Optical and electronic interaction at metal–organic and organic–organic interfaces of ultra-thin layers of PTCDA and SnPc on noble metal surfaces

We investigate the interaction mechanisms at metal–organic and organic–organic interfaces in highly-ordered ultra-thin layers of the dye molecules 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) and tin(II)-phthalocyanine (SnPc) on single crystalline noble metals. The ultra-thin films are characterized by means of in situ differential reflectance spectroscopy (DRS), followed by an extraction of the optical functions by application of a numerical algorithm. For the first time, DRS data of PTCDA and SnPc films on Ag(1 1 1) are presented. We found that for the contact layers of PTCDA and SnPc the well-known covalent interaction between adsorbate and substrate is manifested in broad and structureless absorption spectra. Surprisingly, the optical spectra of the respective first monolayers on Ag(1 1 1) are almost identical despite of the rather different electronic structure of the free molecules. The special character of the optical spectra is emphasized by a comparison with PTCDA and SnPc monolayers on Au(1 1 1) where the electronic interaction at the metal–organic interface is much weaker. Quite differently from the contact layer, the second layer of the same molecule on Ag(1 1 1) clearly shows monomeric behavior which can only be observed if the electronic and optical coupling with the surrounding molecules and the substrate is faint. However, a very weak out-of-plane electronic interaction remains as concluded from the comparison with the spectra obtained on inert mica substrates. We also present structural data acquired with low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) of SnPc on Au(1 1 1).     

Surface‐Modified Low‐Temperature Solid Oxide Fuel Cell

This paper reports both experimental and theoretical results of the role of surface modification on the oxygen reduction reaction in low‐temperature solid oxide fuel cells (LT‐SOFC). Epitaxial ultrathin films of yttria‐doped ceria (YDC) cathode interlayers (<10–130 nm) are grown by pulsed laser deposition (PLD) on single‐crystalline YSZ(100). Fuel cell current–voltage measurements and electrochemical impedance spectroscopy are performed in the temperature range of 350 °C ≈ 450 °C. Quantum mechanical simulations of oxygen incorporation energetics support the experimental results and indicate a low activation energy of only 0.07 eV for YDC, while the incorporation reaction on YSZ is activated by a significantly higher energy barrier of 0.38 eV. Due to enhanced oxygen incorporation at the modified Pt/YDC interface, the cathodic interface resistance is reduced by two‐fold, while fuel cell performance shows more than a two‐fold enhancement with the addition of an ultrathin YDC interlayer at the cathode side of an SOFC element. The results of this study open up opportunities for improving cell performance, particularly of LT‐SOFCs by adopting surface modification of YSZ surface with catalytically superior, ultrathin cathodic interlayers.     

Tool life increase of coated carbide tools by micro blasting

In today’s production engineering nearly every cutting tool is coated. Since using the technology of coating different process chains for reconditioning have been developed. The last innovation is micro blasted coatings, which is the main topic of this paper. Concerning this topic influences on tool life have been investigated. Investigations on the tool life especially of hobbing tools were made thereby and coherences between coating bond, roughness and other attributes were discovered. The investigations were made with an aluminum oxide and a zirconium oxide as blasting abrasives and a variation of the blasting parameters pressure and period. The final result is an optimization of tool wear behavior by micro blasting of the coating.     

LaGaO3-based cermet for solid oxide fuel cell cathodes

A series of La_0.9Sr_0.1Ga_0.85Mg_0.15O_3?δ–Ag cermets with different Ag₂O contents were prepared by conventional sintering, assessing their suitability as cathode material for solid oxide fuel cell (SOFC) in combination with Sr- and Mg-doped LaGaO₃ electrolytes. Ag₂O is found to get dissociated at around 320 °C. The chemical compatibility between La_0.9Sr_0.1Ga_0.85Mg_0.15O_3?δ–Ag (LSGM) and Ag was investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. No reaction or solid solubility between LSGM and Ag was found. Thermal expansion coefficients of the cermets were measured as a function of Ag content and were found to increase with increasing metallic content. Oxygen adsorption at the surface of the cermets could be detected.     

Phase equilibria and thermal analysis of Si–C–N ceramics

The phase reactions, crystallization behaviour and thermal degradation of two Si–C–N ceramics derived from precursors VT50 and NCP200, respectively, were studied by means of CALPHAD type thermodynamic calculations and experimental investigations by DTA/TG, XRD and SEM/EDX. The phase reaction Si₃N₄+3C=3SiC+2N₂ proceeds during the thermal degradation of both ceramics. Additionally, the phase reaction Si₃N₄=3Si+2N₂ occurs during the thermal degradation of the NCP200 ceramic. To explain quantitatively the high temperature behaviour of Si–C–N ceramics, thermodynamic functions, the reaction scheme, isothermal sections, isopleths, phase fraction diagrams and phase composition diagrams (for gas partial pressures) were calculated. The computer simulations were confirmed by the experiments for both ceramics.     

Major flavonoids of Argentinean honeys. Optimisation of the extraction method and analysis of their content in relationship to the geographical source of honeys

In the present research we optimised an extraction procedure for the flavonoid aglycones: myricetin, quercetin and luteolin from honeys (as natural biological matrices), based on Amberlite XAD-4 resin followed by HPLC quantification. In addition, honeys from three geographical regions of Argentina were analysed with regard to the contents of these flavonoids. The extraction procedure was optimised for XAD-4 resin considering: resin/honey ratio, elution volume to desorb flavonoids and colour intensity of honeys. Differences in flavonoid recoveries were observed depending on the colour intensity. The flavonoid aglycones contents, in accordance with differences in geochemical characteristics and typical vegetation, varied with the geographical origin of honeys. The results obtained allowed us to consider these three flavonoids as chemical markers for the phytogeographical origin of honeys. In the case of monofloral honeys, the contribution of each one of the flavonoids was associated with the presence of a dominant pollen kind in these samples.     

A review of lithium niobate modulators for fiber-opticcommunications systems

The current status of lithium-niobate external-modulator technology is reviewed with emphasis on design, fabrication, system requirements, performance, and reliability. The technology meets the performance and reliability requirements of current 2.5-, 10-, and 40-Gb/s digital communication systems, as well as CATV analog systems. The current trend in device topology is toward higher data rates and increased levels of integration. In particular, multiple high-speed modulation functions, such as 10-Gb/s return-to-zero pulse generation plus data modulation, have been achieved in a single device