Figures from Spatially-resolved electrochemistry of the lead sulfide (galena) (001) surface by electrochemical scanning tunneling microscopy", by S. R. Higgins, R. J. Hamers, Surface Science vol. 324, p. 263-281(1995)
All original binhex and zipped figures are Macdraw Pro documents unless otherwise noted.
Figure 1
(a) STM image of cleaved PbS(001) in air. Image size
2000 angstroms X 2000 angstroms. Vsample = 0.68 V,Itip = 0.11
nA. The observed roughness is due to the oxidation
of the surface upon exposure to air. (b) Profile of
line shown in (a) illustrating cleavage step height
and height variations within the terraces.
Figure 4
(a)-(l) Series of STM images acquired under continuously changing electrochemical conditions. Image size = 2000 x 2000 angstroms. Itip = 0.17 nA in all images, and Etip was in the range of 0.75 - 0.94 V. (a)
Esample = (0.20 --> 0.24, Etip=0.94 V. (b) Esample = (0.24 --> 0.29 V), Etip = 0.94 V. (c) Esample = (0.29 --> 0.33 V), Etip = 0.94 V. (d) Esample = (0.33 --> 0.38 V), Etip = 0.94 V. (e) Esample = (0.38 --> 0.43 V), Etip = 0.94 V. (f) Esample = (0.43 --> 0.38 V), Etip = 0.94 V. (g) Esample = (0.38 --> 0.34 V), Etip = 0.94 V. (h) Esample = (0.06 --> -0.16 V), Etip = 0.90 V. (i) Esample = (-0.16 --> 0.38 V), Etip = 0.86 V. (j) Esample = (-0.38 --> -0.45 V), Etip = 0.75 V. (k) Esample = (-0.23 --> -0.01 V), Etip = 0.80 V. (l) Esample = (-0.01 --> 0.20 V), Etip = 0.94 V. (a)-(e) represent the initial oxidation sweep which results in etch pit formation and enhanced step edge etching. (f)-(j) were acquired during a cathodic potential sweep. Oxidation continues in (f) and (g) as the potential was still positive of the OCP. The images in (h), (i), and (j) show the potential dependent topography undergoing modification as the potential is changed to increasingly negative values with respect to the OCP. (j) shows the dramatic effect on surface topography resulting from bulk electrochemical deposition of Pb from solution. For (k) and (l), the potential was slowly returned to the OCP resulting in stripping of the Pb overlayer as shown in (k). This process exposes the galena surface shown in (l) which displays a higher step density than prior to Pb deposition.
Figure 5
I-E plot corresponding to the images shown in figure 4.4. The sweep rate began at 0.7 mV/sec and was increased to 3.7 mV/sec following figure 4.4(g).
Figure 6
Sequence of STM images taken under increasingly
cathodic conditions. Image size = 2000 x 2000 angstroms.
Itip was 0.21 nA throughout the series.
(a) Esample = (-0.10 --> -0.25 V), Etip = 0.66 V.
(b) Esample = (-0.25 --> -0.40 V), Etip = 0.65 V.
(c) Esample = (-0.40 --> -0.55 V), Etip = 0.31 V.
(d) Esample = (-0.69 --> -0.78 V), Etip = -0.06 V.
(e) Esample = (-0.78 --> -0.64 V), Etip = -0.06 V.
(f) Esample = (-0.64 --> -0.50 V), Etip = -0.06 V.
Figure 7
I-E plot corresponding to the images shown in Figure 6
Figure 8
STM image showing result of anisotropic etching as
galena undergoes cathodic dissolution. Image size =
1200 x 1200 angstroms. Esample = -0.72 V, Etip = -0.04
V, Itip = 0.25 nA.
Figure 9
High resolution image (113 x 113 angstroms) establishing
the crystallographic orientation of the galena sample
used in figure 4.9 and 4.11. (a) Atomic resolution
image of PbS(001) in 0.02 M HClO4. A primitive unit
cell with sides of length 4.2 angstroms is shown. The long
parallel lines show the shift in registry across the
monatomic step, demonstrating that only one type of
atom is imaged. (b) Two-dimensional Fourier
Transform of (a) showing the symmetry of the
lattice.
Figure 10
PbS(001) surface schematic showing [100] and [110]-type step edges.
Figure 11
I-E plot corresponding to the images shown in figure 4.4. The sweep rate began at 0.7 mV/sec and was increased to 3.7 mV/sec following figure 4.4(g).
STM images showing re-oxidation of Pb islands and
concurrent growth of PbS at step edges. Image size =
1700 x 1000 angstroms. Etip = 0.06 V, Itip = 0.21 nA. (a)
Enlarged section from figure 4.9(f), at potential of
-0.50 V. (b) Same surface region after increasing
potential to -0.06 V.
Figure 12
(a) STM image showing surface topography after
extended reduction at -0.7, showing rounded shapes
of Pb(111) islands grown on PbS surface. Image size
= 1000 x 700 angstroms. Itip = 0.49 nA, Etip = 0.39 V,
Esample = -0.56 V. (b) Profile of line shown in (a)
illustrating 3.0 angstroms step height.
Last updated August 16, 1996