Debye Length Research Articles

Observation of plasma boundary induced Negative Differential Resistance (NDR) in a planar DC discharge system

Observation of Negative Differential Resistance (NDR) in the discharge characteristics of a planar DC discharge system induced by specific combination of plasma boundaries is reported. In a previous work [Barnwal et al 2022 Phys. Plasmas 29 072102] it was shown by the authors that no NDRs are triggered in enclosures that have either a fully conducting boundary (viz., an ss vacuum chamber) or a fully insulating boundary (apart from the electrodes), comprising of glass tubes/mica sheets, etc. In the present work, it is shown that an NDR is triggered when the discharge produced within a small enclosure with an insulating boundary (IB), is allowed to leak out through a small aperture into a larger volume with a conducting boundary (CB). As the plasma density increases with increasing discharge current, the Debye length (λ De), which is initially larger than the gap width at low discharge currents, decreases to become of the order of gap width, triggering the NDR. Since the plasma boundary conditions before and after the NDR are widely different (insulating versus mixed) the NDR, which is unstable electrically, connects a low-current, high-voltage state before the NDR to a high-current, low-voltage state afterward. Further, issues related to changes in the anode sheath before and after the NDR are also explored. When the electrode system is nearly symmetric, the anode sheath prior to the onset of the NDR is an ion sheath that flips into an electron sheath after the NDR. When the electrode system is highly asymmetric, the anode sheath remains an electron sheath throughout (both before and after the NDR). Reasons for such behavior are discussed in the paper.

Electroviscous effects in pressure-driven flow of electrolyte liquid through an asymmetrically charged non-uniform microfluidic device

BackgroundMicro-scale systems depict a different flow behavior from the macro-scale systems due to more vital surface forces such as surface tension, electrical charges, magnetic field, etc., which significantly affect the micro-scale flow. Further, among others, electrokinetic phenomena play a significant role at the micro-scale for controlling practical microfluidic applications. Therefore, it is essential to understand the fluid dynamics in micron-sized channels to develop efficient and reliable microfluidic devices. MethodsThe electroviscous effects in pressure-driven flow of electrolyte liquid through an asymmetrically charged contraction-expansion (4:1:4) slit microfluidic device have been investigated numerically. The mathematical model (i.e., Poisson's, Navier-Stokes, and Nernst-Planck equations) is solved using the finite element method to obtain the electrical potential, velocity, pressure, ion concentration fields, excess charge, an induced electric field strength for the following ranges of parameters: Reynolds number (Re=0.01), Schmidt number (Sc=1000), inverse Debye length (2≤K≤20), top wall surface charge density (4≤St≤16), surface charge density ratio (0≤Sr≤2) and contraction ratio (dc=0.25). Significant FindingsResults show that the charge asymmetry (Sr) at the different walls of the microfluidic device plays a significant role on the induced electric field development and microfluidic hydrodynamics. The total potential (|ΔU|) and pressure drop (|ΔP|) maximally increase by 197.45% and 25.46%, respectively with asymmetry of the charge. The electroviscous correction factor (ratio of apparent to physical viscosity) maximally changes by 20.85% (at K=2, St=16 for 0≤Sr≤2), 34.16% (at St=16, Sr=2 for 2≤K≤20), and 39.13% (at K=2, Sr=2 for 0≤St≤16). Thus, charge asymmetry (0≤Sr≤2) remarkably influences the fluid flow in the microfluidic devices, which is used for controlling the microfluidic processes, such as, mixing efficiency, heat, and mass transfer rates. Further, a simpler analytical model is developed to predict the pressure drop in electroviscous flow considering asymmetrically charged surface, based on the Poiseuille flow in the individual uniform sections and pressure losses due to orifice, estimates the pressure drop 1–2% within the numerical results. The robustness of this model enables the use of present numerical results for design aspects in the microfluidic applications.

