Width determination of SiO2-films in Si-based devices using low-loss EFTEM: image contrast as a function of sample thickness

Energy filtering transmission electron microscopy (EFTEM) has become one of the most efficient tools for specimen characterization at nanometer length scales. EFTEM imaging is most often carried out in the core-loss region but image intensity becomes more and more a limiting factor with decreasing feature size. Alternatively, it is possible to record EFTEM images in the low-loss region, where intensities are essentially higher and where in many cases the images contain material specific contrasts. In this paper we investigate the influence of the important parameters on the material contrast between silicon and silicon dioxide, e.g. specimen thickness, specimen orientation, energy-loss and energy selecting slit width. We show that sample thickness plays an important role and present two methods to calculate material contrast as a function of energy-loss and sample thicknesses. The first method uses spectra taken from both materials at different sample thickness by electron energy-loss spectroscopy, the second calculates contrast directly from a series of energy filtered images. From the results we determine the ideal acquisition parameters for the Si/SiO(2) system and demonstrate imaging at sufficient resolution below 2nm with a test sample of thin SiO(2) layers on Si.     

Peroxidase-ROS interactions

Reactive oxygen species (ROS), such as hydrogen peroxide and superoxide anion radical, have long been recognized as harmful by-products of oxidative metabolism. Under normal physiologic conditions, hydrogen peroxide and superoxide are detoxified by antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx). Heme peroxidases (eosinophil peroxidase (EPO), lactoperoxidase (LPO), myeloperoxidase (MPO), etc.) also consume ROS, but unlike scavenging enzymes, are sources of these species as well. In the present paper, we study a well-tested model of the peroxidase–oxidase (PO) reaction based on horseradish peroxidase (HRP) chemistry with regard to the production and consumption of hydrogen peroxide and superoxide. Our principal results are these:

Scrape-off-layer current model for filament structure observed during edge-localized modes in the DIII-D tokamak

The plasma in tokamaks often exhibits a relaxation oscillation called the edge-localized mode (ELM), which is generally attributed to MHD instability driven by strong gradients at the plasma boundary. It is shown here that field-aligned currents flowing just outside the boundary may also play a role in the ELM process. The poloidal perturbation magnetic field during ELMs in the DIII-D tokamak calculated from measured currents can reproduce prominent observed features, including a narrow magnetic structure at the outboard midplane similar to filaments observed earlier in DIII-D and NSTX.     

Porphyrins XXVIII. Extended Hückel calculations on metal phthalocyanines and tetrazaporphins

Extended Hückel (EH) calculations on Mg, Zn, Cu, Ni, Fe, Mn, and VO complexes of phthalocyanine and tetrazaporphin are reported and the results compared to similar calculations on porphyrins. The smaller ring size of phthalocyanine gives rise to a larger ligand field. The bridge nitrogen atoms give rise to n - ^* transitions, which are probably in the region of the Soret band. In Ni, Co, Fe, and Mn there is strong mixing of the bridge N2p and metal b _2g (d _xy ), which should affect the ligand field. Extra absorption bands observed in the near uv of NiPc and CoPc are attributed to d ^* transitions. A general symmetrized EH program is reported that speeds calculations on large systems.

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Zusammenfassung Für die Komplexverbindungen von Mg, Zn, Cu, Ni, Fe, Mn und Vo mit Phtalocyanin und Tetrazaporphin werden erweiterte Hückelrechnungen (EH) durchgeführt und die Ergebnisse mit ähnlichen Berechnungen an Porphyrinen verglichen. Die geringere Ringgröße des Phtalocyanins gibt Anlaß zu einem größeren Ligandenfeld. Das Brücken-Stickstoffatom gibt Anlaß zu n- ^*-Übergängen, die wahrscheinlich im Gebiet der Soret-Bande liegen. Beim Ni, Co, Fe und Mn tritt eine starke Mischung der Orbitale des Brückenstickstoff-Atoms N2p und b _2g (d _xy ) auf, die das Ligandenfeld beeinflussen sollte. Die zusätzlichen Absorptionsbanden, die im nahen UV bei NiPc und CoPc beobachtet werden, werden d ^*-Übergängen zugeordnet. Ein allgemeines, symmetrisiertes EH-Programm wird mitgeteilt, das die Berechnung großer Systeme beschleunigt.

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Paper XXVII. M. Gouterman, F. P. Schwarz, P. D. Smith, and D. Dolphin, J. chem. Physics, in press (1973).     

Sulfonyl Fluoride‐Based Prosthetic Compounds as Potential 18F Labelling Agents

Nucleophilic incorporation of [¹⁸F]F^? under aqueous conditions holds several advantages in radiopharmaceutical development, especially with the advent of complex biological pharmacophores. Sulfonyl fluorides can be prepared in water at room temperature, yet they have not been assayed as a potential means to ¹⁸F‐labelled biomarkers for PET chemistry. We developed a general route to prepare bifunctional 4‐formyl‐, 3‐formyl‐, 4‐maleimido‐ and 4‐oxylalkynl‐arylsulfonyl [¹⁸F]fluorides from their sulfonyl chloride analogues in 1:1 mixtures of acetonitrile, THF, or tBuOH and Cs[¹⁸F]F/Cs₂CO_3(aq.) in a reaction time of 15 min at room temperature. With the exception of 4‐N‐maleimide‐benzenesulfonyl fluoride ( 3 ), pyridine could be used to simplify radiotracer purification by selectively degrading the precursor without significantly affecting observed yields. The addition of pyridine at the start of [¹⁸F]fluorination (1:1:0.8 tBuOH/Cs₂CO_3(aq.)/pyridine) did not negatively affect yields of 3‐formyl‐2,4,6‐trimethylbenzenesulfonyl [¹⁸F]fluoride ( 2 ) and dramatically improved the yields of 4‐(prop‐2‐ynyloxy)benzenesulfonyl [¹⁸F]fluoride ( 4 ). The N‐arylsulfonyl‐4‐dimethylaminopyridinium derivative of 4 ( 14 ) can be prepared and incorporates ¹⁸F efficiently in solutions of 100 % aqueous Cs₂CO₃ (10 mg mL^?1). As proof‐of‐principle, [¹⁸F] 2 was synthesised in a preparative fashion [88(±8) % decay corrected (n=6) from start‐of‐synthesis] and used to radioactively label an oxyamino‐modified bombesin(6–14) analogue [35(±6) % decay corrected (n=4) from start‐of‐synthesis]. Total preparation time was 105–109 min from start‐of‐synthesis. Although the ¹⁸F‐peptide exhibited evidence of proteolytic defluorination and modification, our study is the first step in developing an aqueous, room temperature ¹⁸F labelling strategy.     

Ueber Trockenbeerweine

Ohne ZusammenfassungBern, im Juni 1885.