Research group of PD Dr. Dirk Dorfs

The working group around PD Dr. Dirk Dorfs is a research group in the Department of Functional Nanostructures and deals with the synthesis of complex colloidally dispersed nanoparticles and the investigation of their (especially optical) properties.

The Dorfs group in February 2019 from left to right : Dirk Dorfs, Zunhao Wang, Max Niemeyer, Franziska Lübkemann, Patrick Bessel, Rasmus Himstedt

OUR MAIN RESEARCH AREAS

FORM AND COMPOSITION CONTROL IN COLLOIDAL CHEMICAL NANOPARTICLE SYNTHESIS

The Dorfs workgroup focuses on the colloidal chemical synthesis of nanoparticles. Special expertise exists in the field of synthesis of nanoparticles with non-trivial (quasi-spherical) form. Thus, e.g. controls nanoparticles produced in the form of rods or branched multipods. Likewise, e.g. controlling hollow or partially concave nanoparticles (the latter being interesting, for example, since they are capable of key-lock recognition reactions).

Influences on the optical properties by the combination of several materials in hybrid particles or property changes by the variation of shape and composition are also intensively researched. Combinations of metals with oxides or chalcogenides may have beneficial synergistic effects with regard to possible technical applications and are therefore of interest to the working group.

ALTERNATIVE PLASMONIC MATERIALS

One focus of the Dorfs group is set on nanoparticles with so-called localized surface plasmon resonance (LSPRs). These LSPRs are bound to freely movable charge carriers and are therefore predominantly investigated in the literature on metallic nanoparticles.

In the Dorfs working group, alternative materials (i.e., non-elemental metals) are examined for their plasmonic properties. These can be for example metallic compounds, (or various copper and nickel chalcogenides) but also degenerately doped materials such as Cu2-xSe or different conductive glasses like ITO or comparable materials.

It is particularly interesting that these alternative plasmonic materials have completely new possibilities, which elementary metals normally don't have (for example, adjustable carrier densities via the doping level or strong temperature-dependent conductivity).

TEMPERATURE GRADIENTS ON THE NANOMETER SCALE

The effects of laser induced strong heating on the shape and the structure of colloidally dispersed nanoparticles are investigated in the Dorfs group. Furthermore, it will be investigated if and how short-term strongly heated nanoparticles are suitable for the activation of chemical reactions on their surface and in the surrounding solution.

For example a plasmonic colloidally dispersed nanoparticle can be heated above 1200 K by a single high-intensity laser pulse (of a few picoseconds or nanoseconds duration) without heating the surrounding solution (because the laser light is only absorbed by the particle but not by the solvent).

Due to this strong heating, for instance a phase transition to a high temperature phase transition can be observed on the nanoparticle itself or chemical reactions can be induced on surface bound molecules.

SCIENTIFIC DEVICES OF THE DORFS GROUP

The devices in the  professorship for functional nanostructures are supervised by employees of the working groups and used across groups.

On request, we also examine samples from other working groups.

  • CARY 5000 UV-Vis-NIR Spektrophotometer

    The Department of Functional Nanostructures has a CARY 5000 spectrophotometer manufactured by Agilent Technologies at hand. This high-end spectrometer is capable of transmission and extinction measurements of liquids, coated transparent materials and powders in a spectral range of 175-3300 nm in high resolution. In addition, if required, the instrument can be equipped with expanding accessories such as a DRA-2500 integrating sphere for the measurement of absorption and reflection spectra or a thermostat-controlled 1x1 Peltier cell holder for temperature-dependent transmission and extinction spectroscopy.

  • Horiba Fluoromax 4 Spectrofluorometer

    The Fluoromax-4 is a bench-top spectrofluorometer which, in addition to recording emission and excitation spectra up to 850 nm, allows time-correlated single-photon counting lifetime measurements (TCSPC with 200 ps lower limit). The device is equipped with a dual monochromator system and allows measurements of liquid and solid samples in special holders. To determine the lifetime of the samples, various NanoLED picosecond laser sources with wavelengths from UV to visible are used.

  • Continuum SL II-10 Pulsed Laser

    The Dorfs group works with a setup which has is a pulsed neodymium-YAG laser manufactured by Continuum as core element. This device is capable of emitting high-energy light pulses of 5 ns length with a wavelength of 1064 nm and a maximum energy of 475 mJ per pulse through nanoparticle solutions. With the help of several exchangeable harmonic crystals, further wavelengths (532nm, 355nm and 266nm) can be generated. The energy hitting the samples can be gradually attenuated in the existing setup using OD filters and detected by a Coherent pyroelectric energy sensor. The irradiated solutions can be stirred with a stirrer enclosed in the cuvette holder of the setup.

     

     

WORKGROUP LEADERSHIP

Priv. Doz. Dr. rer. nat. Dirk Dorfs
Research Staff
Address
Callinstraße 3a
30167 Hannover
Building
Room
205
Priv. Doz. Dr. rer. nat. Dirk Dorfs
Research Staff
Address
Callinstraße 3a
30167 Hannover
Building
Room
205
More informations about PD Dr. Dirk Dorfs