A 3D model of a hollow cathode of a thermal plasma torch was developed to study the motion of the electric arc in the upstream part as well as its influence on the characteristics of the thermal plasma generated at the entrance of the downstream part (anode).The translational motion along the axis and the rotational velocity of the cathodic arc root are studied.The results of the model are presented and compared with those of the literature and also with experimental results.Good agreements on the prediction of the axial arc position and of the rotational speed of the arc root are found with the literature.A correlation is also shown between the theoretical positions of the arc root and the experimental traces of erosion observed on the cathode.
W–Ag thin films are produced by magnetron co-sputtering technique using glancing angle co-deposition configuration. Different samples are prepared with similar conditions (same pressure, thickness and tungsten target current) but with a variable Ag target current changing from 0 to 80 mA. The effect of the Ag target current on the film structure and electrical properties is investigated using scanning and transmission electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction and van der Pauw technique. Thin films with inclined columns are obtained and the columns section becomes more anisotropic for the films prepared with the lowest Ag target currents. The elemental composition of the films also changes as a function of the Ag target current, varying from tungsten-rich (at low current) to homogeneous (at high current). W–Ag thin films exhibit different crystallographic structures. If the fcc Ag phase is always present, the metastable A15 β -W is pointed out only at low Ag target current while at high current, only the bcc α -W phase is present. The microstructural analysis shows that the core of the columns is formed by W while Ag covers the columns as grains. Room temperature electrical resistivity decreases with Ag target current, whereas its anisotropy decreases. This behaviour correlates with the change in the columnar cross-section morphology.
We conducted a thorough experimental and numerical study of the micromagnetic properties of Permalloy (Ni 80 Fe 20 ) microdisks exhibiting target domain structures at remanence. Vortex configurations are quite common in such microdisks and correspond to an in-plane (IP) flux closure configuration of cylindrical symmetry with an out-of-plane (OOP) magnetized core. In contrast, target domain configuration are observed in thicker microdisks and are characterized by a vortex configuration of the IP component of the magnetization superposed to an OOP component of magnetization which oscillates as a function of the distance to the microdisk center resulting in the formation of concentric domains. The ratio of the OOP oscillatory component of the magnetization to the IP vortex one increases with the thickness of the microdisk. Hysteresis loops were measured under IP and OOP field. The results at remanence and under magnetic field could be interpreted by micromagnetic simulations in which the microdisks were described as an assembly of partially coupled columns representing the granular nanostructure of the films from which the microdisks were patterned. Quite original magnetization processes take place in these microdisks exhibiting target domain remanent configuration. These include in particular entire flipping of the domain configuration and annihilation/creation of ring domains.
Here, we introduce a tailorable coupled resonator surface acoustic waveguide (CRSAW), based on a linear defect of elliptical cylinders inside a phononic crystal of ZnO pillars on a Si substrate. The designed elliptical resonators allow the emergence of a minimally dispersive, monomode shear-guiding band inside the local resonance bandgap, owing to their partially broken structural symmetry in comparison with their previously reported counterparts such as pillars and hollow cylinders. Moreover, by introducing reconfigurable waveguide behavior, we benefit from the acoustoelectric-induced elasticity modulation of ZnO, which is a semiconducting piezoelectric material. Switching the conductivity of ZnO structures between two limiting low and high values (0.01 S m −1 and 100 S m −1 ), a considerable waveguide modulation at full width at half maximum (FWHM) (ΔFWHM = −21%) and guiding frequency (Δ f d = −2.81%) are achieved for the designed optimized elliptical cylinder CRSAW while maintaining an acceptable loss value. Benefiting from the proposed ZnO-based elliptical CRSAW, we have achieved simultaneous monomode and low-bandwidth surface acoustic waveguide behaviors, without involving significant fabrication complications. The designed structures open up new horizons toward the realization of promising building blocks for designing reconfigurable and miniaturized SAW RF-filters, demultiplexers, and Mach–Zehnder devices for wireless communications applications.
We have investigated the behavior of the optical transduced signal of a photonic integrated polymer micro resonator as an evaporating water droplet is positioned upon it. The photonic chip is fabricated by means of deep-UV photolithography, and the circuits are made of polymer UV210. The device is then arranged in an optical bench so as to perform relevant measurements thanks to a broadband laser for the excitation of the resonators and an optical spectrum analyzer remotely controlled by a Matlab software for the acquisition and treatment of data. By dynamically tracking the free spectral range (FSR) of the optical mode, we come up with a signature of the thermodynamic evaporation process. In order to correlate this signature to the evaporation speed of the water droplet, a lateral camera is disposed to measure the evolution of the geometrical characteristics of the droplet, while weight measurements are performed thanks to a precision balance. These measurements provide a numerical link between the temporal variation of the FSR and the variation of the distance between the apex of the droplet and the substrate, correlating clearly the variation of the FSR with the mass change of the droplet. The measurements have been performed with 20 mu l droplets for three different substrate temperatures: 21 degrees C, 24 degrees C and 27 degrees C. Then, theoretical investigations have been also performed in order to interpret the dynamics of the FSR in terms of guiding theory.
