摘要:

The determination of the first‐order anisotropy field strength using the torsion pendulum method is described. Since the applied field need not necessarily be in the range of the anisotropy field, this method is particularly useful for characterizing modern permanent magnet materials which have a very high uniaxial anisotropy. The method requires oriented samples. Measurements were made on polycrystalline samples of NdFeB, SmCo, and barium ferrite. The method is described and error sources are discussed. It is pointed out that the torsion pendulum method is closely related to reversible transverse susceptibility measurements. It is shown both experimentally and theoretically, that using susceptibility measurements similar results can be obtained. The susceptibility method is, however, not applicable to conducting materials at present.

ISSN:0021-8979    

DOI:10.1063/1.345408

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report on the microwave properties of single‐crystal YIG/gadolinium gallium garnet/YIG grown in (110) layers, where YIG is yttrium iron garnet. The YIG layers were sufficiently thin so that single domain ferromagnetic resonance (FMR) was observed. FMR fields were measured as a function of field direction and magnitude and frequency. Bulk magnetic parameters deduced from FMR and vibrating‐sample magnetometer measurements agree with published values. In addition, FMR measurements at low fields show typical ‘‘butterfly’’ variations of the FMR fields with a frequency forH, the magnetic field, parallel to either the ⟨100⟩ or ⟨110⟩ axis. However, a new butterfly pattern was also observed for the magnetic field parallel to the ⟨111⟩ axis. This result is intrinsic to layered structures and not to single layer excitations. We attribute this new result to nonuniform distribution of strain in the two YIG layers, and as a consequence, we predict that magnetostatic fringe fields from edges are sufficient to induce spin‐flop magnetic configurations in single‐crystal YIG double layers.

ISSN:0021-8979    

DOI:10.1063/1.345383

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Oblate spheroidal particles of silver have been fabricated on graphite substrates with an additional silicon dioxide separation of the particle film from the substrate. The particles exhibit well‐resolved resonances in absorption spectra. These resonances are affected by the variation of the thickness of the SiO2separation. Calculations based upon a nonretarded, dielectric interaction for this configuration are found to be in agreement with experimental observations.

ISSN:0021-8979    

DOI:10.1063/1.345384

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The current‐voltage (I‐V) characteristics, dc conductivity, and infrared spectra of cuprous chloride (CuCl) thin films of different thicknesses have been experimentally investigated. The absorption peak energy in the infrared spectra and the activation energy obtained from resistivity measurements were found to be the same. This may be attributed to the existence of an indirect gapE&Ggr;X=0.41 eV. It was also observed that as the thickness of the samples decreased the absorption peaks shifted toward higher energies. This is thought to be due to the creation of strain within the lattice when the samples are prepared by molecular‐beam epitaxy and has been explained on the basis of quantum size effects.

ISSN:0021-8979    

DOI:10.1063/1.345385

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The nonparabolicity of the Si conduction band is investigated from the analysis of the optical response of heavily doped samples in the range 1019– 6×1021cm−3at 300 K. The data enable us to determine an optical effective mass which is found to exhibit a systematic increase for doping levels above 1020cm−3. The fitting of experimental results gives a nonparabolicity parameter &agr;=0.27 eV−1, which compares well with less direct estimates provided by the analysis of transport coefficients. The effect of the impurity potential, while providing a significant band tailing of the density of states, is found to have negligible influence on the value of the optical effective mass at the given impurity concentration.

ISSN:0021-8979    

DOI:10.1063/1.345386

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effects of chemical etching and aging under atmospheric conditions have been investigated in In doped, bulk CdTe using photoluminescence (PL) spectroscopy. The etchants studied included Br2/CH3OH, KOH/CH3OH, Na2S2O4/NaOH, and K2Cr2O7/HNO3. The results indicate a large enhancement of the 1.5896‐eV excitonic feature due to chemical treatment and aging. The 1.5896‐eV peak was previously shown to originate from a native defect involving a Cd vacancy. On this basis, we interpret the primary perturbation to be a small loss of Cd within the sampling region. Previous studies have reported substantial loss of Cd in the near‐surface region, within ∼25 A of the surface, as a result of etching in Br2/CH3OH. In contrast, a much smaller loss over a possibly larger depth is observed here. The Cd loss is, most likely, substantial nearest to the surface and extends deeper in but with less severity. The implications of these results on interpreting PL spectra, device processing, and long term stability are considered.

