realizing the basic electron emission process from low dimension
materials such as graphene and carbon nanotube. Using a control-
lable capacitive coupled radio frequency (rf) sputtering deposition
system [98], without any catalyst, the vertically aligned ultrathin
graphene nanosheets can be synthesized as shown in Fig. 2. For
the vertical graphene sheets growth process, hydrogen was used
for glow discharge as well as for sputtering carbon coming from
a high-purity graphite target. Utilizing the mixture gas of methane
and hydrogen as precursor, the vertically aligned few-layer gra-
phene was synthesized in the absence of any metallic catalyst by
MPECVD [70]. The unique geometry of the PECVD synthesis
vertical orientation graphene can provide us investigation for the
field emission performance directly. After that the vertically
aligned few-layer graphene were constructed by many researchers
[74–76].
2.4. Printing
A sophisticated method which is widely used in large-scale
applications on different substrate is screen printing technology.
Due to its low manufacture cost, larger scale production, preferable
fabrication condition, the screen-printing method would be suit-
able for electronics technology [77–81]. This pioneer works for
preparing graphene field emitters were reported [82]. The gra-
phene power with organic binders was mixed and then the power
was screen-printed on electrical substrates as an emitter cathode.
At last, these samples were annealed to burn out the organic bin-
ders. For the printed samples, some graphene were wrapped with
each other and some were vertical to the surface of the substrate.
The protruding graphene sheets with sharp edges or tips could be
acted as vertical field emission sites. The unique structure of
printed graphene is beneficial to excellent emission properties.
The method of fabricating vertical graphene field emission cath-
odes based on a conventional screen-printing technique and then
following selective photoetching techniques was also developed
[83]. Fig. 3 presents the schematic for the vertical graphene cath-
odes fabrication process. Mixing graphene solution with negative
ultraviolet (UV) photoresist ink, the photoresist: graphene paste
was prepared and then the paste was screen-printed on the
cleaned indium tin oxide-coated (ITO) glass substrate as shown
Fig. 2. Schematic illustration of the capacitively coupled radio frequency (rf) sputtering system used for the GNS growth. Reproduced with permission from Ref. [98].
Copyright 2013, Elsevier Ltd.
Fig. 1. Schematic of the graphene exfoliation on carbon cloth. (a) Carbon Cloth was woven by carbon fiber. (b) Amplifying diagram for carbon fibers consisted of anisotropic
graphite layers and amorphous carbon. (c) After chemical oxidation, the outside graphite layers were terminated by functional groups. (d) The graphene were exfoliated from
outside graphite layers after heating. Reproduced with permission from Ref. [62]. Copyright 2011, American Institute of Physics.
46 L. Chen et al. / Materials Science and Engineering B 220 (2017) 44–58