Plasma Frequency Research Articles

Interplay between the heat treatment and structural and optical properties of Nb2O5 thin films

Thin films of Nb2O5 were synthesized by RF sputtering. The effect of annealing, at different temperatures (100, 150, 200, 250, 300, 350, and 400 °C), on the structural and optical properties was studied. The crystallinity and structural characteristics of the Nb2O5 thin films were examined employing the X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD and SEM analyses showed an amorphous nature for the as-deposited and annealed samples from 100 to 350 °C and crystalline structure for the annealed sample at 400 °C. The high values of the transmittance and low reflection make these films used as a window layer in solar cell systems. Upon increasing annealing temperature, the energy band gap Eg increased from 4.039 to 4.175 eV. Eg high values again make these films suitable to be used as a window layer in solar cell system. Urbach tail, EU, decreased with increasing annealing temperature. The refractive index showed the normal dispersion. The dispersion energies were found to have the same behavior with respect to annealing temperature, besides, the single oscillator energy Eₒ had a lower value compared to the dispersion energy Ed. The plasma frequency ωp\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\omega }_{p}$$\\end{document} was found to increase with annealing temperature. The first and third optical moments had peak values depending on the incident photon energy.

Validation of the IRI-2020 model for the topside-plasmasphere using GNSS TEC measurements

The 2020 update of the International Reference Ionosphere (IRI) model introduces a new topside option, COR2, for the formulation of its electron density profile, as well as two plasmaspheric extension options based on the GCPM model of Gallagher et al. (2000) and the IMAGE/RPI model of Ozhogin et al. (2012). We validate the COR2-Gallagher and COR2-Ozhogin topside-plasmasphere options of IRI-2020 using GNSS VTEC measurements and compare them to the NeQuick model used as the default option in IRI-2016. VTEC data from a total of 21 GNSS ground-based receivers are compared to predictions of the IRI model, ranging from low (< 30°) to middle (30°-60°) magnetic latitudes, during high (year 2014; F10.7∼140 sfu) and low (year 2019; F10.7∼70 sfu) solar activity. Peak plasma frequency (foF2) data from co-located digisondes are ingested into the model to ensure the relevance of the comparison. The three topside-plasmasphere options perform equally well at mid-latitudes (RMSE∼3 TECU). At low latitudes, the NeQuick option (RMSE∼9 TECU) performs better than both the COR2-Gallagher and COR2-Ozhogin options (RMSE > 10 TECU). For all options, the modeled VTEC is consistently overestimated during the autumn/winter daytime at mid-latitudes regardless of solar activity, and throughout the day at low latitudes during low solar activity.

Plasma compressibility and the generation of electrostatic electron Kelvin–Helmholtz instability

This study explores the generation of electrostatic (ES) electron Kelvin–Helmholtz instability (EKHI) in collisionless plasma with a step-function electron velocity shear akin to that developed in the electron diffusion region in magnetic reconnection. In incompressible plasma, ES EKHI does not arise in any velocity shear profile due to the decoupling of the electric potential from the electron momentum equation. Instead, a fluid-like Kelvin–Helmholtz instability (KHI) can arise. However, in compressible plasma, the compressibility couples the electric potential with the electron dynamics, leading to the emergence of a new ES mode EKHI on Debye length λDe, accompanied by the co-generation of an electron acoustic-like wave. The minimum threshold of ES EKHI is ΔU&amp;gt;2cse, i.e., the electron velocity shear is larger than twice the electron acoustic speed cse. The corresponding growth rate is Im(ω)=((ΔU/cse)2−4)1/2ωpe, where ωpe is the electron plasma frequency.

