Michael Pabst

Patterned self-assembly of gold nanoparticles on chemical templates fabricated by soft UV nanoimprint lithography

Chemical templates for the patterned immobilization of gold nanoparticles were fabricated by soft UV nanoimprint lithography. The template structures were fabricated by means of the consecutively performed process steps of nanoimprint lithography, reactive ion etching, chemical functionalization with amino groups, and lift-off of imprint resist. These chemical templates were used for the defined assembly of 20 nm diameter citrate stabilized gold nanoparticles from aqueous solution. By reducing the ionic strength of the solution, one- and zero-dimensional particle assemblies were generated on sub-100-nm template structures. By this means, the pattern resolution predefined by the lithography process could be easily enhanced by dilution of the nanoparticle solution.

Simulation of bionic electrolocation sensor based on weakly electric fish

Weakly electric fish employ active electrolocation for orientation and navigation in their environment at night and are thus able to perceive an electrical image of their surroundings even in complete darkness. This principle of active electrolocation is adopted to design a technical sensor system, which will able to detect and to analyze the walls of blood vessels and obstacles within them. The main objective involves the construction and testing of the artificial sensor, including the electronic circuits for signal analysis. To establish effective and optimal parameters for the sensor FEM analysis is done. Simulation results demonstrate the feasibility of proposed design of catheter based electrolocation sensor. Further by implementing efficient design of amplifier and signal processing circuit it is possible to develop biologically inspired technical sensor for routine blood vessel diagnostics and be adopted for finding and analyzing pathologic changes of artery walls.

Interfacing Neurons and Silicon-Based Devices

The combination of biological signal processing elements such as membrane proteins, whole cells, or even tissue slices with electronic transducers for the detection of physical signals creates functional hybrid systems that bring together the living and the technical worlds. Functional coupling of physiological processes with microelectronic and nanoelectronic devices will have great impact for a wide range of applications. The high sensitivity and selectivity of biological recognition systems with a manufactured signal-detection and processing system will open up exciting possibilities for the development of new biosensors as well as for new approaches in neuroscience and computer science. This includes: (a) pharmacological as well as toxicologically lab on a chip concepts, which allows fast, high-throughput screening of potential drugs; (b) the use of the high sensitivity and selectivity of biological recognition systems with signal-amplification cascades for the development of biosensors with unprecedented detection threshold; and (c) the multisite interfacing of neuronal networks with arrays of electronic devices on the microscopic level of individual nerve cells or cell processes would facilitate spatiotemporal mapping of brain dynamics.

Halo containment in the ESS linac to ring transfer line

The key issue of the accelerator part of the European Spallation Source ESS is the loss free ring injection. For achieving this goal, the linac beam has to be collimated in both transverse planes and limited in energy spread. By a bunch rotation cavity, positioned 75 m after the linac, the energy spread is reduced by a factor 3. In addition the mean kinetic energy has to be ramped during the injection pulse. For a bunch current of 214 mA, space charge forces are present in all 3 planes. They act quite drastically longitudinally due to the lack of focusing. After the bunch rotation cavity, where the bunch length is larger than the pipe radius, image forces in all 3 planes can no longer be neglected. In order to fulfill the collimation requirements for loss free ring injection under various beam current conditions, transverse beam scraping and a longitudinal two stage collimation system are foreseen. There are two independently phased cavities, one for energy ramping and another for bunch rotation. The bunc...

Bioelectronic Detection Schemes for Biomedical and Environmental Sensing

An artificial nose or tongue could be a real benefit at times: this kind of biosensor could sniff or taste out poisons, explosives or drugs, for instance. The senses of living organisms function using various mechanisms, among other things utilizing membrane proteins as receptors. Membrane proteins have several important functions in the cell, one of which is to act as receptors, passing on signals from molecules in the air or liquid, for example, to the cell interior. This article is focusing on the functional coupling of biological signal processing and recognition elements with micro- and nanoelectronic semiconductor devices and circuits for the development of future biosensors and molecular diagnostics tools.

High intensity H− injector linacs

Abstract An overview is given for the at NuFact ’99 as most promising identified 4 MW proton driver concepts for neutrino factories. The H− injector linac needs at least 25 mA ionsource current and more than 0.1 MW beam power at the linac end. The dominating design feature of any high intensity injector linac is to bring particle losses down to 1 W/m at the linac end and to guarantee loss-free ring injection afterwards. Halo formation of mismatched bunched beams in periodic focusing systems is discussed. RF control problems are summarized for at 100 Hz rep. rate pulsed medium β superconducting cavities either made as bulk niobium or as niobium sputtered copper cavities. The high rep. rate leads to remaining cavity wall deformation from pulse to pulse.

Core and halo particle dynamics of high intensity proton beams

A very critical design issue for a high intensity proton linac is to keep particle losses below 1 W/m at the high energy end allowing unconstrained hands-on maintenance. For the ESS linac, with its 214 mA peak current, Monte Carlo simulations with up to one million particles are performed. Single particle trajectories are shown along the linac demonstrating the existence of a space charge potential with non-linear terms and transverse-longitudinal coupling. Radial halo particles at the final energy of 1.334 GeV start at 70 MeV at the boundary of the longitudinal phase space and also transversely close to a boundary of a 4D waterbag distribution. The single particle motion of these halo particles is characterised, on the average, by conservation of the sum of all three emittances. Trajectories are presented for both horizontal-vertical coupling and also transverse-longitudinal coupling. Core particles have a very different behaviour. For core particles, located around the rms emittances at 70 MeV, the single particle emittances can be either increased or decreased.

Particle dynamics in a DTL for high intensity heavy ion beams for inertial fusion

Multi-particle beam dynamics calculations in presence of large beam currents have been carried out for a heavy ion Drift Tube Linac (DTL), in the framework of a European study group on Heavy Ion Driven Inertial Fusion (HIDIF). Linac design parameters were determined for high transmission and low emittance growth; then statistical errors as well as on-axis mismatch were added. The influence of field errors and different mismatch combinations on beam halo formation and emittance increase has been studied numerically, e.g. phase and amplitude jitters of the rf field, small changes of quadrupole gradients, mismatch of beam bunches at linac input. For proper ring injection, a transfer line and a bunch rotation cavity have to be inserted between linac and storage rings. The energy spread reduction after bunch rotation has been investigated both numerically and analytically, comparing an ideal case with a more realistic one which includes rf errors and mismatch.