A systematic study of arc faulting between two cables in aeronautic conditions is performed and a power balance of the arc is realized. Electrical characteristics and radiative heat flux are recorded. The effect of the current mode (AC/DC), cable material and pressure is highlighted with the assessment of the power balance, which includes the mean power of the arc, power transferred to the cables that can cause melting and vaporization, and the power lost by radiation, conduction and convection in the arc column. The evaporated mass of the cables can be estimated in this way. Optical emission spectroscopy measurements of the induced plasma are performed rendering the overall temperature of the arc using a Boltzmann plot method. The overall temperature is higher for copper-contaminated plasma than for aluminium-contaminated plasma. Despite the erratic behaviour of the plasma, the trend shows that the DC as well as the use of lighter aluminium-based cables lead to higher power.
To achieve quasi-atomic precision etching of thin film materials in advanced transistors, a method based on light ion implantation and consisting of two sequential steps-(1) surface modification in hydrogen ICP or CCP plasmas, and (2) selective removal of modified layers in wet solutions or remote plasmas-was recently proposed. In this paper, to better understand this process (called Smart Etch thereafter), molecular dynamics simulations are performed to study the modification of crystalline Si (100) substrates under low-energy H-x(+) (x = 1-3) ion implantation and mixed H-x(+) ion/H radical bombardment. In agreement with the experiments, simulations of H-x(+)(x = 1-3) ion bombardment of Si show a self-limited implantation with a surface evolution composed of two stages: a rapid volume modification (with no etching) followed by a slow saturation and the formation of a stable [a: Si-H] layer at a steady state. The mechanisms of ion-induced damage (Si-Si bond breaking, formation of H-2 molecules, creation of SiHx groups) are investigated and allow us to bring new insights to both the wellknown Smart Cut(TM) and more recent Smart Etch technologies. Si exposure to both H-x(+) ions and H radicals (H-2 plasma) also shows a self- limited transformation but the modified layers are simultaneously etched during the implantation. Both the modified layer thickness and the ion dose required to reach the steady state increase with the ion energy. The ion composition and the radical-to-ion flux ratio (F) must be considered as well. In particular, the etch rate strongly increases with F, compromising even the possibility to achieve a Smart Etch of silicon.
Cold atmospheric plasma is thought to be a promising tool for numerous biomedical applications due to its ability to generate a large diversity of reactive species in a controlled way. In some cases, it can also generate pulsed electric fields at the zone of treatment, which can induce processes such as electroporation in cell membranes. However, the interaction of these reactive species and the pulse electric field with cells in a physiological medium is very complex, and we still need a better understanding in order to be useful for future applications. A way to reach this goal is to work with model cell membranes such as liposomes, with the simplest physiological liquid and in a controlled atmosphere in order to limit the number of parallel reactions and processes. In this paper, where this approach has been chosen, 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) small unilamellar vesicles (SUV) have been synthesized in a phosphate buffered aqueous solution, and this solution has been treated by a nanosecond pulsed plasma jet under a pure nitrogen atmosphere. It is only the composition of the plasma gas that has been changed in order to generate different cocktails of reactive species. After the quantification of the main plasma reactive species in the phosphate buffered saline (PBS) solution, structural, surface charge state, and chemical modifications generated on the plasma treated liposomes, due to the interaction with the plasma reactive species, have been carefully characterized. These results allow us to further understand the effect of plasma reactive species on model cell membranes in physiological liquids. The permeation through the liposomal membrane and the reaction of plasma reactive species with molecules encapsulated inside the liposomes have also been evaluated. New processes of degradation are finally presented and discussed, which come from the specific conditions of plasma treatment under the pure nitrogen atmosphere.
