Evelin Fisslthaler

High resolution electron microscopy of Ag-clusters in crystalline and non-crystalline morphologies grown inside superfluid helium nanodroplets

We present a first investigation of structural properties of Ag clusters with a diameter of up to 5.5 nm grown inside superfluid helium nanodroplets (He(N)) and deposited on an amorphous C surface. With high resolution transmission electron microscope images we are able to show that in addition to the crystalline face centered cubic (fcc) structure, noncrystalline icosahedral (Ih), and decahedral (Dh) morphologies are grown. Relative abundances (56% fcc, 31% Dh, and 13% Ih) as well as the size distribution of each morphology (mean diameters d(fcc)=2.62(5) nm, d(Dh)=3.34(7) nm, and d(Ih)=3.93(2) nm) do not reflect the situation expected from pure energetic considerations, where small Ihs should be followed by medium sized Dhs and large fccs. Instead, kinetic factors seem to play an important role in the formation of these structures, as it appears to be the case for clusters formed by inert gas aggregation. Considering the low temperatures (0.37 K) and extremely high cooling rates, we discuss basic ideas that might lead to a qualitative picture of the cluster formation process inside He(N).

Printing functional nanostructures: a novel route towards nanostructuring of organic electronic devices via soft embossing, inkjet printing and colloidal self assembly of semiconducting polymer nanospheres

A new method for nanostructure formation from conjugated polymers is presented: an aqueous dispersion of semiconducting polymer nanospheres (SPNs) is deposited by inkjet printing onto a polymer surface patterned by soft embossing. By interaction between the spheres and the undulated surface a self assembly process is triggered, resulting in the formation of SPN nanostructures determined by the template. Both template layer and assembled SPNs can be incorporated into a device structure. We demonstrate a light emitting structure for use in polymer light emitting devices including analyses by atomic force microscopy and Kelvin probe force microscopy.

Inkjet printed polymer light-emitting devices fabricated by thermal embedding of semiconducting polymer nanospheres in an inert matrix

An aqueous dispersion of semiconducting polymer nanospheres was used to fabricate polymer light-emitting devices by inkjet printing in an easy-to-apply process with a minimum feature size of 20μm. To form the devices, the electroluminescent material was printed on a nonemitting polystyrene matrix layer and embedded by thermal annealing. The process allows the printing of light-emitting thin-film devices without extensive optimization of film homogeneity and thickness of the active layer. Optical micrographs of printed device arrays, electroluminescence emission spectra, and I∕V characteristics of printed ITO/PEDOT:PSS/PS/SPN/Al devices are presented.

An EBIC Model for TCAD Simulation to Determine the Surface Recombination Rate in Semiconductor Devices

A 3-D electron-beam-induced current (EBIC) model was implemented in technology computer aided design simulations. The model uses a carefully designed charge carrier generation profile that describes how an electron beam induces charge carriers in a semiconducting device and then drift-diffusion equations are solved to determine the resulting current. The simulation provides a map of the EBIC signal, which can be compared with experimental 2-D profiles. This comparison can be used to fit parameters such as the surface recombination rate which is otherwise difficult to fit in completed devices. Additional experimental data for these fits are obtained by performing the experiments at different electron beam energies and thereby generating carriers at different depths in the sample. The experiments were performed on cross sections of silicon photodiodes with varying surface preparations. A strong influence of the surface preparation method on the charge carrier diffusion was observed.