Structural and magnetic features of heterogeneously nucleated Fe-oxide nanoparticles

Article abstract of DOI:10.1016/j.jmmm.2008.01.028

Iron oxide nanoparticles of diameter 14 nm were synthesized by applying Pt seed-assisted heterogeneous thermal decomposition of Fe(CO)₅ in a two-stage procedure. The intense heating treatment resulted in a remarkable mean volume increment compared to previous studies. This method is able to control the nanoparticle mean diameter, keeping the demand for thermal energy at low levels. High-resolution electron microscopy images and the corresponding electron diffraction patterns revealed the appearance of a FePt₃ core in each nanoparticle, surrounded by highly crystallized inverse spinel Fe₃O₄ formed after atmospheric oxidation, as shown by a combination of X-ray diffraction and chemical analysis. Magnetic measurements indicated that the presence of Pt-rich core does not cause any visible modification to the values of saturation magnetization and anisotropy constant of nanoparticles, compared to homogeneously nucleated iron oxide particles of the same size.

Full text of DOI:10.1016/j.jmmm.2008.01.028

ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 320 (2008) 1631–1638
www.elsevier.com/locate/jmmm
Structural and magnetic features of heterogeneously
nucleated Fe-oxide nanoparticles
K. Simeonidisa, S. Mourdikoudisa, I. Tsiaoussisa, M. Angelakerisa,
Ã
C. Dendrinou-Samarab, O. Kalogiroua,
aDepartment of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
bDepartment of Chemistry, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
Received 6 December 2007; received in revised form 10 January 2008
Available online 24 January 2008
Abstract
Iron oxide nanoparticles of diameter 14 nm were synthesized by applying Pt seed-assisted heterogeneous thermal decomposition of
Fe(CO)5 in a two-stage procedure. The intense heating treatment resulted in a remarkable mean volume increment compared to previous
studies. This method is able to control the nanoparticle mean diameter, keeping the demand for thermal energy at low levels.
High-resolution electron microscopy images and the corresponding electron diffraction patterns revealed the appearance of a FePt3 core
in each nanoparticle, surrounded by highly crystallized inverse spinel Fe3O4 formed after atmospheric oxidation, as shown by a
combination of X-ray diffraction and chemical analysis. Magnetic measurements indicated that the presence of Pt-rich core does not
cause any visible modification to the values of saturation magnetization and anisotropy constant of nanoparticles, compared to
homogeneously nucleated iron oxide particles of the same size.
r 2008 Elsevier B.V. All rights reserved.
PACS: 75.50.Tt; 61.46.Df; 75.75.+a; 75.50.Bb
Keywords: Iron oxide; Nanoparticle; Heterogeneous nucleation; Core–shell; FePt
1. Introduction
first case or improve energy product in the second, binary
nanocomposite systems are a promising approach [8,9].
Despite significant progress in the development of
synthetic routes, further research is needed to optimize or
revise the preparation methods and characterization
techniques of the nanoparticles. Among the bottom-up
methods, thermal decomposition of metal precursors in an
organic solvent is used by many scientists who work on
nanoparticle systems [10]. The relative technical simplicity,
low cost and efficient control of the size, shape, mono-
dispersity and desired crystalline structure of the synthe-
sized nanoparticles are the major advantages of the
aforementioned method.
Uniform iron oxide particles are usually prepared via
homogeneous nucleation reactions. The decomposition or
reduction of iron precursors in the presence of surfactants
often yields nanoparticles with narrow size distribution and
good crystallinity. In order to achieve high monodispersity,
separation of the nucleation stage and the growth of the
Controllable synthesis and assembly of magnetic nano-
particles has recently received special attention. Their novel
or enhanced physical properties, compared to the bulk
state, arise mainly due to finite size and surface effects,
which dominate the magnetic behavior of individual
nanoparticles. In particular, iron oxide nanoparticles,
usually maghemite and magnetite, have gained much
interest because of their applicability in biomedical fields
such as magnetic resonance imaging (MRI), magnetic fluid
hyperthermia, targeted drug delivery, magnetic cell separa-
tion and magnetorelaxometry [1–5]. Moreover, they can be
used as basic components in technological applications like
magnetic recording and permanent magnets [6,7]. In order
to override the difficulties following miniaturization in the
Ã
Corresponding author. Tel.: +30 2310 998148; fax: +30 2310 998003.
