Electron Cyclotron Resonance Conditions Research Articles

Performance and analysis of an electron cyclotron resonance plasma cathode

A scalable electron cyclotron resonance (ECR) plasma source was investigated for plasma cathode applications. The rectangular source utilized permanent magnets to establish the ECR condition. The microwave applicator region was windowless, making the source applicable to sputtering environment applications. The source was characterized using primarily two diagnostics: (1) a near-field and far-field Langmuir probe and (2) a downstream electron extraction electrode. Source operation and plasma properties were characterized at low pressures ranging from 0.2to5mTorr and power levels up to 250W. Evidence of grad-B drift in the plane of the source was observed. Extracted currents agreed well with predictions.

Electron cyclotron resonance acceleration of electrons to relativistic energies by a microwave field in a mirror trap

Results are presented from experiments on the acceleration of electrons by a 2.45-GHz microwave field in an adiabatic mirror trap under electron cyclotron resonance conditions, the electric and wave vectors of the wave being orthogonal to the trap axis. At a microwave electric field of ≥10 V/cm and air pressures of 10−6–10−4 Torr (the experiments were also performed with helium and argon), a self-sustained discharge was initiated in which a fraction of plasma electrons were accelerated to energies of 0.3–0.5 MeV. After the onset of instability, the acceleration terminated; the plasma decayed; and the accelerated electrons escaped toward the chamber wall, causing the generation of X-ray emission. Estimates show that electrons can be accelerated to the above energies only in the regime of self-phased interaction with the microwave field, provided that the electrons with a relativistically increased mass penetrate into the region with a higher magnetic field. It is shown that the negative-mass instability also can contribute to electron acceleration. The dynamic friction of the fast electrons by neutral particles in the drift space between the resonance zones does not suppress electron acceleration, so the electrons pass into a runaway regime. Since the air molecules excited by relativistic runaway electrons radiate primarily in the red spectral region, this experiment can be considered as a model of high-altitude atmospheric discharges, known as “red sprites.”

RIE of GaSb with an ECR Source Using Methane/Hydrogen Chemistry in an Argon Plasma

Reactive ion etching (RIE) of samples was investigated under electron cyclotron resonance (ECR) conditions using gas mixtures. Different etching parameters [e.g., microwave and radio-frequency (rf) power levels, gas ratios, chamber pressure, etc.] were systematically varied to observe their effects on the etch characteristics. For microwave powers up to the etch rate was found to increase with increasing microwave power. Above the etch rate appears to saturate for lower rf power levels but at higher rf power the etch rate continues to increase linearly with microwave power over the range investigated. Gas ratios of of 4:16:7.6 and 8:12:25 were used with the latter ratio yielding higher etch rates. The etch rate decreased with increasing chamber pressure over the range of . Etching of the mask was observed and the corresponding etch rates were adjusted to account for this mask erosion. Excellent feature geometries were observed with vertical sidewalls and a smooth surface morphology.

Preparation of aligned Cu nanowires by room-temperature reduction of CuO nanowires inelectron cyclotron resonance hydrogen plasma

Aligned Cu nanowires were prepared by the reduction of aligned CuO nanowiresin electron cyclotron resonance (ECR) hydrogen plasma at room temperature.They are single-crystalline and maintain the original alignment of the CuOnanowires. In contrast, the reduction of CuO nanowires by thermal processing inH2 has failed to produce the expected Cu nanowires because of morphological changes and thecoalescence of newly formed Cu nanowires, leading to the formation of films consisting ofmicron-sized particles. The morphological changes and coalescence of Cu nanowires resultfrom their low melting temperature. The reduction mechanism under ECR conditions hasbeen discussed. The application of ECR plasma can effectively avoid the hightemperature demand for CuO reduction when using the thermal processing method.This template-directed method assisted by ECR plasma can be extended for thetransformation of other one-dimensional (1D) nanomaterials at low temperature and lowpressure.

