, with an approximate four times reduction in the per unit area variation in emission current density. Our findings suggest that plasma treatments, and particularly hydrogen and hydrogen-containing precursors, may provide an efficient, simple, and low cost means of realizing enhanced nanocarbon-based field emission devices via the engineered degradation of the nascent lattice, and adjustment of the surface work function.
Highlights
Graphene has attracted great attention in recent years because of its outstanding opto-electronic characteristics[1,2,3] and its increasingly wide range of potential applications.[4,5,6,7,8] Previous studies have extensively investigated the electron emission properties of graphene sheets lying at on substrates.[9,10] little has been reported on the fabrication and performance of vertically aligned graphene on conventional substrates.[11]
We report a widely applicable, generalized posttreatment method to improve the eld emission performance of GF-based electron emitters, where the as-grown graphene samples are treated with hydrogen plasma to enhance their electron emission performance via the derivation of a partially hydrogenated structured graphene foam
To better understand the underlying mechanisms for the enhanced emission, pristine and treated GFs samples were inspected using a FEI Qunata 200 scanning electron microscope (SEM) and a Horiba JobinYvon HR800 Raman spectrometer operated with a laser excitation of 532 nm and an impinging power of
Summary
Planes which provide a high density of efficient eld emission sites.[14]. signi cant work is required to achieve practical graphene-based eld emitters with low turn-on elds, high current densities, high temporal stabilities and uniform areal emission, all of which must be coupled with reliable function and inexpensive fabrication over large areas. The unique networked structure, coupled with the high speci c surface area of the GF, provides outstanding electrical and morphological properties that may enable the realization of many hitherto non-manufacturable devices, such as novel eld electron emission devices. Such pristine GF is, in its as-grown pristine state, an enclosed hollow structure with few sharp edges. The possible underlying mechanism of the enhanced emission current is attributed to lattice degradation and the formation of a partially hydrogenated graphane derivative
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