Electrodeposition of bismuth from nitric acid electrolyte

Article abstract of DOI:10.1016/j.electacta.2007.04.002

The electrodeposition of Bi from acidic nitrate solution was examined. Bismuth deposition was determined to be quasi-reversible on Au, with a current efficiency of 100%, based on integration of deposition and stripping voltammetric waves. No interference from nitrate reduction was found on Bi and Au, whereas nitrate reduction occurred on W and Cu electrodes. Analysis of current-time transients clearly shows nucleation on Au to be instantaneous. Field emission SEM revealed nodular deposits with moderate surface roughness. Nodule size varied from 1 to 5 μm depending on deposition potential and deposit thickness. X-ray diffraction (XRD) patterns for all deposits were indexed to rhombohedral bismuth. The deposits showed fairly strong (0 1 2) crystallographic texture at high deposition overpotentials.

Full text of DOI:10.1016/j.electacta.2007.04.002

Electrochimica Acta 52 (2007) 6221–6228
Electrodeposition of bismuth from nitric acid electrolyte
E. Sandnes, M.E. Williams, U. Bertocci1, M.D. Vaudin, G.R. Stafford∗
Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
Received 22 September 2006; received in revised form 23 February 2007; accepted 1 April 2007
Available online 5 April 2007
Abstract
The electrodeposition of Bi from acidic nitrate solution was examined. Bismuth deposition was determined to be quasi-reversible on Au, with a
current efficiency of 100%, based on integration of deposition and stripping voltammetric waves. No interference from nitrate reduction was found
on Bi and Au, whereas nitrate reduction occurred on W and Cu electrodes. Analysis of current-time transients clearly shows nucleation on Au to be
instantaneous. Field emission SEM revealed nodular deposits with moderate surface roughness. Nodule size varied from 1 to 5 ␮m depending on
deposition potential and deposit thickness. X-ray diffraction (XRD) patterns for all deposits were indexed to rhombohedral bismuth. The deposits
showed fairly strong (0 1 2) crystallographic texture at high deposition overpotentials.
© 2007 Elsevier Ltd. All rights reserved.
Keywords: Electrodeposition; Bismuth; Nucleation; Texture; Thin film
1. Introduction
glassycarbon[22]andsemiconductors[9–11]. Thereisapaucity
of bismuth electrodeposition literature involving the growth of
continuous films onto metallic substrates [23,24]. In this paper,
we examine the electrodeposition of bismuth films, up to 15 ␮m
thick, from nitric acid electrolyte. The electrochemical reduc-
tion of Bi3+ on Au was explored using cyclic voltammetry
(CV), chronoamperometry, and an electrochemical quartz crys-
tal nanobalance (EQNB). The surface morphology and crystal
structure of bismuth, electrodeposited onto both gold and copper
substrates, were characterized by X-ray diffraction (XRD) and
with a field emission scanning electron microscope (FE-SEM)
equipped with a focused ion beam (FIB).
In recent years, bismuth deposition has become an interesting
subject for the electrochemical community because of bismuth’s
uniqueelectrical, physicalandchemicalproperties. Bismuththin
films have shown large magnetoresistance [1–3], thermoelectric
efficiency [4] and interesting quantum effects [5]. Bismuth is
also used in electrochromic devices, [6,7] and for contact forma-
tion on semiconductors [8]. Highly textured Bi films have been
electrodeposited onto semiconductor substrates [9–11]. Uses of
thin bismuth film electrodes in electrochemical stripping analy-
sis offer a very attractive alternative to mercury electrodes due
to the much more environmentally friendly bismuth [12–14].
Sub-monolayers of bismuth on some noble metal surfaces have
shown enhanced catalytic activity for a variety of electrochemi-
cal processes, most notably the two-electron reduction of H2O2
to H2O, often the limiting step in the reduction of O2 in aqueous
fuel cells [15,16], as well as the oxidation of formic acid on Pt
[17–21].