Numerical Solutions of Van Der Pol-Mathieu Type Nonlinear Ordinary Differential Equation in Complex Plasma

The description dust plasma behavior via a multi-fluid model, Where it represents that Boltzmann distributed electrons and ions, the dust momentum and Poisson's equations, in addition to the continuity equation that has a source term for the dust grains. The Runge-Kutta technique of fourth order was then used to numerically solve the equation. The solution shows a variety of behaviors under wide range of parameters changes. In particular, the solution of the equation shows a chaotic behavior at α= 1.0. In this study, the chaotic behavior in the plasma complex is graphically studied and discussed for some certain parameters. The aim of this study can be helped the researchers to investigate several nonlinear oscillations in different plasma and fluid mechanics models.

Numerical Solutions of Van Der Pol-Mathieu Type Nonlinear Ordinary Differential Equation in Complex Plasma

The description dust plasma behavior via a multi-fluid model, Where it represents that Boltzmann distributed electrons and ions, the dust momentum and Poisson's equations, in addition to the continuity equation that has a source term for the dust grains. The Runge-Kutta technique of fourth order was then used to numerically solve the equation. The solution shows a variety of behaviors under wide range of parameters changes. In particular, the solution of the equation shows a chaotic behavior at α= 1.0. In this study, the chaotic behavior in the plasma complex is graphically studied and discussed for some certain parameters. The aim of this study can be helped the researchers to investigate several nonlinear oscillations in different plasma and fluid mechanics models.

Electron–ion collision and polarization of X-ray fluorescence radiation under hot quantum plasma conditions

In the current article, the spectral properties and electron collision (total and magnetic) excitation cross sections of ions taking placed in quantum plasmas are investigated. These cross sections are further used to study the polarization and angular distribution characteristics of the de-excitation radiation X-ray spectra, which play an important role in basic theoretical research, the diagnosis of the plasma environment, and the design of optical devices. To do so, a distorted wave method within the relativistic Dirac–Coulomb atomic structure scheme is suggested. The effective interaction potential between electrons and particles in hot quantum plasmas in the method is determined using a quantum approach that incorporates the influence of effective plasma screening effects caused by collective plasma oscillations. This potential replaces the traditional Coulomb interaction potential and is used in solving the modified Dirac equation to obtain the bound and continuum electron wave functions. Higher-order relativistic effects, such as the Breit interaction and the dominant quantum electrodynamics corrections, are added to enhance the accuracy of the method. Detailed calculations for the relativistic atomic structure and collision excitation dynamics process are carried out, taking the highly stripped H-like O7+ ion of astrophysical importance as an illustrative example. Detailed investigations are also conducted on the variation of energies, collision cross sections, and fluorescence polarizations as functions of the plasma parameters. Our results suggest that the joint effects of shielding and plasma coupling lead the energies, cross sections and fluorescence polarizations decrease (compared with the isolated case). The angular distribution of the X-ray fluorescence emission shows large change, suggesting their sensitivity to these effects. This study not only offers a valuable approach to investigating the plasma shielding and plasmon coupling effects in quantum plasmas but also holds significant relevance for applications in controlled nuclear fusion, astrophysical plasmas and so on.

Electric field modulated electronic, thermoelectric and transport properties of 2D tetragonal silicene and its nanoribbons

Using both first principles and analytical approaches, we investigate the role of a transverse electric field in tuning the electrical, thermoelectric, optical and transport properties of a buckled tetragonal silicene (TS) structure. The transverse electric field transforms the linear spectrum to parabolic at the Fermi level and opens a band gap. The gap is similar at the two Dirac points present in the irreducible Brillouin zone of the TS structure and increases in proportion to the applied field strength. However, a sufficiently strong electric field converts the system into a metallic one. A comparable band opening is also seen in the TS nanoribbons. Electric field-induced semiconducting nature improves its thermoelectric properties. Estimated Debye temperature reveals its superiority over graphene in terms of thermoelectric performance. The optical response of the structures is very asymmetric. Large values of imaginary and real components of the dielectric function are seen. The absorption frequency lies in the UV region. Plasma frequencies are identified and are red-shifted with the applied field. The current–voltage characteristics of the symmetric type nanoribbons show oscillation in current whereas the voltage-rectifying capability of anti-symmetric type nanoribbons under a transverse electric field is interesting.

