Surface Plasma Waves Research Articles

Tunable distributed SPR sensors with symmetrical structures excited by planar waveguides

Measurement ranges of the traditional surface plasmon resonance (SPR) sensors, which use intensity detection method and are excited by waveguides, are limited by the equivalent refractive index of the excited waveguide, not only makes it non-adjustable but also difficult to realize multi-range detection. To solve the above problems, tunable distributed SPR sensors with symmetrical structures excited by planar waveguides are designed. By studying several metrics of a metal-medium-metal SPR sensing structure exited by a planar waveguide, the influence of a metallic material’s thickness, and the medium thickness between the gold films on the measurement characteristics, are accordingly optimized to design the detection system. Double attenuation peaks can be generated under certain conditions, which embodies distributed sensing characteristics. Here, changing the resonance condition by changing the thickness of the measured medium between the metal films makes the measured refractive index range tunable. The planar waveguide with the Fermi refractive index distribution is prepared and the symmetrical sensing structures are arranged longitudinally alongside the direction of light propagation to achieve multiple attenuation peaks, and thus distributed sensing in different measured ranges is realized. The structure of different medium thicknesses excited by planar waveguides is used to test the honey solution with refractive indices varying between 1.33299 and 1.53246 in exciting the surface plasma waves with double attenuation peaks. For any refractive index range, the linear correlation coefficients are all above 0.99232, which demonstrates that the refractive index detection can be carried out within multiple ranges. This result constitutes a theoretical and practical basis for tunable distributed online measurement of the intensity SPR sensors.

Unstable electrostatic surface waves in a turbulent plasma containing streaming ions: transverse truncation approach

The unstable modes of surface waves propagating in a sharply bounded turbulent plasma containing streaming ions are investigated by employing the specular reflection condition and the transverse truncation method. We have found that the bounded turbulent plasma supports damping and growing modes. The damping mode propagates for all values of the ion streaming speed modes and their behavior is similar to the case of surface waves in a turbulent plasma without ion streaming. If the speed of ion streaming is larger than the ion-acoustic speed, growing mode exists for all values of the wave number. However, if the ion stream is slower than the ion acoustic speed, then the growing mode appears under a certain condition. We derive the dispersion relations for such modes of surface waves and investigate the condition for propagation.

Relativistic electron acceleration by surface plasma waves excited with high intensity laser pulses

The process of high energy electron acceleration along the surface of grating targets (GTs) that were irradiated by a relativistic, high-contrast laser pulse at an intensity $I=2.5\times 10^{20}~\text{W}/\text{cm}^{2}$ was studied. Our experimental results demonstrate that for a GT with a periodicity twice the laser wavelength, the surface electron flux is more intense for a laser incidence angle that is larger compared to the resonance angle predicted by the linear model. An electron beam with a peak charge of ${\sim}2.7~\text{nC}/\text{sr}$ , for electrons with energies ${>}1.5~\text{MeV}$ , was measured. Numerical simulations carried out with parameters similar to the experimental conditions also show an enhanced electron flux at higher incidence angles depending on the preplasma scale length. A theoretical model that includes ponderomotive effects with more realistic initial preplasma conditions suggests that the laser-driven intensity and preformed plasma scale length are important for the acceleration process. The predictions closely match the experimental and computational results.

Study on CF4/O2 plasma resistance of O-ring elastomer materials

The CF4/O2 plasma resistance of the O-ring elastomer samples was investigated using a microwave-excited surface-wave plasma source. The elastomer samples include a fluoroelastomer (FKM) and a perfluoroelastomer (FFKM), both of which are widely used for plasma process equipment. In semiconductor manufacturing, the CF4/O2 plasma was widely used for plasma etching and cleaning processes. To investigate the relation between the plasma resistance of the elastomers and plasma parameters, the Langmuir probe measurement was carried out. The kinetic energy of bombarding ions was increased by applying an rf power to a wafer substrate in some of the experiments. The results suggested that both FKM and FFKM were eroded by the low-energy (less than 10 eV) ion bombardment. The kinetic energy of bombarding ions was also a dominant factor to determine the amount of erosion of both the FKM and the FFKM elastomers. In addition, it is suggested that neutral radical attacks were also a dominant factor to increase the erosion of the elastomer for the FKM elastomer, whereas the stability of the FFKM elastomer against neutral radicals was much better than that of the FKM elastomer.

Compact water-cooled surface wave plasma source for remote plasma cleaning.

