摘要:

The magnetic energy stored in a cylinder or torus is optimized by adopting a special current distribution with helical windings. A cylindrical cable wound following a Bessel‐function distribution that reverses on the surface has greatly reduced self‐force and self‐stresses. This result applies to energy storage in large‐scale superconducting magnets, and is also of importance in plasma physics and astrophysics.

ISSN:0021-8979    

DOI:10.1063/1.347701

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Considerable modulation ratios are achieved for GaAs multiple‐quantum‐well reflector modulators grown on Si by inserting an AlAs/AlGaAs dielectric mirror into the device structure. Modulation ratios of up to 4:1 is attained as the external bias voltage is increased to 9 V and the 1C‐1HH exciton absorption peak undergoes quantum‐confirmed Stark shift. Measurements also indicate that cavity effects arising from the front surface reflection and that of the imbedded dielectric mirror strongly modify the reflectivity spectra.

ISSN:0021-8979    

DOI:10.1063/1.347702

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Intracavity spatial filtering in a copper vapor laser is demonstrated to achieve low divergence output beam. The output beam characteristics were monitored. The average beam divergence of 0.45 mrad (∼two times the diffraction limit) was achieved. Temporal pulse width of 3‐ns full width at half maximum was obtained.

ISSN:0021-8979    

DOI:10.1063/1.347703

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The direct and indirect band gaps of Si1−x−yGexSnyare inferred from the calculated energy‐band structure of &agr;‐Sn and from the known structures of Ge and Si. Our assumptions are: that the energy‐band shapes of the binaries Sn1−xGex, Ge1−ySiyand Si1−ySnychange smoothly withxandy, and that the energy gap of SiGeSn can be estimated by interpolation from the gaps of SnGe, GeSi, and SiSn. The optical indices of refraction of SiGeSn are also estimated.

ISSN:0021-8979    

DOI:10.1063/1.347704

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report the application of the technique of infrared transmission to measure the temperature of silicon wafers during the growth of silicon‐germanium alloy heteroepitaxial layers in a rapid thermal processing system. The silicon‐germanium alloy layers have negligible absorption at 1.3 and 1.55 &mgr;m over wide ranges of thickness, composition, and strain condition. The substantial improvement of the uniformity of layers grown using the technique to measure the temperature for feedback control of the lamp power has also been demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.347705

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A large second harmonic generation (SHG) intensity, which was 60 times as large as that of urea was observed in ap‐nitroaniline(PNA)/N‐(p‐nitrophenyl)ethylenediamine (NPEN) system. This SHG intensity was related to the cooling rate for solidification. The optimum cooling rate for SHG intensity was in the range of 2–10 °C/s. X‐ray and thermal analysis done for this new system show that the hydrogen bond and the unique nonplanar structure of NPEN play an important role for SHG and its stability.

ISSN:0021-8979    

DOI:10.1063/1.347652

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The reaction of Cl atoms with intrinsic andn+‐doped polycrystalline silicon has been studied at a Cl partial pressure of 0.17 Torr and in the temperature ranges from 150 to 290 °C and 25 to 90 °C for the two materials, respectively. The reaction withn+‐doped silicon was observed to proceed 90 times faster than with intrinsic silicon at any given temperature, i.e. within experimental error the difference in the rate constants for the two materials was found to be entirely attributable to a change in the pre‐exponential factor, with the activation energy remaining unchanged. The rate constant for the reaction is given by (9±2)×105nm min−1 Torr−1 exp−28.2±1.2 kJ/mol)/RTfor the intrinsic material and (7±3)×107nm min−1 Torr−1 exp−(27.8±1.5kJ/mol)/RTfor the phosphorus doped material with a dopant density of 5×1018cm−3.

ISSN:0021-8979    

DOI:10.1063/1.347653

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Silicon crystals grown by the CZ process have recently been studied with eddy current techniques to determine thermal profiles within the growing crystal. A key question concerning heat transfer in this semiconductor system during CZ growth is whether optical semitransparency in the infrared is important in affecting the high‐temperature thermal distribution within the crystal. From normal Fourier’s law calculations, well behaved profiles with rather flat radial isotherms are predicted in CZ growth. Eddy current data, though, show abrupt temperature changes near the crystal outer surface, indicating sharp radial thermal gradients. It is proposed that these sharp gradients are due in part to the onset of optical semitransparency in the crystal in the infrared. It is expected that such a transparency phenomenon will occur below a transition temperature. Any sharp gradients can be responsible for creep damage during growth.

ISSN:0021-8979    

DOI:10.1063/1.347654

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The noise of YBa2Cu3O7−xand Tl2Ba2Cr2Cu3O10−xthin films in the frequency range from 0.5 Hz to 100 kHz was studied. In the normal state, it was found that 1/fnoise dominated, with a magnitude strongly dependent on temperature. In the superconducting state, the noise was only observable at frequencies below 5 Hz with our present setup. Equilibrium thermal fluctuation noise was not observed in these films.

ISSN:0021-8979    

DOI:10.1063/1.347655

出版商:AIP    

年代:1991

数据来源: AIP