E-mail address: orestis.kalogirou@physics.auth.gr (O. Kalogirou).
0304-8853/$ - see front matter r 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2008.01.028

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nuclei is an essential condition. However, the use of high
surfactant concentration favors the formation of inter-
mediate complexes between metal ions and surfactant
molecules, which increases the nucleation temperature [11].
A better control of the average size of metal particles can
be obtained by seeding the reactive medium with other
element particles acting like catalytic centers for the
building of iron nanocrystals. The reduction of total
surface energy results in lesser thermal energy require-
ments for iron nucleation compared to the homogeneous
mechanism. Furthermore, much lower surfactant concen-
tration is needed and therefore, the temperature at
which decomposition of precursor initiates, decreases
dramatically. Thus, during a heterogeneous pathway,
nucleation and growth procedures are completely sepa-
rated, while it is possible to work at somewhat lower
temperatures [12].
In this work we describe the preparation of 14 nm sized
iron oxide nanoparticles obtained by heterogeneous
nucleation synthesis. Platinum seeds are used as the
nucleating agent. Structural and magnetic characterization
revealed a two-phase arrangement (core–shell) of the
nanoparticles under study, with interesting technological
features if properly tailored.
Maintaining the temperature at the reflux point for a
short period of time, in both stages, leads to a remarkable
growth of the diameter over the reported 7 nm [13].
However, the formation of large nanoparticles by the
method described resulted in a negligible variation of the
diameter standard deviation.
The structural properties of iron oxide nanoparticles
were analyzed by powder X-ray diffraction (XRD) with a
Philips PW 1820 diffractometer under CuKa radiation
˚
(1.5406 A). Information concerning the size distribution
and the arrangement of nanoparticles was obtained
by high-resolution transmission electron microscopy
(HRTEM). The specimens for HRTEM analysis were
prepared by room temperature deposition of n-hexane
dispersions of nanoparticles on carbon-coated copper
grids. HRTEM images were acquired using a JEOL 2011
at an accelerating voltage of 200 kV. Additional structural
analysis was carried out from the corresponding selected
area electron diffraction (SAED) patterns. The existence of
surfactant coating on the magnetic nanoparticle surface
was investigated using a Fourier transform infrared
(FT-IR) spectrometer (Perkin-Elmer FT-IR 1650). Trans-
mission IR spectra with baseline corrections were taken for
the analysis. Nanoparticle powder was dried and pelletized
with KBr powder for the FT-IR study. Quantitative
determination of the surfactant percentage and any phase
transformations during heating were studied by thermo-
gravimetric analysis (TGA) in a SETARAM SetSys-1200
instrument from room temperature to 1000 1C at a heating
rate of 10 1C min–1 under a nitrogen atmosphere.
Magnetic hysteresis loops were carried out in the
temperature range of 5–300 K using a MPMS-5 Quantum
Design SQUID magnetometer. The zero-field cooled
(ZFC) curve was obtained by cooling the system in zero
magnetic field to 5 K and then applying a constant field of
100 Oe while increasing the temperature to 300 K. For the
field-cooled (FC) curve the sample was cooled under the
same magnetic field and magnetization was measured in
the direction of increasing temperature. Magnetization
values were normalized to iron oxide content determined
by a chemical analysis method [14].
2. Experimental
Iron oxide nanoparticles were synthesized by a variation
of the heterogeneous nucleation method of Farrell et al.
[13]. The reaction conditions were optimized to produce
larger nanoparticles. Thus, longer heating times were used.
The procedure followed in our case consists of two stages:
growth of iron on platinum seeds and size increment by
adding excess of iron precursor.
For the preparation of 14 nm sized iron oxide nanopar-
ticles, platinum nuclei were initially formed after reduction
of 0.01 mmol Pt(acac)2 (Aldrich, 99.99%) by 0.58 mmol
1,2-hexadecanediol (Aldrich, 90%) in the presence of
1 mmol oleic acid (Aldrich, 90%) and 1 mmol oleylamine
(Fluka, 470%) into 15 ml dioctyl ether (Fluka, 497%)
solution under an Ar atmosphere. Then the mixture was
heated at a 6 1C minꢀ1 rate to 100 1C and 1.5 mmol
Fe(CO)5 (Aldrich, 99.999%) was added. The yellow
solution was further heated at the same rate until reflux
at 290 1C where it remained for 10 min before cooling.
