Transcript The Study of Bi Electrodeposition on Au(100) by in

In-situ Scanning Tunneling Microscopy Study of Bismuth Electrodeposition on Au(100) and Au(111)
S.H. Zhenga, C.A. Jeffreya,b, D.A. Harringtonb E. Bohannanc, S.G. Chena and S. Morina
of Chemistry,York University, Toronto, ON and bDepartment of Chemistry, University of Victoria, Victoria, BC.
and cDepartment of Materials Science and Engineering and Graduate Center for Materials Research, University of Missouri-Rolla, Rolla, MO, USA.
aDepartment
Single crystalline bismuth thin films and nanostructures display very large
magnetoresistance (MR) [1-4] . While UHV-based deposition methods are
usually used to produce high quality Bi thin films, electrodeposition was
shown recently to be a suitable method to obtain Bi thin films and
nanostructures with interesting magnetic properties [3,4] .
In this study the early stages of Bi OPD and Bi bulk deposition on Au(100)
in 0.1 M HClO4 are investigated by in-situ STM and XRD. We observed that
the morphology of Bi OPD on Au(100) substrate was similar as that of Bi
OPD on Au(111)[5,6], films have similar morphology which develops from
needles (anisotropic) and two-dimensional isotropic growth modes. Our
electrodeposited Bi films were crystalline on Au(100) substrates, and they
were (012) oriented based on a hexagonal unit cell. Epitaxial orientations of
the Bi(012) film were confirmed using x-ray pole figure analysis.
Useful properties:
• Bismuth thin films and nanostructures have very large positive
magneto- resistance (MR)
• Bismuth oxides are semiconductors with 3-4 eV band gaps
a
0.26 V
d
-0.08 V
b
e
9 min
0.15 V
-0.09 V
25 min
c
f
0.05 V
1
5min
-0.10 V
4
20min
b
c
Bi(024)
Bi(036)
Figure 1: STM images for Bi early stage OPD on Au(100) single-crystal in
120 µM Bi3+ / 0.1 M HClO4. Scan size was 500 × 500 nm2. Sample
potential was (a) 0.26 V; (b) 0.15 V; (c) 0.05 V; (d) -0.08 V; (e) -0.09 V; (f)
–1.0 V. The time was counted from the first scan in the experiment to the
end of the certain scan. The tip bias is 0.055 V. The tunneling current is 0.3
nA (a-c), 0.248 nA (d,e) and 0.203 nA (f).
Figure 2: STM images for Bi early stage OPD on Au(111) single-crystal in
1mM Bi3+ / 0.1M HClO4. 1-5 scanned over the same area. Sample potential
was –0.08 V. Tip bias was 0.06 V. The tunneling current was 0.20 nA. Scan
size were 500 × 500 nm2(1-3), 300 × 300 nm2 (4,5). The time was counted at
the onset of Bi growth i.e. when the potential reached a value of –0.08 V.
Arrows indicate scan direction.
Figure 4: a) Bi (202) pole figure; b) Au(222) pole
figure and c) 2.5 D plot of Fig. 4 a).
[01-4]
films are crystalline and that it is (012)
oriented based on an (1×1) unit cell. The
film’s second and third order reflections are
also visible in the scan. A strong contribution
from the underlying Au surfaces is also
observed.
[2-10]
• A crystalline Bismuth film oriented (012) has
[01-4]
Au(222)
Bi(012)
a
b
c
Bi(024)
Bi(036)
Figure 5: Bragg-Brentano (2θ)
Scan of a thick Bi film on
Au(111) ca. 50-100 layers.
Figure 6: a) Bi (202) pole figure; b) Au(220) pole
figure and c) 2.5 D plot of Fig. 6 a).
[01-4]
(-111)
(11-1)
(01-1)
(111)
(110)
(1-11)
(101)
[2-10] (-111)
[-210]
(101)
(-111)
(101)
[-210]
[2-10]
[2-10]
(011)
(01-1)
[-210]
[01-4]
also been observed on p-GaAs substrates, but
only after the deposit was annealed [7].
