arXiv subjects

Yevgeny Raitses

Publications and source records attributed to Yevgeny Raitses.

At least 19 recordsLinked to original sources

arXiv2026

Background-Pressure Effects on Charge-Exchange Measurements in Plasma Flows at Elevated Pressures

Charge-exchange (CEX) collisions can affect measurements of plasma plumes and neutralized ion flows in vacuum facilities, particularly when the background gas pressure increases and the CEX mean free path becomes comparable to the characteristic plume or facility dimension. Here, we investigate that regime in the plasma plume of a gridded ion source operating with a 400 eV argon ion beam. The fast-ion flux and low-energy ion flux were measured using a retarding potential analyzer (RPA) and planar probes, while the fast-neutral flux was inferred from deposited-power measurements with a thermal flux probe using a power-balance analysis. The low-energy ion flux increases with both background gas pressure and axial distance and its detection also depends on probe geometry. After the fast-ion component is isolated, its attenuation is described more accurately by an analytical reduced semi-empirical quasi-2D model that includes charge exchange and the experimentally observed plume divergence than by a one-dimensional attenuation law. The inferred fast-neutral flux also increases with pressure; however, the model underpredicts it at small axial distance and overpredicts it at elevated pressure and larger axial distance. This discrepancy suggests additional angular and collisional effects, as well as possible fast-neutral production near or inside the ion source, that are not captured by the present model. These results show that background gas pressure affects both the plasma plume and the diagnostic response, and that complementary electrostatic, thermal, and energy-selective diagnostics are required to distinguish source behavior from facility-induced effects.

physics.plasm-ph↗

arXiv2025

Decomposition of Methane Diluted with Inert Gas in an RF Discharge Cell

Decomposition of methane using non-thermal plasmas is an attractive route for producing hydrogen-rich gases and valuable carbon nanomaterials. Understanding how plasma discharge modes influence methane decomposition in optimizing plasma-assisted chemical conversion remains unexplored. This study explores the coupling between the discharge structure and product selectivity in RF capacitively coupled discharges operating in methane/inert gas mixtures in the pressure range of 2 to 3 torr. The discharge exhibits mode transitions from uniform to striated in Ar and Kr and from diffuse to contracted in Ar and Kr with 5 percent or less CH4. The discharges in He and Ne remained uniform under our operating conditions, and their mixtures with CH4 remained diffuse. A 0-D model for Ar/CH4 discharge established a threshold for contraction while also asserting the importance of Ar metastable in the dissociation and ionization processes. The highest degree of methane decomposition, 99.7% with the main products of acetylene and graphitized solid carbon was achieved in the contracted discharge mode for both Kr or Ar with 5% or less CH4. We demonstrate that contraction can play a crucial role in the effective decomposition of methane with value-added products and that both the electronic and thermal properties of plasma gas are responsible for this effect.

physics.plasm-ph↗

arXiv2025

In situ studies of a molten metal anode ablation in a nearly atmospheric pressure DC arc

A DC arc with a meltable metal anode in a near-atmospheric pressure hydrocarbon gas is an emerging method for producing single-walled carbon nanotubes (SWCNTs). In these systems, evaporation of the molten metal anode determines the formation of catalyst seed particles needed for SWCNT growth, and therefore, should be monitored, controlled, and optimized. Evaluating the anode ablation rate by weighing the anode before and after a synthesis run is unfeasible due to anode carburization in the hydrocarbon atmosphere. To overcome this, we implemented a high-speed, 2D, 2-color pyrometry for reliable temperature measurements of the molten anode in a DC arc. The obtained temperature fields were used to calculate the anode ablation rates. Results showed the importance of resolving the arc and molten pool dynamics, as well as addressing the issue of reflections. Furthermore, significant changes in ablation rates were revealed upon addition of CH4, which must be considered when scaling up the production of SWCNTs.

physics.plasm-ph↗

arXiv2025

Planar Laser-Induced Fluorescence system for Space and Phase-resolved Ion Velocity Distribution Function Measurements

In this work, we present a planar laser-induced fluorescence (PLIF) system for two-dimensional (2D) spatial and phase-resolved ion velocity distribution function (IVDF) measurements. A continuous-wave tunable diode laser produces a laser sheet that irradiates the plasma, and the resulting fluorescence is captured by an intensified CCD (ICCD) camera. Fluorescence images recorded at varying laser wavelengths are converted into 2D IVDFs using the Doppler shift principle. Comparing six image filters, the singular-value decomposition (SVD)-based noise filtering is identified as the most effective for enhancing the signal-to-noise ratio while preserving the IVDF structure. The developed ICCD-based PLIF system is tested in an electron-beam generated $E \times B$ plasma with a moderate bulk plasma density of $\sim10^{10}$ $cm^{-3}$. The PLIF measurements are validated against a conventional single-point LIF method using photomultiplier tube (PMT)-based detection at various positions. The phase-resolving capability of the system is tested by oscillating the plasma between two nominal operating modes with different density profiles and triggering the ICCD camera with the externally driven plasma oscillation. The resulting oscillations in fluorescence intensity show good agreement with plasma density variations measured by electrostatic probes, demonstrating the systems ability to resolve phase-dependent dynamics. The measured IVDFs reveal several signatures of ion dynamics in this plasma source, including radially outflowing ions and anomalous ion heating in the plasma periphery, as anticipated by theoretical studies.

