摘要:

The magnetostriction and magnetic induction calculated by a continuous, anisotropic, anhysteric, magnetization model are compared with magnetostriction and magnetic induction measurements on burst and nonburst magnetostrictiveTb0.3Dy0.7Fe1.9twinned single crystal rods. The model shows that the magnetostriction and permeability suppression occurring at low applied field is the result of the rotation, and subsequent capture, of initial field antiparallel magnetization into field transverse [111¯] or [1¯1¯1] local magnetoelastic energy minima. The model further shows that the interval of high magnetostriction applied field derivative,d&lgr;/dH, characteristic of burst magnetostrictive material, is the result of the rotation of field transverse [111¯] or [1¯1¯1] oriented magnetization into the [111] near field magnetocrystalline minima. The occurance of burst magnetostriction is therefore contingent on obtaining sufficient magnetocrystalline anisotropy and sufficiently tight magnetization energy distribution in experimentalTb0.3Dy0.7Fe1.9twinned single crystal rods so as to minimize the applied field interval over which this magnetization rotation process occurs. A final analysis shows that the present model is able to correctly approximate the applied field dependence of the burst magnetostriction response and the applied field dependence of the simultaneous magnetostriction and permeability suppression with a single set of parameters for a range of constant [112] applied compressive stresses. The model additionally exhibits approximately correct saturation magnetostrictions for a range of experimentally applied compressive stresses. However, the model fails to match the experimental behavior above a simultaneousd&lgr;/dH, permeability and field hysteresis transition, located approximately 1000 microstrain from the saturation magnetostriction. The experimental transition clearly indicates a change in magnetization mechanism not accommodated by the present model. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364992

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We measured the magnetic hysteresis loops for several obliquely deposited amorphous TbFeCo films. The experimental results show that the direction of the average magnetic anisotropy (i.e., the easy axis of magnetization) is no longer along the surface normal. With the help of computer simulations, we have quantified the effects of oblique deposition in terms of the deviations of local anisotropy directions from the surface normal. We also found that, with the increasing of the deposition angle, the compensation point shifts toward the Fe-rich side and the films become thinner. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364959

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Nuclear magnetic resonance (NMR) spectra of93Nb,45Sc, and207Pb, as well as dielectric permittivity temperature dependence in a wide frequency range, were investigated in the solid solution of ferroelectric relaxors(x)PbMg1/3Nb2/3O3—(1−x)PbSc1/2Nb1/2O3(0⩽x⩽1). The peculiar behavior of the observed quantities and parameters, e.g., disappearance of dielectric dispersion forx∼0.5, is revealed. The analysis of the dependence of45ScNMR spectra onxhas shown that ordering of the regions containing Sc ions takes place forx>0.45. The investigation of the temperature dependence of93Nband45ScNMR linewidths inPbSc1/2Nb1/2O3had shown that atT<TmaxNb and Sc ions are shifted from their equilibrium lattice sites (Tmaxcorresponds to dielectric permittivity maximum). Latter shifts contribute to the temperature dependence of lattice polarizationP, whereas the jump ofPatT=Tmaxis determined by shifts of Pb ions. The peculiarities of NMR line shape in the investigated materials gave evidence of randomness in the directions and values of Nb, Sc, and Pb dipole moments. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364993

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We performed simultaneous measurements of all the layer thicknesses in six layer silicon on oxide film structures. Visible-near-infrared spectrophotometry was combined with beam profile reflectometry to produce enough information to discriminate between potential solutions; the spectrometer or beam profile reflectometer alone is insufficient to solve such a complicated film stack. Development of a robust measurement recipe required a new global optimization method working in parameter spaces of up to 12 parameters. The recipe obtained was applied to a 50 site mapping of the wafer. We found excellent agreement between our optical measurement results and scanning electron micrograph data for all thicknesses. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364994

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have directly measured the birefringence&Dgr;nofCdGeAs2using polarized light interference spectra obtained in transmittance from 2.4 to 18 &mgr;m over a temperature range of 14–450 K. Four different samples, exhibiting a wide range of free carrier concentrations, were studied. It was found that free carriers can have a significant effect on the room-temperature birefringence. At 14 K, however, the data from all samples were virtually identical. The temperature dependence of&Dgr;nwas obtained from a sample with low carrier concentration(≈1015/cm3)and high resistivity (9 &OHgr; cm). Its temperature derivatived(&Dgr;n)/dTwas determined at 50 K increments over the entire 14–450 K temperature range, and was found to vary from2.6×10−5/Kat 100 K to5.1×10−5/Kat 400 K. A least-squares fit to the data yielded a temperature coefficient for&Dgr;nof8.2×10−8/K. Hall-effect measurements indicate that the resistivity, mobility, and carrier concentration all exhibit a significant temperature dependence. The resistivity for one sample increased by a factor of108when cooled from room temperature to 14 K. Our results suggest that previously published&Dgr;nvalues were probably obtained from samples with relatively high carrier concentrations, and that our results more accurately describe the true intrinsic birefringence of the material. The value of&Dgr;ndecreases by 0.0004 per1016carriers a factor of 10 less than suggested by theory but still significantly large. The heavy to light hole effective mass ratio in the uppermost valence band was found to be 7.1.

