Surface Plasma Waves Research Articles

Observation of Hot Electrons in Surface-Wave Plasmas Excited by Surface Plasmon Polaritons

The electron energy distribution functions (EEDFs) are studied in the planar-type surface-wave plasma (SWP) caused by resonant excitation of surface plasmon polaritons (SPPs) using a single cylindrical probe. Sustained plasma characteristics can be considered as a bi-Maxwellian EEDF, which correspond to a superposition of the bulk low-temperature electron and the high-energy electron beam-like part. The beam component energy is pronounced at about 10eV but the bulk part is lower than 3.5eV. The hot electrons included in the proposed plasmas play a significant role in plasma heating and further affect the discharge chemistry.

Influence of nitrogen impurities on the formation of active species in Ar-O2plasmas

A self-consistent kinetic model was developed in order to study the production of active species in Ar-O 2 surface-wave microwave plasmas with a relatively small N 2 addition. It is shown that the Ar-O 2 -N 2 mixture produces efficiently the same active species as an Ar-O 2 discharge, including oxygen atoms, metastable O 2 ( a 1 ∆ g ) molecules and the VUV emitting Ar(4 s ) states. Furthermore, active N-containing species are additionally produced, in particular N atoms and NO ground-state and excited molecules, which makes the ternary mixture very interesting for numerous plasma applications.

Electron Density Range Measurable by Microwave Resonator Probe with Higher Mode Resonance

A microwave resonator probe is a simple tool for measuring the electron density of 1010–1012 cm-3 based on the plasma-induced shift Δf in the resonance frequency of a U-shaped wire antenna. However, when the electron density is as low as 108–1010 cm-3, the measurement becomes difficult because of the small Δf (low-density limit), and partly because of the reduction in resonance signal amplitude (high-density limit). Here, the measurable electron density range for the given antenna length is elucidated by taking into account these limitations and the instrumental limit of the network analyzer system used in the measurement. To expand the measurable electron density range to measure lower densities, we propose the use of the second-harmonic resonance. In addition to the analysis of the measurable electron density range, the experiments using the harmonic resonance are presented in terms of the electron density dependences on the discharge power and pressure in a surface wave plasma at 2.45 GHz.

Alfvén Surface Waves in a Partially Ionized Resistive Medium

We study the joint effects of viscosity, resistivity and ion-neutral collisions on Alfvén surface waves propagating along a partially ionized plasma - vacuum interface. Applying boundary conditions at plasma-vacuum interface, we obtain the dispersion relation for Alfvén surface waves and solve it numerically. For different values of resistivity and neutral gas friction parameters, the variation of real and imaginary parts of wave number with viscosity parameter are shown graphically. It is found that two-mode structure of Alfvén surface waves results due to the combined effects of resistivity, viscosity and ion-neutral collisions. These results might be useful for studying the behavior of Alfvén surface waves in laboratory and space plasmas.

Electrostatic Dust-Cyclotron Surface Waves

The existence of electrostatic dust-cyclotron (EDC) surface waves in a uniform magnetized plasma containing dust particles is predicted. We show that the dispersion relation of the wave can be derived by employing the plasma dielectric permittivity and the specular re∞ection boundary condition. We flnd that the phase velocity tends to be enhanced by increasing the magnitude of the magnetic fleld except at very large wave numbers. The group velocity is, however, suppressed, in general, as the magnetic fleld is increased.

Physical principles of plasma antenna operation

Basic principles of operation of plasma antennas based on volume and surface plasma waves are presented. It is demonstrated that the efficiency of plasma antennas does not yield to that of metal antennas and that the controllability (frequency tuning for reception and transmission) and radar invisibility (a small radar cross section) are significantly higher. Plasma antennas of two types are considered: dipole antennas operating based on the surface plasma wave, and slotted waveguide antennas operating based on the volume plasma wave.

Efficient laser-overdense plasma coupling via surface plasma waves and steady magnetic field generation

The efficiency of laser overdense plasma coupling via surface plasma wave excitation is investigated. Two-dimensional particle-in-cell simulations are performed over a wide range of laser pulse intensity from 1015 to 1020 W cm−2 μm2 with electron density ranging from 25 to 100nc to describe the laser interaction with a grating target where a surface plasma wave excitation condition is fulfilled. The numerical studies confirm an efficient coupling with an enhancement of the laser absorption up to 75%. The simulations also show the presence of a localized, quasi-static magnetic field at the plasma surface. Two interaction regimes are identified for low (Iλ2 < 1017 W cm−2 μm2) and high (Iλ2 > 1017 W cm−2 μm2) laser pulse intensities. At “relativistic” laser intensity, steady magnetic fields as high as ∼580 MG μm/λ0 at 7 × 1019 W cm−2 μm2 are obtained in the simulations.

