Showing papers by "Johannes Kepler University of Linz published in 2002"

A low-bandgap semiconducting polymer for photovoltaic devices and infrared emitting diodes

Abstract: A novel low-bandgap conjugated polymer (PTPTB, E-g = similar to1.6 eV), consisting of alternating electron-rich N-dodecyl-2,5-bis(2'-thienyl)pyrrole (TPT) and electron-deficient 2,1,3-benzothiadiazole (B) units, is introduced for thin-film optoelectronic devices working in the near infrared (NIR). Bulk heterojunction photovoltaic cells from solid-state composite films of PTPTB with the soluble fullerene derivative [6,6]-phenyl C-61 butyric acid methyl ester (PCBM) as an active layer shows promising power conversion efficiencies up to 1% under AM1.5 illumination. Furthermore, electroluminescent devices (light-emitting diodes) from thin films of pristine PTPTB show near infrared emission peaking at 800 nm with a turn on voltage below 4 V. The electroluminescence can be significantly enhanced by sensitization of this material with a wide bandgap material such as the poly(p-phenylene vinylene) derivative MDMO-PPV.

The shadow economy

Abstract: Measurement of the shadow economy is notoriously difficult as it requires estimation of economic activity that is deliberately hidden from official transactions. Surveys typically understate the size of the shadow economy but econometric techniques can now be used to obtain a much better understanding of its size. The shadow economy constitutes approximately 10 per cent of GDP in the UK; about 14 per cent in Nordic countries and about 20 - 30 per cent in many southern European countries. The main drivers of the shadow economy are (in order): tax and social security burdens, tax morale, the quality of state institutions and labour market regulation. A reduction in the tax burden is therefore likely to lead to a reduction in the size of the shadow economy. Indeed, a virtuous circle can be created of lower tax rates, less shadow work, higher tax morale, a higher tax take and the opportunity for lower rates. Of course, a vicious circle in the other direction can also be created.

On the Political Economy of Environmental Policy

Abstract: In the past there was hardly any use of economic instruments in environmental policy, mainly command and control measures were used. More recently, ecological taxes as well as tradable permits became more popular and voluntary agreements have been implemented. Using the Public Choice approach we ask for the reasons of this wider acceptance of economic instruments. We conclude that the use of market based instruments in environmental policy has not increased very much and their impact on the actual situation is still rather low, but there is hope of at least some increase in the future.

Double-cable polymers for fullerene based organic optoelectronic applications

Abstract: Conjugated polymers are used increasingly for the fabrication of electronic and optoelectronic devices like light emitting diodes (LEDs) and photovoltaic (PV) elements. A breakthrough in realising a promisingly efficient conversion of solar energy into electrical energy has been achieved by using blends of soluble electron-donor type conjugated polymers with fullerenes as electron-acceptor, transporting component. This “bulk heterojunction” approach suggests the preparation of intrinsically bipolar materials as a way to control both electronic and morphological properties at once. On these bases, the covalent grafting of fullerene moieties to conjugated backbones seems promising for the preparation of intrinsically bipolar polymeric materials (double-cable polymers) alternative to conjugated polymer/fullerene composites. The recent developments on the design, the characterisation and the application of this novel class of fullerene functional materials are reviewed.

Collective symbolic coping with new technology: knowledge, images and public discourse

Abstract: Using data from policy analyses, media analyses and a European-wide survey about public perceptions of biotechnology conducted in 1996 and again in 1999, it is shown how a country's public develops an everyday understanding of a new technology (genetic modification) construed as potentially harmful by the media. To understand the reliance on images and related beliefs, we propose a theory of collective symbolic coping. It identifies four steps: first, the creation of awareness; second, production of divergent images; third, convergence upon a couple of dominant images in the public sphere; fourth, normalization. It is suggested that symbolic coping occurs in countries where a recent increase in policy activity and of media reporting has alerted the public; that this public show a high proportion of beliefs in menacing images; that these beliefs are relatively independent of pre-existing popular science knowledge; and that they are functionally equivalent to scientific knowledge in providing judgmental confidence and reducing self-ascribed ignorance. These propositions are shown to be true in Austria and Greece. Several implications of the theory are discussed, including social representation theory and public understanding of science.

