Potential double layers in double plasma device

Results of the investigation on the formation of double layers in double plasma device are presented. By appropriate modifications in the biasing conditions, we have been able to obtain both weak (eΔφ<10KT _e ) and strong double layers (eΔφ>10kT _e ) in the device. Unlike previous experiments, we have not been limited to potential jumps equal to ionisation potential of the neutral gas. A detailed investigation has been carried out to find out why earlier experiments in similar devices were limited to only weak double layers. We have also investigated the phenomenon of the so-called psuedo-double layers and have shown that they are potential jumps over the thickness of the order of Debye length and precede plasma expanding with velocity many times the ion-acoustic velocity. They do not represent metastable states of the plasma as suggested by earlier investigators.     

Adjustment of the ion energy distribution in double plasma and other synthesized plasma devices

The parallel ion energy distribution of a synthesized plasma can be readily controlled via plasma potential gradients in the ion source chamber(s). Alternatively, layers of electrically biased metal filaments can introduce an isotropic ion heating.     

Weak electron acoustic double layers in a multicomponent plasma

Formation of electron acoustic double layers in a magneto-plasma with two ion species is investigated. The existence of double layers propagating almost perpendicular to the magnetic field in a plasma with two distinct ion species and cold electron is discussed.     

Double layers in an inhomogeneous magnetized bi‐ion plasma

A simpler analytical approach is employed to obtain energy integral equation for a pseudo‐particle in a pseudo‐potential, which admits double layer (DL) solutions for the non‐linear low‐frequency electrostatic perturbations in non‐uniform plasma consisting of electrons and two kinds of ions. One of the ion species has field‐aligned shear flow and electrons are superthermal kappa distributed. This theoretical model is applied to the upper ionospheric oxygen‐dominated plasma that has small concentration of protons along with upward flow of oxygen ions. Under suitable boundary conditions, both rarefactive (density dip) and compressive (density hump) DLs are obtained solving energy integral equation using the plasma parameters of ionosphere around altitude of 800 km. The amplitude and width of the DLs depend upon the scale lengths of density and temperature gradients as well as on the ratio of equilibrium densities of oxygen and hydrogen.     

Cylindrical and spherical Gardner solitons and double layers in a dusty electronegative non-thermal plasma with two-temperature electrons

A precise theoretical investigation has been made on the cylindrical and spherical (nonplanar) Gardner solitons (GSs) and double layers (DLs) in a dusty electronegative plasma (composed of inertial positive and negative ions, Maxwellian cold electrons, non-thermal hot electrons, and negatively charged static dust). The reductive perturbation method has been used in derivation of the modified Gardner (MG) equation describing the nonlinear propagation of the dust ion-acoustic (DIA) waves. The MG equation admits solitary waves (SWs) and DLs solutions for σ around its critical value σ c (where σc is the value of σ corresponding to the vanishing of the nonlinear coefficient of the Korteweg de-Vries (K-dV) equation). The nonplanar SWs and DLs solutions are numerically analyzed and the parametric regimes for the existence of the positive as well as negative SWs and negative DLs are obtained. The basic features of nonplanar DIA SWs and DLs, which are found to be different from planar ones, are also identified. The implications of our results to different space and laboratory dusty plasma situations, are discussed.     

Negative plasma potential in unmagnetized DC electropositive plasma with conducting walls

Negative plasma potentials were obtained in DC hot filament unmagnetized electropositive argon plasma for sufficiently low neutral pressure. Double layers provide ion and electron confinement near the walls. The potential profiles from the center of the plasma to the potential minima are quite similar in shape to those observed when the plasma has positive plasma potentials. The primary electrons emitted from the filaments are important for charge conservation and for modification of the Bohm criteria but are not important for current balance.     

黏滞等离子体中双撕裂模不稳定性的数值模拟研究

本文采用磁流体力学模型,数值研究了平板位形下双撕裂模线性增长率关于等离子体电阻η和黏滞v的定标关系.结果表明,对于有理面间距较大的情况,线性增长率关于电阻和黏滞的指数定标率随着黏滞的增加逐渐由γ∝ η3/5v0的定标变化到γ∝η5/6v-1/6的定标;而对于有理面间距较小的情况,其指数定标率随着黏性的增加从γ∝η 1/3 v0的定标逐渐变化到γ∝η2/3v-1/3的定标.本文还给出了初始阶段对称的双撕裂模的非线性演化,发现在非线性阶段对称的双撕裂模将转化为反对称的双撕裂模,并解释了相应的物理机理.     