Exploring the energy harvest of droplet flow over inducted film for the rainy-shiny solar panel application

An equivalent electrical circuit (EEC) based on transient pseudo-capacitive and electrostatic induction is established to understand the operating mechanism using voltage-time curve decomposition. All relative parameters including top electrode dimension and the instantaneous droplet area variation are used to demonstrate our droplet-base electricity generation (DEG) mechanism and illustrate the principle of the reverse voltage. Moreover, the Debye length concept is introduced to explain charge density at the interface between ionic droplet and the PTFE surface by various ion concentrations and valent number solutions. This work provides insightful and valuable perspective to explain the exponential decay of output voltage by instantaneous droplet area variation during leaving away from the PTFE surface. Moreover, the multi-functions of fluorinated ethylene propylene film coating on the solar panel by correct circuit design can improve 30% which is novel concept at rainy days alternated with dry ones.

Energy and charge conserving semi-implicit particle-in-cell model for simulations of high-pressure plasmas in magnetic traps

The paper presents a new particle-in-cell model for fully kinetic simulations of plasma confinement regimes with high relative pressure. These regimes are considered as the most promising ones for fusion reactor proposals based on field reversed configurations, mirror and multi-cusp magnetic traps. Formation of an equilibrium high-pressure plasma with a fully excluded or reversed magnetic field cannot be investigated using the simplified magnetohydrodynamic and gyrokinetic approaches. A correct description of the electron dynamics under close proximity of zero and strong magnetic field regions can only be achieved within the framework of the kinetic theory that can be implemented most efficiently by the particle-in-cell method. The full-scale particle-in-cell simulations of modern fusion experiments require the use of finite-difference schemes in which temporal steps exceed the period of fastest electron oscillations at the plasma or even cyclotron frequencies and spatial steps do not have to resolve the Debye radius. This requirement is satisfied by implicit schemes capable of conserving the total energy of the system. The particle-in-cell model presented in this paper is based on the energy conserving semi-implicit approach as a predictive step and a new method for suppressing the electrostatic noise inherent in it as a corrective step. This two-step algorithm provides not only accurate energy conservation, but also the exact local fulfillment of the Gauss law.

The breakdown characteristic of porous dielectric discharge based on percolation structure

Porous dielectrics have received increasing attention in plasma sterilization, all-solid-state battery technology, and surface functionalization of biological tissue materials. Due to their complex structure and discharge characteristics, the current researches are hard to quantify the stochastic properties of porous dielectrics. In this paper, we used a percolation structure to simulate the discharge process in a 2D porous dielectric. The simulation results of the 2D percolation model are similar to that of 2D real porous slices, which can characterize the physical properties of the porous dielectric well while greatly reducing the time required for simulation. In addition, simulations on percolation models with different porosity and lattice size are performed. When the porosity and lattice size remain constant, tortuosity and Debye radius are the main factors affecting the breakdown of the percolation model. With the decrease in porosity, the Pashcen curve shifts to the upper right. With the decrease in lattice size, the Pashcen curve moves higher. The results show correlations between random parameters and Paschen curves. This study presents a novel simulation approach for the theoretical analysis of porous dielectric and improves the simulation efficiency at the same time. In addition, this new model is also applied to quantify the impact mechanism of random parameters such as porosity and lattice size on porous dielectric discharge.

Spherically confined hydrogenic atoms under classical non‐ideal plasmas: Scaling law for the critical cage size

AbstractAn elegant calculation is carried out to investigate the effects of the non‐ideality of classical plasma on the energy levels of the hydrogenic atoms held in a spherical cage. Organized effect of the non‐ideal classical plasma is described by an analytical pseudopotential which contains the Debye length and non‐ideality parameter as parameters. Convergent results for the bound states are obtained variationally by utilizing a large trail function containing cosine term which automatically takes care of the requisite boundary conditions. For the plasma‐free case, our results are in excellent agreement with the most accurate results available in the literature. An inclusive study is made to explore the changes emerging in the energy levels due to the variation of the plasma parameters and cage size. Special emphasis is made on the determination of critical cage size precisely. The present study specifically reveals that the increasing plasma non‐ideality leads to the elongation of the critical cage size. Moreover, it is empirically found that the critical cage size for a given hydrogenic atom can be obtained from a scaling law.