During this process, the color of the solution gradually
became black at about 180 1C, indicating the formation of
iron nanoparticles.
The solution was diluted by 15 ml dioctyl ether and
9 mmol Fe(CO)5 were added at 100 1C during reheating.
The mixture was heated to reflux point observed at 285 1C
and kept at this temperature for 20 min. After cooling to
room temperature, ethanol was added to yield a black
precipitate, which was then separated by centrifugation.
The final product of this process was diluted in n-hexane
with additional surfactant quantities and kept under a dry
air environment.
3. Results and discussion
3.1. XRD analysis
The XRD pattern of the obtained nanoparticles at the
first and second stage, given in Fig. 1, reveals the existence
of a spinel-structured iron oxide. This indicates complete
oxidation of iron after exposing nanoparticles to atmo-
sphere, though the exact product of this process is very
difficult to be identified due to the similar crystal structures
of Fe3O4 and g-Fe2O3. The absence of platinum or
iron–platinum alloy peaks is attributed to the low molar
ratio of platinum precursor in the reaction (Fe:PtE1000:1).
The weak diffraction signal of coated Pt alloy has been
observed even in FePt/Fe3O4 core–shell nanoparticles,

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Fig. 2. Low-magnification HRTEM images of heterogeneously nucleated
nanoparticles in the final (a) and the intermediate product (b). Overgrown
core in an individual nanoparticle (c).
Fig. 1. X-ray powder diffraction patterns of heterogeneously nucleated
iron oxide nanoparticles after first stage (a) and second stage (b) of
growth. Symbols represent magnetite (.) and maghemite (,) peaks.
Although the slight increment of the mean diameter in
the final product is equal to the doubling of the size in
terms of volume, it is far from the expected value according
to the quantity of iron precursor added in the second stage.
The low yield of the second-stage reaction is explained by
the partial consumption of iron precursor in a parallel
homogeneous growth of iron oxide nanoparticles. TEM
images indicate that such nanoparticles exist even before
the second stage and lead to a variation of the size
distribution to lower diameters (Fig. 3b).
The undesirable growth of iron nanoparticles by a
homogeneous supersaturation route possibly takes place
during reflux when both growth and nucleation mechan-
isms occur. However, in this case, where the aim is the
synthesis of relatively large nanoparticles, higher tempera-
tures and certain reflux times are unavoidable, thus the
effect is more significant in monodispersity. The presence
of such particles indicates that the homogeneous nucleation
synthesis under similar conditions would result in smaller
nanoparticles because of the low surfactant-to-iron pre-
cursor ratio and the higher energy that is required for the
initiation of growth. The production of spinel iron oxide
nanoparticles larger than 13 nm without Pt seeds requires a
surfactant-to-precursor ratio of at least 4:1 in the first stage
and similar thermal aging conditions as well as a higher
excess of iron precursor than for a heterogeneous
procedure in the second stage [17].
Further investigation of single nanoparticles via SAED
patterns (Fig. 4) revealed that the shell of large-size
nanoparticles as well as the fraction of small nanoparticles
consists of very well crystallized iron oxide. Although
natural oxidation is difficult to be controlled for the
formation of g-Fe2O3 versus Fe3O4 there are some
indications that the main part is magnetite. The titration
analysis of Fe2+ and Fe3+ determined the percentage of
magnetite as at least 80%. Low maghemite’s content is also
suggested by the absence of its characteristic (1 1 0)
reflection, unlike cases where it is the dominant phase.
although the platinum percentage is many times higher
than in our case [15]. Applying Scherrer’s formula for the
(3 1 1) iron oxide peak, the size of nanocrystals before and
after the addition of Fe(CO)5 excess was calculated as
8.471.1 and 12.971.5 nm, respectively.