Ultrafast Hot‐Electron Transfer and Plasmonic Coupling Enable Au/MXene Nanohybrids with Broadband Excellent Nonlinear Absorption

AbstractAchieving coupling between plasma oscillators can significantly modulate their intrinsic optical characteristics. In this paper, strong coupling generated by the surface plasma of MXene and Au nanobipyramids (NBPs) for broadband ultrafast nonlinear optical modulation is reported. The femtosecond transient absorption spectra reveal that the ultrafast hot electron transfer occurred in the Au/MXene nanohybrids at &lt;200 fs. Au/Ta4C3Tx nanohybrids outperform the outstanding broadband saturable absorption (SA), with a saturation intensity 106 times less than that of the initial MXene. Laser excitation at 1100 nm results in reverse saturable absorption for Ta4C3Tx nanosheets and a strong SA for Au/Ta4C3Tx nanohybrids, which extends the range of SA. Theoretical calculations indicate that excellent nonlinearity is synergistically achieved via hot electron transfer and plasmon coupling. Femtosecond transient absorption spectra reveal that Au NBPs offer the additional occupied state for carriers through the transfer process and extend the carrier lifetime considerably. This study provides theoretical guidance for the exploration of remarkable novel nonlinear‐active 2D layer‐based materials and candidates for the practical applications of saturable absorbers.

Exact dispersion relation of the quantum Langmuir wave.

The normal modes, i.e., the eigensolutions to the dispersion relation equation, are the most fundamental properties of a plasma. The real part indicates the intrinsic oscillation frequency while the imaginary part the Landau damping rate. In most of the literature, the normal modes of quantum plasmas are obtained by means of small damping approximation, which is invalid for high-k modes. In this paper, we solve the exact dispersion relations via the analytical continuation scheme, and, due to the multi-value nature of the Fermi-Dirac distribution, reformation of the complex Riemann surface is required. It is found that the topological shape of the root locus in quantum plasmas is quite different from classical ones, in which both real and imaginary frequencies of high-k modes increase with k steeper than the typical linear behavior in classical plasmas. As a result, the time-evolving behavior of a high-k initial perturbation becomes ballistic-like in quantum plasmas.

Unlocking the Potential of Hafnia Ferroelectrics: Achieving High Reliability via Plasma Frequency Modulation in Very High-Frequency Plasma-Enhanced Atomic Layer Deposition

Unlocking the Potential of Hafnia Ferroelectrics: Achieving High Reliability via Plasma Frequency Modulation in Very High-Frequency Plasma-Enhanced Atomic Layer Deposition

Radiation induced non-linear oscillations in ITER baseline scenario plasmas in DIII-D

This work shows how the radiation brought about by metals or metal-equivalent radiators such as Kr and Xe produces non-linear dynamics on otherwise stationary β N flattops of DIII-D ITER Baseline Scenario demonstration discharges. The Kr and Xe gases are used to reproduce the radiative loss rates of W in present machines that operate at core temperatures much lower than the expected ITER temperature. Experiments on DIII-D with injection of Kr and Xe, as well as with sources of intrinsic metals reach the range of radiated fraction values expected in the ITER core and experience slow oscillations in temperature and radiated power. In many cases of high radiated fraction, the core temperature decreases enough for the safety factor profile to rise above the 1/1 rational surface, naturally eliminating sawteeth and occasionally producing a persistent helical core. The oscillations can be reproduced by a modified Lotka–Volterra system for temperature and radiated fraction if diffusion and noise are included, which indicates that the interplay between temperature and radiation can be the main cause of the cyclic nature of the system. A new physics based model which includes equations for temperature, density and input power can also reproduce the oscillations observed in the experiments. The present results suggest that the non-linearity of the system can be increased by the inclusion of the inherently non-linear alpha heating term, which is proportional to ∼n e 2 T i 2, and obtains oscillations in the model when added to an otherwise more stationary system.

