Implementation of electron beam grey scale lithography and proximity effect correction for silicon nanowire device fabrication

An electron beam lithography exposure strategy combining efficient proximity effect correction (PEC) with multi-pass grey scale is compared with a more conventional strategy based on a single-pass exposure without PEC. Exposure results for different types of nanowire structures are presented. Line edge and line width roughness (LER and LWR) values for both approaches are determined. The novel exposure strategy presented in this work reduced LER by ∼25% and LWR by ∼40%.     

Inverted Organic Solar Cells with Sol–Gel Processed High Work‐Function Vanadium Oxide Hole‐Extraction Layers

For large‐scale and high‐throughput production of organic solar cells (OSCs), liquid processing of the functional layers is desired. We demonstrate inverted bulk‐heterojunction organic solar cells (OSCs) with a sol–gel derived V₂O₅ hole‐extraction‐layer on top of the active organic layer. The V₂O₅ layers are prepared in ambient air using Vanadium(V)‐oxitriisopropoxide as precursor. Without any post‐annealing or plasma treatment, a high work function of the V₂O₅ layers is confirmed by both Kelvin probe analysis and ultraviolet photoelectron spectroscopy (UPS). Using UPS and inverse photoelectron spectroscopy (IPES), we show that the electronic structure of the solution processed V₂O₅ layers is similar to that of thermally evaporated V₂O₅ layers which have been exposed to ambient air. Optimization of the sol gel process leads to inverted OSCs with solution based V₂O₅ layers that show power conversion efficiencies similar to that of control devices with V₂O₅ layers prepared in high‐vacuum.     

Gallium gradients in Cu(In,Ga)Se2 thin‐film solar cells

The gallium gradient in Cu(In,Ga)Se₂ (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co‐evaporation processes, plays a key role in the device performance of CIGS thin‐film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradients in CIGS solar cells. The formation of gallium gradients is analyzed in real time during a rapid selenization process by in situ X‐ray measurements. In addition, the gallium grading of a CIGS layer grown with an in‐line co‐evaporation process is analyzed by means of depth profiling with mass spectrometry. This gallium gradient of a real solar cell served as input data for device simulations. Depth‐dependent occurrence of lateral inhomogeneities on the µm scale in CIGS deposited by the co‐evaporation process was investigated by highly spatially resolved luminescence measurements on etched CIGS samples, which revealed a dependence of the optical bandgap, the quasi‐Fermi level splitting, transition levels, and the vertical gallium gradient. Transmission electron microscopy analyses of CIGS cross‐sections point to a difference in gallium content in the near surface region of neighboring grains. Migration barriers for a copper‐vacancy‐mediated indium and gallium diffusion in CuInSe₂ and CuGaSe₂ were calculated using density functional theory. The migration barrier for the In_Cu antisite in CuGaSe₂ is significantly lower compared with the Ga_Cu antisite in CuInSe₂, which is in accordance with the experimentally observed Ga gradients in CIGS layers grown by co‐evaporation and selenization processes. Copyright © 2014 John Wiley & Sons, Ltd.     

The Effect of Gradual Fluorination on the Properties of FnZnPc Thin Films and FnZnPc/C60 Bilayer Photovoltaic Cells

Motivated by the possibility of modifying energy levels of a molecule without substantially changing its band gap, the impact of gradual fluorination on the optical and structural properties of zinc phthalocyanine (F_nZnPc) thin films and the electronic characteristics of F_nZnPc/C₆₀ (n = 0, 4, 8, 16) bilayer cells is investigated. UV–vis measurements reveal similar Q‐ and B‐band absorption of F_nZnPc thin films with n = 0, 4, 8, whereas for F₁₆ZnPc a different absorption pattern is detected. A correlation between structure and electronic transport is deduced. For F₄ZnPc/C₆₀ cells, the enhanced long range order supports fill factors of 55% and an increase of the short circuit current density by 18%, compared to ZnPc/C₆₀. As a parameter being sensitive to the organic/organic interface energetics, the open circuit voltage is analyzed. An enhancement of this quantity by 27% and 50% is detected for F₄ZnPc‐ and F₈ZnPc‐based devices, respectively, and is attributed to an increase of the quasi‐Fermi level splitting at the donor/acceptor interface. In contrast, for F₁₆ZnPc/C₆₀ a decrease of the open circuit voltage is observed. Complementary photoelectron spectroscopy, external quantum efficiency, and photoluminescence measurements reveal a different working principle, which is ascribed to the particular energy level alignment at the interface of the photoactive materials.     

