摘要:

The electrical transport properties of epitaxial Se‐Al0.1Ga0.9As grown by molecular beam epitaxy were studied. The carrier concentration was deduced from the Shubnikov–de Haas oscillations. At low temperature, persistent photoconductivity was not observed.

ISSN:0021-8979    

DOI:10.1063/1.349350

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The coercivity of anisotropic cast–hot‐pressed Pr19Fe74.5B5Cu1.5magnets is investigated. The microstructure features and virgin magnetization curve reveal a nucleation‐controlled coercivity mechanism. Regression analysis shows that the intrinsic coercivity varies inversely as the logarithm of the average grain size:iHc(kOe) = 21.7550 − 6.0517 ln d(&mgr;m), which is in good agreement with the nucleation statistical model. Investigation of Cu addition and Nd substitution shows that Cu mainly plays a role of suppressing grain growth during the final annealing. Higher coercivity is thus obtained with Cu addition. Nd19Fe74.5B5Cu1.5magnets exhibit a much lower coercivity due to their coarse‐grained cast structure.

ISSN:0021-8979    

DOI:10.1063/1.349351

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Single‐phase aluminum nitride thin films with preferred crystallographic orientations have been grown on single‐crystal sapphire by pulsed‐laser ablation. The orientation of the films was found to be determined by the atmosphere and the nitrogen pressure during deposition and the substrate temperature. The films were examined by x‐ray diffraction, and scanning electron microscopy.

ISSN:0021-8979    

DOI:10.1063/1.349352

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The positron mobility in thermally grown SiO2is deduced from Doppler broadening lineshape data on a metal‐oxide‐semiconductor sample for positrons implanted into the oxide layer. The fitted mobility is ∼13(10)×10−3cm2/s V. This value is between that of the electron and hole mobilities in the same system and is two orders of magnitude smaller than the previous estimate from positron measurements.

ISSN:0021-8979    

DOI:10.1063/1.349353

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We applied slow positrons to both as‐etched GaP and (NH4)2Sx‐treated GaP. The results show that the surface of as‐etched GaP is active for the adsorption of oxygen atoms when the etched surface was exposed to air for several minutes before the measurement. On the other hand, the monolayer of chemisorbed sulfur in (NH4)2Sx‐treated GaP is effective to protect the clean surface from the adsorption of the oxygen atoms. The mean diffusion length of positrons in the etched GaP is shorter than that in (NH4)2Sx‐treated GaP. This suggests that the centers for the positron trapping, such as Ga vacanciesVGaand/orVGa‐related complexes, are created by the adsorption of oxygen atoms.

ISSN:0021-8979    

DOI:10.1063/1.349354

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The use of a novel nonaxisymmetric quadrupole ion trap for frequency standard applications is suggested. The properties of such an elongated trap are examined using a cold‐ion‐cloud model. It is shown that increasing the elongation of the trap, while keeping either the smallest dimension or the volume of the trap constant, substantially increases the ratio of the number of ions that can be stored to the magnitude of the second‐order Doppler shift of the ions. This indicates that a frequency standard incorporating an elongated rf ion trap can achieve greater precision than one based on the currently favored circular rf or Paul trap.

ISSN:0021-8979    

DOI:10.1063/1.349355

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

TheFA(II) color centers of KCl:Li crystals were observed to reorientate at room temperature under the exposure of a ruby laser. The linear dichroism of the centers, induced by ruby laser light, is presented here.

ISSN:0021-8979    

DOI:10.1063/1.349356

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A high performance GaAsp‐metal‐semiconductor field‐effect transistor (MESFET) using carbon as thep‐dopant is demonstrated. The channel and contact layers were grown by metalorganic molecular beam epitaxy (MOMBE). The cap contact layer was highly doped with carbon (5×1020cm−3) in order to minimize the parasitic resistance in the FET structure. The sheet resistivity and transfer resistance of the contacts were 220 &OHgr;/&laplac; and 0.2 &OHgr; mm, respectively. These are comparable to values achieved onn‐type GaAs. The room temperature extrinsic transconductance andK‐factor values were 50 mS/mm and 165 mS/V⋅mm with 1 &mgr;m gate length and 3.5 &mgr;m source‐to‐drain spacings. These are the highest room temperature values ever demonstrated forp‐GaAs MESFET.

ISSN:0021-8979    

DOI:10.1063/1.349357

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Fluoropolymer films deposited on quartz crystals by radio‐frequency sputtering of polychlorotrifluoroethylene can be used for molecular sensing probes. For several organic materials, the piezoelectric responses of these sensing probes can be classified into characteristic categories. These responses are especially distinctive for highly fluorinated molecules. A film with highly halogenated frameworks shows slow sorption‐desorption response to alternate exposures to acetone atmosphere and to air.

ISSN:0021-8979    

DOI:10.1063/1.349358

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report laser‐induced breakdown studies of laboratory air using 0.266, 0.355, 0.532, and 1.06 &mgr;m radiation for focal spot varying from 30 to 100 &mgr;m. The breakdown intensities were measured for two pulse widths for all four wavelengths. We observe at−0.5pdependence of pulse width on threshold field at 0.532, 0.355, and 0.266 &mgr;m while for 1.06 &mgr;m the pulse width dependence oft−0.35pis observed.

ISSN:0021-8979    

DOI:10.1063/1.349359

出版商:AIP    

年代:1991

数据来源: AIP