Open Journal of Physical Chemistry, 2011, 1, 6-10
doi:10.4236/ojpc.2011.11002 Published Online May 2011 (
Copyright © 2011 SciRes. OJPC
Hydrothermal Synthesis and Properties of Diluted
Magnetic Semiconductor Zn1-xMnxO Nanowires
X. Y. Zhang1*, J. Y. Dai2, H. C. Ong3
1Department of C hemic al Eng i neering, Mo na sh U ni versi t y, Melbourne, Au st ral ia
2Department of Appl i ed Physics, Hong Kong Pol y t echnic Uni versi t y , Kowloo n, H on g K o n g, C hi n a
3Department of Physics, Chinese University of Hong Kong , Shatin, Hong Kong, China
Received April 7th, 2011; revised April 28th, 2011; accepted May 11th, 2011.
We report the synthesis of oriented single crystalline Mn doped ZnO nanowires through a hydrothermal
method. Structural characterizations using X-ray diffraction and transmission electron microscopy revealed
that the Mn was doped into the lattice structure, forming solid solution. The Mn doped ZnO nanowires pos-
sess wurtzite structure with a c-axis growth orientation. The physical properties of the nanowires were inves-
tigated. Mn doped ZnO nanowires were found to be ferromagnetic with Curie temperature of about 30 K. A
deep level emission band at about 566 nm was observed at room temperature.
Keywords: Semiconductors, Nanowire, Crystal Growth, Electron Microscopy, Curie Temperature, Photolu-
1. Introduction
One-dimensional nanostructures have attracted a great
deal of interest not only because of their basic scientific
richness, but also of their potential utilization in optical
and electronic devices [1-6]. ZnO is one of the most im-
portant semiconductors due to its wide direct band gap
(3.37 eV) and large exciton binding energy (60 meV). To
date, ZnO in bulk and thin film format has been widely
used in field emission display, solar cell, chemical sensors,
and other devices [7-9]. Recently, dilute magnetic semi-
conductors (DMSs) have attracted a great deal of atten-
tion in the past few years as enabling materials in the
emerging field of “spintronics”. DMSs are semiconductor
solid solutions, where a small percentage of cations are
replaced by magnetic impurities such as Mn. Unusual
magnetotransport and magnetooptical phenomena like
large Faraday rotations, giant negative magnetoresis-
tances, and magnetic field induced metalinsulator transi-
tions have been observed. Among the DMSs, Mn- doped
II-VI compounds have been extensively studied. However,
most of the II-VI compounds studied are chalcogenides;
the corresponding oxides are comparatively less investi-
gated. Theoretical calculations predict that ZnO should
exhibit ferromagnetism above room temperature on dop-
ing with Mn [10,11]. This prediction has initiated in-
creasing efforts on Mn doping of ZnO nanostructures.
Diluted magnetic semiconductor (DMS) behavior has
been observed in many transition-metal doped ZnO films
[12-14], and Curie temperatures above room temperature
were achieved [15,16]. Although the efforts aimed at un-
derstanding the origin of the ferromagnetism resulted in
hundreds of papers, substantial debate still remains. The
available data cannot further advance our understanding
of the mechanism since the data obtained so far on Mn
doped ZnO are not quite consistent, for example, besides
the ferromagnetic behavior, behavior of spin glass [17]
and paramagnet [18] have also been observed. Therefore,
more detailed works are essential to understand the be-
havior of these materials. Mn doped ZnO nanowires (or
nanobelts) have been obtained by doping Mn into ZnO by
using various techniques, such as ion implantation [19],
thermal evaporation [20-23]. These methods generally
require high temperature and expensive equipments. On
the other hand, wet chemical method has been proven to
be a simple and versatile approach for preparing ZnO
nanowires or nanorods due to its relatively low growth
temperature and good potential for mass production [24-
27]. However, to the best of our knowledge, there is no
report on the synthesis of Mn doped ZnO nanowires by
using wet chemical method. Here, we report a simple
hydrothermal method to prepare the Mn doped ZnO
Copyright © 2011 SciRes. OJPC
nanowires. The structure and light-emitting properties are
also investigated.