2. Experimental
The electrodeposition of bismuth was examined in
1.0 mol L−1 HNO3 containingcontrolledadditionsofBi(NO3)3.
The solutions were made from 99.999% Bi(NO3)3·H2O
(Sigma–Aldrich, Inc., USA2) and nitric acid, 69.4% (J.T. Baker,
USA). In order to dissolve the Bi(NO3)3·H2O, an acidic solu-
tion was required. Distilled water was further purified (to
18.3 Mꢀ cm) using an EASY pure UV ultrapure water system
(Barnstead). All electrolytes were purged with nitrogen prior to
Much of the bismuth deposition literature has focused either
on its underpotential deposition (upd) onto noble metals or its
nucleation and growth onto non-metallic substrates, such as
∗
Corresponding author. Tel.: +1 301 975 6412; fax: +1 301 926 7679.
E-mail address: gery.stafford@nist.gov (G.R. Stafford).
ISE member.
2
Certain trade names are mentioned for experimental information only, in no
case does it imply a recommendation or endorsement by NIST.
1
0013-4686/$ – see front matter © 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2007.04.002

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E. Sandnes et al. / Electrochimica Acta 52 (2007) 6221–6228
and during experiments. The electrochemical experiments were
carried out using a potentiostat/galvanostat (model 173) together
with a universal programmer (model 175) both from Princeton
Applied Research, EG&G Company. Data were digitized from
the analog output by means of a MacAdios II data acquisition
board in a MacIntosh IIcx personal computer.
cell had a magnetic stirrer, and N2 could be bubbled into the main
compartment to deaerate the solution, or could flow above the
solution, maintaining a small positive pressure inside the cell.
The measurements were carried out in galvanostatic mode.
3. Results and discussion
The electrochemical measurements were performed at room
temperature, in a single-compartment cell covered with a
polyethylene film to prevent air entering the compartment. A
platinum counter electrode was positioned in the same compart-
ment as the working electrode. A saturated Hg sulfate electrode
(SSE) was used as a reference electrode. All potentials are given
with respect to this reference. A Vycor-tipped bridge filled with
0.1 mol L−1 H2SO4 separated the SSE from the working com-
partment.
A variety of electrode materials was used in the voltammetric
examination. These included a polycrystalline gold rod measur-
ing 4.5 mm in diameter and 1.6 cm in length, a 250 nm thick
Au film which had been vapor-deposited onto a borosilicate
glass substrate, a copper wire measuring 0.8 mm in diameter
and 2.0 cm in length, a cross-section of a 1.0 mm diameter gold
wire sealed in epoxy, and a cross-section of a 0.8 mm diameter
tungsten wire sealed in glass. The gold wire and the tungsten
wire cross-sections were wet-polished with #2400 and #4000
SiC-paper. All electrodes were rinsed thoroughly with acetone,
ethanol and distilled water prior to use. The Au electrodes
were further cleaned by continuously sweeping the potential
for 30 min prior to the voltammetric measurements.
Gold and copper electrodes were used for preparation of
the Bi deposits for microscopic and X-ray examination. The
gold electrode consisted of a 250 nm thick gold film which had
been vapor-deposited onto a borosilicate glass substrate which
had first been coated with a Ti bonding layer. The film had
a strong (1 1 1) crystallographic orientation. The copper sub-
strates were polycrystalline sheets, wet-polished in the same
manner as the cross-sectioned electrodes. All deposits were
made in 1.0 mol L−1 HNO3 containing 0.10 mol L−1 Bi(NO3)3.
Deposition was terminated when the charge reached the value
corresponding to the desired thickness. The deposits were imme-
diately removed from the cell, rinsed in distilled water and
blown dry with air. The electrodeposits were examined by X-
ray diffraction, using a Siemens D-500 diffractometer and Cu
K␣ radiation, and by field emission SEM using a Hitachi S4700
operating at 5 kV and 30 ␮A. Bismuth cross-sections were pre-
pared using a dual beam FIB (FEI Company) model DB620
operating at 30 kV and milling currents down to 350 pA.