Spectroscopic Diagnostic of Laser-Induced Zn Plasma

The sample's physical characteristics and laser parameters impact the generation and characterization of Laser-Induced Plasma (LIP), which is a relevant phenomenon in many applications. We investigated the effect of laser energy on laser-induced Zn plasma characterization in this study. A Zn plasma with a repeating frequency of 6 Hz, a first wavelength of 1064 nm, a pulse duration of 10 ns, and a laser energy range of 300 mJ to 500 mJ was created using a Q-switched ND: YAG laser. The basic plasma properties, such as electron temperature and density, were estimated using optical emission spectroscopy (OES). The electrons' temperature was measured by the Boltzmann plot method, and the value of the electrons' temperature ranged from 1.6 eV to 2.051 eV in the laser energy range (300-500) mJ. In electron density estimation using the Stark broadening methods, the density value range from 12.75×1017 cm-3 to 19.50×1017 cm-3, in laser energy range (300-500 ) mJ. In addition, various plasma characteristics such as plasma frequency (fp), the number of particles in the Debye sphere (ND), and Debye length (λD) were estimated. We found that laser energy affects every plasma parameter.

ZnO tetrapod morphology influence on UV sensing properties.

The aim of this work was to investigate how ZnO tetrapod (ZnO-T) morphology, structure, and surface charge properties (i.e. Debye length) influence their UV sensing properties, shedding light on the underlying photoresponse mechanisms. ZnO-Ts were synthesized and centrifuged to obtain three different fractions with tuned morphology, which were characterized by scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy microscopies, x-ray diffraction analysis, Brunauer-Emmett-Teller measurements, FTIR and UV-vis spectroscopies. ZnO-T UV sensors were fabricated and tested comparing among ZnO-T fractions and commercial ZnO nanoparticles. ZnO-T photoresponse was mostly influenced by ZnO-T leg diameter, with the optimal value close to the double Debye length. We also demonstrated how fractionating ZnO-Ts for morphology optimization can increased the responsivity by 2 orders of magnitude. Moreover, ZnO-T showed 3 orders of magnitude higher responsivity compared to commercial ZnO nanopowder. These results are beneficial for the engineering of efficient UV sensors and contribute to a deeper understanding the overall mechanism governing UV photoresponse.

Label-Free Neuropeptide Detection beyond the Debye Length Limit.

Biosensors with high selectivity, high sensitivity, and real-time detection capabilities are of significant interest for diagnostic applications as well as human health and performance monitoring. Graphene field-effect transistor (GFET) based biosensors are suitable for integration into wearable sensor technology and can potentially demonstrate the sensitivity and selectivity necessary for real-time detection and monitoring of biomarkers. Previously reported DC-mode GFET biosensors showed a high sensitivity for sensing biomarkers in solutions with a low salt concentration. However, due to Debye length screening, the sensitivity of the DC-mode GFET biosensors decreases significantly during operation in a physiological fluid such as sweat or interstitial fluid. To overcome the Debye screening length limitation, we report here alternating current (AC) mode heterodyne-based GFET biosensors for sensing neuropeptide-Y (NPY), a key stress biomarker, in artificial sweat at physiologically relevant ionic concentrations. Our AC-mode GFET biosensors show a record ultralow detection limit of 2 × 10-18 M with an extensive dynamic range of 10 orders of magnitude in sensor response to target NPY concentration. The sensors were characterized for various carrier frequencies (ranging from 30 kHz to 2 MHz) of the applied AC voltages and various salt concentrations (10, 50, and 100 mM). Contrary to DC-mode sensing, the AC-mode sensor response increases with an increase in salt concentration in the electrolyte. The sensor response can be further enhanced by tuning the carrier frequency of the applied AC voltage. The optimum response frequency of our sensor is approximately 400-600 kHz for salt concentrations of 50 and 100 mM, respectively. The salt-concentration- and frequency-dependent sensor response can be explained by an electrolyte-gated capacitance model.

