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Neue Wege in der Energieeffizienzpolitik Ein Positionspapier von Mitgliedern des Think Tank 30
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Vertical bonding distances and interfacial band structure of PTCDA on a Sn-Ag surface alloy
Molecular materials enable a vast variety of functionalities for novel
electronic and spintronic devices. The unique possibility to alter or
substitute organic molecules or metallic substrates offers the opportunity to
modify and optimize interfacial properties for almost any desired field of
application. For this reason, we extend the successful approach to control
molecular interfaces by surface alloying. We present a comprehensive
characterization of the structural and electronic properties of the interface
formed between the prototypical molecule PTCDA and a Sn-Ag surface alloy grown
on an Ag(111) single crystal surface. We monitor the changes of adsorption
height of the surface alloy atoms and electronic valence band structure upon
adsorption of one layer of PTCDA using the normal incidence x-ray standing wave
technique in combination with momentum-resolved photoelectron spectroscopy. We
find that the vertical buckling and the surface band structure of the SnAg
surface alloy is not altered by the adsorption of one layer of PTCDA, in
contrast to our recent study of PTCDA on a PbAg surface alloy [Phys. Rev.
Lett. 117, 096805 (2016)] . In addition, the vertical adsorption geometry of
PTCDA and the interfacial energy level alignment indicate the absence of any
chemical interaction between the molecule and the surface alloy. We attribute
the different interactions at these PTCDA/surface alloy interfaces to the
presence or absence of local -bonds between the PTCDA oxygen atoms and
the surface atoms. Combining our findings with results from literature, we are
able to propose an empiric rule for engineering the surface band structure of
alloys by adsorption of organic molecules
Vertical structure of Sb-intercalated quasi-freestanding graphene on SiC(0001)
Using the normal incidence x-ray standing wave technique as well as low
energy electron microscopy we have investigated the structure of
quasi-freestanding monolayer graphene (QFMLG) obtained by intercalation of
antimony under the reconstructed
graphitized 6H-SiC(0001) surface, also known as zeroth-layer graphene. We found
that Sb intercalation decouples the QFMLG very well from the substrate. The
distance from the QFMLG to the Sb layer almost equals the expected van der
Waals bonding distance of C and Sb. The Sb intercalation layer itself is
mono-atomic, very flat, and located much closer to the substrate, at almost the
distance of a covalent Sb-Si bond length. All data is consistent with Sb
located on top of the uppermost Si atoms of the SiC bulk
Coherent and incoherent excitation pathways in time-resolved photoemission orbital tomography of CuPc/Cu(001)-2O
Time-resolved photoemission orbital tomography (tr-POT) offers unique
possibilities for tracing molecular electron dynamics. The recorded
pump-induced changes of the angle-resolved photoemission intensities allow to
characterize unoccupied molecular states in momentum space and to deduce the
incoherent temporal evolution of their population. Here, we show for the
example of CuPc/Cu(001)-2O that the method also gives access to the coherent
regime and that different excitation pathways can be disentangled by a careful
analysis of the time-dependent change of the photoemission momentum pattern. In
particular, we demonstrate by varying photon energy and polarization of the
pump light, how the incoherent temporal evolution of the LUMO distribution can
be distinguished from coherent contributions of the projected HOMO. Moreover,
we report the selective excitation of molecules with a specific orientation at
normal incidence by aligning the electric field of the pump light along the
molecular axis
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Structural and electronic properties of metal‐organic contacts and heteromolecular hybrid interfaces
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