Ab initio property characterisation of thousands of previously unexplored 2D materials

We perform extensive density functional theory calculations to determine the stability and elementary properties of 4249 previously unexplored monolayer crystals. The monolayers comprise the most stable subset (energy within 0.1 eV/atom of the convex hull) of a larger portfolio of two-dimensional (2D) materials recently discovered using a deep generative model and systematic lattice decoration schemes. The relaxed 2D structures are run through the basic property workflow of the Computational 2D Materials Database (C2DB) to evaluate the dynamical stability and obtain the stiffness tensor, piezoelectric tensor, deformation potentials, Born and Bader charges, electronic band structure, effective masses, plasma frequency, Fermi surface, projected density of states, magnetic moments, magnetic exchange couplings, magnetic anisotropy, topological indices, optical- and infrared polarisability. We provide statistical overviews of the property data and highlight a few specific examples of interesting materials. Our work exposes previously unknown parts of the 2D chemical space and provides a basis for the discovery of 2D materials with specific properties. All data is available in the C2DB.

Terahertz wave propagation characteristics in SMM-based three-dimensional plasma fluid

During the return to the atmosphere of a hypersonic vehicle in adjacent space, a plasma sheath forms on the surface of the vehicle, which blocks normal electromagnetic communications. The ‘blackout’ phenomenon caused by plasma sheaths has received much attention. This paper focuses on the American RAM-C vehicle as the research object, and utilizes the fluid simulation software USim to numerically simulate the pressure, temperature, and electron density under different flight conditions, and based on the simulation results, selects the appropriate electron density and plasma collision frequency, introduces the terahertz (THz) wave, and adopts the scattering matrix method (SMM) to study the propagation characteristics of the vertically incident non-uniform magnetized plasma with the terahertz wave. Among other things, the transmission characteristics of terahertz waves in the plasma are affected by the flight altitude and flight angle of attack of the vehicle. The conclusions indicate that the transmissivity of terahertz wave transmission in plasma increases, and the reflectivity and absorptance decrease with increasing flight altitude and flight angle of attack. Under the condition of controlling other flight parameters unchanged, the plasma frequency and collision frequency decrease with the increase of flight altitude. The larger the flight angle of attack is, the larger the plasma frequency and collision frequency are. The electron density on the wall surface of the vehicle was also tested, and it was found that the lowest electron density was found at the tail end of the leeward surface. This study can provide some theoretical references for mitigating the ‘blackout’ phenomenon of re-entry vehicles.

Observation of Momentum Space Josephson Effects in Weakly Coupled Bose-Einstein Condensates.

The momentum space Josephson effect describes the supercurrent flow between weakly coupled Bose-Einstein condensates (BECs) at two discrete momentum states. Here, we experimentally observe this exotic phenomenon using a BEC with Raman-induced spin-orbit coupling, where the tunneling between two local band minima is implemented by the momentum kick of an additional optical lattice. A sudden quench of the Raman detuning induces coherent spin-momentum oscillations of the BEC, which is analogous to the ac Josephson effect. We observe both plasma and regular Josephson oscillations in different parameter regimes. The experimental results agree well with the theoretical model and numerical simulation and showcase the important role of nonlinear interactions. We also show that the measurement of the Josephson plasma frequency gives the Bogoliubov zero quasimomentum gap, which determines the mass of the corresponding pseudo-Goldstone mode, a long-sought phenomenon in particle physics. The observation of momentum space Josephson physics offers an exciting platform for quantum simulation and sensing utilizing momentum states as a synthetic degree.

