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Journal ArticleDOI

Particle agglomeration study in rf silane plasmas: In situ study by polarization-sensitive laser light scattering

TL;DR: In this article, the authors used a Brownian free molecule coagulation model to determine the time evolution of particle size and their number density in situ multi-angle polarization-sensitive laser light scattering.
Abstract: To determine self-consistently the time evolution of particle size and their number density in situ multi-angle polarization-sensitive laser light scattering was used. Cross-polarization intensities (incident and scattered light intensities with opposite polarization) measured at 135 degrees and ex situ transmission electronic microscopy analysis demonstrate the existence of nonspherical agglomerates during the early phase of agglomeration. Later in the particle time development both techniques reveal spherical particles again. The presence of strong cross-polarization intensities is accompanied by low-frequency instabilities detected on the scattered light intensities and plasma emission. It is found that the particle radius and particle number density during the agglomeration phase can be well described by the Brownian free molecule coagulation model. Application of this neutral particle coagulation model is justified by calculation of the particle charge whereby it is shown that particles of a few tens of nanometer can be considered as neutral under our experimental conditions. The measured particle dispersion can be well described by a Brownian free molecule coagulation model including a log-normal particle size distribution. (C) 1996 American Institute of Physics.

Summary (1 min read)

Jump to: [Context] and [Conclusion]

Context

  • The following general measures are set out in the Action Plan: improving deployment of environmental compliance assurance expertise; identification of necessary professional skillsets and training needs for environmental professionals in member states, facilitating the sharing of good practices and capacity building and use of geospatial intelligence for compliance assurance.
  • The poor compliance record in certain environmental sectors is explained by complex environmental legislation which is based on “wide array of techniques, such as product standards, state-of-the-environment objectives, prohibitions and restrictions, economic instruments, sensitive area designations, plans and programmes, and public participation and information provisions”.

Conclusion

  • The success of the Environmental Compliance Assurance Action Plan depends on the clear division of responsibilities between actors involved in its implementation.
  • Unlike many previous policy initiatives, this Action Plan sets out a clear structure, timeline and responsibilities allocated to actors involved, especially non-state actors.
  • Their involvement has proven to be very beneficial especially in infringement procedures under the enforcement approach.
  • The Guidance document on hunting under the "Birds Directive", http://ec.europa.eu/environment/nature/conservation/wildbirds/hunting/docs/hunting_guide_en.pdf.
  • In those instances, the Commission has to use enforcement mechanisms more forcefully as only the complementary use of both approaches will address non-compliance in the EU.59 59 See above n. 15 and n. 18.

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Citations
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Journal ArticleDOI
TL;DR: The fundamentals of nanocrystal formation in plasmas are discussed, practical implementations of plasma reactors are reviewed, the materials that have been produced with nonthermal plAsmas and surface chemistries that have be developed are surveyed, and an overview of applications of plasma-synthesized nanocrystals is provided.
Abstract: Nonthermal plasmas have emerged as a viable synthesis technique for nanocrystal materials. Inherently solvent and ligand-free, nonthermal plasmas offer the ability to synthesize high purity nanocrystals of materials that require high synthesis temperatures. The nonequilibrium environment in nonthermal plasmas has a number of attractive attributes: energetic surface reactions selectively heat the nanoparticles to temperatures that can strongly exceed the gas temperature; charging of nanoparticles through plasma electrons reduces or eliminates nanoparticle agglomeration; and the large difference between the chemical potentials of the gaseous growth species and the species bound to the nanoparticle surfaces facilitates nanocrystal doping. This paper reviews the state of the art in nonthermal plasma synthesis of nanocrystals. It discusses the fundamentals of nanocrystal formation in plasmas, reviews practical implementations of plasma reactors, surveys the materials that have been produced with nonthermal pla...

