Short Summaries of Individual NanoBiC Projects
piOligo – Optical and charge transport properties of rationally designed p -systems on the nanoscale
The goal of this project is to develop highly tunable organic nanostructures on (metal) surfaces. The surface plays a dual role, initially as a support during the synthesis of the nanostructures from soluble, lower molecular-weight precursors and subsequently for electronically addressing the nanosystems prepared. The wealth of potential applications for these composites includes dyesensitized solar-cells, organic field-effect transistors and organic light-emitting diodes.
Precursors will be selected from boron-doped or perfluorinated conjugated p-systems. Crosslinking of these molecular building blocks on the surfaces will be attempted in a variety of ways ranging from mere heating to spatially focused energy intake by electron beam techniques.
For the rational design of the corresponding materials, quantum chemical investigations with specifically developed methods are essential and will be carried out at all stages of the project: (1) prediction of the most promising monomeric structures, (2) analysis of key elementary steps during the oligomerization, (3) analysis of cooperative interactions between the subunits in the ensemble, and (4) rationalization and prediction of material properties.
This will result in a deeper insight into fundamental charge transport processes and provides, in addition, novel materials for micro- and optoelectronic applications. In the long run, the construction of functional devices such as field effect transistors, light-emitting devices and possibly also sensors can be envisaged.
eNet – Irradiation-induced formation of silicon nanostructures from oligoand polymeric precursors
Nano- and micrometer-scaled silicon structures are of central importance not only for microelectronic but also for photovoltaic and ultimately optoelectronic applications. The goal of this project is to explore alternative production methods for these kinds of structures by application of procedures for the highly localized chemical transformation of precursors or preformed structures. The size of the resulting structures will be controlled through application of spatially localized particle beams.
Strategy 1 starts from a class of oligo- and polymeric (perchloro)silanes that recently became available in kg-quantities by a route developed by one of us (N. Auner). By introduction of energy into these molecules, either with or without added catalysts, elemental silicon can be formed. The goal of this strategy is to use highly focused electron beams to write silicon wires and nanodots of relevance for microelectronics or photovoltaic applications.
The same precursors will be used in strategy 2, but now to form thin silicon films by thermal treatment. These films will then be punctured by energetic heavy ions to establish nanosized holes. We expect that these holes disturb the density of states (DOS) of the solid in a specific way, thereby generating new optical and electronic properties. As a long-term perspective, we intend to develop techniques to lift these punctured films off the substrate and to use them as highly stable (mechanically and chemically) membranes, e.g., for electron spectroscopy or ultrafiltration.
EBID – Electron beam induced deposition for nanostructures. Microscopic growth simulation
Electron beam induced deposition (EBID) is a method suitable for template free fabrication of nanostructures. Although this method has been used extensively in recent years, a rigorous understanding and control of the growth process is still missing.
By a combination of theoretical simulations and control experiments we plan to unveil some of the growth steps in the EBID process. Our goal is to obtain a multi-scale insight into the EBID process.
Granem – Granular electronic materials – from disordered nanocomposites to nanodot lattices(Prof. Dr. Michael Huth)
Granular electronic materials are (dis-) ordered arrays of metallic or semiconducting particles of a typical size ranging from a few to hundred nanometers. The particles are embedded in an insulating matrix. For small-diameter particles the phrase „artificial atoms“ has been coined. Granular electronic materials have been recognized as artificial solids with adjustable electronic properties making them important model systems for nanotechnological applications and more fundamental studies on the interplay of electronic correlations, size effects, dimensionality and disorder.
Electron beam induced deposition (EBID) is a direct writing technique for the preparation of micron to nanometer sized structures of amorphous, granular (nanocomposite) or polycrystalline nature. This technique can provide granular electronic metals with lateral control on the nanometer scale.
The project aims at studying the electronic properties of two- and one-dimensional nanodot arrays of metallic islands. It furthermore aims at developing the EBID techniques towards binary alloy sytems for the realization of metallic nanocomposite structures of Pt and Au with Co impurities, as well as for magnetically highly anisotropic alloys and intermetallic compounds, such as CoPt.
