摘要:

We review the physical properties of diluted magnetic semiconductors (DMS) of the type AII1−xMnxBVI(e.g., Cd1−xMnxSe, Hg1−xMnxTe). Crystallographic properties are discussed first, with emphasis on thecommonstructural features which these materials have as a result of tetrahedral bonding. We then describe the band structure of the AII1−xMnxBVIalloys in the absence of an external magnetic field, stressing the close relationship of thespelectron bands in these materials to the band structure of the nonmagnetic AIIBVI‘‘parent’’ semiconductors. In addition, the characteristics of the narrow (nearly localized) band arising from the half‐filled Mn 3d5shells are described, along with their profound effect on the optical properties of DMS. We then describe our present understanding of themagneticproperties of the AII1−xMnxBVIalloys. In particular, we discuss the mechanism of the Mn++‐Mn++exchange, which underlies the magnetism of these materials; we present an analytic formulation for the magnetic susceptibility of DMS in the paramagnetic range; we describe a somewhat empirical picture of the spin‐glasslike freezing in the AII1−xMnxBVIalloys, and its relationship to the short range antiferromagnetic order revealed by neutron scattering; and we point out some not yet fully understood questions concerning spin dynamics inDMS revealed by electron paramagnetic resonance. We then discuss thesp‐dexchange interaction between thespband electrons of the AII1−xMnxBVIalloy and the 3d5electrons associated with the Mn atoms. Here we present a general formulation of the exchange problem, followed by the most representative examples of its physical consequences, such as the giant Faraday rotation, the magnetic‐field‐induced metal‐to‐insulator transition in DMS, and the properties of the bound magnetic polaron. Next, we give considerable attention to the extremely exciting physics of quantum wells and superlattices involving DMS. We begin by describing the properties of the two‐dimensional gas existing at a DMS interface. We then briefly describe the current status of the AII1−xMnxBVIlayers and superlattices (systems already successfully grown; methods of preparation; and basic nonmagnetic properties of the layered structures). We then describe new features observed in the magnetic behavior of the quasi‐two‐dimensional ultrathin DMS layers; and we discuss the exciting possibilities which thesp‐dexchange interaction offers in the quantum‐well situation. Finally, we list a number of topics which involve DMS but which have not been explicitly covered in this review such as elastic properties of DMS, DMS‐based devices, and the emerging work on diluted magnetic semiconductors other than the AII1−xMnxBVIalloys—and we provide relevant literature references to these omitted topics.

ISSN:0021-8979    

DOI:10.1063/1.341700

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Sodium atoms (108–1011cm−3) effused from an oven were stepwise excited from their ground state to a Rydberg statensornd(20≤n≤26) by two pulsed dye lasers (∼5–10 ns, ∼100 &mgr;J, ∼1.6‐mm‐diam spot). The laser energy density necessary to saturate the excitation processes from the ground state to the Rydberg state is ∼ several mJ/cm2. About 50 ns after the laser irradiation, a pulsed electric field (0.5–5.5 kV/cm) was applied to the Rydberg atoms to ionize them and accelerate the resulting ions. Thus, a pulsed sodium ion beam of purity >99.99% was obtained with a maximum total electric charge of ∼5 pC and a pulse width of ∼120 ns full width at half maximum. The total electric charge of the ion beam is estimated including the effect of space‐charge field of the beam ions, and is in good agreement with the experimental values.

ISSN:0021-8979    

DOI:10.1063/1.341809

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The electron‐attachment rate constants of HCl diluted in Ar and N2were measured as a function of the reduced electric fieldE/N. These data were converted to the electron‐attachment cross section of HCl using the electron‐energy distribution functions of pure Ar and N2. The dependence of the electron‐attachment rate constant and the mean electron energy on the fraction of HCl in each buffer gas was investigated. A comparison of the current result with both available experimental data and theoretical calculations is made.

ISSN:0021-8979    

DOI:10.1063/1.341810

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Theoretical expressions for the internal and external electromagnetic fields for an arbitrary electromagnetic beam incident upon a homogeneous spherical particle are derived, and numerical calculations based upon this theoretical development are presented. In particular, spatial distributions of the internal and near‐surface electric field magnitude (source function) for a focused fundamental (TEM00mode) Gaussian beam of 1.06 &mgr;m wavelength and 4 &mgr;m beam waist diameter incident upon a 5‐&mgr;m‐diam water droplet in air are presented as a function of the location of the beam focal point relative to the sphere center. The calculations indicate that the internal and near‐surface electric field magnitude distribution can be strongly dependent upon relative focal point positioning and may differ significantly from the corresponding electric field magnitude distribution expected from plane‐wave irradiation.

ISSN:0021-8979    

DOI:10.1063/1.341811

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The paraxial equation for rotationally symmetric magnetic lenses is integrated numerically by using the Numerov method. The normalized third‐order aperture and second‐order chromatic aberration coefficients (C3NandCcN) are calculated. A Fourier representation of the lens field is used, and a search for minimumC3Nis carried out by varying the Fourier coefficients. Comparisons with comparable quadrupole doublets, and calculations ofC3NandCcNfor actual coil systems are presented. The main conclusion is that magnetic round lenses are about a factor of 2 better than comparable magnetic quadrupole doublets as far as the third‐order aperture aberration is concerned, but the chromatic aberrations in both systems are comparable.