Gasdynamic ECR source of multicharged ions based on a cusp magnetic trap

One of the modern trends in the development of electron cyclotron resonance (ECR) sources of multicharged ions is enhancement of the power and frequency of microwave pumping. Therefore, gyrotrons—powerful sources of radiation in the millimetre wavelength range—are now used for the creation and heating of plasma. These generators of microwave radiation are capable of producing and confining plasma of very high density (1013 cm−3 and higher), thus providing conditions for a substantial increase in the extracted ion beam current. Most ECR sources use for plasma confinement mirror magnetic traps with ‘min B’ configuration, which suppress MHD plasma instabilities. However, it is extremely difficult to construct such systems for pumping frequencies higher than 30 GHz because strong magnetic fields of complicated configuration are needed. All this makes the search for simpler axisymmetric MHD-stable systems for plasma confinement very topical.A cusp trap produced by two coils with opposite currents is the simplest MHD-stable magnetic trap. Magnetic lines at any point of plasma in such a trap have a curvature that suppresses MHD perturbation in the plasma. In the present work the possibility of creation of an effective ECR source of multicharged ions based on a cusp magnetic trap was investigated numerically and in experiments. The pioneer result is the realization of the quasi-gasdynamic regime of plasma confinement in the trap of the multicharged ion ECR source of multicharged ions with cusp configuration of the magnetic field. Experiments were made with a small cusp trap which was designed for plasma creation by 37.5 GHz gyrotron radiation under ECR conditions. The total current and ion charge state distribution in the extracted ion beam were studied. The results of experiments with the simplest kind of cusp trap have demonstrated good correspondence with theoretical calculations, and therefore the adequacy of the developed approach and the possibility to build more effective source on this basis. Two ways of possible evolution of ECR ion sources based on a cusp magnetic trap are proposed.

Photomagnetic effect in bilayer two-dimensional electron–hole systems

In tilted magnetic fields a bilayer electron–hole system is found to generate a photocurrent under terahertz radiation as the system is tuned to electron cyclotron resonance conditions. The photoinduced current amplitude oscillates with the magnetic field in correlation with Shubnikov–de Haas oscillations for electrons. The phenomenon is accounted for by a photomagnetic effect in electron–hole systems in the quantum Hall regime and has potentialities for terahertz detection and spectroscopy.

Effects of hydrogen on majority carrier transport and minority carrier lifetimes in long-wavelength infrared HgCdTe on Si

We present extended results on the use of a hydrogen plasma to passivate the effects of defects in long-wave ir HgCdTe/Si. Annealed and as-grown epilayers, in situ doped with indium, were exposed to a hydrogen plasma generated in an electron cyclotron resonance (ECR) reactor. Secondary ion mass spectrometry was used to measure the extent of hydrogen incorporation into the epilayers. Hall and photoconductive lifetime measurements were used to assess the efficacy of passivation. The passivation of defects responsible for the scattering and recombination of electrical carriers was observed for most ECR conditions over a range of dislocation densities.

Effects of hydrogen on majority carrier transport and minority carrier lifetimes in long wavelength infrared HgCdTe on Si

We present the results of using an electron cyclotron resonance (ECR) plasma to incorporate hydrogen into long wavelength infrared HgCdTe layers grown by molecular beam epitaxy. Both as-grown and annealed layers doped in situ with indium were hydrogenated. Secondary ion mass spectroscopy confirmed the incorporation of hydrogen. Hall and photoconductive lifetime measurements were used to assess the effects of the hydrogenation. Increases in the electron mobilities and minority carrier lifetimes were observed for almost all ECR conditions.

Effectiveness of electron-cyclotron and transmission resonance heating in inductively coupled plasmas

The electron-cyclotron and transmission resonances in magnetically enhanced low-pressure one-dimensional uniform inductively coupled plasmas are studied analytically within a simple model of two driven electrodes. The results of our approach are also applicable to the case of one grounded electrode. It is shown that, for a high discharge frequency, the plasma resistance is greatly enhanced at electron-cyclotron and transmission resonances, but normally does not exhibit a sharp peak at the electron-cyclotron resonance (ECR) condition. For a low discharge frequency, the ECR heating is not effective. Conditions of strong transmission resonances are identified. A transition from a bounded to semi-infinite plasma with overlapping of transmission resonances is also considered.

Generation of multiply charged refractory metals in an electron-cyclotron resonant discharge in a direct magnetic trap

The possibility of additional ionization of refractory metal ions in the vacuum arc plasma injected to a magnetic trap due to additional heating of electrons by microwave radiation under the conditions of electron-cyclotron resonance is demonstrated. High-power short-wave radiation of gyrotrons used in experiment makes it possible to work with a higher (on the order of 1013 cm−3) density of the plasma and to ensure the confinement parameter at a level of 3 × 108 cm−3 s at an electron temperature sufficient for multiple ionization.

