Grinding of optical glasses with cup wheels - Α new way to generate polishable surfaces

Conventionally the machining sequence of optical glass lenses consists of rough grinding, fine grinding and polishing. At this time the research in glass machining techniques concentrates on rough grinding and fine grinding, especially tool and process optimisation. The shown results of rough grinding tests offer the possibility to eliminate the fine grinding process out of the machining sequence. The surface quality which can be reached depends, besides other circumstances like machine parameters, on the glass material. This is described just as the used research methods and measuring techniques

QuateXelero : an accelerated exact network motif detection algorithm

Finding motifs in biological, social, technological, and other types of networks has become a widespread method to gain more knowledge about these networks’ structure and function. However, this task is very computationally demanding, because it is highly associated with the graph isomorphism which is an NP problem (not known to belong to P or NP-complete subsets yet). Accordingly, this research is endeavoring to decrease the need to call NAUTY isomorphism detection method, which is the most time-consuming step in many existing algorithms. The work provides an extremely fast motif detection algorithm called QuateXelero, which has a Quaternary Tree data structure in the heart. The proposed algorithm is based on the well-known ESU (FANMOD) motif detection algorithm. The results of experiments on some standard model networks approve the overal superiority of the proposed algorithm, namely QuateXelero, compared with two of the fastest existing algorithms, G-Tries and Kavosh. QuateXelero is especially fastest in constructing the central data structure of the algorithm from scratch based on the input network

Von der (Un-)Möglichkeit ausgeglichener Haushalte

Staatsverschuldung wird hier als ein negativer externer Effekt verstanden, den Politiker ausüben, um die Kosten ihres politischen Angebots zu senken und somit im politischen Wettbewerb bestehen zu können. Die Gegebenheiten des politischen Wettbewerbs und die Möglichkeit diesen externen Effekt auszuüben, versetzen die Politiker in eine Dilemma-Situation, welche die Vermeidung von Defiziten, also eine Zusammenarbeit zum allgemeinen Vorteil, unmöglich macht und zwangsläufig zu immer neuen Defiziten führt. Ausnahmen ergeben sich nur, wenn die Kosten der Staatsverschuldung internalisiert werden. Da eine vollständige Internalisierung über den Markt aber in der Regel nicht gelingen kann, wird eine erfolgreiche Bekämpfung des Verschuldungsproblems nur mit Hilfe von Regulierung gelingen. Wir plädieren daher für eine Kombination aus Intensivierung des Wettbewerbs, um eine verstärkte Internalisierung der negativen externen Effekte zu erreichen, und Kanalisierung des Wettbewerbs, also Regulierung, um den Einsatz von Staatsverschuldung zu begrenzen und die Dilemmastruktur aufzubrechen. --

Modulation of the Work Function by the Atomic Structure of Strong Organic Electron Acceptors on H-Si(111)

Advances in hybrid organic/inorganic architectures for optoelectronics can be achieved by understanding how the atomic and electronic degrees of freedom cooperate or compete to yield the desired functional properties. Here we show how work-function changes are modulated by the structure of the organic components in model hybrid systems. We consider two cyano-quinodimethane derivatives (F4-TCNQ and F6-TCNNQ), which are strong electron-acceptor molecules, adsorbed on H-Si(111). From systematic structure searches employing range-separated hybrid HSE06 functional including many body van der Waals contributions, we predict that despite their similar composition, these molecules adsorb with significantly different densely-packed geometries in the first layer, due to strong intermolecular interaction. F6-TCNNQ shows a much stronger intralayer interaction (primarily due to van der Waals contributions) than F4-TCNQ in multilayered structures. The densely-packed geometries induce a large interface-charge rearrangement that result in a work-function increase of 1.11 and 1.76 eV for F4-TCNQ and F6-TCNNQ, respectively. Nuclear fluctuations at room temperature produce a wide distribution of work-function values, well modeled by a normal distribution with {\sigma}=0.17 eV. We corroborate our findings with experimental evidence of pronounced island formation for F6-TCNNQ on H-Si(111) and with the agreement of trends between predicted and measured work-function changes

Molecular p-doping induced dielectric constant increase of polythiophene films determined by impedance spectroscopy Editor’s Pick

The dielectric constant (εr) is a fundamental material parameter that governs charge transfer processes in organic semiconductors, yet its value is often assumed rather than measured. Here, we use impedance spectroscopy to determine εr in regioregular poly(3-hexylthiophen-2,5-diyl) (P3HT) thin films p-doped with the molecular dopants hexafluoro-tetracyanonaphthoquinodimethane and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). We fit the impedance spectra using a single RC circuit model to determine the frequency-dependent capacitance and extract εr. The value of the dielectric constant increases by around two-thirds from 2.9 ± 0.1 (undoped polymer) to 4.9 ± 0.6 on the addition of one F4TCNQ molecule per 500 P3HT monomer units. In contrast, the addition of the weak dopant 7,7,8,8-tetracyanoquinodimethane (TCNQ), which does not undergo ground state charge transfer with P3HT, has no effect on the dielectric constant. Our results support the hypothesis that molecular doping has a considerable impact on the materials dielectric constant via polarizable host-dopant complexes.Peer Reviewe