This paper describes the design and operation of a compact surface wave plasma source for remote plasma processing [i.e., plasma enhanced chemical vapor deposition chamber cleaning, dry etching (SiO2, Si3N4, and silicon), photoresist stripping (SU-8), and decapsulation of microchips]. In order to get higher radical generation and increased industrial throughput, the source is designed to generate plasma at a high flowrate. The source is designed to be compact so that it can be more beneficial in the case of positioning multiple sources on a large processing chamber for faster radical cleaning with better uniformity. The source can operate from low to high flowrates (i.e., 100 SCCM H2 or 10 slm NF3) and provide high decomposition rates for NF3. The etching rate for SiO2 (higher than 450 nm/min) is achieved with 2.5 kW microwave power and 3-5 slm. The key advantages of the source are compactness, higher microwave coupling due to indirect water-cooling, and thereby high operating flow and decomposition rates.

Low Temperature Growth of CVD Nanocrystalline Diamond Thin Film by Designed SWP-CVD with Various Working Pressures

Nanocrystalline diamond (NCD) is exceptionally useful for a variety of applications and is of significant interest to researchers in technological and scientific fields due to its excellent mechanical and chemical properties, such as its hardness and high thermal conductivity. We have modified a microwave plasma chemical vapor deposition (MPCVD; Astex Inc.) system with a slot antenna designed for surface wave plasma (SWP) and successfully fabricated high quality thin NCD film. This SWP-CVD process fabricates high quality diamond film at 300 °C, while a normal MPCVD process requires the temperature of the substrate to be above 800 °C. We studied the fabricated NCD samples in detail, measuring their surface morphology by field emission scanning electron microscopy (FESEM); their structural-chemical properties by Raman spectroscopy; and their surface roughness by atomic force microscopy (AFM).

Electron acceleration of a surface wave propagating in wiggler-assisted plasma

In this paper, we study the electron acceleration by a surface plasma wave (SPW) propagating through two parallel metal sheets in the presence of wiggler magnetic field strength. The configuration of interest consists of a helical magnetostatic wiggler, an external magnetic field and two parallel metal half-spaces. Dispersion relation of SPW in the attendance of helical magnetostatic wiggler is recognized and observed as compared with that of without wiggler field. A numerical calculation in Matlab software was developed by employing the fourth-order Runge–Kutta method for studying the electron energy and electron trajectory in SPW. Numerical results depict that with increasing of [Formula: see text]-parameter [Formula: see text] is the ratio of wiggler frequency to plasma frequency), minimum modes of SPW have an increasing trend and with increase of the wiggler frequency, the normalized frequencies decreased and a gap appeared between them. Furthermore, it is seen that with increase of the [Formula: see text]-parameter, the value of the kinetic energy as compared with the absence of the wiggler magnetic field increased. In fact, the electron energy gained is higher in the presence of a helical magnetostatic wiggler as compared with the absence of wiggler field. In addition, it is observed that due to effects of the wiggler field and SPW field, the electron traverses more distance in the propagation direction of the laser pulse.

Excitation of Surface Waves during by an Inhomogeneous Electromagnetic Wave Incident on the Plasma Boundary

We have studied the excitation of surface plasma waves during the propagation of a cylindrical electromagnetic wave in a layered plasma–dielectric medium. The dielectric—vacuum—plasma and vacuum–plasma–plasma layers have been considered. It is shown that no surface waves are excited by the cylindrical electromagnetic wave at the plasma–dielectric boundary (like in the case of a plane wave). A surface wave in a layered medium is excited in a quite narrow range of frequencies and angles of propagation. We have calculated the structures of the electromagnetic field and the electromagnetic energy flux and determined the integral reflection and transmission coefficients using both numerical an analytic asymptotic methods. It is shown that the contribution of the field from the lateral wave is negligibly small in all cases.

Influence of gas flow on the axial distribution of densities, temperatures and thermodynamic equilibrium degree in surface-wave plasmas sustained at atmospheric pressure

In this paper, a discussion about the influence of the gas flow on the axial distribution of plasma densities, temperatures and thermodynamic equilibrium degree in argon surface-wave discharges sustained at atmospheric pressure is presented. It was found that increasing the gas flow produces a decrease in gas temperature and electron density which is explained in terms of a decrease of residence time of both heavy particles and electrons. Moreover, the dependence of the dynamics of argon molecular ions on gas temperature also explains the decrease in electron density and the increase in the population of 4p excited levels. Thermodynamic equilibrium is also affected by gas flow, whose increase drives the 5p levels out of partial Saha equilibrium, although they remain in the collisional regime for their population processes. Furthermore, the linear power density was measured to complete the characterization of surface-wave plasmas with different gas flows. From the linear power density, it is possible to conclude that increasing the gas flow means that the energy supplied to the discharge is being used not only for ionization processes, but also for the excitation of argon atoms from the ground to metastable states, thus, increasing the populations of 4p levels.