Mass changes during Bi deposition were monitored by
means of an electrochemical quartz nanobalance (EQNB). The
instrument was a RQCM (Maxtek, Inc.). The quartz crystals
used were polished 2.54 cm AT cut blanks (Maxtek, Inc.),
onto which first Ti and then Au was evaporated. Their reso-
nance frequency was 5 MHz. The EQNB as well as the EG&G
273 potentiostat/galvanostat were run by LabviewTM software
on a Macintosh Power PC computer. The cell, in which the
Au-covered quartz crystal was the working electrode, had a
separated compartment for the Pt counter electrode and a SSE
reference electrode connected via a Luggin-Haber capillary. The
Initial experiments on tungsten in 1.0 mol L−1 HNO3
revealed a large nitrate reduction peak at a potential positive
to hydrogen evolution. The reduction started at a potential of
−0.70 V versus SSE. Several reactions are suggested for nitrate
reduction in the literature [25]. The only reaction occurring in
the same potential range as that observed experimentally is the
reaction:
NO3− + H2O + 2e− = NO2− + 2OH−
(1)
which is reported to have a standard potential of 0.010 V versus
the standard hydrogen electrode (SHE) which corresponds to
−0.630 V versus the SSE [25]. In electrolytes containing Bi3+,
any occurrence of nitrate reduction in the potential range where
Bi3+ reduction or hydrogen evolution occur would complicate
the interpretation of the voltammograms due to the unknown
current contribution from Reaction (1). As a consequence, infor-
mation about the ability of bismuth, gold and copper to reduce
nitrate or evolve hydrogen then becomes significant. Fig. 1
presents voltammograms for Bi, Au, Cu and W electrodes in
1.0 mol L−1 HNO3. Tungsten and Cu both show a catalytic
activity for nitrate reduction. In the case of W, reduction starts
at −0.70 V, and a current peak is observed at a potential of
−0.83 V. At about −1.0 V hydrogen evolution begins on the
tungsten surface. Nitrate reduction on Cu occurs positive of the
H2 reversible potential and about 0.1 V anodic of that observed
for W. In the case of Bi, hydrogen evolution was the only reaction
observed, starting at a potential of about −0.90 V. The Au elec-
trode showed a reduction current starting at −0.65 V, which is
about10 mVnegativeofthereversiblehydrogenpotential. Addi-
tional voltammograms for a Pt electrode (not shown in Fig. 1)
showed a reduction current starting at the same potential. Con-
Fig. 1. Voltammograms for (a) Bi, (b) W, (c) Au, and (d) Cu electrodes in
1.0 mol L−1 HNO3. Sweep rate is 100 mV s−1
.

E. Sandnes et al. / Electrochimica Acta 52 (2007) 6221–6228
6223
Fig. 3. Cyclic voltammograms on Au wire electrode in 1.0 mol L−1 HNO3 con-
taining 0.020 mol L−1 Bi(NO3)3 at sweep rates of (a) 0.5 V s−1, (b) 2.0 V s−1
(c) 5.0 V s−1, and (d) 10.0 V s−1
Fig. 2. Cyclic voltammogram (1.0 V s−1) of evaporated (1 1 1)-textured Au in
1.0 mol L−1 HNO3 containing 0.020 mol L−1 Bi(NO3)3. Bulk deposition of Bi
starts at −0.500 V vs. SSE.
,
.
relation between the peak current versus the square root of the
sweep rate, [32]:
sidering the high catalytic activity for hydrogen reduction on Au
and Pt, the observed reduction current on Au is probably due to
hydrogen evolution. These observations support reports in the
literature where Au voltammetry in a solution of 0.5 mol L−1
H2SO4 + 0.1 mol L−1 NaNO3 showed that the electroreduction
of nitrate is very slow and marginally detectable [26]. The activ-
ity for nitrate electroreduction was reported to decrease in the
order:Cu > Ag > Au. WeconcludethatAuelectrodesaresuitable
for examining the reduction of Bi3+ in acidic nitrate solutions.
