Electrodeposition of Fe thin films on Si(1 1 1) surfaces in the presence of sodium saccharin

Article abstract of DOI:10.1016/j.electacta.2007.08.058

In this work we describe the fabrication of metallic Fe deposits onto Si(1 1 1) substrates using potentiostatic electrodeposition technique. The addition of sodium saccharin in the aqueous ammonium-sulfated solutions tends to inhibit the solid-state reaction between Fe and Si and enhance the protection against oxidation under air exposition compared to deposits without additive. Sodium saccharin shows to be a leveling, brightening, and stress reducing agent capable to alter the ferromagnetic behavior of the films at room temperature. The influence of the additive on the surface morphology, crystalline structure, microchemistry, and magnetism of deposits is discussed.

Full text of DOI:10.1016/j.electacta.2007.08.058

Available online at www.sciencedirect.com
Electrochimica Acta 53 (2007) 2002–2008
Electrodeposition of Fe thin films on Si(1 1 1) surfaces
in the presence of sodium saccharin
a
a
b
b
J. Zarpellon , H.F. Jurca , J.J. Klein , W.H. Schreiner ,
a
a,∗
N. Mattoso , D.H. Mosca
a
Laborat o´ rio de Nanoestrutura para Sensores, Universidade Federal do Paran a´ ,
Centro Polit e´ cnico CP 19091, 81531-990 Curitiba, Paran a´ , Brazil
Laborat o´ rio de Superf ´ı cies e Interfaces, Universidade Federal do Paran a´ ,
b
Centro Polit e´ cnico CP 19091, 81531-990 Curitiba,
Paran a´ , Brazil
Received 6 June 2007; received in revised form 16 August 2007; accepted 28 August 2007
Available online 1 September 2007
Abstract
In this work we describe the fabrication of metallic Fe deposits onto Si(1 1 1) substrates using potentiostatic electrodeposition technique. The
addition of sodium saccharin in the aqueous ammonium-sulfated solutions tends to inhibit the solid-state reaction between Fe and Si and enhance
the protection against oxidation under air exposition compared to deposits without additive. Sodium saccharin shows to be a leveling, brightening,
and stress reducing agent capable to alter the ferromagnetic behavior of the films at room temperature. The influence of the additive on the surface
morphology, crystalline structure, microchemistry, and magnetism of deposits is discussed.
©
2007 Elsevier Ltd. All rights reserved.
Keywords: Electrodeposition of metals on silicon; Saccharin as additive; Iron thin films
1
. Introduction
Direct electroplating of ferromagnetic transition metal thin
films onto silicon, in special Fe, is intrinsically complex due
to the mutual chemical reactivity and local pH flutuations
with hydrogen bubbles generating on the working electrodes.
Recently, different groups demonstrated that plating solutions
alternative to a Watts bath conventional consisting of metal sul-
fate/chloride with pH-controlling agent by boric acid, can be
used to grow iron thin films and nanostructures onto silicon
surfaces. Zarpellon et al. [11] reported that the Fe films elec-
trodeposited on a Si(1 1 1) substrate exhibit submicron grains
with slightly flat surfaces along with the presence of iron sili-
cides. Lee et al. [12] have shown that ␣-Fe(1 1 0) films with
nearly monosized nanostructures of spherical shapes on an
n-type Si(1 1 1) substrate could be grown by pulsed electrode-
position in a non-aqueous solutions and Zhao et al. [13] reported
the synthesis of near-monosized Fe oval-shaped nanorod parti-
cles and spherical nanoparticles by using electrodeposition on
a hydrogen-terminated Si(1 0 0) surface from aqueous FeCl3
solutions. Although these Fe core–shell nanostructures could
be deposited uniformly with well defined shapes, a consider-
able amount of oxide shells was found, which consequently is
detrimental for the magnetic properties of the Fe core itself.
