Applied

Surface

Science

257 (2011) 10134–

10140
Contents

lists

available

at

ScienceDirect
Applied

Surface

Science
jou

rn

al

h


layer

and

patterning

of

ZnO

nanowires

arrays

via

surface

modification

of
substrate
Jin

Zhang
a
,

Wenxiu



of

Electronic

and

Information

Engineering,

Xi’an

Jiaotong

University,

Xi’an

710049,

Shaanxi,

People’s

Republic

of

China


of

China
a

r

t

i

c

l

e

i

n

f

o
Article

history:
Received


Nanowires
Seed

layer
Fluorination
Photoluminescence
a

b

s

t

r

a

c

t
ZnO

nanowire

(NW)

arrays

are

temperature

and

growth

time

of

the

hydrothermal

process

on

morphological

and
photoluminescence

properties

of

the

as-assembled

the

ZnO

NWs

increase

with

a

lengthening

of

the

growth

time
at

80
◦
C

and

the

of

the

ZnO

NW

arrays.

The

patterned

AZO

seed

layer

is

fabricated

on

a

silicon
substrate

fluorination

technique,

and

then

the

ZnO

NW

arrays

are

selectively

grown

on

those

patterned

regions
of

NW

arrays

shows

that

only

a

strong

UV

emission

at

about

380

nm

is

observed,


is

a

semiconductor

with

exceptional

electronic

and

pho-
tonic

properties

as

well

as

great

thermal

stability


led

to

novel
and

enhanced

properties

as

compared

to

its

bulk

form,

and

thus
enabling

it

for

nanodevice

assembly

and
applications

in

blue-UV

light

emitters

[4]

and

photodetectors

[5],
field

emission

devices


on

GaN,

AlN,

Al
1−x
Ga
x
N,

6H–SiC,

and

ZnO

buffer

layers

[8–10],

but
the

optical

properties

impurity

and

defect
distribution,

which

can

hinder

the

applications

of

the

NW

arrays.
In

recent

years,



for

the

manipulation
of

their

optical

and

electrical

properties,

the

Al-doped

ZnO

(AZO)
thin

films

are


+86

29

82668794.
E-mail

address:



(W.

Que).
parency

and

relatively

low

cost

[11,12].

In

view


lead

to

potential

integration

with

silicon

micro-
electronics

[13–15].

Therefore,

the

luminescent

and

electron

field
emission

by

many

research

groups

[16,17].

Further-
more,

in

order

to

achieve

an

immense

potential

of

the


arrangements

and

properties

of

the

ZnO

NW

arrays

[16].
In

this

paper,

the

ZnO

NW



hydrother-
mal

method,

and

effects

of

the

temperature

and

growth

time

of
the

hydrothermal

process

on


discussed.

In

addition,

what

we

believe

to

be

the

first

report
on

the

fabrication

of



electron-beam
lithography

process,

as

well

as

a

surface

fluorination

technique,
which

can

eliminate

the

effect

of

ZnO

NW
arrays

could

be

successfully

grown

on

the

patterned

regions

of

the
AZO

seed

layer


arrays

were

also

characterized

and

investigated.
0169-4332/$

–

see

front

matter ©

2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apsusc.2011.06.163
J.

Zhang

et

al.

the

ZnO

NW

arrays

on

silicon

substrate.
2.

Experimental
2.1.

Preparation

of

the

AZO

seed

layer
In

the

ZnO

and

AZO

seed

layers

were

pre-
pared

by

the

sol–gel

technique.

Here,

the

Al-doped

its
relatively

outstanding

performance

than

other

doping

concentra-
tions

as

shown

in

our

previous

report

[18].


first

dissolved

in

a

2-methoxyethanol

monoethanolamine

(MEA)-
deionized

water

solution

at

room

temperature.

The

molar

ratio


and

the

concentration

of

the

zinc

acetate
was

0.75

mol/L.

For

the

AZO

sol,

an


as-prepared

precursor

solution.

Then,

the

final

solution

was

stirred
at

60
◦
C

for

30

min

until

onto

a

quartz

glass
substrate

by

a

multi-spin-coating

process

for

20

s

at

3000

rpm.

It


air

at

200
◦
C

for

10

min

and
thus

the

one-layer

thin

film

with

about


at

a

temperature

of

500
◦
C

for

1

h

in

the

air

[19].
2.2.