Sulfur: an alternative to mercury for UV emission in low-pressure low-power fluorescent discharges

The objective of this exploratory study is to demonstrate that sulfur can offer an advantageous alternative to mercury for the production of UV photons in fluorescent discharges not only in terms of environment and health impacts, but also in terms of Stokes shift energy losses for the conversion of UV photons by luminophors into visible light. The experiments are performed in surface-wave plasma columns sustained at the output end of a coaxial applicator by microwaves at 2.45 GHz frequency and 10 W applied microwave power. After introducing 10 mg sulfur in argon at 1 Torr, it can be observed that most of the emission spectrum due to sulfur is maximum in the UV range between 300 and 400 nm, well above the 253.7 nm resonant peak line met with mercury in low-pressure discharges. Therefore, by comparison with mercury, the Stokes shift is considerably reduced in the case of sulfur. By surrounding the silica discharge tube with a segment of commercial fluorescent tube coated inside with luminophors, the UV spectrum of sulfur appears quite efficiently transferred into visible light.

Enhanced Corrosion Resistance of Silicone-Modified Epoxy Coatings by Surface-Wave Plasma Treatment

Enhanced Corrosion Resistance of Silicone-Modified Epoxy Coatings by Surface-Wave Plasma Treatment

Investigation of role of the discharge tube in pulse modulated surface-wave argon plasma column at atmospheric pressure by optical emission spectroscopy

The axial profiles of the pulse modulated atmospheric pressure surface-wave argon plasma confined in discharge tubes of different diameters are measured by means of optical emission spectroscopy with respect to the emission intensity, gas temperature, and electron density and temperature. Then, the role of the discharge tube is investigated with respect to its diameter. Furthermore, a simplified theoretical model for high collision frequency is proposed for analysis of the experimental results of electron density obtained by the Stark broadening technique, achieving a good agreement between them for discharge tubes of different diameters.

Surface Amino Group Regulation and Structural Engineering of Graphitic Carbon Nitride with Enhanced Photocatalytic Activity by Ultrafast Ammonia Plasma Immersion Modification.

Surface amino group regulation and structural engineering of graphitic carbon nitride (g-CN) for better catalytic activity have increasingly become a focus of academia and industry. In this work, the ammonia plasma produced by a microwave surface wave plasma generator was developed as a facile source to achieve fast, controllable surface modification, and structural engineering of g-CN by ultrafast plasma treatment in minutes, thus enhancing photocatalytic performance of g-CN. The morphology, surface hydrophilicity, optical absorption properties, and states of C-N bonds were investigated to determine the effect of plasma immersion modification on the g-CN catalyst. The structure and photoelectric features of the plasma-modified samples were characterized by X-ray diffractometry, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. The results indicate that the ammonia plasma-treated g-CN-NH3 exhibits an ultrathin nanosheet structure, enriched amino groups, and an ideal molecular structure, a narrower band gap (2.35 eV), extended light-harvesting edges (560 nm), and enhanced electron transport ability. The remarkably enhanced photocatalytic activity demonstrated in the photoreduction and detoxification of hexavalent chromium (Cr(VI)) can be ascribed to the optimization of the structural and photoelectric properties induced by the unique ammonia plasma treatment. The effective and ultrafast approach developed in this work is promising in the surface amino group regulation and structural engineering of various functional materials.

A universal macroscopic theory of surface plasma waves and their losses

Recently, we have revealed an intrinsic instability of metals due to surface plasma waves (SPWs) and raised the prospect of using it to create lossless SPWs. The counter-intuitive nature of this finding prompts one to ask, why had not this instability been disclosed before, given the long history of this subject? If this instability does exist, how far is it from reality? The present work is devoted to answering these questions. To this end, we derive a unified macroscopic theory of SPWs that applies to any type of electron dynamics, be they local or non-local, classical or quantum-mechanical. In light of this theory, we analyze the behaviors of SPWs according to several electron dynamics models, including the widely used local dielectric model, the hydrodynamic model and the specular reflection model, in addition to the less common semi-classical model. We find that, in order to unveil the instability, one must (i) self-consistently treat surface effects without any of the usually imposed auxiliary conditions and (ii) include translation symmetry breaking effects in electron dynamics. As far as we are concerned, none existing work had fulfilled both (i) and (ii). To assess the possibility of realizing the instability, we analyze two very important factors: the dielectric interfacing the metal and inter-band transitions, which both were ignored in our recent work. Whereas inter-band absorption—together with Landau damping—is shown adverse to the instability, a dielectric brings it closer to occurrence. One may even attain it in common plasmonic materials such as silver under not so tough conditions.