ISSN:0021-8979    

DOI:10.1063/1.346091

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Infrared absorption, electron paramagnetic resonance (EPR) spectra, and the electrical resistivity of semi‐insulating liquid encapsulated Czochralski GaP crystals irradiated by fast neutrons with a dose of 7.6×1018n cm−2have been studied. The electrical resistivity decreases with irradiation from 106&OHgr; cm to 1.5 k&OHgr; cm. The temperature dependence of resistivity at low temperature is fitted to exp(b/T1/4). The strong continuous optical absorption extends to 0.32 eV and its tail spreads until 0.12 eV. The EPR spectrum exhibits a broad singlet at 77 K and a doublet with five line structures at room temperature, which is attributed to antisite defects PGa. The strong infrared absorption begins to be annealed at 150 °C, and the EPR broad singlet decreases with anneals in the same temperature range. The strong infrared absorption is assumed to arise from interstitial phosphorus clusters. A discussion is given concerning the species responsible for the EPR singlet.

ISSN:0021-8979    

DOI:10.1063/1.345387

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Absolute rates for the intrinsic reaction between Cl atoms and surfaces of P‐doped polycrystalline silicon, P‐doped Si(100) and As, Sb‐doped Si(111) substrates were measured for the first time as a function of dopant concentration (Ne) and substrate temperature in a downstream reaction system. This study clearly shows that when there is no ion bombardment, increasingNeincreases the Si‐Cl reaction rate even when silicon is lightly doped (∼1015cm−3), in contrast to in‐discharge studies. Moreover, results showed that crystal orientation influences the Cl‐Si reaction more thanNe, forNe<1020cm−3. The data are fitted to a modified Arrhenius expression,R=&ngr;N&ggr;enClT1/2e−E/kT, withRthe etch rate andnClthe gas phase Cl concentration. The calculated values of the activation energyEare 4.1–4.7 kcal/mole for all doping levels and crystallographic orientations. Therefore, the doping effect is manifested solely in the preexponential (&ngr;N&ggr;e) of the Arrhenius expression, and the data qualitatively agree with a charge‐transfer mechanism which facilitates chemisorption of chlorine.

ISSN:0021-8979    

DOI:10.1063/1.345388

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Ion‐beam mixing of tin on iron provides corrosion protection against high‐temperature oxidation. Previous studies have been inconclusive as to the exact composition and distribution of alloys produced at the Fe/Sn interface. This study provides a detailed diagram of Fe‐Sn specimens after ion‐beam mixing with Ar+at 40 keV and a dose of 5×1016ions/cm2. The interface was isotopically labeled with 7.5 nm of57Fe and119Sn so that dual perspective conversion electron Mo¨ssbauer spectroscopy could be performed. Analyses in this manner allowed comparison of119Sn conversion electron Mo¨ssbauer spectroscopy (CEMS) and57Fe CEMS spectra to accurately assign spectral components which could not be conclusively assigned using a single CEMS perspective. Information from Rutherford backscattering spectrometry confirmed the layered nature of specimens prior to implantation and was used for depth determination of the mixed region after implantation. X‐ray photoelectron spectroscopy, secondary ion mass spectrometry, and scanning electron microscopy also provided information after implantation. Data indicate the formation of a uniform amorphous surface during implantation resulting in a heterogeneous mixture of components consisting mainly of dilute tin in iron (approximately 8‐at. % Sn) and FeSnx(x≊1). About 80% of the 37.5‐nm tin overlayer was removed by sputtering. The components identified are somewhat more iron rich than previous assignments and illustrate the difference in surface structures resulting from various implantation parameters.

ISSN:0021-8979    

DOI:10.1063/1.345389

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report on a tungsten‐oxide‐based, nonvolatile, electrically reprogrammable, variable resistance device as an analog synaptic memory connection for electronic neural networks. A voltage controlled, reversible injection of H+ions in electrochromic thin films of WO3is utilized to modulate its resistance. A hygroscopic thin film of Cr2O3is the source of H+ions. The resistance of the device can be tailored and stabilized over a wide dynamic range (∼four orders of magnitude), and the programming speed is modulated by the control voltage. The suitability of such a device in terms of its response speed, reversibility, stability, and cyclability for its use in electronic neural networks is discussed.

ISSN:0021-8979    

DOI:10.1063/1.345390

出版商:AIP    

年代:1990

数据来源: AIP