In the last 30 days

• Open/close Investigation of discharge mechanisms in helium plasma jet at atmospheric pressure by laser spectroscopic measurements

  Keiichiro Urabe et al  2010 J. Phys. D: Appl. Phys. 43 095201 Tag this article

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  We have measured spatiotemporal structures of excited species by laser spectroscopic methods in a plasma jet, which was driven by a bipolar impulse voltage pulse train of the order of kilohertz repetition rate applied across a pair of electrodes wrapped around a glass tube with a helium gas flow. We noticed the differences between the positive and the negative phases of the voltage applied to the front-side electrode placed closer to the tube exit while the back-side electrode was grounded. The experimental results showed that the radial distribution of the excited species had a hollow shape at the centre in the positive voltage phase, while it had a more uniform shape in the negative phase. The peak density of the helium metastable atom in the positive phase was almost constant irrespective of the peak applied voltage. However, it increased with the increase in the peak applied voltage in the negative phase. The mechanism causing these differences was argued from the respects of positive and negative corona discharges. We have also investigated the property of the plasma plume under conditions similar to material processing with a conductive substrate placed in front of the plasma jet. In this case, the plasma production by electron impact ionization became dominant near the substrate as was revealed from the spatiotemporal distributions of helium metastable atom and nitrogen ion densities.

• Open/close Removal of cyclohexanone in transition electric discharges at atmospheric pressure

  Zdenko Machala et al  2000 J. Phys. D: Appl. Phys. 33 3198 Tag this article

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  Two new types of streamer-induced electric discharges operating in a non-uniform electric field in air at atmospheric pressure were applied to the removal of volatile organic compounds (VOCs). The first type is a pulseless dc discharge with physical properties corresponding to the glow discharge. The second, also supplied by a dc high voltage of both polarities, is a spontaneously pulsing discharge operating in the regime of the streamer-to-spark transition, the spark phase being too short to reach local thermodynamic equilibrium conditions. Both discharges are able to generate a non-thermal plasma, as resolved from their rotational and vibrational temperatures.

  The influences of these discharges on the removal of cyclohexanone at various gas flow rates and concentrations (600-6000 ppm) were compared. The removal efficiencies achieved were about 50-60%, and the energy costs were 16-100 eV/molecule at various energy densities. Special conditions where CO ₂ and other gaseous products are minor and dominant products appear in the condensed phase can be obtained, especially in the spontaneously pulsing transition discharge.

  We explain some plasmochemical processes induced by the discharges by considering heterogeneous effects of the copper electrode surface. The role of active nitrogen and the formation of the NCO radical are probably key factors leading to the formation of the condensation product based on amino acids, here produced for the first time from VOCs, as well as in the overall energy cycle resulting in low energy costs of the process.

  The small pilot-scale reactor based on the spontaneously pulsing transition discharge has been successfully applied to the removal of cyclohexanone in the mixture with other VOCs with no noxious gas output. This validates the possibility of the application of such a type of reactor for larger scales.

• Open/close Effect of additives on distributions of lamellar structures in sheared polymer: a study of synchrotron small-angle x-ray scattering

  Peng-Wei Zhu et al  2009 J. Phys. D: Appl. Phys. 42 245406 Tag this article

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  The effects of additives on the distributions of lamellar morphology and orientation in sheared isotactic polypropylene were investigated using the small beam of synchrotron small-angle x-ray scattering. The Cu-phthalocyanine can template the lamellar orientation even under low shear rates, whereas the ultramarine blue cannot. The surface contact is suggested to play a role in stabilizing the formation of oriented nuclei which subsequently direct the growth of oriented lamellae. The additives have no notable effects on the long spacing in the shear region. However, at high shear rates, they decrease the thickness of crystalline lamellae or increase the thickness of amorphous lamellae. Since the additives increase the degree of volume crystalline in the shear region, the number of crystalline lamellae should be increased. The results are helpful in designing and selecting suitable additives for controlling lamellar morphology and orientation.

• Open/close The transition from longitudinal to perpendicular recording

  H J Richter  2007 J. Phys. D: Appl. Phys. 40 R149 Tag this article

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  After more than 30 years of research, hard disk drives using perpendicular recording are finally commercially available. This review is a follow-up of a review written in 1999 and addresses the basic physics of perpendicular recording with special emphasis on the read and the write process and the magnetic aspects of the recording media. The paper also surveys various technical difficulties which prevented an earlier implementation of perpendicular recording. The paper closes with a short overview of alternative technologies that allow even higher storage densities.

• Open/close Numerical investigation of relationship between micro-scale pattern, interfacial plasma structure and feature profile during deep-Si etching in two-frequency capacitively coupled plasmas in SF₆/O₂

  Fukutaro Hamaoka et al  2009 J. Phys. D: Appl. Phys. 42 075201 Tag this article

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  The feature profile of deep-Si etching in the presence of plasma moulding in two-frequency capacitively coupled plasmas in SF ₆/O ₂ has been numerically simulated to investigate the relationship between the micro-scale pattern on a Si wafer, the interfacial structure of the plasma (i.e. the sheath) and the etching profile. We have also discussed the deep-Si etching profile as functions of the SF ₆/O ₂ gas mixture ratio and the total gas pressure. The result shows that the plasma moulding has no influence on the sheath structure when the sheath thickness is an order of magnitude longer than the width of the hole pattern. In the presence of a large number of F radicals, the chemical etching of Si causes isotropic etching with a significant undercut profile, reducing the plasma moulding's influence on the etching profile due to the F radicals' much higher Si etching rate compared with the rate of etching by ions. On the other hand, with the increase in the oxygen mixture ratio, a passivation layer grows up on the inside wall, and the removal of the layer at the bottom corner is strengthened by the distorted ion by plasma moulding. Thus, the etching is enhanced particularly at the bottom corner. As the pattern width decreases and the oxygen mixture ratio increases, the etching profile becomes anisotropic by the formation of the passivation layer at the sidewall. In addition, the bottom profile becomes flat because of the uniform ion flux under the reduced influence of the plasma moulding.