3.2. HRTEM
Low-magnification HRTEM images of the sample
(Figs. 2(a) and (b)) are consistent with the XRD analysis
results concerning nanoparticle size. In the case of
nanoparticles formed during the first stage (Fig. 2(b)), the
average size was 9.1 nm with an 11% standard deviation,
while after the further-growth process (Fig. 2(a)) it was
13.6 nm with a 17% deviation. The iron oxide nanocrystal
size exported by Scherrer’s formula appears slightly
different from the value obtained by TEM analysis due
to the existence of a Pt core, as explained below.
In a typical region of the final product, two types of
nanoparticles are observed: large 14 nm nanoparticles
consisting of a dark core of about 3 nm diameter
surrounded by a light-colored thick shell and smaller
8 nm single-phase nanoparticles. This type of core–shell
nanoparticles is the result of heterogeneous growth of iron
on platinum seeds. Platinum participates in the reduction
of surface energy for iron nucleation initiation but is not
recovered at the end of the reaction. The core appears
darker due to the higher electron density of Pt and it is not
necessarily centered. The same situation is described for
Au/Fe3O4 ‘‘dumbbell-like’’ nanoparticles [16] and derives
from induced charge compensation during Fe growth in a
non-polar solvent like dioctyl ether. The core reaches 8 nm
in certain individual nanoparticles, but seems rather
centered (Fig. 2(c)). The relative percentage of single-phase
nanoparticles, grown following the homogeneous decom-
position of Fe(CO)5, is approximately 10% and affects the
magnetic features of the sample slightly.

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Fig. 3. Size distribution graphs of heterogeneously nucleated nanoparticles after first stage (a) and second stage (b) of growth.
magnetic properties. The atomic diffusion of iron in
platinum core requires thermal energy, which is available
at relatively high temperatures. Despite the core being
covered by a thick oxide shell, lattice fringes belonging to
the FePt3 structure are visible in some nanoparticles, as the
HRTEM image of Fig. 5(a) indicates. The measured d
spacing of 0.193 nm corresponds to (2 0 0) lattice planes of
the cubic FePt3 phase, whereas the (3 1 1) planes of Fe3O4
(d311 ¼ 0.253 nm) are mainly observed in the shell or in
homogeneously nucleated particles (Fig. 5(b)).
Fig. 6 suggests a possible mechanism of heterogeneous
synthesis of large iron oxide nanoparticles. Platinum nuclei
are formed at lower temperatures by the reduction of
Pt(acac)2 (Fig. 6(a)). During the first stage of synthesis,
amorphous iron coats Pt seeds (Fig. 6(b)) and atomic
diffusion of Fe takes place when the temperature reaches
the boiling point of dioctyl ether (Fig. 6(c)). After adding
an excess of iron precursor and raising the temperature,
enlargement of nanoparticles and Fe enrichment of the
core continues until the end of the process (Fig. 6(d)).
Finally, natural oxidation of iron and crystallization in
inverse spinel structure occur immediately after exposure to
ambient conditions (Fig. 6(e)). This pathway resembles the
formation mechanism of FePt/Fe3O4 core–shell nanopar-
ticles proposed by Chen et al. [19].
Fig. 4. Electron diffraction pattern of heterogeneously nucleated iron
oxide nanoparticles.
We have shown that under similar conditions iron is
spontaneously converted to magnetite rather than maghe-
mite [14]. In agreement with this, Sun et al. [18] reported
that magnetite is usually the product of iron oxidation
when it takes place at room temperature. However, in spite
of the experimental indications, we consider these nano-
particles generally as spinel iron oxides. In any case, such a
consideration does not affect our discussion.
On the other hand, the core of large nanoparticles does
not consist of pure platinum but a platinum-rich Fe–Pt
alloy that remains embedded in the center. Platinum (1 1 1)
and (2 0 0) crystal planes appear shifted and coincide with
the corresponding values of disordered FePt3 phase. This
fact proves that Pt seeds initially act like catalytic centers
for the nucleation of iron but finally they participate in the
formation of a magnetic phase that may affect the observed
3.3. FT-IR spectrometry
FT-IR analysis of the powder from the final product
provides additional information for iron oxide identifica-
tion and the organic coating of nanoparticles as well. The
wide peak that the sample presents at 590 cmꢀ1 is similar to
the standard spectrum of Fe3O4 (Aldrich, 498%) as the
corresponding g-Fe2O3 (Alfa, 99+%) consists of multiple
peaks in the range 580–650 cmꢀ1 (Fig. 7(b)). The broad-
ening of the peak corresponding to Fe3O4 is attributed to
the existence of surfactants and traces of the organic
solvent. The Fe–O stretching of magnetite is also evidenced
by the pair of lower wavelength bands at 395 and 450 cmꢀ1
unlike maghemite, which presents only one [20]. This may
,

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Fig. 6. Schematic demonstration of the heterogeneous synthesis of Fe3O4
nanoparticles. Formation of Pt seeds (a), nucleation and growth of Fe
during first stage (b), diffusion of Fe in the core at high temperatures (c),
Fe shell enlargement during second stage (d) and oxidation of Fe shell
after exposure to atmosphere (e).