Low-temperature Preparation of Crystallized Zirconia Films by ECR Plasma MOCVD

ABSTRACTIt is known that zirconia has excellent thermal and chemical stability, and oxide ion conduction. Therefore, YSZ is expected to be used as oxide ion conducting materials, optical mirror materials, catalytic materials and heat-resistant materials. Zirconia films have been fabricated by PVD (ex. sputtering and laser-ablation), chemical vapor deposition (CVD) and sol-gel methods. CVD is capable to prepare high quality zirconia films with excellent conformal coverage; however, deposition temperature of conventional CVD was usually high than PVD. On the other hand, an electron cyclotron resonance (ECR) plasma is high-activity plasma and high quality crystalline films can be obtained at low temperature by using ECR plasma. In the present study, zirconia thin films were prepared at low temperatures on quartz, polycarbonate and polyimide substrates by ECR plasma MOCVD.Zr-hexafluoroacetylacetonato solution was used as a precursor. The source, which was placed in a glass bubbler, was carried into a reactor by Ar gas. A microwave (2.45 GHz, 500 W) was introduced into the ion chamber through a rectangular wave guide. A magnetic field (875 Gauss) was applied to the ion chamber to satisfy the ECR condition. A mirror-type magnetic field (450 Gauss at the substrate stage) was applied in order to raise a plasma density, which results in an increase of the deposition rates of films. Substrate temperature (Ts) was from 30 to 700 C by water-cooling holder and infrared lamp heater. Microwave power was changed from 0 to 900 W. The deposition time was from 30 to 120 minutes.Cubic, monoclinic and tetragonal zirconia films were obtained over Ts=400 C, and cubic and monoclinic zirconia films were obtained below Ts= C. Cubic and monoclinic zirconia films were also obtained at no heating. The deposition rate increased from 10 to 20 nm/min with increasing Ts from no heating to 600 C. Crystallized zirconia films were obtained on polycarbonate and polyimide substrates at no heating. The ECR plasma was significantly effective to prepare crystallized zirconia films at low temperatures.

Lasing without inversion and electromagnetically induced transparency under electron cyclotron resonance conditions

Parametric effects of lasing without inversion and electromagnetically induced transparency in classical systems are considered. The characteristic features of the effect of lasing without inversion in ensembles of classical electrons are analyzed using an “inversionless” cyclotron maser as an example. A theory of the effect of electromagnetically induced transparency is developed for electron cyclotron waves in a high-temperature plasma. Possible applications of these two effects in plasma physics and microwave electronics are discussed.

ECR plasma etching of GaAs in CCl2F2/Ar/O2 discharge and IR studies of the etched surface

The etching of GaAs materials under electron cyclotron resonance conditions has been performed in an ECR etching system with rf biasing using the CCl2F2/Ar/O2 plasma chemistry. Etching experiments were carried out at a pressure between 0.015 and 0.020 mbar, rf power 0.39 W/cm2, and dc bias voltage 200 V. The surface morphology and etch depth were taken by scanning electron microscopy and Dektek Profilometry respectively. The use of ECR conditions with additional rf biasing provides the good etching of the surface and fast etch rates. Moreover, the surface of the GaAs material display smooth and stoichiometric surfaces at higher ECR powers. The surface damages on the GaAs samples after the plasma exposure have been studied using IR spectroscopy.

Plasma and electrical characteristics of inductive discharge in a magnetic field

The electron energy distribution function and the azimuthal rf electric field (magnitude and phase) have been measured in a cylindrical inductively coupled plasma (ICP) immersed in a weak magnetic field and driven at 29 MHz. The measurements were performed under conditions of controlled rf power delivered to the plasma electrons taking into account power loss in the induction coil. It has been found that considerable modification of plasma parameters at electron cyclotron resonance (ECR) conditions occurs only at relatively small discharge power and plasma density, when electron–electron collisions are negligible. It is shown that enhancement in the plasma density with application of magnetic field found in earlier experiments is mainly due to a rise in the power transfer efficiency caused by reduction in the ICP sustaining rf electric field. The rf field reduction is due to strong cyclotron damping at ECR conditions and due to the onset of propagation and absorption of the wave for which the phase velocities were found to be close to the electron thermal velocity. This wave regime occurs at magnetic fields higher than that at ECR but much smaller than that in typical helicon plasma sources.

X-Ray Source Based on Electron Cyclotron Resonance Discharge in a Magnetic Mirror Trap

A new concept of the x-ray source based on a low-pressure microwave discharge that is confined in a magnetic mirror trap and heated at electron cyclotron resonance conditions is described. It is demonstrated that the energetic electrons accelerated on the resonance hyperboloid of one sheet surface type, form a rotating ring, which is located in the middle cross section of the trap. When the ring strikes a metal target, an x-ray radiation is produced. A 100 keV radiation is obtained by using 2.45 GHz microwaves of 150 W.

Effect of ECR Plasma Treatment on Lithium Niobate Surface State*

The comparative scanning electron microscopy investigations of lithium niobate surface state before and after microwave plasma etching at the electron cyclotron resonance (ECR) conditions were carried out. The differences in the surface relief of +C and −C domains were explained by the effect of pyroelectric charges arising due to sample heating under etching. Subsurface layer was observed to charge after etching, domains of different polarity had charge of opposite sign. A number of structure defects in subsurface layers was found to decrease after ECR plasma treatment. This decrease can be associated with removing surface defect layer or disappearing of these defects due to their interaction with point defects created by plasma. *Paper originally presented at 10th European Meeting on Ferroelectricity, Cambridge, U.K., August 3–8, 2003.

