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Journal ArticleDOI

Electron microphysics at plasma–solid interfaces

12 Nov 2020-Journal of Applied Physics (AIP Publishing LLCAIP Publishing)-Vol. 128, Iss: 18, pp 180908
TL;DR: In this paper, the authors proposed a method for measuring the wall charge by infrared reflectivity to couch the discussion about the relationship between plasma and solid interfaces, which would open up a new arena for applied as well as fundamental research.
Abstract: The most fundamental response of a solid to a plasma and vice versa is electric. An electric double layer forms with a solid-bound electron-rich region—the wall charge—and a plasma-bound electron-depleted region—the plasma sheath. However, it is only the plasma sheath that has been studied extensively ever since the beginning of plasma physics. The wall charge received much less attention. Particularly, little is known about the operando electronic structure of plasma-facing solids and how it affects the spatiotemporal scales of the wall charge. The purpose of this Perspective is to encourage investigations of this terra incognita by techniques of modern surface physics. Using our own theoretical explorations of the electron microphysics at plasma–solid interfaces and a proposal for measuring the wall charge by infrared reflectivity to couch the discussion, we hope to put together enough convincing reasons for getting such efforts started. They would open up—at the intersection of plasma and surface physics—a new arena for applied as well as fundamental research.

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Citations
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Journal ArticleDOI
05 Jul 2022
TL;DR: The latest edition of the Journal of Physics D's "Plasma Roadmap" as discussed by the authors was published with the intent to identify important outstanding challenges in the field of low-temperature plasma (LTP) physics and technology.
Abstract: The 2022 Roadmap is the next update in the series of Plasma Roadmaps published by Journal of Physics D with the intent to identify important outstanding challenges in the field of low-temperature plasma (LTP) physics and technology. The format of the Roadmap is the same as the previous Roadmaps representing the visions of 41 leading experts representing 21 countries and five continents in the various sub-fields of LTP science and technology. In recognition of the evolution in the field, several new topics have been introduced or given more prominence. These new topics and emphasis highlight increased interests in plasma-enabled additive manufacturing, soft materials, electrification of chemical conversions, plasma propulsion, extreme plasma regimes, plasmas in hypersonics, data-driven plasma science and technology and the contribution of LTP to combat COVID-19. In the last few decades, LTP science and technology has made a tremendously positive impact on our society. It is our hope that this roadmap will help continue this excellent track record over the next 5–10 years.

64 citations

01 Nov 2004
TL;DR: In this article, a range of sheaths and presheaths in weakly collisional plasmas are described and a key diagnostic is emissive probes operated in the limit of zero emission.
Abstract: Sheaths in low temperature collisionless and weakly collisional plasmas are often viewed as simple examples of nonlinear physics. How well do we understand them? Closer examination indicates that they are far from simple. Moreover, many predicted sheath properties have not been experimentally verified and even the appropriate “Bohm velocity” for often encountered two-ion species plasma is unknown. In addition, a variety of sheathlike structures, e.g., double layers, can exist, and many two- and three-dimensional sheath effects have not been considered. Experimental studies of sheaths and presheaths in weakly collisional plasmas are described. A key diagnostic is emissive probes operated in the “limit of zero emission.” Emissive probes provide a sensitive diagnostic of plasma potential with a resolution approaching 0.1V and a spatial resolution of 0.1cm. Combined with planar Langmuir probes and laser-induced fluorescence, they have been used to investigate a wide variety of sheath, presheath, and sheathlike structures. Our experiments have provided some answers but have also raised more questions.

23 citations

Journal ArticleDOI
TL;DR: In this article , the physics of plasma jets and their interactions with surfaces through a pedagogical approach are discussed, along with the benchmarking of different experimental measurements in literature and recent efforts for direct comparisons between simulations and measurements.
Abstract: Plasma jets are sources of repetitive and stable ionization waves, meant for applications where they interact with surfaces of different characteristics. As such, plasma jets provide an ideal testbed for the study of transient reproducible streamer discharge dynamics, particularly in inhomogeneous gaseous mixtures, and of plasma–surface interactions. This topical review addresses the physics of plasma jets and their interactions with surfaces through a pedagogical approach. The state-of-the-art of numerical models and diagnostic techniques to describe helium jets is presented, along with the benchmarking of different experimental measurements in literature and recent efforts for direct comparisons between simulations and measurements. This exposure is focussed on the most fundamental physical quantities determining discharge dynamics, such as the electric field, the mean electron energy and the electron number density, as well as the charging of targets. The physics of plasma jets is described for jet systems of increasing complexity, showing the effect of the different components (tube, electrodes, gas mixing in the plume, target) of the jet system on discharge dynamics. Focussing on coaxial helium kHz plasma jets powered by rectangular pulses of applied voltage, physical phenomena imposed by different targets on the discharge, such as discharge acceleration, surface spreading, the return stroke and the charge relaxation event, are explained and reviewed. Finally, open questions and perspectives for the physics of plasma jets and interactions with surfaces are outlined.

