Erosion and cathodic arc plasma of Nb-Al cathodes: composite versus intermetallic
20 Feb 2020-Plasma Sources Science and Technology (IOP Publishing)-Vol. 29, Iss: 2, pp 025022-025022
TL;DR: Zohrer et al. as mentioned in this paper investigated the influence of morphology and phase composition of multi-element cathodes on cathodic arc properties, including pure Nb and Al cathodes, intermetallic Nb3Al, Nb2Al and NbAl3 cathodes and three composite Nb-Al cathodes.
Abstract: Author(s): Zohrer, S; Golizadeh, M; Koutna, N; Holec, D; Anders, A; Franz, R | Abstract: Many properties of cathodic arcs from single-element cathodes show a correlation to the cohesive energy of the cathode material. For example, the burning voltage, the erosion rate, or, to a lesser extent, plasma properties like electron temperatures or average ion energy and charge states. For multi-element cathodes, various phases with different cohesive energies can initially be present in the cathode, or form due to arc exposure, complicating the evaluation of such correlations. To test the influence of morphology and phase composition of multi-element cathodes on cathodic arc properties, a Nb-Al cathode model system was used that includes: pure Nb and Al cathodes; intermetallic Nb3Al, Nb2Al and NbAl3 cathodes; and three composite Nb-Al cathodes with atomic ratios corresponding to the stoichiometric ratios of the intermetallic phases. Pulsed cathodic arc plasmas from these cathodes were examined using a mass-per-charge and energy-per-charge analyzer, showing that charge-state-resolved ion energy distributions of plasmas from the intermetallic and corresponding composite cathodes are nearly identical. An examination of converted layers of eroded cathodes using x-ray diffraction and scanning electron microscopy indicates the formation of a surface layer with similar phase composition for intermetallic and their corresponding composite cathode types. The average arc voltages do not follow the trend of cohesive energies of Nb, Al and intermetallic Nb-Al phases, which have been calculated using density functional theory. Possible reasons for this effect are discussed based on the current knowledge of multi-element arc cathodes and their arc plasma available in literature.
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TL;DR: In this paper, a 10'μm thick Mo/Al multilayer coating was sputter-deposited onto a standard Ti arc cathode for a short duration enabling the observation of single craters formed by type 1 and 2 cathode spots.
Abstract: Nowadays, multi-element cathodes are frequently employed to grow multi-element thin films and coatings using cathodic arc deposition processes. During cathode erosion, the cathode spot sequentially ignites on the cathode surface and imposes melting–solidification cycles that lead to material intermixing and the formation of a modified layer on the cathode surface. To allow us to study these surface modifications, a 10 μm thick Mo/Al multilayer coating was sputter-deposited onto a standard Ti arc cathode. This cathode was eroded by a dc steered arc discharge for a short duration enabling the observation of single craters formed by type 1 and 2 cathode spots. Furthermore, separated clusters of overlapping craters and a fully eroded surface caused by different stages of erosion were differentiated when scanning the erosion track in the lateral direction. Cross sections of single craters were prepared by focused ion beam techniques while metallographic methods were applied to obtain cross sections of overlapping craters and the modified layer. The layers of the multilayer coating acted as trace markers providing new insights into the material intermixing within craters, the material displacements during crater formation, the plasma pressure acting on the craters, and the temperature gradient (heat-affected zone) below the craters. The observations are discussed within the framework of established arc crater formation models.
12 citations
TL;DR: In this paper, a multilayer cathode design was used to reveal temporal and spatial progress of cathode spots by enabling three-dimensional visualization of the craters left behind on the cathode surface.
Abstract: The cathode spot behavior influences the arc plasma chemistry and film growth conditions during reactive cathodic arc deposition of nitride and oxide films. Cathode spots can be studied using their characteristic craters left behind on the cathode surface. The multilayer cathode design used in this study reveals temporal and spatial progress of cathode spots by enabling three-dimensional visualization of the craters. The surface nitridation or oxidation of the cathode, also known as cathode poisoning, was found to give rise to a repeated switching between cathode spots of type 1 and 2. The surface oxide layers, however, more significantly promote the ignition of type 1 spots due to their thermodynamically privileged formation and/or their more favorable physical properties building up a stronger electric field within the insulating layer. The crater depths and their contribution to the surface modification of multilayered cathodes are discussed in detail. These results may contribute to a better understanding of macroparticle generation and arc plasma properties in cathodic arc deposition processes.
