摘要:

We have performed time‐resolved photoluminescence on GaAs/AlxGa1−xAs single quantum well structures with an electric field applied perpendicular to the well plane. The quantum wells are coupled to the GaAs continuum through a thin barrier; the escape time of the electrons in the well was measured by time‐resolved photoluminescence. The dependence of the decay time on applied bias was found to agree very well with a simple semiclassical model.

ISSN:0003-6951    

DOI:10.1063/1.100835

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

At North Carolina State University, we have recently employed photoassisted molecular beam epitaxy to successfully preparep‐type modulation‐doped HgCdTe. The modulation‐doped HgCdTe samples were grown on lattice‐matched (100) CdZnTe substrates cut from boules grown at Santa Barbara Research Center. In this letter, we report details of the growth experiments and describe the structural, optical, and electrical properties that this new infraredquantumalloyof HgCdTe possesses.

ISSN:0003-6951    

DOI:10.1063/1.100836

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The Hall mobility and magnetoresistance of Si0.5Ge0.5/Ge heterostructures grown by molecular beam epitaxy have been studied in the temperature range 1.5<T<300 K. Shubnikov–de Haas oscillations observed atT=1.5 K indicate that selective doping of the alloy with boron generates a two‐dimensional hole gas in the Ge. The oscillation period yields a surface carrier density of 2×1012cm−2, in reasonable agreement with the value of 3×1012cm−2obtained by Hall measurements. The mobility atT=4.2 K in a sample with an undoped alloy setback layer of 4 nm was &mgr;H=3.2×103cm2/V s and in other samples was found to decrease with decreasing setback layer thickness.

ISSN:0003-6951    

DOI:10.1063/1.100837

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

By roller quenching and water quenching melts of Bi2(Ca, Sr)3Cu2O8+&dgr;, glasses have been obtained. These glasses exhibit two glass transitions as well as two crystallization transitions. Microwave absorption studies show the glass to be weakly superconducting at 77 K, probably due to the presence of ultramicrocrystallites. The glass on crystallization at 870 K gives the crystallinen=1 member of the homologous series Bi2(Ca, Sr)n+1CunO2n+4and then=2 member on annealing at 1100 K. The glass route provides a unique means of obtaining then=2 member of the series. On prolonged annealing of the glass at 1120 K, then=3 member seems to be formed.

ISSN:0003-6951    

DOI:10.1063/1.101436

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Critical current densities and resistivities were measured in a single crystal of the highTcsuperconductor Bi2Sr2CaCu2O8within theabbasal plane (∥) and along thecdirection (⊥). A large anisotropy in critical current density is found,Jc∥/Jc⊥≊103, in quantitative agreement with the large normal‐state resistivity anisotropy nearTc. The data provide strong evidence for a two‐dimensional layered structure of metallic planes separated by semi‐insulating barriers.

ISSN:0003-6951    

DOI:10.1063/1.101437

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The use of cw laser ablation for defining narrow tracks in YBa2Cu3O7thin films on (001) SrTiO3substrates is described. Critical current densities have been observed up to 5×105A/cm2in 4‐&mgr;m‐wide tracks at 77 K. For these films, it is found that the value of critical current density calculated is insensitive to the length of track and the voltage criterion used.

ISSN:0003-6951    

DOI:10.1063/1.101438

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We explore the magnetization patterns and domain walls which may occur in ferromagnetic cylinders and spheres in a certain range of sizes, placed in a uniform external magnetic field below saturation. The solutions found are field‐free inside the sample. The analysis is explicitly carried out for circular and elliptic cylinders and spheres, and may be extended to general ellipsoids.

ISSN:0003-6951    

DOI:10.1063/1.100838

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Abinitiomethods (Hartree–Fock, generalized valence bond, and configuration interaction) have been used to characterize the electronic states of molecular analogs to trimethylaluminum. An understanding of the mechanism of photoexcitation and subsequent dissociation emerges as the calculations reveal that optical excitation results in a metastable bound state rather than a directly dissociative state. The substantial excess energy associated with the transition is stored in electronic and vibrational degrees of freedom other than those associated with the dissociation coordinate. This interpretation allows a large body of observations to be simply understood and has implications for the implementation of the technology of laser photolysis for thin‐film deposition.

ISSN:0003-6951    

DOI:10.1063/1.100840

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A recently observed rapid decrease in oscillator strength of2E(E¯)→4A2(R1line) of ruby with static pressure is quantitatively explained with the help of other observed spectral shifts and a scaling procedure used earlier to model wavelength shifts with pressure. Oscillator strength is also predicted to decrease forR’lines, but forBlines it increases with pressure.

ISSN:0003-6951    

DOI:10.1063/1.100841

出版商:AIP    

年代:1989

数据来源: AIP