S. Oh et al. / Journal of Alloys and Compounds 803 (2019) 499e504
501
spectrophotometer (Agilent Technologies Inc., Agilent 89090A) was
used to measure the UV absorption of the dispersion. A current-
voltage curve was obtained for the temperature range of
which adsorbed moisture and residual iodine were removed. The
ꢁ
changes occurring near 464 C were confirmed by the formation of
ꢁ
MoO
decomposition of Mo
process is illustrated in Fig. 4b as the XRD pattern analysis of heat-
2
and mass reduction at 762 C that resulted from the complete
100e500 K.
6 3 6 2 3
S I to metallic Mo and Mo S phases; this
ꢁ
ꢁ
treated Mo
6
S
3
I
6
samples at 500 C and 800 C. Thus, Mo
6
S
I
3 6
was
3
. Results and discussion
ꢁ
confirmed to be a very stable material up to 450 C (The results of
other experiments also show that Mo
atmosphere [28]).
6 3 6
S I is stable in the ambient
Fig. 2a shows a digital photograph (quartz ampoule) and the
XRD patterns of the synthesized materials in the source zone and
transport zone when MoI was used as a precursor. In the source
phases were mixed at a temperature
6 3 6
The electrical properties of the synthesized Mo S I
2
(100e500 K) were observed to be dependent on the temperature
zone, the Mo
of 1070 C and above. However, a few MoS
at a temperature of 1020 C. On the other hand, in the transport
6
S
3
I
6
and Mo
6
S
6
I
2
(Fig. 4c). As the temperature increased, the electrical conductivity
ꢁ
2
phases were observed
increased. The electrical conductivity is known to be proportional
to the mobility and concentration of the charge. Considering that
mobility was assumed to be constant, the results of Arrhenius
fitting (slope: -E /k T, where E is the bandgap, k is the Boltzmann
g B g B
constant, and T is the absolute temperature) were most similar to
ꢁ
6 3 6
zone, only the pure Mo S I phase, which corresponded to a thin
and long centimeter-scale hair-like shape, was observed. The SEM
image of Fig. 2b shows that nanorods, micro-cubes which are act as
seed of Mo
purities such as MoS
6
S
3
I
6
nanowires (Mo
6
S
6
I
2
), and other micro-sized im-
the measured results corresponding to the 0.159 eV bandgap
ꢁ
2
(Fig. 2b and 1020 C) were mixed in the
6 3 6
(Fig. 4d) [29]. More specifically, the Mo S I is a material with a very
source zone, whereas a thin and long single phase (Mo
well grown in the transport zone.
6 3 6
S I ) was
small bandgap, and it can be inferred that the transition from the
valence band to the conduction band is active even at room tem-
perature. The reason for the discrepancy between the measured
value and fitting value in the low-temperature region is that the
concentration of the charge is low when the temperature is low;
therefore, there are few collisions between the charges, and the
absolute mobility is large.
Fig. 3a is a photograph of the quartz ampoule that was syn-
thesized by using various precursors. Although it is possible to
synthesize Mo S I by using a pure molybdenum source, such as
6 3 6
Mo powder or Mo foil (see the supplementary figure Fig. S2), the
shape observed in the transport zone is very different. More spe-
cifically, in the case of the MoI precursor, a large amount of
6 3 6
centimeter-scale, hair-like Mo S I was synthesized, whereas when
2
The results of high-strength magnetization (1 T) of the synthe-
6 3 6
sized Mo S I demonstrate an upturn below 50 K that infers the
the Mo powder or Mo foil precursor was used, the yield of trans-
ported Mo was very low. We measured the transport yield of
the Mo synthesized in the transport zone by using the
following formula (Fig. 3b). The transport yield was calculated by
determining the amount of transported Mo with respect to
each initial total mass under the condition that the same mole of
Mo was used regardless of the Mo source. In the case of MoI , the
pure Mo phase occurred at a rate that was 5e15 times higher
than that of other metallic Mo sources. The diameter of the Mo
presence of paramagnetic centers (Fig. 5a) [31]. The central atom of
6
S
3
I
6
4
Mo
6
S
3
I
6
, Mo, is 2þ (4d ), and is surrounded by octahedrally sym-
6 3 6
S I
metric S or I atoms. Considering the arrangement of the four
electrons in the Mo 4d orbital, four unpaired electrons are gener-
6 3 6
S I
ated when the value of 10 Dq (i.e., the gap between e
very small according to the crystal field theory. Therefore, the
synthesized Mo is applicable to the case in which the value of
0 Dq is large, and it can be deduced that a paramagnetic charac-
teristic exists in which there are one pair of paired electrons and
two unpaired electrons. Raman analysis of the synthesized Mo
g
and t2g) is
2
6 3 6
S I
6 3 6
S I
1
6 3 6
S I
synthesized through continuous SEM was also confirmed to be
constant (Fig. 3c), and it is expected that very long 1D nano-chains
can be obtained when dispersion is performed.
6 3 6
S I
was performed to analyze the crystallinity (Fig. 5b). It can be seen
that the measurement results are consistent with the previously
6 3 6
The stability of Mo S I was confirmed by performing ther-
reported results for Mo
6
S
3
I
6
peaks [32]. As shown in Figs. 4 and 5,
as a precursor had
mogravimetric characterization in an N
initial mass reduction below 100 C corresponds to the process by
2
atmosphere (Fig. 4a). The
the Mo that was synthesized by using MoI
6
3
S I
6
2
ꢁ
Fig. 2. (a) Optical image of quartz ampoule after reaction, and XRD patterns of samples in each zone; source zone (left) and transport zone (right). (b) SEM images of source zone
ꢁ
(
left) and transport zone (right) for T ranging from 1020 to 1120 C. (MoI
2
-to-S ratio: 6:3).