AlGaN/GaN双异质结F注入增强型高电子迁移率晶体管

理论模拟了不同GaN沟道厚度的双异质结(AlGaN/GaN/AlGaN/GaN)材料对高电子迁移率晶体管(HEMT)特性的影响,并模拟了不同F注入剂量下用该材料制作的增强型器件的特性差异.采用双异质结材料,结合F注入工艺成功地研制出了较高正向阈值电压的增强型HEMT器件.实验研究了三种GaN沟道厚度制作的增强型器件直流特性的差异,与模拟结果进行了对比验证.采用降低的F注入等离子体功率,减小了等离子体处理工艺对器件沟道迁移率的损伤,研制出的器件未经高温退火即实现了较高的跨导和饱和电流特性.对14 nm GaN沟道厚度的器件进行了阈值电压温度稳定性和栅泄漏电流的比较研究,并且分析了双异质结器件的漏致势垒降低效应.     

Electrostatic double layers in a warm negative ion plasma with nonextensive electrons

The electrostatic double layer (DL) structures are studied in negative ion plasma with nonextensive electrons q-distribution. The extended Korteweg–de Vries (EKdV) equation is derived using a reductive perturbation method. It is found that both fast (compressive) and slow (rarefactive) ion acoustic (IA) DLs can propagate in such type of plasmas. The effects of various plasma physical parameters; such as nonextensivity of electrons, presence of negative ions, temperature of both positive and negative ions and different mass ratios of positive to negative ions on the formation of DL structures are discussed in detail with numerical illustrations.     

延迟双脉冲激光产生大气等离子体的实验研究

利用马赫-曾德尔干涉仪获得了延迟双脉冲激光和三种单脉冲激光产生大气等离子体的时间序列干涉图,得到了等离子体中心区域在不同时刻的电子密度．把延迟双脉冲激光与三种单脉冲激光产生的等离子体电子密度进行比较的结果显示：第二束光作用后的相同时刻,延迟双脉冲激光产生的等离子体电子密度大于三种单脉冲激光产生的等离子体电子密度．对注入相同能量的延迟双脉冲激光与单脉冲激光产生等离子体的电子密度时间变化进行理论分析的结果表明：延迟双脉冲激光的第二束光与等离子体相互作用,使得作用结束时等离子体的电子密度增加得很多,进而造成了第二束光作用后延迟双脉冲激光产生的等离子体电子密度大于单脉冲激光产生的等离子体电子密度．进一步的分析表明,注入能量相同时延迟双脉冲激光有效延长了等离子体的存在时间．     

Slow electron acoustic double layer (SEADL) structures in bi-ion plasma with trapped electrons

The properties of ion acoustic double layer (IADL) structures in bi-ion plasma with electron trapping are investigated by using the quasi-potential analysis. The κ-distributed trapped electrons number density expression is truncated to some finite order of the electrostatic potential. By utilizing the reductive perturbation method, a modified Schamel equation which describes the evolution of the slow electron acoustic double layer (SEADL) with the modified speed due to the presence of bi-ion species is investigated. The Sagdeev-like potential has been derived which accounts for the effect of the electron trapping and superthermality in a bi-ion plasma. It is found that the superthermality index, the trapping efficiency of electrons, and ion to electron temperature ratio are the inhibiting parameters for the amplitude of the slow electron acoustic double layers (SEADLs). However, the enhanced population of the cold ions is found to play a supportive role for the low frequency DLs in bi-ion plasmas. The illustrations have been presented with the help of the bi-ion plasma parameters in the Earth's ionosphere F-region.     

Acoustic double layers in multispecies plasma

Particle simulation in a one-dimensional bounded system is used to examine the formation of acoustic double layers in the presence of two ion species. Double-layer formation depends critically on the details of the distribution functions of the supporting ion populations, and their relative drifts with respect to the electrons. The effect of having two ion components, an H⁺ and an O⁺ beam, on double-layer evolution from ion acoustic turbulence driven by an electron drift relative to the H⁺ beam of ≈0.5u _e, where uu_e is the electron thermal speed, is examined. The ratio of ion drifts is taken to be consistent with acceleration by a quasi-static auroral potential drop (i.e. V _H/V_O=√M_O/ M_H=4.0). Acoustic double layers form in either ion species on the time scale τ≈100ω_ps^-1, where ω_ps is the ion plasma frequency for species `s' and s=H or O, and for drifts relative to the electrons lower than that required for double layer formation in simulations of single ion component plasma     