Fig. 2 shows the Bi3+ voltammetry on (1 1 1)-textured evap-
orated Au in 1.0 mol L−1 HNO3 containing 20 mmol L−1 Bi3+
in the Bi upd region. Bismuth upd occurs in three steps that
commence at about −0.10 V, about 0.3 V negative of the Au
oxide region. The location of these voltammetric peaks is very
similar to that reported by others in HNO3 [27,28]. Bismuth
forms two surface structures on Au (1 1 1) in the upd region. At
low coverage, Bi forms a (2 × 2) structure, commensurate with
the underlying Au surface [16,23,29–31]. At higher coverage,
ip = 367n3/2AC0D1/2υ1/2
(2)
where the variables and units are: ip (current at peak [A]),
n (equivalents mol−1), A (electrode area [cm2]), C0 (bulk
electroactive concentration [mol L−1]), D (diffusion coefficient
[cm2 s−1]), and υ (sweep rate [V s−1]). Fig. 4 shows a plot of
the peak current density versus the square root of the sweep rate
for the voltammograms presented in Fig. 3. For 0.020 mol L−1
Bi(NO3)3 in 1.0 mol L−1 HNO3 a linear relation is observed for
sweep rates in the range of 0.010–10.0 V s−1. An extrapolated
linear regression of the data crosses the current axis near the
origin, indicating a diffusion controlled process. Based on
the slope of the linear regression, a Bi3+ diffusion coefficient
was found to be 1.72 × 10−6 cm2 s−1. This is reasonably
close to the 2.75 × 10−6 cm2 s−1 value we calculated from
similar voltammetric data reported by Vereecken and Searson
[11] using n+-GaAs electrodes in nitrate-based electrolyte.
In an electrolyte containing 0.10 mol L−1 Bi(NO3)3 we have
the (2 × 2) structure is replaced by a uniaxially commensurate
√
(p × 3)-2Bi adlayer [16,23,29–31]. Bismuth upd is an impor-
tant step in the bulk deposition of Bi onto Au since nucleation
√
and growth proceeds on the (p × 3)-2Bi adlayer.
Fig. 3 shows the voltammetry for Bi deposition onto a
cross-sectioned Au wire electrode in 1.0 mol L−1 HNO3 con-
taining 0.020 mol L−1 Bi(NO3)3 as a function of sweep rate.
The voltammetry is consistent with that typically observed in
metal deposition–stripping processes, although the overpoten-
tial associated with Bi nuclei formation on Au is not particularly
significant. This is likely due to the presence of the Bi upd layer.
No co-evolution of hydrogen occurs since the Bi reduction wave
is completed prior to the potential where H2 evolution begins
on either Au or Bi. Thus, the peak current for bismuth reduc-
tion has no contribution from other electrochemical reactions. In
addition, we observe a negative shift in the cathodic peak poten-
tial with sweep rate. Such a shift is typically associated with
quasi-reversible electrochemical reactions. For a reversible pro-
cess with an insoluble product, a theoretical treatment of the
diffusion equations and boundary conditions yields a linear cor-
Fig. 4. Plot of the peak current vs. the square root of the sweep rate for the
voltammograms presented in Fig. 3. The slope of the linear regression line is
s .
50.0 mA V1/2 −1/2 cm−2

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E. Sandnes et al. / Electrochimica Acta 52 (2007) 6221–6228
Fig. 5. Cyclic voltammograms on polycrystalline Au cylinder in 1.0 mol L−1
HNO3 containing 0.10 mol L−1 Bi(NO3)3. The cathodic vertex was varied to
(a) −0.55 V, (b) −0.65 V, (c) −0.85 V, (d) −0.95 V, and (e) −1.0 V at constant
Fig. 6. Current transients for Bi deposition onto a Au wire electrode in
1.0 mol L−1 HNO3 containing 0.020 mol L−1 Bi(NO3)3 for different deposition
potentials. The starting potential was −0.40 V. Inset plot shows i vs. t−1/2
.
