摘要:

There is increased interest in developing color variable light emitting devices. We report here the fabrication of color variable bipolar/ac light-emitting devices based on conjugated polymers. The devices consist of blends of pyridine-phenylene and thiophene-phenylene based copolymers sandwiched between the emeraldine base form and the sulfonated form of polyaniline. ITO and Al are used as electrodes. The devices operate under either polarity of driving voltage with different colors of light being emitted, red under forward bias, and green under reverse bias. The relative fast time response allows the rapid switching of colors and ac operation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119129

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We perform extensive band structure computation for two-dimensional (2D) periodic arrays of rigid stainless steel cylinders in air, with Bloch vector being perpendicular to the cylinders. For cylinders 2.9 cm in diameter and period of 10 cm (i.e., filling fractionf=0.066) there is no acoustic gap for frequencies below 6.4 kHz. However, the density of states reveals prominent minima at 1.7 and 2.4 kHz. These frequencies do agree with those of the first two attenuation maxima observed in the experiment [Nature378, 241 (1995)] and are indeed related to diffraction from the [100] and [110] planes. Thus, even with idealization, Sempere’s sculpture exhibits pseudogaps—not full gaps. We stress that, for any value of the period, there is no acoustic gap forf⩽30&percent;;magnitude of the gap, forf>30&percent;,is inversely proportional to the period of the system. Moreover, if the filling fraction exceeds 40&percent;, a second gap, higher in frequency, opens up. In addition, we propose the fabrication of a multiperiodic system in tandem that could create a huge hole in sound within the human audible range of frequencies. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119130

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Superlattice reflections observed for the first time in the room temperature powder neutron diffraction patterns of(Pb0.5Ca0.5)TiO3(PCT50) are shown to arise due to an orthorhombic distortion (space group Pbnm) resulting from tiltedTiO6octahedra and off-center location ofPb2+/Ca2+. From a study of the temperature dependence of the real and imaginary parts of the dielectric constant at various frequencies, PCT50 is found to be a relaxor ferroelectric. It is proposed that the structural frustration introduced by the tilted octahedra may be responsible for the relaxor behavior.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119131

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The reduction of the dislocation density in relaxed SiGe/Si heterostructures using a low-temperature Si(LT-Si) buffer has been investigated. We have shown that a 0.1 &mgr;m LT-Si buffer reduces the threading dislocation density in mismatchedSi0.85Ge0.15/Siepitaxial layers as low as∼104 cm−2.Samples were grown by both gas-source molecular beam epitaxy and ultrahigh vacuum chemical vapor deposition. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119132

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated the interaction of Pt with single-crystalSrTiO3(001)and polycrystallineBa0.7Sr0.3TiO3thin films using photoemission spectroscopies. Significant band bending is caused by interface formation, determining the Schottky barrier height. We have depth profiled the band bending forBa0.7Sr0.3TiO3thin films, giving a direct measurement of the depletion depth and built-in potential. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119148

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The thermal stability of the icosahedral phase(iphase) inTi45Zr38Ni17alloys is demonstrated. As-cast alloys containing initially only the C14 hexagonal Laves and &agr;-solid-solution phases transformed primarily to the icosahedral phase upon annealing in vacuum for 64 h at 570 °C. This confirms previous evidence fori-phase stability and firmly establishes this quasicrystal as the first nonaluminum stable icosahedral phase. Diffraction data show that this stableiphase is primitive; energy dispersive x-ray spectroscopy measurements place its composition nearTi41.5Zr41.5Ni17.These and other results suggest that the structure of thisiphase is similar to that ofi(AlLiCu). ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.119133

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on a method for detectingC60and otherC2nmolecules in the vapor phase during their initial growth stage. The technique, which utilizes a Langmuir probe, was originally proposed by Fukuzawa &etal; [T. Fukuzawa, M. Shiratani, and Y. Watanabe, Appl. Phys. Lett.64, 3098 (1994)] for the detection of dust particles in silane plasmas. By measuring the positive and negative saturation currents in the afterglow plasma, the mass ratio of negative and positive ions can be determined. We found that aM−/M+=56±10occurs only for discharge times greater than 0.5 s. As most of the positively charged species are expected to be singly charged carbon, a mass ratio of 56 is close enough to be attributed to theC60molecule, in agreement with mass spectroscopy results. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119134

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Far fields in perpendicular direction to the junction are investigated in double heterostructure (DH) and multiple quantum well (MQW) midwave-infrared InAsSb/InPAsSb/InAs lasers(&lgr;=3.2–3.6 &mgr;m).Strong broadening of the far fields in the DH lasers was observed with increases in temperature and/or current. On the contrary, MQW lasers with otherwise identical structure exhibit very stable far fields as narrow as 23° for all the operating conditions investigated. Our experiment and theoretical modeling suggest that these different behaviors of far fields in DH and MQW lasers are attributed to the refractive index fluctuation in the InAsSb laser active region. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119135

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the longitudinal optical (LO) phonon frequencies for thin films of the ternary alloyCdSxTe1−xand their composition dependence for the full range ofxvalues from pure CdTe to pure CdS. Pulsed laser deposition was used to prepare the polycrystalline thin films including compositions well inside the miscibility gap. We find that this ternary system exhibits a “two-mode” behavior with CdS- and CdTe-like longitudinal optic phonon modes. The modified random-element isodisplacement model yields a good description of the composition dependence of the LO phonon frequencies. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119136

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

High quality layers ofGaAs1−xNxwere grown on (001)GaAs by metal–organic molecular beam epitaxy. The growth conditions, and especially the nitrogen to arsenic flux ratio, were carefully explored to assure epitaxial crystal growth. We show well behaved and reproducible growth of single phaseGaAs1−xNxwith the GaN mole fraction as high asx=0.10.The nitrogen content of epitaxial layers was determined directly by secondary ion mass spectroscopy and high resolution x-ray diffraction. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119137

出版商:AIP    

年代:1997

数据来源: AIP