摘要:

Measurements by Langmuir probes have been performed in a capacitively coupled, parallel‐ plate rf discharge of He and Ar with pressures ranging from 0.1 to 2 Torr and discharge power from 10 to 50 W at 27 MHz. The first part of this paper is devoted to a discussion of the preparation of the electrostatic probe technique, for which a rf discharge is well known to be a very hostile environment, and of its intrinsic limitations, in order to assess the reliability of the measurements. Results showing a marked non‐Maxwellian character of the electron‐energy distribution function are then presented and discussed in the light of the most recent theories about the sustainment of this kind of gas discharge.

ISSN:0021-8979    

DOI:10.1063/1.348935

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A two‐dimensional fully electromagnetic particle‐in‐cell code is used to simulate the interaction of a relativistic electron beam injected into a finite‐size background neutral plasma. The simulations show that the background electrons are pushed away from the beam path, forming a neutralizing ion channel. Soon after the beam head leaves the plasma, a virtual cathode forms which travels away with the beam. However, at later times a second, quasi‐stationary, virtual cathode forms. Its position and strength depends critically on the parameters of the system which critically determines the efficiency of the ion acceleration process. The background ions trapped in the electrostatic well of the virtual cathode are accelerated and at later times, the ions as well as the virtual cathode drift away from the plasma region. The surfing of the ions in the electrostatic well produces an ion population with energies several times the initial electron beam energy. It is found that optimum ion acceleration occurs when the beam‐to‐plasma density ratio is near unity. When the plasma is dense, the beam is a weak perturbation and accelerates few ions, while when the plasma is tenuous, the beam is not effectively neutralized, and a virtual cathode occurs right at the injection plane. The simulations also show that, at the virtual cathode position, the electron beam is pinched producing a self‐focusing phenomena.

ISSN:0021-8979    

DOI:10.1063/1.347748

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A two‐dimensional fluid model is developed to study the equilibrium flow of electrons in the vacuum gap between the cathode and the plasma of a plasma opening switch. The dynamics of electron flow in the vacuum gap region is illustrated by the distributions of the magnetic field, the electrostatic potential, and the electron density. The dependencies of the switch current and its interruption in the vacuum gap on the dimensions of the vacuum gap, the load impedance, and the electrostatic potential across the gap are investigated. The two‐dimensional aspect of the electron flow in the vacuum gap and its effects on the performance of a plasma opening switch are emphasized.

ISSN:0021-8979    

DOI:10.1063/1.347749

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A magnetized low‐pressure rf plasma used for thin‐film preparation has been observed with probe measurements. The sheath structure near the rf electrode was also obtained by measuring the potential profile in the sheath with an emissive probe. The results revealed that the magnetic field increases the electron density but has no effect on the electron temperature. Further the magnetic field increases the magnitude of the self‐bias potential of a rf electrode, and it decreases the effective sheath thickness. The application of a magnetic field to the conventional rf processing plasma is confirmed to be useful for control of a low‐pressure rf plasma.

ISSN:0021-8979    

DOI:10.1063/1.347735

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

ion‐production mechanism in an indirectly heated Penning source has been studied at NIRS. Taking the number of primary electron passages between two cathodes into account, we calculated the effective electron current density,Ji; it is the order of kA/cm2for Ar, where the index ‘‘i’’ is the charge state. In a pulsed arc condition of 2.6 A and 1300 V with a neutral atom density of 4×1013/cm3(cw), the calculated ionization times for Ar5+→Ar6+and Ar6+→Ar7+are 18 and 28 &mgr;s if their production process is step‐by‐step. These values agree well with the experimental value of 20 &mgr;s.Jiis proportional to the arc voltage and inversely proportional to the neutral‐atom densityN. The yield of multiply charged ions is in proportion to 1/Ni−2. This expression agrees well with the experimental results, which suggest that multiply charged ions are produced from Ar2+through step‐by‐step ionization by primary electrons.

