“Writing–Reading–Erasing” on Tungsten Oxide Films Using the Scanning Electrochemical Microscope (original) (raw)
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The Theory and Measurement of Partial Discharge Transients
A theoretical approach to partial discharge transients is presented. This approach is based on the relationship between the charge induced on the measurement electrode by those created in the inter-electrode volume during partial discharge activity. The starting point of the analysis is the formulation of the measured-transient /induced-charge relationship. Thereafter the general relationship between the induced and the inducing charge is derived. This latter relattonship is disc_ussed with respect to both the D field and the P field. The D-field approachjs the more relevant from a practical point of view, but the P-field approach provides a greater insight into the molecular physics of the phenomenon. An exposition of the currents related to these transient phenomena is then under-taken. The theory of void partial discharge transients based on the D-field approach is thereafter reviewed and extended. This theory has allowed the influence of all relevant void parameters to be quantitatively assessed. A general derivation of the measured transients associated with the time dependence of the induced charge is presented, and the application to multiple electrode systems of practical interest is illustrated. A discussion of the salient features and practical aspects of the theory concludes the work.
Diagnostics of PDP micro-discharges
IEEE Transactions on Plasma Science, 2000
Plasma display panel emission measurements are correlated with panel efficacy trends, and directions for the improvement of the discharge efficiency are derived. An increase of the ratio of the phosphor emission in the visible to the Xe emission in the infrared indicates an increased Xe excitation efficiency. Also, the time dependence and the spatial distribution of the Xe emission are important discharge characteristics. Experiments reveal that a high panel efficacy is obtained, especially for design and driving conditions that govern a fast and spatially distributed discharge development. A high sustain voltage 200 V causes a "high efficiency discharge mode." It is proposed that in this mode, the cathode sheath is not, or is incompletely, formed during the rise of the discharge current. Then the electric field in the discharge cell is dominated not by the space charges, but by the externally applied voltage. The effective discharge field is lowered, resulting in a lower effective electron temperature and more efficient Xe-excitation. Under the fast discharge buildup conditions also the electron-heating efficiency increases due to a decrease of the ion heating losses in the cathode sheath. A high sustain voltage combines well with a high Xe content gas mixture, that further increases the discharge efficiency. Changes in the phosphor to Xeand Ne-emission ratio show that for higher Xe content, a lower electron temperature accounts for a more efficient Xe excitation. Further, the use of a TiO 2 -layer underneath the phosphor causes an increase of the ratio of the phosphor emission in the visible to the Xe emission in the infrared, i.e., an increased Xe excitation efficiency. As a result, a high efficacy of 5 lm/W and a high luminance of 5000 cd m 2 have been realized in a 4-in color plasma display test panel design with a 50% Xe in Ne gas mixture, a TiO 2 -layer underneath the phosphor, and a high sustain voltage 260-290 V.
Polystyrene thin films treatment under DC pulsed discharges conditions in oxygen
European Physical Journal-applied Physics, 2001
This paper is devoted to atactic polystyrene (aPS) thin films treatment under DC pulsed discharge in nitrogen. The experiments were performed using a symmetrical plane-to-plane of electrodes configuration in order to improve the treatment homogeneity and also to compare the treatment efficiency when the aPS is on the cathode or on the anode. During these experiments, the pressure and the electrical conditions were maintained unchanged. The experimental results were compared for the two positions of samples, when the gap length and the afterglow duration time were varied. It appears that the treatment depends on the sample position and an interpretation is proposed. The physical conditions and the reaction processes in the plasma bulk and on the aPS surface were analysed in order to understand their influence on the surface treatment. The importance of metastables is pointed out and it is deduced that these long-life excited states are firstly produced near the anode and fill the gap following the evolution and distribution of the electron current density.
Study of W/WC films produced by plasma assisted vacuum arc discharge
physica status solidi (c), 2005
.Pv W/WC films were grown by the PAPVD repetitive pulsed vacuum arc technique on 304 stainless steel substrates. To produce the coatings, a target of W with purity of 99.9999% was used. The system is composed by a reaction chamber with two opposite electrodes placed inside it. The target is located on the cathode and the samples on the anode. A pulsed power supply is used to generate the discharge. For the production of the W layer, the chamber was filled with Ar gas at a pressure of 3 mbar, and the voltage of the discharge was 270 V with 3 pulses. WC films were grown in an atmosphere of methane at 3 mbar and a voltage discharge of 275 V with 4 pulses. The active and passive times of the discharge were 1 s and 0.5 s, respectively. XRD technique was employed to study the coatings, to study the present phases and the crystallographic orientation of the films, the XRD analyses were carried out varying the temperature of the systemcoating-substrate between room temperature and 600 °C, when the WC coatings are degradated, leaving just the tugsten. XPS analyses present the apparition of WC, WO and WO 2 compounds. AFM analyses allowed to measure the morphological properties and the thickness around 3 µm.
