Chemistry Letters Vol.33, No.7 (2004)
TEM) images, NiS2 clusters in products 2 and 3 were composed
831
(
a)
b)
0
0
0
0
.7
.6
.5
.4
of the spherical nanoparticles with narrow size distribution (Fig-
ures 1c, d). And the average particle sizes are both about 40 nm.
For measuring the dimensions of NiS2 fractals, FESEM im-
ages were digitized, and the fractal dimension (D) was calculated
1
6
by a box-counting method. The digitized images were covered
with boxes with a size R (R ꢃ 1). The number of nonvacant box-
es (N) could be counted. Images can be viewed as fractal ones if
the plot of log N versus logð1=RÞ yields a straight line, namely
0.3
.2
0.1
.0
2
0
240
300
360
420
480
ꢅD
1
Wavelength/nm
NꢄR . The slope of this line is the fractal dimension.
0
200
300
400
500
600
700
800
8
Wavelengh/nm
II
I
7
6
5
4
3
2
1
0
Figure 3. a) UV–vis absorption spectra of NiS2 crystals(curve 1
for product 1, curve 2 for product 2, 3). b) Photoluminescence
spectra of NiS2 crystals in product 2, 3 (excitation wavelength
was 266 nm).
A literature search shows that investigation on similar optical
properties of NiS2 has not been reported so far.
In this synthesis route, when poly(MMA-co-EA) gel was
immersed in the benzene solution containing CS2 less than 5 h,
only NiS2 nanospheres were obtained. While the time was pro-
longed to more than 12 h until poly(MMA-co-EA) gel became
very soft, no dendritic crystals were formed because the gel net-
works was destroyed. The mechanism is the different length of
the first immersion time altered the polymer networks of the ab-
sorbent correspondingly, and then the polymer networks affect
the aggregation of NiS particles. In conclusion, dendritic NiS
-
4.5
-4.0
-3.5
-3.0
-2.5
log (1/R)
-2.0
-1.5
-1.0
-0.5
0.0
Figure 2. log N vs logð1=RÞ for the clusters(marked I, II) in
Figures 1a, b (line I for cluster I in Figure 1a, line II for cluster
II in Figure 1b).
Figure 2 shows the double logarithmic plot of N versus 1/R
based on the cluster (marked I, II) in Figures 1a, b. The data
points are well fitted by a straight line and the values of D are
.56 (cluster I) and 1.69 (cluster II) respectively. The fractal di-
mension of any cluster is 1:55 ꢆ 0:02 in Figure 1a and 1:69 ꢆ
:01 in Figure 1b. The aggregation patterns of NiS2 nanoparti-
cles in products 2 and 3 share common characteristics with
DLA model such as the ramified structure starting from a unique
seed. And the fractal dimension from Figure 1b is close to the
one in DLA model (ꢇ1:67), while that from Figure 1a is smaller.
It indicates that with the first immersion time gone, NiS2 fractal
patterns are more approximate to the DLA model. The fractal
growth in the present case is believed to arise from the nuclea-
tion and growth of NiS2 nanoparticles within a polymer matrix
saturated with NiS2 atoms produced by the the reaction between
2
2
nanostructures have been prepared using poly(MMA-co-EA) gel
as a host. We think this work could be of interest in that it pro-
vides the first example of transition metal dichalcogenides of
dendritic nanostructures as well as suggests a new way to pre-
pare similar structures of hybrid materials.
1
0
References
1
H. S. Jarrett, W. H. Cloud, R. J. Bounchard, S. R. Butter, C. G.
Frederich, and J. L. Gilison, Phys. Rev. Lett., 21, 217 (1968).
J. M. Honig and Spelik, J. Chem. Mater., 10, 2910 (1998).
A. Ennaoui, S. Fiechter, W. Jaegermann, and H. Tributsch, J. Elec-
trochem. Soc., 133, 97 (1986).
2
3
4
5
S. H. Yu and M. Yoshimura, Adv. Mater., 14, 296 (2002).
X. G. Peng, L. Manna, W. D. Yang, J. Wickham, E. Scher, A.
Kadavanich, and A. P. Alivisatos, Nature, 404, 59 (2000).
L. Manna, E. C. Scher, and A. P. Alivisatos, J. Am. Chem. Soc.,
.
NiCl2 6H2O and CS2 by the radiation reduction process. The
clusters are generated by the random walk movement of the NiS2
atoms on to a growing cluster.
6
1
S. T. Selvan, Chem. Commun., 1998, 351.
22, 12700 (2000).
7
8
To investigate the intrinsic optical properties of the dendritic
NiS2 crystals, optical characterizations were carried out by UV–
vis absorption and photoluminescence spectra. In Figure 3a, A
sharp absorption peak at 283.5 nm (Eg ¼ 4:38 eV) (curve 2) is
found for products 2 and 3 dispersed in benzene, with poly-
MMA-co-EA) gel dispersed in benzene as reference. While
for product 1, no absorption peak is observed (curve 1). Figure
b shows the photoluminescence (PL) spectrum of NiS2 crystals.
In this figure, the excitation wavelength was 266 nm and the fil-
ter wavelength was 310 nm. Two emission peaks at 336 and
355 nm are found for products 2 and 3. The highly structured
shape of the emission suggests that the interaction is not of an
J. P. Xiao, Y. Xie, R. Tang, M. Chen, and X. B. Tian, Adv. Mater.,
1
3, 1887 (2001).
Y. Zhou, S. H. Yu, C. Y. Wang, X. G. Li, Y. R. Zhu, and Z. Y.
Chen, Adv. Mater., 11, 850 (1999).
9
1
1
1
1
1
0 T. A. Witten and L. M. Sander, Phys. Rev. Lett., 47, 351 (1981).
1 P. Meakin, Phys. Rev. Lett., 51, 1119 (1983).
2 T. A. Witten and L. M. Sander, Phys. Rev. Lett., 47, 1400 (1981).
3 T. A. Witten and L. M. Sander, Phys. Rev. B, 27, 5658 (1983).
4 M. Kolb, R. Botet, and R. Jullien, Phys. Rev. Lett., 51, 1123
(1983).
(
3
15 R. Janes, A. D. Stevens, and M. C. R. Symons, J. Chem. Soc.,
Faraday Trans., 85, 3973 (1989).
1
1
1
6 D. A. Russell, J. D. Hanson, and E. Ott, Phys. Rev. Lett., 45, 1175
1980).
7 B. Broklehurst, D. C. Bull, M. Evans, P. M. Scott, and G. Stanney,
J. Am. Chem. Soc., 97, 2977 (1975).
8 R. M. Hochstrasser and M. Kasha, Photochem. Photobiol., 3, 317
(1964).
(
17
excimer, but rather a consequence of intermolecular exciton
interactions.18 While for product 1, there is no emission peak.
On the basis of above results, it can be found that the optical
properties of NiS2 crystals are strongly depended on its structure.
Published on the web (Advance View) June 7, 2004; DOI 10.1246/cl.2004.830