Variational radial sheath solutions for a kinetic model of a cylindrical Langmuir probe

We study qualitative and quantitative properties of the solutions of a Vlasov–Poisson system modeling the interaction between a plasma and a cylindrical Langmuir probe. In particular, we exhibit a class of radial sheath solutions for which the electrostatic potential is increasing and strictly concave with a strong variation in the vicinity of the probe which scales as the inverse of the Debye length. These solutions are proven to exist provided the incoming distributions of particles from the plasma verify the so‐called generalized Bohm condition of plasma physics. It extends our previous studies.

Equation of State of Charged Rod Dispersions.

We study the accuracy of the theory of Stroobants, Lekkerkerker, and Odijk [Macromolecules 1986, 19, 2232-2238], called SLO theory, to describe the thermodynamic properties of an isotropic fluid of charged rods. By incorporation of the effective diameter of the rods according to SLO theory into scaled particle theory (SPT), we obtain an expression for the rod concentration-dependent free volume fraction and the osmotic pressure of a collection of charged hard spherocylinders. The results are compared to Monte Carlo simulations. We find close agreement between the simulation results and the SLO-SPT predictions for not too large values of the Debye length and for high rod charge densities. The deviations increase with rod density, particularly at concentrations above which isotropic-nematic phase transitions are expected.

An energy-conserving Fourier particle-in-cell method with asymptotic-preserving preconditioner for Vlasov-Ampère system with exact curl-free constraint

We present an efficient and accurate energy-conserving implicit particle-in-cell (PIC) algorithm for the electrostatic Vlasov system, with particular emphasis on its high robustness for simulating complex plasma systems with multiple physical scales. This method consists of several indispensable elements: (i) the reformulation of the original Vlasov-Poisson system into an equivalent Vlasov-Ampère system with divergence-/curl-free constraints; (ii) a novel structure-preserving Fourier spatial discretization, which exactly preserves these constraints at the discrete level; (iii) a preconditioned Anderson-acceleration algorithm for the solution of the highly nonlinear system; and (iv) a linearized and uniform approximation of the implicit Crank-Nicolson scheme for various Debye lengths, based on the generalized Ohm's law, which serves as an asymptotic-preserving preconditioner for the proposed method. Numerical experiments are conducted, and comparisons are made among the proposed energy-conserving scheme, the classical leapfrog scheme, and a Strang operator-splitting scheme to demonstrate the superiority of the proposed method, especially for plasma systems crossing physical scales.

Direct implicit and explicit energy-conserving particle-in-cell methods for modeling of capacitively coupled plasma devices

Achieving large-scale kinetic modeling is a crucial task for the development and optimization of modern plasma devices. With the trend of decreasing pressure in applications, such as plasma etching, kinetic simulations are necessary to self-consistently capture the particle dynamics. The standard, explicit, electrostatic, momentum-conserving particle-in-cell method suffers from restrictive stability constraints on spatial cell size and temporal time step, requiring resolution of the electron Debye length and electron plasma period, respectively. This results in a very high computational cost, making the technique prohibitive for large volume device modeling. We investigate the direct implicit algorithm and the explicit energy conserving algorithm as alternatives to the standard approach, both of which can reduce computational cost with a minimal (or controllable) impact on results. These algorithms are implemented into the well-tested EDIPIC-2D and LTP-PIC codes, and their performance is evaluated via 2D capacitively coupled plasma discharge simulations. The investigation reveals that both approaches enable the utilization of cell sizes larger than the Debye length, resulting in a reduced runtime, while incurring only minor inaccuracies in plasma parameters. The direct implicit method also allows for time steps larger than the electron plasma period; however, care must be taken to avoid numerical heating or cooling. It is demonstrated that by appropriately adjusting the ratio of cell size to time step, it is possible to mitigate this effect to an acceptable level.

