摘要:

Nanosized amorphous alloy powders ofFe20Ni80,Fe40Ni60,andFe60Ni40were prepared by sonochemical decomposition of solutions of volatile organic precursors,Fe(CO)5andNi(CO)4in decalin, under an argon pressure of 100 to 150 kPa at 273 K. Magnetic susceptibility ofFe40Ni60andFe60Ni40indicates blocking temperatures of 35 K and a magnetic particle size of about 6 nm. Thermogravimetric measurements ofFe20Ni80give Curie temperatures of 322 °C for amorphous and 550 °C for crystallized forms. Differential scanning calorimetry exhibits an endothermic transition at 335 °C from a combination of the magnetic phase transition and alloy crystallization. The Mo¨ssbauer spectrum of crystallizedFe20Ni80shows a sextet pattern with a hyperfine field of 25.04 T. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365250

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A basic study of the differences in elastic properties between single- and multi-domain crystals ofLiTaO3is conducted by measuring the longitudinal velocities forX-,Y-, andZ-cut specimens and the shear velocities forZ-cut specimens. Two sets ofX-,Y-, andZ-cut specimens are prepared: one is for normal (single-domain) specimens and the other is for perfectly depoled (multi-domain) specimens. For the longitudinal wave propagation directions along theYandZaxes, the velocities for the single-domain specimens, due to piezoelectricity, are 91.5 m/s (1.59&percent;) and 92.7 m/s (1.50&percent;) larger than those for the multi-domain specimens, respectively. On the other hand, for theX-axis longitudinal andZ-axis shear wave propagation directions, piezoelectricity is uncoupled, but the very interesting velocity changes are that the longitudinal and shear velocities for the single-domain specimens are 48.4 m/s (0.87&percent;) and 135.6 m/s (3.79&percent;) smaller than those for the multi-domain specimens, respectively. These differences are introduced by the poling operation for multi-domainLiTaO3crystals. Four elastic constants ofc11,c33,c44,andc14in the multi-domain state are determined. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365251

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Tantalum oxide(Ta2O5)is an important material for future dynamic random access memory application owing to its high dielectric constant. This work examines the structural and electrical properties ofTa2O5thin films deposited by plasma-enhanced chemical vapor deposition using a penta ethoxy tantalumTa(OC2H5)5liquid source. The x-ray diffraction patterns indicate that the as-deposited thin films are amorphous and become polycrystalline after rapid thermal annealing above 650 °C. The level of carbon contamination is below that which can be detected by Auger electron spectroscopy measurement. Electrical measurements performed on amorphousTa2O5using aAu/Ta2O5/Pt/Ti/Simetal-tantalum oxide-metal structure exhibit a low leakage current, reasonable breakdown field (5.4 MV/cm), and high dielectric constant (23–25). The leakage current is2×10−8A/cm2at 1 MV/cm. In addition, the leakage current mechanism of amorphousTa2O5capacitors is investigated by plotting theln(J)vsE1/2curves at a low electric field (<2 MV/cm) and plottingln(J/E)vsE1/2curves at a high electric field (>2 MV/cm). The dominant conduction mechanism is due to Schottky emission at low electrical field and Poole–Frenkel emission at high electrical field. According to our results, theTa2O5thin films annealed inN2orO2at 800 °C exhibit a much higher leakage current than amorphousTa2O5 ,possibly due to the out-diffusion of Ti during high temperature annealing. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365252

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A series ofInxAl1−xAssamples(0.51<x<0.55)coherently grown on InP was studied in order to measure the band-gap energy of the lattice matched composition. As the substrate is opaque to the relevant photon energies, a method is developed to calculate the optical absorption coefficient from the photoluminescence excitation spectra. The effect of strain on the band-gap energy has been taken into account. Forx=0.532,at 14 K we have obtainedEg0=1549±6 meV.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365253

