摘要:

In this letter, we present an atomic-force-microscopy investigation of the Stranski–Krastanov growth of Ge on Si(100). Upon increasing the base width of the islands, two morphology transitions are found. The first transition occurs at a base width of ∼50–60 nm and marks the evolution from few-monolayer-thick terraces to square-base pyramidal islands. In the second transition, which takes place when the base width exceeds ∼300 nm, the island shape changes from square base pyramids to tetragonal truncated pyramids. Both transitions are brought about by the need for the system to minimize the elastic energy. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118191

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Positron annihilation spectroscopy (PAS) is used to study Si-rich SiO2samples prepared by implantation of Si (160 keV) ions at doses in the range 3×1016–3×1017cm−2and subsequent thermal annealing at high temperature (up to 1100 °C). Samples implanted at doses higher than 5×1016cm−2and annealed above 1000 °C showed a PAS spectrum with an annihilation peak broader than the unimplanted sample. We discuss how these results are related to the process of silicon precipitation inside SiO2.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118315

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Voltage-pulse stimulated capacitance transient measurements on a seriesa-Si:H/a-Si, Ge:H devices disclose a large density of hole traps at or very close to the heterojunction interface. The transient signal magnitude is independent of temperature or applied bias, ruling out charge polarization effects or a defect creation process caused by the filling pulse. While the areal density of such hole traps is considerable (within a factor of 2 of1011 cm−2for all samples) these traps do not appear to behave as recombination centers. Also, the treatment of thea-Si:H/a-Si,Ge:H interface during growth can significantly alter the concentration of these traps. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118192

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The scattering property of tertiarybutylarsine (TBAs) on a GaAs(001)-(4×6) surface at room temperature was studied by supersonic-molecular-beam scattering. Polar angle measurements show that the scattering signal is due to thermal desorption of trapped molecules combined with a direct-inelastic scattering. The measurement of the sticking coefficient shows a precursor-mediated adsorption behavior. The time decay curve can be divided into two components with activation energies of 6.9 and 8.3 kcal/mol, revealing that TBAs molecules can physisorb into two different potential wells on the GaAs (001)-(4×6) surface. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118193

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated the photoluminescence spectrum of self-assembled InAs quantum dots embedded in a GaAs matrix in magnetic fieldBup to 23 T and under hydrostatic pressure up to 8 kbar. A strong anisotropy in the diamagnetic shift is found depending on whetherBis applied parallel or perpendicular to the growth direction. In the former case, the spatial extent of the carrier wave function in the dot is estimated to be 60 Å. The pressure coefficient for the dot emission line is (9.1±0.2) meV/kbar, about 20&percent; smaller than for the &Ggr;-point band gap in bulk GaAs. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.118194

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have measured the temperature dependence of preferentially oriented growth of hydrogenated microcrystalline silicon films, prepared by reactive hydrogen plasma sputtering of silicon. X-ray-diffraction measurements showed that the relative number of (110) grains increased rapidly at the expense of the (111), but not (311), directions with increasing substrate temperature between 60 and 400 °C. Over the same temperature range grain sizes for all orientations increased in scale with each other. Calculations of the step energy for grains of different sizes and orientations suggest that the changing number of dangling bonds with increasing grain size may be responsible for the observed temperature dependence of the preferential growth. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118195

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Hydrogenated amorphous silicon with small amounts of erbium (Er/Si concentration ∼5 at. &percent;) was prepared by radio frequency sputtering from a Si target partially covered by tiny metallic Er chunks. Four sets of samples were studied: nonintentionally contaminated hydrogenated and nonhydrogenated amorphous silicon-erbium (a-SiEr:H anda-SiEr); nitrogen dopeda-SiEr(N):H and oxygen contaminateda-SiEr(O):H. Samples from the first two sets present only faint 1.54 &mgr;m photoluminescence characteristic fromEr3+ions even at 77 K. Samples from the other sets show this luminescence at 77 K as deposited, without any further annealing step. Thermal annealing up to 500 °C increases the photoluminescence intensity, and room temperature emissions become strong enough to be easily detected. These results indicate that in an amorphous silicon environment the chemical neighborhood of theEr3+ions is crucial for efficient 1.54 &mgr;m emission. Raman scattering from both as-deposited and annealed samples showed that network disorder relaxation by annealing is not determinant for efficientEr3+luminescence. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118196

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An anomalous position of the central peak of magnetic hysteresis loops is observed in (Bi,Pb)-2223/Ag tapes at positive external fieldsBextfordBext/dt<0.We model the grain structure by a system of superconducting disk-shaped grains touching each other in small, but highly conducting contacts at the disk circumferences. The sign of the internal fieldBiat the circumference of large, thin well oriented grains in the tape plays an important role. While in great majority of the sample volumeBiis delayed behindBext,just at the grain circumferencesBimight be considerably ahead ofBext.Based on these considerations, a model sample which should exhibit similar features of the central peak is proposed.

ISSN:0003-6951    

DOI:10.1063/1.119069

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We experimentally investigate the effect of flux penetration into the electrodes of a thin-filmYBa2Cu3O7−&dgr;grain boundary Josephson junction using the field-dependent critical current as a probe. Above a temperature-dependent threshold field for flux trapping we observe that the maximum critical currentIcmaxis reduced, and occurs at an applied fieldHpeakshifted from zero. The critical current also has an increasingly complex field-dependent structure. Despite this complexity, we experimentally find thatIcmaxfollows a simple power lawHpeak−0.30.We present a model that predictsIcmax∝Hpeak−1/3due to fluxons trapped in the electrodes. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118197

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A novel method for determining magnetic anisotropies from hysteresis loops is presented. While sweeping the loop, a magnetic field is applied perpendicularly to the sweep-field axis. This causes the magnetization to rotate reversibly in a wide field range and still reach saturation at finite fields. An example is given whereby surface and volume anisotropies are determined from magneto-optical Kerr effect loops in Co films grown on stepped Cu(001). ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118316

出版商:AIP    

年代:1997

数据来源: AIP