Microwave absorption/reflection and magneto-transport experiments on high-mobility electron gas

We have performed simultaneous measurements of microwave absorption/reflection and magneto-transport characteristics of a high-mobility two-dimensional electrons in GaAs-AlGaAs heterostructure in the regime of microwave-induced resistance oscillations (MIROs). It is shown that the electrodynamic aspect of the problem is important in these experiments. In the absorption experiments, a broad cyclotron resonance line was observed due to a large reflection from the highly conductive electron gas. There were no additional features observed related to absorption at harmonics of the cyclotron resonance. In near-field reflection experiments, a very different oscillation pattern was revealed when compared to MIROs. The oscillation pattern observed in the reflection experiments is probably due to plasma effects occurring in a finite-size sample. The whole microscopic picture of MIROs is more complicated than simply a resonant absorption at harmonics of the cyclotron resonance. Nevertheless, the experimental observations are in good agreement with the model by Ryzhii et al. involving the photo-assisted scattering in the presence of a crossed magnetic field and dc bias. The observed damping factor of MIROs may be attributed to a change in the electron mobility as a function of temperature.     

Modeling of wave propagation and absorption in electron cyclotron resonance ion source plasmas

The performance of electron cyclotron resonance ion sources (ECRIS) is critically dependent on the resonant absorption of microwave power. However, currently there is little understanding of the propagation and absorption of electromagnetic waves in these ion sources. Measurement of the electromagnetic fields in a source is difficult without perturbing the plasma, and theory is hindered by the complex interaction between the waves, the plasma, the walls of the device, and the magnetic field. In this paper we present the results of quantitative 1D and qualitative 3D simulations of wave propagation and absorption in an electron cyclotron resonance ion source. The 1D simulations use the hot plasma dielectric tensor, which has not previously been applied to ECRIS modeling. The 3D simulations are the first attempt to include absorption by the plasma in calculating the structure of the electromagnetic fields in an ECRIS. These simulations demonstrate that the wave propagation and absorption is strongly dependent on the plasma. The results of the simulations are compared to experimental measurements of the mode structure, energy absorption, and frequency scaling.     

The role of radiative damping in shaping of the cyclotron resonance line in a two-dimensional electron system

It is shown that the broadening of a cyclotron resonance line in a two-dimensional (2D) electron system relative to the inverse scattering time of electrons is connected with the radiative damping accompanying the cyclotron motion of electrons. Using the radiative damping concept, a simple and physically informative formula describing the cyclotron resonance curve shape in a 2D electron system was obtained.     

Control of the electron temperature by varying the resonance zone width in ECR plasma

The electron temperature (T_e) in an electron cyclotron resonance plasma is clarified to depend on the spatial profiles of the microwave-power absorption by both the electromagnetic-waves measurement and the simulation of microwave power absorption. It is found that T_e is controlled by varying the magnetic field configuration and/or the microwave frequency since the power absorption profile is influenced by the effective resonance width. In fact, T_e is observed to decrease with decreasing the magnetic field gradient at the resonance point for N₂, Ar and O₂/Ar plasma.     

Electron paramagnetic resonance (a review)

For the purposes of this review, the termelectron paramagnetic resonance is taken to refer to the resonant absorption of electromagnetic radiation by electronic systems which possesspermanent magnetic moments (due, in general, to the orbital as well as to the spin angular momentums of electrons) and which are therefore paramagnetic. The termparamagnetic resonance, which is frequently encountered, refers strictly to the magnetic resonance of permanent magnetic dipoles of any type, including nuclear magnetic resonance. On the other hand, the termelectron resonance includes cyclotron resonance (diamagnetic resonance).In a short article of this nature, it is clearly impossible to discuss, in detail, all aspects of such a wide field. Rather, the intention is to discuss the basic principles of the electron paramagnetic resonance technique together with some results in certain fields which illustrate its range, applications, and potentialities.     

Design,fabrication, and characterization of a solenoid system to generate magnetic field for an ECR proton source

Solenoid coils with iron jacket (electromagnets) have been designed and developed for generation and confinement of the plasma produced by an electron cyclotron resonance source operating at 2450MHz frequency. The magnetic field configurations designed using the solenoid coils are off-resonance, mirror, and flat, satisfying electron cyclotron resonance condition along the axis of the plasma chamber. 2D Poisson software was used for designing. Details of design, fabrication, and magnetic field mapping of the solenoid coils are presented in this paper.     

