19 research outputs found
Surface-confined 2D polymerization of a brominated copper-tetraphenylporphyrin on Au(111)
A coupling-limited approach for the Ullmann reaction-like on-surface
synthesis of a two-dimensional covalent organic network starting from a
halogenated metallo-porphyrin is demonstrated.
Copper-octabromo-tetraphenylporphyrin molecules can diffuse and self-assemble
when adsorbed on the inert Au(111) surface. Splitting-off of bromine atoms
bonded at the macrocyclic core of the porphyrin starts at room temperature
after the deposition and is monitored by X-ray photoelectron spectroscopy for
different annealing steps. Direct coupling between the reactive carbon sites of
the molecules is, however, hindered by the molecular shape. This leads
initially to an ordered non-covalently interconnected supramolecular structure.
Further heating to 300{\deg}C and an additional hydrogen dissociation step is
required to link the molecular macrocycles via a phenyl group and form large
ordered polymeric networks. This approach leads to a close-packed covalently
bonded network of overall good quality. The structures are characterized using
scanning tunneling microscopy. Different kinds of lattice defects and,
furthermore, the impact of polymerization on the HOMO-LUMO gap are discussed.
Density functional theory calculations corroborate the interpretations and give
further insight into the adsorption of the debrominated molecule on the surface
and the geometry and coupling reaction of the polymeric structure.Comment: 9 pages, 6 figure
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(Metallo)porphyrins for potential materials science applications
The bottom-up approach to replace existing devices by molecular-based systems is a subject that attracts permanently increasing interest. Molecular-based devices offer not only to miniaturize the device further, but also to benefit from advanced functionalities of deposited molecules. Furthermore, the molecules itself can be tailored to allow via their self-assembly the potential fabrication of devices with an application potential, which is still unforeseeable at this time. Herein, we review efforts to use discrete (metallo)porphyrins for the formation of (sub)monolayers by surface-confined polymerization, of monolayers formed by supramolecular recognition and of thin films formed by sublimation techniques. Selected physical properties of these systems are reported as well. The application potential of those ensembles of (metallo)porphyrins in materials science is discussed
(Metallo)porphyrins for potential materials science applications
The bottom-up approach to replace existing devices by molecular-based systems is a subject that attracts permanently increasing interest. Molecular-based devices offer not only to miniaturize the device further, but also to benefit from advanced functionalities of deposited molecules. Furthermore, the molecules itself can be tailored to allow via their self-assembly the potential fabrication of devices with an application potential, which is still unforeseeable at this time. Herein, we review efforts to use discrete (metallo)porphyrins for the formation of (sub)monolayers by surface-confined polymerization, of monolayers formed by supramolecular recognition and of thin films formed by sublimation techniques. Selected physical properties of these systems are reported as well. The application potential of those ensembles of (metallo)porphyrins in materials science is discussed
Investigation of the supramolecular self-assembly, electronic properties, and on-surface reactions of porphyrin and phthalocyanine molecules
Das grundlegende VerstĂ€ndnis der Adsorption, der Eigenschaften, und der Wechselwirkungen von komplexen organischen MolekĂŒlen auf FestkörperoberflĂ€chen ist fĂŒr die Entwicklung neuer Anwendungen in der Nanotechnologie von entscheidender Bedeutung. Die in dieser Arbeit untersuchten funktionellen Bausteine gehören zu den Porphyrinen und Phthalocyaninen. Deren Adsorption, elektronische Struktur, und Reaktionen der MolekĂŒle auf EdelmetalloberflĂ€chen wurden mit mehreren Methoden charakterisiert, insbesondere der Rastertunnelmikroskopie, Rastertunnelspektroskopie, Röntgen-Nahkanten-Absorptions-Spektroskopie und Photoelektronenspektroskopie, welche zudem durch theoretische Simulationen unter Verwendung der Dichtefunktionaltheorie ergĂ€nzt wurden.
