Controllable Synthesis of TiO 2 Crystals with Variable Morphology by
Atmospheric Pressure Plasma Jet
Dexin wang1, Qinyu Yang2, Ying Guo2, Yuguang Shao2, Jianjun Shi2, Jing Zhang2
1
College of Material Science and Engineering, State Key Laboratory for Modification of Chemical Fibers and
Polymer Materials, Donghua University, Shanghai, 201620, P. R. China
2
College of Science, Donghua University, Shanghai, 201620, P. R. China
Abstract: TiO 2 crystals may be one of the most important materials for a variety
of potential applications in photocatalysts, biomedical materials and dyesensitized solar cells due to their high chemical stability, avirulence and strong
photo-induced oxidation. The traditional chemical wet method for preparing
TiO 2 crystals often involved multiple steps and long and tedious period with
shape controlling agents, catalysts, masks, post heating and agents and catalysts
removing. It is also difficult to get TiO2 crystals by physical deposition without
masks or catalysts. Here, we report a fast one step synthesis of TiO 2 crystals by
atmospheric pressure plasma jet (APPJ) .Through adjusting the residence time of
and dissociation of the precursor particles by changing the carrier gas flow rate
and discharge power , the deposited samples can be fully amorphous or multi
crystalline TiO 2 with morphology varying from network, microsphere, nanorod
to truncated bipyramid. The size of the TiO 2 crystals can be changed from
several hundred nanometers to several micrometers.
Keywords: Atmospheric pressure plasma jet (APPJ), Plasma enhanced chemical
vapor deposition (PECVD), TiO 2 , Crystal
1. Introduction
period such as adding and removing the shape
controlled agents, catalysts or heat post treatment.
TiO 2 has become one of the most investigated
inorganic materials due to its great applications in
dye-sensitized solar cells[1], hydrogen-generating
devices[2], photo-degradation of organic pollutant[3]
and purification of water and air[4,5] etc.. The
morphologies and microstructures of the TiO 2
crystals play a key role for their application effects.
Preparation of TiO 2 with unique morphologies and
structures becomes one of the hot studies. Numerous
chemical or physical methods have been
successfully applied to prepare amorphous and
crystalline TiO 2 with different shapes including
nanospheres[6],
nanorods[7],
nanotubes[8],
nanobelts[9], nanoflowers[10], and u-donuts[11].
But among the methods mentioned above, almost all
of them involved multiple steps, long and tedious
Plasma enhanced chemical vapor deposition
(PECVD) represents a relatively simple and versatile
method for micro and nanostructure fabrication[12].
In a typical conventional PECVD process to get
TiO 2 crystals, the process is carried out in low
pressure with the substrate heated to several hundred
degree Celsius. In recent years, some researchers
attended to deposit TiO 2 crystals at atmospheric
pressure without heating the substrates[13] in a more
simple and fast way. However, to the best of our
knowledge, there is no such report on the formation
of TiO 2 with well controlled shapes and structures in
this way.
This paper presents a new atmospheric pressure
plasma jet (APPJ) approach to synthesize TiO 2
1
crystals with controllable shapes by one step.
Through adjusting the residence time of the
precursor particles by changing the carrier and
dissociation of the gas flow rate and discharge
power , the deposited samples can be fully
amorphous or multi crystalline TiO 2 with
morphologies varying from network, microsphere,
nanorod to truncated bipyramid. The size of the
TiO 2 crystals can be changed from several hundred
nanometers to several micrometers. Compared to the
conventional chemical method, this new approach is
low cost, robust, simple and fast.
The morphology and crystallinity analysis of the
deposited samples was done using scanning electron
microscopy (SEM, Phenom, FEI) and X-ray
diffraction (XRD, D/Max-2550 PC, RIGAKU, Japan)
respectively.
2. Experimental
The apparatus used in this presentation was a
homemade atmospheric pressure plasma jet, as
shown in Figure 1. The jet was composed of two
coaxial quartz glass tubes and the gap between them
was about 1.5 mm. A 13.56 MHz radio-frequency
power supply was applied to the inside and outside
electrodes. Glow discharge was generated between
the two coaxial quartz glass tubes and then ejected
out into the surrounding ambient air in the form of a
plasma jet. Titanium tetrachloride (TiCl 4 ) heated by
water bath of 50℃ and oxygen were used as the
precursors. Oxygen was also used to carry the vapor
TiCl 4 into the discharge zone. Argon was used as the
background gas. The TiCl 4 gas line was heated to
60℃ to avoid condensation. The substrate of quartz
glass slide was placed under the end of the jet and
kept a distance of about 3 mm away from the nozzle
of the quartz tube. TiO 2 crystals were deposited on
the quartz substrate by one step and the whole
deposition time is only about 10 minutes. The whole
process was operated at atmospheric pressure with a
chamber around the reactor, no vacuum system was
needed.
Fig. 1 Schematic of the reactor used for the deposition
Fig.2 Typical curves of the applied voltage and the discharge
current.