sweep rate of 50 mV s−1
.
observed a plot similar to that in Fig. 4 except for a slight
deviation from linearity at higher sweep rates due to IR drop as
a result of the higher deposition currents.
sion zones overlap to form a linear diffusion gradient [33]. At
deposition potentials more negative than −0.51 V, the Cottrell
currents are identical, indicating that deposition is diffusion-
limited. Plots of i versus t−1/2 yield straight lines of equal slope
that intersect the origin. This is shown in the inset plot of Fig. 6.
Transients containing two current maxima in the nucle-
ation region, like those shown in Fig. 6, are often observed
in Stranski-Krastanov growth where one or more monolay-
ers grow two-dimensionally prior to three-dimensional island
growth [34–36]. Palomar-Pardave et al. have developed a quan-
titative treatment by simulating the various contributions to
the nucleation and growth process [36,37], specifically double
layer charging, two-dimensional instantaneous nucleation, and
three-dimensional diffusion controlled growth. Details can be
found in reference [36]. We have applied this treatment to the
−0.52 V current transient in Fig. 6 and have estimated that the
charge associated with the two-dimensional growth process is
approximately 85 ␮C cm−2. As stated previously, the Au elec-
trode is covered with a partial upd layer at the starting potential
of −0.40 V. Upon applying the −0.52 V deposition potential,
the remainder of the complete Bi monolayer is formed. This
is the equivalent of the 3rd voltammetric wave in Fig. 2. The
charge under this peak is consistent with the 85 ␮C cm−2 charge
obtained from the theoretical two-dimensional current transient.
We therefore conclude that the small current peaks in the depo-
sition current transients are associated with the completion of
the Bi upd layer.
The current efficiency for the Fig. 3 voltammetry was
calculated by integrating the current associated with the depo-
sition and dissolution reactions. In 0.020 mol L−1 Bi3+ the
current efficiency was independent of sweep rate in the
range of 0.050–10.0 V s−1. The average current efficiency was
101% 1%. Changing the lower vertex down to −0.90 V at a
constant sweep rate of 0.050 V s−1, did not affect the current
efficiency, which was 101% 2%. The voltammograms for the
latter set of experiments are shown in Fig. 5. Decreasing the
cathodic vertex beyond −0.90 V resulted in a rapid loss of cur-
rentefficiencyaslooselyattacheddendritesformedanddetached
from the electrode. The increase of the cathodic current in this
same potential window reflects the morphological instability as
the dendrites escape the diffusion layer and benefit from spher-
ical diffusion. The formation of dendrites at the most negative
potentials also altered the shape of the anodic dissolution peaks.
Nucleation transients from potential step measurements are
shown in Fig. 6. Prior to initiating the potential step, the elec-
trode was pre-conditioned at a potential of −0.40 V. Since this
potential is in the Bi upd region (see Fig. 2) a sub-monolayer of
Bi is present on the Au surface prior to deposition. After apply-
ing the potential step, the initial current increase arises from the
charging of the double layer. Within the first 25 ms, a very small
current peak is observed which we attribute to the completion of
the Bi upd monolayer. This is followed by a larger potential-
dependent current maximum which is typically attributed to
nucleation and growth. In this latter region, the current max-
imum (imax) increases while the time (tmax) required to reach
imax decreases with increasing overpotential as a consequence
of the higher nucleation densities. At deposition potentials more
negative than −0.53 V, the maximum in the nucleation current
becomes less defined due to relatively higher currents from dou-
ble layer charging. The final feature in the current transients is
a Cottrell-type (t−1/2) relaxation as individual spherical diffu-
A non-dimensional plot of the current transient obtained at
−0.52 V is shown in Fig. 7 together with the theoretical curves
for instantaneous and progressive nucleation following the treat-
ment of Scharifker and Hills [33]. The plot clearly suggests that
Bi deposition onto Au proceeds by instantaneous nucleation.