Tetra(p-hydroxyphenyl)porphyrin MolekĂŒle ordnen sich durch Selbstorganisation zu verschiedenen, durch WasserstoffbrĂŒckenbindungen stabilisierten Nanostrukturen an, welche in AbhĂ€ngigkeit von dem SubstratoberflĂ€chengitter untersucht wurden um das komplizierte Zusammenspiel von MolekĂŒlâMolekĂŒl und MolekĂŒlâSubstrat-Wechselwirkungen bei der Selbstorganisation zu verstehen. Erhitzen der Adsorbatschichten dieses MolekĂŒls fĂŒhrt zu einer schrittweisen Deprotonierung, und auĂerdem konnte auch ein Schalten der LeitfĂ€higkeit einzelner Porphyrin-MolekĂŒle durch lokale Deprotonierung mittels Spannungspulsen demonstriert werden. Eine Polymerisationsreaktion, welche auf der Ullmann-Reaktion basiert, aber direkt auf einer OberflĂ€che stattfindet, wurde fĂŒr Kupfer-octabromotetraphenylporphyrin MolekĂŒle, die auf Au(111) adsorbiert sind, gefunden. Nach einer thermischen Abspaltung der Bromatome von den MolekĂŒlen reagieren dabei die RadikalmolekĂŒle bei hohen Temperaturen miteinander und bilden geordnete, kovalent gebundene Netzwerke aus. Die Bromabspaltung und die nachfolgenden Reaktionen und VerĂ€nderungen der elektronischen Struktur der MolekĂŒle wurden ausfĂŒhrlich fĂŒr die SubstratoberflĂ€chen Au(111) sowie Ag(110) untersucht. Weiterhin, wird die Adsorption und Selbstorganisation von metall-freien Phthalocyanin-MolekĂŒlen auf einer Ag(110)-OberflĂ€che, und deren Selbstmetallierungsreaktion mit Silberatomen des Substrats umfassend und verstĂ€ndlich beschrieben. Zuletzt wurden organische Hybrid-GrenzflĂ€chen zwischen verschiedenen Metall-Phthalocyaninen untersucht, wobei ein Ladungstransfer zwischen Kobalt- und Platin-Phthalocyanin-MolekĂŒlen gefunden wurde. Dotierung gemischter Metall-Phthalocyanin-Filme durch Einlagerung von Kaliumatomen und deren selektive Adsorption im MolekĂŒlgitter fĂŒhrt zu einer deutlichen VerĂ€nderung der elektronischen Eigenschaften, aufgrund einer LadungsĂŒbertragung an die Kobalt-Phthalocyanin MolekĂŒle.:List of publications
List of abbreviations
1 Introduction
2 Methods
2.1 Scanning tunneling microscopy
2.1.1 Theoretical description
2.1.2 STM imaging modes
2.1.3 Scanning tunneling spectroscopy
2.1.4 Technical aspect of the STM instrument
2.2 Low energy electron diffraction
2.3 Photoelectron spectroscopy
2.3.1 Principle
2.3.2 Theoretical description
2.3.3 Initial state effects
2.3.4 Final state effects
2.3.5 X-ray source
2.3.6 Technical aspects of PES
2.3.7 Resonant Photoelectron spectroscopy
2.4 Near-edge X-ray absorption fine structure spectroscopy
2.4.1 Principle
2.4.2 Polarization dependence
2.5 Density Functional Theory
2.5.1 Fundamental equations
2.5.2 Exchange-correlation functionals
2.5.3 Dispersion correction
2.5.4 Hubbard U correction
2.5.5 Basis set
2.5.6 Grid-based projector augmented wave (GPAW) method
2.6 Fundamentals of epitaxy and growth of molecular films
3 Experimental and computational details
3.1 Experimental setup
3.2 Sample preparation
3.3 Technical details for measurements
3.3.1 STM
3.3.2 PES
3.3.3 NEXAFS
3.4 Computational details
4 Metal-free tetra(p-hydroxylphenyl)porphyrin (H2THPP)
4.1 Interplay of hydrogen bonding and molecule-substrate interaction in self-assembled supra-molecular structures of H2THPP
4.1.1 Adlayer structures of H2THPP on Au(111)
4.1.2 Adlayer structures of H2THPP on Ag(111)