Metallic thin films directly integrated on silicon are of
significant importance due to their applications as Schottky
barriers, ohmic contacts, and diffusion barriers in the inte-
grated circuit industry. Notably, electrodeposition processes
have been used to improve interconnects in large-scale inte-
gration metallization [1], to built Schottky diodes [2,3] as well
as to integrate ferromagnetic materials with semiconductor
microelectronics exploiting the spin injection from the ferro-
magnetic/semiconductor interface [4] for ultrahigh density data
storage and spintronic devices technologies [5,6]. In spite of
this, the processes involved in the early stage of the metal elec-
trodeposition, especiallyonsemiconductorsurfaces, arenotwell
understood. It is generally found that electrodeposition on semi-
conductors starts from surface defects and the growth itself
follows a Volmer–Weber mode [7–10].
∗
Corresponding author. Tel.: +55 41 33613405; fax: +55 41 33613418.
E-mail address: mosca@fisica.ufpr.br (D.H. Mosca).
0
013-4686/$ – see front matter © 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2007.08.058

J. Zarpellon et al. / Electrochimica Acta 53 (2007) 2002–2008
2003
In order to enhance the metallic character and to explore
physical properties of Fe deposits for Si-based spin electronics,
we investigated the influence of sodium saccharin in the same
ammonium sulfate solution of a previous work of our group
toelectron spectroscopy (XPS) measurements were carried out
using a commercial VG ESCA3000 system with a base pressure
−
8
of 3 × 10 Pa, while XPS profiles were obtained by sputtering
+
with Ar ions (2 keV, 3 ␮A). A previous calibration of the sput-
[
11]. Saccharin is an organic additive commonly used as level-
ing, brightening, andstressreducingagentiniron-groupdeposits
14–19]. Indeed, sodium saccharin salt is reported as more solu-
tering rate for pure iron films gives approximately 10 nm/h. The
spectra were collected using unmonochromated Mg (1253.6 eV)
X-ray source and a hemispherical energy analyzer with an over-
[
◦
ble than saccharin and its presence alters the corrosion resistance
properties of CoFe deposits [20].
all resolution of 0.8 eV at emission angle of 45 . The binding
energy scale was calibrated to that of the Si 2p3/2 photopeak of
bulk Si (99.3 eV) to avoid energy position shifts due to charging
effects. Magnetization versus magnetic field curves (hysteresis
loops) were performed at room temperature using an alternat-
ing gradient force magnetometer (AGFM) by applying magnetic
fieldsparalleltothefilmsurfaceatascanningfieldrateof90 Oe/s
and taking points at each 300 ms.
In this work, we investigated the morphology, crystalline
structure, as well as magnetic and electronic properties of elec-
trodeposited Fe films onto hydrogen-terminated n-type Si(1 1 1)
surfaces in the presence of sodium saccharin (SSac) salt in the
ammonium sulfate solutions.
2
. Experimental details
3. Experimental results
All the electrodeposition experiments were performed at
room temperature using a stationary three-electrode cell with
a commercial galvanostat/potentiostat (EG&G model 273A).
The working electrodes were single-sided polished rectangu-
lar (4 mm × 5 mm) phosphorous-doped n-type Si(1 1 1) wafers
with a resistivity of50–80 ꢀ cmatroomtemperature. Hydrogen-
terminated (1 1 1) Si surfaces were prepared after chemical
removal of the native silica layer in 10% HF solution. The
HF-etching is known to lead to hydrogen-terminated Si(1 1 1)
surfaces which are almost atomically flat and rather stable to
oxygen exposure at room temperature [21]. Gallium–aluminum
alloying was used on the rear of the HF-etched Si wafers to form
ohmic contacts with electrical resistance of 12 kꢀ from back-to-
front side. A standard saturated Ag/AgCl electrode was used as
the reference electrode, being all potentials of this work given
with respect to this reference electrode. A platinum disk was
used as the counter electrode. Potentiostatic depositions were
performed at cathodic potential of −1200 mV during 10 min
from solutions of 10 mmol/L Fe(NH4)2(SO4)2, denoted as neat
solution hereafter, and solutions with SSac concentrations of 0.5,
3.1. Electrochemical analyses
Fig. 1(a) shows a set of cyclic voltammograms obtained at
a sweep potential rate of 10 mV/s from the solution contain-
ing 10 mmol/L Fe(NH ) (SO ) (named neat solution) and two
4
2
4 2
0
.8, 1.0, 1.2, and 1.5 g/L (from 2.1 to 6.2 mmol/L). The deposits
with SSac salt are adherent with dimmed metallic shine after
0 min. The uniformity of deposits strongly depends on both the
1
ohmic contact on the rear Si wafers and the illumination of the Si
electrolyte junction. All the electrochemical experiments were
performed in bi-distilled water solutions with pH values fixed
at 2.5 by addition of appropriate amounts of sulfuric acid. The
electrochemical experiments were performed in a dark cham-
ber under illumination of the electrolyte/Si interface through
solution using a dichroic 12 V–50 W halogen lamp, providing
a fairly uniform beam of visible light with emission spectrum
mainly distributed between 400 and 700 nm. Photoelectrons in
Si (energy band gap = 1.1 eV) can be generated at wavelengths
below 1100 nm.
