Fast and safe synthesis of micron germanium in an ammonia atmosphere using Mo2N as catalyst

Article abstract of DOI:10.1039/c8ra07352j

Here, we reported a new method for fast and safe synthesis of a micron germanium (Ge) semiconductor. The Ge was successfully prepared from mixed GeO₂ with a low amount of MoO₃ by the NH₃ reduction method at 800 °C for an ultra-short time of 10 min. XRD patterns show that the Ge has a tetragonal structure. SEM images show that the size of the Ge particles is from 5 μm to 10 μm, and so it is on the micron scale. UV-visible diffuse reflectance spectroscopy shows that the Ge has good light absorption both in the ultraviolet and visible regions. The formation of Ge mainly goes through a two-step conversion in the NH₃ flow. Firstly, GeO₂ is converted to Ge₃N₄, and then Ge₃N₄ is decomposed to generate Ge. The comparison experiments of MoO₃ and Mo₂N demonstrate that Mo₂N is the catalyst for the Ge synthesis which improves the Ge₃N₄ decomposition. The presented fast and safe synthesis method of Ge has great potential for industrialization and the proposed Mo₂N boosting the Ge₃N₄ decomposition has provided significant guidance for other nitride decomposition systems.

Full text of DOI:10.1039/c8ra07352j

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Fast and safe synthesis of micron germanium in an
ammonia atmosphere using Mo N as catalyst
2
Cite this: RSC Adv., 2018, 8, 35753
Baojun Ma, * Dekang Li, Xiaoyan Wang and Keying Lin
Here, we reported a new method for fast and safe synthesis of a micron germanium (Ge) semiconductor.
2 3 3
The Ge was successfully prepared from mixed GeO with a low amount of MoO by the NH reduction
ꢀ
method at 800 C for an ultra-short time of 10 min. XRD patterns show that the Ge has a tetragonal
structure. SEM images show that the size of the Ge particles is from 5 mm to 10 mm, and so it is on the
micron scale. UV-visible diffuse reflectance spectroscopy shows that the Ge has good light absorption
both in the ultraviolet and visible regions. The formation of Ge mainly goes through a two-step
conversion in the NH
generate Ge. The comparison experiments of MoO
the Ge synthesis which improves the Ge
method of Ge has great potential for industrialization and the proposed Mo
decomposition has provided significant guidance for other nitride decomposition systems.
3
flow. Firstly, GeO
2
is converted to Ge
3
N
4
, and then Ge
3
N
4
is decomposed to
Received 3rd September 2018
Accepted 7th October 2018
3
and Mo N demonstrate that Mo
2
2
N is the catalyst for
N
3 4
decomposition. The presented fast and safe synthesis
N boosting the Ge
DOI: 10.1039/c8ra07352j
2
3 4
N
rsc.li/rsc-advances
commonly prepared by the reduction of GeO in hydrogen ow
at 650–680 C, and then Ge with high purity is obtained by
2
1
Introduction
ꢀ
With the development of advanced electronic information chemical gasication and decomposition of rough Ge. However,
industries, semiconductor materials have attracted widespread in the process of preparing rough Ge, the produced hydrogen is
1
–6
attention due to their unique optical and electrical properties.
a dangerous gas due to its large range of the explosion limit. In
Ge as an important semiconductor material with stable chem- addition, a leak of hydrogen is not easy to discover due to it
ical properties and obvious non-metallic properties has many being colorless and tasteless. So, it is necessary to develop and
advantages, such as non-toxicity, biocompatibility, electro- improve a safe and low-cost method to produce rough Ge.
chemical stability, current microelectronics compatibility,
etc.
Ammonia is an important chemical raw material, which has
At present, Ge has extensive and important applications important applications in industrial and agricultural produc-
7
–13
in elds such as semiconductors, aerospace measurement and tion. At the same time, ammonia is also a reducing gas capable
42–45
control, nuclear physics detection, optical ber communica- of reducing various metal oxides.