4.1.3 Adlayer structures of H2THPP on Ag(110)
4.1.4 Calculation of the adsorption energies and discussion
4.2 Manipulation of the electronic structure by local reversible dehydrogenation
4.2.1 STM and STS results
4.2.2 Discussion of the interconversion
4.2.3 Dosing of hydrogen gas on H2THPP
4.3 Photoelectron spectroscopy investigation of the temperature-induced deprotonation
and substrate-mediated hydrogen transfer
4.3.1 Protonation and deprotonation at nitrogen atoms
4.3.2 Deprotonation at carbon atoms
4.3.3 Evolution of the valence band
4.4 Summary
5 Copper-octabromotetraphenylporphyrin (CuTPPBr8)
5.1 Introduction to surface-confined polymerization
5.2 Adsorption and polymerisation of CuTPPBr8 on Au(111)
5.2.1 XPS investigations
5.2.2 STM investigations of the molecular adlayer
5.2.3 DFT calculations
5.3 Adsorption and temperature-dependence of CuTPPBr8 on Ag(110)
5.3.1 XPS and NEXAFS investigations of CuTPPBr8 on Ag(110)
5.3.2 Adlayer structure and adsorption geometry of CuTPPBr8 on Ag(110)
5.4 Summary
6 Metal-free phthalocyanine (H2Pc) on Ag(110)
6.1 Adlayer structures of H2Pc on Ag(110)
6.2 Self-metalation of H2Pc on Ag(110) with silver surface atoms
6.2.1 Introduction to self-metalation
6.2.2 XPS investigations of the self-metalation
6.2.3 STM results of the self-metalation
6.2.4 DFT simulations of the metalation reaction path
6.3 Summary
7 Charge transfer in metallophthalocyanine blends and doping with potassium atoms
7.1 Charge transfer in platinum phthalocyanine â cobalt phthalocyanine dimers
7.1.1 XPS of PtPcâCoPc dimer layers
7.1.2 Resonant photoelectron spectroscopy of PtPcâCoPc dimer layers
7.2 Potassium doping of copper phthalocyanine â cobalt phthalocyanine mixed films
7.2.1 XPS of CuPcâCoPc mixed layers
7.2.2 UPS of CuPcâCoPc mixed layers
7.2.3 NEXAFS of CuPcâCoPc mixed layers
7.2.4 DFT calculations of the CuPcâCoPc dimer and K doping
7.3 Summary
8 Conclusion and outlook
Bibliography
ErklÀrung
Lebenslauf
Danksagun
Investigation of the supramolecular self assembly, electronic properties, and on surface reactions of porphyrin and phthalocyanine molecules
Investigation of Ultrathin Layers of Bis(phthalocyaninato)lutetium(III) on Graphite
We present a comprehensive study of the adsorption of
bisÂ(phthalocyaninato)ÂlutetiumÂ(III)
(LuPc<sub>2</sub>) on highly oriented pyrolytic graphite(0001) (HOPG).
The growth and self-assembly of the molecular layers as well as the
electronic structure has been investigated systematically using scanning
tunneling microscopy and scanning tunneling spectroscopy combined
with density functional theory (DFT) calculations and molecular mechanics
simulations. We reveal that the adsorption of LuPc<sub>2</sub> leads
to the formation of a square-like close-packed structure on the almost
inert surface of HOPG, which is corroborated by simulations. Moreover,
we observed a parallel orientation of the LuPc<sub>2</sub> molecules
in the first monolayer, whereas in subsequent layers an increasing
tilt out of the surface plane was found. Tipâsample distance-dependent
tunneling spectroscopy measurements allowed us to detect a shift in
the energy positions of the peaks assigned to the lowest unoccupied
molecular orbital toward the Fermi energy with decreasing tipâsample
separation