Using the equations derived in reference [33], imax and tmax
yieldedanucleationdensityof3.96 × 106 cm−2 fordepositionat
−0.52 V. The Bi upd contribution to the current transient is read-
ily apparent in the non-dimensional plot. We have also examined
the non-dimensional plot of the theoretical three-dimensional

E. Sandnes et al. / Electrochimica Acta 52 (2007) 6221–6228
6225
Fig. 9. Current density and resonant circuit resistance, R1, during the same time
period as Fig. 8.
Fig. 7. Normalized −0.52 V current transient from Fig. 6 (- - - - -) compared to
theoretical treatments (—) for three-dimensional instantaneous and progressive
nucleation.
current (from the Palomar-Pardave treatment) and see that it
superimposes the theoretical curve for instantaneous nucleation.
The EQNB used in this study measures both the resonant
frequency and the resistance R1 of the equivalent resonant
circuit, where shifts in the resonant frequency correspond to
mass changes. The mass/charge ratio (m/Q) for the deposi-
tion or dissolution of Bi/Bi3+ assuming 100% current efficiency
is 720 ␮g C−1. Fig. 8 shows the values of the m/Q ratio dur-
ing deposition and dissolution at various current densities up
to 10 mA cm−2 in 1.0 mol L−1 HNO3 containing 0.1 mol L−1
Bi(NO3)3. The experimental values tend to be somewhat lower,
about 80% of the theoretical. The lower efficiency is due to inho-
mogeneous deposition of Bi, which tends to accumulate at the
rim of the electrode where the mass sensitivity of the EQNB
is at a minimum [38,39]. The reduced sensitivity of the EQNB
was confirmed by weighing the quartz crystal on an analyti-
cal balance before and after depositing about 3 mg of Bi. In
spite of its lower precision, gravimetry gave an efficiency of
0.96 0.04. This is a clear indication that the experimental m/Q
ratio is depressed due to non-uniform current distribution.
While shifts in the resonant frequency correspond to mass
changes, the value of R1 is an indication of the mechanical losses
caused by entrainment of the solution in contact with the vibrat-
ing metal surface, and is therefore a sensitive indication of the
roughness of the deposit [40]. Fig. 9 shows the changes in R1 as
measured during the same experiment and thus the same time
frame as the data presented in Fig. 8. The initial values of R1 of
the originally smooth gold surface were close to 400 ꢀ, while
rough Bi deposits gave values up to 1 kꢀ. The roughening occurs
very rapidly if the current density exceeds about 10 mA cm−2
.
At current densities less than 10 mA cm−2, R1 increases rather
sharply initially but tends to level off as the roughness reaches
a steady state value. As the figure shows, R1 decreases rapidly
at the onset of the first anodic dissolution current. R1 can be
brought back to the original value by completely stripping the
deposit from the Au surface.
Bismuth was electrodeposited onto planar substrates of evap-
orated Au and polycrystalline Cu using a variety of deposition
potentials. All deposits were made from 1.0 mol L−1 HNO3 con-
taining 0.10 mol L−1 Bi(NO3)3. The coverage of the deposited
films and surface morphology were characterized using FE-
SEM. Fig. 10 shows the surfaces of 1.0 and 15 ␮m films on both
Au and Cu electrodeposited at −0.50 V. The 1.0 ␮m films are
nodular with grains measuring 1–2 ␮m. The 15 ␮m films have
the same nodular morphology as the 1.0 ␮m thick films except
that the average grain size is about a factor of four larger. Fig. 10
indicates that the surface morphology is identical for deposits
formed on polycrystalline Cu and evaporated Au substrates
under similar deposition conditions. The reversible potential for
bismuth in 0.10 mol L−1 Bi(NO3)3 solution is approximately
−0.45 V versus SSE. Deposits made at a deposition potential of
−0.50 V had a “frosty-white” appearance. The average depo-
sition current at this potential was about 20 mA cm−2. The
visual appearance of the deposits became gradually darker due to
roughening of the surface as more negative deposition potentials
were applied.
