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which features are of similar chemical composition. This allows
determining whether the surface features may be the result of a
specific chemical component, or if the surface is homogeneous.
The phase signal changes when the probe encounters regions of
different composition.
It is obvious that the roughness (Rms) of the zinc is smaller,
(Rms¼15.4 nm), than that of the cobalt film, (Rms¼20.1 nm) and of
the zinc–cobalt alloy, Rms¼23.5 nm under the same conditions.
Also, in the case of Zn–Co alloy, crystalline grains formed at film
surface are larger in size. Phase images obtained for the samples
of Zn, Co (represented in Fig. 5b,d) demonstrate a relatively
homogeneous disposition of phases on the surface of the layer.
The image from Fig. 5f suggests the deposition of different phases
starting from different nucleation sites, because the contrast in
the phase image is primarily a result of material inhomogeneity.
This separation of phases was predicted since the examination of
Zn–Co alloy phase diagram. We conclude that the granular Co–Zn
films may consist of Co micro- or nanoparticles embedded in a
heterogeneous zinc, zinc oxide and hydroxide matrices, and have
varied particle sizes, and crystalline orientations. The heteroge-
neity of films could be a favorable condition to increase the film
magnetoresistance.
From the preliminary SEM experiments, the film composition
depended on electrodeposition potential. For example, the films
deposited at 3.5 V contain 92 at% Zn, 8 at% Co and those deposited
at 4.5 V contain 84 at% Zn, 16 at% Co.
The chemical composition of electrodeposited Zn–Co alloys
and the chemical state of constituent elements were investigated
using the X-ray photoelectron spectroscopy (XPS). A typical XPS
spectrum of electrodeposited Zn–Co alloys is shown in Fig. 6(a). It
reveals the presence of zinc (Zn 2p3/2 and Zn 2p1/2 peaks), cobalt
(Co 2p3/2 and Co 2p1/2 peaks) and oxygen incorporated in the
Zn–Co matrix (O 1s peak).
In the high-resolution spectra of Zn 2p (Fig. 6(b)) both the Zn
2p1/2 and the Zn 2p3/2 covers can be deconvoluted into two
distinctive components corresponding to zinc oxide (1021.9 eV
for Zn 2p3/2 and 1044.6 eV for Zn 2p1/2) and hydroxide, (1023.2 eV
for Zn 2p3/2 and 1046.2 eV for Zn 2p1/2), respectively.
Fig. 4. X-ray diffraction patterns of the samples S5 (a) and S7 (b), from Zn–Co
alloys granular films deposited at 3.50 and 4.50 V, respectively. (c) shows the
comparison between the patterns of the two samples for 35–381.
˚
˚
As it is seen in Fig. 6(c), the peak O 1s is asymmetric, which
reveals the presence of a multi-component peak of oxygen and it
can be decomposed into three component peaks. The right
centered at 530.7 eV (O1) can be associated with the zinc oxide
groups, the medium centered at 531.7 eV (O2) is related to the
presence of hydroxyl type groups, and the left centered at
532.9 eV (O3) could be assigned to the presence of loosely bound
oxygen on the surface of Zn–Co films, as it was established in
Ref. [16].
a¼2.75 A and c¼4.92 A for Zn–Co film (S5, S7), which show a
much distorted structure. XRD showed, together with the lines of
the substrate, the lines of an undistorted hexagonal zinc
Z-phase,
as it was found in Ref. [15] and Cohcp phase, which confirmed our
hypothesis concerning formation of Zn and Co granular films. The
cell parameter modification affected mainly the c crystallographic
axis, which was clearly lower than that of pure zinc.
The particle sizes of the films were calculated using the
Scherer equation (5) [7,12]:
The Co 2p3/2 and Co 2p1/2 peaks are localized at the binding
energies of 778.1 and 792.2 eV, respectively (Fig. 6(d)), each of
them being determined by three Co-containing components
obtained after deconvolution. Metallic Co is localized at
778.1 eV for Co 2p3/2 and 792.5 eV for Co 2p1/2; the energy
difference between peaks is around 15.05 eV, and it proved that
Co exists as a metal cluster in our electrodeposited Zn–Co
alloys [17]. The Co(OH)2 groups were localized at 782.1 and
797.8 eV and the two satellites also appeared at about 786.9
and 803.4 eV.
The magnetic measurements were carried out at room tem-
perature with a torsion magnetometer in 300 kA/m maximum
field. Fig. 7 shows as an example the torsion magnetometer
curves of the samples S6 and S7 for Zn–Co alloys granular
films. Fig. 7(a) and (b) shows the static torque curves performed
for clockwise and anticlockwise rotation of the magnetic field, for
the samples (S6 see Fig. 7(a)) and S7 (Fig. 7(b)). The shape of the
curves obtained by the torsion magnetometer was a very sensi-
tive function of the sample magnetic microstructure. The film
0:9
l
yÞ
D ¼
ð5Þ
are the X-ray wavelength (1.5406 A), diffraction
ð
b
cos
˚
where
l,
y
and
b
angle and full width at half the maximum (FWHM) of the Zn, Co
and Zn–Co alloy peaks, respectively. The average grain size of the
crystallites from the zinc deposit was 25 nm, for the cobalt
deposit was 16 nm and it was 27 nm for the zinc–cobalt alloy
granular thin films.
Atomic force microscopy (AFM) has also been used to inves-
tigate the surface morphology of Zn, Co and Zn–Co alloy films.
Some AFM phase images of the Zn, Co and Zn–Co electrodeposited
samples (S2, S3 and S7) are shown in Fig. 5 (topography-left
(a,c,e) and phase images-right (b,d,f)).
It is known that a phase image, collected simultaneously with
a topographical image, shows maps the local changes in the
material’s physical or mechanical properties of the material. In
the left image, we see the many interesting surface features of the
film. When combined with the phase image (right), we can tell