Effect of immerse duration on the structural and optical properties of zinc oxide nanorod

Article abstract of DOI:10.1080/15533174.2010.486821

Zinc oxide (ZnO) is an emerging optoelectronic material in large area electronic applications that are due to its various functional behaviors. We present the fabrication and characterizations of ZnO nanorods. The ZnO nanorods were synthesized using sol-g

Full text of DOI:10.1080/15533174.2010.486821

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Synthesis and Reactivity in Inorganic, Metal-Organic,
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Effect of Immerse Duration on the Structural and
Optical Properties of Zinc Oxide Nanorod
Sharul Ashikin Kamaruddin a b , Mohd Zainizan Sahdan a c , Kah-Yoong Chan b , Ho-Kwang
Yow b , Mohamad Rusop c & Hashim Saim a
a Faculty of Electrical and Electronic Engineering , Universiti Tun Hussein Onn Malaysia ,
Johor, Malaysia
b Faculty of Engineering , Multimedia University , Selangor, Malaysia
c Faculty of Electrical Engineering , Universiti Teknologi MARA , Selangor, Malaysia
Published online: 27 May 2010.
To cite this article: Sharul Ashikin Kamaruddin , Mohd Zainizan Sahdan , Kah-Yoong Chan , Ho-Kwang Yow , Mohamad
Rusop & Hashim Saim (2010) Effect of Immerse Duration on the Structural and Optical Properties of Zinc Oxide Nanorod,
Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:5, 333-336
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:333–336, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2010.486821
Effect of Immerse Duration on the Structural and Optical
Properties of Zinc Oxide Nanorod
Sharul Ashikin Kamaruddin,1,2 Mohd Zainizan Sahdan,1,3 Kah-Yoong Chan,2
Ho-Kwang Yow,2 Mohamad Rusop,3 and Hashim Saim1
1Faculty of Electrical and Electronic Engineering, Universiti Tun Hussein Onn Malaysia,
Johor, Malaysia
2Faculty of Engineering, Multimedia University, Selangor, Malaysia
3Faculty of Electrical Engineering, Universiti Teknologi MARA, Selangor, Malaysia
material has wide bandgap energy of 3.37 eV and large exciton
binding energy of 60 meV, which make ZnO a promising candi-
date for many applications such as electronic, optoelectronic and
information technology devices including sensors, displays, and
solar cells.[12] However, in many applications both the size and
the shape of the ZnO particles determine the material properties
and therefore the performance of the devices.[6,12]
The 1-D nanostructured ZnO with different morpholo-
gies have been reported, for instances, nanorods, nanowires,
nanobelts and quantum dots.[1−11] Several techniques have been
employed to grow 1-D ZnO nanostructures, such as sol-gel tech-
nique, hydrothermal or solvothermal treatment, chemical pre-
cipitation method, molecular beam epitaxy and chemical vapor
deposition. Among these techniques, the sol-gel method has dis-
tinctive advantages due to its lower crystallization temperature,
ability to tune microstructure via sol-gel chemistry, conformal
deposition ability, compositional control and large surface area
coating capability.[1]
Zinc oxide (ZnO) is an emerging optoelectronic material in
large area electronic applications that are due to its various func-
tional behaviors. We present the fabrication and characterizations
of ZnO nanorods. The ZnO nanorods were synthesized using sol-
gel hydrothermal technique on oxidized silicon (Si) substrates. In
the fabrication of ZnO nanorods, the oxidized Si substrates were
immersed in ZnO aqueous solution for different durations rang-
ing from 3 hours to 5 hours. The surface morphologies of the
ZnO nanorods were examined using scanning electron microscope
(SEM). In order to investigate the structural properties, the ZnO
nanorods were measured using X-ray diffractometer (XRD). The
optical properties were measured using ultraviolet-visible (UV-Vis)
spectroscopy. The effect of the immerse duration on the material
properties of the realized ZnO nanorods will be revealed and dis-
cussed in this paper.
Keywords hydrothermal, immerse duration, nanorods, sol-gel, zinc
oxide, ZnO
In the present research work, we realized the ZnO
nanorods using sol-gel hydrothermal technique. The unique
ZnO nanorods were formed on oxidized silicon substrates,
which were immersed in ZnO aqueous solution for different
durations. The effect of immerse duration on the morphologi-
cal, structural and optical properties of the sol-gel hydrothermal
synthesized ZnO nanorods will be revealed and discussed in this
paper.
1. INTRODUCTION
One-dimensional (1-D) zinc oxide (ZnO) nanostructures
such as nanorods, nanoneedles, nanobelts and nanowires of de-
sirable dimension have lately attracted significant attentions due
to their unique electronic and optical properties compared to
bulk structure.[1−11] The functional nanostructures possess ex-
cellent physical properties, owing to their geometry with high
aspect ratio that modifies the light-matter interaction. The ZnO
2. EXPERIMENTAL
Silicon (Si) (100) substrates used for the growth of ZnO
nanorods were cleaned and etched in diluted hydrofluoric acid.
Received 21 August 2009; accepted 15 April 2010.
The authors thank M. T. Nasir from Material Science Laboratory
of University Tun Hussein Onn Malaysia (UTHM) for technical assis- The Si substrates were then rinsed and cleaned with de-ionized
tance during the research project. This work is financially supported
water. After that, the seed layer of silicon oxide (SiO2) was
by the Fundamental Research Grant (Vot No. 0214) from UTHM.
grown on the Si substrates. The SiO2 seed layer is necessary
Address correspondence to Sharul Ashikin Kamaruddin, Fac-
in order to enhance the growth of the ZnO nanorods on the
ulty of Electrical and Electronic Engineering, Universiti Tun Hus-
Si substrates since there is a lattice mismatch between Si and
zinc.[13] The oxidation process was carried out in 1 atmospheric
sein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia. E-mail:
sharul.ashikin@mmu.edu.my
333