2. Experimental Section
Materials. Zinc sulfate hydrate (ZnSO4·7H 2O), manga-
nese sulfate hydrate (MnSO4·H2O), carbamide (CON2H4),
sodium hydroxide (NaOH), and ethanol were of analytical
grade and used without further purification. Dou-
ble-distilled water was employed for all experiments.
Synthesis. In a typical synthesis of Mn dopped ZnO
nanowires, a solution of 50 ml 0.1M ZnSO4, 3 ml 0.1M
MnSO4, 15 ml 1M carbamide (CON2H4) and 10 ml
C2H5OH was placed in a sealed Teflon autoclave with
the pH of the solution adjusted to 14 by NaOH. The so-
lution was then heated at 180 for 12 hours and the re-
sulting products were obtained by washing and drying
the yellowish precipitates at 60 for 12 hours.
Characterization. The microstructure and composi-
tion of the nanowires were investigated using an X-ray
diffractometer (XRD, PW1140/90) with Cu K radiation
(25 mA and 40 kV), a scanning electron microscope
(SEM, JEOL JSM-6300), transmission electron micro-
scope (TEM, JEOL-2010), energy dispersive spectros-
copy (EDS), and electron energy-loss spectroscopy
(EELS). Quantitative EDS analysis shows the molar ratio
of Mn is around 3%. The magnetic properties of the
nanowires were studied using a Superconducting Quantum
Interference Device (SQUID) magnetometer (MPMS-
5S). The photoluminescence (PL) measurements were
performed by using a Kimmon HeCd laser (325 nm, 55
mW) in a closed cycle Oxford cryostat. The optical sig-
nal was dispersed by a 0.25 m Oriel spectrometer and
captured by an Andor CCD detector.
3. Results and Discussion
Figure 1 shows the XRD spectrum of the Zn1-xMnxO
nanowires, the reflection peaks of hexagonal structured
ZnO are distinguishable, revealing that the doping of Mn
does not change the wurtzite structure of ZnO. No Mn-
related impurity phases were observed. Figure 2 (a) and
(b) show the typical SEM and TEM images of the
Zn1-xMnxO nanowires, respectively. The nanowires have
uniform diameters along their entire length, the diame-
ters and lengths are in the range of 10 to100 nm and 2 to
10 m, respectively. Figure 3(a) shows TEM image of a
typical long Zn1-xMnxO nanowire, the right inset shows
the selected-area electron diffraction (SAED) pattern
taken from a single nanowire, the analysis of the SAED
reveals that the Zn1-xMnxO nanowire is single crystalline
and grows along the [0001] orientation. The presence of
Mn in the lattice was confirmed by the EELS measure-
ment, the spectrum shows that Zn and Mn coexist along
with O (Figure 3(b)). The Mn-L3/L2 intensity ratio in-
dicates one electron in the d-orbital suggesting Mn to be
in the +2 oxidation state. The nature of single-crystal
structure of the Zn1-xMnxO nanowires and the growth
orientation were further confirmed by high-resolution
TEM (HRTEM) image as shown in Figure 4. The
HRTEM images analysis shows that the Zn1-xMnxO
nanowires are structurally uniform without any signify-
30 40 50 60 70
Intensity (a.u.)
2 theta (degree)
Figure 1. The XRD spectrum of the Zn1-xMnxO nanowires.
Figure 2. (a) SEM; (b) TEM images of Zn1-xMnxO nanowires.
Copyright © 2011 SciRes. OJPC
Figure 3. (a) TEM image of a Zn1-xMnxO nanowire; (b) the corresponding electron diffraction pattern of the Zn1-xMnxO
nanowire; (c) the corresponding electron energy loss spectroscopy spectrum of the Zn1-xMnxO nanowire.
cant defect. These characteristics of the Zn1-xMnxO
nanowires are similar to those ZnO nanowires synthe-
sized by hydrothermal methods.