Particle-in-cell investigation on the resonant absorption of a plasma surface wave

The resonant absorption of a plasma surface wave is supposed to be an important and efficient mechanism of power deposition for a surface wave plasma source. In this paper, by using the particle-in-cell method and Monte Carlo simulation, the resonance absorption mechanism is investigated. Simulation results demonstrate the existence of surface wave resonance and show the high efficiency of heating electrons. The positions of resonant points, the resonance width and the spatio-temporal evolution of the resonant electric field are presented, which accord well with the theoretical results. The paper also discusses the effect of pressure on the resonance electric field and the plasma density.

Selectivity of SPR fiber sensors in absorptive media: An experimental evaluation

Conventional surface plasmon resonance (SPR) fiber sensors show selective behavior when resonance wavelengths are tuned to absorption peaks of the surrounding medium, as it is experimentally shown and evaluated in this paper by using a doubly-deposited uniform-waist tapered optical fiber (DLUWT) and a dye as a test material. This behavior is clearly distinguishable from the usual response to nonabsorbing media and can be used to develop a new concept of SPR transducers. At the same time, the obtained results, which are in accordance with the theoretical predictions permit to increase the basic knowledge on surface plasma waves excitation in optical fibers.

Immobilization of L-Cysteine onto Poly(ethylene glycol) Polymerized by Surface-Wave Plasma

Poly(ethylene glycol) (PEG) terminated with hydroxyl functional groups is expected to play the roles of a hydrophilic layer to alleviate the aging effect and an intermediate for the subsequent covalent immobilization of L-cysteine. A plasma-induced grafting-polymerization or crosslinking technique using microwave-excited surface-wave plasma for grafting PEG molecules on a polyurethane (PU) surface is presented. The effects of Ar plasma pretreatment and post-treatment on the in situ polymerization or crosslinking of PEG molecules are investigated. The effect of Ar plasma pretreatment on the surface shows that pretreatment can induce the adsorption of more PEG molecules on the surface for the subsequent post-treatment. Increasing the post-treatment power and post-treatment time can achieve the in situ polymerization or crosslinking of PEG molecules, whereas excessively increasing the post-treatment power and post-treatment time can induce excessive damage to the hydroxyl functional groups.

Immobilization of L-Cysteine onto Poly(ethylene glycol) Polymerized by Surface-Wave Plasma

Immobilization of L-Cysteine onto Poly(ethylene glycol) Polymerized by Surface-Wave Plasma

Effects of N2–O2 Gas Mixture Ratio on Microorganism Inactivation in Low-Pressure Surface Wave Plasma

In this study, the effect of N2/O2 gas mixture ratio on low-pressure surface wave plasma inactivation of spore-forming bacteria was investigated. It was experimentally confirmed from the quadrupole mass spectrometry measurements that the spores were etched by atomic oxygen via converting the hydrogen atoms constituting microorganisms into H2O and the carbon into CO2. On the basis of results of plasma diagnostics by optical emission spectroscopy and the results of inactivation efficiency by colony-forming units and scanning electron microscope, we found that although there is the highest ultraviolet (UV) emission intensity in pure N2 plasma and the highest etching efficiency in 90% O2/10% N2 plasma, the inactivation rate of microorganisms was not so efficient. The best inactivation result was obtained in 30–80% O2 gas mixture ratios after 60 s plasma irradiation. The present results indicated that more efficient inactivation is achieved by the synergetic effects between atomic oxygen etching and the vacuum ultraviolet (VUV)/UV emission by combining both effects via optimizing N2/O2 gas mixture ratio.

Effects of Nitrogen and Oxygen Radicals on Low-Temperature Bio-Molecule Processing

The mechanism by which microwave plasma is able to modify the structure and function of proteinaceous molecules is investigated. The biomolecule cystine, a dimer aminoacid, was exposed to microwave surface wave plasma produced in reactive gases, such as oxygen and nitrogen, in different conditions. Except for the physical interactions of the charged particles with the samples and the photophysical reactions induced mostly by ultraviolet radiation, these plasmas contain reactive species which promote chemical interactions. In this study we focus on the changes of biomolecules due to neutral particles inside reactive plasmas. The results proved that the effects of neutrals and charged species are not cumulative. Moreover, it seems that the charged species inside the nitrogen plasma promote nitrogen addition while the outcome of neutral exposure is cleavage. Strong oxidation occurs for oxygen treatments, most reactive species which cause oxygen addition being the oxygen molecular ions O2+.

