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From Benzenetrithiolate Self-Assembly to Copper Sulfide Adlayers on Cu(111): Temperature-Induced Irreversible and Reversible Phase Transitions
journal contribution
posted on 2014-02-20, 00:00 authored by Thomas Sirtl, Matthias Lischka, Johanna Eichhorn, Atena Rastgoo-Lahrood, Thomas Strunskus, Wolfgang M. Heckl, Markus LackingerSelf-assembly and
thermally activated surface chemistry of 1,3,5-benzenetrithiol
(BTT) on Cu(111) are studied under ultrahigh vacuum (UHV) conditions
by different complementary surface sensitive techniques. Low-energy
electron diffraction (LEED) patterns acquired at room temperature
and during subsequent heating reveal irreversible phase transitions
between in total four different long-range-ordered phases termed α-phase
to δ-phase. X-ray photoelectron spectroscopy (XPS) of the different
phases facilitates the identification of major chemical changes for
the first phase transition from α- to β-phase, whereas
in the succeeding phase transitions, no significant chemical shifts
are observed anymore. The structural characterization of each phase
is carried out by high-resolution scanning tunneling microscopy (STM),
and adsorption geometries of the phenyl rings are derived from C 1s
near-edge X-ray absorption fine structure (NEXAFS). The combination
of the results from this array of experimental techniques leads to
a consistent picture of the various phases and underlying processes.
Upon room-temperature deposition, BTT fully deprotonates and planar-adsorbed
molecules self-assemble into an ordered monolayer. With a temperature
onset of 300 K, the carbon–sulfur bonds start dissociating.
Sulfur forms a copper sulfide superstructure, whereas the organic
remainders form disordered structures. Further heating converts an
initial metastable and rarely observed (√3 × √3)R ± 30° copper sulfide superstructure into the
more stable and well-known (√7 × √7)R ± 19.1° polymorph.