Integrated Service Modelling for Online One-stop Government

Abstract: One-stop government is an important development within the current initiatives of e-government. It refers to a single point of access to electronic services and information offered by different public authorities. Online one-stop government requires all public authorities to be interconnected and that the customer (citizen, private enterprise or other public administration) is able to access public services by a single point even if these services are provided by different public authorities or private service providers. It further requires that the customer be able to access these services in a well-structured and understandable manner meeting his/her perspectives and needs. Developing a national one-stop government portal calls for an integrated service modelling that requires a holistic reference framework. This paper discusses the general requirements for one-stop government. It then introduces the requirements for providing electronic public services in a one-stop platform. This is followed by an inv...

Optical constants of conjugated polymer/fullerene based bulk-heterojunction organic solar cells

Abstract: The performance of organic solar cells consisting of multiple layers, which are a few hundred nanometers thick, is determined by strong optical interference effects. In order to model their optical and photoelectrical behavior, we determined the optical constants of all components of this system. This was done by fitting model dielectric functions to reflection and transmission spectra of all layers in the solar cell device. We put a special emphasis on understanding the optical behavior of the photoactive bulk heterojunction film, which consists of a composite of semiconducting polymers with fullerenes.

Analysis of iterative methods for saddle point problems: a unified approach

Abstract: In this paper two classes of iterative methods for saddle point problems are considered: inexact Uzawa algorithms and a class of methods with symmetric preconditioners. In both cases the iteration matrix can be transformed to a symmetric matrix by block diagonal matrices, a simple but essential observation which allows one to estimate the convergence rate of both classes by studying associated eigenvalue problems. The obtained estimates apply for a wider range of situations and are partially sharper than the known estimates in literature. A few numerical tests are given which confirm the sharpness of the estimates.

Low-density spin susceptibility and effective mass of mobile electrons in Si inversion layers.

Abstract: We studied the Shubnikov-de Haas (SdH) oscillations in high-mobility Si-MOS samples over a wide range of carrier densities n approximately (1-50)x10(11) cm(-2), which includes the vicinity of the apparent metal-insulator transition in two dimensions (2D MIT). Using a novel technique of measuring the SdH oscillations in superimposed and independently controlled parallel and perpendicular magnetic fields, we determined the spin susceptibility chi(*), the effective mass m(*), and the g(*) factor for mobile electrons. These quantities increase gradually with decreasing density; near the 2D MIT, we observed enhancement of chi(*) by a factor of approximately 4.7.

Automating requirements traceability: Beyond the record & replay paradigm

Abstract: Requirements traceability (RT) aims at defining relationships between stakeholder requirements and artifacts produced during the software development life-cycle. Although techniques for generating and validating RT are available, RT in practice often suffers from the enormous effort and complexity of creating and maintaining traces or from incomplete trace information that cannot assist engineers in real-world problems. In this paper we will present a tool-supported technique easing trace acquisition by generating trace information automatically. We will explain the approach using a video-on-demand system and show that the generated traces can be used in various engineering scenarios to solve RT-related problems.

An algebraic multigrid method for finite element discretizations with edge elements

Abstract: This paper presents an algebraic multigrid method for the efficient solution of the linear system arising from a finite element discretization of variational problems in H0(curl,Ω). The finite element spaces are generated by Nedelec's edge elements. A coarsening technique is presented, which allows the construction of suitable coarse finite element spaces, corresponding transfer operators and appropriate smoothers. The prolongation operator is designed such that coarse grid kernel functions of the curl-operator are mapped to fine grid kernel functions. Furthermore, coarse grid kernel functions are ‘discrete’ gradients. The smoothers proposed by Hiptmair and Arnold, Falk and Winther are directly used in the algebraic framework. Numerical studies are presented for 3D problems to show the high efficiency of the proposed technique. Copyright © 2002 John Wiley & Sons, Ltd.

Excitonic condensation in a symmetric electron-hole bilayer.

Abstract: Using diffusion Monte Carlo simulations we have investigated the ground state of a symmetric electron-hole bilayer and determined its phase diagram at T = 0. We find clear evidence of an excitonic condensate, whose stability however is affected by an in-layer electronic correlation. This stabilizes the electron-hole plasma at large values of the density or interlayer distance, and the Wigner crystal at low density and large distance. We have also estimated pair correlation functions and low-order density matrices to give a microscopic characterization of correlations as well as to try and estimate the condensate fraction.