NOIRE-Net–a convolutional neural network for automatic classification and scaling of high-latitude ionograms

Millions of ionograms are acquired annually to monitor the ionosphere. The accumulated data contain untapped information from a range of locations, multiple solar cycles, and various geomagnetic conditions. In this study, we propose the application of deep convolutional neural networks to automatically classify and scale high-latitude ionograms. A supervised approach is implemented and the networks are trained and tested using manually analyzed oblique ionograms acquired at a receiver station located in Skibotn, Norway. The classification routine categorizes the observations based on the presence or absence of E− and F-region traces, while the scaling procedure automatically defines the E− and F-region virtual distances and maximum plasma frequencies. Overall, we conclude that deep convolutional neural networks are suitable for automatic processing of ionograms, even under auroral conditions. The networks achieve an average classification accuracy of 93% ± 4% for the E-region and 86% ± 7% for the F-region. In addition, the networks obtain scientifically useful scaling parameters with median absolute deviation values of 118 kHz ±27 kHz for the E-region maximum frequency and 105 kHz ±37 kHz for the F-region maximum O-mode frequency. Predictions of the virtual distance for the E− and F-region yield median distance deviation values of 6.1 km ± 1.7 km and 8.3 km ± 2.3 km, respectively. The developed networks may facilitate EISCAT 3D and other instruments in Fennoscandia by automatic cataloging and scaling of salient ionospheric features. This data can be used to study both long-term ionospheric trends and more transient ionospheric features, such as traveling ionospheric disturbances.

Correlation of ctDNA and radiographic imaging features derived from 18F-FDG PET/CT for patients with metastatic melanoma treated with immunotherapy.

3057 Background: 18F-FDG PET/CT scans are used to assess tumor response for patients undergoing immunotherapy for metastatic melanoma (MM). Evaluating the relationship between features derived from quantitative medical image analysis and markers in blood samples such as circulating tumor DNA (ctDNA) may present an opportunity to discover imaging and blood biomarkers that can influence future patient care. This study evaluates the correlation of ctDNA and radiographic imaging features derived from FDG PET/CT. Methods: Whole-body FDG PET/CT scans from MM patients between 2014-2020 were retrospectively collected under IRB-approved protocol. Patients received pembrolizumab (n=20), ipilimumab (n=4), nivolumab (n=7), or a combination of ipilimumab and nivolumab (n=19). TRAQinform IQ software (AIQ Solutions) identified and quantified regions of interest suspicious of cancer (lesion-ROI), enabling extraction of imaging features including SUVmax, SUVmean, and SUVtotal in baseline (BL) and follow-up (FU) images and change. Plasma ctDNA concentration (copies/ml) and frequency abundance (FA) were evaluated for the first sample (1) after immunotherapy had started (between baseline and first on-treatment scan), and the next available sample (2). Patients were further grouped by ctDNA mutation for analysis. Correlation between imaging features and ctDNA features was assessed using Spearman coefficient (ρ). Results: The patient cohort included 32 males and 19 females with average age of 62 years (range 23-83). For all 51 patients, moderate correlation was observed in SUVmax,BL with ctDNA copies/ml1 (ρ = 0.48, p&lt;&lt; 0.001) and ctDNA FA1 (ρ = 0.49, p &lt;&lt; 0.001) and in SUVtotal,BL with ctDNA FA1 (ρ= 0.41, p &lt; 0.001). In BRAF mutation patients (N=32), moderate correlations existed between SUVmax,BL with ctDNA copies/ml1 (ρ = 0.49, p = 0.0041 and ctDNA FA1 (ρ = 0.05, p = 0.0035), and SUVtotal,BL with ctDNA copies/ml2 (ρ = 0.42, p = 0.017), ctDNA FA1 (ρ = 0.40, p = 0.023), and ctDNA FA2 (ρ = 0.43, p = 0.012). All the other combinations displayed weak correlations (ρ &lt; 0.39, p &gt; 0.05). Conclusions: This study shows that in patients with MM receiving immunotherapy, quantitative features from blood biomarkers such as ctDNA correlate with FDG PET/CT imaging features. Combining blood biomarkers with imaging features that are spatially localizable may strengthen prognostication in this patient group. Further analysis is being performed with more types of ctDNA mutations.