The surface morphology of the deposits was analysed by
ex situ atomic force microscopy (AFM), with a scanning
probe microscope (Shimadzu SPM-9500J8) working in con-
tact mode in air at room temperature. The X-ray diffraction
Fig. 1. (a) Cyclic voltammograms obtained from the solution of 10 mmol/L
Fe(NH4)2(SO4)2 without SSac as well as containing 0.5 g/L SSac and 1.5 g/L
SSac are shown. The voltammograms were arbitrarily shifted in the vertical
scale for the sake of clarity. (b) Detail of the onset of nucleation interval in the
cathodic potential scans.
(
XRD) measurements were performed in the conventional
Bragg–Brentano geometry using Cu K␣ radiation. X-ray pho-

2
004
J. Zarpellon et al. / Electrochimica Acta 53 (2007) 2002–2008
of SSac tends to increase the initial growth rate by change in
kinetic factors It is probably associated with SSac adsorption
in the H-terminated Si/electrolyte interface as well as on freshly
nucleated Fe, promoting variations in the ion discharging ability
along the substrate surface and affecting the hydrogen evolution,
grain size of deposits (in general, the higher current density tend
to have more grain boundaries and defects) and their crystalline
orientation as will be shown below.
3.2. Morphology of deposits
The surface morphology of the deposits was studied by AFM.
SSac addition changes significantly the morphology of the Fe
deposits, as shown in Fig. 3. Even by visual observation, we
can notice that the addition of SSac produced brighter samples
than Fe deposits prepared without SSac. Deposits obtained in
the presence of SSac exhibit a surface morphology consisting
of micrometer grains having smooth surfaces, similarly to Fe
deposits without SSac which are mat with root mean square
(RMS) roughness of ∼70 nm and sub-micrometer average gran-
ule size of ∼0.25 ␮m [11]. The RMS roughness and average
granule sizes obtained from AFM analyses for deposits in the
presence of SSac are summarized in Table 1. Addition of SSac
tends to promote a leveling and brightening of deposits with a
more compact juxtaposition of the grains. An exception of this
general trend is found for sample obtained from solution con-
taining 1.0 g/L SSac. This higher roughness value is perhaps a
fluctuation since the RMS roughness values were averaged over
sampling areas as large as 10 ␮m× 10 ␮m in the set of samples.
Fig. 2. Potentiostatic current transients during Fe depositions at potential of
1200 mV from solutions containing different SSac amounts.
−
other ones with SSac concentrations of 0.5 and 1.5 g/L. For
the neat solution, the potential sweep in the cathodic direc-
tion reveals a progressive reduction with a broad peak centered
around −1650 mV. Superimposed to the reduction wave there
is a hydrogen evolution contribution with visible bubbling at
the surface of the working electrode. When the potential is
scanned in the positive direction, nucleation occurs accompa-
nied by a progressive hydrogen evolution. At the end of the
cyclic voltammogram, i.e., in the potential region of −900 to
3.3. Crystalline structure
XRD analyses were performed to determine the crystalline
0
mV, an anodic current interval is observed. As previously
structure and phase formation in the Fe deposits grown at poten-
tial of −1200 mV. XRD patterns (θ–2θ scans) obtained for all
deposits in the presence of SSac are shown in Fig. 4(a). All
XRD patterns were normalized with respect to the intensity
described, this anodic region can be assigned with oxidation of
Fe to Fe2 and Fe to Fe (or Fe to Fe in some part) [11,13].