• Open/close Thin-film transistors with transparent amorphous zinc indium tin oxide channel layer

  M S Grover et al  2007 J. Phys. D: Appl. Phys. 40 1335 Tag this article

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  Thin-film transistors (TFTs) with transparent amorphous zinc indium tin oxide (ZITO) channel layer are demonstrated. Optical transmission of the channel layer is approximately 85% in the visible portion of the electromagnetic spectrum. The channel layer is formed via rf magnetron sputter deposition and then furnace annealed in air. Peak incremental mobilities of 5–19 cm ² V ⁻¹ s ⁻¹ and turn-on voltages of −4 to −17 V are obtained for devices annealed post-deposition at 100–300 °C, respectively. Current–voltage measurements indicate n-channel, depletion-mode transistor operation with excellent drain current saturation and a drain current on-to-off ratio greater than 10 ⁶. ZITO is one example of an emerging class of high performance TFT channel materials involving transparent amorphous multicomponent oxides composed of heavy-metal cations with ( n − 1) d ¹⁰ ns ⁰ ( n ≥ 4) electronic configuration.

• Open/close Prospects for non-thermal atmospheric plasmas for pollution abatement

  R McAdams  2001 J. Phys. D: Appl. Phys. 34 2810 Tag this article

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  For approximately the past ten years, atmospheric pressure non-thermal plasmas have been increasingly promoted as a technology for a number of applications in the area of pollution abatement. In such plasmas, the electrons have a significantly higher temperature compared to the ions, atoms and molecules. This paper provides an overview of both the technologies involved and the diverse potential application areas. A general description of these atmospheric plasmas and the basic principles involved in the destruction or removal of gaseous phase pollutants, based on the nature of the processes taking place within these plasmas, are given. A number of examples of the different plasma technologies are described. The technologies described are pulsed corona, microwave and dielectric barrier plasmas. Their suitability and use in various application areas are also discussed including incinerator off gas treatment, industrial process off gas treatment and diesel exhaust aftertreatment. The use of modelling of the physical and chemical processes involved to predict system performance and as a tool for sizing systems to meet customer requirements is also discussed.

• Open/close Applications of magnetic nanoparticles in biomedicine

  Q A Pankhurst et al  2003 J. Phys. D: Appl. Phys. 36 R167 Tag this article

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  The physical principles underlying some current biomedical applications of magnetic nanoparticles are reviewed. Starting from well-known basic concepts, and drawing on examples from biology and biomedicine, the relevant physics of magnetic materials and their responses to applied magnetic fields are surveyed. The way these properties are controlled and used is illustrated with reference to (i) magnetic separation of labelled cells and other biological entities; (ii) therapeutic drug, gene and radionuclide delivery; (iii) radio frequency methods for the catabolism of tumours via hyperthermia; and (iv) contrast enhancement agents for magnetic resonance imaging applications. Future prospects are also discussed.

• Open/close Chemical kinetics with electrical and gas dynamics modelization for NO_x removal in an air corona discharge

  O Eichwald et al  2002 J. Phys. D: Appl. Phys. 35 439 Tag this article

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  A non-stationary reactive gas dynamics model in a mono-dimensional geometry, including radial mass diffusion, gas temperature variation and chemical kinetics, is developed in this paper. The aim is to analyse the spatio-temporal evolution of the main neutral species involved in a corona discharge used for NO pollution control in polluted air at atmospheric pressure and ambient temperature. The present reactive gas dynamics model takes into account 16 neutral chemical species (including certain metastable species) reacting following 110 selected chemical reactions. The initial concentration of each neutral species is obtained from a 1.5D electrical discharge model. The gas temperature variations are due to direct Joule heating during the discharge phase, and also result from the delayed heating due to the relaxation of the vibrational energy into a random thermal energy during the post-discharge phase. The simulation conditions are those of an existing experimental setup (anode voltage of 10 kV in the case of a point to plane geometry with an interelectrode distance of 10 mm). The obtained results show that the diffusion phenomena and the gas temperature rise affect quite well the gas reactivity and the neutral species evolution. This allows us to better understand the different reaction processes and transport phenomena affecting the NO concentration magnitude inside the discharge channel.

• Open/close Nanoparticle catalysts

  A Z Moshfegh  2009 J. Phys. D: Appl. Phys. 42 233001 Tag this article

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  In this review, the importance of nanoparticles (NPs), with emphasis on their general and specific properties, especially the high surface-to-volume ratio ( A/ V), in many technological and industrial applications is studied. Some physical and chemical preparation methods for growing several metallic and binary alloy NP catalysts are reviewed. The growth and mechanism of catalytic reactions for synthesis of 1D nanostructures such as ZnO nanowires and multiwall carbon nanotubes (MWCNTs) are discussed. Gas-phase production with emphasis on dependence of catalytic activity and selectivity on size, shape and structure of NPs is also investigated. Application of NP catalysts in several technological processes including H ₂ production and storage as well as antibacterial effect, gas sensors and fuel cells is discussed. The mechanism of H ₂ production from catalytic photoelectrochemical and photocatalytic degradation reactions of some organic dyes is discussed. Finally, the future outlook of NP catalysts in various disciplines is presented.