Hydrothermal

synthesis


were

grown

in

a

Teflon-lined
stainless

steel

autoclave

by

immersing

the

substrates

deposited
with

the

ZnO

mol/L)

and

NaOH

(0.8

mol/L),
at

80–180
◦
C

for

1–3

h.

The

obtained

samples

were

then


of

the

patterned

ZnO

NW

arrays

on

silicon
substrate
Fig.

1

shows

the

fabrication

process

of


Corp.)

was

first

spin-coated

on

the

silicon

sub-
strate

and

followed

the

coated

sample

was



was

exposed

for
patterning

at

30

kV

under

a

high-resolution

electron-beam

lithog-
raphy

system

(CABL-9000C

Crestec


(Methyl

isobutyl

ketone

89%

and

Isopropyl

alcohol

11%)
solution

for

1

min

to

remove

the


resist

was

immerged

into

the

solution,

which

consists
of

2.0

vol.%

(Heptadecafluoro-1,1,2,2-tetradecyl)

trimethoxysilane
(SC-1060F,

from

Sicong



then

picked

out.

Fol-
lowed

that

the

immerged

sample

was

heated

at

150
◦
C

in


removed

from

the

silicon

substrate

by

rinsing

it

with
chlorobenzene,

thus,

the

template

was

obtained.

Finally,


selectively

grown

on

the

patterned

regions

of

the
AZO

seed

layer

by

the

hydrothermal

process.
The

diffraction

spectrometer
(Rigaku)

with

Cu

K␣

radiation

and

operated

at

40

kV

and

100

mA
from



0.02
◦
.

The

morphological

properties

of

the

ZnO

NW

arrays

were
observed

by

a

JEOL


(a)

SEM

image

of

the

ZnO

seed

layer,

(b)

SEM

image

of

the

AZO

seed


films

were

characterized

by

a
JASCO

V-570

UV/VIS/NIR

spectrometer

and

the

photoluminescence
spectra

of

the

ZnO



and

XRD

patterns

of

both

the

ZnO

and

AZO

seed
layer,

which

are

deposited

on



from

Fig.

2

that
the

AZO

seed

layer

has

a

smaller

grain

size

as

compared



AZO
seed

layer

in

intensity

is

higher

than

that

of

the

ZnO

seed

layer
as

seen

orientation

(0

0

2)

than

that

of

the

ZnO

seed

layer,

which
coincides

with

those

reported

AZO

seed

layers
as

well

as

the

corresponding

ZnO

NW

arrays

grown

on

these

seed
layers.



85%

in

the

visible

region.

However,

it
is

worthy

to

note

that

the

transmittance

of



layer,

which
is

probably

related

to

the

optimized

crystalline

orientation

of

the
(0

0

2)

and

which

are

grown

on

the

ZnO
20 30 40 50 60 70
Intensity (a.u.)
2 Th

eta / de

gree
ZnO
AZO
(002)
Fig.

3.

XRD

patterns

of

h,

is

still

above

40%

in

the

visible
region.

In

addition,

the

transmittance

of

the

ZnO

seed

layer
owing

to

its

high

light

scattering

and

decrease

light

transmittance
[18].

Fig.

4(b)

shows



AZO

thin

film

layer

has

a
blue

shift

as

compared

to

that

of

the

ZnO


1
2
3
4
5
325 350 375 400 425
0.0
0.1
0.2
0.3
0.4
0.5
0.6
ZnO
AZO
Abs (a.u.)
Wavelength /

nm
Fig.

4.

(a)

Transmittance

spectra

of


ZnO

NW

arrays

grown

on

the

ZnO

seed

layer

at

80
◦
C

for

1

h

for

1

h

(curve

5).

(b)

Absorption

spectra

of

the

ZnO

and

AZO

thin

films.
J.

ZnO

NWs

grown

on

the

ZnO

and

AZO

seed

layers:

(a),

(b)

and

(c)

are


for

1

h,
2

h

and

3

h,

respectively,

(d),

(e)

and

(f)

are

SEM

images


h,

2

h

and

3

h,

respectively,

(g)

and

(h)

are

SEM

images

of
the


C,

respectively,

(i)

and

(j)

are

SEM

images

of

the

ZnO

NWs

grown

on

the


SEM

images

of

the

ZnO

NW

arrays

grown

on
the

ZnO

and

AZO

seed

layer

at

cross-section

of

the

ZnO

NWs
arrays.

Fig.

6

shows

that

the

TEM

images

and

the

selected


at

80
◦
C

for

1

h.

Fig.

