摘要:

A device comprising a low-resistivity, n-type, Si substrate as a back gate to a p-type (boron), remote-doped, SiGe quantum well has been fabricated and characterized. Reverse and forward voltage biasing of the gate with respect to the two-dimensional hole gas in the quantum well allows the density of holes to be varied from8×1011 cm−2down to a measurement-limited value of4×1011 cm−2. This device is used to demonstrate the evolution with decreasing carrier density of a re-entrant insulator state between the integer quantum Hall effect states with filling factors 1 and 3. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118729

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Synchrotron radiation soft x-ray photoemission spectroscopy was used to directly observe Se3dcore-level binding energy shifts from surface atoms of the (100) face of epitaxialCuInSe2/ GaAs(100). High-resolution spectra show two sets of Se3d5/2,3/2spin-orbit components separated by 0.6 eV, with the low-binding-energy peaks being associated with the surface atoms. However, surface state emission from Sepstates in the valence band was not observed due to the low photoionization cross sections. Cation bonding-antibonding states were observed in the valence band and are centered at about 1.0 and 3.1 eV below the valence band edge. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118717

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Gettering of Fe impurities by bulk stacking faults in Czochralski-grown silicon are investigated by means of the electron-beam-induced-current technique and transmission electron microscopy. It is found that Fe impurities only precipitate on Frank partial dislocations bounding stacking faults when the specimen is cooled slowly; however, both Frank partials and fault planes are decorated by Fe impurities when the specimen is cooled rapidly. It is explained that small oxygen precipitates on fault planes serve as the gettering centers for Fe impurities in the fast cooled specimen. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118718

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The ultrafast transient behavior of the transport parameters in InSb subjected to high parallel electric and magnetic fields is studied. The filling of high Landau subbands is considered in the numerical calculations. It is shown that the high magnetic field reduces the electron drift velocity and energy. An overshoot in the electron drift velocity can occur, but the magnetic field does not favor its existence and can even eliminate it. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118719

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Using near-field scanning optical microscopy (NSOM), we observe an inhomogeneous distribution of submicron-sized structural defects at the fusion boundary of polishedSrTiO3bicrystal substrates. Both NSOM and scanning force microscopy show that these substrate defects cause the grain boundary of aYBa2Cu3O7thin film grown on the bicrystal to wander up to a micron in the film. These structural defects are shown to correlate qualitatively with the electrical characteristics of grain-boundary Josephson junctions patterned on theYBa2Cu3O7film. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118720

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have applied tunneling of electrons between a normal metal and a superconductor to refrigerate a thin dielectric membrane attached to the normal electrode of a superconductor/ insulator/normal-metal/insulator/superconductor (SINIS) structure. Starting fromT≈200mK, a decrease in temperature of several mK was observed, measured by a separate thermometer on the membrane. It should be straightforward to improve the refrigerator performance to the level of the recently demonstrated SINIS electron cooling method, such that the drop in the lattice temperature would be more than an order of magnitude larger. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118721

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A suitablein situmonitoring technique for growth of thin films is reflection high energy electron diffraction (RHEED). Deposition techniques, like pulsed laser deposition (PLD) and sputter deposition, used for fabrication of complex oxide thin films use relatively high oxygen pressures (up to 100 Pa) and are, therefore, not compatible with ultrahigh vacuum RHEED equipment. We have developed a RHEED system which can be used for growth monitoring during the deposition of complex oxides at standard PLD conditions. We are able to increase the deposition pressure up to 50 Pa using a two-stage differential pumping system. Clear RHEED patterns are observable at these high pressures. The applicability of this system is demonstrated with the study of homoepitaxial growth ofSrTiO3as well as the heteroepitaxial growth ofYBa2Cu3O7−&dgr;onSrTiO3.Intensity oscillations of the RHEED reflections, indicating two-dimensional growth, are observed up to several tens of nanometers film thickness in both cases. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118687

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The same physics that correctly predicted superconductivity ofPrBa2Cu3O7also explains flux pinning by Ba-site magnetic rare-earth ions in(rare-earth)1+uBa2−uCu3Oxcompounds withx≈7.The customary cuprate-plane picture of superconductivity must be revised in the same way to consistently explain the observations either of flux pinning or ofPrBa2Cu3O7superconductivity withTc≈90K. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118722

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new excitation technique is described for the measurement of weak magnetic fields (<0.01 Oe). The resistance variation of a magnetoresistive element due to an oscillating excitation field is converted into a voltage proportional to the environmental field. The excitation field amplitude is set large enough to saturate the magnetization during each half-cycle, greatly reducing hysteresis effects in the output signal. Both anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR) structures have been used to measure fields with sufficient accuracy for compass applications. Such devices could be made with extremely small dimensions and power requirements. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118723

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present the electrical properties of polycrystallineLa0.7−xPrxSr0.3MnO3in which the average ionic radius of the A site⟨rA⟩is systematically varied while keeping the carrier concentration fixed. Below the Curie temperatureTc,the spin-disorder scattering process has been regarded to play an important role in the resistivity. With decreasing⟨rA⟩,the structure transition from rhombohedral to orthorhombic phase accompanied with the sharp increase in resistivity atTcand the increase of the activation energies has been observed. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118724

出版商:AIP    

年代:1997

数据来源: AIP