3. Results and discussion
Discharge power and gas flow rate is the most
frequently used parameters to control the
morphology and structure of the deposited products
during the process of PECVD. In our experiments, it
is found that small variation of the deposition
parameters of the discharge power and gas flow rate
dramatically affects the morphology and structure of
the deposited samples. Figure 3 is the SEM images
of the deposited samples with different discharge
conditions. It is shown in Fig. 3(a) that the net-work
The typical I-V curve of the plasma discharge is
shown in Figure 2. The peak value of the applied
voltage and current is 1189 V and 26 mA,
respectively. Both the waveform of the applied
voltage and current of the discharge is sinusoidal and
the phase of the current leads the voltage.
2
shown in Fig. 4(b). After a carful XRD analysis it is
found that these peaks belong to the structures of
structure was obtained for the deposited samples
with plasma power of 40 W, argon flow rate of 1
SLM and oxygen flow rate of 50 SCCM. This
deposition is typical of porous multilayer network
structures. If the precursor percentage of TiCl 4 was
reduced by decreasing the carrier gas oxygen flow
rate to 10 SCCM while the other parameters
maintained invariant as in Fig.3 (a), microsphere
structure of deposited product could be obtained, as
shown in Fig. 3(b). The size of these micro-spheres
is very uniform and the average diameter is about
1.5 um, except for some small spheres with size of
several hundred nanometers. If the discharge power
was increased while the flow rate of gases remained
unchanged as in Fig. 3(b), the deposition could be
with micro-rods structure. As displayed in Fig. 3(c),
the micro-rods were formed on the surface of a
nano-particulate film. The diameter of these microrods is between 100 and 500 nm and their length is
several micrometers. The micro-rods on the
substrate appear massive in quantity. Most of them
tend to lie parallel to the background nanoparticulate
layer. But small part of them grow vertically from
the background nanoparticulate layer and protrude
directly upward from it, indicating their close
structural and compositional relationship with the
background layer. Keep increasing the discharge
power to 100 W but reducing the argon gas flow rate
to 0.5 SLM, micro-sized block product was
deposited, as shown in Fig. 3(d). The size of these
blocks ranged from 1 um to over 10 um. These
blocks with thick center and thin border are thought
to be the initial stage of the growth of the truncated
bi-pyramids TiO2.
TiO 2 crystals and Ti 4 O 7 .The peaks at 2  25.3 ,
2  37.8 , 2  38.6 , 2  48.1 , 2  53.9 ,
2  62.7 , 2  68.8 ,
2  70.4 ,
2  75.3 and 2  82.7 can be well indexed to
the anatase phase of TiO 2 with Miller indices of
(101), (004), (112), (200), (105), (211), (204), (116),
(220), (215) and (224) respectively. The peaks
at 2  27.4
,
2  41.8 ,
2  56.4
and 2  84.0 can be well indexed to the rutile
phase of TiO 2 with Miller indices of (110), (111),
(220) and (400) respectively. The peaks at
2  31.7 and 2  45.4 belong to the Ti 4 O 7
structure of (-1 0 1) and (-1 0 3).
4. Conclusions
A new method was presented to fabricate TiO 2 with
controllable crystallinity and morphology. With
only varing the discharge power and flow rate of the
carrier gas, the deposited samples can be fully
amorphous or multi crystalline TiO2 with
morphologies varying from network, microsphere,
nanorod to truncated bipyramid with micro-size.
Therefore, it is great applicable to the one step
fabrication of crystal inorganic materials with
potentially excellent properties and wide range of
applications.
a
The typical XRD patterns of the same samples
deposited as in Fig. 3(a) and Fig. 3(d) are shown in
Fig. 4. As is illustrated in Fig. 4(a), the XRD
patterns is typical of amorphous structure of TiO 2
for the samples deposited with small discharge
power and large supply of precursors.. Increasing
the discharge power and reducing the precursor
supply, the XRD pattern of the deposited sample is
characteristic of multicrystallization of TiO 2 , as
3
b
c
108:3492-3495.
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d
Fig.3 SEM images of the as deposited TiO 2 with different
conditions: (a) plasma power 40 W, argon 1 SLM, Oxygen 50
SCCM, (b) plasma power 40 W, argon 1 SLM, Oxygen 10
SCCM, (c) plasma power 80 W, argon 1 SLM, Oxygen 10
SCCM, (d) plasma power 100 W, argon 0.5 SLM, Oxygen 10
SCCM.
a
b
Fig. 4 XRD patterns of the deposited samples in Fig.3(a) and
Fig. 3(d)
Acknowledgements: The authors are grateful
to the Nature Science Foundation of China
(No.10835004, 10775031), and the supporting
program from Science and Technology Commission
of Shanghai Municipality (No. 10XD1400100). The
authors also thank for the support and cooperation
from the State Key Laboratory for Modification of
Fibers and Polymer Materials.
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