Spectroscopic Diagnostics of Spectral Lines Emission from Cu Plasma within the Visible Spectrum Range

The creation and characterization of laser-induced plasma (LIP), a significant phenomenon in several applications, are influenced by the sample’s physical qualities as well as the laser’s parameters. In this research, we created Cu plasma in the atmosphere using an Nd: YAG laser operating at a wavelength of 532 nm with a laser irradiance energy range (400-800) mJ. The effect of the laser’s irradiance energy on the plasma characteristics was investigated using optical emission spectroscopy (OES). Using the two ratio and Stark broadening methods, we successfully measured the two most important plasma properties (electron temperature and electron density). The electron’s plasma temperature value ranged from 2.3 to 3 eV. The value of electron plasma density is in the range from 6.75×1017 to 15×1017 cm−3. Also, we found that other plasma parameters like plasma frequency (fp), particles in the Debye sphere (ND), and Debye length (?D) are affected by laser energy. Where plasma frequency ranged from 7.378 to 10.998×1012 Hz, the Debye sphere ranged from 7.294 to 7.022×103, and the range of Debye length from 1.372 to 1.038×10−5 cm.

Plasma Parameters Diagnosis of Laboratory Ar/O2 Cold Atmospheric Plasma Jet using Different Potential Discharges

This paper offers a clear methodology for the characterization of cold atmospheric plasmas and their development. The optical emission spectra of an Ar/O2 plasma jet produced in a plasma jet system at constant flow rates and for various potential discharges between 14 kV and 18 kV revealed that variations in voltage caused a significant difference in the intensity of the Ar/O2 emission. The plasma characteristics of electron temperature (Te), electron density (ne), plasma frequency (fp), Debye length (λD), and the number of particles in the Debye sphere (ND), were estimated using the technique of optical emission spectroscopy (OES). The obtained data are subject to further analysis and discussion. It was determined that potential discharges increased, and an electron temperature increased from 1.34 eV to 1.54 eV. With rising potential discharges, the Debye length decreases while the electron density, plasma frequency, and number of particles in the Debye sphere increase.

Numerical investigation of the electrostatic dust transport around a lunar lander

Since the Apollo era, lunar dust has been one of the major problems for lunar surface explorations, since these very abrasive and adhesive grains are harmful for both the instruments and the human beings. Normally, the lunar surface can get charged with an electric field of several V/m, which is not strong enough to launch the dust grains from the surface. However, the electric field may be enhanced when the solar wind and the sunlight are shadowed by an obstacle. Such a shadowing effect can be caused by either a natural topographic feature or a man-made object. Here we study the shadowing effect of a lunar lander with particle-in-cell simulations. It is found that the shadowed region is negatively charged, with a surface potential as low as −30 V and an electric field as large as 20 V/m. A local dust cloud is caused by the electrostatic dust transport around the lander, with a number density of about 104 m−3 at 1 m altitude and up to 105 m−3 near the surface. The surface potential is determined by the temperature of solar wind, but a higher temperature can bring a weaker electric field and a smaller dust cloud, due to the enhanced Debye length. The electrostatic dust transport favors a larger shadowed area, caused by either a larger solar zenith angle or a higher lander height. In addition, the dust transport favors a conductive lander surface, where the maximum dust density can reach 106 m−3. Our results are helpful for the future lunar explorations and have general implications in studying the dust environment of other airless bodies.

Spectroscopic Assessment of Electron Temperature and Density of Open-Air FHG Laser-Induced Zinc Titanium Plasma

This work used spectroscopic plasma emission analysis to investigate the parameters of ZnTi plasma formed in the atmosphere by a Q-switched Nd:YAG nanosecond laser system emitting infrared (1064 nm) laser light with an energy output spanning 200-500 mJ. The spectrometer was used to examine and record the emission spectrum profiles of (ZnTi), which helped to extract crucial plasma characteristics (i.e., [Formula: see text] and [Formula: see text]. The electron density was measured using the Stark broadening, and the plasma temperature was calculated using the Boltzmann plot technique. The electron temperature was between 2.04 and 2.15 eV, and the electron density was between (15.72 and 18.99) × 10[Formula: see text] cm[Formula: see text]. The Debye length ([Formula: see text], the number of particles in the Debye sphere ([Formula: see text], and the plasma frequency ([Formula: see text] can all be estimated from the electron temperature ([Formula: see text] and the electron density ([Formula: see text] ([Formula: see text].