292 citations

Journal ArticleDOI
TL;DR: In this paper, a novel scheme to fabricate nano-composite membrane materials containing fully dispersed nano-size zeolitic imidazolate frameworks (ZIFs) has been proposed for the first time.
Abstract: In this study, a novel scheme to fabricate nano-composite membrane materials containing fully dispersed nano-size zeolitic imidazolate frameworks (ZIFs) has been proposed for the first time. By mixing the as-synthesized ZIF-7 nano-particles without the traditional drying process with polybenzimidazole (PBI), the resultant membranes not only achieve an unprecedented ZIF-7 loading as high as 50 wt%, but also overcome the low permeability nature of PBI. The membranes exhibit characteristics of high transparency and mechanical flexibility, together with enhanced H2 permeability and ideal H2/CO2 permselectivity surpassing both neat PBI and ZIF-7 membranes. Advanced instrument analyses have confirmed the unique ZIF–polymer interface and elucidated the mixed matrix structure that contributes to the high ZIF loading and enhanced gas separation performance superior to the prediction from the Maxwell model. The high thermal stability, good dispersion of ZIF nanoparticles with minimal agglomeration and the attractive gas separation performance at elevated temperatures up to 180 °C indicate the practicability of this nano-composite material for hydrogen production and CO2 capture in realistic industrial applications under harsh and extreme environments.

279 citations

Journal ArticleDOI
TL;DR: In this article, mixed matrix membranes (MMMs) with uniform morphology comprising ZIF-8 nanoparticles were fabricated for industrial nature gas purification and C 3 H 6 /C 3 H 8 separation.

232 citations

Journal ArticleDOI
TL;DR: An overview of the most recent experimental and modelling efforts on powder formation in reactive plasmas is given in this paper, where particle charging and charge fluctuations regarding the particle agglomeration is emphasised.
Abstract: An overview of the most recent experimental and modelling efforts on powder formation in reactive plasmas is given. The physics and chemistry of these dusty plasmas and their fundamental mechanisms leading to the production of nanometre-sized particles and their successive agglomeration leading to micrometre-sized particles are reviewed. The central role of particle charging and of charge fluctuations regarding the particle agglomeration is emphasised. Finally, the influence of the dust particles on the plasma parameters is described and an outlook on the most eminent problems towards the understanding of the reactive, dusty plasmas is given.

205 citations

Journal ArticleDOI
TL;DR: In this paper, a combination of IR absorption spectroscopy and mass spectrometry has been applied to dusty radiofrequency (RF) plasmas in methane, acetylene and ethylene.
Abstract: Infrared (IR) absorption spectroscopy and mass spectrometry have been simultaneously applied to dusty radiofrequency (RF) plasmas in methane, acetylene and ethylene. The combination of IR absorption spectroscopy and mass spectrometry allows the chemical composition and structure of the most relevant plasma-produced neutral species, the ionic plasma composition and the chemical composition of the nanometer-sized particles to be precisely identified. The production of acetylenic compounds (C2Hx) seems to be a key mechanism for the powder formation in all the investigated hydrocarbon plasmas. Electron attachment to acetylenic compounds and the following ion-neutral reactions might lead to the high-mass carbon anions, which are trapped in the plasma and finally end in powder formation. The hydrogenation of the monomer strongly influences the composition of the ions. Finally the composition of the plasma-produced particles is mainly sp3 bonded carbon and the infrared spectra show similarities to that of polyethylene.

201 citations

References
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Book
01 Jan 1983
TL;DR: In this paper, a Potpourri of Particles is used to describe surface modes in small Particles and the Angular Dependence of Scattering is shown to be a function of the size of the particles.
Abstract: BASIC THEORY. Electromagnetic Theory. Absorption and Scattering by an Arbitrary Particle. Absorption and Scattering by a Sphere. Particles Small Compared with the Wavelength. Rayleigh--Gans Theory. Geometrical Optics. A Potpourri of Particles. OPTICAL PROPERTIES OF BULK MATTER. Classical Theories of Optical Constants. Measured Optical Properties. OPTICAL PROPERTIES OF PARTICLES. Extinction. Surface Modes in Small Particles. Angular Dependence of Scattering. A Miscellany of Applications. Appendices. References. Index.

