Ion charge state fluctuations in vacuum arcs

Anders, André; Fukuda, Kentaro; Yushkov, G. Yu.

doi:10.1088/0022-3727/38/7/009

Cited by 14 publications

(7 citation statements)

References 34 publications

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“…3) , where n is the number of active emission sites. The same argument was brought forward to explain a reduction in noise of collected ion current when the arc current was enhanced 38 .…”

Section: Lbnl-57025mentioning

confidence: 81%

Cathodic arcs: Fractal voltage and cohesive energy rule

Anders

Окс

Yushkov

2005

Applied Physics Letters

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The noise of the burning voltage of cathodic arcs in vacuum was analyzed for a range of cathode materials (C, Mg, Ti, V, Ni, Cu, Zr, Nb, Ag, Hf, Ta, W, Pt, Bi, and Si). Cathodic arcs were generated in a coaxial plasma source, and the voltage noise was measured with a broadband (250 MHz) measuring system. Each measurement of 50,000 points was analyzed by Fast Fourier Transform, revealing a power spectrum ~ 1/f 2 for all metals over several orders of magnitude of frequency f (brown noise). The absence of any characteristic time down to possible cutoffs at high frequencies supports a fractal model of cathode spots. Our preliminary research indicate that materials of high cohesive energy have a cutoff of self-similarity at 50 MHz while no cutoff could be found up to 100 MHz for non-refractory metals. The amplitude of colored noise scaled approximately linearly with the cathode's cohesive energy, which is another manifestation of the Cohesive Energy Rule. a) electronic address: aanders@lbl.gov LBNL-57025 1The plasma of cathodic vacuum arcs is produced at non-stationary cathode spots 1 . Much research, both theoretically 2-7 and experimentally [8][9][10][11][12][13][14] , has been done for decades to understand the spot phenomena that produce non-equilibrium plasmas containing multiply ion charge states. The plasma is mesosonic 15 ,i.e., subsonic for electrons and supersonic for ions, with respect to the local ion sound velocity. Difficulties in experimentation and modeling are associated with the spots' fast changes, small sizes, and extreme gradients of power density and particle densities. The formation of spot plasma is often described as a sequence of microexplosions, where cathode material transitions through various phases, from solid to liquid, non-ideal plasma and/or gas phases, finally turning into in a non-equilibrium, expanding, fully ion ionized plasma 6,16 .With improvement of experimental techniques, faster and smaller phenomena have been discovered. This becomes especially striking when the issue of current density is considered. As the apparent area of electron emission was found to be smaller than previously thought, the corresponding current density increased accordingly 17,18 . There were arguments what constitutes an electron-emitting site.In one extreme, electron emission should occur from areas much larger than the molten crater due to intense ion bombardment of the crater vicinity. On the other hand, the most relevant electron emission area might be smaller than the later visible crater because crater formation could be the result of the action of several spot fragments or cells.In order to make any useful statements on cathode processes and parameters of cathodic arc plasma, many researches decided to repeat measurements and average the measured data. For example, one can find data on average ion charge states 10,19 , average burning voltages 20,21 , average ion velocities 15 , or average ion velocity distribution functions 22 .All parameters fluctuate with large amplitude; in some cases up to...

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“…3) , where n is the number of active emission sites. The same argument was brought forward to explain a reduction in noise of collected ion current when the arc current was enhanced 38 .…”

Section: Lbnl-57025mentioning

confidence: 81%

Cathodic arcs: Fractal voltage and cohesive energy rule

Anders

Окс

Yushkov

2005

Applied Physics Letters

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“…This allows us to determine ICSDs averaged over the measured pulses, the standard deviation for each charge state, and the mean charge state. It has been pointed out in the literature that the plasma parameters in the highly dynamic cathodic arc plasma are not constant but fluctuate [27], [28]. The fluctuation depends on the cathode material [29].…”

Section: A Discharges In Vacuummentioning

confidence: 99%

Ion Charge State Distributions of Al and Cr in Cathodic Arc Plasmas From Composite Cathodes in Vacuum, Argon, Nitrogen, and Oxygen

Franz

Polcik

Anders

2013

IEEE Trans. Plasma Sci.

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Multielement cathodes are increasingly used for advanced coatings, yet most cathodic arc plasma measurements have been reported for pure element cathodes. In this contribution, we measure the charge state distributions of aluminum and chromium ions from Al-Cr composite cathodes of different Al to Cr ratios. The arc discharges are pulsed, with pulse duration of around 300 µs and currents of 175 A, operated at high vacuum and in gases with a pressure of up to 1.3 Pa of Ar, N 2 , and O 2 . For comparison with literature data, the measurements also included the plasma compositions of discharges using pure Al and Cr cathodes. As expected, the charge distributions are found to be affected by the cathode conditions, the type of gas, and the pressure of the gas into which the arc spot plasma is expanding. Generally, large effects of gas are observed when the pressure exceeded 0.1 Pa, which can be mainly associated with the ions' mean-free path with respect to charge exchange collisions. Differences between ions can be attributed to the energy-and species-dependent charge-exchange cross sections. Considering different cathode compositions, we found that Cr ions tend to have lower charge states from the composite cathodes compared with the pure element cathode, whereas Al ions are relatively unaffected by the cathode composition. Despite the wealth of detailed experimental results, it is difficult to discern trends and rules that could be generalized because measured data involve a convolution of cathode phenomena and gas collisional effects.

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“…The plasma drifts past the anode into an electromagnetic filter, through which only ions exit the 90°bend. Ion energy at the exit of the filter is of order 50 eV [23]. The sample to be implanted is placed on a metal sample holder 2-5 cm below the exit of the filter (see Fig.…”

Section: Fabrication Of the Samples: Implantationmentioning

confidence: 99%

Electrical conductivity and Young’s modulus of flexible nanocomposites made by metal-ion implantation of polydimethylsiloxane: The relationship between nanostructure and macroscopic properties

Niklaus

Shea

2011

Acta Materialia

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The mechanical and electrical properties of nanocomposites created by gold and titanium implantation into polydimethysiloxane (PDMS) are reported for doses from 10 15 to 5 Â 10 16 at. cm À2, and for ion energies of 2.5, 5 and 10 keV. Transmission electron microscopy (TEM) cross-section micrographs allowed detailed microstructural analysis of the implanted layers. Gold ions penetrate up to 30 nm and form crystalline nanoparticles whose size increases with ion dose and energy. Titanium forms a nearly homogeneous amorphous composite with the PDMS up to 18 nm thick. Using TEM micrographs, the metal volume fraction of the composite was accurately determined, allowing both electrical conductivity and Young's modulus to be plotted vs. the volume fraction, enabling quantitative use of percolation theory for nanocomposites <30 nm thick. This allows the composite's Young's modulus and conductivity to be linked directly to the implantation parameters and volume fraction. Electrical and mechanical properties were measured on the same nanocomposite samples, and different percolation thresholds and exponents were found, showing that, while percolation explains both conduction and stiffness of the composite very well, the interaction between metal nanoparticles occurs differently in determining mechanical and electrical properties.

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Ion charge state fluctuations in vacuum arcs

Cited by 14 publications

References 34 publications

Cathodic arcs: Fractal voltage and cohesive energy rule

Cathodic arcs: Fractal voltage and cohesive energy rule

Ion Charge State Distributions of Al and Cr in Cathodic Arc Plasmas From Composite Cathodes in Vacuum, Argon, Nitrogen, and Oxygen

Electrical conductivity and Young’s modulus of flexible nanocomposites made by metal-ion implantation of polydimethylsiloxane: The relationship between nanostructure and macroscopic properties

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