The addition of SSac increases the anodic current values when
potential is scanned towards 0 V. The reduction wave as well
as cathodic and anodic current peaks become larger and intense
with addition of SSac. Notably, the voltammograms for potential
scans in the cathodic direction are shifted towards more negative
potentials. Consequently, the onset of nucleation potentials are
also shifted towards more negative potentials with respect to the
voltammogram of the neat solution, as shown in Fig. 1(b).
The nucleation and growth processes were investigated by
the evolution of potentiostatic current transients. Fig. 2 shows
some representative potentiostatic current transients. For solu-
tion with SSac concentration of 0.5 g/L, a cathodic current
density minimum about 14 s after switching on the potential
of −1200 mV is observed. It is followed by a rapid increase of
the cathodic current density and a subsequent stationary regime
reached after 400 s. By increasing the SSac concentration to
+
2+
3+
3+
◦
of the Si(1 1 1) Bragg reflection positioned at 2θ = 28.3 (not
shown), which was used to orient the samples maximizing the
diffracted intensity in the experiments. Fig. 4 shows the diffrac-
tograms vertically shifted in a logarithmic scale for the sake
of clarity. Besides the remanescent forbidden (2 2 2) Si Bragg
Table 1
Structural and surface morphology data of the deposits obtained from the solu-
tions containing different SSac concentrations
SSac concentration
g/L)
RMS roughness
(nm)
Granule
size (␮m)
Strain
ꢁd/d (%)
(
0
0
1
1
1
.5
.8
.0
.2
.5
–
44
110
56
0.6
0.9
1.3
1.0
1.1
+2.20
+2.18
+2.17
+2.17
+2.10
1
.0 g/L, the cathodic current density increases more slowly and
54
a lower stationary current density is observed. For SSac concen-
tration of 1.5 g/L, the cathodic current density exhibits a rapid
increase, reaching a maximum after ∼100 s, and subsequently
it remains stationary after 250 s. We can state that the addition
Root mean square roughness and average grain size were determined with ded-
icate software by probing sampling areas of 10 ␮m × 10 ␮m for deposits in the
presence of different SSac concentrations. Strain values (ꢁd/d) were calculated
from the angular shift of Fe(1 1 0) Bragg reflection peak with respect to bulk Fe.

J. Zarpellon et al. / Electrochimica Acta 53 (2007) 2002–2008
2005
Fig. 4. (a) X-ray diffraction patterns of Fe deposits in the presence of SSac salt.
SSac amounts and identification of Bragg reflections are indicating alongside
diffractograms which are vertically shifted in a logarithmic scale for the sake of
clarity. (b) Area ratio of Bragg reflection peaks (2 0 0) and (2 1 1) with respect
to (1 1 0) indicating the texture in the polycrystalline deposits. The asterisk (*)
indicates a peak from the Cu K␤ radiation.
of (1 1 0) peak with respect to (2 0 0) and (2 1 1) ones. We eval-
uate the strain in the deposits by taking into account the angular
shift of the Fe(1 1 0) Bragg reflection peaks with respect to bulk
Fe value (namely ꢁd/d). The strain values (∼2%) displayed in
Table 1 were calculated from the angular shift (typically is found
◦
◦
ꢁ
(2θ) ∼ 0.9 for angular steps of ∼0.03 in the XRD patterns)
of the centroid of the peaks corresponding to the Fe(1 1 0) reflec-
tion shown in Fig. 4. The addition of SSac tends to reduce the
strain, promoting a stress relaxation in the expanded Fe lattice.
Thus, the influence of SSac is similar to that of saccharin which
is an effective internal stress reducer [14,22–24].
Fig. 3. AFM images of Fe deposits grown on Si(1 1 1) surfaces at −1200 mV
after a time deposition of 10 min from solutions containing: (a) 1.5 g/L SSac;
(
b) 1.0 g/L SSac; (c) 0.5 g/L SSac.
