Novel principle for 2D molecular self-assembly : self-intermixed monolayer phases of sub-phthalocyanine and C60 on Ag(111)

In this thesis, a novel route to highly perfect bi-molecular self-assembly on a metallic surface
is presented. Two kinds of organic molecules, the polar Chloro-[subphthalocyaninato]-
boron(III) (SubPc) and the polarizable C60-Buckminster fullerene, were co-deposited onto
atomically clean Ag(111) under UHV conditions. Depending on the relative surface coverage
of the two species, di�erent well-ordered intermixed monolayers are formed: At a mixing
ration SubPc/C60 = 2:3, an anisotropic stripe structure consisting of C60-chains with an
inter-chain periodicity of 3.3nm is found. A mixing ration SubPc/C60 = 1:1 leads to a 2D
hexagonal pattern with periodic vacancies. At room-temperature, the structures spontaneously
emerge by self-organization and are stable at the same. The mixed structures show
interesting and unusual features. One of the ordered bi-molecular overlayer, the 3:2-stripe-
phase, exists in two chiral forms, although the individual molecules themselves are achiral.
Di�erent phases can co-exist simultaneously, and also a 2D molecular gas phase can be observed.
The appearance of the molecular stripe domains in STM measurements strongly
depends on the applied bias-voltage. The structural parameters and the schematic binary
\phase-diagram" of this system are deduced from detailed room-temperature Scanning Tunneling
Microscopy (STM) studies. The underlying interactions and the relevant properties of
the molecules are discussed, based on STM, XPS and UPS measurements and on numerical
simulations. The pattern formation is further treated under thermodynamic aspects of a
two-component mixture. A counter-example to the intermixed system is further presented:
silated Perylen and C60 molecules, co-adsorbed on clean Ag(100), do not intermix but lead
to a 2D segregation.
These novel Self-Intermixed Monolayer Phases (SIMP) are di�erent from previously known
self-assembled molecular monolayers in that they form intermixed patterns at room temperature
on uniform, unreconstructed atomically clean terraces. These self-organized patterns,
as well as the additionally shown conformational changes of Porphyrin molecules, inspire to
be incorporated in building blocks of possible molecular electronic devices.