Low temperature wafer-scale synthesis of hexagonal boron nitride by microwave assisted surface wave plasma chemical vapour deposition

Here, we report on the large-area synthesis of hBN layer at a comparatively lower temperature using ammonia borane as precursor by microwave assisted surface wave plasma (MW-SWP) chemical vapour deposition (CVD). The solid precursor was sublimed inside the CVD chamber and decomposed to form plasma radicals, which allowed the growth of hBN layer at a lower temperature (∼500 °C). The growth of hBN on Cu catalyst and Si wafer was confirmed by X-ray photoelectron spectroscopy, ultraviolet absorption spectroscopy, Fourier-transform infrared spectroscopy and transmission electron microscopy analysis. The hBN film synthesized on Cu catalyst showed a sharp absorption peak at 276 nm wavelength corresponding to an optical band gap of ∼4.1 eV, owing to the incorporation of carbon and oxygen doping impurities. The reduction of optical band gap of the hBN film with impurity doping can be significant to tune its optoelectronic properties. Thus, the demonstrated MW-SWP-CVD process can be significant to synthesize hBN layers independent of the catalytic behaviour of the substrate, thereby opening enormous possibilities of transfer-free application for device fabrication and as transparent coating on various surfaces.

Second harmonic generation by crossed surface plasma waves over a metallic surface

Excitation of second harmonic radiation by nonlinear mixing of two surface plasma waves (SPWs), propagating at an angle to each other over an air–metal interface, is investigated. The SPWs exert a ponderomotive force on electrons, driving a nonlinear surface current and producing the second harmonic. Depending upon the angle between the SPWs and the electron density of metals, the excited radiation could be a radiation mode or a surface mode. The latter requires a surface ripple for phase matching. The efficiency of radiative second harmonic increases with the free electron density of the metal. It is sensitive to the angle between the interacting SPWs. The surface mode second harmonic is relatively more efficient.

Investigation of MoS2 on coated titanium surface plasmon resonance side-polished optical fiber sensor

In this paper, we propose a rigorous configuration of 2D-material using MoS2 coated on titanium (Ti) surface plasmon resonance (SPR) optical fiber sensor. The present configuration is included side-polished optical fiber sensor, titanium (Ti) coating, MoS2 and sensing medium. The SPR sensing device uses a standard single-mode optical fiber with locally removed cladding and a thin Ti film supporting a surface plasma wave (SPW). We perform the performance characteristics of the design sensor in terms of sensitivity, detection accuracy and quality factor. Addition of MoS2 layer on the Ti-SPR will increase the overall sensitivity of the device. The polishing region is covered by metallic layer acted as active sensing medium as the interaction between the SPW, fiber mode and consequently the fiber mode attenuation which depends strongly on the refractive index of analytes. Variations of analytes used such as water, 60% alcohol, sodium chloride, glucose and sucrose can be determined by monitoring changes in the wavelength at which the resonant attenuation of the fiber mode occurs.

Enhancement of the surface emission at the fundamental frequency and the transmitted high-order harmonics by pre-structured targets

Laser interaction with an ultra-thin pre-structured target is investigated with the help of both two-dimensional and three-dimensional particle-in-cell simulations. With the existence of a periodic structure on the target surface, the laser seems to penetrate through the target at its fundamental frequency even if the plasma density of the target is much higher than the laser’s relativistically critical density. The particle-in-cell simulations show that the transmitted laser energy behind the pre-structured target is increased by about two orders of magnitude compared to that behind the flat target. Theoretical analyses show that the transmitted energy behind the pre-structured target is actually re-emitted by electron ‘islands’ formed by the surface plasma waves on the target surfaces. In other words, the radiation with the fundamental frequency is actually ‘surface emission’ on the target rear surface. Besides the intensity of the component with the fundamental frequency, the intensity of the high-order harmonics behind the pre-structured target is also much enhanced compared to that behind the flat target. The enhancement of the high-order harmonics is also related to the surface plasma waves generated on the target surfaces.

Gas dependent growth study of hexagonal boron nitride synthesized by microwave assisted surface wave plasma chemical vapor deposition process

Gas dependent growth study of hexagonal boron nitride synthesized by microwave assisted surface wave plasma chemical vapor deposition process

Numerical Investigation of the Gas Flow Effects on Surface Wave Propagation and Discharge Properties in a Microwave Plasma Torch

Gas flow plays an important role in determining the discharge properties in microwave plasma torches sustained by the propagating surface wave. This paper aims to investigate the gas flow effects on the plasma column length, the surface wave propagation, and the heavy species temperature in a surface wave plasma torch operated at atmospheric pressure. The steadystate discharges of pure argon gas at atmospheric pressure under different gas inflow rates in the plasma torch are characterized by an improved 2-D axisymmetric fluid model. The obtained results demonstrate that increasing the gas inflow rate is able to decrease the surface wave propagation distance, accelerating the contraction of the plasma column length. The discharge instability is found to be motivated by the disappearance of the sustaining surface wave at high gas inflow rates. Besides, a temperature drop of about 64 °C is observed at the temperature-maximum point of the glass tube with an increase in the gas inflow rate from 1 to 16 L · min -1 . Therefore, for the surface wave plasma torch operated with only the axial gas flow, increasing the gas inflow rate cannot solve the glass overheating problem.