Chemistry Reference
In-Depth Information
Figure 4.7. (a) STM image showing the Ge(111)-
c
(2
×
8) surface with isolated
C
60
adsorbates (
V
t
=
05 nA). The section enclosed in the rectangle
represents the most common molecule-induced defect. Reprinted with permis-
sion from K. R. Wirth and J. Zegenhagen,
Physical Review B
,
56
, 9864 (1997).
Copyright (1997) by the American Physical Society. (b) Representation of the
Ge(111)-
c
(2
1V,
I
t
=
0
.
8) surface with the shift on one row induced by an individual C
60
molecule. The large, distorted circle is the reproduction of the C
60
imaged by the
STM.
×
chemisorption of the molecule with the surface, hence the low diffusion. In addition
to this molecule-induced defect other perturbations have been also observed.
Our second example deals with the adsorption of a C
90
H
98
molecule on a clean
Cu(110) surface. The Lander molecule can be regarded as a conducting board
(
-system) and four spacer legs that elevate the board from the substrate, with
the aim of electronically isolating it from the surface. By manipulating individual
molecules at low temperature, it is found that a single Lander molecule can act as a
template, self-fabricating metallic nanostructures at step edges. This restructuring
process can be described in terms of the structure of the molecule, which reshapes
a portion of the step edge, leading to the formation of a nanostructure two Cu atoms
wide and seven Cu atoms long below the molecular board.
In principle a STM should be adequate to measure the electrical resistance of a
singlemolecule since it suffices tomeasure
I
-
V
curves of themetal (tip)-molecule-
metal (substrate) system. However, published results in the literature concerning
this subject have to be considered cautiously because of the generally unknown
nature of the molecule-metal contacts. An illustrative experiment demonstrates
the relevance of the interface (Kushmerick
et al.
, 2002). This experimental work
studies charge transport using the cross-wire tunnel junction technique, where two
π