Au(100) planes
Au(111) planes
Bi(012) planes
• Epitaxial
Au(111)
25min
is also shown in Fig. 2.
Bi(012)
Figure 3: Bragg-Brentano (2θ)
Scan of a thick Bi film on
Au(100) ca. 50-100 layers.
15min
31 min
• Figs. 3 and 5 clearly indicate that the bismuth
Au(100)
5
3
• The early stages of Bi electrodeposition were observed for films up to 6 monolayers in thickness (Fig. 1 & 2).
• At the onset of Bi OPD, Bi growth starts at step edges and terraces through the formation of mono- and bi- layers islands Fig. 1d & 2.1).
• Two growth modes are identifiable, namely needles (anisotropic) and two-dimensional isotropic, both propagate as mono- and bi- layers.
• Bi growth on Au(111) proceeded in a very similar way. For comparison, STM images of the morphology of a Bi film formed on Au(111)
Applications:
• Solid electrolytes for fuel cells
(δ-phase Bi2O3 has the highest known oxide-ion mobility)
• Oxygen sensors and oxygen pumps
• Electrochromic devices
• Electronic/magnetic materials
a
10min
2
orientation of the Bi(012) film on
the Au(100) and Au(111) substrates is
confirmed using x-ray pole figure analysis.
Figure 7: Epitaxy relationship between Bi(012) plane and the
Au(100)(left) and Au(111)(right) surfaces. Note that for clarity only
one Bi layer corresponding to the bulk film structure is shown. A
single atomic arrangement accounts for the peaks in the pole figures
(Fig.4&6). Note that the Bi atoms are shaded differently to emphasize
the slight modulation (0.11Å) of Bi atoms above and below the (012)
plane.
• The Bi(012) surface unit cell is rectangular. The spacing
corresponding to the interatomic distances (center-to-center in Å)
are shown by line diagrams at the bottom of the figure.
• The dotted line vectors represent one corner of a coincidence
lattice with the lengths of the arrows indicating the relative lengths
of the sides. The coincidence lattice is 36.63 Å × 56.98 Å on
Au(100) and 31.9 Å × 95 Å on Au(111), much larger than the
figure.
• At the onset of Bi OPD, Bi growth starts at step edges and terraces through the
formation of mono- and bi-layer islands.
• The morphology of Bi OPD on Au(100) substrate proceeds in a similar way to that of
Bi OPD on Au(111), island nucleation is followed by isotropic and anisotrophic
growth mode. The former mode follows specific crystallographic directions on the
substrate.
• The electrodeposited Bi films are crystalline and the domains are (012) oriented based
on the square unit cell of the Au(100) surface.
• The Bi(202) diffraction pole figure yield four peaks due to the orientation of the Bi
needle along the [001] directions of the Au(100) surface.
Figure 8: Stereographic representation of Bi(012) (full circles) on Au(100)
substrate (left) and Au(111) substrate (middle). The 2D unit cell of Bi(012)
(right).
• Four peaks and twelve peaks are observed in
the Bi(202) pole figure on Au(100) and
Au(111) substrates, respectively. These
support the presence of needles (domains)
that are oriented at 90 and 120 degree from
each other on Au(100) and Au(111),
respectively.
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5.
6.
7.
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Yang et al., Appl. Phys. Lett., 1998, 73, 1436.
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Yang et al., Science, 1999, 284, 1335.
C.A. Jeffrey, D.A. Harrington and S. Morin, Surf. Sci. (2002) 512, L367
C.A. Jeffrey, S.H. Zheng, E. Bohanna, D.A. Harrington and S. Morin, Surf. Sci. (2006) 600, 95-105
Vereecken et al., J. Electrochem. Soc., 2003, 150, C131 and Appl. Phys. Lett., 2000, 88, 6529.
This work was financially supported by the Natural Sciences and Engineering
Research Council (NSERC) of Canada, the Canadian Foundation for Innovation,
the Ontario Innovation Trust and York University. S. M. also acknowledges the
financial support from the Canada Research Chair Program.