Observation of a Large Spin–Orbit Interaction in Photoexcited In x Ga1−x As/In y Al1−y As Heterostructures

Far-infrared magneto-optical absorption measurements of photoexcited InGaAs/InAlAs heterostructures are carried out. The resonance peak positions of cyclotron resonance due to spin-up and -down electrons can be determined from modulated absorption signals quantitatively. The photopulse excitation by band gap light changes the resonance positions. The amplitude of the spin splitting is found to depend on the excitation intensity and delay time. The change in the spin splitting energy is dominated by the modulation of confinement potential by photoexcitation.     

Observation of a Large Spin–Orbit Interaction in Photoexcited InxGa1?xAs/InyAl1?yAs Heterostructures

Far-infrared magneto-optical absorption measurements of photoexcited InGaAs/InAlAs heterostructures are carried out. The resonance peak positions of cyclotron resonance due to spin-up and -down electrons can be determined from modulated absorption signals quantitatively. The photopulse excitation by band gap light changes the resonance positions. The amplitude of the spin splitting is found to depend on the excitation intensity and delay time. The change in the spin splitting energy is dominated by the modulation of confinement potential by photoexcitation.     

Ion and neutral temperatures in an electron cyclotron resonance plasma

Transverse ion and neutral temperatures at the electron cyclotron resonance position were measured in an electron cyclotron resonance (ECR) plasma using a high-resolution optical emission spectroscopy of Doppler profiles of Ar and Ar⁺ transition. The transverse ion temperature increase from approximately 0.4 to 1.0 eV as the operating gas pressure is lowered from 1.0 to 0.1 mTorr. On the other hand, the transverse neutral temperature is much lower than the transverse ion temperature. By means of Langmuir probe measurement, large-amplitude potential fluctuation was observed at the ECR position under the low gas pressure. These observations suggest that the large-amplitude potential fluctuation directly affects the transverse ion temperature.     

Gallium-assisted growth of silicon nanowires by electron cyclotron resonance plasmas

The use of gallium droplets for growing Si nanowires (SiNWs) by electron cyclotron resonance plasmas is investigated. First, the relationship between evaporation time and resultant size of the gallium droplets is studied. Through the use of spectroscopic ellipsometry, the dependence of the surface plasmon resonance (SPR) energy on the droplet size is determined. From these gallium droplets, SiNWs were grown at 300 and 550?°C in electron cyclotron resonance plasmas containing SiH(4), Ar, and H(2). Scanning electron microscopy results show that tapered NWs are obtained for a wide range of growth conditions. Besides, it is found that H(2) plays an important role in the parasitic axial growth of the SiNWs. Namely, H(2) inhibits the radial growth and contributes dramatically to increasing the SiNW defects.     

Fourier-transform design and electron cyclotron resonance plasma-enhanced deposition of lossy graded-index optical coatings

A Fourier-transform synthesis technique is applied to the design of inhomogeneous refractive-index optical thin films with dispersion of refractive index and absorption taken into account. Using measured properties of SiO(x) N(y), we have designed a broadband reflector and two three-line filters with high reflectance. One of the three-line filters was manufactured by electron cyclotron resonance plasma-enhanced chemical vapor deposition from a mixture of SiH(4), N(2), O(2), and Ar. Good agreement between design and measured performance proves the feasibility of applying the Fourier-transform technique to the design of reflection filters even in the case of highly dispersive, absorbing material, if its optical properties are well characterized.     

电子回旋共振等离子体用于聚四氟乙烯材料表面改性

在电子回旋共振 (ECR)等离子体装置中 ,使用Ar气 ,N2 气 ,H2 气和普通空气放电 ,对聚四氟乙烯 (PTFE)材料进行表面处理以提高其表面粘结性能。详细研究了在不同的放电气压 ,微波功率 ,处理时间 ,气体种类的情况下 ,样品表面的接触角的变化。同时也讨论了样品导电性能和外观等的变化。使用红外吸收谱对样品结构处理前后的变化进行了测量 ,对等离子体处理的机理进行了初步的讨论。使用Langmuir探针测量了Ar气和N2 气等离子体中的离子密度 ,用能量分析器测量了离子的能量。发现在对样品的处理中 ,ECR等离子体的离子密度是影响表面性能的主要因素 ,离子能量的作用不明显     

基片温度对微晶硅薄膜微观结构和光学性能的影响

以Ar＋SiH_4作为反应气体,采用电子回旋共振等离子体增强化学气相沉积（ECR-PECVD）方法制备微晶硅薄膜,研究了基片温度对薄膜微观结构、吸收系数、光学禁带宽度的影响。结果表明,随着基片温度的升高,薄膜的微观组织逐渐由非晶转化为微晶,薄膜的粗糙度单调增大,而H含量则单调减小。薄膜的光学吸收系数随基片温度的升高而增...     

