摘要:

An Al/SiO2interfacial structure is investigated by cross‐sectional transmission electron microscopy (TEM) and x‐ray photoelectron spectroscopy (XPS) before and after post‐metallization annealing. An interfacial reacted layer with uniform thickness of 2.5 nm is observed by TEM for samples annealed at 450 °C for 1 h. Further reaction is suppressed at higher annealing temperatures up to the eutectic point (577 °C) of an Al‐Si system. XPS analysis of the interfacial structure is performed by removing the unreacted metallic Al layer selectively from the surface. The XPS spectra of the reaction products show that the interface has a layered structure of Al/Al2O3/Si/SiO2. This is discussed in relation to thermodynamic stability. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359536

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have studied the temporal variation of the visible photoluminescence from rapid thermally oxidized porous silicon prepared fromn+substrates. In contrast to the red (slow band) emission, which is observable immediately after high‐temperature oxidation, the blue (fast band) emission is shown to become prevalent only after samples are stored in ambient air. The intensity of the blue emission increases with progressive aging, the magnitude of the increase being dependent on the temperature at which the material is oxidized. Thermal treatment of aged rapid thermally oxidized material can reduce and even quench the blue photoluminescence. Quenching is reversible in that the photoluminescence re‐appears after further aging at room temperature. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358587

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Campbell’s method for measuring the critical current in superconductors has been used to obtain the critical current density and the pinning strength in Bi1.7Pb0.3Sr2Ca2Cu3O10−yceramics synthesized by a vitreous route. The intragrain critical current is much higher than 105A/cm2at 40 K in zero dc magnetic field. A large increase of the pinning strength is observed near the grain surface. The decrease with depth is hyperbolic. The role of the precursors in the synthesis route is emphasized for introducing specific pinning centers. The analysis takes into consideration the ceramics granular nature, i.e., the existence of intergrain and intragrain currents. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358588

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

It has been found that the high‐Tcrf superconducting quantum interference devices (SQUIDs) with oxygen‐ion‐irradiated weak links show white noise spectrum down to frequencies of about 0.2 Hz. The observed noise at lower frequencies is Lorentzian with a characteristic time constant of about 30 s. In contrast, in SQUIDs fabricated from pre‐irradiated and thermal annealed films, the measured noise power scaled as 1/ f. This fact is explained as a result of defect generation in YBa2Cu3O7. The study can provide a new insight into the microscopic origin of the 1/ fnoise in high‐TcSQUIDs, because the observed 1/ fnoise in the high‐TcSQUID is caused by introduced defects. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358589

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The infrared transmission spectra of (GaAs)n(AlAs)nsuperlattices (1≤n≤5) grown on (001) GaAs have been studied in the region of the AlAs‐like phonons using polarized light and oblique incidence. The longitudinal optical (LO) phonon frequency decreases with increasing confinement. Forn<3 the width of the LO phonon band increases due to disordering at the interfaces. The width of the transverse optical (TO) phonon band is substantially larger than that of the LO one. The LO phonon linewidth is mainly attributed to intrinsic damping, whereas that of the TO one is ascribed to radiative damping of polaritons. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358590

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present a complete analytical treatment of elliptical field emitting structures in a diode geometry which correctly includes image charge effects off axis and the variation of field along the tip. The methodology may be extended to other geometries. The angular distribution of electron emission along the tip, the total emitted current, and the area factor may all be calculated as a function of emitter to anode distance, tip radius, tip height, and the anode‐tip voltage difference. We show not only where errors arise if the planar Fowler–Nordheim (FN) equation is used to govern electron emission, but also how the FN equation may be modified to correctly address the complications due to atomically sharp tips. Finally, we present an analytic form of the area factor and compare it to the exact calculation and the various approximations. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358591

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Crystalline films of fullerene C60have been grown on amorphous substrates by a physical vapor deposition technique. X‐ray diffraction has shown that these C60films are highly oriented in either (111)/(glass substrate) or (220)/(fused silica substrate) orientations. The explanation for such growth behavior is that the orientation of C60crystals can be adjusted during growth by the rotation of individual C60molecules at elevated temperatures. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358592

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A scheme to achieve stationary continuous‐wave (cw) lasing in the vacuum‐ and extreme‐ultraviolet spectral region is proposed. It is based on recombination pumping in a freely expanding plasma produced in a high pressure, high temperature plasma jet. Stationary cw‐lasing at 1640 A˚ or 729 A˚ can be expected by inverting the He II (2←3) or Li III (2←3) Balmer‐&agr; transition following three‐body recombination of bare He2+or Li3+ions, respectively. The expected gain coefficients are calculated using a time dependent collisional‐radiative model and estimates of the required pumping power as well as considerations on the technical feasibility of the concept are presented. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358593

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report on the use of shadow masks for the growth of GaAs quantum wells with spatially varying thicknesses. Using cathodoluminescence we observe a clear shift of the luminescence energy as a function of the lateral position. Combining masked and directional epitaxy, the quantum wells can be both laterally and vertically patterned. This way, stacked, two‐dimensional electron gases are realized which can be selectively contacted without the use of complicated in‐situ or post‐growth patterning techniques. The quality of the epitaxial material grown through the openings of the masks is investigated by optical and electrical characterization. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358594

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A 500 A˚ erbium (Er) film was deposited on potassium titanyl phosphate (KTiOPO4or KTP) by electron‐beam evaporation. The doping of Er into KTP was induced by mega‐electron‐volt Ar+with different doses. The doping amount was investigated by Rutherford backscattering of 3.0 MeV He+. The results show that the doping concentrations of Er in KTP were 2.88 and 1.88 at. % induced by 2.0 and 3.0 MeV Ar+with the dose of 2×1016ions/cm2at room temperature, respectively. Perhaps the present result can provide an important approach not only for the laser and waveguide laser fabrication, but also for the high‐concentration dopants (atomic percent levels) into KTiOPO4at room temperature. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358595

出版商:AIP    

年代:1995

数据来源: AIP