20 citations

Journal ArticleDOI
TL;DR: In this article, a theory that links electron emission and breakdown mechanism theories from quantum scales to Paschen's law was derived and yields asymptotic solutions for quantum space-charge limited emission (QSCL), classical space charge limited emissions (CSCL), space charge limit emission with collisions (MG), Fowler-Nordheim field emission (FN), field emission driven gas breakdown, and classical gas breakdown defined by Paschens law (PL).
Abstract: Numerous applications such as micro- and nanoelectromechanical systems, microplasmas, and directed energy increasingly drive device miniaturization to nanoscale and from vacuum to atmospheric pressure. This wide range of operating conditions and relevant mechanisms complicates the derivation of a single scaling law for electron emission and gas breakdown; therefore, theoretical studies often unify two or three mechanisms piecemeal. This study defines a common set of scaling parameters across the range of dominant mechanisms to derive a theory that links electron emission and breakdown mechanism theories from quantum scales to Paschen's law and yields asymptotic solutions for quantum space-charge limited emission (QSCL), classical space-charge limited emission (CSCL), space-charge limited emission with collisions (MG), Fowler–Nordheim field emission (FN), field emission driven gas breakdown, and classical gas breakdown defined by Paschen's law (PL). These non-dimensionalized equations are universal (true for any gas) across all regimes except for PL, which contains a single, material-dependent parameter. This approach reproduces various nexuses corresponding to the transitions across multiple mechanisms, such as QSCL to CSCL, CSCL to FN, CSCL to MG to FN, and field emission-driven breakdown as described by FN to PL, using a single non-dimensionalization scheme to facilitate experimental designs concerned with crossing these regimes. Furthermore, we demonstrate the conditions for more complicated nexuses, such as matching QSCL, CSCL, MG, and FN. This provides valuable information to experimentalists concerning regimes where slight perturbations in conditions may alter the electron emission mechanism and to theorists concerning the applicability of the asymptotic solutions or reduced nexus theories.

17 citations

Journal ArticleDOI
TL;DR: In this article , the electron emission yield for metal surfaces at very low electron impact energies is calculated based on an invariant embedding principle for the backscattering function, and the results suggest that in order to get secondary electrons out of metals, the large energy loss due to inelastic electron-electron scattering has to be compensated for by incoherent elastic electron-ion core scattering irrespective of the crystallinity of the sample.
Abstract: Based on an invariant embedding principle for the backscattering function we calculate the electron emission yield for metal surfaces at very low electron impact energies. Solving the embedding equation within a quasi-isotropic approximation and using the effective mass model for the solid, experimental data are fairly well reproduced provided (i) incoherent scattering on ion cores is allowed to contribute to the scattering cascades inside the solid and (ii) the transmission through the surface potential takes into account Bragg gaps due to coherent scattering on crystal planes parallel to the surface as well as randomization of the electron's lateral momentum due to elastic scattering on surface defects. Our results suggest that in order to get secondary electrons out of metals, the large energy loss due to inelastic electron-electron scattering has to be compensated for by incoherent elastic electron-ion core scattering, irrespective of the crystallinity of the sample.

3 citations

References
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Journal ArticleDOI
TL;DR: In this paper, a compilation of all published measurements of electron inelastic mean free path lengths in solids for energies in the range 0-10 000 eV above the Fermi level is presented.
Abstract: A compilation is presented of all published measurements of electron inelastic mean free path lengths in solids for energies in the range 0–10 000 eV above the Fermi level. For analysis, the materials are grouped under one of the headings: element, inorganic compound, organic compound and adsorbed gas, with the path lengths each time expressed in nanometers, monolayers and milligrams per square metre. The path lengths are vary high at low energies, fall to 0.1–0.8 nm for energies in the range 30–100 eV and then rise again as the energy increases further. For elements and inorganic compounds the scatter about a ‘universal curve’ is least when the path lengths are expressed in monolayers, λm. Analysis of the inter-element and inter-compound effects shows that λm is related to atom size and the most accuratae relations are λm = 538E−2+0.41(aE)1/2 for elements and λm=2170E−2+0.72(aE)1/2 for inorganic compounds, where a is the monolayer thickness (nm) and E is the electron energy above the Fermi level in eV. For organic compounds λd=49E−2+0.11E1/2 mgm−2. Published general theoretical predictions for λ, valid above 150 eV, do not show as good correlations with the experimental data as the above relations.