Here, we successfully
tion, infrared optics, solar cells, chemical catalysts, and prepared micron Ge material in ammonia atmosphere using
14–20
biomedicine.
there is almost no concentrated Ge deposit in the Earth's crust. formation process from GeO
Thus, it is particularly important to nd suitable methods to catalyst were determined. The synthesis method of Ge has the
enrich, prepare and purify Ge.
advantages of safe, fast and low cost, which is benecial to
Ge is one of the most dispersed elements and GeO
2
as raw material with some MoO
3
in 10 min. The trans-
2
to Ge and the molybdenum based
The synthetic method of Ge can be divided into physical and industrial production.
chemical methods. The physical methods mainly include
2
1
22
chemical vapor deposition, gas phase pyrolysis, plasma
23–25
26,27
28,29
30
technology,
sputtering,
etching,
laser ablation and 2 Experimental
so on. However, these technological processes need extreme
temperatures and pressures and are expensive. Chemical
methods mainly include room temperature reduction of
2
.1 Synthesis of Ge
All the chemical agents are from China National Pharmaceu-
tical Group Corporation. GeO as raw material and a small
amount of MoO are mixed and milled in a mortar for 30
minutes. The mixed samples are the calcined in an ammonia
31,32
2
a GeCl
precursor,
position method
4
/Br
4
precursor,
2
high temperature reduction of a GeI /
a one-step synthesis method,
3
3,34
35,36
3
I
4
an electrode-
37–41
and so on. In the industry, rough Ge is
ꢁ
1

ow of 100 mL min at different temperature and for different
time. The synthesis of Ge in H ow is same as that in NH ow
2
3
except H instead of NH .
2
3
State Key Laboratory of High-efficiency Coal Utilization and Green Chemical
Engineering, College of Chemistry and Chemical Engineering, Ningxia University,
Yinchuan, 750021, People's Republic of China. E-mail: bjma@nxu.edu.cn
Also, in this paper A/B means A mixed with B. For example,
Mo N/GeO means Mo N mixed with GeO
2
2
2
2
.
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2
.2 Characterization
The structure of the as-prepared Ge was determined by X-ray
diffraction (D/MAX2500, Rigaku, Japan) with a Cu-K radia-
a
tion at a voltage of 4 kV at room temperature. The ultraviolet-
visible diffuse reectance spectra (UV-vis DRS) were obtained
on a spectrometer (U-4100), and BaSO was used for the cor-
4
rected base line. The size and morphology were examined by
scanning electron microscopy (SEM, JSM7500F) with the
accelerating voltage of 0.5–30 kV and transmission electron
microscopy (TEM, F20) with the accelerating voltage of 120 kV.
3
Results and discussion
3
.1 Synthesis of Ge in NH ow using Mo based catalyst
3
Fig. 1 shows the XRD patterns of GeO
temperatures in an ammonia atmosphere. The XRD of the GeO
2
calcined at different
Fig. 2 XRD patterns of commercial GeO
2
and samples of 5.0 wt%
2
MoO /GeO calcined in NH flow at different temperatures for 2 h.
3
2
3
is also present for comparison. When the reaction temperature
ꢀ
is lower than 800 C, GeO2 (PDF # 36-1463) still remain
ꢀ
unchanged. At 800 C, all GeO changed into Ge N (PDF # 38-
1
2
3 4
ꢀ
ꢀ
374). At 900 C, a part of Ge (PDF # 04-0545, 2q ¼ 27.5 )
generates which indicates a small part of Ge
overhigh temperature.
3 4
N decomposes at
Fig. 2 shows the XRD patterns of 5.0 wt% MoO
3 2
/GeO
calcined in NH ow at different temperatures for 2 h. It can be
3
ꢀ
seen that when the reaction temperature is at or above 800 C,
almost all the GeO2 are changed into Ge (PDF # 04-0545).
Comparing with Fig. 1, the introduction of the Mo element
decreases the reaction temperature of Ge generation over
ꢀ
1
00 C.
Fig. 3 shows XRD patterns of 5.0 wt% MoO
3
/GeO
ow at 800 C for different time. The process of Ge
can be reduced
to Ge in 10 min. Fig. 4 shows the XRD pattern of MoO /GeO
2
calcined in
ꢀ
NH
3
generation is ultra fast and almost all the GeO
2
3
2
with different mass ratio calcined in ammonia ow. When the
amount of MoO is less than 5.0%, the reaction product is Ge
3
Fig. 3 XRD patterns of commercial GeO
.0 wt% MoO /GeO calcined in NH
2
, 5.0 wt% MoO
flow at 800 C for different time.