The magnetic properties of the as-prepared Zn1-xMnxO
nanowires were investigated using a SQUID magnetometer.
Figure 5 shows the temperature dependence of the mag-
netization (M-T) during cooling in a magnetic field of 5 T,
the magnetization shows a slight increase from 100 to 40 K,
followed by a steep increase below 30 K until 5 K. It can
be seen that the FC curve shows a sharp increase at low
temperature, this behavior has been considered as the effect
of randomness and disorder on percolating FM clusters in
most diluted magnetic semiconductor materials. So the
Curie temperature of Zn1-xMnxO nanowires is about 30 K,
which is higher than 25 K and lower than 50 K, observed
for ZnMnO thin film and Mn doped ZnO nanotetrapods,
respectively [28, 29]. It seems that data reported so far on
Mn doped ZnO are not quite consistent. These discrepan-
cies may be due to the different fabrication methods. Ob-
viously, more detailed works are essential to understand the
magnetic behaviors of these materials.
The photoluminescence (PL) of the Zn1-xMnxO nanowires
and undoped ZnO nanowires was investigated at room
temperature. Usually, the PL spectrum of the undoped
ZnO nanowires shows characteristic UV emission and
broad green emission, in agreement with previously re-
ported results for ZnO nanowires [30]. However, the
photoluminescence of the Zn1-xMnxO nanowires is ap-
parently different from that of undoped ZnO nanowires.
It can be observed from Figure 6 that a strong green
emission appears, while the violet emission completely
disappears. The mechanism of green emission has been
suggested to be mainly due to the existence of various
points that can easily form recombination centers [31]. In
the present situation, the strong green emission suggests
that these Zn1-xMnxO nanowires should have many point
Copyright © 2011 SciRes. OJPC
Figure 4. HRTEM image of a Zn1-xMnxO nanowire.
0 20406080100
B = 5 T
T (K)
m (emu)
Figure 5. Temperature dependent magnific ation (M-T) curv e
of the Zn1-xMnxO nanowires at a magnetic field B = 5T.
200 300 400 500600 700 800 900
intensity (a.u.)
wavelength (nm)
Figure 6. The photoluminescence (PL) spectrum recorded
from the Zn1-xMnxO nanowires at room temperature.
defects, such as oxygen vacancies O
V [32,33]. It can be
inferred that the ZnO formed during the hydrothermal
process features a high density of oxygen vacancies, which
enhanced the green emission intensity. It has been sug-
gested that the violet emission band could be assigned to
the VZnP
- centers, and the violet emission intensity depends
on the density of Zn
. The high density of VOP
+ resulted
during the hydrothermal process can lead to a decrease in
the density of Zn
centers and a increase of nonradiative
recombination processes. Furthermore, the doping of Mn in
the ZnO may change the electronic structure of ZnO such
as the position of the Fermi level [34]. These should be
responsible for the quench of the violet emission.
4. Conclusions
In conclusion, large quantity and single crystalline
Zn1-xMnxO nanowires have been synthesized through a
hydrothermal method. Structural characterization by
x-ray diffraction and transmission electron microscopy
revealed that the Zn1-xMnxO nanowires possess wurtzite
structure with c-axis growth orientation. Mn doped ZnO
nanowires are ferromagnetic with Curie temperature ~30
K. The Zn1-xMnxO nanowires exhibit a deep level emis-
sion at 566 nm. This simple approach shows promise for
fabricating nanoscale sensor and other devices.
5. Acknowledgments
This work was funded by the Australian Research Coun-
cil and Monash University. One of the authors (X. Zhang)
Copyright © 2011 SciRes. OJPC
thanks the Australian Research Council for the Austra-
lian Research Fellowship.
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