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New ways have to be explored if the miniaturization of electronic devices
is to continue at the same pace as in the last decades. Besides incurring
in exponentially increasing fabrication costs, the down-scaling of (optical)
lithographic processes in the ‘‘top–down’’
approach for silicon chip manufacturing will soon lead to fundamental
physical limits. An alternative possibility is to explore the so-called
‘‘bottom–up’’ approach, which is based on
the formation of functional devices out of prefabricated molecular building
blocks with intrinsic electronic properties, an area generally referred
to as molecular electronics. Molecules can be considered as the ultimate
limit of electronic devices, since their size is about 1 nm. By using
appropriately designed largish molecules, the density of transistors per
chip might potentially be increased by up to a factor of 105 compared
to present standards.
Suitable organic molecules may self-assemble on semiconductor or metal
surfaces so as to gather in complex ordered structures, so–called
supramolecular assemblies, which may themselves yield the key towards
nanoscale molecular circuitry. The goal of this project is to investigate
the self-assembly of organic molecules at surfaces, as well as their electronic
properties and their alterations induced by the substrate or external
factors. Our aim is to gain new insight into this class of surface processes,
which may lead to the design of molecular structures with new functionalities.
Constant height STM image of HO(CH2)14CO2H
(sketched in the inset) physisorbed at a freshly cleaved basal plane of
HOPG. This image was obtained under ambient conditions at a bias voltage
of -880 mV and current set point of 750 pA. A Moiré pattern is
clearly visible in the image. This phenomenon suggests that the molecules
lie incommensurate with the graphite lattice. Image dimensions: 35.6 nm
X 8.2 nm.
STM image of HtBDC (hexa-tert-butyl decacyclene)
on Cu(110). Image dimensions: 182 nm X 182 nm, tunnelling parameters:
I = 0.77 nA, V = -1.61 V.
STM image of trimesic acid at the heptanoic
acid-graphite interface (13.1 nm x 6.7 nm). From the image, we see the
expected “chickenwire” structure where each molecule is bound
to three neighbouring ones through hydrogen bonding of the carboxylic
groups. |