The Size and Development of the Shadow Economies of 22 Transition and 21 OECD Countries

Abstract: Using the currency demand and DYMIMIC approaches estimates are presented about the size of the shadow economy in 22 Transition and 21 OECD countries. Over 2001/2002 in 21 OECD countries is the average size of the shadow economy (in percent of official GDP) 16.7% of "official" GDP and of 22 Transition countries 38.0%. The average size of the shadow economy labor force (in percent of the population of working age) of the year 1998/99 in 7 OECD-countries is 15.3% and in 22 Transition countries is 30.2%. An increasing burden of taxation and social security contributions combined with rising state regulatory activities are the driving forces for the growth and size of the shadow economy (labor force).

Domination of aggregation operators and preservation of transitivity

Abstract: Aggregation processes are fundamental in any discipline where the fusion of information is of vital interest. For aggregating binary fuzzy relations such as equivalence relations or fuzzy orderings, the question arises which aggregation operators preserve specific properties of the underlying relations, e.g. T-transitivity. It will be shown that preservation of T-transitivity is closely related to the domination of the applied aggregation operator over the corresponding t-norm T. Furthermore, basic properties for dominating aggregation operators, not only in the case of dominating some t-norm T, but dominating some arbitrary aggregation operator, will be presented. Domination of isomorphic t-norms and ordinal sums of t-norms will be treated. Special attention is paid to the four basic t-norms (minimum t-norm, product t-norm, Lukasiewicz t-norm, and the drastic product).

RF system concepts for highly integrated RFICs for W-CDMA mobile radio terminals

Abstract: The standardization phase for third-generation wide-band CDMA systems like the universal mobile telecommunication system, which will add broad-band data to support video, Internet access, and other high-speed services for untethered devices is running toward its finalization. As is typical for mobile communication systems standardization, sufficient RF performance has been assumed and most efforts have been put to digital baseband issues. This is especially true for the mobile phone transceivers, the RF part of which is (although its baseband part is much more complex in terms of number of devices) still the bottleneck of the entire system. Meanwhile, in the RF concept engineering of today's commercial products, an accurate prediction of the needed RF performance by using RF system simulation is indispensable. This is, in particular, the case with third-generation wireless systems, which, from the RF design point-of-view, are quite different from second-generation time-division multiple access/frequency-division multiple-access systems due to the fact that the user signals are now separated in the code domain rather than in the time and/or frequency domain. The paper gives an insight of how to derive receiver requirements for third-generation mobiles in terms recognizable by microwave designers, reports on the system simulation-based design, and performance of silicon-based RF integrated circuits for mobile terminal use, and discusses some future technologies and techniques and their possible impact on portable wireless devices.