In this paper, we investigate DBDs in the medium frequency range (MF, 0.3-3 MHz). More precisely, for a 2 inter-dielectric gap in helium at atmospheric pressure, the frequency is varied from 1.0 to 2.7 MHz. The generated discharge shows similarities with both the low-frequency atmospheric-pressure glow discharge (APGD) and the atmospheric pressure capacitively coupled radio-frequency (CCRF) discharge. In the frequency range under investigation, two diffuse discharge modes can be observed depending on the voltage applied between the electrodes. At low applied voltage, the discharge emissions are barely visible and are concentrated in the center of the gas gap similarly to CCRF discharges in the Omega mode where the electron density is concentrated in the bulk. Ohmic heating is the main power transfer mechanism. At higher applied voltage, the discharge emissions are 10 times more intense and are closer to the dielectric surfaces similarly to the more common radio-frequency a mode. These two discharge modes can be observed in the same experimental conditions with the amplitude of the applied voltage as sole control parameter. The gas temperature obtained from N-2 impurities rotational spectrum increases from room temperature to about 500 K while the power density rises from 10(-1) to 101 W cm(-3) when the applied voltage is increased. In addition, when the discharge transits back and forth from the Omega to the a mode, a hysteresis is observed. The transition from the Omega to the a mode occurs abruptly with a large RMS current increase while the transition from the a to the Omega mode is rather smooth with no significant discontinuity in the RMS current.
Carrying out molecular dynamics (MD) simulations is a relevant way to understand growth phenomena at the atomic scale. Initial conditions are defined for reproducing deposition conditions of plasma sputtering experiments. Two case studies are developed to highlight the implementation of MD simulations in the context of plasma sputtering deposition: ZrxCu1-x metallic glass and AlCoCrCuFeNi high entropy alloy thin films deposited onto silicon. Effects of depositing atom kinetic energies and atomic composition are studied in order to predict the evolution of morphologies and atomic structure of MD grown thin films. Experimental and simulated x-ray diffraction patterns are compared.
The percolation threshold problem in insulating polymers filled with exfoliated conductive graphite nanoplatelets (GNPs) is re-examined in this 3D Monte Carlo simulation study. GNPs are modelled as solid discs wrapped by electrically conductive layers of certain thickness which represent half of the electron tunnelling distance. Two scenarios of 'impenetrable' and 'penetrable' GNPs are implemented in the simulations. The percolation thresholds for both scenarios are plotted versus the electron tunnelling distance for various GNP thicknesses. The assumption of successful dispersion and exfoliation, and the incorporation of the electron tunnelling phenomenon in the impenetrable simulations suggest that the simulated percolation thresholds are lower bounds for any experimental study. Finally, the simulation results are discussed and compared with other experimental studies.
Micro- and nanocantilevers, which have traditionally played a vital role in the development of force microscopy, and more recently a special role in biological, chemical and physical sensing and detection, have received comparatively little attention in optical spectroscopy. We present an investigation of the optical response of microcantilevers towards their utilization in integrated spectrometers in a broad part of the spectrum. By discussing the overall actuation mechanism we describe how surface modes may effectively contribute to the final signal. Using Fourier transform infrared (FTIR) spectroscopy, a series of multilayered microcantilevers are characterized for their spectral response in the range from 7800 to 400 cm−1. Transmission FTIR and FTIR photothermal spectroscopy are carried out using polystyrene with well-established infrared spectra.
Diamond-like amorphous carbon (DLC) films have been grown by pulsed-dc plasma-enhanced chemical vapour deposition on silicon wafers, which were previously patterned by means of colloidal lithography. The substrate conditioning comprised two steps: first, deposition of a self-assembled monolayer of silica sub-micrometre spheres (similar to 300 nm) on monocrystalline silicon (similar to 5 cm(2)) by Langmuir-Blodgett technique, which acted as lithography template; second, substrate patterning via ion beam etching (argon) of the colloid samples (550 eV) at different incidence angles. The plasma deposition of a DLC thin film on the nanotextured substrates resulted in hard coatings with distinctly different surface properties compared with planar DLC. Also, in-plane anisotropy was generated depending on the etching angle. The samples were morphologically characterized by scanning electron microscopy and atomic force microscopy. The anisotropy introduced by the texture was evidenced in the surface properties, as shown by the directional dependences of wettability (water contact angle) and friction coefficient. The latter was measured using a nanotribometer and a lateral force microscope. These two techniques showed how the nanopatterns influenced the tribological properties at different scales of load and contact area. This fabrication technique finds applications in the industry of microelectromechanical systems, anisotropic tribological coatings, nanoimprint lithography, microfluidics, photonic crystals, and patterned surfaces for biomedicine.
This paper deals with a dc laminar pure argon plasma jet operating at atmospheric pressure in ambient air that was experimentally studied in order to obtain temperature and velocity. Plasma jet temperature was evaluated by optical emission spectroscopy and the plasma jet velocity was determined by various methods using a pressure sensor. It is shown that the maximum plasma jet temperature is 15 000 K and the maximum plasma jet velocity is 250 m s−1 at the plasma jet centre. Finally, a study of the ambient air amount entrained into the plasma jet is presented.