16,859 citations

Journal ArticleDOI
TL;DR: Light scattering by small particles as mentioned in this paper, Light scattering by Small Particle Scattering (LPS), Light scattering with small particles (LSC), Light Scattering by Small Parts (LSP),
Abstract: Light scattering by small particles , Light scattering by small particles , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

9,737 citations

Book
01 Dec 1981
TL;DR: Light scattering by small particles as mentioned in this paper, Light scattering by Small Particle Scattering (LPS), Light scattering with small particles (LSC), Light Scattering by Small Parts (LSP),
Abstract: Light scattering by small particles , Light scattering by small particles , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

6,623 citations

Frequently Asked Questions (19)
Q1. What are possible mechanisms which may lead to the observed high particle densities?

Trapping of negative ions and/or attachment-detachment cycling47 are possible mechanisms which may lead, in different works, to the observed high particle densities. 

To determine self-consistently the time evolution of particle size and their number density in situ multi-angle polarization-sensitive laser light scattering was used. Later in the particle time development both techniques reveal spherical particles again. It is found that the particle radius and particle number density during the agglomeration phase can be well described by the Brownian free molecule coagulation model. Application of this neutral particle coagulation model is justified by calculation of the particle charge whereby it is shown that particles of a few tens of nanometer can be considered as neutral under their experimental conditions. The measured particle dispersion can be well described by a Brownian free molecule coagulation model including a log-normal particle size distribution. 

The charges on the large particles only influence the electron density considerably for low values of ni , since then the number of charges localized on these large particles becomes comparable to the ion density. 

To solve the indetermination problem of four unknown quantities (Rp ,Np ,mr ,mi) from three independent measurements ~W'' , W ii , and T/T0!, the scattering angular dissymmetry method can be used. 

It should be noted that small size particles of about 40 nm remain in the discharge all along the time development, whereas large particles increase in size with time. 

The large particle number density of very small particles is responsible for a drastic decrease of the electron density in spite of the low number of charges attributed to each particle. 

Twelve TEM grids can successively be exposed to the plasma during a certain time, through a 3 mm hole positioned 43 mm off electrode axis. 

The advantage of the polarization-sensitive laser light scattering with respect to circular polarization methods21 is the sensitivity to the crosspolarization intensity. 

if each of the small particles constituting an agglomerate is counted separately instead of considering the nonspherical cluster as a single particle with a radius calculated from the sum of the volume of individual sticking particles in the agglomerate, this will lead to a bimodal size distribution. 

Therefore particles in the order of up to a few tens of nanometers behave under their conditions like neutrals, at least at the beginning of the coagulation phase. 

it has been shown that for long times into the coagulation phase the geometric standard deviation approaches s51.35 independently of its initial value. 

At the beginning of this agglomeration phase particles as small as a few nm are present in the plasma with a particle number density 

In this simplified model forces such as the van der Waals attractive force, the Coulomb repulsive force, and the laminar shear effect are not taken into account. 

More sophisticated neutral coagulation schemes, including increasing charging of the particles with time and coagulation between charged and uncharged particles, may be necessary to understand in detail the physics of the agglomeration in dusty plasmas. 

According to this, the authors can say that agglomeration ‘‘saves’’ the plasma from extinction by decreasing the net total charge on the particles. 

For their measurements of the scattered intensities at three angles ~45°, 90°, and 135°!, the authors used the same iterative method as applied for one angle to determine the time development of the radius and the number density of particle. 

Two explanations can describe this phenomena, evaporation of the particles by the laser beam and/or the thermophoretic effect caused by a temperature gradient between the laser path and the rest of the plasma. 

A supplementary study was devoted to the laser fluencepowder interaction which, it was found, could also lead to misinterpretation of the measurements. 

Placing the detectors just above the laser path allowed to estimate the multiple-scattering contribution which did not exceed 5%–10% of the direct polarization intensity.