3
/GeO
2
and
and Ge
amount of MoO
In view of the fact of that GeO
3
N
4
(e.g. the sample of 2.0 wt% MoO
is 5.0%, almost all the GeO
3 4
changed into Ge N
3
/GeO
is converted to Ge.
(Fig. 1, 800
2
). When the
ꢀ
5
3
2
3
3
2
2
Fig. 1 XRD patterns of commercial GeO
flow at different temperatures for 2 h.
2
and GeO
2
calcined in NH
3
Fig. 4 XRD patterns of GeO
loading mass ratio calcined in NH
2
and MoO
3 2 3
/GeO with different MoO
ꢀ
3
flow at 800 C for 0.5 h.
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ꢀ
C) without any catalyst, we inferred the process Ge generation
is that rst the GeO transfers into Ge N , and then the Ge N
3 4
2
3
4
decomposes into Ge with the Mo base catalyst. This ultra fast
method of Ge generation using Mo based catalyst has major
advantages of low cost and high efficiency.
3.2 Determination of the catalyst of Ge generation
It is well known the molybdenum oxide will change into
molybdenum nitride in NH atmosphere at high temperature.
3
So, it is necessary to judge which Mo species play the catalytic
role in the Ge generation. Fig. 5 shows XRD patterns of MoO
3
ꢀ
calcined in the NH
3
ow at different temperatures. At 600 C,
Fig. 6 XRD patterns of GeO
2
, 5.0% Mo
2
N/GeO
2
, 5.0% MoO
3 2
/GeO ,
some MoO (PDF # 35-0609) is reduced into MoO
3
2
(PDF # 32-
5
.0% Mo
N/Ge N
2 3 4
and 5.0% MoO /Ge
3
3
N
4
calcined in N
2
atmosphere
ꢀ
0671). When the temperatures reach at and above 700 C, all
ꢀ
at 800 C for 2 h.
MoO is converted to Mo N (PDF # 25-1366). In Fig. 2, Ge is
3
2
ꢀ
ꢀ
generated at 800 C from MoO /GeO . At this moment (800 C),
3
2
ꢀ
the MoO had been reduced into Mo N (Fig. 5, 800 C), and the
3
2
ꢀ
GeO
2
had been reduced into Ge N (Fig. 1, 800 C). These results
3 4
indicate that the Mo
improves the decomposition of the Ge
2
N generated by MoO
3
acts as a catalyst and
into Ge.
3
N
4
2 3
In order further determine the origination (Mo N or MoO )
of the catalysis role in Ge generation, the calcination experi-
ments in nitrogen ow using GeO and Ge N as raw materials
2
3 4
have been designed. Fig. 6 shows the XRD patterns of Mo N/
2
GeO , MoO /GeO , Mo N/Ge N and MoO /Ge N calcined in N
2
2
3
2
2
3
4
3
3
4
ꢀ
atmosphere at 800 C for 2 h. It can be seen that there are all
a small amount of Ge generated by the addition of Mo
whether the raw material is GeO or Ge . However, by the
addition of MoO , there is no Ge generation for both MoO
GeO and MoO /Ge . These again demonstrate that Mo
2
N
2
3 4
N
3
3
/
2
N
2
Fig. 7 XRD patterns of GeO calcined in hydrogen atmosphere at
different temperatures for 4 h.
2
3
3
N
4
plays the catalysis role in Ge generation, whereas MoO is not
3
the catalyst.
chosen generally in the industry. Fig. 8 shows the XRD pattern
ꢀ
of GeO
Ge can be produced in the H
with the industrial method in the H
method in the NH ow with Mo N catalyst has the advantages
2
calcined in hydrogen ow at 500 C for different time.
3
.3 Comparison with the industrial preparation method of
2
ow in 2 hours. So, compared
ow, our preparation
Ge in H ow
2
2
In order to compare our preparation method with industrial
method, GeO is reduced into Ge in hydrogen atmosphere has
been carried out. Fig. 7 shows the XRD patterns of GeO2
calcined in hydrogen ow at different temperatures for 4 hours.
