Thomas A. Wagner

An agent-oriented approach to industrial automation systems

Multi-agent systems have been successfully used in a number of industrial applications. However, in the domain of industrial automation systems, little practical experience about the use of agents in such a demanding environment exists. Nowadays automation systems face new challenges and therefore new concepts are needed to meet them. This paper presents a vision of using agents within industrial automation systems from the point of view of automation engineering. To this end, the characteristic structures of automation systems are analyzed and opportunities, as well as advantages, of applying agent-oriented concepts are investigated. A possible approach for the integration of a multi-agent system into existing automation systems is introduced and illustrated by an application example.

Applying Agents for Engineering of Industrial Automation Systems

Designing, operating and maintaining industrial plants require extensive and complex engineering processes. An integrated engineering process considering all different aspects, data and workflow of plant automation design as well as interoperability to other systems is the key to more efficiency and lower costs of engineering tasks in the plant life cycle. There exists no comprehensive and satisfying solution to this problem today. However, an agent-oriented view can lead to fundamentally new and promising approaches to an integrated plant engineering process. The goal of this paper is to clearly identify the specific goals and challenges in engineering industrial plants and to show that agents are a beneficial approach to meet them. To this end, an agent-oriented solution for integrated engineering of automation systems is presented, applying the advantages of agent concepts while considering the constraints of existing automation structures.

Single to polycrystalline transition in silicon growth by ion-assisted deposition at low temperatures

We investigate the microstructure of thin silicon films produced at temperatures below 450 °C by ion-assisted deposition. Our transmission electron microscopy investigations show that in this temperature regime epitaxial growth breaks down at a critical film thickness beyond which the growth changes to polycrystalline or amorphous. The critical thickness increases with an increase in temperature. We use this effect that is well known from molecular beam epitaxy to analyze and quantify growth on silicon substrates with different surface normal orientations at various temperatures. Our results indicate that epitaxy works by far the best for the 〈001〉 surface normal orientation. The critical epitaxial thickness hepi decreases in the sequence hepi(001)≫hepi(113)>hepi(011)>hepi(111). The respective activation energies of 0.6, 2.1, 1.2, and 1.4 eV are evaluated from the temperature dependence.

Ion-Assisted Deposition of Silicon Epitaxial Films with High Deposition Rate Using Low Energy Silicon Ions

Ion-assisted deposition (IAD) enables low temperature (≥ 435°C), high-rate (≤ 0.5 μm/min) epitaxial growth of silicon films. Therefore, IAD is an interesting deposition technique for microelectronic devices and thin film solar cells. The Hall-mobility of monocrystalline epitaxial layers increases with deposition temperature T dep and reaches values comparable to those of bulk Si at T dep ≥ 540°C. Polycrystalline epitaxial layers exhibit inhomogeneous electrical properties, as shown by Light Beam Induced Current measurements. Recombination within the grains dominates over recombination at grain boundaries. Secco etching identifies an inhomogeneous density of extended structural defects in the polycrystalline epitaxial layers and in the substrate. A major part of the extended defects in the epitaxial layers originates from defects in the substrate.

Flexible monocrystalline Si films for thin film devices from transfer processes

Transfer of monocrystalline silicon films to arbitrary foreign substrates is a promising way for the fabrication of high quality silicon films on foreign substrates, demonstrated by solar cell efficiencies on glass as high as 16.6 % in the past. Transfer technologies also enable the use of flexible substrates. This paper investigates the mechanical stability of the separation layer for two different morphologies. First measurements on the minimum bending radius of unsupported silicon films are presented that allow us to estimate minimum curvatures for flexible monocrystalline devices. Finally, we report the first flexible monocrystalline thin film silicon solar cell of 4 cm 2 with an independently confirmed efficiency of 14.6 %.

A Simple Method to Extract the Diffusion Length from the Output Parameters of Solar Cells - Application to Polycrystalline Silicon

This work presents a simple method to obtain the effective diffus ion length Leff of a solar cell directly from measured values of open circuit voltage, shor t circuit current density, and the doping density in the base of the cell. In the second part of this pa per, we extract Leff from literature data of polycrystalline silicon cells, with grain sizes from 10 -2 to 10 μm, modeling the extracted Leff as a function of the grain size g, and the recombination velocity SGB at the grain boundaries. For g > 1 μm, our model predicts 10 5 < SGB < 10 7 cm/s. Cells with g < 1 μm, are understood with 10 1 < SGB < 10 cm/s. This finding supports the hypothesis that the key to high effic ienc es at small grain sizes is the use of {220}-textured films.