I studied physics at the University of Karlsruhe (Germany) where I also obtained my diploma degree in the Thomas Schimmel group. In March 2000 I joined the group of Klaus Kern at the Institute of Experimental Physics of the EPFL (Lausanne, Switzerland).

From 2003 onwards, I worked as Post-Doc at the IBM TJ Watson Research Center (Yorktown Heights, USA) in the Phaedon Avouris group. In 2006 I became member of the Horst Weller group at the University of Hamburg (Germany) and in 2007 I became assistant professor at the University of Hamburg.

In 2009 I received the German Nanotech Prize (Nanowissenschaftspreis, AGeNT-D/BMBF).

My research is supported by an ERC Starting Grant (2012) and a Heisenberg fellowship of the German Funding Agency DFG.

In 2017 I became associate professor at Swansea University.

Areas of Expertise

  • Colloidal nanostructures
  • Optoelectronic transport

Publications

  1. & Molecular Doping of Electrochemically Prepared Triazine-Based Carbon Nitride by 2,4,6-Triaminopyrimidine for Improved Photocatalytic Properties. ACS Omega 3(12), 17042-17048.
  2. & Colloidal lead iodide nanorings. Nanoscale 10(45), 21197-21208.
  3. & Copper sulfide nanosheets with shape-tunable plasmonic properties in the NIR region. Nanoscale 10(44), 20640-20651.
  4. & Colloidal tin sulfide nanosheets: formation mechanism, ligand-mediated shape tuning and photo-detection. Journal of Materials Chemistry C 6(35), 9410-9419.
  5. (2005). Charge-transferred doping and electroluminescence in carbon nanotube transistors.

See more...

Teaching

  • CH-240 Computational and Theoretical Chemistry

    The area of computational chemistry is of ever increasing importance in industry; from designer materials to prediction of likely drug targets, the falling cost of computational power is allowing the simulation of ever more complex molecular systems, lowering the cost of real-world research. This module will take the foundations of theoretical chemistry covered in Year One and further develop these in order to apply to in silico chemistry. Note: it is expected that material, techniques and skills covered in the course of this module will require understanding of any prior core module.

Supervision

  • Synthesis of colloidal quantum nanomaterials and characterization by X-ray synchrotron-based method. (current)

    Student name:
    PhD
    Other supervisor: Dr Moritz Kuehnel
    Other supervisor: Dr Christian Klinke
  • Untitled (current)

    Student name:
    PhD
    Other supervisor: Prof Juan Mareque-Rivas
    Other supervisor: Dr Christian Klinke

Awards And Prizes

Date Description
2013 Heisenberg Fellowship of the German Funding Agency DFG
2012 ERC Starting Grant
2009 Nanowissenschaftspreis (AGeNT-D/BMBF Nano science award, Germany)
2004 Fellowship of the Alexander-von-Humboldt Foundation
2004 Invention Achievement Award for the First IBM Patent
2003 Fellowship of the Swiss National Science Foundation

News

04/06/2018 We published a new paper in ACS Omega.
Poly (triazine imide) (PTI) is a material belonging to the group of carbon nitrides and has shown to have competitive properties compared to melon or g-C3N4, especially in photocatalysis. As most of the carbon nitrides PTI is usually synthesized by thermal or hydrothermal approaches. We present and discuss an alternative synthesis for PTI which exhibits a pH dependent solubility in aqueous solutions. This synthesis is based on the formation of radicals during electrolysis of an aqueous melamine solution, coupling of resulting melamine radicals and the final formation of PTI. We applied different characterization techniques to identify PTI as the product of this reaction and report the first liquid state NMR experiments on a triazine-based carbon nitride. We show that PTI has a relatively high specific surface area and a pH dependent adsorption of charged molecules. This tunable adsorption has a significant influence on the photocatalytic properties of PTI which we investigated in dye degradation experiments.
Reference: Leonard Heymann et al., ACS Omega 3 (2018) 3892.

03/28/2018 We published a new review article in Zeitschrift für Physikalische Chemie.
In this review, we highlight the role of halogenated compounds in the colloidal synthesis of nanostructured semiconductors. Halogen-containing metallic salts used as precursors and halogenated hydrocarbons used as ligands allow stabilizing different shapes and crystal phases, and enable the formation of colloidal systems with different dimensionality. We summarize recent reports on the tremendous influence of these compounds on the physical properties of nanocrystals, like field-effect mobility and solar cell performance and outline main analytical methods for the nanocrystal surface control.
Reference: Frauke Gerdes et al., Z. Phys. Chem. (2018) online.

