Johannes Windeln

Wilhelm Büchner Hochschule

We have performed density functional theory calculations using the HSE06 hybrid functional to investigate the energetics, atomic, and electronic structure of intrinsic defects as well as Na and K impurities in the kesterite structure of the Cu2ZnSnSe4 (CZTSe) solar cell material. We found that both Na and K atoms prefer to be incorporated into this...

We have studied the energetics, atomic, and electronic structure of Na and K point defects, as well as the (Na-Na), (K-K), and (Na-K) dumbbells in CuInSe2 and CuIn5Se8 solar cell materials by hybrid functional calculations. We found that although Na and K behaves somewhat similar; there is a qualitative difference between the inclusion of Na and K...

The smart grid concept introduces more software control at both endpoints of the energy consumption chain: The consumer is integrated into the grid management using smart metering, whereas the producer will be host to a distributed agent-based software approach. Including more renewable energy sources in the energy mix will increase the necessity f...

The chalcopyrite semiconductors CuIn1−xGaxSe2 (CIGS) and CuInSe2 (CIS) are excellent materials for high efficiency and low cost thin-film solar cells. This is due to the effective absorption of the solar spectrum and the inherent resilience to defects and composition fluctuations. Although the CIGS and CIS material in solar cells is highly inhomoge...

Solar cells with CuInSe2 absorbers are among the most promising thin-film technologies, but the role of defects is not yet understood. Monte Carlo (MC) simulations based on density functional theory have been employed to investigate the formation conditions and properties of Cu-poor defect structures. We find that CuIn5Se8 undergoes a discontinuous...

Cu In,Ga Se2 absorber deposition on commonly used soda lime glass is constrained in temperature by the softening of the substrate. To overcome this limitation, a high temperature resistant glass was employed as a substrate for the growth of Cu In,Ga Se2 absorbers by multi stage coevaporation at standard 530 C and elevated 610 C temperatures. Absorb...

Woven fiberglass cloths are by far the most common reinforcement material used in PCBs. The glass yarns are coated with silane-based coupling agents designed to improve the bond between the glass filaments and the resin matrix. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was utilized in order to garner a better understanding of the ob...

Thin-film solar cells with CuIn(x)Ga(1-x)Se2 (CIGS) absorber are still far below their efficiency limit, although lab cells already reach 20.1%. One important aspect is the homogeneity of the alloy. Large-scale simulations combining Monte Carlo and density functional calculations show that two phases coexist in thermal equilibrium below room temper...

Thin-film solar cells with CuInxGa1-xSe2 (CIGS) absorber are still far below their efficiency limit, although lab cells already reach 20.1%. One important aspect is the homogeneity of the alloy. Large-scale simulations combining Monte Carlo and density functional calculations show that two phases coexist in thermal equilibrium below room temperatur...

An overview is given on the present status of the comCIGS project funded by the German BMU (Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit). Five partners are heading this effort which represents a framework of virtual and experimental Labs: IBM Germany, Schott AG, Helmholtz Zentrum Berlin, Universities of Mainz and Jena. All the p...

In this paper, we describe atomic force microscope (AFM) friction experiments on different polymers. The aim was to analyze the influence of the physical architecture of the polymer on the degree and mode of wear and on the wear mode. Experiments were carried out with (1) linear polystyrene (PS) and cycloolefinic copolymers of ethylene and norborne...

We report on the magnetotransport properties of Co2Cr0.6Fe0.4Al mixed with insulating Al2O3. The powder compacts show a maximum magnetoresistance of 88% at a saturation moment of 0.125 T at 295 K. Different explanations for the reversible mechanism will be discussed, such as tunneling between contiguous ferromagnetic grains, particle movement, and...

We present heat transfer experiments using a heated silicon cantilever/tip at or near contact with a variety of surfaces. Under ambient conditions cooling of the cantilever results from conduction through the air, through the cantilever beam and through the tip-surface contact, as well as from radiation cooling. By varying the ambient conditions, t...

First Page of the Article

N-{2-[4-(N-tert-Butoxycarbonylamino)benzoylamino]ethoxycarbonyl}anthranilic acid (1) was synthesized as a reagent for the stepwise elimination of monomeric units from the chain ends of oligoesters and polyesters, especially of poly(ethylene terephthalate) and poly(tetramethylene terephthalate) type. The reagent is supposed to be applied for a stepw...

Summary form only given. Materials which display large changes in resistivity in response to an applied magnetic field (magnetoresistance) are currently of great interest due to their potential for applications in magnetic sensors, magnetic random access memories, and spintronics-a new kind of electronics based on spin instead of charge. Although f...

There is a continuing pressure to miniaturise almost all electronic components, including those used in data processing. This is matched with simultaneous demands in terms of preCision and the lowering of production costs. Using as example, components from computer hard disk drives, it is shown how their manufacture involves both vacuum and electro...

This paper gives a synopsis of today’s challenges and requirements for a surface analysis and materials science laboratory with a special focus on magnetic recording technology. The critical magnetic recording components, i.e. the protective carbon overcoat (COC), the disk layer structure, the read/write head including the giant-magnetoresistive (G...

Nitrogenated carbon coatings (CNx) are widely used as protective coatings on magnetic hard disks. In this paper, the mechanical properties of such coatings produced with d.c. magnetron-sputtering and filtered high-current vacuum arcs (HCA) are compared. An AFM-based scratching technique has been used that allows the generation and characterization...

Die moderne Datentechnik, die weltweite Vernetzung und die zunehmend komplexeren Informations- und Kommunikationssysteme haben einen exponentiell wachsenden Bedarf an Speichertechnik zur Folge. Magnetische Festplattenspeicher stellen dabei bis heute die dominierende Speichertechnologie dar, wenn man die jährlich umgesetzte Speichermenge betrachtet....

As a protective coating for hard disks in magnetic storage applications, amorphous carbon nitride (a-C:N) thin films have proved superior to DLC (diamond-like carbon) a-C:H films in terms of durability, wear-resistance and adhesion properties. In this study, we present Raman spectroscopy investigations of a-C:N films which were produced by DC-magne...

A specifically tailored reagent was used to label the hydroxyl end groups of poly(ethylene/butylene terephthalate), which is synthesized by transesterification of the corresponding homopolymers. The terminal monomeric unit was then eliminated, together with the attached label, as a low molecular-weight cyclic compound. Specially synthesized referen...

Model reactions for the sequential analysis of polyesters, especially those of the poly(ethylene terephthalate) and poly(butylene terephthalate) type, by stepwise chemical degradation were performed. The cyclic degradation products, containing the reagent and an ethylene terephthalate or butylene terephthalate unit, terephthalic acid mono(2- left b...

Cyclic oligomers of butylene terephthalate (16a – d) were synthesized by cyclocondensations of the corresponding dicarboxylic acid dichlorides (2 or 13) with diols (4, 10, or 15). The linear educts 2, 4, 10, 13, and 15 were obtained by stepwise synthesis. The resulting cyclic esters 16a – d were characterized by IR, NMR, and mass spectroscopy.