Development of a hybrid PIG-ECR ion source

A combined ion source with 20 cm beam diameter, utilizing both a cold-cathode Philips or Penning ionization gauge (PIG) discharge and an electron cyclotron resonance (ECR) discharge, has been built and tested. The ion source has been designed to study what effects, if any, might be induced by superimposing microwave power at the ECR condition onto a cold-cathode PIG ion source at low pressures (≤10 −4 Torr). The first experiments with argon gas indicate that the ECR coupling at low pressures results in: (a) transformation of the PIG discharge mode with a dominant anode fall into the hybrid discharge mode with a dominant cathode fall; (b) stabilization of the PIG discharge; and (c) enhanced ion beam output due to increased ionization inside the ion source. The ion beam current is 150 mA (with a beam current density at its axis of 0.35 mA/cm 2), at an anode voltage of 750 V, a microwave power of 200 W and a gas pressure of 0.05 mTorr. The ion source design and the results of preliminary experiments are presented. A stable low-pressure operation mode of the ion source might be promising for broad ion beam production.

Sheet-shaped plasma production using microwave-plasma interaction with ECR region

New phenomena in producing sheet-shaped plasma under electron cyclotron resonance (ECR) condition have been found and investigated by experiment. Sheet-shaped Ar plasma with density of /spl sim/10/sup 18/ m/sup -3/ was successfully obtained at /spl sim/10/sup -3/ torr by using 2.45-GHz microwave with ECR condition. The plasma was generated uniformly and stably in the cross section of 15.5 cm width/spl times/2.0 cm thickness with the use of waveguide of the rectangular cross section under the quartz window in vacuum. The parameter region of stable sheet-shaped plasma production was made clear by experiments clarifying criteria in parameter map. It was found that the magnetic field strength corresponding to the position and the shape of ECR region was the most effective parameter affecting microwave propagation to control the shape of plasma. However, the uniformity of the sheet-shaped plasma width was poor over the distance of microwave wavelength /spl lambda/ under 1 kW of input power. Therefore, it was concluded that the microwave was absorbed quickly near ECR region and hardly propagates farther than /spl sim//spl lambda/ to the direction of perpendicular to the magnetic field. The double sheet-shaped plasma was produced at some region and two peaks were relatively shifted to the direction of E/spl times/B. Also, the condition of sheet-shaped plasma production was different for helium gas. By the electron density measurement and semi-one-dimensional analysis, the differences of ionization cross section and diffusion coefficient perpendicular to the magnetic fields were important factors for electron density and the shape of sheet plasma. The qualitative interpretation of sheet-shaped plasma production is discussed.

Observation of Barrier Recrystallization Process and Properties of Ramp-Edge Josephson Junctions with Interface-Modified Barrier

We have studied the recrystallization process and the microstructure of the interface-modified barrier, and the electrical properties of Josephson junctions with the barrier. Electron cyclotron resonance (ECR) ion bombardment was used for making an amorphous layer at the YBa2Cu3O7-δ (YBCO) film surfaces. Then, the samples were annealed to form an interface-modified barrier from the amorphous. A halo pattern showing the existence of an amorphous was changed to three types of patterns by changing the ECR and annealing conditions. The YBCO surface damaged at an ion acceleration voltage of 700 V showed clear recrystallization to YBCO. The surface damaged at lower voltages showed reflection high energy electron diffraction (RHEED) patterns different from that of YBCO. In these cases, regions with a cubic or pseudo-cubic structures were observed at the interface by transmission electron microscopy (TEM). Ramp-edge Josephson junctions with an interface-modified barrier have been fabricated. The junction properties strongly depend on the distance between the sample and the laser plume when upper layer YBCO is deposited. The junctions fabricated under optimum conditions exhibited resistively and capacitively shunted junction (RCSJ)-like I–V curves with a typical IcRn product at 4.2 K of 1.0–3.2 mV. We show that the recrystallization of an interface-modified barrier from an amorphous layer strongly depends on the kinetic energy from laser plume plasma as well as the thermal energy from substrate heating, and the Ic values of the junctions strongly depend on the actual bombardment energy of ions incident on the ramp surface. The difference of Ic may be explained in terms of the difference of the barrier microstructure which depends on the ion bombardment energy.

Electron cyclotron resonance in a weakly magnetized radio-frequency inductive discharge.

The evolution of the electron energy distribution function (EEDF) over a weak magnetic field range is investigated in magnetized radio-frequency (rf) inductive discharges under a collisionless regime where an anomalous skin effect and electron cyclotron resonance (ECR) can occur. A significant change in the low-energy range of the EEDF is found in the ECR condition during the evolution. The observed result reveals the low-energy electrons are efficiently heated by the rf ECR in the presence of the anomalous skin effect. The calculated result of the electron distribution based on kinetic theory is in good agreement with the experiment.