Surface charge measurements on different dielectrics in diffuse and filamentary barrier discharges
Journal of Physics D: Applied Physics, 2017
Previously, we reported on the measurement of surface charges during the operation of barrier discharges (BDs) using the electro-optic Pockels effect of a bismuth silicon oxide (BSO) crystal. With the present work, the next milestone is achieved by making this powerful method accessible to various dielectrics which are typically used in BD configurations. The dynamics and spatial distribution of positive and negative surface charges were determined on optically transparent borosilicate glass, mono-crystalline alumina and magnesia, respectively, covering the BSO crystal. By variation of the nitrogen admixture to helium and the pressure between 500 mbar and 1 bar , both the diffuse glow-like BD and the self-stabilized discharge filaments were operated inside of a gas gap of 3 mm. The characteristics of the discharge and, especially, the influence of the different dielectrics on its development were studied by surface charge diagnostics, electrical measurements and ICCD camera imaging. Regarding the glow-like BD, the breakdown voltage changes significantly by variation of the cathodic dielectric, due to the different effective secondary electron emission (SEE) coefficients. These materialspecific SEE yields were estimated using Townsend's criterion in combination with analytical calculations of the effective ionization coefficient in helium with air impurities. Moreover, the importance of the surface charge memory effect for the self-stabilization of discharge filaments was quantified by the recalculated spatio-temporal behavior of the gap voltage.
Characterisation of discharge events during plasma electrolytic oxidation
Surface and Coatings Technology, 2009
A study has been made of the electrical characteristics and optical emission spectra exhibited when discharge events take place during plasma electrolytic oxidation processing. Both conventional and small area experimental arrangements have been employed, allowing detailed measurement of durations, and temporal distributions, as well as such characteristics as charge transfer, and power. Individual discharges are of short duration, typically tens to hundreds of microseconds, but there is a strong tendency for them to occur in cascades that commonly last between several ms and several tens of ms. The composition, temperature and electron density of the plasma formed during PEO processing are inferred from characteristics of the emission spectra. This confirms that there are two distinct regions of plasma; a lower density peripheral region at~3500 K, and a higher density core at 16,000 ± 3500 K. The implications of these results are considered in terms of the interpretation of different types of experimental measurement, and attention is also briefly given to how such behaviour might relate to the mechanisms of growth.
Using heated probes in plasma polymerising discharges
Surface & Coatings Technology, 2004
Using a heated probe, a technique has been developed to measure the spatial variation of the electron temperature (T ) plasma e density (N ), floating (V ), and plasma potentials (V ), and the electron energy distribution function (eedf) in low-pressure e f p polymerising plasma. During the non-data acquisition times, the probe was heated using an external current, so minimising deposition of an insulating layer on its surface. Typically the insulating film deposition rate was between 2 and 4 nm s y1 depending on the discharge conditions. To obtain a Langmuir probe characteristic (and derive the quantities N , T , V and eedf), e e f the heating current was switched off and the data collected over a short time (10 to 30 s). By heating the probe to strong electron emission, it was also possible to obtain an accurate measurement of V . The technique has been applied to a new two-stage p reactor (source and diffusion chambers separated by a mesh) in which acrylic acid is plasma polymerised to form thin films with functional surface chemistry at low pressure (5.2 Pa). The probe results show that in the polymerising chamber, with increasing distance from the mesh, (15 to 70 mm), N fall from 1.7=10 to 2=10 m and T falls from 3.7 to 1.3 eV. However, at a 14 13 y3 e e fixed distance of 70 mm, with increasing discharge power, T remains constant, while N increases over an order of magnitude. e e
Physics of Plasmas, 2018
By comparing time-resolved optical emission spectroscopy measurements and the predictions of a collisional-radiative model, the evolutions of electron temperature (Te) and number density of argon metastable atoms (n(Ar m)) were determined in argon-ethyl lactate dielectric barrier discharges. The influence of a square pulse power supply on Te, n(Ar m), and the discharge current is evaluated and correlated to the chemistry and the topography of the plasma-deposited coatings. Pulsed discharges were found to have shorter (100 ns) but stronger (1 A) current peaks and higher electron temperatures (0.7 eV) than when using a 35 kHz sinusoidal power supply (2 µs, 30 mA, 0.3 eV). The n(Ar m) values seemed rather stable around 10 11 cm-3 with a sinus power supply. On the contrary, with a pulse power supply with long time off (i.e. time without discharge) between each pulse, a progressive increase of n(Arm) from 10 11 cm-3 up to 10 12-10 13 cm-3 was observed. When the time off was reduced, these increases were measured in sync with the current peak. The chemical composition of the coatings was not significantly affected by using a pulse signal whereas the topography was strongly influenced and led to powder formations when reducing the time off.
Numerical investigation of the discharge characteristics of the pulsed discharge nozzle
Physical Review E, 2005
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