3.2 Surface Reconstruction
73
prepared Au (100)-(hex) surface during the first anodic potential scan. The Au (100)(hex) surface has a one-dimensional stripe structure with every sixth row of Au atoms
along a [110] direction residing on top of the substrate Au atoms rather than in the
fourfold hollow site [17, 19]. A statistical analysis of the virgin Au specimens by
scanning tunnel microscopy (STM) indicated that about 50% of the surface area is
reconstructed [8, 9]. The change and disappearance of the stripe patterns during the
first anodic potential scan revealed that the reconstructed Au (100)-(hex) surface
begins to dissolve at 0.26 V (SCE) and the reconstruction is lifted at 0.51 V (SCE).
Furthermore, it was observed that the Au atoms removed by lifting form islands on
top of the surface.
The curve shifts upward during the second anodic potential scan after the potential returned to −0.14 V (SCE) and then attains to the steady state represented by
the dotted curve after 3 or 4 cycles. After 3 or 4 cycles, the surface displayed the
unreconstructed Au (100)-(1 × 1) structure even at −0.14 V (SCE). The potentiodynamic STM images [17] indicated that the Au (100)-(hex) surface in 0.1 M HClO 4
solution is restored at potentials more negative than −0.25 V (SCE), supporting that
the Au (100)-(1 × 1) surface is stable at −0.14 V (SCE). As shown in Fig. 3.4, both
solid and dotted curves coincide at about 0.9 V (SCE) where the reconstruction is
completely rifted. In Fig. 3.4, the value of g = 4.57 J m
−2 obtained by first-principles
calculations [15] is employed for the Au (100)-(1 × 1) surface at −0.14 V (SCE)
since the absolute value of g cannot be measured by a cantilever bending method.
The difference in g between the Au (100)-(hex) and -(1 × 1) surfaces at – 0.14 V
(SCE) in Fig. 3.4 is g = −0.123 J m
−2 , which is corrected to g = −0.25 J m
−2 for
the fully reconstructed Au (100)-(hex) surface since about 50% of the total surface
area is reconstructed. As a result, the absolute value of g = 4.32 J m
−2 is obtained for
the Au (100)-(hex) surface. It is noteworthy that the difference of g = −0.25 J m
−2
between the Au (100)-(hex) and -(1 × 1) surfaces at – 0.14 V (SCE) is about 7 times
as much as the difference of γ pzc = −0.035 J m
−2 between both surfaces at E pzc .
The positive value of g for a clean metal surface means that the surface is subjected
to tensile stress. A clean metal surface has always tensile stress (g > 0) since the
redistribution of the electronic charge which does not participate in bonding increases
the charge density between the surface atoms to reduce the bond distance between
the surface atoms in addition to the contraction of the interlayer distance due to the
enhancement of the charge between the first and second layers [7, 20]. When the
Au (100)-(1 × 1) surface is reconstructed to the Au (100)-(hex) surface, the tensile
stress is spontaneously released since the reconstructed Au (100)-(hex) surface has
the high atom density as compared to the unreconstructed Au (100)-(1 × 1) surface.
In Fig. 3.4, the value of g for the Au (100)-(1 × 1) surface decreases monotonously
with increasing potential from −0.14 to 0.96 V (SCE). The potential dependence
of g is named “potential-induced surface stress” [20], which does not resemble the
corresponding electrocapillary curve in Fig. 3.3. For the Au (100)-(1 × 1) surface,
the absolute value of g at E pzc = 0.03 V (SCE) is three times as much as that of
γ pzc . In addition, the potential dependence of g for the Au (100)-(1 × 1) surface is
significantly larger than the potential dependence of γ in the potential region more
positive than E pzc .
73
prepared Au (100)-(hex) surface during the first anodic potential scan. The Au (100)(hex) surface has a one-dimensional stripe structure with every sixth row of Au atoms
along a [110] direction residing on top of the substrate Au atoms rather than in the
fourfold hollow site [17, 19]. A statistical analysis of the virgin Au specimens by
scanning tunnel microscopy (STM) indicated that about 50% of the surface area is
reconstructed [8, 9]. The change and disappearance of the stripe patterns during the
first anodic potential scan revealed that the reconstructed Au (100)-(hex) surface
begins to dissolve at 0.26 V (SCE) and the reconstruction is lifted at 0.51 V (SCE).
Furthermore, it was observed that the Au atoms removed by lifting form islands on
top of the surface.
The curve shifts upward during the second anodic potential scan after the potential returned to −0.14 V (SCE) and then attains to the steady state represented by
the dotted curve after 3 or 4 cycles. After 3 or 4 cycles, the surface displayed the
unreconstructed Au (100)-(1 × 1) structure even at −0.14 V (SCE). The potentiodynamic STM images [17] indicated that the Au (100)-(hex) surface in 0.1 M HClO 4
solution is restored at potentials more negative than −0.25 V (SCE), supporting that
the Au (100)-(1 × 1) surface is stable at −0.14 V (SCE). As shown in Fig. 3.4, both
solid and dotted curves coincide at about 0.9 V (SCE) where the reconstruction is
completely rifted. In Fig. 3.4, the value of g = 4.57 J m
−2 obtained by first-principles
calculations [15] is employed for the Au (100)-(1 × 1) surface at −0.14 V (SCE)
since the absolute value of g cannot be measured by a cantilever bending method.
The difference in g between the Au (100)-(hex) and -(1 × 1) surfaces at – 0.14 V
(SCE) in Fig. 3.4 is g = −0.123 J m
−2 , which is corrected to g = −0.25 J m
−2 for
the fully reconstructed Au (100)-(hex) surface since about 50% of the total surface
area is reconstructed. As a result, the absolute value of g = 4.32 J m
−2 is obtained for
the Au (100)-(hex) surface. It is noteworthy that the difference of g = −0.25 J m
−2
between the Au (100)-(hex) and -(1 × 1) surfaces at – 0.14 V (SCE) is about 7 times
as much as the difference of γ pzc = −0.035 J m
−2 between both surfaces at E pzc .
The positive value of g for a clean metal surface means that the surface is subjected
to tensile stress. A clean metal surface has always tensile stress (g > 0) since the
redistribution of the electronic charge which does not participate in bonding increases
the charge density between the surface atoms to reduce the bond distance between
the surface atoms in addition to the contraction of the interlayer distance due to the
enhancement of the charge between the first and second layers [7, 20]. When the
Au (100)-(1 × 1) surface is reconstructed to the Au (100)-(hex) surface, the tensile
stress is spontaneously released since the reconstructed Au (100)-(hex) surface has
the high atom density as compared to the unreconstructed Au (100)-(1 × 1) surface.
In Fig. 3.4, the value of g for the Au (100)-(1 × 1) surface decreases monotonously
with increasing potential from −0.14 to 0.96 V (SCE). The potential dependence
of g is named “potential-induced surface stress” [20], which does not resemble the
corresponding electrocapillary curve in Fig. 3.3. For the Au (100)-(1 × 1) surface,
the absolute value of g at E pzc = 0.03 V (SCE) is three times as much as that of
γ pzc . In addition, the potential dependence of g for the Au (100)-(1 × 1) surface is
significantly larger than the potential dependence of γ in the potential region more
positive than E pzc .