In order to view a Bi film in cross-section, an electrodeposit
was selectively ion milled using a FIB operating at 30 kV. Fig. 11
shows the cross-section of a nominal 15 ␮m Bi film deposited
galvanostatically at 5 mA cm−2. The initial trench was made
using 6600 pA and polishing of the cross-sectioned surface was
Fig. 8. The m/Q ratio during deposition and dissolution of Bi from 1.0 mol L−1
HNO3 containing 0.1 mol L−1 Bi(NO3)3.

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E. Sandnes et al. / Electrochimica Acta 52 (2007) 6221–6228
Fig. 10. FE-SEM of as-deposited Bi surface following deposition at −0.50 V vs. SSE from 1.0 mol L−1 HNO3 containing 0.10 mol L−1 Bi(NO3)3 (a) 1 ␮m thick Bi
on evaporated Au, (b) 15 ␮m thick Bi on evaporated Au, (c) 1 ␮m thick Bi on polycrystalline Cu, and (d) 15 ␮m thick Bi on polycrystalline Cu.
completed with 350 pA. The FE-SEM image reveals that the size
of the grains varies between 1 and 5 ␮m. The copper substrate
is visible beneath the Bi layer. There is no visible reaction at
the Cu–Bi interface as expected since Cu and Bi have negligible
mutual solubility and no intermetallic compounds form in this
system [41]. Small voids are occasionally observed at the Bi
grain boundaries. This is likely due to the nodular growth of the
electrodeposit where intergranular regions fail to fill completely.
Fig. 12 shows powder X-ray diffraction patterns of 1.0 ␮m
thick bismuth films electrodeposited onto evaporated Au sub-
strates at various overpotentials. The positions of reflections due
to the gold substrate are designated by triangles at the top of the
figure; however only the 1 1 1 is visible due to the strong crys-
tallographic texture of the evaporated Au film. Bismuth has a
rhombohedral crystal structure (space group R − 3m); however,
a hexagonal primitive cell is usually used to describe the bis-
muthlattice. Inthispaperweusethethree-indexMillersystemof
Fig. 11. FE-SEM of a FIBed cross-section of a nominal 15 ␮m thick Bi deposit
made at constant current density of 5 mA cm−2
.

E. Sandnes et al. / Electrochimica Acta 52 (2007) 6221–6228
6227
Fig. 12. XRD patterns (Cu K␣) of 1.0 ␮m bismuth films electrodeposited
onto evaporated Au substrates at 25 ◦C from 1.0 mol L−1 HNO3 containing
0.10 mol L−1 Bi(NO3)3 (a) −0.50 V, (b) −0.55 V, and (c) −0.65 V. The triangles
at the top of the figure represent the reflections due to the gold substrate.
Fig. 13. Texture profiles (0 2 4) for 1.0 ␮m thick bismuth films electrodeposited
at 25 ◦C from 1.0 mol L−1 HNO3 containing 0.10 mol L−1 Bi(NO3)3 onto evap-
orated Au at (a) −0.50 V, (b) −0.55 V, and (c) −0.65 V; and polycrystalline Cu
at (d) −0.50 V, (e) −0.55 V, and (f) −0.65 V.
indicesratherthanthefour-indexMiller-Bravaissystem[42];the
third of the four indices is omitted. All of the diffraction patterns
can be indexed to bismuth with lattice parameters a = 0.455 nm
and c = 1.186 nm. It is readily apparent from Fig. 12 that the
texture of the Bi electrodeposit changes with overpotential. As
the deposition potential is made more negative, the intensity of
the 0 1 2 and 0 2 4 reflections increases significantly while the
intensity of several other reflections, such as the 0 0 3, 1 1 0 and
2 0 2, decrease, suggesting preferred orientation of (0 1 2) planes
parallel to the film.