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S. A. KAMARUDDIN ET AL.
reveal the evolution of the surface morphology of ZnO nanorods
realized on oxidized Si substrates under the influence of dif-
ferent immerse durations of the substrate in the ZnO aqueous
solution. In general, the growth of ZnO nanorods is enhanced
with increasing immerse duration. The phenomenon can be ex-
plained as the ZnO nanorods underwent crystal restructuring
when immersed in the aqueous solution. The longer the im-
merse duration, the better the nanorods formed on the growing
substrates. ZnO nanorods with moderate sizes were observed
when the immerse durations were 3 hours and 3.5 hours, as
shown in Figure 2 (a) and (b). The mean diameter of the moder-
ate nanorods is about 600 nm. Besides, the estimated length of
the ZnO nanorods is about 5 µm. When the immerse duration
was increased to 4 hours and above (Figure 2 (c), (d) and (e)),
the size and density of the ZnO nanorods increase compared to
ZnO nanorods realized with 3 hours and 3.5 hours of immerse
durations. The mean diameter of the larger nanorods is around
900 nm, while the estimated length of the ZnO nanorods is about
7 µm.
Figure 3 presents typical XRD patterns of the ZnO nanorods
realized with different immerse durations. The sharp and narrow
diffraction peaks indicate that the ZnO materials exhibit high
crystallinity. Furthermore, no characteristic diffraction peaks
from other material phases or impurities except ZnO and silicon
(which arises from the silicon substrates) were detected from
the measured XRD patterns. The crystal growth orientation of
the ZnO nanorods is preferential at [101] and [100] directions,
followed by [002] direction, and finally [110] and [102] direc-
tions. In general, the XRD patterns show that, the intensity of
the ZnO diffraction peaks increase with increasing immerse du-
ration, which reveals that the quality of the ZnO nanocrystals
overall is enhanced with longer immerse duration. Of partic-
ular, the enhancement in the [002] diffraction peak indicates
a more preferential growth orientation along c-axis for longer
immerse duration. The improvement in the ZnO nanorod crys-
tallinity with increased immerse duration can be explained by
the fact that the longer the immerse duration, the atoms gain
sufficient time to move and settle at proper sites, which leads
to improvement of structural properties. Due to the principle of
minimization of Gibbs free energy at the most stable condition,
the atoms slowly move into the lowest energy sites in its crystal
structure to reduce the Gibbs free energy, and therefore form
higher crystal quality of ZnO.
FIG. 1. Sol-gel hydrothermal fabrication process of the ZnO nanorods.
ambient and 900◦C for 15 minutes. Solution for ZnO nanorods
growth was prepared using an aqueous solution of zinc nitrate
hexahydrate [Zn(NO3)2.6H2O] mixed with hexamethylenete-
tramine [C6H12N4]at precursor concentration of 0.001
M (M = molarity). The solutions were diluted in 200 ml de-
ionized water. The solutions were then stirred at 60◦C for 2
hours and aged at room temperature for 24 hours. The oxidized
Si substrates were immersed in the solutions at 95◦C for dif-
ferent durations ranging from 3 hours to 5 hours. After drying,
the ZnO coated oxidized Si samples were annealed at 500◦C for
1 hour. The fabrication process of the ZnO nanorod is depicted in
Figure 1.
Figure 4 demonstrates the ultraviolet-visible absorption spec-
tra measured for the ZnO nanorods realized at different immerse
durations. All samples in general have high absorption at UV
region (below 400 nm). The UV-Vis absorption spectra exhibit
an increase in the absorbance in the UV region with increasing
immerse duration. The highest absorbance occurs for the longest
immerse durations of 4.5 hours and 5 hours, indicating an en-
hanced presence of the ZnO phases in the realized nanorods
when the immerse duration is extended. The density of the ZnO
The ZnO nanorod coated samples were characterized for sur-
face morphologies using scanning electron microscope (SEM)
(JOEL JSM6380LA). X-ray diffractometer (XRD) (D8 Ad-
vance Bruker) was used to investigate the structural properties
of the ZnO samples. The optical properties of the ZnO nanorods
were measured using ultraviolet-visible (UV-Vis) spectroscopy.
3. RESULTS AND DISCUSSION
Figure 2 shows the two-dimensional (2-D) SEM images mea- nanorods determines the sensitivity of the sample to the light
sured for the ZnO nanorod coated samples. The SEM images absorption in the UV region. The more enhanced growth of the