6(a)

is

a

typical

low-
magnification

image

of



atomic

arrangements
10138 J.

Zhang

et

al.

/

Applied

Surface

Science

257 (2011) 10134–

10140
Fig.

6.

TEM

images


image,

(c)

corresponding

selected

area

electron
diffraction

pattern

(SAED).
of

the

ZnO

NW

are

seen

in

axis

are

on

average

separated

by
0.26

nm,

indicating

the

crystalline

ZnO

NWs

growth

along

the


single

crystalline

growth

along

ZnO

(0

0

2)

as

shown
in

Fig.

6(c).

In

addition,



at

80
◦
C

for

1

h.

The

values
of

the

length

and

diameter

of

the



different

seed
layers

(ZnO,

AZO),

the

ZnO

NWs

grown

on

the

ZnO

seed

layer

are
labeled

ZnO-NWA.

It

can

be

seen

from

Fig.

5

that

all

the
ZnO

NW

arrays

obtained

under


80
◦
C

and

the

growth

time

between

1

and

3

h,

the

length
and

diameter



in

Fig.

7.

However,

it

is
also

interesting

to

note

for

the

same

growth

time


eter

of

the

ZnO-NWA

is

much

smaller

than

that

of

the

ZnO-NWZ.
These

results

are

probably

bigger

the

crystal

grain

size

is,

the
shorter

and

wider

the

grown

ZnO

NW

is

as

than

that
of

the

ZnO-NWZ.

Moreover,

the

distance

among

the

ZnO-NWA

is
bigger

than

that

among



crystal

interspaces
and

the

crystal

grain

size

of

the

seed

layer.

As

can

be

seen


seed

layer

is

more

than

that

of

the

ZnO

seed

layer,

which

leads

to

a
larger

in

Fig.

5.

Furthermore,

it

is

also

observed

for

the

same
growth

time

(1

h)

but

ZnO-NWZ
enlarge

extremely

with

the

increase

of

the

hydrothermal

tempera-
ture

as

compared

to

that

of



restricts

the
cross-growth

of

the

ZnO

NWs.

The

length

of

the

ZnO-NWA

also
increases

with

the

temperature

is

further
up

to

180
◦
C,

the

length

of

the

ZnO-NWA

is

shorter

than

that


Refs.

[23,24],

the

hydrothermal

synthesis

of

the

ZnO
NWs

is

a

dynamic

balance

process

as


ZnO

+

2[OH]
−
→

[ZnO
2
]
2−
+

H
2
O

(2)
Thus,

the

[Zn(OH)
n
]
n−2−
groups

dehydrate

molecules

and
[OH]
−
,

and

the

formed

[OH]
−
dissolves

the

ZnO

molecules

to

form
[ZnO
2
]
2−


the

growth

rate

of

the
ZnO

NWs

will

be

much

higher

than

the

dissolution

rate.


the

[Zn(OH)
n
]
n−2−
groups

achieve
the

best

values,

which

leads

to

a

fast

growth

rate

of

3
(a)

(b)
Length of th

e Zn

O NWs / µmGrowth time / hour
80
100
120
140
160
180
Temperature of chemical bath /
o
C
0 50 100 150 200 250 300 350
1
2
3
Diameter of th

e Zn

O NWs / n

temperature

on

the

length

and

diameter

of

the

ZnO

NWs:

(a)

a

relationship

between

the



the

diameter

of

the

ZnO

NWs

and

the

hydrothermal

growth

time

and

temperature.
J.

Zhang



ZnO

NWs

decreases

due

to

the
decrease

of

the

supersaturation

of

the

[Zn(OH)
n
]
n−2−
groups.


ZnO

NWs

is

determined

by

the

supersaturation
of

the

[Zn(OH)
n
]
n−2−
groups

and

the

concentration

of


at

130
◦
C.

Due

to

the

effect

of

the

Al-doping

on

the

seed
layer,

the



for

those

potential

applications

in

the
dye-sensitized

solar

cells,

luminescent

and

electron

field

emission
devices.
Fig.



the

ZnO

NW

arrays

grown

on
the

AZO

seed

layers

at

different

temperatures

of

80
◦

PL

spectra

from

390

to

420

nm.

The

intensities

of

these

PL

spectra
are

also

normalized

the

increase

the

hydrothermal

temperature,
the

position

of

the

peaks

occurred

red-shift

and

the

intensity

of


the

ZnO

NW

arrays

due

to

higher

growth

tem-
perature

[25–27].

