Easiest synthesis procedure of GeO2 nano-rod
and its characterization
Mrinal Seal1
Sampad Mukherjee2
Department of physics, Indian
Institute of Engineering Science and
Technology, Howrah, India Pin711103
Email-id: mrinal.phy@gmail.com
Department of physics, Indian
Institute of Engineering Science and
Technology, Howrah, India Pin711103
Email-id:
smukherjee.besu@gmail.com
ABSTRACT
horizontal tube furnace [7]. Bulk-quantity GeO2
nanorods and nanotubes have been synthesized by
simple thermal evaporation of metallic germanium
powders [8]. However, it is established for Zinc
Oxide that the shape of the nano particles produced
through solvothermal technique can be controlled by
changing the solvent [9]. The presence of organic
solvent in the solvothermal process creates mainly a
mixture of sphere and rod like structure [10].
In this communication, we have followed the
technique of using a mixture of organic solvent and
water in hydrothermal process and report a novel as
well as an economical synthesis procedure of GeO2
nanorods. Prepared sample is characterized with
various techniques and compared with the results as
obtained for the GeO2 nano crystals.
Germanium oxide nanorods have been prepared
hydrothermally using a mixture of water and acetone
as organic solvent. The XRD pattern shows a new
peak and PL spectrum reveals presence of a blue
emission respectively as characteristic of the rod
shaped sample. The SEM and HRTEM images
confirm the rod shaped structure of the sample. The
EDX pattern is a confirmation for the constituents of
the rods are Germanium and Oxygen only. Finally,
the magnetic behaviour of the sample is studied with
the help of SQUID magnetometer and explained the
origin of such behaviour with the help of oxygen
vacancy.
Keywords- Oxide, Hydrothermal Synthesis, Nanorod, Optical property, Magnetic property
2. EXPERIMENTAL PROCEDURE
Analytical grade GeO2 powder (Alfa Aesar, 99.99%)
is used to prepare a stock solution with moderately
hot double distilled water. 40ml of this solution is
taken in an in-house designed autoclave where 4 ml
of acetone (organic solvent) is added. After sealing
properly, the autoclave is heated in a furnace at
temperature 3600C corresponding to 170 bar
pressures as measured with a pressure gauge attached
with the autoclave for twenty-four hours. After that,
the autoclave is cooled naturally to ambient
temperature and the samples are collected from the
solution by evaporating water. Collected samples
were grinded with mortar and pestle and prepared for
different types of characterization.
1. INTRODUCTION
Germanium oxide (GeO2) is an important material
due to its wide band gap and high refractive index
leading to possible applications in opto-electronic
devices. Such opto-electronic applications need
GeO2 mostly in rod or wire shaped form. There are so
many reports of GeO2 nano wire synthesis using
different techniques like
thermal evaporation [1], Carbon nano-tube confined
reaction of Germanium [2], laser ablation [3], thermal
oxidation [4], carbothermal reduction [5] etc. All
these techniques have performed at the temperature
range of 820-13000C to generate sufficient vapour
pressure of Germanium (Ge) or germanium mono
oxide (GeO) in an oxidizing or inert environment to
prepare GeO2 nanowires or whiskers. The GeO2
nanowires were also synthesized utilizing the vapourliquid-solid (VLS) growth mechanism [6] in a simple
The X-ray diffraction (XRD) pattern is obtained
using Mini Flex2 X-ray powder diffractometer with
Cukα (wave length-1.54Ǻ) radiation and operating in
a step scan mode with 0.010 in 2θ per step. High-
1
resolution Transmission Electron Microscope
(HRTEM) (TECNEI20) photographs are obtained
after preparing the grids following conventional
methods. Scanning Electron Microscope (SEM)
image as well as the Energy Dispersive X-ray (EDX)
pattern of the same also obtained with Hitachi
(S3400N) microscope. Photo luminescence (PL)
spectroscopy is performed with Spectrophotometer
(Perkin Elmer Model: Lambda45) at different
excitation energies. The prepared nano rods show
some unusual features regarding magnetization effect
as observed through SQUID magnetometer (magnetic
property measurement system, Quantum Design).
3. RESULTS AND DISCUSSIONS
Figure 1 shows the XRD pattern of the sample. The
peaks as indicated with hkl values are in fair
agreement with the XRD pattern obtained for αquartz GeO2 nano crystals as prepared by
hydrothermal technique [11-12], except the peak
nearly 310 as marked with a circle.
Fig.2. SEM image of GeO2 nanorods.
Fig.3. HRTEM image of GeO2 nano rods.
Fig.1. XRD Pattern of GeO2 nanorods.
From the SEM image it is observed that rod shaped
structures appears with the usual GeO2 crystal forms
[11], which is comparable to the phenomenon as
occurs due to use of organic solvent [10]. The length
of the rod shaped sample as observed from the SEM
image is of the order of a few micrometers and the
diameter as observed from the TEM image is
measured nearly 100 nm. EDX spectrum as shown in
figure 4 confirms existence of germanium and
oxygen only inside the sample.