Codierte Modulation in modernen Übertragungssystemen

Modern communication systems offer high speed and reliable data transmission services. The quality of these services is achieved by combining coded multi-level modulation techniques and modern digital signal processing (Viterbi-decoding) in the receiver. In this paper we first present an introduction to Trellis Coded Modulation (TCM) and then some new results on unversal techniques adapted for the AWGN-channel as well as for the fading channel. It is shown that TCM is well suited for communication channels with time variant characteristics (e.g. mobile communication channels), especially when our new codes are applied.     

Dielectric function and degradation process of poly(triarylamine) (PTAA)

We investigated the optical properties and the degradation process of the organic p-type semiconductor poly(triarylamine) (PTAA) in the mid infrared region. The dielectric function of PTAA was determined in the spectral region of 700 up to 6000 cm⁻¹ by modeling ellipsometric measurements. Due to degradation at 65 °C, PTAA thin films developed carbonyl and hydroxyl features in the infrared spectra. Degradation under 85% RH additionally led to absorption signals of water. A degradation of the bare gold substrates was also observed. For bare gold films, morphology changed upon degradation and adsorption of hydrocarbons from the ambience took place.     

Implementing polarization shift keying over satellite – system design and measurement results

Polarization shift keying (PolSK) is a digital modulation technique using the state of polarization of an electromagnetic wave as the signalling quantity. PolSK comes from fibre communications, where the channel offers two orthogonal states of polarization. This article develops on the idea to adapt this technology to satellite communications, where similar channel conditions exist. For this purpose, a digital PolSK modem was implemented on a programmable logic board. A proposal for constellation design as well as thoughts on synchronization of PolSK over satellite is presented. The modem was used to demonstrate a 16‐state Polarization Shift Keying link over a commercial satellite in K_u band. Measurements have been conducted in a back‐to‐back setup on intermediate frequency and on a K_u band transponder simulator to assess the impact of path‐length differences, carrier recovery and non‐linearity. Copyright © 2015 John Wiley & Sons, Ltd.     

Persistence of vector replacement systems is decidable

Summary In a persistent vector replacement system (VRS) or Petri net, an enabled transition can become disabled only by firing itself. Here, an algorithm is presented which allows to decide whether an arbitrary VRS is persistent or not, and if so, to construct a semilinear representation of the set of states reachable in the system.     

Resistant starch—An accessible fiber ingredient acceptable to the Western palate

Dietary fiber intakes in Western societies are concerningly low and do not reflect global recommended dietary fiber intakes for chronic disease prevention. Resistant starch (RS) is a fermentable dietary fiber that has attracted research interest. As an isolated ingredient, its fine particle size, relatively bland flavor, and white appearance may offer an appealing fiber source to the Western palate, accustomed to highly refined, processed grains. This review aims to provide a comprehensive insight into the current knowledge (classification, production methods, and characterization methods), health benefits, applications, and acceptability of RS. It further discusses the present market for commercially available RS ingredients and products containing ingredients high in RS. The literature currently highlights beneficial effects for dietary RS supplementation with respect to glucose metabolism, satiety, blood lipid profiles, and colonic health. An exploration of the market for commercial RS ingredients indicates a diverse range of products (from isolated RS2, RS3, and RS4) with numerous potential applications as partial or whole substitutes for traditional flour sources. They may increase the nutritional profile of a food product (e.g., by increasing the fiber content and lowering energy values) without significantly compromising its sensory and functional properties. Incorporating RS ingredients into staple food products (such as bread, pasta, and sweet baked goods) may thus offer an array of nutritional benefits to the consumer and a highly accessible functional ingredient to be greater exploited by the food industry.     

Solubility and absorption rate of carbon dioxide into non-respiring foods. Part 3: Cooked meat products

The solubility and diffusion of carbon dioxide into cooked meat products (cooked ham and meat sausage with different pH-levels) was determined at different starting pressures and gas to product volume ratios by monitoring pressure changes over time in a closed chamber at constant temperatures (0, 4, and 8 °C). Good correlation of the CO₂ solubility between the packaging parameters (gas to product volume ratio and initial partial pressure) and the meat products water content was found. The solubility of CO₂ followed Henry’s law and the initial partial pressure of CO₂ influenced the solubility mostly. Only small variations in the diffusion constants and absorption rates were found within the experimental design. A pH difference of 0.5 in the two meat sausage types did not influence either solubility or diffusion significantly.