Surface and Thin-Film Analysis

Abstract: The article contains sections titled: 1. Introduction 2. Electron Detection 2.1. X-Ray Photoelectron Spectroscopy (XPS) 2.1.1. Principles 2.1.2. Instrumentation 2.1.2.1. Vacuum Requirements 2.1.2.2. X-Ray Sources 2.1.2.3. Synchrotron Radiation 2.1.2.4. Electron Energy Analyzers 2.1.2.5. Spatial Resolution 2.1.3. Spectral Information and Chemical Shifts 2.1.4. Quantification, Depth Profiling, and Imaging 2.1.4.1. Quantification 2.1.4.2. Depth Profiling 2.1.4.3. Imaging 2.1.5. The Auger Parameter 2.1.6. Applications 2.1.6.1. Catalysis 2.1.6.2. Polymers 2.1.6.3. Corrosion and Passivation 2.1.6.4. Adhesion 2.1.6.5. Superconductors 2.1.6.6. Interfaces 2.2. Ultraviolet Photoelectron Spectroscopy (UPS) 2.3. Auger Electron Spectroscopy (AES) 2.3.1. Principles 2.3.2. Instrumentation 2.3.2.1. Vacuum Requirements 2.3.2.2. Electron Sources 2.3.2.3. Electron Energy Analyzers 2.3.3. Spectral Information 2.3.4. Quantification and Depth Profiling 2.3.4.1. Quantification 2.3.4.2. Depth Profiling 2.3.5. Applications 2.3.5.1. Grain Boundary Segregation 2.3.5.2. Semiconductor Technology 2.3.5.3. Thin Films and Interfaces 2.3.5.4. Surface Segregation 2.4. Scanning Auger Microscopy (SAM) 2.5. Other Electron-Detecting Techniques 2.5.1. Auger Electron Appearance Potential Spectroscopy (AEAPS) 2.5.2. Electron Energy Loss Methods 2.5.2.1. Electron Energy Loss Spectroscopy (EELS) and Core-Electron Energy Loss Spectroscopy (CEELS) 2.5.2.2. High-Resolution Electron Energy Loss Spectroscopy (HREELS) 2.5.3. Diffraction Methods 2.5.3.1. Low-Energy Electron Diffraction (LEED) 2.5.3.2. Reflection High-Energy Electron Diffraction (RHEED) 2.5.4. Ion-Excitation Method 2.5.4.1. Ion (Excited) Auger Electron Spectroscopy (IAES) 2.5.4.2. Ion-Neutralization Spectroscopy (INS) 2.5.4.3. Metastable Quenching Spectroscopy (MQS) 2.5.5. Inelastic Electron Tunneling Spectroscopy (IETS) 3. Ion Detection 3.1. Secondary Ion Mass Spectrometry 3.1.1. Static Secondary Ion Mass Spectrometry (SSIMS) 3.1.1.1. Principles 3.1.1.2. Instrumentation 3.1.1.2.1. Ion Sources 3.1.1.2.2. Mass Analyzers 3.1.1.3. Quantification 3.1.1.4. Spectral Information 3.1.1.5. Applications 3.1.1.5.1. Oxide Films 3.1.1.5.2. Interfaces 3.1.1.5.3. Polymers 3.1.1.5.4. Biosensors 3.1.1.5.5. Surface Reactions 3.1.1.5.6. Imaging 3.1.1.5.7. Ultrashallow Depth Profiling 3.1.2. Dynamic SIMS 3.1.2.1. Principles 3.1.2.2. Instrumentation 3.1.2.2.1. Ion Sources 3.1.2.2.2. Mass Analyzers 3.1.2.2.3. Detectors 3.1.2.3. Spectral Information 3.1.2.4. Quantification 3.1.2.5. Mass Spectra 3.1.2.6. Depth Profiles 3.1.2.7. Imaging 3.1.2.8. Applications 3.1.2.8.1. Implantation Profiles 3.1.2.8.2. Layer Analysis 3.1.2.8.3. 3D Bulk Element Distribution 3.2. Secondary Neutral Mass Spectrometry (SNMS) 3.2.1. General Principles 3.2.2. Electron-Beam and HF-Plasma SNMS 3.2.2.1. Principles 3.2.2.2. Instrumentation 3.2.2.3. Spectral Information 3.2.2.4. Quantification 3.2.2.5. Element Depth Profiling 3.2.2.6. Applications 3.2.3. Laser-SNMS 3.2.3.1. Principles 3.2.3.1.1. Nonresonant Laser-SNMS 3.2.3.1.2. Resonant Laser-SNMS 3.2.3.1.3. Experimental Setup 3.2.3.1.4. Ionization Schemes 3.2.3.2. Instrumentation 3.2.3.3. Spectral Information 3.2.3.4. Quantification 3.2.3.5. Applications 3.2.3.5.1. Nonresonant Laser-SNMS 3.2.3.5.2. Resonant Laser-SNMS 3.3. Ion-Scattering Techniques 3.3.1. Rutherford Backscattering Spectroscopy (RBS) 3.3.1.1. Principles 3.3.1.2. Instrumentation 3.3.1.3. Spectral Information 3.3.1.4. Quantification 3.3.1.5. Applications 3.3.2. Low-Energy Ion Scattering (LEIS) 3.3.2.1. Principles 3.3.2.2. Instrumentation 3.3.2.3. Information 3.3.2.4. Quantification 