NanoC – Preparation, modification and characterization of nanochannels in polymer membranes(Prof. Dr. Wolfgang Ensinger)
The objective of this project is the controlled fabrication of nanochannels for future application as highly sensitive and selective nanoanalyzers. The nanochannels are generated by irradiation of polymer foils with GeV heavy ions and subsequent chemical etching of the tracks along the ion paths. Chemical functionalization of the channel walls allows the adjustment of selective properties of the nanoanalyzers.
NanoMag – Spin-dependet scattering in magnetic and Kondo nanowires(Prof. Dr. Michael Huth)
Metallic nanowires of well-defined shape and composition are well-suited for studying spindependent scattering resistance contributions for ferromagnets and Kondo systems. First, the scattering of spin-polarized electrons at magnetic domain walls formed in bi-conical Co nanowires and cylindrical multilayered Co1-xCux/Co1-yCuy (x≥0, y>x) nanowires shall be analyzed. Second, cylindrical multilayered Co1-xCux/Cu (x≥0.90) nanowires shall be employed for studying resistance contributions from the Kondo effect in multilayers in conjunction with the Kondo screening cloud concept. For the preparation of the metallic nanowires electrochemical deposition in etched iontrack membranes will be employed. By heavy-ion irradiation of polycarbonate foils at the UNILAC accelerator of GSI, and subsequent chemical etching, membranes with conical, bi-conical and cylindrical pores, and diameters ranging between few nm and micrometers, will be fabricated. Nanowire composition, and multilayer dimensions (diameter and height), will be determined by temperature, voltage, and electrolyte employed during the electrodeposition process.
NanoL – Nanolesions induced by heavy ions in tissue slices(Prof. Dr. Ingo Bechmann)
In a low dose field of g -rays, such as that normally experienced on Earth due to background radiation, each human cell is traversed by very few electrons, which produce little damage. However, for energetic heavy ions, the situation is different. A low dose, such as the one experienced in a manned mission to the International Space Station or the Moon, corresponds to only a few tracks, but each track can affect a whole tissue or organ, and each cell which is found in the path of the ion. The central part of the track, where most of the energy is deposited, has a radial extension of only a few nm, while a lower energy is deposited at larger distance by energetic d -rays. So, each heavy ion will produce a nanochannel in neighborhood cells in the living organ, a situation that make the concept of low dose itself useless. Although the concept of „microlesion“ induced by heavy ions in space was acknowledged long ago, there is a lack of experimental models for testing the hypothesis that they represent a distinct, unique damage at tissue level. In fact, „strikes“ of DNA damage can now be visualized in living cells exposed to heavy ions at GSI, but not yet in tissues. Indirect evidence of microlesions comes form „light flashes“ reported by astronauts in space missions, where a visible „strike“ is actually produced by the passage on an energetic particle in the eye, and by the constant effectiveness per unit dose of very heavy ions in intestinal tissue, contrary to the decrease observed in single cells, which could correspond to the fact that the biological effect is caused in the tissue not by the dose, but by the number of tracks producing nanochannels. The recent method of organotypic tissue slices developed at the University of Frankfurt makes it possible to study the hypothesis of nanochannels in tissue. In fact, the thin tissue slices obtained from animals or humans can be kept alive for weeks after resection, and exposed to heavy ions at GSI. Our goal is to study the tissue damage with molecular markers (for apoptosis or necrosis) and high-resolution microscopy, in order to determine the putative effect of the correlated nanochannel-like damage in the tissue. The damage will then be compared with that on isolated cells. Studies will be performed using organotypic human slice cultures of the hippocampus exposed to heavy ions accelerated at GSI and we will study their effects on stem cell survival, proliferation and differentiation by combining established methods of live-imaging and immune cytochemistry (BRDU, nestin, NTDPase, doublecortin, βIII-tubulin, NeuN, activated caspase 3), as well as fluorescent dye leaking through the nanopores. The experimental efforts accompanied by the development of theoretical calculations (i.e. large scale numerical simulations) for the interactions of heavy ions with DNA, individual cells and tissue. This will be done by exending the established simulation package GEANT4 to include realistic interaction probabilities nd microscopic models for the focused energy deposition. The major tasks here are the multiple scales of the problem at hand (resulting in a tremendous need for computational resources) and the up to now not well known interaction cross sections. We intend to solve these problems by use of novel computational techniques employing state of the art graphic processing units and strong interactions with the experimental side of this project.
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