03/27/2018 We published a new article in Advanced Functional Materials.
Colloidally synthesized nanomaterials are among the promising candidates for future electronic devices due to their simplicity and the inexpensiveness of their production. Specifically, colloidal nanosheets are of great interest since they are conveniently producible through the colloidal approach while having the advantages of two-dimensionality. In order to employ these materials, according transistor behavior should be adjustable and of high performance. We show that the transistor performance of colloidal lead sulfide nanosheets is tunable by altering the surface passivation, the contact metal, or by exposing them to air. We found that adding halide ions to the synthesis leads to an improvement of the conductivity, the field-effect mobility, and the on/off ratio of these transistors by passivating their surface defects. As a possible solution for the post-Moore era, realizing new high quality semiconductors such as colloidal materials is crucial. In this respect, our results can provide new insights which helps to accelerate their optimization for potential applications.
Reference: Mohammad Mehdi Ramin Moayed et al., Adv. Funct. Mater. (2018) online.

02/09/2017 We published a paper in Nanoscale.
We present a colloidal synthesis strategy for lead halide nanosheets with a thickness of far below 100 nm. Due to the layered structure and the synthesis parameters the crystals of PbI2 are initially composed of many polytypes. We propose a mechanism which gives insight into the chemical process of the PbI2 formation. Further, we found that the crystal structure changes with increasing reaction temperature or by performing the synthesis for longer time periods changing for the final 2H structure. In addition, we demonstrate a route to prepare nanosheets of lead bromide as well as lead chloride in a similar way. Lead halides can be used as a detector material for high-energy photons including gamma and X-rays.
Reference: Eugen Klein et al., Nanoscale 10 (2018) 4442.

10/13/2017 We published a review article in the Journal of Materials Chemistry
We modeled a prototype of a photovoltaic window, a passive source of clean energy, using a Monte Carlo ray-tracing method. We considered different geometries, material properties, and edge solar cells to determine the optimal conditions and possible electrical power yield. The modeled photovoltaic window prototype was based on colloidal luminescent low-toxic I–III–VI quantum dots (core/shell CuInS2/ZnS nanocrystals) with large Stokes shifts, high quantum yields, and tunable spectral properties. We also showed the influence of the quantum dot absorption/emission spectra on the resulting spectrum of transmitted light using a chromaticity diagram.
Reference: Rostyslav Lesyuk et al., J. Mater. Chem. C 5 (2017) 11790. 

10/13/2017 We published a review article in EPL (Europhys. Lett.)
Colloidal nanoparticles developed as interesting objects to establish two- or threedimensional super-structures with properties not known from conventional bulk materials. Beyond, the properties can be tuned and quantum effects can be exploited. This allows understanding electronic and optoelectronic transport phenomena and developing corresponding devices. The state-of-the-art in this field will be reviewed and possible challenges and prospects will be identified.
Reference: Christian Klinke, EPL (Europhys. Lett.) 119 (2017) 36002. 

My Research

ERC Starting Grant 2012: 2D-SYNETRA

Novel nanoscaled electrical devices rely on the design of tailored architectures. For this purpose nanoparticles are intensively investigated. So far, electrical characterizations concentrated mainly on thin films, but it is still a challenge to establish reliable, high quality assemblies of nanocomponents. We will develop truly two-dimensional continuous materials and two-dimensional monolayer films composed of individual nanocrystals by the comparatively fast, inexpensive, and scalable colloidal synthesis method. The synthesis mechanisms and the materials’ properties will be studied in detail, especially regarding their (photo-) electrical transport. Using these structures we will develop new types of device structures, such as Coulomb blockade and field enhancement based transistors. Recently, we demonstrated the possibility to synthesize, in a controlled manner, truly two-dimensional colloidal nanostructures. We will investigate their formation mechanism, synthesize further materials as “nanosheets”, develop methodologies to tune their geometrical properties, and study the (photo-) electrical properties of individual nanosheets. Furthermore, we will use the Langmuir-Blodgett method to deposit highly ordered monolayers of monodisperse nanoparticles. Such structures show interesting transport properties governed by Coulomb blockade effects known from individual nanoparticles. This leads to semiconductor-like behavior in metal nanoparticle films. The understanding of the electrical transport in such “multi-tunnel devices” is still very limited. Thus, we will investigate this concept in detail and take it to its limits. Beside improvement of quality and exchange of material we will tune the nanoparticles’ size and shape in order to gain a deeper understanding of the electrical properties of supercrystallographic assemblies. Furthermore, we will develop device concepts for diode and transistor structures which take into account the novel properties of the low-dimensional assemblies. Nanosheets and monolayers of nanoparticles truly follow the principle of building devices by the bottom-up approach and allow electrical transport measurements in a 2D regime. Highly ordered nanomaterial systems possess easy and reliable to manipulate electronic properties what makes them interesting for future (inexpensive) electronic devices. Based on our experiences and investigations and with the integrated physico-chemical approach with different expertise we will investigate the electrical transport mechanisms in modern nanoparticle superstructures.

