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Prof. Dr. Michael Gottfried

Research profile

Chemistry at surfaces and interfaces, Surface analysis, Photoelectron spectroscopy, Scanning probe microscopy, Molecular and ion beam techniques

We study chemical reactions at complex surfaces and interfaces with spectroscopic, microscopic and molecular beam / ion beam techniques. The experiments are performed on well-defined surfaces of metals, organic thin films or liquids in ultrahigh vacuum (UHV). We are active in Marburg since 2012 and were located at the University of Erlangen-Nürnberg before.



Current projects

Current research areas include (a) Elementary steps of surface reactions, (b) New materials through on-surface synthesis, (c) Internal metal-organic interfaces for organic electronics and renewable energy applications, (d) Model catalysis, (e) Functional nanomaterials with novel electronic, chemical and catalytic properties, and (f) Development of novel techniques for surface and interface science.



Methods

For these studies, we use a wide range of spectroscopic, microscopic, diffraction, and molecular/ion beam techniques: Photoelectron Spectroscopy (XPS, UPS, HAXPES), X-Ray Absorption Spectroscopy (NEXAFS, XANES), Scanning Tunneling Microscopy (STM), Low-Energy Electron Diffraction (LEED), Nanojoule Adsorption Calorimetry (NAC), Molecular Beam and Thermal Desorption Techniques, Ion Beam Deposition Techniques (ESI-IBD). Many measurements are performed with synchrotron radiation.

methods_1  methods_2


Some projects in detail

1. Metal/organic interfaces: Metal/organic interfaces play an important role in organic-electronic devices such as organic light-emitting diodes (OLEDs), which are widely used in displays. The performance of these devices depends on the properties of the metal/organic interface, i.e., its electronic, chemical and geometric structure. The interfaces can be atomically sharp and chemically stable, if the pure phases are sufficiently inert and immobile under the preparation and working conditions. Other systems undergo diffusion processes and chemical reactions, which lead to the formation of diffusion and reaction zones or interphases that separate the pure metal from the pure organic phase. We explore the processes which lead to the formation of interphases, the chemical, electronic and energetic properties of the interphases, as well as strategies for suppressing or enhancing their formation. These investigations are performed with a combination of Hard X-ray Photoelectron Spectroscopy (HAXPES), Nanojoule Calorimetry and Molecular Beam Techniques. An example is the interface between cobalt and tetraphenylporphyrin, which leads to an interphase consisting of the cobalt(II)-tetraphenylporphyrin complex ( Chen 2016).
This project is supported by the SFB 1083.

interphase
Further reading: J.M. Gottfried, New J. Phys. 2016



The HAXPES technique is generally useful for studying buried interfaces, for example in electrodes ( Sachs 2015). Below: HAXPES measurements at the synchrotron radiation facility BESSY-II in Berlin.

Synchrotron_AG_Gottfried0005 Synchrotron_AG_Gottfried0014 Synchrotron_AG_Gottfried0012

 
2. Surface coordination chemistry:  We study reactions between adsorbed ligand molecules and metal atoms on surfaces in ultrahigh vacuum. In contrast to coordination chemistry in solution, this is a largely unexplored field. Under these solvent-free conditions, unusual reactions can occur. An example is the reaction of porphyrins, phthalocyanines and corroles with metal atoms, which get coordinated and oxidized. With bifunctional ligands such as tetrapyridylporphyrin, 2D coordination networks with alternating oxidation state can be obtained. Coordination of additional ligands on the coordinated metal centers can affect the surface coordinative bond a way that is closely related to the classical trans effect ( Gottfried 2015).

porphyrins
Further reading:
C. Wang et al., Nanoscale 2016
  I.P. Hong et al., Chem. Comm. 2016

C. Wang et al., Chem. Comm. 2014


3. Surface-assisted organic synthesis: Monolayers of organic molecules on surfaces are often produced by vapor-deposition in ultrahigh vacuum. A drawback of this approach is that large molecules often decompose before they evaporate. To overcome this problem, we deposit smaller precursor molecules on the surface, which then form larger molecules or polymers. Many of these species cannot be synthesized in solution, such as the large unsubstituted oligophenylene macrocycles, the [n]-honeycombenes (Chen 2017).


30-HC
Further reading:
M. Chen et al., ACS Nano 2017
  Q. Fan et al., ACS Nano 2016

Q. Fan et al., Acc. Chem. Res. 2015


4. Nanojoule adsorption calorimetry: The adsorption energy is a direct measure for the strength of the adsorbate-substrate bond and as such an important parameter for the quantitative characterization of the surface chemical bond. We measure adsorption energies with molecular beam techniques in combination with highly sensitive pyroelectric detectors. Based on the work of C.T. Campbell, one of the pioneers in this field, we have developed a nanojoule adsorption calorimeter to measure adsorption energies of large organic molecules and metal complexes as well as the interface formation energies when metals are deposited onto organic layers.

calorimetry1 calorimetry2
Further reading:
J.M. Gottfried, R. Schuster, Surface Microcalorimetry, In: K. Wandelt (Ed.), Surface and Interface Science, Volume 5: Solid-Gas Interfaces I, Wiley-VCH Verlag, 2015. 
  O. Lytken et al., Adsorption Calorimetry on Well-Defined Surfaces, In: G. Bracco, B. Holst (Eds.), Surface Analytical Techniques, Springer 2013. 

H.-J. Drescher, Dissertation, Marburg 2016


5. Electrospray Ionization – Ion Beam Deposition (ESI-IBD): Vapour deposition of molecular organic materials requires that the substances reach sufficiently high vapour pressures before it decomposing. For many interesting molecules, such as functionalized porphyrins and phthalocyanines, this is not the case. A possible alternative is the ionisation of the molecules by electrospray from solution. The gaseous ions are separated from the solvent molecules and charged fragments by a combination of radio frequency ion guides and mass filters. This technique is not commercially available, however, several groups worldwide have started to develop their own systems. Our design consists of four differential pumping stages. It contains an HV electrospray unit, an ion funnel (first stage), a collimation quadrupole (second stage), a mass selection quadrupole (third stage) and the deposition chamber (fourth stage). The first two stages are equipped with roots pumps, the other two stages with turbomolecular pumps.

ESI_Photo ESI
      

6. Development and construction of scientific apparatus: The nanojoule calorimeter and the ESI-IBD apparatus shown above are two examples for the development of scientific instruments in our laboratory. Other examples include an apparatus for temperature-programmed desorption and an ultrahigh-vacuum preparation chamber for molecular on-surface synthesis.

apparatus



Zuletzt aktualisiert: 13.03.2017 · Marco Hill

 
 
 
Fb. 15 - Chemie

Fb. 15 - Chemie, Hans-Meerwein-Straße 4, 35032 Marburg
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