3
2
2
of ultra short reaction time (10 min vs. 2 h) and more safety
NH vs. H ), though the reaction temperature is higher (800 C
ꢀ
(
3
2
ꢀ
ꢀ
At or over 500 C, Ge is generated in H ow, and 650 C is
2
ꢀ
2 2
flow at Fig. 8 XRD patterns of GeO calcined in H flow at 500 C for different
Fig. 5 XRD patterns of MoO
different temperatures for 2 h.
3
and MoO
3
calcined in NH
3
time.
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ꢀ
vs. 650 C). We also performed the experiment which the GeO
2
ꢀ
was calcined in H ow at 800 C for the further contrast. The
2
Fig. 9 shows the XRD pattern of GeO calcined in hydrogen ow
2
ꢀ
at 800 C for different time. The GeO was converted into Ge in
1
2
ꢀ
0 min under the hydrogen atmosphere at 800 C. It is similar to
that of in the NH
3 2
ow reduction. However, calcining GeO in
an ammonia atmosphere means more secure.
3
.4 The physical properties of prepared Ge
Fig. 10 shows the morphologies of the raw material GeO
the prepared Ge in NH ow with different magnications. The
GeO particles (Fig. 10a–c) are uniform and show sharp angular
2
and
3
2
shapes. The prepared Ge in NH3 ow (Fig. 10d–f) shows
a smooth surface and some agglomeration, indicating the
3 2
Fig. 11 HRTEM of Ge prepared in the NH flow from GeO mixed with
ꢀ
5.0% MoO at 800 C for 2 h.
3
structure changes from GeO to Ge. The size of Ge is between 5
2
mm and 10 mm. Fig. 11 shows the HRTEM of prepared Ge in NH
ow, the lattice fringes of Ge with interplanar distances of
3

(
Fig. 12a) decreases and the large smooth-surfaced Ge (Fig. 12b)
0.237 nm is indexed to the (111) planes of Ge.
increases with the reaction time prolonging. Associate with XRD
patterns in Fig. 4, the rod-shaped material can be inferred as
Ge
there is hardly any Ge
that almost all Ge N transforms into Ge with the increase of
In order to further explore the morphology changes in the
formation process of Ge, SEM as shown in Fig. 12 has been
carried out for the samples prepared from MoO /GeO for
3
N
4
. Compared the Fig. 12c with Fig. 12b, it can be seen that
3
2
3 4
N
particles in the Fig. 12c, indicating
different times and with different MoO mass ratios. Compared
3
the Fig. 12b with Fig. 12a, it is found the rod-shaped material
3 4
MoO . Here, the MoO had been converted into Mo N due to in
the NH ow at 800 C (Fig. 5, 800 C). Fig. 12 again demon-
3
3
2
ꢀ
ꢀ
3
strates the process of Ge generation goes through two stages.
Firstly, GeO
into Ge by the catalysis of Mo
Fig. 13 shows the UV-vis diffuse reectance spectra of MoO
GeO calcined in the NH ow with different mass ratios of
MoO . The raw material of GeO show a strong light absorption
2
is reduced to Ge
3
N
4
, and then Ge
3 4
N decomposed
2
N.
3
/
2
3
3
2
at ultraviolet region with the absorption edge of 218 nm, which
means it is a large gap semiconductor. With the amount of
MoO increasing from 0 to 5.0%, the light absorption region
3
gradually extends from ultraviolet region to visible region and
the absorption strength gradually increases. The Ge prepared
3 2
from 5.0% MoO /GeO shows the most strongest light absorp-
tion in the range from 200 nm to 800 nm. The light absorption
curve of the Ge prepared in NH ow is same as that prepared in
H2 ow except the absorption strength. The difference of
absorption strength can be attributed to the small amount of
3
ꢀ
Fig. 9 XRD patterns of GeO
time.
2
calcined in H
2
flow at 800 C for different
2
Mo N catalyst.
Fig. 12 SEM images of samples prepared in the NH
3
flow from 2.0%
at 800 C for 2 h
ꢀ
ꢀ
Fig. 10 SEM images of the raw material of GeO
prepared from 5% MoO /GeO in NH
2
(a–c) and the Ge (d–f) MoO
3
/GeO
2
at 800 C for 0.5 h (a), 2.0% MoO
3
/GeO
2
ꢀ
ꢀ
3
2
3
flow at 800 C for 2 h.
(b) 5% MoO
3
/GeO
2
at 800 C for 2 h (c).
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