Table 1
The FWHM of the 024 texture profiles shown in Fig. 13 for 1.0 ␮m thick bismuth
films electrodeposited onto evaporated Au and polycrystalline Cu substrates
Substrate
Potential
FWHM
Au
Au
Au
−0.50
−0.55
−0.65
−0.50
−0.55
−0.65
180.0
18.3
11.2
Cu
Cu
Cu
40.0
28.5
23.9
The texture of the films was further investigated with a tech-
nique developed for analyzing fiber texture using a powder
diffractometer [43,44]. The Bragg peak of the textured planes
was scanned and the detector was then set at the position of
the peak center (2θB). The diffracted intensity was measured
as the sample was rotated over as large an angular range as
possible, from glancing incidence to incidence at close to 2θB,
and corrections were applied to the intensity profile to allow for
defocusing and absorption, yielding a corrected rocking curve.
The Bragg peaks selected for texture analysis were the most
intense in Fig. 12, the 0 1 2 and the 0 2 4, which both measure
texture on (0 1 2) planes. The 0 1 2 peak is more intense, but the
0 2 4, with its larger Bragg angle allows texture to be measured
over a larger angular range. The 0 2 4 rocking curves for the Bi-
on-Au and Bi-on-Cu films deposited at various overpotentials,
normalized to a maximum value of 1.0 in all cases, are given in
Fig. 13. The curves show that the level of texture (as indicated
by the sharpness of the rocking curve profile) increased as the
overpotential increased. For each profile the full width at half
maximum intensity (FWHM) was measured and the results are
given in Table 1. In the case of Bi-on-Au deposited at −0.50 V,
there was no peak in the texture profile, indicating no preferred
orientation of the (0 1 2) planes and so the FWHM could not be
measured. Table 1 clearly shows that FWHM of the 0 2 4 rock-
ing curve decreases with increasing overpotential and that the
texture of the Bi-on-Au films at the higher overpotentials was
greater than for the Bi-on-Cu deposits.
Bismuth films with preferred (0 1 2) orientation have been
reported in the literature. Vereecken has shown that polycrys-
talline Bi films electrodeposited onto p-GaAs (1 0 0) form large
grains with preferred 0 1 2 orientation after annealing at temper-
atures just below the melting point [10], suggesting that (0 1 2) is
a low energy plane. The fact that the preferred (0 1 2) orientation
occurs at higher overpotential is somewhat surprising since films
grown at higher deposition rates typically have a more random
structure. The stronger preferred (0 1 2) orientation on (1 1 1)-
textured Au than polycrystalline Cu may be attributed to the Bi
√
upd layer that forms on Au (1 1 1). The fully formed (p × 3)-
2Bi adlayer consists of a rectangular array of atoms measuring
0.447 nm by 0.49 nm [16,23,29–31]. Similarly, the (0 1 2) plane
of Bi consists of a rectangular lattice of atoms, 0.455 nm by
√
0.475 nm. This matches well with the spacing of the (p × 3)-
2Bi adlayer. The mismatch in the first dimension is +1.8% and in
the second it is −3.1%. Although the bulk deposition of Bi onto
Au proceeds by three-dimensional nucleation and growth, these
√
islands are formed on the (p × 3)-2Bi adlayer which influences
the crystallographic orientation of the Bi nuclei.
4. Conclusions
The electrodeposition of bismuth on a number of metallic
substrates from nitrate solutions can be performed successfully,

6228
E. Sandnes et al. / Electrochimica Acta 52 (2007) 6221–6228
obtaining compact, although rather rough, deposits, with 100%
current efficiency. The deposits appear to begin by instantaneous
nucleation over the whole substrate surface, and have a grain size
varying from 1 to 5 ␮m. The texture of the Bi deposits on Cu
and Au was investigated in detail as a function of the deposition
voltage. It was found that at more negative potential, that is at
higher current density, there is a pronounced tendency to develop
a (0 1 2) texture, particularly on the (1 1 1)-textured Au substrate.
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