摘要:

The quantum mechanical effects in silicon single-electron transistors have been investigated. The devices have been fabricated in the form of point contact metal–oxide–semiconductor field-effect transistors with various channel widths using electron beam lithography and the anisotropic etching technique on silicon-on-insulator substrates. The device with an extremely narrow channel shows Coulomb blockade oscillations at room temperature. At low temperatures, negative differential conductances and fine structures are superposed on the device characteristics, which are attributed to the quantum mechanical effects in the silicon quantum dot in the channel. The energy spectrum of the dot is extracted from the experimental results. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120483

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Twinning was observed in a GaN buffer layer. The twin boundaries in the buffer layer can extend into the epitaxial layer to form domain boundaries during growth of the epilayer. The domain boundaries, which initiated from the twin boundaries in the buffer layer, are determined to be inversion domain boundaries. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120484

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The optical absorption of ZnS semiconductor nanocrystals inside pores of silica has been investigated. These ZnS nanoparticles were synthesized through sol–gel processing, followed by firing. X-ray diffraction and nitrogen adsorption/desorption results show that the ZnS nanocrystals are highly defective. Based on the analysis of x-ray and nitrogen adsorption–desorption results, the surface layers of ZnS nanocrystals can be regarded as being amorphous. It was found that, compared with that of the bulk ZnS, the optical absorption edge of ZnS nanoparticles shifts to a longer wavelength. We believe that the amorphous surface layers of ZnS nanocrystals can mainly be responsible for the observed redshift of the optical absorption edge. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120485

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Irreversible formation of a network of linear defects has been observed for images showing recombination luminescence from injection diodes in hexagonal silicon carbide. The defects are related to dislocations that are initially formed as a result of thermal stress near the tip of the contact probe and subsequently propagate through the diode area. The dislocation network appears in the images of the electroluminescence as bright-line defects, in contrast to the well-known dark-line defects due to degradation of gallium–arsenide-based light-emitting devices. Higher forward currents are found to promote the dislocation growth. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120486

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The origin of noise inYBa2Cu3O7−x(YBCO) bicrystal SQUID magnetometers onSrTiO3substrates is investigated by comparing the microstructure of actual low-noise and high-noise devices. The most obvious difference in the microstructure is the presence ofa-axis oriented particles in the high-noise devices, whereas the low-noise devices consist exclusively ofc-axis oriented YBCO films. The growth of thea-axis particles in the YBCO films induces many defects, including amorphous regions, distortion inc-axis lattice planes and extraa-cinterfaces. The quality of the junction boundary is also degraded by thea-axis particles. The existence of these defects are expected to affect the superconducting current and the motion of the magnetic flux in the films and hence generate extra noise in the devices. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120487

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effects of Ce-based additions (CeO2andBaCeO3) in combination with MgO additions on the magnetic properties of melt texturedYBa2Cu3O7−&dgr;have been investigated. The additions lead to improvements in the magnetic properties ofYBa2Cu3O7−&dgr;compared to samples with either addition alone or with no additions. The Ce–Mg addition combination produces a “peak effect” in the magnetic hysteresis loop without significantTcdegradation. This is postulated to be due to the formation of a new type of pinning center. Both Ce and Mg ions are thought to substitute in theYBa2Cu3O7−&dgr;lattice, creating defects that produce a peak effect in the magnetic hysteresis loop. Mg additions alone lead to a reduced Tc, while Ce additions restore the Tc and enhance the magnitude of the peak. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120488

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Magnesium ions were implanted into highly crystallineYBa2Cu3O7(YBCO) thin films for the purpose of patterning. Films were implanted at doses corresponding to Mg contents ofx=0.008,0.02, and 0.04 in the formulaYBa2(Cu1−xMgx)3O7.High temperature annealing (900 °C) of films implanted below the solubility limit was successful in obtaining single phase, Mg doped YBCO films with finite resistivities at 77 K and x-ray (005) rocking curve widths<0.15°.An electron probe microanalysis on a film patterned using Mg implantation revealed that lateral diffusion of Mg ions resulting from annealing was limited to only a few microns. The superior quality of a top layer film indicated that Mg ion implantation is suitable for multilayer patterning. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120489

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new technology utilizing a self-limiting mechanism for the Bi content is demonstrated forBi2Sr2CuOy(2201) thin film growth by an atomic layer controlled molecular beam epitaxy. This technology is based on peculiar behavior of the Bi sticking coefficient that depends on the kinds of oxide thin films to be grown. When Bi atoms are supplied in excess with ozone molecular beam, only Bi atoms, being necessary for forming the structural unit (2201 half unit cell), are just incorporated in the film. Surplus Bi is reevaporated from the surface. Using this technique, high quality 2201 thin films are obtained with good reproducibility. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120490

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A technique for large enhancement of the diffraction efficiency of a guided-wave magnetooptic (MO) Bragg cell modulator using a nonuniform bias magnetic field in bismuth-doped yttrium iron garnet-gadolinium gallium garnet waveguide is reported. Since the velocity of propagation of the magnetostatic forward volume wave (MSFVW) varies with the bias magnetic field, a bias magnetic field of proper spatial distribution will modify its wave front and, thus, create a lensing effect upon the MSFVW. This lensing effect in turn reduces the angular beam spread of the MSFVW, and results in a higher MO Bragg diffraction efficiency. The experimental data obtained for the cases with uniform and nonuniform bias magnetic fields at the carrier center frequency range of 2.0–3.5 GHz have demonstrated a diffraction efficiency enhancement by two to six times. A diffraction efficiency as high as 70&percent; has also been accomplished. Furthermore, the measured frequency responses indicate that the nonuniform bias magnetic field has had only a mild effect on the bandwidth of the MO Bragg cell modulator. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120491

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The magnetic and transport properties of(La,Gd)1−xSrxMnO3+&dgr;(x=0.15,0.2, 0.25, and 0.3) with a fixed tolerance factort=0.913are studied. Special attention is paid to the postannealing effects of the compounds. Two magnetic transitions are observed in samplesx=0.2and 0.25 which are single phase in structure according to powder x-ray diffraction. Different effects on the two resulting states are produced by the postannealing. Accompanying the weakening of the state at lower temperature, the magnetic ordering of high-temperature state is enhanced substantially by the introduction of excess oxygen due to annealing the samples inO2.One typical paramagnetic–ferromagnetic transition occurs in samplesx=0.15and 0.3. There is a strong indication that the magnetic states inx=0.15and 0.3 are, respectively, the developments of the high- and low-temperature states inx=0.2(orx=0.25). The occurrence of two metal–semiconductor transitions inx=0.15–0.25and their responses to postannealing suggest magnetic heterogeneity in the compound. By assuming the coexistence of vacancy-rich and vacancy-deficient domains in the compounds, these observations can be understood qualitatively. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120492

出版商:AIP    

年代:1997

数据来源: AIP