摘要:

The evolution of GaAs ridge structure formation by molecular beam epitaxy on a patterned substrate has been investigated using an ultrahigh vacuum atomic force microscope. It is found that the morphology of ridges can be quite irregular with random formation of various facets in the intermediate phase of growth, but self-smoothing processes of the lateral facets take place later on, leading to very sharp and smooth ridge structures in the end. The ridge top is quite sharp and straight with the height fluctuation of within 1–2 nm over the length of 1.4 &mgr;m. The role of the Ga atom flows from the side (111)B surfaces to the top (001) surface and their local modulations are considered to account for these observations. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118303

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of hydrogen ion implantation damage on the resistivity ofn-type 4H–silicon carbide is investigated. The variation of resistivity as a function of measurement temperature and postimplant annealing temperature is studied. Calculated resistivities obtained from resistance measurements are as high as8×106&OHgr; cm when resistances are measured at room temperature. When measured at 250 °C, the resistivity of the implanted layer is1×104&OHgr; cm. The resistivity is almost constant for annealings up to 1000 °C. The high-resistance behavior is believed to be related to implantation damage caused by 350 keVH+implantation. The results of this study can be used to obtain high-resistance regions for device isolation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118304

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Optical emission consisting of pulses with temporal widths of less than 270 ps has been detected from fully functional silicon integrated circuits fabricated using submicron complementary metal– oxide–semiconductor (CMOS) logic gates. Emission is observed under normal bias conditions and occurs when the gates are switching. The emission arises from the hot electron populations created by the transient current pulses present in the transistors during switching. The speed and spectral characteristics of the emission suggest future applications in the measurement of timing in high speed CMOS circuits. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118305

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The optical functions of amorphous and polycrystalline silicon thin films deposited on single oxidized silicon substrates by chemical vapor deposition in a wide range of deposition temperatures have been determined using spectroscopic ellipsometry. The data analysis is performed by direct inversion of the experimental spectra, therefore, obtaining results independent of any film modeling. The optical results indicate that the film structure changes as the deposition temperature increases from amorphous to polycrystalline with different grain size and distribution. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118306

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Combining the use of a UV storage ring free electron laser and of synchrotron radiation, a time resolved core level spectroscopy study has been performed on photoexcited Si(111)2×1 surfaces with subnanosecond resolution. This enabled us to measure band bending fluctuations, caused by surface carrier dynamics, during the first nanosecond after photoexcitation; differences in theSi2pcore level lineshape, dependent on the pump-probe time delay, were also observed. The presence of defects was found to reduce the fluctuations and make the carrier recombination process faster. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118307

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the ac response of structured thin, narrow rings of high-Tcsuperconducting films at ac and dc fields⩽1mT. The ac susceptibility as a function of reduced ac fieldh/hm(hmbeing the ac field at the dissipation maximum) shows no temperature dependence and can be well described by a model presented in this work. We show that the measurement of the magnetic moment of samples with ring geometry enables the identification of regions with degraded superconducting properties. The response of the ring shows up to∼1000 times smaller critical current density than the bulk. The magnetic moment shows a crossover from the ring to strip response upon increasing the applied ac field. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118308

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Artificial pinning center (APC) wires containing Nb 47 wt.&percent; Ti with 24 vol.&percent; of round Nb pins have produced very high critical current densities(Jc)which are attributed to a sharply defined, nanometer-scale Nb-pin array. By reducing both the number of warm extrusion steps from four to three and the temperature of the third extrusion from 650 °C to 250 °C, the degree of pin-matrix interdiffusion has been reduced andJcvalues at all applied magnetic fields increased by 25–45&percent; over those for a previous composite of almost identical design. The best wire achieved the very highJc(5 T, 4.2 K) value of 4600A/mm2. These results underscore the importance of the thermomechanical treatment in determining the maximum flux pinning properties of APC Nb–Ti wires. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118238

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Magnetic entropy change ofLa0.75Ca0.25MnO3with different particle size has been investigated. Magnetic entropy change∼4.7 J/kg Klarger than that ofGdhas been observed at224 Kunder a magnetic field of1.5 Tin comparatively big particles. This phenomenon of large magnetic entropy change indicates that the perovskite-type manganese oxides have potential applications for magnetic refrigerants in high temperature.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118309

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The performance of cyclotron autoresonance maser amplifiers can be significantly improved by using a properly spatially profiled helical wiggler. The proposed configuration is able to alleviate the severe problem of performance degradation by beam velocity spread. Simulation results show that more than 20&percent; output efficiency can still be attained at 94 GHz, even with 5&percent; beam velocity spread. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118310

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.119072

出版商:AIP    

年代:1997

数据来源: AIP