NANOSTRUCTURED SURFACES AND TRANSPORT PROPERTIES
OF Ni-Zn ALLOY ELECTRODEPOSITS
J. Matador 1, L. Deriquerel 1 and P. Iniesta 2
Department of Chemical Engineering, University of….
Departmemt of Materials Science and Engineering, University of ,…….
1
2
Alloying zinc by iron group elements (Ni or
Co) has been the subject of intensive research
mainly devoted to corrosion and catalytic activities.
In both areas, it is well established that the surface
feature may play a determining role in the behavior
of material thin films [1,2]. Nowadays, nanoscaled
surface irregularities are increasingly concerned, the
device systems made of thin films being ruled by
the modern trend of miniaturization. In that frame,
very little is cleared up on the dependence of thin
films properties on their surface feature. Most of the
reported results for that purpose seem almost quite
empirical, which implies a lack of systematic works
on that subject. This first requires a monitoring of
the surface irregularities evidently associated with
the material growth process. We here investigate on
the relationship between the transport properties of
Ni-Zn alloy electrodeposits on copper substrates
and their related topology parameters. A theoretical
approach of this dependence is proposed, which is
illustrated by an experimental study of the
considered material.
The study is undertaken with 2 µm thick
electrodeposits prepared from in a three-electrode
cell system made of: a stationary cooper working
electrode of 0.5 cm2 area mechanically polished on
successive rotating disks; a platinum sheet counter
electrode of the same area facing the first one 2.5
cm away and a saturated calomel electrode (SCE),
taken as reference for the potential measurements.
The electrolyte is a mixed bath of pH=3.5 made of a
0.9M NiSO4.6H2O solution added to a 0.1M
ZnSO4.7H2O one, both prepared from FLUKA
products. The film deposition process proceeds
from the chronoamperometry method using a
Radiometer PGP 2001 galvanostat. The chemical
composition of the electrodeposit is analyzed by Xray energy dispersive spectometry with an EDAX
9100 set-up. The topology aspect is examined with
a Digital Instruments Nanoscope II atomic force
microscope (AFM) used in a constant force contact
mode with a cantilever made of a Si3N4 tip of
approximately 50 nm apex radius, its spring
coefficient being equal to 0.06 Nm-1. The study is
performed in ambient atmosphere, the collected
images being digitized into 400x400 pixels with a
scanning frequency of about 1 Hz.
The morphological evolution of a material
surface goes together with its formation, including
the roughening dynamics on the substrate. This
implies the mobility of the ad-atoms formed during
the electrochemical process. Their evolvement can
be assessed from the size increase of the coalescing
particle radius r obeying the law [3]
 
2  a 4 Ds
 r4

t
T
(1),
where a is the lattice parameter; Ds, the surface
diffusion coefficient; γ and εT, respectively the
interface and thermal energies. The grain size is
hereby determined by integrating equation (1) from
zero to time t. That leads to the radius expression
r4 
2  a 4 Ds t
(2),
T
knowing that r is directly connected to the deposit
interface roughness, . We showed elsewhere [4]
that σ is related to Ds through the expression

Mq
 2  a Ds
3 
 T
4




1/ 4
(3)
z F t
1/ 4
with M, the molar weight of the species involved; F,
the faraday number; ρ, the material density; z, the
molar charge of these species and q, the charge
density. For the specimens of the same thickness
value, obtained by varying their growth rate v, the
dynamics of the sample’s topography corresponds
to
1
 sat
  2  a4D
s
 3 
   T




1/ 4
 z F  1 / 4

 t
(4),

M
q


with σsat, the saturation surface roughness of the
electrodeposits.
This topology parameter is determined by the
family-Vicsek approach [5] from the sample’s AFM
images, following the scaling behavior of the local
interface roughness  (nm) against the scan length,
L (nm). One sees in Fig. 1 that sat ≈ 44 nm is here
reached for the growth rate value v = 0.36 µm/s.
We showed that the dependence of σsat on v
value is non monotonous within our v investigation
region. Fig.3 evidences three growth regimes of the
ad-atoms formed on the copper substrate. The film
thickness being constant, the variation of v implies
the one of the deposition time, t, since both
parameters are each other inversely proportional.
1.8
80
Saturation roughness,  sat (nm)
Surface roughness, log[  (nm)]
1.6
1.4
1.2
 0.83 ± 0.02
1
0.8
L
60
40
Lc
20
0.6
1.5
2
2.5
3
3.5
4
Scan length, log[L (nm)]
4.5
5
5.5
Fig.1 - Evolution of the local interface roughness versus
scan length
A variety of surface features is obtained in respect
to the growth rate, v(µm/s). This suggests a possible
monitoring of the electrodeposit topography, which
is of great interest for specific application fields.
nm
a)
0
0,1
Growth
1
nm
nm
b)
nm
Fig. 2 – AFM images of Ni-Zn deposits obtained at:
v = 0.12 µm/s (a) and v = 0.05 µm/s (b)
The surface of Fig. 2(a) exhibits a wide active area
[6] relevant for catalytic investigations while the
one of Fig. 2(b) depicts a lower active area suitable
for corrosion resistance studies
0,4
0,5
The drawing of experimental σsat versus t curves for
each of the regimes allows the determination of the
related material diffusion coefficient (Ds) and length
() as reported below.
Regime
nm
0,3
Fig.3 - Dependence of the saturation roughness versus
the electrodeposit growth rate.
regimes
nm
0,2
Growth velocity, v (µm/s)
v

(cm /s)
(µm)
v < 0.17
1.76x10-10
0.85
2.10x10-10
0.45
2.40x10-8
3.47
0.17 <v <
2
0.35
3
2
(µm/s)
Regime
Regime
Ds
v > 0.35
References [1] N. R. Short, A. Abibsi, J. K. Dennis, Trans. Inst.
Metal Finish, Vol. 67, Pages 73- (1989)
[2] K. Lohrberg, P. Kohl, Electrochim. Acta, Vol.
29, Pages 2557- (1984)
[3] C. Alonso, R. C. Salvarreza, J. M. Vara, A. J.
Arvia, L. Vàzquez, A. Bartolome, A. M. Baro, J.
Electrochem. Soc., Vol. 137, Pages 2161- (1990)
[4] M. Hiane, J. Ebothé, Eur. Phys. J. B, Vol. 22,
Pages 485-495 (2001).
[5] F. Family, T. Vicsek, J. Phys. A, Vol. 18, Pages
L75- (1985)
[6] J. Ebothé, M. Hiane, Appl. Surf. Sci, Vol 183,
Pages 93-102