Chemistry Reference
In-Depth Information
3D interactions of the 1D system with its surroundings. These interactions modify
the properties of a 1D system and need to be controlled precisely, therefore. On
the other hand, control of these interactions may allow tuning of certain physical
properties, e.g., suppression of the metal-insulator transition.
An obvious strategy of making 1D conductors is the use of nano-assemblies
on semiconducting or insulating solid surfaces as well as highly anisotropic (and
possibly modified) surface superstructures, which provide excellent model systems
to study electron transport and its modification on the atomic scale accurately and
under well-defined conditions [
7
-
9
]. Examples are chain structures on uniaxial sur-
faces generated by adsorption of submonolayer amounts of metals and subsequent
self-organization and/or reaction with a strongly anisotropic (vicinal) single crys-
talline surface. These structures have several advantages: The geometry can be con-
trolled on the atomic scale and the electronic properties can be changed gradually
by adsorbate concentrations, by adatom mixing, and by varying the degree of local-
ization, e.g., by changing terrace widths.
Very few studies on such systems have been performed so far, e.g., for Au
nanowires on highly stepped Si(111) [
10
] and the system (4
×
1)-In/Si(111) [
11
]. In
both cases, the metallic nanowires exhibit a CDW instability. Notably the properties
of chains on stepped substrates can be varied to some extent by changing the terrace
width defined by the miscut, e.g., using Si(553) surfaces as compared to Si(557).
This leads to changes in both band filling and the CDW transition temperature [
12
].
It is important to note that these realizations of 1D reconstructions contain multi-
ple bands derived from the various constituent atoms. Therefore, while one band
may undergo a Peierls distortion, other bands may remain metallic. This reflects
that real-world systems are much more complex than a simple one-band scenario.
While dc transport measurements form the basis for a deeper understanding also of
related properties, such as optical or plasmonic excitations [
13
], they turn out to be
extremely demanding [
14
] and are still extremely scarce for metallic wires [
9
,
15
].
Furthermore, no information exists so far about the magnetotransport properties in
these systems. An important prerequisite for such measurements is the formation of
reliable contacts on the atomic or at least on the nanoscale. While the existence of
such contacts, e.g., in break junctions [
16
], is well established, the control on the
atomic scale is still at its beginning [
17
].
Here we want to present a short overview of Pb nanowires on Si(557) close to the
concentration of a physical monolayer, which represent a completely different phys-
ical scenario than all of those mentioned above. Because of the high concentration
of Pb, coupling between the wires cannot be neglected. This leads to an interesting
interplay between 1D and 2D properties, as seen, e.g., by the close dependence of
electronic transport behavior on the geometric structure.
9.2 Experimental
10
−
11
mbar.
For the LEED experiments we used an instrument that allows high-resolution pro-
file analysis (SPALEED). STM data were taken in a different chamber with a
All experiments were carried out in UHV at base pressures of 3-5
×