physics.plasm-ph↗

arXiv2024

Multimodal azimuthal oscillations in electron beam generated $\textbf{E} \times \textbf{B}$ plasma

Electron beam (e-beam) generated plasmas with applied cross electric and magnetic $\left( \textbf{E} \times \textbf{B} \right)$ fields are promising for low-damage material processing. However, these plasmas can be subject to the formation of azimuthally propagating structures that enhance the radial transport of energetic charged species, which can harm the gentle processing capability of the plasma. In this work we investigate the azimuthal structure formation in an e-beam generated $\textbf{E} \times \textbf{B}$ plasma using experimental diagnostics and 2D3V particle-in-cell simulations. Our findings demonstrate the formation of multiple simultaneously occurring azimuthally propagating modes that exhibit a nontrivial radial dependence. It is suggested that the multimodal azimuthal spectrum is caused by the complex nature of the ion dynamics in the plasma.

physics.plasm-ph↗

arXiv2024

Anticathode effect on electron kinetics in electron beam generated $\mathbf{E} \times \mathbf{B}$ plasma

Electron beam (e-beam) generated plasmas with applied crossed electric and magnetic $\left(\mathbf{E} \times \mathbf{B}\right)$ fields are promising for low damage processing of materials with applications to microelectronics and quantum information systems. In cylindrical e-beam $\mathbf{E} \times \mathbf{B}$ plasmas, radial confinement of electrons and ions is achieved by an axial magnetic field and radial electric field, respectively. To control the axial confinement of electrons, such e-beam generated plasma sources may incorporate a conducting boundary known as an anticathode, which is placed on the axially opposite side of the plasma from the cathode. In this work, it is shown that varying the anticathode voltage bias can control the degree to which the anticathode collects or repels incident electrons, allowing control of warm electron (electron energies in 10-30 eV range) and beam electron population confinement. It is suggested that the effect of the anticathode bias on the formation of these distinct electron populations is also associated with the transition between weak turbulence and strong Langmuir turbulence.

physics.plasm-ph↗

arXiv2024

Report on laser-induced fluorescence transitions relevant for the microelectronics industry and sustainability applications

A wide variety of feed gases are used to generate low-temperature plasmas for the microelectronics and the sustainability applications. These plasmas often have a complex combination of reactive and non-reactive species which may have spatial and temporal variations in the density, the temperature and the energy. Accurate knowledge of these parameters and their variations is critically important for understanding and advancing these applications through validated and predictive modeling and design of relevant devices. Laser-induced fluorescence (LIF) provides both spatial and temporally resolved information about the plasma-produced radicals, ions, and metastables. However, the use of this powerful diagnostic tool requires the knowledge of optical transitions including excitation and fluorescence wavelengths which may not be available or scattered through a huge literature domain. In this manuscript, we collected, analyzed and compiled the available transitions for laser-induced fluorescence for more than 160 chemical species relevant to the microelectronics industry and the sustainability applications. A list of species with overlapping LIF excitation and fluorescence wavelengths have been identified. This summary is intended to serve as a data reference for LIF transitions and should be updated in the future.

physics.plasm-ph↗

arXiv2024

Importance of Gas Heating in Capacitively Coupled Radiofrequency Plasma-assisted Synthesis of Carbon Nanomaterials

In pursuit of diamond nanoparticles, a capacitively-coupled radio frequency (CCRF) flow-through plasma reactor was operated with methane argon gas mixtures. Signatures of the final product obtained microscopically and spectroscopically indicated that the product was an amorphous form of graphite. This result was consistent irrespective of combinations of the macroscopic reactor settings. To explain the observed synthesis output, measurements of C2 and gas properties were carried out by laser-induced fluorescence and optical emission spectroscopy. Strikingly, the results indicated a strong gas temperature gradient of 100 K per mm from the center of the reactor to the wall. Based on additional plasma imaging, a model of hot constricted region (filamentation region) was then formulated. It illustrated that, while the hot constricted region was present, the bulk of the gas was not hot enough to facilitate diamond sp3 formation: characterized by much lower reaction rates, when compared to sp2, sp3 formation kinetics are expected to become exponentially slow. This result was further confirmed by experiments under identical conditions but with a H2/CH4 mixture, where no output material was detected: if graphitic sp2 formation was expected as the main output material from the methane feedstock, atomic hydrogen would then be expected to etch it away in situ, such that the net production of that sp2-hybridized solid material is nearly a zero.