3
.4. X-ray photoemission spectroscopy
◦
◦
reflection at 2θ = 58.9 and a small peak at 2θ = 83.1 from the
Si(3 3 3), only (1 1 0), (2 0 0), and (2 1 1) Bragg reflections of
body-centered cubic (bcc) iron (␣-Fe) are observed when SSac
concentration >0.8 g/L is present in the solutions. XRD pattern
for deposit corresponding to addition of 0.5 g/L SSac is still
XPS analyses indicate that all deposits exhibit an elemen-
tal composition consisting of Fe, Si, and O with a superficial
residual layer with N and C adsorbates. XPS analyses for all
deposits obtained at potential of −1200 mV do not show the
presence of neither sulfur nor sodium i.e., SSac incorporation in
the deposits is not observed. The S incorporation was detected
only for deposits obtained from the solutions containing 1.5 g/L
SSac under a potential of −1500 mV. Besides, the incorpora-
tion of S in these deposits occured without trace of Na, strongly
indicatingthe dissociation of the SSac andtheir complexation, as
already reported by several groups [25–28]. We address here the
◦
observed a weak and broad reflection peak at 2θ = 38.3 asso-
ciated with Fe silicide. These results differ from our previous
work, showing that SSac is essential to inhibit the formation of
Fe silicides underlayers and oxy-hydroxides [11]. The increase
in SSac amount improves the preferential (1 1 0)-texture of Fe
deposits, as shown in Fig. 4(b). As can be seen, the increase of
SSac in the solutions has an exponential influence on the area

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J. Zarpellon et al. / Electrochimica Acta 53 (2007) 2002–2008
Fig. 6. Hysteresis cycles measured at room temperature for deposits obtained
from solutions containing different SSac concentrations. The magnetic field was
applied in the film plane which behaves as an isotropic magnetic plane and the
magnetization is normalized to the saturation magnetization.
to pure iron films which are covered by Fe oxides. Since the
presence of Fe oxides are superficial compared to total thick-
ness of samples, the significant lowering of coercive field values
with addition of SSac in the solutions is probably due to dif-
ferent crystalline structures and the size and separation of the
grains. Both coercive field and remanence ratio values are given
in Table 2. All deposits exhibit easy magnetic plane in the film
plane with equivalent remanence ratio with respect to saturation
magnetization. Deposits obtained from solutions without SSac
exhibited a small hysteretic loop at low fields superimposed to
a predominant linear paramagnetic response at room tempera-
ture, indicating the detrimental influence of silicides as well as
oxy-hydroxide formations for ferromagnetism [11].
Fig. 5. Fe 2p core-level spectra for Fe deposits obtained from the solutions
containing (a) 0.5 g/L and (b) 1.5 g/L SSac. XPS spectra of as-deposited samples
and after cummulative exposure to argon ion bombardment for several etching
times are shown. Spectral components associated with superficial oxide and
metallic Fe are indicated.
deposits obtained at the potential of −1200 mV in which sulfur
incorporation is not observed. The small silicon photoemission
signal is observed for all the deposits obtained in the presence
of SSac. It is indicating that a three-dimensional islands effec-
tively occurs onto Si substrate which confirm the Volmer–Weber
growth mode. Fig. 5(a) and (b) shows the Fe 2p core-level spec-
tra for Fe deposits grown in the presence of 0.5 and 1.5 g/L SSac,
respectively. XPS spectra collected from as-deposited samples
and after argon ion bombardment for several etching times are
shown. The sputter-etching progressively reveals a metallic Fe
component underneath a superficial oxygen-rich layer, consist-
ing of Fe oxide.
4
. Discussion
The mechanism of saccharin action during iron and iron
alloys deposition has been discussed many times in the lit-
erature [14–19]. The saccharin is pointed out as one of the
most effective internal stress reducer, caused by inclusion of
sulfur in the deposit by the intermediary sulfonamide group,
and often helps to decrease or eliminate hazes of the deposits
[14–24]. The sulfur incorporation may be realized by elec-
trostatic interaction with a negative charged electrode or by
chemisorption. Shifts of nucleation potentials towards more neg-
ative potentials are expected due to the decrease of the deposition
rate through a surface blocking and solution chelating process
3
.5. Magnetic behavior
[14].