Influence of radio frequency wave driving frequency on capacitively coupled plasma discharge

A two-dimensional symmetric fluid model is established to study the influence of radio frequency (RF) wave driving frequency on the capacitively coupled plasma discharge. The relationship between the driving frequency and electron density is obtained by solving the electron energy balance equation. The calculation results show that the average electron density first increases rapidly with the increase in driving frequency and then gradually tends to saturation at a threshold frequency. A fluid simulation is also carried out, which provides similar results. Physical studies on this phenomenon are conducted, revealing that the essence of this phenomenon is due to the inability of electrons to quickly respond to potential changes within the boundary sheath when the driving frequency of RF exceeds the plasma frequency. In addition, it is also found that increasing gas pressure can enhance the electron density and the type of gas can also affect the electron density.

Low-frequency conductivity of low wear high-entropy alloys

High-entropy alloys (HEAs) provide new research avenues for alloy combinations in the periodic table, opening numerous possibilities in novel-alloy applications. However, their electrical characteristics have been relatively underexplored. The challenge in establishing an HEA electrical conductivity model lies in the changes in electronic characteristics caused by lattice distortion and complexity of nanostructures. Here we show a low-frequency electrical conductivity model for the Nb-Mo-Ta-W HEA system. The cocktail effect is found to explain trends in electrical-conductivity changes in HEAs, while the magnitude of the reduction is understood by the calculated plasma frequency, free electron density, and measured relaxation time by terahertz spectroscopy. As a result, the refractory HEA Nb15Mo35Ta15W35 thin film exhibits both high hardness and excellent conductivity. This combination of Nb15Mo35Ta15W35 makes it suitable for applications in atomic force microscopy probe coating, significantly improving their wear resistance and atomic-scale image resolution.

Identification of nonlinear effects of background asymmetry on solitary oscillations in a cylindrical plasma

A symmetry-breaking in rotational spatial pattern of quasi-periodic solitary oscillations is revealed with tomography measurement of plasma emission, simultaneously with background asymmetry in stationary plasma structure. Although the oscillatory pattern deformation is a natural course in the presence of asymmetry, elaborate analyses identify existence unfeatured nonlinear effects of the background asymmetry, i.e., its nonlinear couplings with harmonic modes of rotational symmetry, to produce non-harmonic mode to break the symmetry and cause the oscillatory pattern to be chaotic. The findings suggest the unrecognized fundamental process for plasmas to be turbulent.

Radial Variations in Solar Type III Radio Bursts

Type III radio bursts are generated by electron beams accelerated at reconnection sites in the corona. This study, utilizing data from the Parker Solar Probe’s first 17 encounters, closely examines these bursts down to 13 solar radii. A focal point of our analysis is the near-radial alignment (within 5°) of the Parker Solar Probe, STEREO-A, and Wind spacecraft relative to the Sun. This alignment, facilitating simultaneous observations of 52 and 27 bursts by STEREO-A and Wind respectively, allows for a detailed differentiation of radial and longitudinal burst variations. Our observations reveal no significant radial variations in electron beam speeds, radio fluxes, or exponential decay times for events below 50 solar radii. In contrast, closer to the Sun we noted a decrease in beam speeds and radio fluxes. This suggests potential effects of radio beaming or alterations in radio source sizes in this region. Importantly, our results underscore the necessity of considering spacecraft distance in multispacecraft observations for accurate radio burst analysis. A critical threshold of 50 solar radii emerges, beyond which beaming effects and changes in beam speeds and radio fluxes become significant. Furthermore, the consistent decay times across varying radial distances point toward a stable trend extending from 13 solar radii into the inner heliosphere. Our statistical results provide valuable insights into the propagation mechanisms of type III radio bursts, particularly highlighting the role of scattering near the radio source when the frequency aligns with the local electron plasma frequency.