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Zinc Oxide Nanostructures
range of applications, such as photovoltaic devices [49, 50] lexible
batteries [51], and LEDs [52]. While there has been much progress
toward the development of lexible organic LEDs, a similar level of
maturity has not yet been achieved in lexible inorganic LEDs. One
approach to improve the mechanical stability of lexible devices the
electronic industry is moving to a different approach such as printed
electronics (PE). Printed electronics has a potential to develop
new devices, e.g., lightweight lexible LEDs. In this approach, the
expensive material and complex method is replaced with a cheap
material and low-temperature, low-cost manufacturing techniques,
such as inkjet printing, roll-to-roll coasting and screen printing to
print devices at large scale. Until now, research has been focused in
PE to organic materials, much less effort has been devoted to use
inorganic semiconductor. Despite this, some inorganic NSs such
as NRs, nanoparticles, and nanowires have an extra advantage for
printing; they can be easily fabricated in large amount by solution
method, which makes it very suitable for PE [53].
Scaling up the production of surface grown and precipitated
ZnO NRs was done by arranging a stack of glass plates supported
on a plastic frame immersed in the nutrient growth solution in a
10 L rectangular polypropylene plastic box. The frame for
supporting a stack of glass slides was manufactured without using
glues, adhesives, or metal connectors, from materials that are cheap
and stable to the conditions of ZnO NRs growth, preparation, and
washing. Before synthesis, the plastic box, the rack and the glass
panes were cleaned with acetone, iso-propanol and deionized water
(DI). A seed layer on the glass panes, prepared by the Pacholski et al.
method [54] was spray coated on each slide to enhance the density
and crystallinity of the ZnO NRs. A 10 L nutrient growth solution
containing equimolar (0.075 M) zinc nitrate hexahydrate (Zn
(NO
3
)
2
.
6H
2
O) and hexamethylenetetramine (HMT, C
6
H
12
N
4
) was
prepared and after continuous stirring for half an hour it was poured
in the plastic box. The rack along with the seeded glass plates was
lowered into the nutrient solution and was placed in the ordinary
laboratory oven at 95°C for several hours. After terminating the
reaction, the growth plates were withdrawn from the vessel and
placed in the oven at 100°C until they were dried. Finally, from
each growth plate the grown NRs were mechanically scraped by a
glass microscopy slide. They were collected, washed with acetone,
deionized water several time and then dried. The morphological and

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