Local enhanced evaporation of carbon pellets in a Wendelstein 7-AS stellarator

Technical Physics Letters - Experiments with second-harmonic electron cyclotron resonance plasma heating performed on a Wendelstein 7-AS stellarator revealed a new regime of the carbon pellet...     

低温技术在受控核聚变实验中的应用

在中国环流器一号（ＨＬ－１）等离子体物理实验中，增加了弹丸注入和电子回旋共振加热系统。对低温技术在其中的应用情况，液氦输送系统，输液方法及氦气回收系统做了介绍。在一次等离子体物理实验中，总共使用液氦２７３３Ｌ。在弹丸注入系统中，使装置的等离子体密度提高了１～２倍。在装置上成功地实现了电子回旋共振加热，使等离子体电子温度增加３０％以上。     

Emission spectroscopy of a dipolar plasma source in hydrogen under low pressures

Low-temperature hydrogen plasma has been investigated under the conditions of electron cyclotron resonance by emission spectroscopy. The molecular distribution functions over the low rotational and vibrational levels of the hydrogen molecule in the d³Π_u^- triplet state have been measured. The translational, rotational, and vibrational temperatures of the ground and excited triplet states of the hydrogen molecule are determined. The obtained translational and vibrational temperatures indicate that low-temperature hydrogen plasma under the conditions of electron cyclotron resonance is a more efficient source of vibrationally excited hydrogen molecules in comparison with the other gas discharges.     

The effects of the operational parameters of the reactor on ECR plasma characteristics

A two-dimensional axis-symmetric model is adopted to investigate the characteristics of an electron cyclotron resonance plasma. The mass conservation equations of electrons, positive ions, and metastable atoms, the electron energy equation, and the Poisson equation are used in this multi-component system. The magnetic field generated by coils was computed numerically. The distributions of temperature and density of electrons are calculated by the finite difference method. The results of the numerical simulation for argon plasma shows that, in the phase of a long-time discharge, the electron temperature in the resonance chamber is higher than that in the reactor chamber, and electron density in the resonance chamber is lower than that in the reactor chamber. In addition, the effects of pressure on the two distributions are illustrated and discussed.     

ECR等离子体中电子能量分析器实验曲线的修正

对电子回旋共振等离子体中使用的电子能量分析器实验曲线偏离理想情况的几种现象进行了讨论 ,并提出了相应的修正和拟合的方法     

气相沉积硅薄膜微结构及悬挂键缺陷研究

在单晶Si(100)基体上利用电子回旋共振等离子体增强化学气相沉积法制备硅薄膜,并采用X射线衍射谱(XRD)、透射电镜(TEM)、Raman光谱、电子自旋共振(ESR)波谱等实验方法研究了不同Ar流量下硅薄膜微结构及悬挂键密度的变化。XRD及TEM实验结果得出,制备的硅薄膜的晶粒尺寸为12~16 nm,属纳晶硅薄膜。薄膜结晶度随镀膜时Ar流量增大而增大,而悬挂键密度则先迅速减小而后缓慢增大。当Ar流量为70 ml/min(标准状态)时,薄膜的悬挂键密度达到最低值4.42×1016cm-3。得出最佳Ar流量值为70 ml/min。     

The effect of interference in the substrate on the electromagnetic wave polarization transformation under cyclotron resonance conditions in a two-dimensional electron system

The effect of interference in the substrate on the polarization transformation of an electromagnetic wave in the presence of cyclotron resonance in a two-dimensional (2D) electron system is studied theoretically. It is predicted that the interference can dramatically enhance the transformation if the 2D electron system is situated on the rear face of a quarter-wave substrate plate. As a result, the reflected wave exhibits a virtually complete polarization transformation.