Effect of ground state charge transfer and photoinduced charge separation on the energy level alignment at metal halide perovskite/organic charge transport layer interfaces

One of the most promising routes for the future fabrication of solution-processable high-performance solar cells is to employ metal halide perovskites as photoactive material combined with organic semiconductors as charge extraction layers. An essential requirement to obtain high device performance is a proper energy level alignment across the device interfaces. Here, we investigate the interface between a triple cation perovskite and a prototypical electron acceptor molecule. Photoemission spectroscopy reveals a ground state charge transfer induced band bending on either side of the junction, which significantly alters the charge extraction barriers as compared to assumed vacuum level alignment and flat-band conditions. In addition, we demonstrate that upon white light illumination, the energy levels of the organic layer exhibit rigid shifts by up to 0.26 eV with respect to those of the perovskite, revealing a non-constant energy offset between the frontier energy levels of the two materials. Such level shifts of the organic transport layer are fully reversible upon switching on/off the light, indicating an electrostatic origin of this phenomenon caused by unbalanced distribution of photogenerated charge carriers. We therefore stress the importance of determining the energy level alignment at perovskite-based interfaces not only in the electronic ground state (dark) but also under device operating conditions (operando) to enable for a reliable correlation with the device performance.Peer Reviewe

Recrystallization of MBE‐Grown MoS2 Monolayers Induced by Annealing in a Chemical Vapor Deposition Furnace

A systematic study of MoS2 grown by a combination of physical vapor deposition and post-growth annealing treatment has been conducted. Hereby, MoS2 thin films with thicknesses between 1 and 2 layers are first grown on sapphire by molecular beam epitaxy at different growth temperatures and then transferred to S environment inside a tube furnace for an annealing process. Depending on the growth temperature, the as-grown layers are either amorphous or form a crystalline structure composed of closely packed nanometer-size grains. The annealing process leads to recrystallization of these layers significantly increasing the size of the MoS2 crystalline domains to the range of 50–100 nm. While the originally amorphous layer displays rotational domains after annealing, recrystallization of samples grown at high temperatures yields single crystalline layers. All samples display an increase of the crystallite dimension, which is accompanied by the disappearance of the defect-related peaks in the Raman spectra, sharpening of the excitonic signatures in absorption, and strong enhancement of the photoluminescence yield. The results represent a promising way to combine advantages of physical vapor deposition and a post-growth annealing in a chemical vapor deposition furnace toward fabrication of wafer-scale single crystalline transition metal dichalcogenide mono- and multilayer films on non-van der Waals substrates.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe

Stark Effect of Hybrid Charge Transfer States at Planar ZnO/Organic Interfaces

We investigate the bias-dependence of the hybrid charge transfer state emission at planar heterojunctions between the metal oxide acceptor ZnO and three donor molecules. The electroluminescence peak energy linearly increases with the applied bias, saturating at high fields. Variation of the organic layer thickness and deliberate change of the ZnO conductivity through controlled photo-doping allow us to confirm that this bias-induced spectral shifts relate to the internal electric field in the organic layer rather than the filling of states at the hybrid interface. We show that existing continuum models overestimate the hole delocalization and propose a simple electrostatic model in which the linear and quadratic Stark effects are explained by the electrostatic interaction of a strongly polarizable molecular cation with its mirror image

Y‐Stabilized ZrO2 as a Promising Wafer Material for the Epitaxial Growth of Transition Metal Dichalcogenides

Y-stabilized ZrO2 (YSZ) as a promising single-crystal wafer material for the epitaxial growth of transition metal dichalcogenides applicable for both physical (PVD) and chemical vapor deposition (CVD) processes is used. MoS2 layers grown on YSZ (111) exhibit sixfold symmetry and in-plane epitaxial relationship with the wafer of (1010) MoS2 || (211) YSZ. The PVD-grown submonolayer thin films show nucleation of MoS2 islands with a lateral size of up to 100 nm and a preferential alignment along the substrate step edges. The layers exhibit a strong photoluminescence yield as expected for the 2H-phase of MoS2 in a single monolayer limit. The CVD-grown samples are composed of triangular islands of several micrometers in size in the presence of antiparallel domains. The results represent a promising route toward fabrication of wafer-scale single-crystalline transition metal dichalcogenide layers with a tunable layer thickness on commercially available wafers.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Interreg http://dx.doi.org/10.13039/100013276Peer Reviewe