Electronic Transport in Ultrathin Gold Films on Si(111)

The morphology and electronic transport of ultrathin Au films with thicknesses d = 1 ? 5 monolayers (ML) deposited on Si(111)7 × 7 surfaces is investigated by in situ scanning tunneling microscopy and electrical resistance measurements for temperatures T = 2 ? 300 K. With decreasing film thickness, i.e. decreasing sheet conductance G_s, a transition from a weakly conducting regime described by a logarithmic temperature dependence to an insulating regime occurs. In the insulating regime, the temperature dependence is described by G_s ∝ exp[?(T ₀ /T) ⁿ] with an exponent n which gradually changes from 0.69 to 1 with decreasing film thickness. In contrast, for the Si(111)6 × 6-Au reconstruction obtained after annealing, an exponent n = 1/2 is found suggesting the formation of a soft Coulomb gap due to electron-electron interaction. PACS numbers: 68.37.-d, 68.55.-a, 73.50.-h, 73.25.+i, 81.15.-z     

Oxidative erosion of graphite in air between 600 and 1000 K

The oxidative erosion of seven types of graphite has been investigated by heating in air at temperatures between 600 and 1000 K. The specimens include pyrolytic graphite, fine-grain graphites, carbon-fibre composites (CFC), and graphites doped with Si and Ti. The weight loss was measured using a microbalance, the surface morphology by scanning electron microscopy, and the composition of the surface layer by MeV ion beam techniques. Pyrolytic graphite is least affected by erosion, while pure and Si-doped CFCs erode particularly fast. Typical erosion rates for specimens with a surface area of ?4 cm² are below 0.2 μg/m² s at 600 K for all graphite types, and at 900 K range from 0.34 mg/m² s for pyrolytic graphite to about 9 mg/m² s for the strongest eroding types. The temperature dependence of the erosion rate of all types of graphite studied is well described by an activation energy of 1.7 eV. The erosion rates of these graphites are by far lower than the removal rates for deposited amorphous hydrocarbon layers. In contrast to all other types, the Ti-doped graphite absorbs a significant amount of oxygen reaching up to ?5% of its original mass. Once the oxygen uptake is saturated, it erodes with rates similar to those of the strongest eroding types.     

Plasma printing: patterned surface functionalisation and coating at atmospheric pressure

A new plasma-based micropatterning technique, here referred to as plasma printing, combines the well known advantages given by the nonequilibrium character of a dielectric barrier discharge (DBD) and its operation inside small gas volumes with dimension between tens and hundreds of micrometres. The discharge is run at atmospheric pressure and can be easily implemented for patterned surface treatment with applications in biotechnology and microtechnology. In this work the local modification of dielectric substrates, e.g. polymeric films, is addressed with respect to coating and chemical functionalisation, immobilisation of biomolecules and area-selective electroless plating.     

Development of a multifunctional coating system for laser-induced material transport

The aim of our research is to develop a novel surface coating for the use in laser microdissection and laser pressure catapulting (LMPC). LMPC is a contact- and contamination-free technique to separate histologic material and living cells for further proteomic and genomic analysis. Several physico-chemical functions must be included within the optimum coating system designed for this purpose, like optical absorption at the laser wavelength, combined with optical transparency in the visible region, a control of the laser ablation process, mechanical stability and biocompability for the adhesion of the histologic material.To achieve the optimum system the combination of several layers is required. The optical absorbance to capture the radiation energy from a frequency-tripled Nd:YAG laser (λ = 355 nm) is reached by a thin layer of zinc oxide (ZnO), deposited by hollow cathode gas flow sputtering. The laser ablation process is controlled by a polyelectrolyte multilayer, consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS). The evaporation of chemisorbed water from the film is used to promote the catapulting process. For the mechanically stable, laser-dissectible layer organic coatings, like photoresists or lacquers, are suitable. Silica-containing polyacrylate nanocomposites were employed for this purpose.The investigation of the coating system included LMPC experiments with varying compositions of the layer system. The best results were obtained using a system consisting of ZnO, a polyelectrolyte multilayer deposited from 0.1 M Na₂SO₄ containing polymer solutions, and a 1.5-μm thick layer of the polyacrylate nanocomposite.To check the quality of the developed system, experiments with the commonly used poly(ethylene naphthalate) (PEN) foil were performed simultaneously. In addition to the determination of the parameters required for LMPC, quantitative real-time Polymerase Chain Reaction (rt-PCR) of the dissected material verified the benefit of the new system.     