7 citations
Journal Article•
TL;DR: Byon et al. as discussed by the authors proposed an ion energy distribution function of vacuum arc plasmas in the context of particle physics, which was later extended to the case of particle accelerators.
Abstract: LBNL-51488 Submitted to the Journal of Applied Physics Ion energy distribution functions of vacuum arc plasmas Eungsun Byon and Andre Anders Lawrence Berkeley National Laboratory, University of California, 1 Cyclotron Road, MS 53, Berkeley, California 94720-8223 September 13, 2002 Corresponding Author: Andre Anders Lawrence Berkeley National Laboratory 1 Cyclotron Road Berkeley, CA 94720-8223, USA Tel. + (510) 486-6745 Fax + (510) 486-4374 e-mail aanders@lbl.gov This work was supported by the U.S. Department of Energy, under Contract No. DE-AC03-76SF00098, Eungsun Byon was supported by the post-doctoral fellowship program of the Korean Science and Engineering Foundation (KOSEF)
6 citations
TL;DR: A combination of both conventional and advanced high-resolution characterization techniques was applied to study the modified layers on the surface of three composite Al-Cr arc cathodes with identical nominal composition of Al-50 at.% Cr but varying powder grain sizes.
5 citations
TL;DR: In this paper, a 2D chemical non-equilibrium model considering the space charge sheath is established to investigate the plasma-electrode interaction in an argon DC plasma torch working at atmospheric pressure.
Abstract: A 2D two-temperature chemical non-equilibrium model considering the space-charge sheath is established to investigate the plasma-electrode interaction in an argon DC plasma torch working at atmospheric pressure. In order to validate the model, the predicted arc voltage is compared with experimental values under different working conditions and a reasonable agreement is obtained. The distributions of arc characteristics in the plasma column and electrodes regions of DC arc plasma torch are analyzed in detail. Moreover, the effects of different types of cathodes on the plasma characteristics inside the DC plasma torch are investigated. Three different types of cathodes are considered in this study, including thoriated tungsten, pure tungsten and non-uniform thoriated tungsten cathodes. It is found that a constricted arc attachment with the highest current density is obtained at the non-uniform cathode, leading to the largest velocity and electric potential drop in the plasma column. The pure tungsten cathode produces the highest temperatures and heat flux along the cathode surface, which is caused by the largest arc voltage and intense space-charge sheath heating. The temperature and heat flux density on thoriated tungsten cathode are the lowest, leading to the diffuse distribution of current density. The results indicate that the different cathodes can exert an important influence upon the plasma behaviors near the cathode, while the torch exit parameters have been less affected, which are determined by the overall input power.
5 citations
References
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Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif
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TL;DR: An efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set is presented and the application of Pulay's DIIS method to the iterative diagonalization of large matrices will be discussed.
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81,985 citations
TL;DR: In this paper, the formal relationship between US Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived and the Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional.
Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.
57,691 citations
Book•
01 Jan 1973TL;DR: CRC handbook of chemistry and physics, CRC Handbook of Chemistry and Physics, CRC handbook as discussed by the authors, CRC Handbook for Chemistry and Physiology, CRC Handbook for Physics,
Abstract: CRC handbook of chemistry and physics , CRC handbook of chemistry and physics , کتابخانه مرکزی دانشگاه علوم پزشکی تهران
52,268 citations
TL;DR: In this article, a method for generating sets of special points in the Brillouin zone which provides an efficient means of integrating periodic functions of the wave vector is given, where the integration can be over the entire zone or over specified portions thereof.
Abstract: A method is given for generating sets of special points in the Brillouin zone which provides an efficient means of integrating periodic functions of the wave vector. The integration can be over the entire Brillouin zone or over specified portions thereof. This method also has applications in spectral and density-of-state calculations. The relationships to the Chadi-Cohen and Gilat-Raubenheimer methods are indicated.
51,059 citations