CuO/TiO2 heterostructure-based sensors for conductometric NO2 and N2O gas detection at room temperature

Nitrous oxide (N2O) is hazardous gas extensively used in surgeries as an anesthetic and released into the atmosphere without any treatment. Despite low concentrations in the atmosphere, it has for 300 times larger warming coefficient to the greenhouse effect than CO2. There are only a few studies dedicated to the development of N2O gas sensors, but not for room temperature (RT) and ultra-low concentrations. In this study, we developed an ultrasensitive gas-sensing device operating at RT based on CuO/TiO2 heterojunctioned nanointerfaces prepared by scalable reactive magnetron sputtering technique with glancing angle deposition. The CuO/TiO2 heterojunctioned nanointerfaces demonstrated N2O gas sensitivity for ∼2 times higher than TiO2 mono-layer, and the device exhibits an outstanding detection limit of 50 ppb at RT, quick response and recovery times (∼36 s and ∼50 s). The ultrasensitivity of gas sensor is achieved by providing control over nanoarchitecture and comparable size of the nanorods-like structure to the doubled Debye lengths (∼70–80 nm). The applied nanoarchitecture design opens a flexible platform for different gas sensing devices where the array of p-n heterojunction nanorods was utilized efficiently and with technological simplicity. The statistical analysis of variances shows that obtained data is more confident and reproducible.

Determination of forced convection effects on the response of membrane-based ion-selective electrodes via numerical solution to the Navier-Stokes-Nernst-Plank-Poisson equations

Ion selective electrodes (ISEs) enable measurements via the build-up of a phase boundary potential at the surface of a sensing membrane. While a framework exists to understand the performance of ISEs in stagnant samples, the influences of fluid flow on ISEs are less studied. We model the transport of ions in solution occurring near interfaces between ISE membranes and aqueous samples when subject to an external flow. We developed a numerical model extending the Pressure-Implicit with Splitting of Operators (PISO) algorithm to incorporate the Navier-Stokes-Nernst-Plank-Poisson system of equations. We find that external flow distorts the aqueous side of the formed double layer at the ISE membrane and aqueous sample interface, leading to an increase in the phase boundary potential. The change in potential is shown to be a function of a novel set of dimensionless numbers, most notably the Debye Length Reynolds number, i.e., the Reynolds number with the Debye Length as the system dimension.

Highly Effective and Efficient Self-Assembled Multilayer-Based Electrode Passivation for Operationally Stable and Reproducible Electrolyte-Gated Transistor Biosensors.

To ensure the operational stability of transistor-based biosensors in aqueous electrolytes during multiple measurements, effective electrode passivation is crucially important for reliable and reproducible device performances. This paper presents a highly effective and efficient electrode passivation method using a facile solution-processed self-assembled multilayer (SAML) with excellent insulation property to achieve operational stability and reproducibility of electrolyte-gated transistor (EGT) biosensors. The SAML is created by the consecutive self-assembly of three different molecular layers of 1,10-decanedithiol, vinyl-polyhedral oligomeric silsesquioxane, and 1-octadecanethiol. This passivation enables EGT to operate stably in phosphate-buffered saline (PBS) during repeated measurements over multiple cycles without short-circuiting. The SAML-passivated EGT biosensor is fabricated with a solution-processed In2O3 thin film as an amorphous oxide semiconductor working both as a semiconducting channel in the transistor and as a functionalizable biological interface for a bioreceptor. The SAML-passivated EGT including In2O3 thin film is demonstrated for the detection of Tau protein as a biomarker of Alzheimer's disease while employing a Tau-specific DNA aptamer as a bioreceptor and a PBS solution with a low ionic strength to diminish the charge-screening (Debye length) effect. The SAML-passivated EGT biosensor functionalized with the Tau-specific DNA aptamer exhibits ultrasensitive, quantitative, and reliable detection of Tau protein from 1 × 10-15 to 1 × 10-10 M, covering a much larger range than clinical needs, via changes in different transistor parameters. Therefore, the SAML-based passivation method can be effectively and efficiently utilized for operationally stable and reproducible transistor-based biosensors. Furthermore, this presented strategy can be extensively adapted for advanced biomedical devices and bioelectronics in aqueous or physiological environments.