4,486 citations

Journal ArticleDOI
TL;DR: In this article, the authors discuss the history, discharge physics, and plasma chemistry of dielectric-barrier discharges and their applications and discuss the applications of these discharges.
Abstract: Dielectric-barrier discharges (silent discharges) are used on a large industrial scale. They combine the advantages of non-equilibrium plasma properties with the ease of atmospheric-pressure operation. A prominent feature is the simple scalability from small laboratory reactors to large industrial installations with megawatt input powers. Efficient and cost-effective all-solid-state power supplies are available. The preferred frequency range lies between 1 kHz and 10 MHz, the preferred pressure range between 10 kPa and 500 kPa. Industrial applications include ozone generation, pollution control, surface treatment, high power CO2 lasers, ultraviolet excimer lamps, excimer based mercury-free fluorescent lamps, and flat large-area plasma displays. Depending on the application and the operating conditions the discharge can have pronounced filamentary structure or fairly diffuse appearance. History, discharge physics, and plasma chemistry of dielectric-barrier discharges and their applications are discussed in detail.

2,730 citations

Journal ArticleDOI
TL;DR: In this paper, the authors have developed a technique which allows optical absorption measurements to be made using a pulsed light source and offers a sensitivity significantly greater than that attained using stabilized continuous light sources.
Abstract: We have developed a technique which allows optical absorption measurements to be made using a pulsed light source and offers a sensitivity significantly greater than that attained using stabilized continuous light sources. The technique is based upon the measurement of the rate of absorption rather than the magnitude of absorption of a light pulse confined within a closed optical cavity. The decay of the light intensity within the cavity is a simple exponential with loss components due to mirror loss, broadband scatter (Rayleigh, Mie), and molecular absorption. Narrowband absorption spectra are recorded by scanning the output of a pulsed laser (which is injected into the optical cavity) through an absorption resonance. We have demonstrated the sensitivity of this technique by measuring several bands in the very weak forbidden b1Σg−X3Σg transition in gaseous molecular oxygen. Absorption signals of less than 1 part in 106 can be detected.

1,540 citations

Journal ArticleDOI
26 Mar 2010-Science
TL;DR: The state of the art of this emerging field of electronics is traced and some of the challenges and pitfalls that may lie ahead are discussed.
Abstract: Extraordinary electron systems can be generated at well-defined interfaces between complex oxides. In recent years, progress has been achieved in exploring and making use of the fundamental properties of such interfaces, and it has become clear that these electron systems offer the potential for possible future devices. We trace the state of the art of this emerging field of electronics and discuss some of the challenges and pitfalls that may lie ahead.

1,189 citations

Journal ArticleDOI
TL;DR: In this article, the dependence of the strength of the electron-phonon coupling and the electron heat capacity on the electron temperature was investigated for eight representative metals, Al, Cu, Ag, Au, Ni, Pt, W, and Ti.
Abstract: The dependence of the strength of the electron-phonon coupling and the electron heat capacity on the electron temperature is investigated for eight representative metals, Al, Cu, Ag, Au, Ni, Pt, W, and Ti, for the conditions of strong electron-phonon nonequilibrium. These conditions are characteristic of metal targets subjected to energetic ion bombardment or short-pulse laser irradiation. Computational analysis based on first-principles electronic structure calculations of the electron density of states predicts large deviations (up to an order of magnitude) from the commonly used approximations of linear temperature dependence of the electron heat capacity and a constant electron-phonon coupling. These thermophysical properties are found to be very sensitive to details of the electronic structure of the material. The strength of the electron-phonon coupling can either increase (Al, Au, Ag, Cu, and W), decrease (Ni and Pt), or exhibit nonmonotonic changes (Ti) with increasing electron temperature. The electron heat capacity can exhibit either positive (Au, Ag, Cu, and W) or negative (Ni and Pt) deviations from the linear temperature dependence. The large variations of the thermophysical properties, revealed in this work for the range of electron temperatures typically realized in femtosecond laser material processing applications, have important implications for quantitative computational analysis of ultrafast processes associated with laser interaction with metals.

1,165 citations