Two-dimensional colloidal nanostructures

Project-2D-NanosheetsIn regard to inexpensive, high-perfomance photovoltaic applications we investigate the synthesis and the opto-electrical performance of two-dimensional nanomaterials, such as colloidal lead sulfide nanosheets. We are interested in tuning their geometry (lateral extensions and height). Tuning the height allows the manipulation of their effective bandgap, which means that it will be possible to adapt the bandgap to the requirement of the target application. We characterize the structures as individual items or as thin films.

 

Electrical transport through thin films of nanoparticles

Project-Monolayer

Different techniques such as Langmuir-Blodgett and spin-coating are used and optimized in order to deposit thin films of monodisperse nanoparticles on electrode structures defined by electron-beam lithography. We can generate mono- or multi-layer films using metallic or semiconducting nanoparticles. In order to characterize such films we perform electrical transport measurements. They usually show nonlinear characteristics depending on the temperature. Such films can be used as chemical sensors or for cheap electronic devices.



ERCFP7







Other projects

Attachment of inorganic nanoparticles to carbon nanotubes

Project-Attachment

Novel applications in nanotechnology rely on the design of tailored nano-architectures. For this purpose, carbon nanotubes and nanoparticles are intensively investigated. We study the synthesis of inorganic nanoparticles by means of colloidal synthesis and their attachment to carbon nanotubes. We investigate the chemical and electronic properties of such composite structures, since they are potentially interesting for applications in photodetectors, solar cells, and fuel cells.

Electrical transport through individual nanostructures

Project-NanowiresWe synthesize inorganic nanostructures by colloidal synthesis or chemical vapor deposition. For example, needle-shaped nanostructures composed of an In head and an InP tail with lengths up to several micrometers were generated in a one-pot synthesis. Owing to their specific design such In/InP nanoneedles suit the use as ready-made Schottky transistors. Furthermore, we investigate the modification of the electronic properties of carbon nanotube based transistors.

 

 

Carbon nanotube electronics

Project-CNTFETWe are investigating the electronic transport in carbon nanotubes field effect transistors and the influence of organic and inorganic adsorbates. On the one hand such adsorbates could be tailored tetrathiafulvalene derivatives which attach to the nanotube in a pincer-like fashion. On the other hand we investigate the charge transfer upon adsorption of inorganic nanoparticles. Those structures are interesting with regard to sensors and solar cells.

 

 



Videos about the colloidal synthesis of nanostructures

 

 

 


Funding

The research was/is supported by DFGBMBFLexi C1-ChemistryLexi SpintronicsBexi CUIERC Starting Grant 2012

Teaching

Since 2017 Lecture "Quantum chemistry" (Swansea University)
2015 - 2017 Lecture "Physics for chemists II"
2013 - 2017 Lecture "Nano electronics"
2013 - 2015 Lecture "Regenerative energies"
2012 - 2013 Lecture "Advanced Physical Chemistry"
2010 - 2012 Lectures "Physical Chemistry I & II"
2006 - 2010 Lecture "Introduction to Nanotechnology"
Since 2006 Seminars, special lectures, and exercises in physical chemistry and nanotechnology
2000 - 2003 Supervision of trainings and lecture exercises in physics (Lausanne)
1996 - 1999 Supervision of internships in robotics and physics (Karlsruhe)