Applied
Surface
Science
270 (2013) 124–
127
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Applied
Surface
Science
jou
rn
al
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om
epa
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www.elsevier.com/locate/apsusc
Field
emission
from
zinc
oxide
nanorod
bundles
grown
on
silicon
nanoporous
pillar
array
Ling
Li
Wang,
Shang
Dong
Gong,
Li
Hong
Wu,
Xin
Jian
Li
∗
Department
of
Physics
and
Laboratory
of
Materials
Physics,
Zhengzhou
University,
Zhengzhou
450052,
China
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
1
September
2012
Received
in
revised
form
24
December
2012
Accepted
27
December
2012
Available online 4 January 2013
Keywords:
Zinc
oxide
nanorod
bundle
Silicon
nanoporous
pillar
array
Field
emission
a
b
s
t
r
a
c
t
A
large-area
zinc
oxide
(ZnO)
nanorod
bundle
array
was
grown
on
a
silicon
nanoporous
pillar
array
(Si-
NPA)
substrate
by
a
chemical
vapor
deposition
method,
and
its
field-emission
properties
was
studied.
The
structural
characterization
disclosed
that
the
bundles
were
composed
of
hexagonal
ZnO
nanorods
growing
along
c-axis
and
taking
roots
into
the
silicon
pillars
of
Si-NPA.
The
average
diameter
and
length
of
the
ZnO
nanorods
were
∼145
nm
and
∼10
m,
respectively.
The
field-emission
measurements
showed
that
the
turn-on
field
of
ZnO/Si-NPA
was
4.6
V/m
with
an
emission
current
density
(ECD)
of
1
A/cm
2
,
and
an
ECD
of
420
A/cm
2
was
achieved
at
an
applied
field
of
8.89
V/m.
The
field
enhancement
factor
was
calculated
to
be
∼1700
based
on
the
Fowler–Nordheim
theory.
According
to
the
obtained
charge
coupled
device
(CCD)
image,
the
density
and
brightness
of
the
emission
dots
increased
with
the
applied
field,
and
the
high
emission
dot
density
was
attributed
to
the
formation
of
a
large
number
of
ZnO
nanorod
emitting
tips.
Our
results
indicated
that
ZnO/Si-NPA
might
be
a
promising
electron
emission
source.
© 2013 Elsevier B.V. All rights reserved.
1.
Introduction
One-dimensional
(1D)
semiconductor
nanostructures
have
attracted
considerable
attention
in
recent
years
because
of
their
interesting
physical
properties
[1,2]
and
potential
applications
in
various
nanoscale
devices
[3,4].
Among
these
properties,
the
field
emission
behavior
of
1D
nanostructures
with
high
aspect
ratio
such
as
nanotubes
and
nanowires
was
of
particular
interest
due
to
their
relatively
low
turn-on
field,
large
emission
current
density
(ECD)
and
long-term
stability
[5,6].
In
the
past
decade,
as
a
com-
pound
semiconductor
with
the
properties
of
direct
wide
bandgap
(∼3.37
eV),
large
exciton
binding
energy
(∼60
meV),
good
ther-
mal
and
chemical
stability,
and
plentiful
shape
and
morphology,
various
zinc
oxide
(ZnO)
nanostructures
have
been
studied
inten-
sively
in
fabricating
lasers
[7],
light-emitting
diodes
[8],
solar
cells
[9],
chemical
sensors
[10,11],
field
effect
transistors
[12],
and
field
emission
cold
cathodes
[13,14].
Especially,
the
field
emission
prop-
erties
of
various
1D
ZnO
nanostructure
arrays,
including
nanowires
[15–17],
nanorods
[18]
and
nanowhiskers
[19],
have
been
investi-
gated,
and
all
of
the
results
indicated
that
1D
ZnO
nanostructures
might
be
ideal
field
emission
cold
cathode
materials
for
practical
applications.
In
the
previous
study
[20],
we
have
reported
the
preparation
of
silicon
nanoporous
pillar
array
(Si-NPA),
a
micron-nanometer
∗
Corresponding
author.
Tel.:
+86
371
67766629;
fax:
+86
371
67766629.
E-mail
address:
lixj@zzu.edu.cn (X.J.
Li).
structural
composite
system
characterized
by
its
regularly
arrayed
nanoporous
silicon
pillars.
Based
on
Si-NPA,
a
nest
array
of
entan-
gled
multi-walled
carbon
nanotubes
was
prepared
and
a
field
emission
with
low
turn-on
field
and
large
emission
current
den-
sity
(ECD)
was
realized
[21].
This
illustration
indicated
that
the
unique
nanoporous
structure
and
the
regular
pillar
array
of
Si-NPA
might
make
it
an
ideal
template
for
fabricating
silicon-based
field
emission
cathodes.
In
this
paper,
we
report
that
a
large-area
ZnO
nanorod
bundle
array
was
grown
on
Si-NPA
by
a
chemical
vapor
deposition
(CVD)
method
and
its
field-emission
properties
were
investigated.
The
field-emission
properties
of
ZnO/Si-NPA
were
analyzed
by
calculat-
ing
its
field
enhancement
factor
according
to
the
Fowler–Nordheim
theory.
Furthermore,
the
charge
coupled
device
(CCD)
images
of
ZnO/Si-NPA
field
emission
under
different
applied
voltages
were
taken
and
the
performance
was
analyzed
with
respect
to
its
unique
structure
and
morphological
characteristics.
2.
Experimental
details
The
Si-NPA
substrate
was
prepared
by
hydrothermally
etching
(1
1
1)
oriented,
boron-doped
single
crystal
Si
wafers
in
the
solution
of
hydrofluoric
acid
containing
ferric
nitrate
[20].
The
resistivity
of
the
initial
silicon
wafers
was
0.015
cm.
The
ZnO
nanorod
bundles
were
grown
on
Si-NPA
substrate
by
a
CVD
method
in
a
horizon-
tal
tube
furnace.
Here
high-purity
(99.999%)
Zn
powder
was
used
as
the
Zn
source
and
the
Si-NPA
substrate
was
placed
at
1.5
cm
away
from
the
Zn
source
along
the
downstream
direction
of
the
0169-4332/$
–
see
front
matter ©
2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apsusc.2012.12.136