Wirtschaftlichkeitsanalyse für die Auswahl, die Migration und den Betrieb eines Campus-Management-Systems

An increasing number of students, together with organizational and technological requirements, pose new challenges for universities. For these reasons, Campus Management Systems provide a solution for the necessary IS-support in student administration. In order to ensure cost-effectiveness, an extensive cost-utility analysis of the campus management systems under consideration is required. The process model illustrated here facilitates a ten-step cost-utility analysis for the selection, migration and operation of a campus management System. The process-oriented approach addresses the challenges posed by cost and benefit allocation. The subsequent ten steps, using the case analysis of two large German universities, show that the implementation of an integrated campus management system can lead to significant cost saving effects. The presented process model enables comparative calculations of differences with regard to the alternatives. The approach enables a comprehensive decision support system for the selection of a university-specific and individually applicable campus management system.     

The modified outflow funnel — A device to assess the flow characteristics of powders

Flow regulators are added to solid pharmaceutical formulations to improve the flow properties of powder mixtures. During the blending process the glidants adsorb successively at the surface of the host particles and thus lead to a reduction of attractive forces. A large variety of flow additives based on silicon dioxide is commercially available, but not all glidants are just as well suited for each technological problem or each cohesive bulk powder. To assess the improvement of the flowability parameters caused by a glidant a classification system and an adequate measuring device is needed. We would like to present a new measuring device to evaluate the flow enhancing potency of glidants. The modified outflow funnel features a stirrer that acts in the region of bulk arches obstructing the outflow process of a cohesive powder. By destruction of the bulk arches powder outflow is enabled and the time needed for emanation can be measured as a parameter of the flow properties. In addition other measuring parameters like the force needed to destroy the bulk arches are capable to evaluate the flowability of the powder mixture. Binary powder mixtures consisting of corn starch and flow regulator were blended in a Turbula® mixer for a defined period of time. The flow regulators were represented by fumed silica and a selection of various types of SIPERNAT^® precipitated silica provided by Evonik Degussa GmbH, Hanau, Germany. Flowability parameters of the mixtures were characterized with a modified outflow funnel, Hausner Ratio and a shear tester.     

Me-DLC films as material for highly sensitive temperature compensated strain gauges

In technical applications strain gauges are widely used. Apart from conventional polymer foil based strain gauges that are glued to the work piece surface, sputtered strain gauges are already commercially used in special applications. Those sputter strain gauges are typically made of NiCr alloy and the sensor layer is as sensitive to strain as the ones used in the glued strain gauges with a gauge factor of 2, but neglecting problems of creeping and swelling of the involved polymer materials. Diamond-like carbon (DLC) films offer significantly higher strain sensitivity, but usually they are also very sensitive to temperature effects. Using metal doped diamond-like carbon (Me-DLC), higher strain sensitivity than conventional metal based systems, in combination with thermal compensation, is possible. The influence of different process parameters on the gauge factor and temperature coefficient of resistance (TCR) of DLC and Me-DLC films produced in industrial sputtering systems was investigated. Gauge factors up to 13 in combination with a high negative TCR in the range of a few thousand ppm/K were reached with sputtered DLC films. The substrate bias voltage in particular showed a strong influence on the resulting gauge factor of the films. For Me-DLC films different deposition methods (dc and rf sputtering) and various doping metals (Ag, Ni, Ti, and W) were investigated. Using dc sputtering of the Me-DLC films only Ni-DLC showed gauge factors slightly higher than 2. Furthermore, only for Ni-DLC zero crossing of the TCR was observed by variation of the metal content. Using rf excitation especially Ni-DLC films showed gauge factors exceeding values of 15 in combination with a TCR close to zero.     

Site selectivity in praseodymium- and bismuth-substituted gadolinium gallium garnet epilayers

Praseodymium- and bismuth-substituted gadolinium gallium garnet (GGG) layers have been prepared by liquid phase epitaxy on (111)- and (110)-orientated GGG substrates. By an investigation of linear dichroism of Pr³⁺-transitions, the supercooling dependence of dodecahedral site selectivity in Pr-substituted GGG can be shown to differ considerably for (110)- and (111)-epitaxial layers: An increase of site selectivity with supercooling is found in (111) layers while it is constant in (110) layers. The long wavelength ¹S₀ → ³P₁-transition of the Bi³⁺ ion has been utilized to detect site selectivity in (110)- orientated Bi-substituted GGG layers.