 |
Constant-current UHV STM topograph of bare Au(111) herringbone-reconstructed surface. Enlarged area shows ball model of a single (root(3)x23) surface unit cell. Surface layer is 4.4% uniaxially compressed. Compression causes surface-to-subsurface atomic registry to vary from unfaulted (ABC) stacking, to bridging, to faulted (ABA) stacking, to bridging, and back to unfaulted stacking. Bridging rows adopt alternating 60E bends, half of which contain surface-confined dislocation. |
 |
 STM constant-current
topographs showing evolution of the
herringbone-reconstructed Au(111) surface during gas-phase deposition of
mercaptohexanol. Exposure to 350 Langmuirs (L) of mercaptohexanol results
in heterogeneous nucleation and growth of striped-phase islands. Exposure
to a total of 600 L results in lateral island growth and additional island
nucleation.
Complex surface pressure field is reflected in herringbone reconstruction
influenced striped-phase island shape and in island
growth induced lateral migration of herringbone reconstruction ridges.
Single-atom-deep Au vacancy islands (pointing finger) nucleate
preferentially at elbows of herringbone hyperdomains. Exposure to total of
1000 L results in heterogeneous nucleation and growth of a second solid
phase (pointing finger). After exposure of several thousand L, second
phase approaches saturation coverage and growth spontaneously
terminates.  Molecular-resolution STM constant-current
topograph of striped-phase
mercaptohexanol on Au(111). (A) Striped-phase monolayer prepared by exposing
Au(111) to mercaptohexanol vapor. (B), (C) Cross-sectional height
profiles from corresponding line-traces in (A). Periodicities parallel and
perpendicular to corrugated rows are consistent with binding geometry where
molecular axes are aligned with surface-plane and molecules pack
head-to-head, tail-to-tail, as suggested by overlays in (A). Molecular-resolution STM constant-current
topograph of Au(111)
exposed to 1000 L of mercaptohexanol. Topograph was acquired from the
region indictated by the rectangle at the left. Cross-sectional profile
corresponding to red highlight is shown on the right. Striped phase
regions are due
to commensurate crystalline domains in which molecular axes are aligned
with surface plane (image above), bright island features are due to
commensurate
crystalline domains in which molecular axes are aligned with surface
normal. Infinitesimal width of phase boundary indicates that this is a simple
first-order, solid-solid phase transition. The phase transition is driven
by the lateral pressure of the monolayer film. Dark feature in lower right
is a Au vacancy island. |
Sequential constant-current UHV
STM topographs of partial monolayer of
mercaptohexanol on Au(111). (left) Exposure to 180 Langmuirs of
mercaptohexanol results
in nucleation of a single vacancy island (C) at a defected herringbone
elbow. (right) Same
surface region as (left) after exposure to an additional 120 Langmuirs of
mercaptohexanol. Growth of mercaptohexanol monolayer islands induces
migration of herringbone elbow defects along [101]. Additional vacancy
islands nucleate at herringbone elbows (arrows). Opposing 'Y'-Type defects
(D) and (E) counter propagate annihilating 5 herringbone elbow defects and
merging. Vacancy islands do not migrate. |
 |
 | Constant-current UHV STM topograph
of Au(111) exposed to 100
Langmuirs
mercaptohexanol. Blue regions are nominally bare Au(111), striped islands
are commensurate mercaptohexanol rows on relaxed Au(111), dark features are
nascent vacancy islands, isolated protrusions highlighted by red
line are attributed to Au adatoms. The apparent adatom
width is 13 a and height is 1.5 a, the former dimension being dominated by
tip dilation and the later representing the apparent height of the adatom
electron density. Click on picture to view time lapse STM movie (.mov 14.312MB) of Alkanethiol monolayer growth. This movie uses quicktime 3.0 plug-in. |
This work was performed by Gregory E. Poirier, who died September 15, 2000.
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Self-Assembled Monolayers on Au(111)", Langmuir, 10 #9, 2853 (1994).