CNT/graphene/PET cathode fabrication
For fabricating the hybrid graphene/CNT cathode, multiwall
carbon nanotube (MWCNT) solution was spin coated
over graphene/PET substrate. MWCNT solution was prepared
in polyvinyl alcohol (PVA) and DI water mixture. Approximately,
4 wt.% of PVA (with average molecular weight (Mw)
of 88,000–97,000) and 98–99% hydrolyzed (Alfa Aesar) was
mixed into DI water and the resulting mixture was stirred
continuously at 60 C, until PVAwas completely dissolved into
water, forming a clear solution. After cooling down the solution
to room temperature, 1 lg of MWCNT (ILJIN Nanotech
Co. Ltd.) was added into it and dispersed by using high power
ultra-sonication tip. MWCNT in PVA/DI water makes a very
homogeneous and stable solution. Spin coating of MWCNT
solution at 1000 rpm for 30 s produces a homogeneous and
transparent coating of nanotube emitters over graphene/PET
film.
2.2.3. Phosphor/graphene/PET anode fabrication
Anode screen was prepared by dip coating of green phosphor
over graphene/PET substrate. Green phosphor powder
(Phosphor Tech) was mixed into the DI water. Solution was
ultrasonicated which created suspension of phosphor particle
in the water. Graphene/PET film was dipped into the solution
multiple times for uniform phosphor coating.
2.3. Structural characterization
Raman spectrum of graphene grown over Cu foil was obtained
by using argon ion (Ar+) laser system (Spectra Physics,
model 177G02) of wavelength = 514.5 nm. Backscattered spectra
were collected by high throughput holographic imaging
spectrograph (Kaiser Optical Systems, model HoloSpec
f /1.8i) with volume transmission grating, holographic notch
filter, and charge coupled device detector (Andor Technology).
The Raman system has a spectral resolution of 4 cm1 and
the spectra were collected at an exposure of 300 s.
SEM images were obtained using a JEOL-JSM 6330F thermal
emission gun electron microscope operating at 15 kV. Samples
were sputter coated with Au prior to observation.
To observe the cross section image of graphene grown on
Cu substrate under transmission electron microscope (TEM),
site-specific sample preparation technique, using FEI Nova
200 NanoLab dual beam FIB, has been used. The area of interest
has been protected by Ag layer deposition, in order to minimize
the gallium damage during sample preparation. The
interest region was sectioned and milled using gallium ion
beam and lifted out. The sample was attached to a copper-
TEM grid. Additional thinning and cleaning of sample using
FIB, was consequently performed at 30 keV and 5 keV, respectively,
to remove the redeposition and ion beam damage. The
site-specific sample has been characterized using FEI
TECHNAI F20 field emission TEM, operating at 200 kV.