physics.plasm-ph↗

arXiv2024

Growth of metal nanoparticles in hydrocarbon atmosphere of arc discharge

A direct current (DC) arc discharge is a widely used method for large-scale production of metal nanoparticles, core-shell particles, and carbon nanotubes. Here, we explore the growth of iron nanoparticles in a modified DC arc discharge. Iron particles are produced by the evaporation of an anode, made from low-carbon steel. Methane admixture into argon gas serves as a carbon source. Electron microscopy and elemental analysis suggest that hydrocarbons decompose on iron clusters forming a carbon shell, which inhibits iron particle growth until its full encapsulation, at which point the iron core growth is ceased. Experimental observations are explained using an aerosol growth model. The results demonstrate the path to manipulate metal particle size in a hydrocarbon arc environment.

physics.plasm-ph↗

arXiv2024

Wavelength modulation laser-induced fluorescence for plasma characterization

Laser-Induced Fluorescence (LIF) spectroscopy is an essential tool for probing ion and atom velocity distribution functions (VDFs) in complex plasmas. VDFs carry information about kinetic properties of the species critical for plasma characterization, yet their accurate interpretation is challenging due to multicomponent distributions, broadening effects, and background emissions. Our research introduces wavelength modulation (WM) LIF as a solution to enhance VDF sensitivity measurements. WM-LIF, unlike standard amplitude modulation (AM) methods, measures the derivative of the LIF signal, providing greater sensitivity to changes in VDF shape. A numerical model was developed to compare the efficacy of WM and AM signals in lock-in amplifier-based measurements. Experiments were conducted in a weakly collisional argon plasma with magnetized electrons and non-magnetized ions. The argon ion VDFs were measured using a narrow-band tunable diode laser, with its wavelength scanned across the Ar ion transition 4p^4 D_(7/2)-3d^4 F_(9/2) centered at 664.553 nm (in vacuum). A lock-in amplifier detected the second harmonic WM signal, generated by modulating the laser wavelength with an externally controlled piezo-driven mirror. Our findings indicate that WM-LIF can be used to determine VDF parameters, such as distribution components and their temperatures and velocities, serving as an independent method of obtaining such parameters, which can be used for improving analysis of conventional AM approach. This method is especially beneficial in environments with substantial light noise or background emissions e.g., thermionic cathodes and reflective surfaces.

physics.plasm-ph↗

arXiv2023

Optical tuning of the diamond Fermi level measured by correlated scanning probe microscopy and quantum defect spectroscopy

Quantum technologies based on quantum point defects in crystals require control over the defect charge state. Here we tune the charge state of shallow nitrogen-vacancy and silicon-vacancy centers by locally oxidizing a hydrogenated surface with moderate optical excitation and simultaneous spectral monitoring. The loss of conductivity and change in work function due to oxidation are measured in atmosphere using conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM). We correlate these scanning probe measurements with optical spectroscopy of the nitrogen-vacancy and silicon-vacancy centers created via implantation and annealing 15-25 nm beneath the diamond surface. The observed charge state of the defects as a function of optical exposure demonstrates that laser oxidation provides a way to precisely tune the Fermi level over a range of at least 2.00 eV. We also observe a significantly larger oxidation rate for implanted surfaces compared to unimplanted surfaces under ambient conditions. Combined with knowledge of the electron affinity of a surface, these results suggest KPFM is a powerful, high-spatial resolution technique to advance surface Fermi level engineering for charge stabilization of quantum defects.

quant-ph↗

arXiv2022

A Theoretical Thrust Density Limit for Hall Thrusters

Hall Thrusters typically operate at thrust densities on the order of 10 N/m2, which is well below the thrust density limits discussed in previous literature. These limits have been considered here and each component of thrust density is analyzed to demonstrate the relative contribution to the total thrust density. Dependencies of the thrust density limits upon the thruster geometry, electron mobility, and the applied magnetic field are revealed and compared with experimental data.

physics.plasm-ph↗

arXiv2022

Fluid and hybrid simulations of the ionization instabilities in Hall thruster

Low-frequency axial oscillations (5-50 kHz) stand out as a pervasive feature observed in many types of Hall thrusters. While it is widely recognized that the ionization effects play the central role in this mode, as manifested via the large scale oscillations of neutral and plasma density, the exact mechanism(s) of the instabilities remain unclear. To gain further insights into the physics of the breathing mode and evaluate the role of kinetic effects, a one-dimensional time-dependent full nonlinear low-frequency model describing neutral atoms, ions, and electrons, is developed in full fluid formulation and compared to the hybrid model in which the ions and neutrals are kinetic. Both models are quasineutral and share the same electron fluid equations that include the electron diffusion, mobility across the magnetic field, and the electron energy evolution. The ionization models are also similar in both approaches. The predictions of fluid and hybrid simulations are compared for different test cases. Two main regimes are identified in both models: one with pure low-frequency behaviour and the other one, where the low-frequency oscillations coexist with higher frequency oscillations (with the characteristic time scale of the ion channel flyby time, 100-200 kHz). The other test case demonstrate the effect of a finite temperature of injected atoms which is shown to have a substantial effect on the oscillation amplitude.

