We discuss the effect of electrode shape on Paschen curves and our ability to seal off microdischarges to prevent long path breakdown. It was found that for structured electrodes at high pressures ...and small gaps, the left-hand side of the Paschen curve is relatively flat, extending the minimum to lower pd values. At high pd values the curves are almost identical to those at standard pressures/gaps and the discharge runs between the top plane of the cathode and the anode. For intermediate pd values the higher electric field at the edge attracts most of the current and the discharge extends along the side wall maintaining the same low breakdown voltage. When the length of the discharge reaches the longest path the voltage starts a rapid increase. We have selected the dimension of the segmented electrode so as to have the same losses to the walls that block or allow the long path breakdown, thus being able to represent situations when the Paschen curve may be properly determined. In general, however, this shows that recording of the left-hand side for open structures (without enclosure by a dielectric) is impossible and conclusions about secondary emission should be focused on the well-defined conditions.
We give preliminary results on the breakdown and low current limit of volt-ampere characteristics of simple parallel plate non-equilibrium dc discharges at standard (centimetre size) and ...micro-discharge conditions. Experiments with micro-discharges are reported attempting to establish the maintenance of E/N, pd and j/p2 scalings at small dimensions down to 20 mum. It was found that it may not be possible to obtain properly the left-hand side of the Paschen curve. The possible causes are numerous but we believe that it is possible that long path prevention techniques do not work at high pressures. Nevertheless, the standard scaling laws seem to be maintained down to these dimensions which are consistent with simulations that predict violation of scaling below 10 mum. Volt-ampere characteristics are also presented and compared with those of the standard size discharges.
Accurate measurement of ion current density and ion energy distributions (IEDs) is often critical for plasma processes in both industrial and research settings. Retarding field energy analysers ...(RFEAs) have been used to measure IEDs because they are considered accurate, relatively simple and cost effective. However, their usage for critical measurement of ion current density is less common due to difficulties in estimating the proportion of incident ion current reaching the current collector through the RFEA retarding grids. In this paper an RFEA has been calibrated to measure ion current density from an ion beam at pressures ranging from 0.5 to 50.0 mTorr. A unique method is presented where the currents generated at each of the retarding grids and the RFEA upper face are measured separately, allowing the reduction in ion current to be monitored and accounted for at each stage of ion transit to the collector. From these
I
–
V
measurements a physical model is described. Subsequently, a mathematical description is extracted which includes parameters to account for grid transmissions, upper face secondary electron emission and collisionality. Pressure-dependent calibration factors can be calculated from least mean square best fits of the collector current to the model allowing quantitative measurement of ion current density.
In this paper we describe a novel method for delivering a precise, known amount of electric charge to a micron-sized solid target. Aerosolised microparticles passed through a plasma discharge will ...acquire significant electric charge. The fluid stability under evaporative stress is a key aspect that is core to the research. Initially stable charged aerosols subject to evaporation (i.e. a continually changing radius) may encounter the Rayleigh stability limit. This limit arises from the electrostatic and surface tension forces and determines the maximum charge a stable droplet can retain, as a function of radius. We demonstrate that even if the droplet charge is initially much less than the Rayleigh limit, the stability limit will be encountered as the droplet evaporates. The instability emission mechanism is strongly linked to the final charge deposited on the target, providing a mechanism that can be used to ensure a predictable charge deposit on a known encapsulated microparticle.
•A mechanism to deliver a precise charge to an encapsulated micron-sized target.•Method relies on aerosolising the target, and passing the aerosol through a plasma.•Abundant free charge accumulates on aerosols from plasma interaction.•Evaporation of aerosols forces a series of Rayleigh instabilities.•Final charge on exposed target is consistently the final Raleigh instability limit.
Surface and bulk properties of the Filtered Cathodic Vacuum Arc prepared nitrogenated tetrahedral amorphous carbon (ta-C:N) films were characterized by X-ray Photoelectron Spectroscopy (XPS), Time of ...Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), Raman spectroscopy, Atomic Force microscopy and contact angle techniques. An increase in the Nitrogen (N) content of the films is accompanied by a reduction in the sp
3 fraction, confirmed via the deconvolution of the C 1
s XPS spectra. Critical Raman parameters such as peak position and peak width of the G band, defect ratio, I
D/I
G and skewness of the G line were analyzed as a function of N content. ToF-SIMS showed the variance of chemical composition with the increase in the sputtering depth. While some amount of incorporated oxygen and hydrogen were observed for all films; for high N content ta-C:N films signature of CN bonds was evident. Surface energies (both polar and dispersive components) for these ta-C:N films were analyzed in a geometric mean approach. Contact angle measurements using both deionized water and ethylene glycol reveal that upon the insertion of nitrogen into ta-C films, the initial change in the contact angle is sharp, followed by a gradual decrease with subsequent increase in N content. The variation of contact angle with increasing N content corresponds to an increase of the total surface energy with an increase of the polar component and a decrease of the dispersive component.
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