摘要:

Using a rigorous lower bound to the magnetostatic self‐energy, it is proved that no buckling can take place in a ferromagnetic prolate spheroid, whose aspect ratio is less than 4.6:1. The only possible reversal modes for this aspect ratio are the coherent rotation for small radii, and the curling for larger ones. Even for more elongated spheroids, a plausible argument suggests that the buckling mode is rather unlikely, except for the limit of aninfinitecircular cylinder.

ISSN:0021-8979    

DOI:10.1063/1.337354

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report detailed optical absorption spectra for Mn2+in CaF2. The spectra from unirradiated samples, reported here for the first time, enable the 495‐nm luminescence emission to be clearly assigned to a transition from the first excited4T1g(4G) level to the6A1g(6S) ground state. On the basis of the absorption curves energy level assignments are made for all of the4G,4D,4P, and4Flevels. Racah parameters are evaluated and the reduction of these from their free‐ion values, due to covalency effects, is estimated. A value ofDq=420 cm−1is calculated and an Orgel diagram for this system is constructed. Finally, oscillator strengths for each of the transitions are estimated from the absorption spectra. The optical absorption spectra from gamma irradiated samples show a complex array of overlapping bands, most of which can be shown to be related to the presence of Mn. The thermal annealing of the bands is associated with the production of thermoluminescence at an emission wavelength of 495 nm. Although no definite models can be offered for the defects involved in these processes, they are believed to be complexes of Mn and radiation‐induced defects (e.g., Mn/F centers).

ISSN:0021-8979    

DOI:10.1063/1.337355

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have examined the properties of (InGa)As/GaAs strained‐layer superlattices (SLSs) that have been disordered by implantation of 5×1015/cm2, 250 keV64Zn+followed by controlled atmosphere annealing at 680 °C for 30 min. Ion channeling techniques indicate that the Zn‐disordered regions of the SLS contain extensive crystalline damage after annealing. Simulations of the disordering process using an analytic ion range code predict that the electrical junction resulting from the implantation process is located outside the disordered region of the SLS in both the vertical and the lateral directions. Junction electroluminescence intensity for given drive current densities from the Zn‐disordered SLS devices is comparable to that from reference Be‐implantation‐doped (SLS retained) devices and greatly exceeds that from heavily dislocated grown‐junction mesa diodes in the homogeneous alloy of the average SLS composition; this result is consistent with the results of the simulations. This study demonstrates that implantation disordering can be as useful for strained‐layer systems as for less severely mismatched heterojunction systems.

ISSN:0021-8979    

DOI:10.1063/1.337356

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report electrolyte electroreflectance studies of the ternary semimagnetic semiconductor Hg1−xMnxTe for compositions belowx=0.2. The dependence ofE1andE1+&Dgr;1transition energies on the composition was determined on the basis of the low field approximation. The present results are compared and discussed in relation to experimental data obtained previously and the theoretical predictions reported in the literature.

ISSN:0021-8979    

DOI:10.1063/1.337357

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A detailed study of the optical properties of amorphous silicon prepared by various methods is presented here. Comparisons of the various major optical parameters like the refractive index and the optical gap and related properties are then made for amorphous silicon films prepared by glow‐discharge, chemical vapor deposition, and sputtered films. Experimental observations of a linear variation of the static refractive index with the Urbach tail parameter for boron‐doped chemically vapor deposited films have been analyzed. Wherever relevant, spectroscopic and band‐structural models like those of Penn and Wemple and DiDomenico are employed to evaluate the optical parameters of the materials. We also examine briefly the optical properties of amorphous silicon dioxide. Extrapolation of conventional models are then made to derive the relevant optical parameters of SiO2.

ISSN:0021-8979    

DOI:10.1063/1.337358

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We show that amorphous alloy powders of Cu and Ti can be produced over a broad composition range by mechanical alloying of the elemental powders in a high‐energy ball mill. The amorphous powders are compared with liquid‐quenched amorphous alloys of the same compositions using the techniques of x‐ray diffraction and thermal analysis of crystallization. The two types of samples are found to have similar characteristics. Chemical analysis shows that only trace amounts of impurities are introduced in the alloys by the milling process.

