Influence of plasma chemistry on oxygen triplets

The plasma chemistry of fluorocarbon-oxygen-argon discharges and its influence on prominent oxygen triplets are studied. The oxygen 777 triplet is very important for the measurement of atomic oxygen in low pressure plasmas, since the 777.417 nm spectral line is frequently used for actinometry. In this paper we identify changes in the individual 777 triplet lines arising from cascade effects from higher energy levels of oxygen, and from resonant energy transfer from energetic carbon atoms in carbon-rich plasmas. The lower energy levels of three oxygen triplets (544 nm, 616 nm, 645 nm) are the upper states of the 777 triplet. Increased emission intensity from the 544, 616, and 645 triplets result in changes to the relative intensity of the individual lines of the 777 triplet, and this can lead to errors in using the 777 triplet, e.g. for actinometry. Also, in operational conditions with strong carbon emission (around 601 nm), the relative intensity of the individual oxygen 777 lines is affected. The upper energy levels of these carbon lines is close to the oxygen 777 upper energy levels, suggesting that resonant energy transfer between the carbon and the oxygen is occurring. The experiments are performed in a commercial semiconductor dielectric etcher operating with dual rf frequencies of 2 MHz and 27 MHz. Pressure (13-19 Pa), rf power (200-1200 W), and gas mixtures (argon with addmixtures of 5-13% oxygen and C4F8) are typical in application to dielectric etching

Whiskey Tongue

Brian Keith Ellingboe - Just the average 20 something artist from Minneapolis, Minnesota, hoping to turn pain into beauty through his work

Effect of driving frequency on the electron energy distribution function and electron-sheath interaction in a low pressure capacitively coupled plasmas

By using a self-consistent particle-in-cell simulation we investigated the effect of driving frequency (27.12–70 MHz) on the electron energy distribution function (EEDF) and electron-sheath interaction in a low pressure (5 mTorr) capacitively coupled Ar discharge for a fixed discharge voltage. We observed a mode transition with driving frequency, changing the shape of EEDF from a strongly bi-Maxwellian at a driving frequency of 27.12 MHz, to a convex type distribution at an intermediate frequency, 50 MHz, and finally becomes a weak bi-Maxwellian at a higher driving frequency i.e. above 50 MHz. The transition is caused by the electric field transients which is of the order of electron plasma frequency caused by the energetic ‘beams’ of electrons ejected from near the sheath edge. Below the transition frequency, 50 MHz, these high energy electrons redistributes their energy with low energy electrons thereby increasing the effective electron temperature in the plasma, whereas, the plasma density remains nearly-constant. Above the transition frequency high-energy electrons are confined between opposite sheaths which increases the ionization probability and therefore the plasma density increases drastically

Natural history of Arabidopsis thaliana and oomycete symbioses

Molecular ecology of plant–microbe interactions has immediate significance for filling a gap in knowledge between the laboratory discipline of molecular biology and the largely theoretical discipline of evolutionary ecology. Somewhere in between lies conservation biology, aimed at protection of habitats and the diversity of species housed within them. A seemingly insignificant wildflower called Arabidopsis thaliana has an important contribution to make in this endeavour. It has already transformed botanical research with deepening understanding of molecular processes within the species and across the Plant Kingdom; and has begun to revolutionize plant breeding by providing an invaluable catalogue of gene sequences that can be used to design the most precise molecular markers attainable for marker-assisted selection of valued traits. This review describes how A. thaliana and two of its natural biotrophic parasites could be seminal as a model for exploring the biogeography and molecular ecology of plant–microbe interactions, and specifically, for testing hypotheses proposed from the geographic mosaic theory of co-evolution

Mukaiyama addition of (trimethylsilyl) acetonitrile to dimethyl acetals mediated by trimethylsilyl trifluoromethanesulfonate

(Trimethylsilyl) acetonitrile reacts smoothly with dimethyl acetals in the presence of stoichiometric trimethylsilyl trifluoromethanesulfonate (TMSOTf) to yield β-methoxynitriles. The ideal substrates for this reaction are acetals derived from aromatic aldehydes. Elimination to the corresponding α,β-unsaturated nitriles is observed as the major product in the case of electron-rich acetals. A mechanistic hypothesis that includes isomerization of the silylnitrile to a nucleophilic N-silyl ketene imine is presented

Influence of select discharge parameters on electric field transients triggered in collisionless very high frequency capacitive discharges

Self-consistent particle-in-cell simulations are carried out to investigate the effect of discharge voltage, driving frequency and extent of electrode gap on the formation of electric field transients. The shape of the electron energy distribution function (EEDF) into the bulk plasma and the nature of the mode transition in plasma den- sity is presented for driving frequency range from 27.12 MHz to 80 MHz. The present results, taken in conjunction with our previous study1 [Physics of plasmas 23, 110701 (2016)] that only looked at the driving frequency dependence in collisionless capaci- tive Ar discharges, provide a comprehensive and detailed account of the dynamics of such discharges over a multi-parameter operational space