physics.plasm-ph↗

arXiv2021

Determination of positive anode sheath in anodic carbon arc for synthesis of nanomaterials

In the atmospheric pressure anodic carbon arc, ablation of the anode serves as a feedstock of carbon for production of nanomaterials. It is known that the ablation of the graphite anode in this arc can have two distinctive modes with low and high ablation rates. The transition between these modes is governed by the power deposition at the arc attachment to the anode and depends on the gap between the anode and the cathode electrodes. Probe measurements combined with optical emission spectroscopy (OES) are used to analyze the voltage drop between the arc electrodes. These measurements corroborated previous predictions of a positive anode sheath (i.e. electron attracting sheath) in this arc, which appears in both low and high ablation modes. Another key result is a relatively low electron temperature (~ 0.6 eV) obtained from OES using a collisional radiative model. This result partially explains a higher arc voltage (~ 20 V) required to sustain the arc current of 50-70 A than predicted by existing simulations of this discharge.

physics.plasm-ph↗

arXiv2020

A low power flexible dielectric barrier discharge disinfects surfaces and improves the action of hydrogen peroxide

There is an urgent need for disinfection and sterilization devices accessible to the public that can be fulfilled by innovative strategies for using cold atmospheric pressure plasmas. Here we explore and evaluate an approach combining a flexible printed circuit design of a dielectric barrier discharge (DBD) with an environmentally safe chemical reagent for surface decontamination from bacterial contaminants. The device operates in ambient air without any additional gas flow at a power density of about 0.5 W/cm^2. Using a 3% hydrogen peroxide solution as a model reagent we demonstrate improved reduction in the bacterial load of a surface contaminant of >6log10 in 90 seconds, about 3log10 and 2log10 faster compared to hydrogen peroxide alone and the flexible DBD alone, respectively, for the same treatment time. The synergistic action of the plasma bioactive properties and hydrogen peroxide result in a dramatic improvement of surface disinfection. This opens new possibilities for using the low power flexible DBD plasma sources for surface disinfection and decontamination.

physics.plasm-ph↗

arXiv2020

Atomic Precision Processing of New Materials for Frontier Microelectronic Applications in High Performance Computing and Artificial Intelligence

This document is a joint response by scientists from the Princeton Plasma Physics Laboratory, IBM T. J. Watson Research Center and Applied Materials, Inc. to the DOE Office of Science (DOE-SC) Request for Information: Basic Research Initiative for Microelectronics (https://www.federalregister.gov/documents/2019/07/12/2019-14869/request-for-information-basic-research-initiative-for-microelectronics). Specifically, we propose DOE-SC to include the following topics in their consideration for future solicitations on Microelectronics: 1) The development of a real-time monitoring and in-situ diagnostic techniques that can provide information on plasma, substrate surface, and interaction between both during atomic precision processing of complex materials for the most advanced microelectronic devices with applications to high performance computing and artificial intelligence, and 2) The development of experimentally validated modeling tools to predict processing dynamics including plasma, chemical and material processes involved.

physics.app-ph↗

arXiv2020

Critical Need for a National Initiative in Low Temperature Plasma Research

In the white paper we describe a national program in Low Temperature Plasma (LTP). The program should take advantage of the research opportunities of 3 rapidly growing areas (nanomaterial plasma synthesis, plasma medicine, microelectronics). The main theme is to achieve a fundamental understanding of Low Temperature Plasmas as they are applied to these different applications. This understanding will allow U.S. industry to meet the challenges of international competition.

physics.plasm-ph↗

arXiv2020

Perspectives on Physics of ExB Discharges Relevant to Plasma Propulsion and Similar Technologies

This paper provides perspectives on recent progress in the understanding of the physics of devices where the external magnetic field is applied perpendicularly to the discharge current. This configuration generates a strong electric field, which acts to accelerates ions. The many applications of this set up include generation of thrust for spacecraft propulsion and the separation of species in plasma mass separation devices. These ExB plasmas are subject to plasma-wall interaction effects as well as various micro and macro instabilities, and in many devices, we observe the emergence of anomalous transport. This perspective presents the current understanding of the physics of these phenomena, state-of-the-art computational results, identifies critical questions, and suggests directions for future research

physics.plasm-ph↗