ISSN:0021-8979    

DOI:10.1063/1.364706

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Light induced grating experiments have been performed at room temperature in CdS nanocrystallites of 2.5 nm radius embedded in sol-gel glass films of different semiconductor volume concentration. The dynamics of the photogenerated carriers at the lowest transition peak has been shown to depend on the excitation intensity. No spatial diffusion is observed up to a nanocrystallite volume concentration of 35&percent;. Below a fewMW/cm2the carriers relax in each nanocrystallite, either radiatively in ∼150 ps or by trapping the electrons 15 meV below their excitation transition. For higher intensities of excitation, a saturation of the excited states occurs which allows the electrons to be trapped in the glass matrix, inducing a permanent grating by the creation of a static electric field. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364995

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thin films of fine grained polycrystalline stoichiometric vanadium pentoxide (85&percent; of bulk density) have been prepared by vacuum evaporation. These films have been made into lithium vanadium bronze,LixV2O5, by inserting lithium, either electrochemically or chemically. In addition, lithium vanadium bronze thin films have been prepared by co-evaporation of Li andV2O5. The optical properties, absorption and refractive index, have been measured from 2000 to about 200 nm. Strong absorption arises from indirect transitions across the main gap and is ≈2.2 eV forx=0. The variation of the energy gap up to anxvalue of 2 has been obtained from the absorption data and the importance of irreversible phase changes noted. Highxvalue bronze is useful as a counter electrode material in glazings, having an energy gap of about 3 eV. There is a considerable, technologically significant, band tail in the absorption spectrum thought to arise from polaronic-type states, perhaps modified by the presence of guest species ions. The optical behavior upon lithium electrochemical insertion has also been examined. It is found that nonstoichiometry gives rise to an overall reduction in optical change per guest atom inserted. These effects are fast compared with electrochemical insertion times. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364996

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electrolyte electroreflectance (EER) experiments were performed onIn0.22Ga0.78As/GaAssingle quantum wells grown by the conventional molecular-beam-epitaxy (MBE) shutter operation, and also by modified MBE shutter operation intended to form more compositionally abrupt normal and inverted interfaces. The latter included controlled thermal desorption of the surface segregated In at the InGaAs layer surface (flash off), and the deposition of In at the InGaAs/GaAs interface to eliminate compositional broadening (predeposition). The fundamental energy gap and subband transitions were determined experimentally, and compared with an accurate calculation of the potential well problem including strain. These results confirmed the segregation of In atoms near the interface. The segregation was maximum in the conventional (normal) MBE sample and least with the modified growth incorporating predeposition and flash off, as expected. The segregated atoms are observed to act as dopants and form junctions near the InGaAs/GaAs interface. This study shows that EER can be used as an effective tool for studying the segregation process in MBE growth. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365476

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Real-space transfer (RST) light-emitting transistors are implemented with a strained GaAs/InGaAs/GaAs quantum well heterostructure fabricated on GaAs substrates. The device energy band diagrams are simulated by using the MEDICI program. Two optical measurements, electroluminescence (EL) and photocurrent, are performed to characterize the RST light-emitting transistors. The RST of hot electrons into the active region is measured by EL at 77 K. The light emitted from the RST device is detected by a separate photodetector and the photocurrent is found to be consistent with the RST current-voltage(IC−VD)characteristics. The 77 K EL emission peak wavelength is about 9000 Å. The EL spectra confirm that the emission is dominated by emission from the GaAs/InGaAs/GaAs quantum well. AtVD=0 V, the EL emission intensity due to hole leakage current is about 2 orders of magnitude lower than that of the electron leakage current. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365477

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Metalorganic vapor phase epitaxy grown InP samples capped with a protective As/P double layer were used to study clean (001) surfaces in ultrahigh vacuum. By the thermal desorption of As and P cap layers, InP surfaces producing sharp 2×4 low energy electron diffraction (LEED) patterns were prepared. The reconstructed surface and intermediate preparation stages were studied by using reflectance anisotropy spectroscopy (RAS), LEED, and Auger electron spectroscopy. Features in the optical anisotropy related to the contribution of P–P and In–In surface bonds are identified and discussed. The results show that the surface-related optical anisotropy of the 2×4 In-rich reconstruction of InP(001) is due to In–In bonds along the [110] direction that produce a large optical anisotropy below 2 eV. Furthermore, at intermediate annealing stages, information by RAS on a P-rich 1×1 reconstructed phase was obtained. The contribution of P dimers to surface reflectance anisotropy above 3 eV is discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365478

出版商:AIP    

年代:1997

数据来源: AIP