Fig. 6 shows a set of normalized hysteresis loops measured
Table 2
at room temperature with magnetic fields applied in the film
plane for deposits obtained from the solutions containing dif-
ferent SSac concentrations. The magnetization is normalized
with respect to saturation magnetization Ms at maximum applied
field. A clear ferromagnetic behavior with moderate remanence
ratio (36–41% Ms) is observed for deposits with different SSac
concentrations. The addition of sodium saccharin is also accom-
paniedbyasignificantreductioninthecoercivefieldwithrespect
Coercive field and remanence ratio (relative to saturation magnetization Ms)
values obtained from hysteresis loops for deposits obtained from the solutions
containing different SSac concentrations
SSac concentration (g/L)
Coercive field (Oe)
Remanence (% Ms)
0
1
1
.5
.0
.5
429
397
336
41
36
39

J. Zarpellon et al. / Electrochimica Acta 53 (2007) 2002–2008
2007
The molecular structure of the SSac is similar to saccharin
with sodium atoms replacing the hydrogen bound to nitrogen.
The influence of SSac in the electrodeposition of Fe deposits on
Sicanbeexpectedtoleadtothesamebehavior. Ourexperimental
observations confirm results published in the literature, concern-
ing the influence of saccharin on Fe-group deposits. Notably,
the addition of SSac results in a fairly broad Fe reduction wave,
superimposed to hydrogen evolution and nucleation potentials
shifts towards more negative potentials with respect to the cycle
of the solution without SSac. It is difficult, however, to ascertain
what is the cause for the observed shifts in the reduction waves,
since different electron transfer paths for the reduction of elec-
troactive species at the Si/electrolyte interface could occur due
to SSac affinity with the ions present in the solution and change
the diffusion of cations towards the cathode because of this com-
plexation [29]. It is also reliable that changes in the hydrogen
evolution occurs due to SSac addition. It has been shown that
the general chemical formula of the metal–saccharin complex
has the iron ion bound to the nitrogen atom in the sulfonamide
group. SSac adsorption in the H-terminated Si/electrolyte inter-
face could promote variations in the ion discharging ability along
the substrate surface altering the Schottky barrier height (SBH)
formation in the n-type Si/eletrolyte interface. A SBH value of
about 0.7 eV is reported for CoFe/Si interface [30], however
this value cannot explain the necessary cathodic potential for
the nucleation wave observed in our experiments. Since Fe sili-
cides formation [11] is tremendously inhibited by addition of
SSac and current densities exhibit drastic changes for deposition
times (smaller than 100 s) corresponding to a coverage fraction
of Si substrate smaller than 30–40% of total area, we cannot
discard that important changes are introduced in the nucleation
and growth processes by the addition of SSac and its adsorption
on the hydrogen-terminated Si surface. Therefore, SSac adsorp-
tion on hydrogen-terminated Si surface and freshly nucleated Fe
together with complexation mechanism in solution are closely
related to the small cathodic shifts observed at the onset the
cathodic current in the cyclovoltammograms presented in Fig. 1.
Many changes in growth kinetics and deposit structure are
introduced by the addition of SSac in the solution indicating the
influence of SSac adsorption on freshly nucleated Fe. The poten-
tiostatic transients taken at a potential of −1200 mV exhibit an
evolution in a time scale of several hundred seconds, as shown
in Fig. 2. We describe the time evolution of potentiostatic tran-
sients as follows. Atthe beginning, a sporadic andheterogeneous
nucleation occurs due to a random occupation of the prefer-
ential active sites on the initial surface. Next, the number of
nuclei growing on the Si surface is rapidly saturated and, sub-
sequently, a further reduction of Fe ionic species on the already
deposited nuclei predominates; i.e., nucleation and growth are
in favor of the deposition on the covered zones. The average
granule sizes scattered in micrometer scale in the AFM images
and Si photoemission signal observed by XPS corroborate these
assumptions and is also indicating that Volmer–Weber three-
dimensional growth mode [14–19] occurs. The addition of SSac
increases the Fe ion discharging ability, facilitating a diffusion-
limited aggregation of ions in juxtaposed three-dimensional
islands with a slightly flat growth front. The inhibition of silicide
and oxy-hydroxide formation occurs with an enlargement of the
granule sizes. As mentioned in Section 3.4, the investigation
of deposition in presence of 1.5 g/L SSac under a potential of
−1500 mV reveals the SSac dissociation with sulfur incorpora-
tion in deposits with evidence of local disruption of the film due
to a severe hydrogen evolution. The potentiostatic transients, in
this case, exhibit current densities reaching stationary values as
2
large as 80 A/cm with high noise level as a consequence of
the hydrogen gas bubble evolution. Compact and smooth (RMS
roughness is 21 nm) deposits are formed with small granule
sizes (0.8 ␮m). However, the formation of Fe silicides and oxy-
hydroxides is observed by XRD. It is indicating that moderate
cathodic potential to inhibit SSac dissociation and incorporation
in the deposits are necessary to avoid silicide and oxy-hydroxide
formation.