极光带下层区电双层及密度空穴

为了得到极光带下层区电双层及密度空穴的形成和演化过程,分析了在静态极限下,强湍动等离子中低频电势、高频调制场及密度扰动之间的非线性耦合方程,并对其进行了数值计算。结果表明,在极光带下层区,坍塌的高频场导致了电双层及密度空穴的形成。所得的电双层为双双层,是一种非线性的实体,即腔子,其电势峰值范围为14～40 V,厚度为100～200 m,几十个Debye尺度;空穴的最大密度扰动率达到80%以上,这与FAST卫星观测结果相一致。     

Observation of first and third harmonic responses in two-dimensional AlGaAs/GaAs HEMT devices due to plasma wave interaction

Plasma waves are oscillations of electron density in time and space, and in deep submicron field effect transistors, typical plasma frequencies, _ωp${\omega }_p$, lie in the terahertz (THz) range and do not involve any quantum transitions. Hence, using plasma wave excitation for detection and/or generation of THz oscillations is a very promising approach. In this paper, the investigation of plasma wave interaction between the plasma waves propagating in a short-channel High-Electron-Mobility Transistor (HEMT) and the radiated electromagnetic waves was carried out. Experimentally, we have demonstrated the detection of the terahertz (THz) radiation by an AlGaAs/GaAs HEMT up to third harmonic at room temperature and their resonant responses show very good agreement with the calculated results.     

Kinematics of isobaric double layers in magnetized plasma

Zaporozh Institute of Mechanical Engineering. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 1, pp. 31–38, January, 1992.     

Improving organic field-effect transistors based on double active layers structure

Organic field-effect transistors (OFETs) were fabricated based on double active layers structure. Different substrate temperatures and thermal treatment were adopted to prepare double active layers and optimize film morphology. The grain size of organic films can be effectively controlled by the change in substrate temperature in the process of deposition. An improved device performance was obtained compared with conventional single layer devices. This result is attributed to the introduction of double active layers. We believe that this kind of optimization will simultaneously improve charge injection and transportation of OFETs.     

Characteristics of anodic glow pulsed plasma

Using the triple Langmuir probe, the characteristics of the glowing plasma adjacent to a constricted anode is obtained. The glow discharge is generated by applying a train of high voltage pulses between the constricted anode and cylindrical cathode with a pulse frequency of 2 kHz at 50% duty cycle. The axial plasma characteristics along the central line of the anode shows crest and trough resembling a double layer. The bulk plasma showed uniform electron density outside the glow. The visual images show an enhancement in the volume of the glow consistent with the discharge current. The mechanism behind the particular double layer characteristics around the anode is being explained in detail.     

Theory of weak modified electron acoustic double layers

Summary We have obtained the double-layer solutions for the small-amplitude modified electron acoustic waves propagating in a plasma having one ion and two electron components. No DLs solutions are found to exist when the temperature of the free and trapped particles is considered to be the same for all the species. However, when the effects of the reflected hot electrons are considered, DL solutions are found to exist.

---

Riassunto Si sono ottenute soluzioni del doppio strato per onde acustiche modificate dall’elettrone di piccola ampiezza, che si propagano in un plasma avente una componente ionica e 2 componenti elettroniche. Si trova che non esistono soluzioni DL quando la temperatura delle particelle libere e intrappolate si considera stessa per tutte le specie. Tuttavia si trova che le soluzioni DL esistono quando si considerano gli effetti degli elettroni caldi riflessi.

---

Резюме Мы получили решения для двойных слоев в случае акустических волн с малой амплитудой, распространяющихся в плазме, имеющей одну ионную и две электронные компоненты. Показано, что не существуют решения для двойных слоев, когда температура свободных и захваченных частиц является одинаковой для всех компонент. Однако, когда учитывается влияние отраженных горячих электронов, решения для двойных слоев существуют.

     

Thermal stability and data retention of resistive random access memory with HfO_x/ZnO double layers

As an industry accepted storage scheme, hafnium oxide(HfO_x) based resistive random access memory(RRAM)should further improve its thermal stability and data retention for practical applications. We therefore fabricated RRAMs with HfO_x/ZnO double-layer as the storage medium to study their thermal stability as well as data retention. The HfO_x/ZnO double-layer is capable of reversible bipolar switching under ultralow switching current( 3 μA) with a Schottky emission dominant conduction for the high resistance state and a Poole–Frenkel emission governed conduction for the low resistance state. Compared with a drastically increased switching current at 120℃ for the single HfO_x layer RRAM, the HfO_x/ZnO double-layer exhibits excellent thermal stability and maintains neglectful fluctuations in switching current at high temperatures(up to 180℃), which might be attributed to the increased Schottky barrier height to suppress current at high temperatures. Additionally, the HfO_x/ZnO double-layer exhibits 10-year data retention @85℃ that is helpful for the practical applications in RRAMs.