This paper deals with the diagnostics of a dc laminar argon plasma jet operating at atmospheric pressure in ambient air using three techniques. Through the pumping effect of ambient air by the laminar jet, it is possible to observe the UV OH spectrum at 306.357 nm (transition A 2 Σ, ν = 0 → X 2 Π, ν′ = 0) and to perform emission spectroscopy in order to find the OH rotational temperature close to the thermodynamic temperature of the gas. In addition, measurements of the refractive index are made by considering two different methods: optical interferometry and quantitative shadowgraphy. It is shown that the temperatures obtained by the three diagnostics techniques are very close.
We report on the recording performances and signal-to-noise ratio (SNR) analyses of perpendicular magnetic bit-patterned media. Two different types of magnetic samples are investigated. They differ by the way that they were patterned (nano-imprint versus e-beam lithography) as well as their magnetic properties (Co/Pt multilayers and CoCrPt alloy are the recording layers).Using a contact read/write quasi-static tester, we were able to characterize the write windows, the bit error rates and measure the SNR. The influence of magnetic properties and media microstructure on the writing processes is studied. We show also that the lithographical method used to replicate the media induces more or less noise due to structural distributions.
The coercivity and energy losses in superparamagnetic (SPM) magnetite and FePt nanoparticle composites subjected to an external, alternating magnetic field have been calculated as a function of the mean particle size and packing density. The effect of interactions has been investigated by fitting the Sharrock law to the coercivity results as a function of the field cycle frequency of the magnetic field. This fitting leads to effective parameters for the anisotropy field and β eff = KV / k B T , which are themselves dependent on the interaction strength. The increase or decrease in the coercivity with interactions depends upon the relative change of and β eff , thus demonstrating the complex effect that interactions have in these nanoparticle composites. The interparticle interactions have a non-trivial effect on the energy loss per cycle. The energy loss is reduced for systems with larger particles since the reduction in coercivity together with a corresponding reduction in the remanence dominates. For small particle sizes, the energy loss is increased. The primary mechanism here seems to be an enhancement of the energy barrier due to interactions, which changes the nature of the particles from SPM to being thermally stable.
GaInP solar cell interfaces were characterized by admittance spectroscopy. Admittance spectroscopy is shown to be sensitive to the band structure at the heterojunction interfaces. In particular, a correlation between activation energy of the capacitance step in a capacitance versus temperature plot and effective potential barrier for majority carriers is demonstrated, indicating a new method for the determination of potential barriers at heterointerfaces. Using this technique, the effective potential barrier for holes at the p-Al0.53In0.47P/p-GaAs interface is found to be equal to 0.6 eV. Effects of interface defects and spreading resistance in the emitter of solar cells are illustrated and discussed.
GaN was implanted with 300 keV Eu ions over a wide fluence range from 1 x 10(13) to 1 x 10(16) Eu cm(-2) at room temperature (RT) or 500 degrees C. Detailed structural and optical characterizations of the samples were performed using Rutherford backscattering spectrometry and channelling, transmission and scanning electron microscopy, wavelength dispersive x-ray emission and RT cathodoluminescence (CL) spectroscopy. RT implantation results in a sigmoidal-shaped damage build-up curve with four regimes that were correlated with the formation of specific kinds of defects. After annealing at 1000 degrees C only samples implanted to fluences below 0.8 x 10(15) Eu cm(-2) showed near complete recovery of the crystal. Implantation at elevated temperature significantly decreases the implantation damage and increases the fraction of Eu incorporated on substitutional Ga-sites. The improved structural properties of samples implanted at elevated temperature are reflected in a higher intensity of Eu-related red light emission after annealing at 1000 degrees C. The RT CL intensity is correlated with the number of Eu ions on substitutional Ga-sites after annealing. Furthermore, a detailed study of optical activation shows that the optimum annealing temperature depends on the implantation fluence due to the sensitive balance of defects removed and created during high temperature annealing.
The present review is intended to revisit the advances and debates in the comprehension of the mechanisms of subcritical crack propagation in silicate glasses almost a century after its initial developments. Glass has inspired the initial insights of Griffith into the origin of brittleness and the ensuing development of modern fracture mechanics. Yet, through the decades the real nature of the fundamental mechanisms of crack propagation in glass has escaped a clear comprehension which could gather general agreement on subtle problems such as the role of plasticity, the role of the glass composition, the environmental condition at the crack tip and its relation to the complex mechanisms of corrosion and leaching. The different processes are analysed here with a special focus on their relevant space and time scales in order to question their domain of action and their contribution in both the kinetic laws and the energetic aspects.