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Real-space transfer (RST) light-emitting devices are implemented with a strained GaAs/InGaAs/GaAs quantum well heterostructure fabricated on GaAs substrates. The device energy band diagrams are simulated by using theMEDICIprogram. The effects of critical thickness, quantum size, and strain-induced band-gap shift on the optical transition energies at 77 and 300 K are calculated. Photoluminescence (PL) measurement is carried out to characterize the RST light-emitting devices. The measured results agree well with calculated values. The narrowest full widths at half-maximum of PL spectra are measured to be 17 meV at 300 K and 9 meV at 77 K for an undopedGaAs/In0.2Ga0.8As/GaAsquantum well heterostructure. The PL spectra confirm that the emission is dominated by emission from the strained GaAs/InGaAs/GaAs quantum well. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365254

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Rather strong third- and fifth-order four-wave mixing (FWM) signals from a 500 &mgr;m thick undoped GaAs and a 350 &mgr;m thick undoped InP in detuning ranges of 80–170 meV below the band gap are observed. The spectrally resolved (SR) FWM signals for both samples far below the band gap are blue-shifted significantly with respect to the spectrum of the excitation laser pulse for negative time delays, whereas they are red-shifted for positive time delays. The temporal and spectral shapes of the FWM signals for both samples far below the band gap are nearly consistent with those of the excitation laser pulse but are remarkably different from the excitonic properties. The shifts of SR-FWM signals far below the band gap are interpreted as due to the instantaneously created virtual states by the temporal overlap of the excitation laser pulses. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365237

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have synthesized a new type of high quality semiconductor doped glass (CdSSe embedded in a fluorine-phosphate matrix) using batch technology. The linear and nonlinear optical properties of this glass are investigated and compared with borosilicate glass doped with the same semiconductor. The optical susceptibility of glass is measured using degenerate four wave mixing technique. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365255

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Absorption spectra ofYAlO3:Ndfor the three crystallographic axes are investigated at room temperature. The spectral strengths indicate that the absorption coefficient ofYAlO3:Ndis anisotropic. The anisotropy of the local electric field acting on the rare-earth ion in a laser crystal is considered. An extended Judd–Ofelt theory is applied to calculate the absorption cross sections and oscillator strengths of the electric-dipole transitions in the different principal directions. Three groups of the phenomenological parameters are derived from a least-squares-fitting procedure. We also analyze theoretically the anisotropy of the optical absorption ofYAlO3:Ndcrystal in detail. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365256

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Infrared transmission spectra were measured systematically in polycrystallineLa1−xCaxMnO3−&dgr;and several systems substituted by other rare earth (RE) ions such asSm3+,Gd3+,Dy3+,etc., atLa3+sites or Fe ions at Mn sites but keeping the nominalMn4+/Mn3+≈3/7.Two strong absorption peaks located around 600 and 350cm−1,which are associated with internal phonon modes, i.e., stretching and bending modes ofMnO6octahedra, have been observed. Both of them are influenced by the concentrations of Ca and other RE ions substituting at the La and Mn sites. The details of the absorption peaks will be discussed on the basis of changes of the bond length of Mn-O and bond angle of Mn-O-Mn inMnO6octahedra. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365234

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The influence of irradiation by &agr; particles and subsequent isochronal annealing onn-GaAs doped with silicon, was investigated. Photoluminescence (PL) studies revealed the formation of an induced radiation center at 1.486 eV. In addition to the PL investigation we also employed capacitance–voltage(C–V)measurements and deep level transient spectroscopy (DLTS). TheC–Vmeasurements indicate a slight reduction inn-type carriers in treated samples and the DLTS spectra showed a number of commonly observed deep levels in irradiated samples (not annealed), which disappear after annealing. Based on the experimental evidence we propose that the 1.486 eV band is due to a donor-acceptor-pair transition. Alternative mechanisms are also discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365257

出版商:AIP    

年代:1997

数据来源: AIP