IMMERSE DURATION ON THE PROPERTIES OF ZINC OXIDE NANOROD
335
FIG. 2. SEM images of ZnO nanorods realized with different immerse durations; (a) 3 hours, (b) 3.5 hours, (c) 4 hours, (d) 4.5 hours, and (e) 5 hours.
FIG. 3. The XRD patterns of ZnO nanorods realized with different immerse
durations; (a) 3 hours, (b) 3.5 hours, (c) 4 hours, (d) 4.5 hours, and (e) 5 hours.
FIG. 4. The UV-Vis spectra of ZnO nanorods realized with different immerse
durations; (a) 3.5 hours, (b) 4 hours, (c) 4.5 hours, and (d) 5 hours.

336
S. A. KAMARUDDIN ET AL.
ZnO nanorods on the growing substrate, the higher the absorp-
tion of light especially in UV region.
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4. CONCLUSION
ZnO nanorods have been synthesized using low cost sol-
gel hydrothermal technique on oxidized silicon substrates with
different immerse durations. The effects of the immerse dura-
tion were observed on the morphological, structural and optical
properties of the realized ZnO nanorods. Characterization from
SEM shows an enhanced growth of the ZnO nanorods with in-
creasing immerse duration. XRD characterizations demonstrate
sharp and narrow diffraction peaks peculiar to ZnO, which im-
plies that the realized ZnO nanorod is of high crystallinity. Based
on the UV-Vis absorption spectra, long immerse duration results
in the high absorption in the UV region. In conclusion, in the
sol-gel hydrothermal synthesis of ZnO nanostructures, the im-
merse duration exerts a strong influence on the growth of the
ZnO, and the morphological, structural and optical properties
of the ZnO nanorods. A longer immerse duration is preferred
in the fabrication of the ZnO nanorod, which is considered as
emerging material system for many advanced electronic and
optoelectronic devices.
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