ISSN:0021-8979    

DOI:10.1063/1.337359

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have studied the morphology and crystallographic angular discontinuities of subboundaries and defect trails in zone‐melting‐recrystallized Si films. These subboundaries and defect trails, which originate at the interior corners of the faceted solidification front, are classified into seven types. Evidence is presented that in‐plane stress due to temperature gradients plays a major role in causing such defects. Various schemes for entraining subboundaries and defect trails are described.

ISSN:0021-8979    

DOI:10.1063/1.337360

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Ti films were deposited onto high‐density polyethylene (HDPE) samples by electron‐beam evaporation. Prior to film deposition the samples wereinsitupretreated by Ar ion bombardment using a sputter ion gun. The adhesion of the films, determined as the pull strength required for film failure, was measured as a function of ion dose. HDPE substrates processed at two different temperatures were examined. The adhesion of the Ti films to HDPE samples processed at ≊150 °C increased with the ion dose to a steady‐state value corresponding to the cohesive strength of the HDPE substrate. The adhesion to the samples processed at ≊200 °C increased to a maximum and then decreased for further ion bombardment to a level of the same order as that for films deposited onto as‐prepared samples. The effects of the ion bombardment upon the HDPE surface chemistry were examined by means of x‐ray photoelectron spectroscopy (XPS). The ion bombardment resulted in dehydrogenation and cross linking of the surface region and for prolonged ion bombardment, a graphitelike surface was obtained. The film/substrate interface as well as the initial Ti film growth were examined by XPS analysis. A chemical interaction which resulted in Ti–C bonds was observed at the interface. The Ti film growth followed a pronounced three‐dimensional growth mode on as‐prepared surfaces whereas the ion bombardment resulted in a change toward a more two‐dimensional growth mode. The difference in adhesion behavior for the two types of HDPE substrates was found to be due to a difference in the amounts of low molecular weight products present within the substrates. The HDPE substrates processed at ≊200 °C contained larger amounts of low molecular weight products and also had a lower degree of crystallinity and a less closely packed structure compared to those substrates processed at ≊150 °C. This resulted in a segregation of low molecular weight products towards the surface of substrates processed at ∼200 °C. This segregation in turn is suggested to lead to a weak boundary layer, reducing the adhesion to as‐prepared samples and to substrates exposed to a high ion dose.

ISSN:0021-8979    

DOI:10.1063/1.337361

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The numerous bulk and surface structural changes observed inc‐Si following melting with 1‐&mgr;m pulses that range from 4 to 260 ps in duration and fluences from about 0.6 to 2.8 J cm−2are examined by Nomarski and transmission electron microscope techniques. For melting pulse widths 30 ps or longer, recrystallization from the melt was observed. By contrast, for the shorter pulses (∼7 ps), the steep temperature gradients that accompany the onset of two‐photon absorption associated with pulses of this width produce an undercooled melt. Under these conditions, the resolidification velocities are evidently too high to allow epitaxial regrowth from the crystalline substrate and, for the first time, regions of amorphous and large‐ and fine‐grain polycrystalline silicon are observed to form directly on a crystalline underlayer. In addition, alternate stripes of amorphous and crystalline material are produced by these short pulses. These are associated with localized melting, demonstrating that uniform surface melting is not always required before a spatial modulation of the absorbed surface energy can occur.

ISSN:0021-8979    

DOI:10.1063/1.337362

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The reaction of Cl2with a Si solid under Ar+ion bombardment is investigated theoretically by the classical trajectory method. The etching yield of Si is calculated and is in good agreement with recent experimental results. The main products of the reaction are atomic Si and Cl together with molecular SiCl and SiCl2. This is also consistent with experimental findings. We report calculations of product, energy, and angular distributions. The relevance of these calculations for the dry etching of semiconductors is discussed.

ISSN:0021-8979    

DOI:10.1063/1.337363

出版商:AIP    

年代:1986

数据来源: AIP