collaborations

within University Duisburg-Essen

Center for Nanointegration (CENIDE)
SFB 616 "Energy dissipation at surfaces"
project: Ab initio theory of elementary excitations at surfaces (B7)

SFB 491 "Magnetic heterostructures: Spin structure and spin transport"
project: Ab initio thermodynamics and magnetism of thin films (A13)

DFG Focussed Programme SPP1386 "Nanostructured thermoelectrics: Theory, model systems, and controlled synthesis"
project: Thermoelectric Properties of Self-Assembled Nanocrystals in Semiconductor Matrix: Experiment and Theory in collaboration with Dr. A. Rastelli, IWF Dresden

Goal of this project is the experimental and theoretical investigation of the thermoelectric properties of conventional semiconductors (Si and GaAs) containing multilayers of defect-free SiGe and InGaAs nanocrystals (quantum dots, QDs). SiGe/Si and InGaAs/GaAs can be regarded as the best known examples of self-assembled QDs, as they have been thoroughly studied for their potential application in novel electronic and optoelectronic devices. While thermal conductivity reduction of SiGe/Si QDs has been reported, little is known on the effect of QDs on other thermoelectric parameters such as thermopower and cross-plane electric conductivity. We will therefore study cross-plane thermoelectric properties of QD multilayers by varying relevant structural parameters, i.e. QD size/composition, density and level of spatial ordering. The comparison between the two model systems (SiGe/Si and InGaAs/GaAs are examples of type-II and type-I band alignment, respectively) is expected to provide a significant advance on the understanding of the thermoelectric properties of nanostructured semiconductors.

DFG Focussed Programme SPP1538 "Spincaloric Transport"
project: Ab initio modelling of spincaloric transport in nanostructured Heusler alloys
in collaboration with Prof. P. Entel, University Duisburg-Essen

The main goal of the present proposal is to provide a microscopic understanding of spincaloric transport and thus a material-specific underpinning for the present-day phenomenological description of spincaloric effects. We will perform a spin-resolved theoretical study of the cross-plane electrical transport, driven by a voltage bias or a temperature gradient, through layered ferromagnetic structures of nanometer thickness. In particular, we aim at predictions of large spincaloric effects to be observed when (at least) one of the layers consists of a Heusler alloy. This class of ordered intermetallic compounds deserves further screening since some of its members have been shown to exhibit unusual magnetic properties and large thermoelectric coefficients. All electronic structure investigations will be performed by means of first-principles calculations, and transport will be studied using a combination of the Kubo-Greenwood/Streda formalism on the atomic scale and the Boltzmann transport equation on larger scales. One issue to be addressed by the calculations is the recently discovered magneto-thermogalvanic voltage and its dependence on the sample material and nanostructuring.
   

DFG-funded project KR2057/5-1 Analysis of the atomic processes in the growth of III-V semiconductor nanowires promoted by metal particles

The growth of nanowires with the help of deposited nanometer-sized metal particles is a very promising route to fabricate nanostructures in a self-organized fashion. This proposal aims at an investigation of the elementary processes involved in nanowire growth on the atomic scale, using methods from computational solid state physics. We will investigate a widely used prototypical system, the growth of gallium-arsenide and indium-arsenide nanowires in molecular beam epitaxy promoted by gold particles. It is proposed to carry out first-principles calculations within the framework of density functional theory in order to obtain reliable values of the surface and interface energies that play a role for the triple-phase boundary vacuum-semiconductor-metal-particle. Moreover, molecular dynamics simulations will be used to determine the free energy barrier associated with nucleation, and kinetic Monte Carlo simulations enable us to follow the subsequent growth of the nuclei. Understanding the atomic details of nucleation will put us in position to develop better-founded macroscopic growth models. These are intended to be used by engineers to control the crystalline polymorphism in the nanowires and the switching between cation species (e.g., gallium and indium) that is required for functionalizing these wires to be used in semiconductor devices.

external collaborations

Dr. Aparna Chakrabarti;
Raja Ramanna Centre for Advanced Technology,
Laser Physics Division, Semiconductor Laser Section,
Indore, India
    A. Rastelli and V.M. Fomin
Institute for Nanointegration
IWF Dresden
    C. Felser
Materials for Optical, Magnetic and Energy Technologies
Max-Planck-Institut für Physik fester Stoffe, Dresden
    A. Mikkelsen
The Nanometer Structure Consortium
Lund University, Box 118, S-221 00 Lund, Sweden