DC-electric-field-induced and low-frequency electromodulation second-harmonic generation spectroscopy of Si(001)-SiO2_2 interfaces

The mechanism of DC-Electric-Field-Induced Second-Harmonic (EFISH) generation at weakly nonlinear buried Si(001)-SiO$_2$ interfaces is studied experimentally in planar Si(001)-SiO$_2$-Cr MOS structures by optical second-harmonic generation (SHG) spectroscopy with a tunable Ti:sapphire femtosecond laser. The spectral dependence of the EFISH contribution near the direct two-photon $E_1$ transition of silicon is extracted. A systematic phenomenological model of the EFISH phenomenon, including a detailed description of the space charge region (SCR) at the semiconductor-dielectric interface in accumulation, depletion, and inversion regimes, has been developed. The influence of surface quantization effects, interface states, charge traps in the oxide layer, doping concentration and oxide thickness on nonlocal screening of the DC-electric field and on breaking of inversion symmetry in the SCR is considered. The model describes EFISH generation in the SCR using a Green function formalism which takes into account all retardation and absorption effects of the fundamental and second harmonic (SH) waves, optical interference between field-dependent and field-independent contributions to the SH field and multiple reflection interference in the SiO$_2$ layer. Good agreement between the phenomenological model and our recent and new EFISH spectroscopic results is demonstrated. Finally, low-frequency electromodulated EFISH is demonstrated as a useful differential spectroscopic technique for studies of the Si-SiO$_2$ interface in silicon-based MOS structures.Comment: 31 pages, 14 figures, 1 table, figures are also available at http://kali.ilc.msu.su/articles/50/efish.ht

CPUT Celebrating Research Day

Conference Poste

Инженерно-геологические условия участка Портового управления города Выборга и проект изысканий под административно-бытовой комплекс

Целью данной работы является оценка инженерно–геологических условий участка на территории портового управления города Выборга, изучение состава и свойства грунтов, геологических процессов и явлений, выбор методики изысканий и обоснование оптимальных видов работ для составления проекта изысканий под строительство административно-бытового комплекса.The purpose of this work is to assess the engineering and geological conditions of the site on the territory of the Port Authority of Vyborg, to study the composition and properties of soils, geological processes and phenomena, to select the survey methodology and to justify the optimal types of work for drafting surveys for the construction of the administrative complex

Handlungsbedarf und anlaufende Aktivitäten vor dem Hintergrund der Bedrohung einheimischer Schwanzlurche durch einen neuen Salamander-Chytridpilz

Seit mindestens 2010 tritt in den Niederlanden ein neuer Amphibien-Chytridpilz auf, der inzwischen auch in Belgien nachgewiesen wurde. Batrachochytrium salamandrivorans (Bs) befällt nur Schwanzlurche und könnte eine Bedrohung für einheimische Arten werden. Der anscheinend aus Asien stammende Pilz verursachte starke Einbrüche der befallenen Feuersalamander-Populationen. Für Molche liegen keine verlässlichen Daten vor. Im Labor konnten jedoch Kamm- und Bergmolch infiziert werden, während der Fadenmolch anscheinend resistent ist (Martel et al. 2014)

Apertureless Near-Field Second Harmonic Microscopy with Bare Tapered Optical Fiber Tips

We present a near-field optical technique for second harmonic imaging using bare tapered optical fiber tip illuminated with femtosecond laser pulses. Enhancement of electric field at the tip of the fiber results in enhanced second harmonic generation (SHG) from the sample region near the tip. This SH emission is collected by the same tapered fiber. Spatial distribution of SHG from thin ferroelectric Pb(Zr_xTi_1-x)O_3 films and model metal-ferroelectric devices has been studied. Spatial resolution on the order of 80 nm has been achieved. This is the first time diffraction limit is surpassed in SH microscopic measurements. Electric field induced changes in SHG from individual grains and/or domains of ferroelectric thin films have been observed.Comment: submitted to Phys.Rev.Letter

New fossil insect order Permopsocida elucidates major radiation and evolution of suction feeding in hemimetabolous insects (Hexapoda: Acercaria)

International audienceWith nearly 100,000 species, the Acercaria (lice, plant lices, thrips, bugs) including number of economically important species is one of the most successful insect lineages. However, its phylogeny and evolution of mouthparts among other issues remain debatable. Here new methods of preparation permitted the comprehensive anatomical description of insect inclusions from mid-Cretaceous Burmese amber in astonishing detail. These ``missing links'' fossils, attributed to a new order Permopsocida, provide crucial evidence for reconstructing the phylogenetic relationships in the Acercaria, supporting its monophyly, and questioning the position of Psocodea as sister group of holometabolans in the most recent phylogenomic study. Permopsocida resolves as sister group of Thripida + Hemiptera and represents an evolutionary link documenting the transition from chewing to piercing mouthparts in relation to suction feeding. Identification of gut contents as angiosperm pollen documents an ecological role of Permopsocida as early pollen feeders with relatively unspecialized mouthparts. This group existed for 185 million years, but has never been diverse and was superseded by new pollenivorous pollinators during the Cretaceous co-evolution of insects and flowers. The key innovation of suction feeding with piercing mouthparts is identified as main event that triggered the huge post-Carboniferous radiation of hemipterans, and facilitated the spreading of pathogenic vectors