Fig. 7. FT-IR spectra of oleic acid/oleylamine capped heterogeneously
nucleated and oleic acid capped homogeneously grown Fe3O4 nanopar-
ticles (a). Magnified area of the spectrum at low wavelengths in
comparison to magnetite and maghemite (b).
Fig. 5. HRTEM images of heterogeneously (a) and homogeneously (b)
nucleated Fe3O4 nanoparticles.
CQO asymmetric vibration. It is attributed to the
physically adsorbed oleic acid remaining on the nanopar-
ticle surface after washing and redispersion process. The
band at 1530 cm–1 appears due to the C–O bond, indicating
that oleic acid molecules are covalently bonded to the
nanoparticle surface. The presence of oleylamine is
evidenced by the peak lying at 1580 cm–1 as a result of
intact adsorption of NH2 onto the particle [22].
be due to the fact that magnetite consists of both Fe2+ and
Fe3+, whereas maghemite contains only Fe3+
.
Fig. 7(a) shows the FT-IR spectrum of the synthesized
Pt-nucleated Fe3O4 nanoparticles in the 1000–3500 cmꢀ1
region. For comparison, the spectrum of 13 nm Fe3O4
nanoparticles, prepared by the homogeneous route, with
only oleic acid added, is also given. The strong CH2 peaks
at 2925 (nas C–H), 2855 (ns C–H) and 1435 (ds C–H) cm–1 as
well as the one at 1620 cm–1 (n CQC) are indicative
of both molecules of oleic acid and oleylamine [21] that
cover the iron oxide nanoparticles. The peak observed at
1705 cm–1 is characteristic of free oleic acid representing the
3.4. TGA measurement
Fig. 8 shows the TGA for the nanoparticles obtained
after the second stage. The initial loss observed up to

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Fig. 8. Temperature dependence of weight loss of heterogeneously
nucleated Fe3O4 nanoparticles.
Fig. 9. Zero-field cooling (ZFC) and field-cooling (FC) curves of
heterogeneously nucleated Fe3O4 nanoparticles under 100 Oe.
100 1C corresponds to humidity or to residual solvent
molecules adsorbed in the powder. From 150 to
400 1C, decomposition of the capping agents takes
place. Weight loss measured 13%, indicating the percen-
tage of organic surfactants in the sample. This is equal to
the value for the full coverage of the surface of 14 nm
spherical nanoparticles by a monolayer of oleic acid and
oleylamine.
Even though complete removal of free oleic acid is
expected at 260 1C [23], significant quantities of surfactants
remain till 500 1C owing to their strong linkage on the
particle surface. The variation in loss rate is due to the
difference in the strength of the surfactant-to-metal bond
between oleic acid and oleylamine as well as to possible
changes in their chain structure introduced at temperatures
over 300 1C.
3.5. Magnetic characterization
Fig. 10. Hysteresis loops of heterogeneously nucleated Fe3O4 nanoparti-
cles at 10 and 300 K.
The temperature dependence of the magnetization under
ZFC and FC conditions for the second-stage product is
shown in Fig. 9 in the range 5–300 K. The behavior of the
two curves is typical for superparamagnetic iron oxide
nanoparticles in spite of the presence of the Pt-rich core
[17]. The initial magnetization in the ZFC branch at low
temperatures reaches zero, reflecting the demagnetized
state of the nanoparticles due to absence of an external
field. Increasing the temperature, in combination with an
applied field of 100 Oe, results in a constant increase of
total magnetization, as more nanoparticles can overcome
their energy barrier and orientate their moments toward
the external field. ZFC curve presents a rounded maximum
at the temperature Tmax ¼ 97 K, after which thermal
activation energy is sufficient to induce transition from
ferrimagnetism to superparamagnetism. In fact, this broad
peak indicates the distribution in blocking temperatures
over a wide range of different particle sizes or anisotropies
[24]. In addition, the fraction of small homogeneously
nucleated nanoparticles and the FePt3 core may contribute
to the shift of the peak.
