摘要:

Unexpected x‐ray diffraction peaks have been observed in some thin film modulated structures in which each constituent element has a nonintegral number of atomic layers. The origin of these peaks has not been clearly identified. The positions and intensities of these peaks were analyzed by numerical calculation from a model superlattice. The results indicate that the positions of the anomalous peaks are caused by a new long range periodicity due to the nonintegral number of atomic layers of each constituent element and that the intensities of the anomalous peaks are determined by the interfacial structure between the two different kinds of atomic layers. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359346

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

One of the problems encountered in designing a waveguide free‐electron laser (FEL) is to suppress the lower‐frequency branch, which may have a higher gain than the more useful higher‐frequency branch. It is shown that the electron pulse length and energy spread strongly influence the competition between the gains at high and low frequency for a waveguide FEL. It is also found that the negative slippage that may take place at the lower‐frequency branch results in larger reduction in gain than the positive slippage. The maximum allowable electron energy spread for both resonance frequencies is derived. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359347

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The dephasing dynamics of the continuum states has been investigated in bulk CdSxSe1−xmixed crystals with two‐ and three‐beam four‐wave mixing experiments using 10 fs pulses. Decay times, varying between 17 and 4 fs as a function of the density of electron‐hole pairs (8×1016–1018cm−3), indicate efficient Coulomb scattering with reduced screening as compared to bulk GaAs. Oscillations with 18 fs period which disappear within a few tens of femtoseconds are attributed to intervalence band quantum beats damped by intraband carrier thermalization. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359348

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Magnetization of RAlO3(R: Dy, Ho, and Er) single crystals along thecaxis have been measured by the superconducting quantum interference device magnetometer. The single crystals are nominally pure and large sized, grown by the Czochralski method. Paramagnetic properties depend on the rare‐earth elements. According to the magnetic entropy change, ErAlO3single crystals are promising materials for the magnetic refrigerants using the Carnot cycle in the temperature range below 20 K. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359349

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Electron‐paramagnetic‐resonance (EPR) has been used to investigate point defects in a single crystal of as‐grown CdGeAs2. Spectra taken at 17 K with the magnetic field parallel to thecaxis show a broad signal (∼165 Gauss wide) centered ongc=2.018 and a sharper signal (∼56 G wide) centered ongc=2.015. Together, these signals represent an unpaired‐spin concentration of approximately 5×1019cm−3. A single broad signal (∼165 G wide) centered onga=1.995 is observed at 17 K when the magnetic field is along theaaxis. It is suggested that these dominant EPR‐active defects in CdGeAs2consist of either a cation vacancy or an antisite cation with the unpaired spin shared by the four neighboring As ions. Additional weak EPR lines appear when the temperature is increased (from 17 to 40 K) and the microwave power is decreased (from 7 to 2.3 mW). ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359600

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thin films of Y‐Ba‐Cu‐O of different composition were grown on MgO and LaAlO3substrates by metal‐organic chemical‐vapor deposition. Using a microwave cavity resonator, their microwave surface resistance at 24.5 GHz was measured at a temperature of 77.5 K. It varies from less than 3 m&OHgr; to more than 50 m&OHgr; depending on the composition of the films. The lowest surface resistances could be obtained with samples having a composition close to the ideal stoichiometry 1:2:3 but with a slight excess of copper and yttrium. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359350

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We investigated the behavior of vertically stacked tunnel junctions in a circuit suitable for voltage standards. Such three‐dimensional (3D) circuits might offer a considerable reduction of chip size when compared with conventional, two‐dimensional circuits. Up to 84 series connected stacks with four junctions in a stack were incorporated into a microstripline. In the current‐voltage characteristic, we measured quantized current steps until 100 mV upon applying microwave irradiation in theWband. We observed both chaotic and nonchaotic behavior. Whether chaos or nonchaotic behavior is observed under microwave radiation depends on the coupling strength which is defined by the intermediate niobium layer thickness between the junctions of a stack. Large thickness corresponds to weak coupling and absence of chaos. We showed that 3D circuits are promising for voltage standard application. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359351

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.359352

出版商:AIP    

年代:1995

数据来源: AIP