ISSN:0021-8979    

DOI:10.1063/1.347736

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High‐energy implantation involves ion velocities such that ions are partially stripped of their electronic charge when moving inside the solid target. Most ion range distribution calculations so far have been using mean charge states as a function of the ion velocity, in order to determine the ion electronic stopping. However, it is known that fluctuations in the ion charge state lead to an increased energy‐loss straggling of the ion beam. In this work the effect of charge‐state fluctuations on ion range distribution calculations is studied. We show that the ion equilibrium charge‐state distributions can be used to account for charge‐state fluctuations inside a Monte‐Carlo formalism, and that this effect can be important in order to understand implanted ion range distributions in the MeV energy range.

ISSN:0021-8979    

DOI:10.1063/1.347737

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Single‐energy Fe implantation at energies in the range 50 keV–2 MeV to achieve a peak Fe concentration of 1–2×1018cm−3is performed into undoped (n‐type) InGaAs layers grown on InP:Fe. The first four statistical moments of the Fe profiles measured by secondary‐ion mass spectrometry are determined. The Pearson IV distribution calculated from these moments matches the implant‐profile closely. Samples implanted with Fe to doses in the range 5x1012–2×1015cm−2at 380 keV are analyzed by Rutherford backscattering measurements to study ion‐induced damage. For 380‐keV implants, amorphization begins at a dose of ≊3×1013cm−2.

ISSN:0021-8979    

DOI:10.1063/1.347738

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of thermal annealing and irradiation in an intense white synchrotron x‐ray beam on the x‐ray reflectance of tungsten/carbon and tungsten/silicon multilayers is reported. Thermal annealing at 400 °C for two hours produces larger effects than irradiation of cooled multilayers in the white beam of a 20‐pole hard x‐ray wiggler with 0.94‐T peak field on the storage ring DORIS operating at 5.42 GeV and electron currents of 20–36 mA for 40 h. Thermal annealing caused the period and first order reflectance of a W/Si sample to decrease, in contrast to a W/C sample whose period and reflectance increased on annealing. Of five actively cooled samples irradiated, one W/C sample showed significant change in reflectance. Preannealing of this multilayer stabilized it to radiation‐induced changes. Irradiation effects also depend on multilayer period and constituent materials. Implications of these results for models describing multilayer reflectance and for multilayer applications in the new generation of synchrotron radiation sources are discussed.   

ISSN:0021-8979    

DOI:10.1063/1.347739

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Silicon‐on‐insulator structures obtained by single‐step implantation of oxygen followed by high temperature annealing were studied byK‐band electron spin resonance (ESR) at 4.3–31 K. The spectrum has a strong line atg=2.0059±0.0001 with a spin density of 7.1×1013cm−2. Various features indicate that it is very similar to that characteristic of dangling Si‐bonds (DBs) ina‐Si but different from the ESR signal of thePbcenter associated with single‐crystal‐Si/SiO2interfaces. Irradiation by &ggr; rays to a dose of 1 Mrad(Si) resulted in a 2.5‐fold increase in DB density and in the appearance of a new, anisotropic signal of spin density 1.1×1012cm−2. The latter signal is similar to that originating from a shallow donor in Si, of axial symmetry and preferentially aligned along [001]. It is tentatively assigned to an oxygen‐related double donor in Si regions close to the Si/SiO2interface and/or in the buried oxide. These donors are not generated by irradiation; rather, their ionization state is altered through band bending tuning resulting from irradiation‐induced charges in the oxide.

ISSN:0021-8979    

DOI:10.1063/1.348934

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Crystals with varied composition were pulled by the As‐partial‐pressure controlled liquid encapsulated Czochralski method. The dislocation density was found to be as low as 2×103cm−2at the cores of the crystals. Lattice spacing (d) was measured with a precision of &Dgr;d/d∼ 5.9 × 10−6using synchrotron radiation. For a variation of 7×10−5in the As‐atom fraction in the crystals, the lattice spacing varied by less than 1×10−5A˚.

ISSN:0021-8979    

DOI:10.1063/1.347740

出版商:AIP    

年代:1991

数据来源: AIP