For an assembly of nanoparticles with log-normal size
distribution, the mean blocking temperature can be found
by Tb ¼ Tmax/c, where cE1.5 [25]. Considering that the
homogeneously grown particle fraction is small enough
and the Pt-rich core represents only 1% in mass of the
heterogeneously nucleated particles, Tb should be close to
the calculated value of 65 K. Compared to magnetite
nanoparticles of similar size that have been studied, such a
low temperature may be attributed to the reduction of
particle interactions and surface anisotropy [23]. Surfactant
coating prevents any kind of aggregation and nanoparticles
can freely align to the external field. The effective
anisotropy constant is found by applying the equation

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Keff ¼ 25kBTb/V [26], where kB is Boltzmann’s constant
4. Conclusion
and V the mean particle volume excluding the Pt-rich
core. The Keff value (1.6 ꢁ 105 erg cmꢀ3) is slightly higher
than the corresponding value of bulk magnetite
(1.3 ꢁ 105 erg cmꢀ3), possibly due to shape anisotropy
arising from the polygonal shape of nanoparticles.
The preparation of Fe3O4 nanoparticles as large as
14 nm, applying a two-stage heterogeneous growth on Pt
seeds, was achieved by increasing the duration of heating at
high temperatures. The low percentage of Pt in the sample
does not affect the macroscopically observed properties,
whereas it participates in the growth mechanism. During
the first stage Pt seeds operate as nucleation centers for iron
growth. The result of diffusion that takes place at the
boiling point is the formation of a Pt-rich Fe–Pt alloy core
inside each nanoparticle.
Although this process leads to a less monodispersed
product, the enlargement of nanoparticles is accompanied
by a fine isolation originating from the surfactant mono-
layer, which completely surrounds each one of them. The
good agreement in the calculation of the mean nanoparticle
diameter by TEM, XRD and magnetic measurements
proves their high crystallinity and the absence of magnetic
interactions between them.
After reaching the maximum magnetization value, ZFC
curve follows a decreasing path till room temperature,
indicating a Curie’s law behavior [10]. This steady
reduction implies physical isolation between the nanopar-
ticles due to the oleic acid coating on their surface
and consequently their fine dispersion [27]. In the case of
field cooling, the curve gets its maximum value at 5 K and
then linearly decreases with rising temperature, coinciding
with ZFC curve over 140 K. After this point, all
nanoparticles display superparamagnetic relaxation. The
divergence of ZFC and FC curves below separation
temperature is attributed to the existence of a magnetic
anisotropy energy barrier that prevents magnetization
reversal [28].
The magnetic hysteresis loops of the same sample were
recorded for the temperatures of 10 and 300 K (Fig. 10). In
principle, the characteristics of each loop verify the
discussion on ZFC–FC measurements. The sample shows
its ferrimagnetism at 10 K, which is fairly below the
blocking temperature, having a coercivity value of 217 Oe
and about 15 emu/g of remanence. On the other hand,
nanoparticles are typically superparamagnetic at room
temperature, as the zero coercivity and the absence of
saturation indicate. The saturation magnetization at 300 K
reaches 59 emu/g, which is very close to iron oxide samples
of similar size [14], but only 65% of bulk magnetite
(90 emu/g). The reason for this declination is the appear-
ance of spin canting effects due to crystal size decreasing
and the existence of the surfactant at nanoparticle surface
[29]. However, the improved crystallinity of nanoparticles
restrains this tendency and maintains saturation magneti-
zation at high values. The value at 10 K is higher (67 emu/
g) as the effect of thermal fluctuations is reduced under the
superparamagnetic limit.
Acknowledgment
This work was supported by the Greek Secretariat of
Research and Technology—Contract no. 03ED667.
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ꢀ
ꢁ
rffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1=3
18 kBT
pMs
wi
3msH0
DM
¼
,
(1)
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