3.3.2.5. Applications 3.4. Other Ion-Detecting Techniques 3.4.1. Desorption Methods 3.4.1.1. Electron-Stimulated Desorption (ESD) and Electron-Stimulated Desorption Ion Angular Distribution (ESDIAD) 3.4.1.2. Thermal Desorption Spectroscopy (TDS) 3.4.2. Glow Discharge Mass Spectroscopy (GDMS) 3.4.3. Fast Atom Bombardment Mass Spectroscopy (FABMS) 3.4.4. Atom Probe Microscopy 3.4.4.1. Atom Probe Field-Ion Microscopy (APFIM) 3.4.4.2. Position-Sensitive Atom Probe (POSAP) 4. Photon Detection 4.1. Total-Reflection X-ray Fluorescence Analysis (TXRF) 4.1.1. Principles 4.1.2. Instrumentation 4.1.3. Spectral Information 4.1.4. Quantification 4.1.5. Applications 4.1.5.1. Particulate and Film-Type Surface Contamination 4.1.5.2. Semiconductors 4.1.5.2.1. Depth Profiling by TXRF and Multilayer Structures 4.1.5.2.2. Vapor Phase Decomposition (VPD) and Droplet Collection 4.2. Glow Discharge Optical Emission Spectroscopy (GD-OES) 4.2.1. Principles 4.2.2. Instrumentation 4.2.3. Spectral Information 4.2.4. Quantification 4.2.5. Depth Profiling 4.2.6. Applications 4.3. Surface-Sensitive IR and Raman Spectroscopy; Ellipsometry 4.3.1. Reflection - Absorption IR Spectroscopy (RAIRS) 4.3.1.1. Principles 4.3.1.2. Instrumentation and Applications 4.3.2. Surface Raman Spectroscopy 4.3.2.1. Principles 4.3.2.2. Surface-Enhanced Raman Scattering (SERS) 4.3.2.2.1. Instrumentation 4.3.2.2.2. Spectral Information 4.3.2.2.3. Applications 4.3.2.3. Nonlinear Optical Spectroscopy 4.3.3. UV - VIS - IR Ellipsometry (ELL) 4.3.3.1. Principles 4.3.3.2. Instrumentation 4.3.3.3. Applications 4.4. Other Photon-Detecting Techniques 4.4.1. Appearance-Potential Methods 4.4.1.1. Soft X-Ray Appearance-Potential Spectroscopy (SXAPS) 4.4.1.2. Disappearance-Potential Spectroscopy (DAPS) 4.4.2. Inverse Photoemission Spectroscopy (IPES) and Bremsstrahlung Isochromat Spectroscopy (BIS) 4.4.3. Ion-Beam Spectrochemical Analysis (IBSCA) 5. Scanning Probe Microscopy 5.1. Atomic Force Microscopy (AFM) 5.1.1. Principles 5.1.2. Instrumentation 5.1.3. Applications 5.2. Scanning Tunneling Microscopy (STM) 5.2.1. Principles 5.2.2. Instrumentation 5.2.3. Lateral and Spectroscopic Information 5.2.4. Applications 6. Summary and Comparison of Techniques 7. Surface Analytical Equipment Suppliers 8. Acknowledgement

Evidence and evaluation of the Bychkov-Rashba effect in SiGe/Si/SiGe quantum wells

Abstract: From spin resonance of two-dimensional (2D) conduction electrons in a modulation doped SiGe/Si/SiGe quantum well structure we find a 2D anisotropy of both the line broadening (dephasing time) and the g factor. Both can be explained consistently employing the Bychkov-Rashba (BR) term H_BR = alpha(k×sigma)·ez, which turns out here to be the dominant coupling between electron orbital motion and spin. We obtain a BR parameter of alpha= 0.55×10–12 eV cm—three orders of magnitude smaller than in quantum well structures based on III-V semiconductors, consistent with the much smaller spin-orbit coupling in Si.

Least-squares fitting of algebraic spline surfaces ∗

Abstract: We present an algorithm for fitting implicitly defined algebraic spline surfaces to given scattered data. By simultaneously approximating points and associated normal vectors, we obtain a method which is computationally simple, as the result is obtained by solving a system of linear equations. In addition, the result is geometrically invariant, as no artificial normalization is introduced. The potential applications of the algorithm include the reconstruction of free-form surfaces in reverse engineering. The paper also addresses the generation of exact error bounds, directly from the coefficients of the implicit representation.