Fe growth on a clean Si surface in non-equilibrium condi-
tions (like electrochemical conditions) easily leads to unusual
silicides formation as a result of stress accommodation at the
interface, variations in the stoichiometry of initial deposit and
islanding kinetic factors. In our previous work [11], XRD and
XPS data present evidence that metastables Fe2Si and Fe Si3 are
5
formed and their Bragg reflection peaks increase upon anneal-
ing together with a clear increase in the Fe crystalline quality
attested by intensity increase of the ␣-Fe(0 1 1). In the present
case, the XRD patterns shown in Fig. 4(a) reveal that ␣-Fe is
formed. Although significant, only small relaxation (2.2–2.1%)
of the expanded Fe lattice is observed in the presence of SSac
(from 0.5 to 1.1 g/L SSac). It was found a crystalline texture
with predominance of the densest atomic plane (1 1 0) of ␣-Fe
in the film plane predominates when increasing SSac, as shown
in Fig. 4(b). However, the addition of SSac while keeping the pH
and temperature of the electrolyte stable have a small influence
in the residual strain. It is probably connected with the higher
growth rates imposed by SSac (as shown in Fig. 2). A faster
nucleation is more effective to inhibit the interface reaction than
induce a strain relaxation in the deposits.
A predominant metallic Fe nature of deposits even exposed to
the air is confirmed by XPS. Comparing the XPS spectra evolu-
tion of Fig. 5(a) and (b) for equivalent etching times, we observe
that a metallic Fe component becomes predominant for deposits
obtained from solutions with a higher SSac concentration. Since
the surface morphology and ion decapping can be considered the
same, we may conclude that SSac tends to inhibit the oxidation
of the samples exposed to the air. This assumption is also cor-
roborated by XRD analyses since a higher (1 1 0)-texture in the
deposits with 1.5 g/L SSac tends to reduce their oxidation front.
The structural changes imposed by SSac present in the solu-
tions are apparently significant to affect the room temperature
hysteresis cycle of the ferromagnetic deposits. The small strain
relaxation and densest juxtaposition of grains are probably asso-
ciated with reduction of the coercive fields when increasing
SSac. Besides, bulk Fe has an easy and hard magnetic axis along
the ꢀ1 0 0ꢁ and ꢀ1 1 1ꢁ crystalline directions, respectively. Then,
the crystalline texture with (1 1 0) planes preferentially oriented
parallel to the strain-relaxed film plane is reasonable to result
in almost isotropic easy magnetic plane with a small remanence
ratio as observed. Thus, concerning the change of the texture of

2
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J. Zarpellon et al. / Electrochimica Acta 53 (2007) 2002–2008
deposits and their influence in the magnetization behavior, we
can state that our results indicate that saturation magnetization is
reached at fields smaller than 5 kOe with all deposits exhibiting
ferromagnetism at room temperaure with easy magnetic plane
in the film plane.
Our present results opens, therefore, the possibility to
explore Si-based spin electronic devices, such as proposed spin
MOSFET in which a MOS gate capacitor is combined with
ferromagnetic source and drain [30].
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5
. Conclusions
In summary, the electrochemical conditions for the direct
electrodeposition of iron thin films onto hydrogen-terminated
Si(1 1 1) surfaces were determined by appropriated dilution of
sodium saccharin salt in the aqueous ammonium-sulfated iron
solutions. Good quality metallic Fe deposits having a body-
centered cubic structure were obtained. The film morphology,
surface chemistry, structure, magnetic, and electronic properties
were analysed by various techniques revealing that spontaneous
reaction between Fe deposits and Si surface, observed at room
temperature with formation of oxides and polycrystalline sili-
cides, havebeeninhibitedbyusingsodiumsaccharin. Webelieve
that electrochemical synthesis of iron films with this additive is
a practical mainstream process for the integration of the ferro-
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