Effects of N2–O2Gas Mixture Ratio on Microorganism Inactivation in Low-Pressure Surface Wave Plasma

Effects of N₂–O₂Gas Mixture Ratio on Microorganism Inactivation in Low-Pressure Surface Wave Plasma

Effects of Nitrogen and Oxygen Radicals on Low-Temperature Bio-Molecule Processing

The mechanism by which microwave plasma is able to modify the structure and function of proteinaceous molecules is investigated. The biomolecule cystine, a dimer aminoacid, was exposed to microwave surface wave plasma produced in reactive gases, such as oxygen and nitrogen, in different conditions. Except for the physical interactions of the charged particles with the samples and the photophysical reactions induced mostly by ultraviolet radiation, these plasmas contain reactive species which promote chemical interactions. In this study we focus on the changes of biomolecules due to neutral particles inside reactive plasmas. The results proved that the effects of neutrals and charged species are not cumulative. Moreover, it seems that the charged species inside the nitrogen plasma promote nitrogen addition while the outcome of neutral exposure is cleavage. Strong oxidation occurs for oxygen treatments, most reactive species which cause oxygen addition being the oxygen molecular ions O2+.

Vacuum electron heating by surface plasma wave

Vacuum heating of electrons by a large amplitude surface plasma wave (SPW) over a metal surface due to the Brunel effect is studied. The surface plasma wave has large normal component of electric vector. The normal field pulls the electrons away from the plasma during the half cycle. Each electron sees, besides the E⊥ of the surface plasma wave, a static space charge field. As the electron returns back to the interface, it possesses kinetic energy that is deposited into the plasma, leading to plasma heating.

Plasmonic-Enhanced Photodetectors for Focal Plane Arrays

Plasmonic enhancement of a quantum-dot infrared photodetector (QDIP) using a corrugated metal surface (CMS) that is fully compatible with conventional focal plane array manufacturing is demonstrated. A CMS consisting of a 2.5-μm period, 2-D square array of 1.1-μ m-high GaAs circular posts passivated with a thick Au film is fabricated into the heavily doped, top GaAs contact layer of an InAs QDIP. For substrate-side illumination, the CMS exhibits strong coupling to surface plasma waves bound to the Au/GaAs interface providing enhancement of the QDIP. At 77 K, the CMS-processed QDIP exhibits up to ~15-fold detectivity enhancement compared with the original detector.

Plasmon delocalization onset in finite sized nanostructures

The transition from localized to delocalized plasmons (i.e. the transition from a situation where the decay length of a travelling surface plasma wave is greater than its propagation distance to a situation where it is smaller) and hence the onset of plasmon delocalization is studied in a single 2D silver nanoparticle of increasing length. A fourier analysis in the near-field of the nanoparticle is used as the main tool for analysis. This method, along with far-field scattering spectra simulations and the near-field profile directly above and along the length of the nanoparticle are used to investigate and clearly show the transition from localized to delocalized modes. In particular, it is found that for a finite sized rectangular nanoparticle, both the emerging odd and even delocalized modes are nothing but a superposition of many standing wave plasmon modes. As a consequence, even very short metal films can support delocalized plasmons that bounce back and forth along the film.

Mass spectrometric study on inactivation mechanism of spore-forming bacteria by low-pressure surface-wave excited oxygen plasma

In this letter, the etching phenomena of the spore-forming bacteria by oxygen plasma were investigated by using quadrupole mass spectrometry. The etching by-products of H2O and CO2 were obviously detected during the oxygen plasma irradiation by the multiple ion detection measurement. Inactivation of roughly 106 spores population was achieved under almost the same reduced spore shapes for three different incident microwave powers. It is considered from the present results that the oxygen radical etching could cause damage to the germinant receptors located in the inner membrane inevitable for germination of spores, without any damage of the DNA in the cores.

Excitation of surface plasma waves by a density modulated electron beam at a conductor-dusty plasma interface

A density modulated electron beam propagating through a conductor-dusty plasma interface drives electromagnetic surface plasma waves (SPWs) to instability via Cerenkov and cyclotron interaction. The SPWs propagate across an external magnetic field parallel to the interface. Numerical calculations of the growth rate and unstable mode frequencies have been carried out for the typical parameters of the SPWs. The frequency and the growth rate of the unstable wave instability increase with the relative density of negatively charged dust grains δ (= nio/neo, where nio is the ion plasma density and neo is the electron plasma density). The phase velocity of the unstable waves also increases with δ. In addition, the growth rate of the instability increases with the beam density and scales as one-third power of the beam density in Cerenkov interaction and square root of beam density in fast cyclotron interaction. Moreover, the dispersion relation of SPWs has been retrieved in the absence of the modulated beam and without dust grains.