When

the

ZnO

NWs



assigned

to

the

intrinsic
excitation

of

ZnO,

dominates

the

PL

spectra

and

no

other

peaks


arrays

grown

on

the

AZO

seed

layer

at

80
◦
C
for

1

h.

It

should

be

on

the

AZO

seed

layer
at

80
◦
C

for

longer

growth

time.

However,

with

the

increase

6
2.0x10
6
Normalized Intensity (a.u.)
Wavelength /

nm
ZnO

NWs

gro

wn at

80
o
C for

1h
ZnO

NWs

gro

wn at

130
o


of

the

ZnO

NW

arrays

grown

on

the

AZO

seed

layer
for

1

h

at



shown

in

the
inset

of

Fig.

7,

indicating

that

some

crystal

defects

start

to

occur


the

decrease

of

the

PL

peaks

in

intensity.

That

is

to
say,

with

the

increase

the

of

the

ZnO
NWs,

and

it

is

probably

to

lead

to

more

crystal

defects

in

the


silicon

substrate

is

first

patterned

with

EB
resist

and

EB

exposal,

then

the

low

surface


on

the

silicon

substrate

by

using

fluoric

organic

solvents.
Fig.

9.

SEM

images

of

the

patterned


␮m,

(c)

line

width

of

500

nm,

(d)

line

width

of

200

nm,

(e)

line


/

Applied

Surface

Science

257 (2011) 10134–

10140
380

390

400

410

420

430

440

450
0.0
2.0x10
5


of

the

patterned

ZnO

NW

arrays

grown

on

the

AZO

seed

layer

at
80
◦
C


a

universal

method

for

patterning

sol–gel

thin

films.
Thus,

when

the

AZO

sol

is

spin-coated

on

due
to

its

low

adhesion,

but

the

AZO

sol

can

be

firmly

deposited

on
those

patterned



of

the

patterned

AZO

seed
layer.

In

order

to

achieve

a

good

photoluminescence

property,

the
patterned

patterned

ZnO

NW

arrays

are

shown

in

Fig.

9.

It

can

be

seen
that

the

ZnO

seed

layer.

Fig.

9(a)

shows

the
patterned

ZnO

NW

arrays

at

a

large

feature

size

area.


1

␮m,

500

nm,

200

nm,

100

nm,

and

50

nm,

respectively.
It

can

be



the

patterned

regions

of

the
AZO

seed

layer.

The

as-grown

ZnO

NW

arrays

show

an


and

50

nm,

respectively.

Fig.

10

shows

the

room
temperature

PL

spectrum

(excite

at

365

nm,

layers.

It

is

found
that

only

a

sharp

and

strong

UV

peak

at

380

nm

dominates


and

no

other

peaks

are

observed

in

the

curve.

These
results

indicate

that

there

are



AZO

seed
layer

at

the

hydrothermal

temperature

of

80
◦
C

for

1

h.
4.

Conclusions
The



hydrothermal

method.

Effects
of

the

hydrothermal

parameters

on

the

morphological

and

pho-
toluminescence

properties

of

the

the

ZnO-
NWA

can

be

obtained

at

130
◦
C

and

the

ZnO-NWA

has

the

higher
aspect



seed

layer.

Furthermore,

the

patterned

ZnO-NWA
arrays

with

strong

PL

emission

and

few

crystal

defects


the

surface

fluorination

technique,
which

is

probably

suitable

for

the

applications

in

the

luminescent
and

electron



China

through

863-project

under

grant

2009AA03Z218,
the

Major

Program

of

the

National

Natural

Science

Foundation



data
Supplementary

data

associated

with

this

article

can

be

found,

in
the

online

version,

at

doi:10.1016/j.apsusc.2011.06.163.

1947–1949.
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Huang,

Y.Y.

Wu,

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Feick,

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Weber,

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Catalytic

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Y.

Liu,

Z.H.

Chen,

Z.H.

Kang,

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Bello,

X.

Fan,

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Shafiq,

W.J.

Zhang,

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Yan,

S.

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R.

Russo,

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nanowires

and

their

optical

prop-
erties

,

Adv.

Funct.

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12

(2002)

323–331.
[5]

C.


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Wang,

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nanowire

UV

photodetectors

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high

internal

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Nano

Lett.

7
(2007)

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field-emission

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zinc

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nanowires

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455–459.
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X.D.

Wang,

J.H.

Song,

P.



arrays

on

GaN,

AlN,
and

Al
0.5
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