This XRD pattern with such peak is very much
similar to the XRD pattern of rod shaped GeO2 as
prepared earlier [8] with different technique.
The figures 2 and 3 show the SEM and HRTEM
images respectively.
2
Fig.4. EDX pattern of GeO2 nano rods.
The PL spectrum of the prepared GeO2 nanorods for
excitation wavelength 300 nm is presented in figure
5. Foremost, it is being observed an emission peak
around 420 nm (Position-a, as marked with solid
straight line in figure 5). Such peak in the blue light
region for nano-crystal GeO2 particles are due to
presence of defects including oxygen vacancy [13, 5].
The peak as observed nearly at 450 nm (Position-b,
as marked with dotted straight line in figure 5) is due
to presence of oxygen
Fig.6. Hysteresis curves of the sample at 295K and
2K respectively.
The figure shows that the area covered by the
hysteresis loop is greater at lower temperature for the
sample, which is obvious. However, ferromagnetism
due to oxygen vacancy in some oxides (viz. SnO2,
CeO2 especially in nano-order phase) is already
reported [14, 15]. The report by Chang et al [14]
illustrated that the sample (nano sized SnO2) loses its
ferromagnetic nature due to absence of Oxygen
vacancy as the material is annealed at 7000C in
oxygen atmosphere. From the study concerning the
magnetic behavior of such samples, it is clear that
oxygen vacancy plays an important role for
exhibiting the property of magnetization. A
schematic diagram of GeO2 crystal structure is shown
in figure 7, where the black and grey coloured
spheres are denoted as Germanium and Oxygen
respectively.
Fig.5. PL Spectrum of GeO2 nano rods excitation
energy 300nm.
vacancy in the rod-shaped sample and comparable
with the PL spectrum as observed by Z. Jiang et
al.[8].
The most unusual property of the sample,
contradictory to the bulk or crystalline GeO2, is the
magnetization effect. Although the amount of
magnetization is not considerable at room
temperature but still a hysteresis curve is obtained for
the sample as placed within high magnetic field.
Figure 6 shows the hysteresis curve as obtained with
SQUID magnetometer at both room temperature
(295K) and at 2K.
Fig.7. Schematic diagram of GeO2 molecules for rod
shaped structure.
Regarding the electronic configurations of
Germanium and Oxygen it must be that, each
electron of 4p shell of Germanium is coupled with
another electron of 2p shell of an Oxygen atom with
exchange interaction. However, from the PL study
3
we have evidence of defects in the sample. Such
defects inside the sample indicate formation of
oxygen vacancies, which is responsible for the
partially filled 4P shell in Germanium. This idea has
been adopted from the explanations given by Han et
al for Oxygen-deficient Cerium Oxide [15] as the
structure of the material is quite similar to GeO2.
Such oxygen-vacancy in the sample creates unpaired
electrons, which is responsible for the magnetic
behavior of the sample. The responsibilities of
oxygen-vacancy in magnetic and transport behaviour
within a few oxides have also been established [1617].
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4. CONCLUSIONS
We have prepared GeO2 nano rod by hydrothermal
technique using a mixture of water and acetone as
solution. The use of such organic-solvent in
solvothermal process to control the shape of the
sample is an established one, which we have used for
GeO2 rod preparation first time and we are
successful. XRD pattern of such sample shows a peak
that presents only for the rod shaped GeO 2 sample
with the other conventional XRD pattern of GeO2
crystals. The elemental analysis of prepared sample is
also done from the EDX pattern. Therefore, we
suggest that the prepared sample is a mixture of rod
and usual crystal form as confirmed from SEM image
also. The XRD peak near 310 is a characteristic peak
for the rod shaped GeO2 sample. The SEM and
HRTEM images established that the length of
produced GeO2 rods are of the order of a few
micrometers and the diameter is nearly 100 nm
respectively. The PL spectroscopy reveals that there
exist defects inside the sample; besides this, a
characteristic blue peak near 450 nm is also observed
for such rod shaped sample. Such peak produced at
low energy region indicates the increment of surface
area due to formation of GeO2 nano rod (a part of the
internal energy is used for the increment of surface
area).The magnetic hysteresis curve as observed for
the sample, both at room temperature (295K) and at
2k are the first ever reported for GeO2 and this
property is certainly due to the presence of oxygenvacancy for the rod shaped sample.
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ACKNOWLEDGEMENT
We acknowledge IISER, Kolkata for the SQUID
magnetometer measurement and for XRD pattern.
We are thankful to the Material Science Department
of IIEST, Shibpur for the SEM micrograph as well as
for EDX. We also extend our thanks to IIEST,
Shibpur for completion of this work.
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