ISSN:0021-8979    

DOI:10.1063/1.341783

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

In an electron microscope equipped with sextupole correctors the ultimate resolution is limited by the fifth‐order spherical aberration of the optical system used to form the electron probe. We have examined the possibilities of using octupoles in order to correct this fifth‐order spherical aberration. We find that for an electrostatic octupole, the fifth‐order aberration is symmetric, while for a magnetic octupole the fifth‐order aberration is asymmetric but it is possible to reduce this asymmetry by properly arranging the initial conditions. Based on these results, we propose a system which could be used to correct fifth‐order aberration in a probe forming system equipped with a sextupole corrector.

ISSN:0021-8979    

DOI:10.1063/1.341784

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

It is shown that the wave equation &psgr;xx−&psgr;yy=0 for the field &psgr;(x,y) in the domainR(xy) can be transformed into a wave equation &PSgr;&xgr;&xgr;−&PSgr;&eegr;&eegr;=0 for the field &PSgr;(&xgr;,&eegr;) in the domainS(&xgr;&eegr;). The transformation is accomplished through a complex functionF(x,y)=&xgr;(x,y) +i&eegr;(x,y), which is not analytic. For the transformation to exist, the real transformation functions &xgr;=&xgr;(x,y) and &eegr;=&eegr;(x,y) have to satisfy wave equations in the domainR(xy) and the first‐order partial equations &xgr;x=±&eegr;yand &xgr;y=±&eegr;x[‘‘±’’ distinguishes transformations of the first (+) and second (−) kinds]. Thus, the hyperbolic transformation theory is different from the conformal mapping theory, where the real transformation functions satisfy the Laplace equation and the Cauchy–Riemann conditions. As applications, the linear Lorentz transformation and nonlinear mappings of time‐varying regions into fixed domains are discussed as solutions of the indicated partial differential equations. Furthermore, an initial‐boundary‐value problem for the electromagnetic wave equation with moving boundary condition is solved analytically (compression of microwaves in an imploding resonator cavity).

ISSN:0021-8979    

DOI:10.1063/1.341785

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The scattering of electromagnetic waves from a randomly perturbed periodic surface is formulated by the extended boundary condition (EBC) method and solved by the small perturbation method (SPM). The scattering from periodic surface is solved exactly and this solution is used in the SPM to solve for the surface currents and scattered fields up to the second order. The random perturbation is modeled as a Gaussian random process. The theoretical results are illustrated by calculating the bistatic and backscattering coefficients. It is shown that as the correlation length of the random roughness increases, the bistatic scattering pattern of the scattered fields show several beams associated with each Bragg diffraction direction of the periodic surface. When the correlation length becomes smaller, then the shape of the beams become broader. The results obtained using the EBC/SPM method is also compared with the results obtained using the Kirchhoff approximation. It is shown that the Kirchhoff approximation results show quite a good agreement with EBC/SPM method results for thehhandvvpolarized backscattering coefficients for small angles of incidence. However, the Kirchhoff approximation does not give depolarized returns in the backscattering direction, whereas the results obtained using the EBC/SPM method give significant depolarized returns when the incident direction is not perpendicular to the row direction of the periodic surface.

ISSN:0021-8979    

DOI:10.1063/1.341786

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have studied the structure and optical stability of Te–Cu thin film alloy candidates for write‐once optical recording. Films prepared by rf diode sputtering with 20–50 at. % Cu are amorphous, as‐sputtered. One of these, Te65Cu35, has a relatively high crystallization temperature (150 °C), as determined by x‐ray diffraction. Near the eutectic composition (∼29 at .% Cu), alloy films have stable optical properties after accelerated aging at 60 °C and 85% relative humidity. The mechanism for film stability near the eutectic was studied by x‐ray photoelectron spectroscopy and depth profiling using ion scattering spectroscopy. We found that a Cu‐enriched surface oxide, formed at ambient conditions, passivates the film and is responsible for its subsequent stability after accelerated aging. We also demonstrated that a 14 in. diam, multilayer optical disk with a Te65Cu35recording medium exhibits excellent linearity for 3 and 8 MHz pulses, good written pulse length stability, and high signal‐to‐noise ratio. Thus, a Te–Cu recording medium can effectively use run‐length‐limited codes, which allow very high data storage capacity and data transfer rates.

ISSN:0021-8979    

DOI:10.1063/1.341787

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The performance of Xe*2as a 172‐nm fluorescence or laser source when pumped by a low‐current, long‐pulse electron beam was determined. The fluorescence efficiency of Xe@B|2is near the theoretical limit of ∼50% at modest pressures over a range of pump rates up to 106W/cm. The laser efficiency is limited to values <1% by a very strong medium absorption that is probably due to Xe*2photoionization. Laser performance is further degraded by early pulse termination that appears related to mirror degradation. An improved kinetics and extraction code was developed to model the performance of the Xe@B|2system. A key component of the model is a more detailed treatment of the interactions between secondary electrons and excited atomic and molecular xenon states. Rates for these processes were derived as described herein. With this model, good absolute agreement was obtained between experiments and calculated parameters at pressures as low as 0.5 atm.

ISSN:0021-8979    

DOI:10.1063/1.342474

出版商:AIP    

年代:1988

数据来源: AIP